Considering a mid size (~32’ long, 6’ beam) deep V hull, stitch-n-glue, what are the pros and cons of building in a keelson, of say 4x2 or 6"x3” lumber, horizontally. It would provide strength for groundings, a flat for beaching, and a slight increase in internal volume, at some increase in weight, of course. I see it tapered at each end with vertical bows.

Deep V hulls often have small flat bottom.  I helped assemble a Wharram Hinemoa,  each hull stood upright, which made the operation much easier.
Your timber sounds much thicker than need be,  1 1/2” ok?  But if it where me, I would contrive a throw-away mould as the bottom panel and make the whole base of GRP.  It could easily be given rounded corners.  If damaged, no worries about rot with GRP.

Mark

I’m not sure, but isn’t a ‘keelson’ typically inside the hull? If I understand you correctly in that the proposed timber is to be on the outside of the hull bottom, then the correct term would be ‘beaching shoe’. I’m not sure though, maybe someone else can clarify… 😊

Anyway; I agree that it sounds like a pretty hefty piece of lumber. Unless you have a very small amount of rocker, you’d have to laminate it from several layers of plywood / wood stock, which would add to labor considerably. Depending on the boat it could add quite a bit to the displacement as well. Also, if you plan to beach regularly, then it might be a good idea to make sure the beaching shoe is isolated from the hull skin (so that the hull is completely sealed with epoxy in its own right) so that moisture getting into the beaching shoe doesn’t get into the hull skin. If you do beach very regularly though, then it would be a good idea to ensure the beaching shoe is easy to repair or replace altogether.

My plan for Firstborne, which will be grounded very regularly, is to give it a grounding fillet. Basically I’m thinking of mixing up epoxy with as much aluminium oxide (or grounded quartz) as feasible, and make a ~1-2cm thick fillet under the hull at the centerline. I’ll probably make it quite wide, wide enough so that most, or all, of the anticipated contact area when beaching in sand is protected (I’m thinking about 5-10cm to either side). I’ll taper it to the sides though to save weight, so the 1-2cm thickness is just at the centerline when the abrasion will be at its worst (see attached sketch).

Fibers (glass or aramid) would improve mechanical properties and abrasion resistance of the grounding fillet considerably, but could make it a little more tedious to do the repair, and add to drag once it’s scratched up a bit and there’s fibers sticking out, so I’m still a bit divided there; when the time comes I’ll probably just test a couple variations on a piece of plywood and see for myself how much abuse and grinding against rocks they can take. 😉

To be able to see clearly when I should start thinking about doing a repair of the grounding fillet, I’ll probably add pigments (like carbon dust or something) to the epoxy-granulate mix for the inner half of the fillet (again, see sketch), that way when the non-pigmented part (probably grey or white in color) is ground away to the point that the black starts showing, I know I’ve ground my way half way through, and that I should contemplate a repair the next time the boat is out of the water.

Overall I’m hoping to protect the boat bottom while avoiding unnecessary weight and drag, and to reduce the amount of time spent with maintenance of the boat bottom. Seeing as my boat will be beached regularly, and will probably spend a lot of quality time getting hauled onto granite rocks (islands) in the northern Baltic, those points have a comparatively high priority for me. 😊

Marco

“I agree that it sounds like a pretty hefty piece of lumber. “
I guess I’m making a mental transition from a heavy displacement woody to a light ply boat 😊
I think my ideas is really a keelson, I’d join the ply to the sides of the plank, then flex them out…
Another idea would be to cut a 4x4 diagonally (so its cross section would be triangular) and fix ply panels at 90 degrees, then flex them in to produce a hull shape not unlike your drawing. Then I could add stainless angle as beaching shoe.
Your beaching shoe buildup plan sounds heavy and laborious. What is the argument against a strip of stainless steel? Its tough for the weight, very abrasion resistant, and a lot less labor !