Glued lap vs framed & riveted lap

[KenC]

I'm thinking of building the L.F.Herreshoff/John Gardner rowboat from Gardner's "Building Classic Small Craft". The design calls for framed (every 8") & rivetted lapstrake construction, but I'd like to try glued lapstrake construction, to save on weight.

I know that some designs, such as Iain Oughtred's (I also considered his Acorn 15) are completely frameless, but they were designed specifically for glued lap technique. So my question is -- would a design originally intended for the heavier framed lapstrake construction be weakened significantly by going to a completely frameless glued lap?

[Bayboat]

It's hard to generalize about this. My reaction is, why eliminate the frames altogether? In theory, a good strong hull built to a frame-lapstrake design would still be strong if many of the frames (not all) were eliminated and the laps were glued. I'm not sure that gluing strakes of solid wood would work all that well, due to differential shrinkage/swelling. Nowadays a number of professional builders are applying the glued lapstrake plywood method to "traditional" looking boats. If you go the plywood route, which I recommend, you might think about installing one frame about amidships and one or two somewhere between this and the bow and stern, as needed to preserve the shape of the hull. I would think that most of the information in Oughtred's or Simmons' book on glued plywood lapstrake construction would be applicable to the Herreshoff/Gardner boat built by that method.

[ 01-20-2003, 01:38 AM: Message edited by: Bayboat ]

[Keith Wilson]

Frames are necessary with solid wood planking to keep the planks from splitting. Solid wood is relatively weak in tension across the grain, so the frames run at 90 degrees to take the tension loads (sort of like plywood, actually), hence lots of little steamed frames in many boats. Frames are only needed with glued plywood planking to hold the hull in shape. For example, Joel White's small glued-lap boats (Nutshell, Shellback, etc.) use a single stout laminated midships frame. Other designs use a small number of relatively large-section frames, bulkheads, knees at the thwarts, strong gunwales, or a combination of these. If I were going to build that boat in plywood, I'd probably use Joel White's method. I think glued plywood would be an excellent way to build that boat; It could be both lighter and stronger than traditional construction.

I've thought about this quite a bit because I built a ply-lapstrake coversion of another design that was a bit more flexible than it should have been.

I wouldn't glue solid wood lapstrake. Mechanically-fastened lap joints can slip a bit in shear as the planks swell and shrink, and still stay tight. This is why traditional lapstrake can handle wet/dry cycles better than carvel. Glued joints are either rigid or broken. As glued solid planks swell, they can either pull away from the frames or, worst case, break something. Plywood is dimensionally stable so you don't have this problem.

[ 01-20-2003, 09:48 AM: Message edited by: Keith Wilson ]

[David Toner]

Ken,
I am in the process of building two of the 17' Herreshoff/Gardner rowboats which you are considering. One of them is complete except for painting and the other is a hull only. I used the glued lap plywood method with 6mm planking on a 18mm floor. I am planning to install sliding seats in both of them. I don't believe that the hull is sturdy enough without some internal bracing in the way of frames. Perhaps if you wanted a very lightweight boat and used a sliding seat row station with the wings attached to the seat and not the gunwales of the boat this could work but I would not suggest it. I have done exactly what Bayboat suggested. I built three laminated frames and installed them evenly along the hull. they measured approx 3/4" x 1". These along with laminated breasthooks fore and aft gave plenty of rigidity and the boat should still be under 85 lbs minus the seats. These boats are on the back burner right now while I build do some commissioned work but I will post some pics of them when they are afloat. Feel free to contact me at tonersboats@msn.com. You are welcome to use my jig if you are anywhere near Seattle.

[Dave Williams]

Ken,

Bayboat sort of said it but I will say it for sure. Gluing laps in solid wood is Not a good idea. Good luck.

Here's to kindness,
Dave

[KenC]

Thanks for the quick replies. Gardner's directions actually call for plywood strakes, on a solid wood flat bottom, even though its unlikely that Herreshoff originally envisioned it that way. My intention, although I guess I didn't make it clear in my original post, is to build in glued-lap plywood.

I had considered compromising with a reduced number of frames, and that sounds like the way to go.

David Toner -- I am nowhere near Seattle, but thanks for the offer. I do have a few questions, since you're miles ahead of me on this project. I'll contact you off the board.

[Paul Scheuer]

David: Pictures of boats afloat are a dime a dozen. We want to see the guts and gore of construction.

Also. Be careful of that back burner stuff, it can go on for far too long.

[JFH]

My expeience has been similar with an old design that I have modernized in the glued lapstrake fashion. I used 6mm ply and overbuilt the first with too many frames and supports and a heavy deck on both ends of a double-ender. I new build lighter and use less frames and am considering 5mm ply for the next one.
You will get a lot of support from decking and seats as well as a few well placed frames below the floor.

See an example of my work innerbayboats (http://www.innerbayboats.com)
The newest one is in the updated section (shop to water)
Enjoy, Jim Hammond
the site will be updated very soon

Wooden Boats...nothin better....