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Thread: Any Experience with Mast-Aft?

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    Default Any Experience with Mast-Aft?

    Nosing about on the web I found Brian Eiland's site "Running Tide Yachts" (http://www.runningtideyachts.com/home/) in which he espouses the benefits of an Mast Aft rig which involves the elimination of inefficient mainsails and booms and the use of stay sails. I wonder if anyone has any experience with this rig?

    Frank

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    Default Re: Any Experience with Mast-Aft?

    What size boat.....and how deep the interest.....
    If you use an aft mounted mast, the simplest way is to build a bipole rig attached to the corner transoms with a headsail luff wire, a roller furler and a single sail....the rig cant s forward and you balance the sail with the furler. Make it boomless......
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    Default Re: Any Experience with Mast-Aft?

    Interesting:


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    Default Re: Any Experience with Mast-Aft?

    Hasn't Phil Bolger designed several boats with a similar rig?

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    Default Re: Any Experience with Mast-Aft?

    Paladin:

    I have in mind a Parker design--the New haven Sharpie--which has a length of 28 feet and is designed to carry an unstayed mast of 26 feet.

    Frank

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    Default Re: Any Experience with Mast-Aft?

    Quote Originally Posted by Jon Etheredge View Post
    Hasn't Phil Bolger designed several boats with a similar rig?
    At least two.
    Simpler is better, except when complicated looks really cool.

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    Default Re: Any Experience with Mast-Aft?

    I have a 46 sq foot jib. Wonder if I could use it with an aft mast to power a dinghy.
    Last edited by JimD; 12-20-2007 at 12:54 PM.

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    Default Re: Any Experience with Mast-Aft?

    Quote Originally Posted by paladin View Post
    What size boat.....and how deep the interest.....
    If you use an aft mounted mast, the simplest way is to build a bipole rig attached to the corner transoms with a headsail luff wire, a roller furler and a single sail....the rig cant s forward and you balance the sail with the furler. Make it boomless......
    ISTR that some French guy demonstrated, via windtunnel testing, that a bipod mast with a single headsail had no net advantage over a conventional masthead sloop of the same sail area, due to the extra drag of the bipod and the loss of the slot effect between the jib and the main.

    However, an aft-mast cutter or ketch (as described here) seems like it would avoid those disadvantages.

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    Default Re: Any Experience with Mast-Aft?

    I've sailed a boat with a mast-aft rig. The luff sagged in the puffs, making the rig inefficient. I think there is very good reason this rig has never been popular. Sharpies developed the first bendy rig, and act quite well in the puffs. I'd go with the leg-of-mutton sprit rig, which is the standard sharpie rig.

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    Default Re: Any Experience with Mast-Aft?

    Quote Originally Posted by JimD View Post
    I have a 46 sq foot jib. Wonder if I could use it with an aft mast to power a dinghy.

    Shouldn't be too much trouble. It would be easy to fabricate a mast from a 4 by 4 and add a step and mast partner. The only hardware needed would be a block and cleat.

    Frank

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    Default Re: Any Experience with Mast-Aft?

    Quote Originally Posted by Circus View Post
    Shouldn't be too much trouble. It would be easy to fabricate a mast from a 4 by 4 and add a step and mast partner. The only hardware needed would be a block and cleat.

    Frank
    Frank, I might have to take a closer look at the idea because the dinghy plans from Selway Fisher arrived in the mail today

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    Default Re: Any Experience with Mast-Aft?

    Quote Originally Posted by Circus View Post
    Shouldn't be too much trouble. It would be easy to fabricate a mast from a 4 by 4 and add a step and mast partner. The only hardware needed would be a block and cleat.

    Frank
    It will take a lot more than that. The compression of the mast(s) and the tension of the backstay will be much greater than the usual sloop rig of the same area and the boat had better be strong enough to take it. Still, it's near impossible to get decent jib luff tension relative to the sloop and the backstay spreader has to be constrained (not easy either) to keep it from swinging to the side which will bring the whole mess down.

    The reasons to build this rig are mostly foggy anyway. Might be best to think of it as an academic exercise and stay with more sensible and proven concepts. Not to tromp on new ideas but this one is not new and has never proven to be an advantage.
    Tom L

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    Default Re: Any Experience with Mast-Aft?

    Quote Originally Posted by Tom Lathrop View Post
    It will take a lot more than that..
    Tom, thanks for the input. Just brainstorming ideas to see if I can use a sail I already have rather than make/buy a new one. Can ya make a lateen rig out of a jib?

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    Default Re: Any Experience with Mast-Aft?

    Jim, the sailmaker will already have cut a curve into the luff to deal with a little bit of sag. If you use a lateen, then you'll have a convex curve instead, pulling even more fullness out of the middle of the sail.

    If you bought the plans, go (initially at least) with the sailplan SF designed for the boat.

    How many plans do you own? I have two, apart from my own doodles

    Cape Cod Frosty (a boat you'd love) and a Dick Newick Kayak.

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    Default Re: Any Experience with Mast-Aft?

    Everything's a trade off. The predumed efficiency of not having a mast to create turbulence is partly off-set by the inefficiency of an airfoil that ends in a point.

    For off-shore use, other considerations are important, like repairability and ease of handling when God has a negative attitude.

    Give me the major sail area with at least two if not three spars any time for that.

    Edited to add: Ever deal with a rolled up jib in a high wind? The vibrating horror.
    Last edited by Ian McColgin; 12-20-2007 at 06:18 PM. Reason: addition

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    Default Re: Any Experience with Mast-Aft?

    Many, many moons ago Ted Brewer designed a similar rig intended for offshore racing, and found that the proposed aluminum spars were too bendy.....another boat was made with carbon fibre spar(s) that worked but also the spar arrangement ended up costing as much as the rest of the boat......and then there's repairs as noted...and how do you jury rig it etc...
    Wakan Tanka Kici Un
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    Default Re: Any Experience with Mast-Aft?

    One of Phil Bolger's comments about this rig in '100 small boat rigs' was that it'd be "fiendishly expensive" because of the very high loads on the mast, its backstays and their supporting structure.
    As for the illustration at the top of this thread, where the mast is stepped atop a catamaran's canopy, the engineering of that will a challenge.The compression load on the mast and the tension of the backstay will be daunting.

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    Default Re: Any Experience with Mast-Aft?

    Scaled up a bit, you get this:



    Note the elaborate structure and the size of it to set sails that are still way undersized for the size and weight of the vessel. Of course, this rig is there mainly for looks, anyway. (Looks for people who don't know what they're looking at, of course.)

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    Default Re: Any Experience with Mast-Aft?

    Gary Hoyt did one of these and put it into production. Don't think may were built. Museum of Yachting has one as I recall. Any way as some have pointed out the problem was getting the mast to be stiff enough and set up enough backstay tension to control jib luff sag.
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    Default Re: Any Experience with Mast-Aft?

    Quote Originally Posted by Hwyl View Post
    Jim, the sailmaker will already have cut a curve into the luff to deal with a little bit of sag. If you use a lateen, then you'll have a convex curve instead, pulling even more fullness out of the middle of the sail.

    If you bought the plans, go (initially at least) with the sailplan SF designed for the boat.

    How many plans do you own? I have two, apart from my own doodles

    Cape Cod Frosty (a boat you'd love) and a Dick Newick Kayak.
    Gareth, I'll probably go with what I've been planning for quite some time - a polytarp junk sail of my own design just to get used to the rig and see if I like it enough to put together a bigger one for da udder boat. I've only purchased nine or ten plans, have built six and the dinghy which will definitey get built this winter will be seven. So only a couple plans out of ten that won't get built.

    What's a Cape Cod Frosty? Tell me more. (Now that I've hijacked the thread).

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    Default Re: Any Experience with Mast-Aft?

    Back to the thread--- Proute cats used to make rigs (perhaps still do?) which had a very large genoa/mainsail ratio with the mast set well back on the coachroof (or the front of the cockpit?) ´The mainsail was high apect and presumably used to retain the slot effect. I would worry about the furling too.
    Andrew

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    Default Re: Any Experience with Mast-Aft?

    The Prouts carried conventional cutter rigs, and for good reason. It keeps the drag centered under bare poles -- they don't sail around their moorings like most multis and are said to ride on a sea anchor quite well. Plus the base of the mast is at the forward end of the cockpit, so going on deck is less often necessary. And finally, there's the flexibility of having three sails to set and reef and needed.
    The Prouts were ahead of their time once. Now they're dead and gone as a company, but there are quite a few boats out there still.



    The other big disadvantage of the aft-mast that hasn't been mentioned is what happens when you reef. You roll up that huge jib, and the center of effort goes forward with it with nothing aft to balance it.

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    Default New Lagoon 52 moves mast back

    Interesting new twist, Lagoon 52 design moves mast aft to carry larger headsails and smaller mainsail.

    http://www.sailmagazine.com/boat-reviews/lagoon-52

    Although you might not immediately notice the differences between this boat and its predecessors, they are dramatic. For example, moving the mast back to the 43 percent point to get a larger foretriangle required moving the center of buoyancy of the hulls aft as well. That, in turn, meant reshaping the hulls and making the bows sharper, not to mention adjusting the overall center of lateral resistance to keep the boat balanced with the big jib and small mainsail.


    Moving the mast aft also required some kind of new support, as the main bulkhead at the forward end of the saloon is no longer usable as a base. That meant creating an entirely new support structure: which Lagoon has done in the form of a big, stiff, reinforced grid concealed within the cabin and hull, and a strong compression post in the middle of the boat


    Putting the helm up on a flybridge created yet more structural challenges due to the strains of the running rigging and the weight of people up there. Finally, the short boom (another result of the aft position of the mast) calls for a taller rig to replace the lost sail area.


    Amazingly, all of it works on the Lagoon 52: the tall rig is efficient; the mainsail is easy to trim, raise and furl (although the standard electric halyard winch is still essential); the roller-furled headsails behave nicely; and the boat really goes. VPLP Design got it right.

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    Default Re: Any Experience with Mast-Aft?

    Quote Originally Posted by Tom Lathrop View Post
    It will take a lot more than that. The compression of the mast(s) and the tension of the backstay will be much greater than the usual sloop rig of the same area and the boat had better be strong enough to take it. Still, it's near impossible to get decent jib luff tension relative to the sloop and the backstay spreader has to be constrained (not easy either) to keep it from swinging to the side which will bring the whole mess down.

    The reasons to build this rig are mostly foggy anyway. Might be best to think of it as an academic exercise and stay with more sensible and proven concepts. Not to tromp on new ideas but this one is not new and has never proven to be an advantage.
    ......except from rigging force review
    http://www.boatdesign.net/forums/sai...tml#post414479
    Let's review the forces we’ve added to the mast column at this point due to the fore/aft rigging arrangement:
    a) At the upper tip in the masthead area we’ve added virtually no additional compression forces over those experienced by a standard straight standing mast under the traditional loading of tight forestay and tight backstay.

    b) In the hounds region we’ve added considerable additional compression loading associated with the diamond jumper stays ’pulling together’ from their upper and lower ‘turning block terminations’. These create extra compression loads within the mast column itself, but they cancel each other in terms of adding extra compression loading to the lower mast and the stepping base. This panel of the mast is relatively short, and the rigging is such that it is not easily drawn out of column, so a reasonably strong mast section for this panel section at the hounds should be able to sustain these higher compression loads.

    c) The lower panels of the mast suffer from the higher compression loads exerted by the shallow lower backstay(s), but not nearly as much as some have exaggerated.

    Compression Loads to Mast Column by Fore/Aft Rigging

    1970 kg.........................Forestay + Backstay......................1970 kg
    ..660 kg.............................Inner Forestay............................660 kg
    ......0 kg.................Shallow angle Lower Backstay...............1900 kg
    1280 kg.................Broader angle Lower Backstay....................0 kg
    3910 kg.................................Totals......... ..........................4530 kg

    These figures don’t appear to be that excessive…certainly no where near the 4 to 6 times loading that some naysayers have claimed. And certainly something that can be dealt with relative ease.

    Have I made any errors in those figures above??

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    Default Re: Any Experience with Mast-Aft?

    A mast aft rig would have a huge jib and huge stress on the mast an fore stay(s). In the 1930's or 40's someone rigged a boat about 35 ft LOA with a mast aft rig named "Atrocia". I don't believe it was very successful.

    You Brits might know if such a rig was tried on the Redwing class. This was a class with a one design hull, not much different than a Dragon, but limited to 200 sq ft of sail in any arrangement one pleased. They settled on a 7/8ths Marconi with about 30% SA in the jib. I believe that Uffa Fox described this class in one of his books.

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    Default Re: Any Experience with Mast-Aft?

    Nothing new there. Prout experimented with similar rigs in the 1970s and 80s.


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    Default Re: Any Experience with Mast-Aft?

    For small boats here's the 'Appledore Pod' rig by Arthur Martin. I have no direct experience with it.

    "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so."

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    Default Re: Any Experience with Mast-Aft?

    Let's review the forces we’ve added to the mast column at this point due to the fore/aft rigging arrangement:
    a) At the upper tip in the masthead area we’ve added virtually no additional compression forces over those experienced by a standard straight standing mast under the traditional loading of tight forestay and tight backstay.
    This poster from another forum does not understand the parallelogram of forces.

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    Default Re: Any Experience with Mast-Aft?

    Quote Originally Posted by rbgarr View Post
    For small boats here's the 'Appledore Pod' rig by Arthur Martin. I have no direct experience with it.

    That would be a totally cool rig for the stripper, make the spars shaped to the gunwale( do a Kenjamin), on with the backstay and you're sailing.

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    Default Re: Any Experience with Mast-Aft?

    Quote Originally Posted by Hwyl View Post
    This poster from another forum does not understand the parallelogram of forces.
    I'm sorry, could you explain exactly where I went wrong with my parallelogram of forces??

    Quote Originally Posted by brianeiland
    MASTHEAD
    Lets start at the masthead. There is the primary forestay, a backstay, and two shrouds…all rather traditional. I’ve chosen to represent the force in the forestay with a 5cm long vector. Lets say this vector represents 1000 force units, thus each 1cm on the force diagram will represent 200 force units.

    At the masthead the forestay force is broken down into two perpendicular forces, the compression load down the mast and the forward pulling force. The fwd force needs to be offset by the aft pull of the backstay. The backstay is at a more shallow angle so it must pull a bit harder to exert its rearward force. At present we know:

    Forestay Force............................................1 000 kg
    Backstay Force...........................................12 60 kg
    Forestay compression Load in Mast.................820 kg
    Backstay Compression Load in Mast..............1150 kg
    Total Compression Load in Mast....................1970 kg
    (at very upper portion & disregarding shroud loads)

    .....nothing very unusual....very conventional. The mast is experiencing compression loads from both the forestay and the backstay force components acting in the vertical direction. And it’s doubtful that those compression loads imparted to the mast by the backstay and forestay are much greater than in the case of a purely vertical standing sloop rig mast.

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    Default Re: Any Experience with Mast-Aft?

    Quote Originally Posted by John B View Post
    That would be a totally cool rig for the stripper, make the spars shaped to the gunwale( do a Kenjamin), on with the backstay and you're sailing.
    Some things I understand are problems is that the rig gets squirrely when sails are raised on a mooring or at a dock, when tacking (getting out of irons is trickier) and when trying to heave to.
    "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so."

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    Default Re: Any Experience with Mast-Aft?

    I cannot remember who, but there was a boat "Atrocia" about the size and shape of NY 30 that was rigged that way. I guess it wasn't all that successful. It was not imitated.

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    Default Re: Any Experience with Mast-Aft?

    Quote Originally Posted by Jon Etheredge View Post
    Hasn't Phil Bolger designed several boats with a similar rig?
    In Boat Designs with an Open Mind he describes his disappointment with these boats which require extreme backpressure on the rig to avoid slack on the fore, and furthermore usually didn't perform as well as conventional rigs in runoffs he made. Said the rig had moments of excellence but was erratic and untuneable IIRC.
    Last edited by rudderless; 08-10-2017 at 03:25 PM.

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    Default Re: Any Experience with Mast-Aft?

    Quote Originally Posted by ahp View Post
    I cannot remember who, but there was a boat "Atrocia" about the size and shape of NY 30 that was rigged that way. I guess it wasn't all that successful. It was not imitated.
    Atrocia was a six meter, and her design was intended to take advantage of the rules for the class.

    http://6metre.blogspot.com/2013/06/a...tion-risk.html



    In Mr. Hoyt’s own words, “We had decided to try a radical experiment where most of the sail area was in the fore triangle with only a small mainsail.” The second iteration of the International Rule was in effect and Mr. Hoyt’s aim was to exploit 2 “loopholes” in the way sail area was measured. First, there was no maximum height imposed on the headsail at the time, which meant he could have a hoist all the way to the masthead. The second part of the measurement rule he exploited was the fact that sail area was rated at 100% of the mainsail area and 85% of the fore triangle area. Mr. Hoyt goes on to explain, “Our object was to gain a much larger sail area off the wind…” It is useful to also note that “balloon” spinnakers were not yet in use, thus a typical spinnaker of the time looked like a billowy regular jib which was flown free with no spinnaker pole. With this solution, it could easily be imagined that the huge jib, eased out on a reach or run and held down and out by the clubbed foot, would have an enormous advantage. The mast was placed well aft and the enormous and heavy club footed jib meant “materially increasing its (the mast’s) strength and weight to take care of the absence of distribution of strain obtained from the luff of a normal mainsail.”

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