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Thread: Wharram Catamarans , discussion required !

  1. #71
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    Default Re: Wharram Catamarans , discussion required !

    I recently saw the Tiki 21 referred to as an ideal option for "dingy cruising", with the open boats. It would be more to my taste, and the open part is realistic, because the only one I saw, I don't think I could have fitted through the hatch.

    By the way. Any small boat you think you want to build. Get some stuff and model the berth for width, walls and ceiling. It can be a deal breaker.

  2. #72
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    Default Re: Wharram Catamarans , discussion required !

    Could someone please explain to me how the whole "flexible lashing" is supposed to work on Wharrams? Especially with polyester ropes or webbing. Polyester rope and webbing is usually prestreched, meaning the rope is streched beyond it's elastic deformation range. All streching from that point forward is plastic, the rope permanently elongates and does not return to it's former lenght. This means once the rope streches you are left with a permanently loose lashing. Even Wharram knows this to be a bad thing, he advocates tight lashings and periodic retightening.
    If one was to use a rope that is not prestreched or rubber bands the effects would be the same as a loose lashing, either the beam and socket grind themself to dust, and/or they slam into eachother. There is no dampening effect anywhere, some energy gets converted to heat by the streching of the lashing and the rest slams the beam to the socket when the rope or rubber contracts back. As I see it Wharrams lashings are just a poor excuse for a bolt. In order to work properly they must be as tight as a bolt. No flexible anything.

    If one wants a flexible platform one has to use springs. Some pacific islanders used for their outriggers beams that act as torsion springs, but the actual connection between beam and outrigger and canoe was as tight as they could make it in order to allow the spring to work. They even developed some specialized knots that tighten with movement. None of this flexible beams is seen on double canoes, only on outriggers. And Wharram catamaran beams do not strike me as beeing engineered to act as torsion springs.

  3. #73
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    Default Re: Wharram Catamarans , discussion required !

    I saw a Tiki21 for sale in the Uk by Scott Brown, only 1750 quid, and owner would like to bring it halfway from Scotland. Better try that one out before you commit yourself to a bigger boat, Ersin.

  4. #74
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    Default Re: Wharram Catamarans , discussion required !

    Quote Originally Posted by Rumars View Post
    Could someone please explain to me how the whole "flexible lashing" is supposed to work on Wharrams? Especially with polyester ropes or webbing. Polyester rope and webbing is usually prestreched, meaning the rope is streched beyond it's elastic deformation range. All streching from that point forward is plastic, the rope permanently elongates and does not return to it's former lenght. This means once the rope streches you are left with a permanently loose lashing. Even Wharram knows this to be a bad thing, he advocates tight lashings and periodic retightening.
    If one was to use a rope that is not prestreched or rubber bands the effects would be the same as a loose lashing, either the beam and socket grind themself to dust, and/or they slam into eachother. There is no dampening effect anywhere, some energy gets converted to heat by the streching of the lashing and the rest slams the beam to the socket when the rope or rubber contracts back. As I see it Wharrams lashings are just a poor excuse for a bolt. In order to work properly they must be as tight as a bolt. No flexible anything..
    --- But it is comparatively flexible, I think that is the point. I talked to someone who did a crossing in Spirit of Gaia (I was bemused by the rudder lashings), and she claimed that the lashings already had about 5000 miles on them and they were still good; same for the cross beams. If they need periodic maintenance and replacement (no doubt they do) this seems acceptable.

    I can only speak personally of my day-sailing outrigger sailing canoes that use lashings -- I replace the lashings with the new season because it is easy since I have to disassemble and store the boat anyway, but the lashings were always sound. The working of the structures led to some wear of bearing surfaces, but I designed for that (wear-pads). I assume a Wharram is also designed to take it? I admit I don't necessarily like the look of the cross-beam channels -- that might seem to constrain movement too much, and in the case of a seriously loosening beam (before you can get to it), a giant lever twisting its bearing channel apart; but this is theory -- does it happen? -- Wade

  5. #75
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    Default Re: Wharram Catamarans , discussion required !

    Many Wharram cats use ss straps and bolts now, often with rubber inner tyre between.

  6. #76
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    Default Re: Wharram Catamarans , discussion required !

    Quote Originally Posted by FF View Post
    Many Wharram cats use ss straps and bolts now, often with rubber inner tyre between.
    I thought that was the old system?

    My Tiki 30 plans incorporate seat belt fittings, not just the webbing but the buckles. I asked whether I could not just use the rope, and again they were a little miffed at my lack of appreciation.

    -----------------------------------------

    However, while I think the lashed beams concept is basically ridiculous, it has to be accepted that where long range yachting is concerned, and in a post spectra world, cordage often does what metal fittings failed trying to do. Though I would not necessarily accept that the reason for using cordage is to achieve flexibility. It is just fantastic at distributing the load. You can have your fiber cast with epoxy, or you can have it free. It works either way.

    ---------------------------------------

    One thing I think is a great idea is beams that drop in from the top. Sockets are great, but they are really hard to manage compared to just placing a beam over something. And using cord to secure it, if you have the time, is fine also. It is the flexibility that is wack. Ideally I prefer to limit any point loads in wood/sheathed structures. It just seems to me if they are moving at the junction they are torquing on something. The boats have been around for 60 years so it isn't as though it doesn't work, but is it optimal.

    -------------------------------------------------------

    Of course the Poly. boats have been around a lot longer, though they didn't have the options we have today throughout that history. What is interesting to me is that some of those designs seem to take the opposite approach from the Wharram. They are massively triangulated at the junction point for rigidity, but the beams themselves flex.

    -----------------------------------------------------

    If you look at something like the 63. There are six beams, they seem like the hourglass sections on my pal's T-46. Those are ingenious hollow tube structure, with the hollows on the outside. Lets say you want to convert 6 beams to 2, roughly you would want to increase the remaining beams sections by a factor of 1.8 and in the bargain they would be quite a lot stiffer. There is maybe enough material in one of those beams to actually do that. Allowing you to toss 4 beams, and tune down 8 main-strength bulkhead structures. Of course, having chosen two masts, they are wedded to more than 2 beams, but that is a different mater.

  7. #77
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    Default Re: Wharram Catamarans , discussion required !

    Speaking of how inefficient the 60 degree V section hulls are, here is an old favourite I dredged for another thread, even this hull has arguably better hydro, and certainly a better section in the water. But then you need to add keels. Oh wait a minute...

    Certainly a fast build.
    Attached Images Attached Images

  8. #78
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    Default Re: Wharram Catamarans , discussion required !

    Quote Originally Posted by Lugalong View Post
    Hobie 16's have a hard wearing bottom of their close to V hull section, by virtue of the glass composite laminate.
    Thi s is one of the characteristic that makes them popular.
    Considering that a wooden hull is the subject of this discussion, any mind with a basic understanding of materials and structures will get it why Wharram hulls opt for this compromise.
    That was why I was disappointed when they tossed that approach on some of the more recent hulls, opting for the "foils". Might be an overall better compromise, but it didn't jump out as such to me.

    Wharram also has other designs that use other approaches, from the strip on the Ethnics designs, to the different shape on the Pahi.

    Performance is about the polar performance, not just what someone hit, once. Though since cruisers try to avoid beating, they are entitled to chose the parts of the graph they want to emphasize. I think that is why Wharrams do so well cruising. They are not pretending they are designed for something they are not. They probably run pretty nicely on rails most of the time.

    There a little details that need to be attended to run the Tikis. Quite often the sails are cut badly. I recently put an owner in touch with some sails at a very reasonable price that had been nicely built but with sail cloth you could use in a bullet proof vest. Way too stiff. Often they are cut too full. One of the great features of the rig for the home builder is that the spar is a tube, and the sail is cut dead flat. I don't think any of that package of effects is intended, but it is an awesome outcome as it is.

  9. #79
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    Default Re: Wharram Catamarans , discussion required !

    Quote Originally Posted by Rumars View Post
    And Wharram catamaran beams do not strike me as beeing engineered to act as torsion springs.
    I am not a believer, but...

    Some of his beams have an hourglass shape, and I assume that is to allow the torsional effect you mention.

    However:

    1) You can't just have a spring, it has to have a recovery that is consistent with whatever you are trying to cushion. If the wave motion induces a motion in a boat that is out of sync with the spring, then it isn't great. This is why shocks are not just springs, but have damping.

    2) Around what center of rotation is a 6 beam boat moving. The Gougeons have made many boats that used a spring recover system, and a pivot, and they were killer in racing. But they used relatively fixed bearings, with the appropriate center of rotation, and independant springs.

    I guess one would have to go seriously to sea in one of these things. You can see how rafts work in rapids, just sloping along. maybe the motion at sea is more pleasant, and it doesn't really mater what the reason is. There are two boats: The marketing and claims, and the actual boats.

  10. #80
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    Default Re: Wharram Catamarans , discussion required !

    Interesting thread.
    One comment about Bermuda rig centres moving forward as you reef and called a negative is not right though. That's a positive thing and has had reams of writing on the subject in nearly any boat design or seamanship book written in the last eon. It's also not the experience of no doubt millions of people who go to sea in Bermuda rig boats. Actually my experience in sailing my Edwardian gaff cutter says the way a gaff sail keeps it's centre well back I see as a negative and one of the problems with the rig at sea.
    If a bermudan boat stalls because it gets reefed then there's something else wrong. We don't in our bermudan ketch, none of my friends do in their sloops, I've never heard of anyone who does.
    Last edited by John B; 11-13-2018 at 02:42 PM.

  11. #81
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    Default Re: Wharram Catamarans , discussion required !

    Quote Originally Posted by Rumars View Post
    Could someone please explain to me how the whole "flexible lashing" is supposed to work on Wharrams? Especially with polyester ropes or webbing. Polyester rope and webbing is usually prestreched, meaning the rope is streched beyond it's elastic deformation range. All streching from that point forward is plastic, the rope permanently elongates and does not return to it's former lenght. This means once the rope streches you are left with a permanently loose lashing. Even Wharram knows this to be a bad thing, he advocates tight lashings and periodic retightening.
    If one was to use a rope that is not prestreched or rubber bands the effects would be the same as a loose lashing, either the beam and socket grind themself to dust, and/or they slam into eachother. There is no dampening effect anywhere, some energy gets converted to heat by the streching of the lashing and the rest slams the beam to the socket when the rope or rubber contracts back. As I see it Wharrams lashings are just a poor excuse for a bolt. In order to work properly they must be as tight as a bolt. No flexible anything.

    If one wants a flexible platform one has to use springs. Some pacific islanders used for their outriggers beams that act as torsion springs, but the actual connection between beam and outrigger and canoe was as tight as they could make it in order to allow the spring to work. They even developed some specialized knots that tighten with movement. None of this flexible beams is seen on double canoes, only on outriggers. And Wharram catamaran beams do not strike me as beeing engineered to act as torsion springs.
    Rumars, the early Wharram designs had steel fittings (straps going over the beams with bolts holding them to bulkheads, frames/webs and stringers inside the hulls).
    As well, there were wads of rubber pads to supply a shock absorbing effect.
    Being on a 45ft Wharram cat at sea ( in 8 metre seas), is certainly an educational experience as regards flexing of this type platform.
    What you really need to understand, is that it is the water that supports both hulls.... the beams and lashings have only to keep the hulls in their relative plan-wise positions, which includes diagonal location on the horizontal plane.
    Since lumpy water is not an even horizontal plane, the required flexibility just calls for a small amount of movement at each connection.
    Comparison with with the outrigger Ama of a Micronesian flying proa, should include the fact that it is the wind working through the weather shroud, that does the lifting of the ama.

    When a catamaran has its weather hull lifted out of the water, it would require a total lack of flexibility for the entire structure to maintain its perfect, as built configuration, and this expectation is unrealistic.
    Wharram has allowed for this small amount of movement, with proven systems of padded bolt, and then the lashings.... which are in turn an improvement on the bolted straps.

    I need to go now and work on the lashing fittings of my SO Pahi, but could explain with illustrations and pics (in the thread on my Pahi), how the various systems pioneered by Wharram have influenced my thoughts on design in this area, since it is high relevant to cost and longevity of a double canoe....as comes across in you're mention of the subject.
    Last edited by Lugalong; 11-13-2018 at 03:58 PM.

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    Default Re: Wharram Catamarans , discussion required !

    Quote Originally Posted by FF View Post
    Many Wharram cats use ss straps and bolts now, often with rubber inner tyre between.
    -- Interesting. I did eventually bolt my ama to my cross-beams (the ama tended to need mid-season re-tightening), but interposed big blocks of rubber. Then I could satisfactorily watch my ama flexing happily in its rubber bushings when sailing with ama-to-lee. -- Wade

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    Default Re: Wharram Catamarans , discussion required !

    Quote Originally Posted by wtarzia View Post
    -- Interesting. I did eventually bolt my ama to my cross-beams (the ama tended to need mid-season re-tightening), but interposed big blocks of rubber. Then I could satisfactorily watch my ama flexing happily in its rubber bushings when sailing with ama-to-lee. -- Wade
    Wade, what you might find, in continuous use in rough water year in and out, is that when these bolts are washed by seas and rain all the while being tightened up, is that there will be degradation and leaking in the area around the bolts.
    Otherwise, working the connections without always tightening up the bolts, will promote wear and tear... spiralling towards increased sloppiness and leaking.
    When cleats are bonded to the hull, there is nowhere for moisture ingress into the hull structure, and the lack of degradation that goes with this.

    Hokulea, the Hawaiian made voyaging canoe, has used lashings and no metal fastenings for more than 40 yers continuously.... one of the skippers (Bruce Blankenfeld), told me that they have only needed to replace the lashings every 8 years.

    Wharram does of course use bolts as locator pins to keep lateral move meant of beams in check, and these have some slop inter fit...... so I am also working on more effective use of bolts on my Pahi build.
    Last edited by Lugalong; 11-13-2018 at 04:35 PM.

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    Default Re: Wharram Catamarans , discussion required !

    Quote Originally Posted by Tomcat View Post
    That was why I was disappointed when they tossed that approach on some of the more recent hulls, opting for the "foils". Might be an overall better compromise, but it didn't jump out as such to me.

    Wharram also has other designs that use other approaches, from the strip on the Ethnics designs, to the different shape on the Pahi.

    Performance is about the polar performance, not just what someone hit, once. Though since cruisers try to avoid beating, they are entitled to chose the parts of the graph they want to emphasize. I think that is why Wharrams do so well cruising. They are not pretending they are designed for something they are not. They probably run pretty nicely on rails most of the time.

    There a little details that need to be attended to run the Tikis. Quite often the sails are cut badly. I recently put an owner in touch with some sails at a very reasonable price that had been nicely built but with sail cloth you could use in a bullet proof vest. Way too stiff. Often they are cut too full. One of the great features of the rig for the home builder is that the spar is a tube, and the sail is cut dead flat. I don't think any of that package of effects is intended, but it is an awesome outcome as it is.
    Tomcat..... some interesting observations and opinions you put forward. Obviously you have a fair amount of time invested in the subject and I would lie to see and hear more of what you have. But right now must go and get some work done on my shunting Pahi.... while the sun is shining and there is no rain, I gotta make use of conditions which, help me make progress working under a tent.

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    Default Re: Wharram Catamarans , discussion required !

    I want to make it clear that I am not against lashings per se. They do work when done right, and there are reasons to use them. What I am against is unsubstantiated marketing claims like flexing and simplicity and selling that to amateurs.

    Installing rubber between the faying surfaces of beam and hull in a catamaran is not the brightest ideea ever. Yes I can really imagine how such a structure would react to big waves. Something like a wet noodle.
    In a bolted or lashed connection where the bolts or lashings work in tension, friction plays the key role in keeping the structure aligned. The bolts or lashings only keep it pressed toghether and must be able to take the weight of the hull and beams if one hull is lifted out of the water, plus a discretionary safety factor.
    Once you secure the beams tightly to the hull you can decide if the beams should be rigid or act as torsion springs. That will influence their form and position.
    Deckhouse catamarans are rigid enough to mantain as buildt configuration, as are open deck cats and tri's that are able to fly a hull. Yes nothing is perfectly rigid if enough force is applied, I am talking here about expected more or less normal sailing conditions. One can design for extremes if desired, but the result will probably be very heavy. BTW it's always the wind lifting the hull trough the weather shrouds regardless of design, as long as there are shrouds. Only unstayed masts would lift the hull by cantilevering the beams.
    If the beams flex like torsion springs then the dampening element (the shock absorber) is the water itself. That's because the hull twists the beams but the motion also presses the hull into the water and energy gets disipated by displacing water and some friction. Cars need dedicated shock absorbers because the road can not be displaced and free air is not dense enough to dissipate the energy. To do that you need to compress the air a lot, meaning pneumatic tires and gas shocks. Fortunately wave patterns are irregular enough that inducing a resonant frecvency into the beams is highly improbable.
    If one wishes to design a system where the movement is in the beam to hull connection then one has to make a platform that is rigid enough by itself and mount the hulls to that. That's how a micronesian flying proa works, the Gougeons tri Adrenalin, and Wades outrigger also. The proa uses torsion bars perpendicular to the outrigger, Adrenalin uses a flat spring in line with the float, and Wade uses rubber torsion elements in the pivot itself. But all have in common that the structure to wich the pivot point is atached is rigid independent of the flexibly atached hull.

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    Default Re: Wharram Catamarans , discussion required !

    Quote Originally Posted by skaraborgcraft View Post
    AS far as the engineering goes, isnt everything that has a long service life over engineered? Airplane wings could be built much much lighter, but are built with significant saftey factors that increase the weight, for obvious reasons. Wharrams have never been aimed at the "performance" crowd, but will mostly be faster than a "normal" monohull off wind. It like complaining that an oil tanker does not spin in its own length and is tricky to berth single handed, or that a tug boat is no good because it cant plane. Horses for courses, pick accordingly.
    Completely agree with the horses for courses comment; like any boat Wharrams have good and weak points.

    IMHO, from what designers have said you can have lots of boats that are built for long service lives that aren't over-engineered. The light beach cats I mentioned earlier have long service lives; with over 300 built in about 35 years, numbers 7 and 70 are still on top at national level - but you have to keep an eye on certain highly-stressed fastenings and you have to watch you don't dent the light outside skin of the foam sandwich or ply construction. There are plenty of 30+ year old Raceboard windsurfers running around that are still in good condition and very light (16kg for a 13 footer) and my 68kg 15 foot dinghy is still fully competitive at 41 years of age - but you can't let it rest on rocks! Even most of the "disposable" IOR lightweight yachts built for 1977 world championships down here when I was a kid are still sailing happily. Sure, nothing comes for free and therefore you may have to pay more initially and impact strength is often lower - but as long as you don't abuse them their service life is very long.

    The thing that makes me wonder is that the smaller Wharrams claim to be getting the same sort of weights with bulkier hulls, bulkier beams, much lower-tech construction, lower costs, simpler structure and (one would assume) none of the same compromise in impact resistance.
    Last edited by Chris249; 11-14-2018 at 05:01 AM.

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    Default Re: Wharram Catamarans , discussion required !

    Im a bit late to the party but i helped out in the builds of two Tiki 38's. One was built meticulously to the plans and was signifigantly below its designed waterlines. It took nearly double the time Wharram claimed for the build. The second Tiki 38 was built by a guy who added stuff. It was way overweight and took the same "double time". I sailed in its company several times in my 24' monohull (designed 1921 so hardly "modern") - I was literally able to sail circles round the Tiki in conditions up to 20 knts wind.

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    Default Re: Wharram Catamarans , discussion required !

    Quote Originally Posted by Rumars View Post
    I want to make it clear that I am not against lashings per se. They do work when done right, and there are reasons to use them. What I am against is unsubstantiated marketing claims like flexing and simplicity and selling that to amateurs.

    Installing rubber between the faying surfaces of beam and hull in a catamaran is not the brightest ideea ever. Yes I can really imagine how such a structure would react to big waves. Something like a wet noodle.
    In a bolted or lashed connection where the bolts or lashings work in tension, friction plays the key role in keeping the structure aligned. The bolts or lashings only keep it pressed toghether and must be able to take the weight of the hull and beams if one hull is lifted out of the water, plus a discretionary safety factor.
    Once you secure the beams tightly to the hull you can decide if the beams should be rigid or act as torsion springs. That will influence their form and position.
    Deckhouse catamarans are rigid enough to mantain as buildt configuration, as are open deck cats and tri's that are able to fly a hull. Yes nothing is perfectly rigid if enough force is applied, I am talking here about expected more or less normal sailing conditions. One can design for extremes if desired, but the result will probably be very heavy. BTW it's always the wind lifting the hull trough the weather shrouds regardless of design, as long as there are shrouds. Only unstayed masts would lift the hull by cantilevering the beams.
    If the beams flex like torsion springs then the dampening element (the shock absorber) is the water itself. That's because the hull twists the beams but the motion also presses the hull into the water and energy gets disipated by displacing water and some friction. Cars need dedicated shock absorbers because the road can not be displaced and free air is not dense enough to dissipate the energy. To do that you need to compress the air a lot, meaning pneumatic tires and gas shocks. Fortunately wave patterns are irregular enough that inducing a resonant frecvency into the beams is highly improbable.
    If one wishes to design a system where the movement is in the beam to hull connection then one has to make a platform that is rigid enough by itself and mount the hulls to that. That's how a micronesian flying proa works, the Gougeons tri Adrenalin, and Wades outrigger also. The proa uses torsion bars perpendicular to the outrigger, Adrenalin uses a flat spring in line with the float, and Wade uses rubber torsion elements in the pivot itself. But all have in common that the structure to wich the pivot point is atached is rigid independent of the flexibly atached hull.
    Speaking of "simplicity" and " marketing" WRT ' selling that to amateurs".... a structure with theoretically no flexibility would be the better hard sell, because the speed potential increases. In other words - lightest and stiffest is good because it is faster.

    Wharram has never gone down this track because he knows that in terms of his reality, the complete deck structure is in a state of active torsion.
    There is simply that much energy to be absorbed by the structure, that sacrifice of material (lost to friction) simply has to be made somewhere..... its a bit like using anodes to take care of electrolytic corrosion.
    Other marketeers would instead be selling plastic hulls (that are non conductors), just like the composite sandwich and carbon extrusion marketeers are selling their rigid and faster product over the wooden cat with beams and tensioned strops.
    There have been Wharram designed cats with bolts fixing the outer ends of beams, and these have apparently worked well, without friction wearing away any of the material.
    At the same time, these beams probably had their inner locating areas cradled in troughs(above the inner gunnels) bedded with rubber paddling, and are/were presumably held by lashings too.
    using a connecting beam as a torsion member, would be Ok if there was but one beam, somewhere near amidships (like the Marshalese proa), and where the weather shroud is least affected by torsion in the plane of the deck structure.
    On a catamaran, the weather shroud situation on different tacks, mucks around with rigging tension, so again, the stiffer structure (with theoretically less impact on rigging tension), would be the thing to sell to amateurs.
    Could be, that these other sprung connecting members ( Gougeon adrenalin etc.) have merit, in terms of active torsionsal effect... I don't know, except that I have a Micronesian style proa, which uses the sprung system effectively.
    But, for catamarans, Wharram was the pleasure yachting pioneer, and has exhibited all the proof we need know of the workability of the demountable beam system...... the crop of contemporary so called traditiona lPolynesian voyaging canoes are pretty much mimicking Wharram.

    Using bolts to fiasten at least one end of a beam to a bulkhead, has got to be a good engineering solution (if the beam is a material like alloy rather than wood....then we have no reason to claim adherence to Oceanic tradition, once any metal components are used.
    Of course , once a wooden beam is through bolted, there is corrosion of the fastening, if not oxygen starvation ( if metal specs discourage bronze), creating a problem where end grain is in any way exposed and in a state of wear and tare.
    Personally, the use of a bolt through a wooden structural member, had better be a clearance fit in an epoxy saturated wood grain, sealed a well with a flexible caulking compound.
    Then, clamping pressure on the surrounding wood needs to be carried over a decently spread area of composite laminate or metal backing, which makes it an all too complex a method compared to an amateur friendly approach, such as Wharram advocates with lashings.
    Last edited by Lugalong; 11-14-2018 at 08:12 AM.

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    Default Re: Wharram Catamarans , discussion required !

    Quote Originally Posted by Foster Price View Post
    Im a bit late to the party but i helped out in the builds of two Tiki 38's. One was built meticulously to the plans and was signifigantly below its designed waterlines. It took nearly double the time Wharram claimed for the build. The second Tiki 38 was built by a guy who added stuff. It was way overweight and took the same "double time". I sailed in its company several times in my 24' monohull (designed 1921 so hardly "modern") - I was literally able to sail circles round the Tiki in conditions up to 20 knts wind.
    Apples and oranges, your 1921 boat might have been a heavily canvassed racing boat of it era! Seriously though, those Tikis should be performing well in 20kts, certainly enough to outpace an average monohull (however you define that).

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    Default Re: Wharram Catamarans , discussion required !

    Lashings are very difficult to get right. Every rope manufacturer has different specs and it requires a good understanding of them to be able to select the rope so that it does not constantly creep. This should actually be the designers job, not the operators. Installing them is a two man job with serving mallets and clamps, takes a while and should ideally be done by an experienced person. Polyester is prone to UV degradation, natural fibers to rot and both to chafing and creep. Even properly installed they will need periodic retightening and eventual replacement. There is nothing amateur friendly to it.

    Bolts are easy. They are manufactured to an exact standard and stamped accordingly. The designer can calculate the loads and specify the appropiate size. Installing them is easy, just tighten the nut with a torque wrench. Bolts can be all external and not go trough any structural member if so desired (U-bolts and plate on top of the beam). They do not degrade from UV, and seawater corrosion can be mitigated by material selection. Galvanized steel gives plenty of warning by rust before it loses strength and other more expensive metals are almost immune to it.

    The Wharram design office knows all about the problems lashings have. They tried to improve by using webbing and ratchets, mounting the beams into sockets and craddles and so on. All their efforts were about trying to minimize movement of the joint and user inexperience.

    Wharram is a pioneer and a visionary, and you can call him a hero of multihulls. He did some things well and some not so well. The problem is the not so well done things trapped him by becoming landmarks of his design. This includes "flexibility", lashings and the wingsail. He tried to improve on the lashings and I believe he really thinks his wingsail is better. It was the aerodynamic understanding of his time after all. I also believe he never understood how the flexible part actually works in ethnic designs.

    Today we are not obliged to adhere to his mistakes. If one wants a flexible design the deflection and forces involved can be calculated. The way flexible ladder frames (that's your basic Wharram cat) work was understood before him, after all the Ford T is buildt that way. We now know that a gap between mast and sail is not detrimental to airflow. If one wants a short gaff one can dispense with the sleeve and actually achieve a better sail profile. The lashing issues are still unresolved. Dyneema has great promise but it does not like kinked fibres and does not lock onto itself by friction so until someone actually designes a good way to use it we are left with the problems of natural fibres and polyester.
    Hull shapes evolved even in his design, there is no dogma of simple symetrical V-hulls.

  21. #91
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    Default Re: Wharram Catamarans , discussion required !

    I'm pretty sure the ratchet and strap is so the boat can be trailerable. (Quick release) That's also why the tiki 30 has 6mm ply, to keep it trailer friendly. Also the beams are box section to keep them light. I wouldn't want to be putting it on and off a trailer myself. But others have done it. I built and lived aboard a tiki 31 for a few years. Movement is minimal and lashings only needed tightening once not long after launch. The tiki 31 is 9mm ply. A very different boat than the 30.

  22. #92
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    Default Re: Wharram Catamarans , discussion required !

    I have also read about a tiki 46 with over 40, 000 miles. Same beam and rudder lashings. Fwiw
    they also got rid of the wing sail and went with traditional gaff lacing

  23. #93
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    Default Re: Wharram Catamarans , discussion required !

    Quote Originally Posted by Rumars View Post
    Lashings are very difficult to get right. Every rope manufacturer has different specs and it requires a good understanding of them to be able to select the rope so that it does not constantly creep. This should actually be the designers job, not the operators. Installing them is a two man job with serving mallets and clamps, takes a while and should ideally be done by an experienced person. Polyester is prone to UV degradation, natural fibers to rot and both to chafing and creep. Even properly installed they will need periodic retightening and eventual replacement. There is nothing amateur friendly to it.

    Bolts are easy. They are manufactured to an exact standard and stamped accordingly. The designer can calculate the loads and specify the appropiate size. Installing them is easy, just tighten the nut with a torque wrench. Bolts can be all external and not go trough any structural member if so desired (U-bolts and plate on top of the beam). They do not degrade from UV, and seawater corrosion can be mitigated by material selection. Galvanized steel gives plenty of warning by rust before it loses strength and other more expensive metals are almost immune to it.

    The Wharram design office knows all about the problems lashings have. They tried to improve by using webbing and ratchets, mounting the beams into sockets and craddles and so on. All their efforts were about trying to minimize movement of the joint and user inexperience.

    Wharram is a pioneer and a visionary, and you can call him a hero of multihulls. He did some things well and some not so well. The problem is the not so well done things trapped him by becoming landmarks of his design. This includes "flexibility", lashings and the wingsail. He tried to improve on the lashings and I believe he really thinks his wingsail is better. It was the aerodynamic understanding of his time after all. I also believe he never understood how the flexible part actually works in ethnic designs.

    Today we are not obliged to adhere to his mistakes. If one wants a flexible design the deflection and forces involved can be calculated. The way flexible ladder frames (that's your basic Wharram cat) work was understood before him, after all the Ford T is buildt that way. We now know that a gap between mast and sail is not detrimental to airflow. If one wants a short gaff one can dispense with the sleeve and actually achieve a better sail profile. The lashing issues are still unresolved. Dyneema has great promise but it does not like kinked fibres and does not lock onto itself by friction so until someone actually designes a good way to use it we are left with the problems of natural fibres and polyester.
    Hull shapes evolved even in his design, there is no dogma of simple symetrical V-hulls.
    Perceived dificultiies in achieving taught lashing vary with individual requirements... apparently some people need tension that would be more easily achievable by using rigging screws, which would need chainplates and which has also been tried on Wharram type cats.
    Two persons working on the lashings of a 40 ft craft, do no doubt
    make the job easier than is the case for one person.
    Could be that this is where the tradition and 'ethnic' concept enters the picture, in that large crews were the norm in early days.
    There is no record of early double canoes being set-up so rigid as to improve performance sailing to weather. In fact the only early catamaran type craft known to be designed for going weather under sai - the Tongan TOngiakil, did not have external beam lashing, although, they do represent a type that has become the model for amateur friendly building, since the use of adhesives has made possible the designs by those such as Woods, Kohler etc.
    So called ethnic designs by Wharram, do not even have beams that are fitted so that they impart torsional rigidity to the structure, and in any case case the old weatherly craft were shunters( having fore and aft rigs which could change tack without having to wear ship).
    Modern rig practice has been de rigour on Wharram's since the outset ( although there was a brief flirtation with Junk rig), but I suspect that using the wrap-around luff sleeve has always been more a case of economising on fittings ( as well as being able to use an alloy extrusion for a mast), rather than a performance trick.
    Notwithstanding, the fact that Wharram has always used his adopted features as selling points......... much like he has used the Pahi label in his design portfolio.

    Sure, lacing the sail luff ( instead of a wrap-around), is logical, although we are yet to see anyone successfully using only bolts to fasten wooden beams.
    True also, V bottom hulls do not follow dogma....... they re just the most effective way of using a chine to create a load-bearing edge ( especially if a composites or steel shoe takes care of abrasion).

    Following Wharram plans is often just the start for amateurs who then go on to make changesthat they think are improvements..... good for them.
    Like wise there are others who start with plans from other designers and go on to add their own changes - there is an interesting one built on the basis of Ron Givens single chine 30footer ( has a shallow V like the Paper Tiger beach cat), that I have a look at on many days that I go working on my Pahi.
    Last edited by Lugalong; 11-15-2018 at 03:27 PM.

  24. #94
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    Default Re: Wharram Catamarans , discussion required !

    I don't think Wharram builders spend time comparing them with other designs. I did and it is a good exercise. I have the Wharram cataloque, and studyplans of Gypsie, a Woods 28footer that can be built for a reasonable sum and was meant a minimum liveaboard for a couple. The other was a 30 footer from Kurt Hughes, designed for plywood with the cylinder mould method, als a small liveaboard. I knew by that time Wharram cats were sold for the price of materials and often less, so I wanted something better. Then I found a Wizard, a 22 ft cat, and she fits my needs well.
    Both Woods and Hughes have lots of moneysafing ideas. Use them.

  25. #95
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    Default Re: Wharram Catamarans , discussion required !

    I try to read any documents about Wharram. I think this threat have lot of important comment. All opinions will help the people like me who is planning to construct a cat.

    Designers aim is important. I mean the purpose of design is important. Wharram's priority according to me is seaworthy first. He did not care cabin hights, or all other home equipments.

    This boats are not " home sweet home " boats. Seaworthy is the first. Lashing is important I think . Because the weak point of any cats is laterial forces.

    Therefore lashing an important advantage for laterial forces. I saw only one accident report for wharram and due to wrong beam construction. There is no any problem reported due to lashing. At least I did not read.

    What I understand , these boats are love or hate type boats. As monohull sailor , I can say that , catamarans have important advantages if compared with monohulls.

  26. #96
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    Default Re: Wharram Catamarans , discussion required !

    Quote Originally Posted by Lugalong View Post
    Wade, what you might find, in continuous use in rough water year in and out, is that when these bolts are washed by seas and rain all the while being tightened up, is that there will be degradation and leaking in the area around the bolts.
    Otherwise, working the connections without always tightening up the bolts, will promote wear and tear... spiralling towards increased sloppiness and leaking.
    When cleats are bonded to the hull, there is nowhere for moisture ingress into the hull structure, and the lack of degradation that goes with this...
    --- I do not disagree, for a blue-water boat and through-hull fastenings. In my case, it is a day-boat with no through-hull holes. The crossbeams mount to struts on the ama, and the rubber-block-mounted bolts are easily inspected. I do not ever remember having to tighten them but that is no real surprise for low-use recreational boating. On the vaka the beams are lashed to external mounts (Gary Dierking style) and so also no through-hulls. --Wade

  27. #97
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    Default Re: Wharram Catamarans , discussion required !

    Quote Originally Posted by wtarzia View Post
    --- I do not disagree, for a blue-water boat and through-hull fastenings. In my case, it is a day-boat with no through-hull holes. The crossbeams mount to struts on the ama, and the rubber-block-mounted bolts are easily inspected. I do not ever remember having to tighten them but that is no real surprise for low-use recreational boating. On the vaka the beams are lashed to external mounts (Gary Dierking style) and so also no through-hulls. --Wade
    OK Wade, bolts and lashings are the way to for both of us....your bolts sound as though they go through the struts after horizontal boring, which keeps the holes up and clear of the hull, also allowing draining of water out and away.
    Assuming the holes have had the end grain epoxy saturated, you are technically in the clear, and the only thing that I am doing differently is to bond a metal sleeve in the hole, in order to bear compression loading and save from hurting the wood grain. Then, my 'strut' is really a deckhouse, so that I am able get inside and fasten the nut, as well as apply sealing caulk compound from that end.

    Lashings, as on your vaka attachment, are imparting tension to hold hull and beam together..... in my case the bolt uses sheer loading to stop lateral movement (of beam relative to hull, much as Wharram does, but without the slop fit he advocates).
    Then also, you have an open vaca, with a fully decked ama, while both my vaca and ama are decked hulls, more like a catamaran.
    Last edited by Lugalong; 11-16-2018 at 03:26 PM.

  28. #98
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    Default Re: Wharram Catamarans , discussion required !

    Quote Originally Posted by Lugalong View Post
    OK Wade, bolts and lashings are the way to for both of us....your bolts sound as though they go through the struts after horizontal boring, which keeps the holes up and clear of the hull, also allowing draining of water out and away.
    Assuming the holes have had the end grain epoxy saturated, you are technically in the clear, and the only thing that I am doing differently is to bond a metal sleeve in the hole, in order to bear compression loading and save from hurting the wood grain. Then, my 'strut' is really a deckhouse, so that I am able get inside and fasten the nut, as well as apply sealing caulk compound from that end.

    Lashings, as on your vaka attachment, are imparting tension to hold hull and beam together..... in my case the bolt uses sheer loading to stop lateral movement (of beam relative to hull, much as Wharram does, but without the slop fit he advocates).
    Then also, you have an open vaca, with a fully decked ama, while both my vaca and ama are decked hulls, more like a catamaran.
    --- I use a locating pin on the outboard end (on the vaka) of the cross-beams to set the lateral positioning of the lashed-on side of the beams. The locating pin in set in a rather loose hole so that swelling would not jam it (though all end-grains, including inside any hole, are epoxy saturated on my boat). For the pin I use a half-inch diameter aluminum rod. --Wade

  29. #99
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    Default Re: Wharram Catamarans , discussion required !

    Quote Originally Posted by wtarzia View Post
    --- I use a locating pin on the outboard end (on the vaka) of the cross-beams to set the lateral positioning of the lashed-on side of the beams. The locating pin in set in a rather loose hole so that swelling would not jam it (though all end-grains, including inside any hole, are epoxy saturated on my boat). For the pin I use a half-inch diameter aluminum rod. --Wade
    Wade, pinning like you do, is pretty much What Wharram includes in some of his designs, meaning that it has to be`duplicated for each hull. Having a proa, though, of course allows us off-set things, an then we can also use both a V bottom and a U bottom on the same hull...... like on the craft in the attached image ( my 23ft proa with V section vaka hull and a fully rounded ama)Proa ITI on mooring.jpg
    Last edited by Lugalong; 11-19-2018 at 02:47 PM.

  30. #100
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    Default Re: Wharram Catamarans , discussion required !

    having posted the pic above, it might be useful to explain how there is a connection to things 'Wharram'.......well, some years ago I had purchased a Wharram Hinemoa, in partnership with my son.
    He liked the fact that the cat had a Bermudan sloop rig with fully battened main and I have to agree that the rig was probably the best thing performance wise, that the platform could carry.
    On the wind in flat water conditions, she could keep up with a 40 ft Keeler under main and Genoa.
    Having had the connect beams lengthened to 4M, she was stable and the lashing system (being as it was, a modification to the standard Hinemoa plan and similar to a Tiki set-up) was a sensible solution to the original all-bolt connection(which has caused rot to set in).
    What Idid not like, was that the sheeting system was a complicated arrangement of blocks, creating a rope sheet-horse, in order to do away with a boom.
    Then again, a boom swinging low across the deck would be a pain on a little cat IMO.
    Also, there was barely enough room below, with a bunk space little more than 1 ft wide.
    So I built the cabin for the 23 ft proa (in above pic), and let my son have complete ownership of the Hinemoa.
    What I had really liked about the cat, was that a portapotti heads could be kept in one hull...separate from the galley in the other.
    Other than going for a bigger Wharram, there did not seem to be much in the way of fixing the shortcomings, and my son did in fact go on to getting a Tiki26 for himself.
    For me it helped in working toward understanding of the gains to be made by breaking away from limits imposed by having to duplicate everything except the rig, in order to have a boat with a bow and stern end, like a rowboat.... which is fine if the boat is or can be rowed.
    But when it needs a motor for propulsion other than sailing, the Wharram configuration can definitely be improved upon.
    Last edited by Lugalong; 11-20-2018 at 02:26 PM.

  31. #101
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    Default Re: Wharram Catamarans , discussion required !

    There is one thing about Wharrams I am curious about. I saw a smallish Wharram at a Wooden Boat Show, and its cross-beams were of a triangular cross section. It seemed that the beams resembled a V-hull construction in the the foreward facing side was the apex of the triangle, and the aft end was open, and the whole was spread apart and locked into place by "bulkheads." This looked like a rapid-build method but I was left to wonder about the structural characteristics of such as cross-beam design. Was this a standard Wharram option or an innovation of the builder? I actually met Wharram that day, but as we met at the public urinal it didn't seem the right moment to start a conversation. --Wade

  32. #102
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    Default Re: Wharram Catamarans , discussion required !

    Quote Originally Posted by wtarzia View Post
    There is one thing about Wharrams I am curious about. I saw a smallish Wharram at a Wooden Boat Show, and its cross-beams were of a triangular cross section. It seemed that the beams resembled a V-hull construction in the the foreward facing side was the apex of the triangle, and the aft end was open, and the whole was spread apart and locked into place by "bulkheads." This looked like a rapid-build method but I was left to wonder about the structural characteristics of such as cross-beam design. Was this a standard Wharram option or an innovation of the builder? I actually met Wharram that day, but as we met at the public urinal it didn't seem the right moment to start a conversation. --Wade
    That would be the Tiki type of beam - basically 3 sides of plywood, with solid batten or laminated timber reinforcing along with the bulkheads.
    As I understand it, these are lighter and more economical to build, than the older type beams, which were mostly solid laminate beams, although some of the Tiki type ( at least on the smaller craft) seem to have a bulkier section.Those on the TIKI 38 are I beams, and having said that I think I should take a walk and check at one moored at the wharf down the road......if this needs correction, ill do so.
    What I know for sure, is that the original types ( the 45ft Oro and the 23ft Hinemoa) had heavy solid beams.
    What I will be making for my Pahi, will be a box section laminated from planks, and having internal sealing and reinforcement with epoxy/glass and as much carbon as I can afford.

  33. #103
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    Default Re: Wharram Catamarans , discussion required !

    Quote Originally Posted by Lugalong View Post
    Th...
    What I will be making for my Pahi, will be a box section laminated from planks, and having internal sealing and reinforcement with epoxy/glass and as much carbon as I can afford.
    --- Where would the carbon be going?

  34. #104
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    Default Re: Wharram Catamarans , discussion required !

    Quote Originally Posted by wtarzia View Post
    --- Where would the carbon be going?
    Long fibres or tow goes in the corners inside the beam.

  35. #105

    Default Re: Wharram Catamarans , discussion required !

    Just became aware of the Okeanus Vaka Motu used in the Pacific islands. They retain a lot of the features that inspired the Wharram designs; lashed beams, relatively small rigs, and use a steering paddle. Interestingly the Pacific Islanders prefer these to the more modern multihull designs. https://okeanos-foundation.org/susta...sea-transport/

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