Lindsay Lord Strip Plank Method

[moTthediesel]

I'd like to know if anyone here has experiance with the Lindsay Lord ultralight strip planking method detailed in Dave Gerr's "Boat Strength" book.
This is a sheathed strip construction using epoxy glue and inner and outer sheathing layers of Vectra or Dynel cloth. It is supposed to result in a very light and strong but flexable hull.
I'm considering it for construction of a 38' semi-displacement ultra-fuel efficent power cruiser. The goal; a long, light, and narrow hull with reasonable interior room that can cruise semi-protected waters at 10 knots burning less than 1 gal diesel/hr.
moT

[skaraborgcraft]

Having recieved my copy of Gerrs book this afternoon,i was just to post that exact same question. Maybe sometime in the past 6 years someone may have tried it.

[Daniel Noyes]

Just a thought, but if you are going long, narrow, semidisplacement, and "power cruiser" then ultra light hull construction using exotic composites may be unnecessarily expensive and difficult...


here's why

By definition a Power Cruiser will be a heavy boat compared with extreme racing sail boats and High speed (100 mph +) powerboats where these materials are most often used, the percentage weight savings over a more conventionnal strip plank hull Vs the total weight of motor, water/holding tanks, interior furniture, stores etc.

also the "long, narrow, semidisplacement" adjectives have you pretty well covered as far as efficiency goes and saving a few more lbs. by using very expensive and tricky to work with composites may not be worth the trouble/money.

[Tonyr]

I would go with Daniel here, in that it may not be worth the trouble to go to serious effort to save a few pounds , when you are building a comparatively slow but seaworthy semi-displacement power boat. I built a 25 foot semi-d lobster type boat, conventionally strip planked with eastern white cedar, using Dave Gerr's scantling rules. If efficiency matters on a particular cruise, I can get 10 MPG at 5 knots (close to an easy nominal displacement speed), much less if I push her. I have to think in an old fashioned way about tides and currents, because at slow speeds a couple of knots tide against you is crippling. One can have lots of fun planning a trip to get the current to work in your favour.

I have deliberately added some 700 pounds of internal ballast, to ensure an easy motion in short head seas. The trade-off is a slightly wetter boat, of course. When you add 20 gallons of water (200 pounds), 30 gallons of gas (240 pounds or so), main motor (50 h.p. Yamaha high thrust, 240 pounds), spare motor (9.9 h.p., 100 pounds), stores for a week for two (guess 100 pounds), serious anchor gear, including chain, two large deep cycle batteries, a tool kit of some substance, a composting head, etc. etc., it soon bcomes clear that any weight savings in hull construction are less important than many other things. If a person wants efficiency and comfort, then slowing down will usually give you a satisfactory result.

I would love to have an extra 10 feet to get better displacement speed, but the 25 foot length was all that could fit into my garage.

Regards, Tony.

[JimConlin]

Just a thought, but if you are going long, narrow, semidisplacement, and "power cruiser" then ultra light hull construction using exotic composites may be unnecessarily expensive and difficult...


here's why

By definition a Power Cruiser will be a heavy boat compared with extreme racing sail boats and High speed (100 mph +) powerboats where these materials are most often used, the percentage weight savings over a more conventionnal strip plank hull Vs the total weight of motor, water/holding tanks, interior furniture, stores etc.

also the "long, narrow, semidisplacement" adjectives have you pretty well covered as far as efficiency goes and saving a few more lbs. by using very expensive and tricky to work with composites may not be worth the trouble/money.

In defense of "the expense of exotic composites" like wood strips, epoxy, glass, dynel or vectra, I'd point out that pounds saved in a boat's structure allows smaller powerplants, smaller tanks and smaller trailers, which have lower original and operating costs.

There might be other functional benefits, too. I have a friend whose Concordia yawl has a dynel sheathed deck. He likes the dryness.

[Daniel Noyes]

so sorry, when I typed that I had Carbon and kevlar in my mind, I must read more carefully... carry on.


though I was once told to sheath the side of a old power skiff with "what we had on hand" (Dynel) and it was a night mare, never did get it smooth, I hear it's nice for decks though.

[skaraborgcraft]

I hear what you are sayin,bur as Mr Conlin points out,a lighter hull takes less power to achieve its design speed. Im not so sure if a 38ft semi-displacement boat is right for this construction,but the scantlings are there. My own thoughts were a craft under 28ft,day boat/ weekender,smallest possible cabin with large cockpit,driven by the smallest engine possible. As someone who has no interest in exotics,this appeared to be a more practical (and dare i say cheaper) way of getting a light strong hull that may be an alternative to cold moulding,and much faster. How much weight can be saved in comparison to regular strip plank for equal strength,i dont know,and would have to work on that one. The system was used on boats from 22 to 80ft 40 knot patrol boats,so it appears to be well tested. Cheers

[Kurt@CYD]

It really is a mystery why more boats haven't been built using Mr. Lord's method. His designs were certainly proven in some of the worst circumstances. I suspect it was the fact that people didn't appreciate the that his boats were designed to flex.

Gerr's sheathed strip plank method is very similar to Lord's method in that a very lightweight relatively inexpensive wood core is encapsulated in resin and glass. The big difference is the type of glass used and the added stiffness. I have analyzed a few designs to compare weight between traditional strip planking and sheathed strip planking and it is hard to beat the traditional. But when you factor in the labor savings, possible material savings, and the fact that much less interior structure is needed when designing for sheathing, it becomes much more intriguing.

[Sayla]

I built a 25 foot semi-d lobster type boat, conventionally strip planked with eastern white cedar, using Dave Gerr's scantling rules.

Regards, Tony.

I've studied that book (it's a textbook benchmark in nautical knowledge as far as I'm concerned) - well done and congrats on your boat.

sayla

[Tonyr]

Thank you Sayla. The boat is in its seventh season, and has been through some pretty nasty conditions over the years. It is a tribute to the building method (sheathed strip), plus modern adhesives, sheathing and plywood (for the upperworks) that the boat's overall condition is as new. I certainly overbuilt it, but have no regrets that I did so. I used Dave Gerr's book as my bible, plus Sam Devlin's philosophy of bonding all the interior components to the hull and to everything else in sight.

Regards, Tony.

[JimD]

...
I'm considering it for construction of a 38' semi-displacement ultra-fuel efficent power cruiser...
moT

May we enquire as to the exact design you are considering? A 38 foot boat is not a trifling matter.

[skaraborgcraft]

May we enquire as to the exact design you are considering? A 38 foot boat is not a trifling matter.

Jim,i would hope he would have finished it by now,originally posted 6 years ago, and never got a reply! Cheers

[TR]

It really is a mystery why more boats haven't been built using Mr. Lord's method.

No it isn't.....With the cost of materials and the amount of labour involved, any reasonably sized boat (above say16') is a major investment. Not many backyard builders are interested in multi-thousand dollar experiments.....And no professional is.

The method is not proven and to all appearances does not exist except in Mr. Gerrs book. That Lord got a few boats built 50 years ago says nothing, where are those boats today? Were they a good investment? Cold-molding with epoxy started almost 40 years ago now and has proven itself as a viable construction system, not so Mr. Lord's system.

In looking at Gerr's source for his publication I find very little. Lord (In Naval Architecture of Planing Hulls) mentions this construction method on a couple of pages almost in passing. The only scantling statements are "averages 25% lighter" and he mentions 2 layers of fabric for hulls to 22', 3 for 40', and 4 for 80'.....and that's it!! Gerr has taken this quite a long way........In comparing Gerr's standard sheathed strip scantling with his Lord rule, I find that for an SN of 6 the Lord core is 3/4" while the standard is 1.125". And while Lord writes "frameless", Gerr recommends 8 longitudinal stringers plus multiple bulkheads, how is one to deal with the stringers/bulkheads and interior sheathing? It's not simple. Also Gerr requires epoxy while Lord recommended polyester as he was writing at the very beginning of epoxy use.

[wizbang 13]

I do not want a flexible boat.

[TR]

I do not want a flexible boat.

+1.......

[skaraborgcraft]

Tad, i didnt realise Lord was using polyester! Bothe Dynel and Vectra polyproylene are not availiable in the UK. Defender will ship from US. I have read though that Vectra has less peel strength than glass or dynel, and that xynole is probably better than either if used to coat a core. However, is Xynole as flexible as either of the others?
I read a hull of 40ft was 1600lbs with normal strip,and with Lords system less than 900! One has to wonder just how much flex these hulls had,and im very surprised that polyester would have been a success in that application. Cheers

[Kurt@CYD]

No, I don't find a flexible boat attractive either. What I find interesting is that at a time when every boatbuilder in the world was expirementing with fiberglass (many with poor results), that there weren't more builders trying this method from a well known designer. He does mention in his chapter, Hull Construction, that "The Lord office has designed patrol boats up to 86 feet which are serving in all parts of the world" using his method but I think even the best internet sleuths would have a hard time finding record of them. He does mention that the U.S. Rubber Company developed a polypropelene fabric to be used in his sandwiched hulls. He claimed the resulting impact resistance was 8030 ft. lb./cu. in. versus 1900 ft. lb./cu. in. for glass. How does that compare to the available xynole?

[skaraborgcraft]

I still dont understand how he used flexible fabrics with polyester????

Can anyone tell me if there is much difference in quantity of epoxy used to wet out equal size and weight of Xynole and Vectra polypropylene? Cheers

[TR]

I don't think Lord was particularly well known or in demand as a designer, apparently he did some patrol boats, some oil field supply boats, and a very few yachts. Phil Bolger worked for him for a short time, I think drawing houses as Lord had no boat work. Lord sent Phil on to John L. Hacker in Detroit where there was real boat design work. Anyway "serving in all parts of the world" ? really....all parts? Iceland? Tasmania? Alaska? Another meaningless statement.

Today we usually see impact force measured in PSI, kPa, or MPa, I don't know what those units might mean(they're totally vague with no supplied detail of materials or test method). Any published laboratory results will be far different than what can be obtained by boatbuilders in the shop. This is why you need to make your own test panels and try them out. If you don't want to do that, build with proven materials.

I'm no expert, my plywood boat is sheathed with 2oz fiberglass set in epoxy (inside and out) and has given no trouble in 11 years of abuse. That light glass sheathing more than doubles the stiffness of the 3/8" ply and increases impact resistance all out of proportion to it's weight. As I understand it the alternatives (Dynel, Vectra, Xynole) were once cheaper than fiberglass (no longer the case from what I can tell), lighter weight, and easier to handle. The heavy glass available at the time was hard to handle and use. The Gougeons claim these alternative fabrics "are parasitic: they contribute weight, but very little strength or stiffness to the structure."

[skaraborgcraft]

If the system had absolutely no merits,i ask why Gerr bothered to print it in his book? One designer currently suggests using a glass layer on the inside and outer skin of a "lightweight" ply core, just as Tad has done with his dinghy, but i have always read that weight for weight,the plywood will be stronger by itself....true or not?

Maybe its fine with a dinghy,but a cruising yacht that would normally be skinned with 12mm ply and instead is built using 6mm and glassed inside and out. It sounds like the Lord method but using plywood instead........and not flexible sheathing.
Glass may be better for adding stiffness, but xynole and dynal are supposed to be far superior in abrasion and flexibility.
I have not used anything but bog standard glass,so im interested in these a possible alternatives. Xynole seems to be a favourite of Reul Parker, and even William Gardner was an advocate of Vectra polypropylene.

[TR]

i ask why Gerr bothered to print it in his book?

I'm sure I couldn't answer that.....

using a glass layer on the inside and outer skin of a "lightweight" ply core,
but i have always read that weight for weight,the plywood will be stronger by itself....true or not?

Thicker will be stiffer, but will not be very abrasion or puncture resistant. And when building shaped boats, the bending of the ply is a big issue, thinner bends easy.

Glass may be better for adding stiffness, but xynole and dynal are supposed to be far superior in abrasion and flexibility.

How much abrasion resistance do you need? The epoxy/glass on Ratty is untouched where the fenders wear the paint off the topsides. We've done a bunch of ply bottoms with Kevlar which is impervious to dragging over oyster/barnacle covered rocks.

In my experience dynel was easy to handle. It's chief reason for being (IMO) was to ensure that we got a really thick coating of epoxy on the entire hull. That boat was my first design built (30 years ago, a 16' cold-molded double-ender) and rotted away quickly because it was built of cheap meranti ply and mostly unsealed inside. The dynel skin in epoxy was still perfect when she crumbled to bits.

I have not used anything but bog standard glass,so im interested in these a possible alternatives. Xynole seems to be a favourite of Reul Parker, and even William Gardner was an advocate of Vectra polypropylene.

And I think you'll find the sheathing is not intended to add structural stiffness, there's an adequate wooden structure, the sheathing is a sealer and adds abrasion/puncture resistance. This is very diferent than the Lord/Gerr claims.

[JimD]

Jim,i would hope he would have finished it by now,originally posted 6 years ago, and never got a reply! Cheers

Ah. I see. Usually I catch these things. My guess is he hasn't finished it. I think we would have heard about it if he had.

[wizbang 13]

dynel and xylene , though different materials, are almost the same.I have used both.
I have never used vectra, ( poly pro cloth) . I imagine it would be similar .
Anyone used all three ,to comment?
Of course , glass. With wood, I like to avoid its use. If I were building a strip canoe, I recon I would use the glass, for stiffness.
The thought of using dynel on a lightweight boat , for strength, just goes against how I think about things.
I am also a bit confused the time transition from Lords use of polyester to epoxy .
Anyway, these seem like 50 year old military experimental boat ideas. Not something for the likes of us.

[skaraborgcraft]

Gerr also mentions the "Ashcroft" system in his book,and says very little about it and thinks it has little place in todays modern building methods. B+B yacht design build the Outer Banks 20,using the Ashcroft system, probably because they got the hull strength they needed for the least amount of weight/labour/cost and its amatuer friendly. There is a few pages in Gerrs book with information and scantlings for the Lord method, and nothing for the Ashcroft system. Both date back to the end of the war,my copy of "boat building simplified" by Ashcroft is a 1947 re-print. Maybe Gerr believes the Lord system is superior to Ashcroft?

My clinker built sail and oar boat is a lot lighter AND flexible in comparison to the same boat built in carvel. When Gerr suggests Lord type hulls with moderately thin wood cores can withstand flexure/deflection,im just thinking clinker Vs Carvel...one is lighter and more flexible than the other. Lords method is just lighter and more flexible than standard strip plank. Does not mean its a bad system,just different,and surely suited to some smaller boats,especially those that get used on and off a trailer on a regular basis? More research needed..... Cheers

[Sayla]

Is the vectra by the same people as make the stretch resistant vectra rope.

[skaraborgcraft]

I have no idea....what about spectra....seems to be the latest all singin an dancin wonder material......but it dosnt seem many have used the above materials enough to make a comparison. I believe Tom L, did an abrasion test on many of them,but thats not the same as flex test.....i did recall he said vectra had lower peel strength....so i wonder why on earth it was suggested as a sheathing on wood cores,and with polyester!

As an example of a boat that could be built in this method,and i know Tad is familiar with it, the Atkin "two brothers", which is a 28ft box keeled seabright type motor sailor. Say that getting the original materials specified is nigh on impossible local,and importing it if you could find it,is just too expensive. Lords method of using smaller,cheaper and lower quality timber as a core,means that this boat could now be a viable projest. The original construction was for a strip planked box keel and bottom,with lapstrake sides.
Apart from losing the lapstrake sides,this boat would be do-able in this method. What you save in hull weight can be replaced by a greater capacity in fuel or water tankage, without going over the original displacement. Perhaps you could use thinner plywood and still retain the lap sides, with glass inside and out? As it gets harder and harder to find suitable timber (yacht quality), and to be able to afford it when you do, i think this system may have merit. Having said that, i dont know how much one pays for foam cores,or whether that would work out cheaper for same relative/thickness/ stiffness/ puncture resitance etc as using say a pine core....and it certainly would not be a wooden boat anymore. I realise that one could use no end of wonder fabrics and resins today to build the same boat with a much thinner skin and 10 times as strong,but that also comes with an exotic price.

I certainly could not afford (or justify to my better half),a new build of "two brothers" as specified by Atkin, but under Lords method,it could mean its a possibility . Definately more research required. Cheers

[moTthediesel]

Jim,i would hope he would have finished it by now,originally posted 6 years ago, and never got a reply! Cheers

Man, how time flies!!

Well, I'm still here, and still working on the design, and still waiting to hear from someone who has real experience with this building method

I have built it in 1"=1' scale, here it is --



Maybe there's a way to make my wife and I one twelfth our current size?

[skaraborgcraft]

Hi M.T.D..... hope you dont mind me bumping your thread?

If the full size boat,runs anything like that model then you have a cracker on your hands! Great job!

How much weight do you figure you can save using Lords method on your design? Cheers

[moTthediesel]

Hi M.T.D..... hope you dont mind me bumping your thread?

Not at all -- but I was a bit shocked to see it!

If the full size boat,runs anything like that model then you have a cracker on your hands! Great job!

Thanks! The model runs flat and smooth with very little wake. I've been doing performance testing with it at various scale displacements to see what effect that has on speed/wave making. I'm not sure how much real usable data can be had from a model this small. But -- it gives me a plausible excuse to just play with my boat

How much weight do you figure you can save using Lords method on your design? Cheers

Hard to say at this point, I'd like to use xynole, as I really like to work with it -- but it soaks up a huge amount of (heavy, expensive) epoxy to fill it. I'm making, and testing for weight, various test panels to try to determine what to expect.

Tom

[skaraborgcraft]

Dosnt dynel soak up a lot of resin too? I have no idea about vectra and how much that takes to wet out. Also, the point about xynole,does it flex just like dynel and vectra?

Model testing only proves so much,some say models of less than 6ft are not accurate enough,but as you say,your model runs flat with very little wake,and i have seen models the same size pushing much bigger wakes, so something must be right! I wanted to make a scale model of "two brothers", but at the scale suggested to me,i may aswell have built a "big surprise" and found out if these seabright hulls perform as Atkin suggested. The only similar hull that has any published data as being a success was "clamskiff" at 17ft. Apparently, their own seabright type "we,re here" did not perform as well as Atkin suggested during the build process. I didnt want to pour money and time into a boat that i liked,if it didnt perform as was suggested. Pat Atkin has been aboard a completed "two brothers". but does not re-call how it performed, which is a great shame. My main interest was speed with low power,its just not been confirmed that, that particular design performed as Atkin suggested it "should". Im still crunching numbers.....its a long term interest. Cheers

EDIT: Will be interested in your test panel result and process if you are willing to share here?
EDIT 2: McNaughton groups paper on scantlings for sheathed strip plank construction is based on Lords work, me thinks i need a copy to compare with other material. Has anyone got this and what did they think? Cheers

[Kurt@CYD]

I would be interested what sheathing McNaughton specifies. Is it a synthetic like xynole or dynel?

I do like sheathed strip plank using glass cloth. Having built a few boats cold molded, the strip planking was much faster even with all the glass work.

Mark Bowdidge is doing a lot of work with sheathed strip planking using Paulownia.

http://bowdidgemarinedesigns.com/

[skaraborgcraft]

Kurt , from what little i have found,McNaughton use glass/and/or xynole......not the stretchy fabrics that Lord used in his system. Been reading through Nicholsons cold moulded and strip plank book, there is a lot of variation in scantlings. I hate glass and goo work, i would rather just glass once outside,but if the weight saving and strength is possible using a pine core with interior sheathing,then i will at least consider it..... Cheers

[TR]

I would be interested what sheathing McNaughton specifies. Is it a synthetic like xynole or dynel?

As published in Boatbuilder magazine of july/aug 1990, Thomas MacNaughton's Scantling Rules for Sheathed-Strip Construction specify only fiberglass or carbon reinforcement in epoxy resin.

Mark Bowdidge is doing a lot of work with sheathed strip planking using Paulownia.

http://bowdidgemarinedesigns.com/

Mark knows what he's up to and (AFAIK) he specifies fiberglass cloth set in epoxy resin.

[skaraborgcraft]

Seems that glass is used to add stiffnes to a smaller core,and those boats built "trad" strip plank without fabrics for strength,seem to use Dynel/Vectra just as an abrasion sheild. I think i will check the average scantlings between Lord/Gerr/ Nicholson and McNaughton,there being much variation on planking thickness depending on station/frame spacings, and propsed service duty of the craft. Cheers

[TR]

I think i will check the average scantlings between Lord/Gerr/ Nicholson and McNaughton,there being much variation on planking thickness depending on station/frame spacings, and propsed service duty of the craft.

Why? You will have to make numerous assumptions as Gerr makes recommendations based on the cubic number, Nicholson uses just length over all, and MacNaughton uses displacement as a basis.

Far better to calculate what the load is and then design a laminate to meet that load. See Principles of Yacht Design, or ISO, ABS, Lloyd's, or DNV, etc. rules.

[Pericles]

Zounds sirrah, but that's a fine model. Be you re-inventing the wheel? Raised foredeck boats have ever been my desire.

http://classicyacht.org/ludreamboat

[skaraborgcraft]

Er......thanks Tad. Someone borrowed my copy of Lloyds....not returned yet. Think some of it is online. The point of this Lord strip plank method is to reduce weight. Surely Lord has(and Gerr) have done calcs for loading as the scantlings are different to Gerrs usual method. It doesnt appear anyone has built or even likes the idea of Lords method. I have a lot of number crunching to do..... cheers

[skaraborgcraft]

Blanchard cruisers are real peachy! But no reason why the same style cannot be built in modern and probably lighter construction,and hence more economical to run.

[jameshow]

i would have thought that cedar strip plank is way to go? Light and stiff like many racing yachts as to the design make sure the beam / length ratio is similar to other designs also check out the hull shape to prevent pounding forward a narrow v or u shape might be better than a Chine? Yours James

s QUOTE=skaraborgcraft;3461625]Blanchard cruisers are real peachy! But no reason why the same style cannot be built in modern and probably lighter construction,and hence more economical to run.[/QUOTE]

[skaraborgcraft]

Yes James,no reason why cedar strip could not be used, at this size though,and tonnage, im all for a stout (guiness) construction and not flexy Lord style.