How big a boat can built with glued lap construction ?

Discussion in 'Boat Design' started by PeterSibley, Feb 10, 2011.

  1. PeterSibley
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    PeterSibley Junior Member

    Hello ,
    this is my first post on Boat Design .I'm normally a contributor to the WoodenBoat Forum but thought I'd ask a question here ...after reading threads quietly for a while .

    I'm considering a 6 ton ,rather traditional design based on a design called Marie Michon ,a 7 ton vessel ..There a reference to her here on Boat Design at post 123 by BATAAN. http://www.boatdesign.net/forums/boat-design/gaff-cutter-35344-9.html.
    I had done a rather nice design (In my opinion !) based on this design but increased to 10 ton .I had begun construction but family circumstances have changed dramatically and a smaller boat is called for ,a boat that should also be dry storable .

    The dry storage part of the requirement seems to indicate glued lap .It had the potential to be quick to build and I hope strong .It is less fiddly than strip planking or cold moulding , both of which would drive me mad ! The appearance of glued lap would well suit the design aesthetically ,in my opinion at least .

    I have been thinking in terms of 17mm or 19mm pressure impregnated (ACQ) ply ,glued and riveted laps with substantial laminated frames on 300mm (12'') centres .I would also glass below the WL to exclude worm ,a necessity in Australia .I certainly appreciate that glassing over clinker will be a pain !

    Could I ask the board if this idea seems feasible ? All and any criticism is welcome .Thank you for your time !
     
  2. PAR
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    PAR Yacht Designer/Builder

    'Glassing over lapstrake isn't a pain, it's imposable, unless you radius the edges so much that it no longer looks like lapstrake. You can 'glass the strakes before fitting, but the edges of the lap are what get abused, so the 'glass isn't helping much.

    If you're going to glue the laps, you don't need the rivets. In fact, it's just inviting a path to the inside of the boat if you do. You'll also not need the frames, if the glued lap design is properly executed.

    I also have issue with the plywood selection. As a rule, particularly on carvel and lapstrake builds, the planking is the finest in the boat, for obvious reasons, it's keeps your socks dry. Using an inferior plywood, to save a small amount (compared to the total project cost) just isn't sound policy.

    In the end, your questions make me wonder about the design considerations for the project as a whole. An experienced designer wouldn't "mix and match" build methods. They'd pick one and stick with it, incorporating the good and bad points as best as possible. Especially, when you've "increased a 6 ton design to 10". Nearly doubling a specific design never really comes out well and can cause unforeseen global load implications. This makes me ask how much design and engineering experience you have?
     
  3. PeterSibley
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    PeterSibley Junior Member

    Thank you for your comments PAR .

    To reply , ACQ isn't low quality ply ,it is pressure impregnated on every ply before glue up and was recommended to me by a boatbuilder and good friend with 40 years of repair experience of boats in our climate .The ACQ material is extremely rot resistant ,certified for in contact with ground exposure and fresh water .Price is not the consideration ,durability is .Rot in ply ,of what ever quality is a severe problem in the sub tropics .

    Yes ,I appreciate that the lap edges would need to be rounded below the waterline .I can live with that and I'm sure the fish won't mind .

    Could you clarify ''mix and match''? My inquiry is to the limits of glued lap as a method .I'm not sure what you are referring to .

    If you are interested in the design process of the previous larger design ,this link will take you to it .
    http://forum.woodenboat.com/showthread.php?97232-A-discussion-....-quot-Marie-Michon-quot
    Ed Burnett was kind enough to involve himself in my efforts and offered considerable extremely valuable advice .The result was a quite a good design in his estimation .
     
  4. bntii
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    bntii Senior Member

    It sounds like you have a quite a nice project going there Peter- welcome to the forum.
     
  5. PeterSibley
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    PeterSibley Junior Member

    Thanks bntii ,I'm really hoping someone with knowledge specific to my question happens along !
     
  6. PAR
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    PAR Yacht Designer/Builder

    ACQ is the treatment process, not the quality of the panel construction. Typically it's used in land based construction and has fewer veneers and restrictions of defects, both internal and external, compared to marine grades. I'm familiar with rotting issues, I'm building the in the sub tropics too and pressure treated ply, for the most part isn't needed, if you're using encapsulation techniques, which glued lapstrake builds require. I'd strongly recommend you use BS-1088 from Joubert. I'm not sure where you are there, but you may want to check with Denman Marine for some Gaboon, maybe Bunnings is worth a look see.

    You're using laminated frames on 12" centers with glued laps, which is a mix of a traditional methodology and modern techniques. A true glued lap needs no frames, though relatively equal spaced, athwart partitions (bulkheads, furniture, etc.) are necessary. This saves a substantial amount of weight and fastener penetrations in the hull shell, which if done as a true glued lap will have zero, other then specific thru hulls for raw water, etc.

    Both methods are valid, traditional lap with sealed (not glued) laps, frames, floors and stringers. This old method permits some movement, which allows some strain transfer and load sharing with neighboring structural elements. It's not good for wet/dry cycling, but is for a moored craft.

    Glued lap is a different animal structurally and doesn't have much load sharing from structural element movement. It relies on a stiff and monocoque hull shell approach. The skin of the boat, being for all essential purposes a single, molded unit bearing all the load, much like a single skin GRP hull. It does need local reinforcement for load concentrations, like the mast step, chain plates and the hull partitions to retain it's athwart shapes, but is devoid of the usual structural elements such as frames, floors, stringers, etc.

    Ed is a good man and one of the few remaining over at WoodenBoat, that isn't involved with the "mob mentality" that has taken over on that forum in recent years. If he signs off on your project, you're in good shape.
     
  7. PeterSibley
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    PeterSibley Junior Member

    Thanks PAR ,Ed has been extremely helpful and is quite brilliant .He took considerable interest in the project as it was quite a good example of developing a design from proven antecedents .That particular design was designed to be carvel.... but as I mentioned before family requirements have changed drastically and dry storage is now requirement ,as is a smaller boat.

    I plan to use very similar methods to develop as smaller boat .I'm not absolutely fixated on glued lap but feel it might just solve a few problems .I take onboard your comments regarding frames .The reason I was considering them was as a result of an article by Joel White (have I got that name right ? ) in WoodenBoat magazine discussing a French designer's work .This gentlemen had specified 15mm glued lap and laminated frames at 19'' centres .Mr White had expressed concern regarding puncture resistance if hit a floating object .

    As a result I had thought to close the frame spacing and use heavier ply .Weight is not really a consideration on a boat of this type .She will have 4000 pound outside ballast and somewhere around 2500 pound inside ,depending on engine and fit out .

    Denman sells lovely ply but is a couple of thousand km South of me .Bunnings is arge box store not noted for quality .There are however plenty of suppliers of quality ply around .
     
  8. PAR
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    PAR Yacht Designer/Builder

    I let the design parameters dictate scantlings, rather then attempt to force my desires on the design. In other words, there will be a range of planking thicknesses for the specific build method, given the basic parameters of the yacht. Thee will be a high end, for the "heavy duty" version, which usually detracts some level of preformance from a sailing yacht and a low end, which is the end you nudge against when trying to get as much as you can from the puppy.

    I remember the design and designer Joel White was discussing at it stirred a fairly healthy debate on the forum of the era (which wasn't WoodenBoat). He had a point, because of size or more importantly momentum. Joel was an interesting man, a minimalist in yacht design. His designs didn't have anything they didn't need and an old school specialist in traditional building methods. His idea of the upper end of the scantling possibilities was much higher then what most today would consider. When he learned design, yachts were still quite heavy, especially with the new wonder material of 'glass. He was taught by designers who enjoyed a hefty boat, with long overhangs and slender proportions, maybe enough headroom to partially stand in the galley.

    I'm not sure of the general dimensions of your boat, but 3/4" lapstrake sounds stout. Personally, I dislike over built boats. To me it's just extra money in the project that doesn't really do anything except slow down the boat. Now, I realize you're not building a 'round the buoys craft, but why mill up material you don't need, let alone pay for it.

    Have you a copy of "Elements of Boat Strength" by Dave Geer? This could ease some of your concerns. In the size range you're getting into, you're going to want someone to sign off on your plans at some point. You insurance company will love you for this.

    Peter have you tried Duck Flats?
     
  9. PeterSibley
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    PeterSibley Junior Member

    The boat I designed , based on Marie Michon is a very old fashioned type ,the aim was a comfortable motion at sea .It is heavily ballasted and if Marie Michon's times are to be believed (and I think they are ) ,not slow ...in fact she would be a very good single hander .

    Stout and overbuilt I like .There is no advantage to lightness in this design ,the weigh may as well go into strength for the day I hit a floating log .
    \
    Thanks for the recommendation ,I'll look for Geer's book .

    Information on the upper end of glued lap seems hard to come by .Thanks for you help .
     
  10. rwatson
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    rwatson Senior Member

    Might be worth an inquiry though - he seems to be far more competitiive even to mainland suppliers, since he ships in fairly large lots.
     
  11. luckystrike
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    luckystrike Power Kraut

    I agree with PAR t... you have to much to many frames planned. In the Netherlands they build the "Waarships" in a variation of glued lanstrake since 1970. They have a stringer behind each gluing where the planks meet and produce bomb proof hulls with that. That makes the build process fast and more precize too. You can srew the new plank easily to the "old" one, which is very effective.

    Just a few bulkheads are in the hull of the "waarschips" only to support local loads or where accomodation seperates the room.

    Grreeetings from the North Sea Coast, Michel
     
  12. PeterSibley
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    PeterSibley Junior Member

    Michel ,thanks .

    Yes I looked at the Waarship site but I couldn't find an English version and I'm afraid I don't read Dutch .Google translate wasn't cooperating .Lap battens is definitely a possibility .I've know of their existence but nothing about them .

    Could you tell me the planking thickness they use in their (heavier) hulls ?

    I'll be back tomorrow ,I'll log off now as it is late at night here .
     
  13. PeterSibley
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    PeterSibley Junior Member

    Michel ?
    Does anyone know anything about the Waarship construction scantlings ?
     
  14. luckystrike
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    luckystrike Power Kraut

    Hi Peter,

    sorry, I'am a little late for a respond.

    Waarships are light displacement boats in general. My old quartertonner, (7,25 x 2,5 x 1,55m, 1,1tons, 1/4 ton world champion in 1974, built 1973 was from 10mm and 8mm plywood. Standart for this boat is 12 and 10mm.

    From which boat do you want to have the scantlings? I have a source to ask questions

    Best Regards, Michel
     

  15. PeterSibley
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    PeterSibley Junior Member

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