Cold Mold over Strip Plank?

Discussion in 'Boat Design' started by stonedpirate, Feb 12, 2012.

  1. stonedpirate
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    stonedpirate Senior Member


    Is it possible or desirable to build a strip plank hull then do a double diagonal over the top?

    I am after a beefy, thick hull that could be picked up and used as a battering ram :p
  2. michael pierzga
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    michael pierzga Senior Member

  3. viking north
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    viking north VINLAND

    From my experience, Stripped plank in itself is one of the strongest and tightest of the wooden building techniques. The best way to reinforce this hull construction is using a good thick GRP overlay.(say 1/4 Money permitting I would use epoxy second choice vinylester resin. GRP will match added stiffness but exceed impact strength of additional veneer overlay. It also would require less wetted surface maintenance and easier to repair when compared to what would be required if the veneer outer coating was comprimised and absorbed moisture. The one drawback is the inside of hull should also be epoxy coated (don't recommend vinylester here) to prevent moisture absorbtion of the strip planked hull from the inside. If it's super strength you are looking for GRP using epoxy is the ultimate with this hull building system.
    Question for the forum-- If a strip planked hull is wood venerred on the outside(using either epoxy or another bonding glue) is it subject to the same downfall of moisture accumilation-veneer seperation-and rot if not coated on the inside with epoxy. Logic tells me yes as that moisture is still captured by the water tight outer veneer and glue sheeting in a similar manner if it was GRP coated. Thus regardless if the strip hull was sheeted in veneer or GRP the hulls inside should also be sealed.--???-

    A yacht is not defined by the vessel but by the care and love of her owner---
  4. Tad
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    Tad Boat Designer

    While 1/4" of epoxy and fiberglass will undoubtedly be bulletproof (small caliber), it's an expensive and heavy solution. Diagonal veneer layers add stiffness and puncture resistance with low weight and cost penalties. Definitely sheath the entire exterior in one layer of cloth (glass, vectran, dynel) and epoxy. Use Douglass Fir for the diagonal layers if you are worried about strength.

    Our current understanding of wood is that it will retain most of it's strength and stiffness almost indefinitely if we keep it relatively dry. Sealing with epoxy keeps the wood dry and thus (as dimensions change with moisture content) minimizes movement which breaks down bonds and allows moisture ingress. For maximum life of a wood structure bond the pieces with epoxy and then seal coat the entire structure (inside and out). For positive sealing use three coats, or light scrim fabric to ensure total coating. Problem areas are point loads with metal fastenings which move under load and eventually allow water to invade, re-bedding regularly will help........
  5. viking north
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    viking north VINLAND

    Thanks TAd I thought so on the interior sealing--I have never veneered a strip planked hull -always use GRP epoxy - layered according to use and requirements of the customes or as recommended by his designer and at times "what do you think" engineering -- Should we add another layer to be sure ?? If weight and money was not a factor the answer "Why Not" :)
  6. PAR
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    PAR Yacht Designer/Builder

    Molding veneers over a stripped hull is pretty common and about the best way to keep the strength to weight ratio reasonably, particularly in larger sizes. Of the dozen or so different strip planking methods, if you remove the versions with molded veneers, you about half the list of possibilities. As far as fastener movement and point loading, in most cases (professional builds),the veneer fasteners are temporary and removed once the epoxy cures. Bagging insures good strip/veneer interface bonds, though stapling through small hunks of thin plywood or my favorite plastic pallet banding strap, can provide enough pressure to insure the veneers lay down and permit easy removal (just pull the banding strap and out they come).

    As to arbitrarily veneering a stripped hull, well this is just as foolish as self designing an ocean going 10' boat. A hull shell needs to be engineered for the loads. Often you'll use more or thicker veneers in key locations, while less in other areas, such as the topside planks, where loads are lighter.

    As to a battering ram hull shell, well this is also silly and expensive, from an engineering point of view. You can have a tougher hull shell, with lighter scantlings, designed to to give a little, then one that's overly stiff and heavy, though able to bash things, will transfer all the force paths right through into the structural elements and break things up internally.
  7. Tad
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    Tad Boat Designer

    As to water ingress via point loaded fastener movement I was thinking of permanent fittings, things like deck hardware, chainplates, rudder hardware, etc.....Fastening of veneers (only necessary while the epoxy sets up) is often done with plastic nails or staples, which can be sanded and don't have to be removed....
  8. viking north
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    viking north VINLAND

    Michael--just got a chance read your link to Gartside Boats-- wow --Paul doesn't think too much of strip planking. The only build experience i've had with it was a few 25-30ft fishing boat builds in my early days in NFLD. We sheeted the exterior with a good heavy layer of glass/epoxy and just painted the interior. They were a little on the heavy side but proved to be very durable and successful craft. Superior to their caravel planked counterparts with the added feature of being easier to build for the average guy. I've never heard anything negative over the years and was caught a little off guard on Pauls evaluation. I can see now the added advantage of the veneer as recommended by TAD and PAR above if not for stength for sure visually. Well StonePirate if you're building a truck for work I'd just lay on the epoxy and glass however if you're building something pretty, looks like the veneer is the way to go. I've learned something new again today,-- If this keeps up for another 40yrs,i'm going to be "some smart" :D
    Last edited: Feb 13, 2012
  9. upchurchmr
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    upchurchmr Senior Member


    Take a look at the Gougeon book on boat building, available free here. 061205.pdf This has been a good reference for a long time. The is some specific information on strip planking then veneering.

    As the other guys say, better to have the boat be designed rather than just adding extra stuff. But diagonal veneers on strip plank has been used for a long time.
  10. bertho
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    bertho bertho

    one good way for very stiff hull ! and easy to built.. good for easy fairing also.
    I add another horizontal strip outside to avoid diagonal print over the fiber..

  11. cthippo
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    cthippo Senior Member

    I'm planning on doing pretty much this when i start on building larger boats. I figure running the firstr layer horizontally will give me a nice, solid, and reasonably smooth base for doing the diagonal layers that follow. I plan to use 1/4" strips for all three or 4 layers and just change the orientation.
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