Plywood Carvel Question

Why not. Is joining the strips at the chine the problem. I would like an explanation instead of saying it isn't wise. I like to learn these things .

 

A hard chine hull has relatively broad expanses of flat panels, which aren't well suited to strip planking from a strength point of view. Strips offer mostly longitudinal stiffness, while the glue lines, cross grain, but oriented in flatish panels, you lose a mechanical advantage, that is assumed, in the well curved shapes, employed in round bilge shapes. You also place a significant load on a just a single glue line, where these panels attach at the chines, which with this hull are 6.

Don't get me wrong, you can do it, but you need heavier strips and logs, which aren't necessary if the hull was round bilge. Simply put, you can use the tedious method of stripping up a a very narrow plank carvel (what strip planking actually is) or use something that offers a lot more bang for the buck, like plywood or much wider planks (like traditional carvel).

Plywood is an obvious and reasonable conversion for this design. You can use others methods, but some are just better suited than others. Strip planking wouldn't be at the top of this list for this set of shapes. Hell, batten seam would be better then strip.

 

Thanks par. Now i know why i have only seen round bilge in strip plank.

 

Would cold molding work on a Sallie Hyde? All my plans for plywood hulls show heavy frames and lots of stringers.
Thanks for all the advice

 

That's the reason for the strip planked build becoming so popular with boaties and small yards.

Its relatively simple to set up temporary formers & frames using scrap timber then flip the finished hull and fit integrated stiffeners/deck and cabin.

There were hundreds of round bilge and hard chine boats built cold moulded in NZ from late 50s using strip plank. Flat head V8 powered ski boats, open motor boats to 45ft launch and sloops

 

Cold molding is pretty much like making your own plywood hull, in place on the hull, so yes, you could cold mold this boat. I wouldn't, just because it's a difficult method for such a conventional set of shapes, one that plywood can handle easily, with is much faster and easier. Boats built with large flatish panels are best built with material of similar qualities, if speed, ease and cost are a concern.

 

I think I would either carve a half-model or import the offsets into a hull design program like FreeShip, to determine if the planks can be developed.

Fully-developed plywood planks permit lighter framing, as most of the strength comes from the ply skin like a monocoque car body. It doesn't have to be stitch and glue BTW (I doubt S&G would work on this design). I often build with ply and chine logs and would also consider tortured ply methods.

How you intend to use the boat? If you intend trailering lightness is important and dimensional stability is necessary to resist cracking when dry-moored. You'd get both with ply.

 

I suspect, judging by the body plan, most of the hull is developed, except as I noted in the very forward and aft sections, where some diagonal planking or slitting will be necessary. There's no reason this boat could be a taped seam build and if the scantlings where reviewed and updated as required, essentially a frame free build, obviously over station molds, until the seams were tightened up. As Terry points out, this isn't the job for a novice, as these changes need to be worked out carefully.

 

Paul, I've mixed ply and strip in a canoe, mostly for curiosity (you’re bound to ask why) and it worked, though I think my effort is a paint job erk erk

For pretty Sallie H, I wonder if the sheer plank could be ply from bow to the stern whereever it can be developed, with just the upper part of near bow - where the flare looks tricky and there is a saddle curve - completed in strips. Armstpat could extend the strips to the stern - which look fabtastic under glass and varnish. If it’s going to be glassed in and out there should be no strength problem.

The Atkin site noted that the original Jersey skiffs were clinker planked with round bilges. Since we’re talking plywood, that kinda suggests glued lapstrake to me if the original design or lines can be found . . .

BTW what is the proper name for the “fat keel” and was this bottom a transitional form between displacement and planing?

 

It's a "box keel" and indicative of the old SeaBright skiffs. Both Billy and John (as well as others) explored the attributes of the box keel for several decades. The shape was refined and improved. I own a 37' box keel Atkins design (carvel, hard chine), built in 1960, one of his last commissions.

Yes, they were a "transition" design, though not intentionally so. They existed before being powered. It's thought they were modified dories initially and only found along the Jersey shore, with the vertical garboards aft. These were sprit rigged and worked the mid Atlantic fishing banks. They routinely had to skid down the breakers in the surf and this bottom helped steer and got the fish load lower too, without dragging a transom. The sailing versions had a pretty narrow box portion, but when power came along, they made it wider as well as the beam/length ratio, so they could carry the 1,000 pound 5 HP engine and it's fuel. The original skiffs, developed this arrangement to help get them off and on a pretty exposed beach (by hand), but once powered it was found they could accept a heavy engine, placing it as low as practical and maintaining a nearly straight shaft as a result and lastly, it offers much better low speed tracking and handling then the flat bottoms and warped bottoms of the era. Gas and oil engines started getting put into everything imaginable. They were still quite heavy for their output, so efforts where made to get this weight down low. This meant your gear was hanging out below the boat, which wasn't practical for a beach launch. The box protected the gear.

On the disadvantage side, they are about the worst boat to back down, unless you have vectored steering, which would be very uncommon in a box keel design (I've seen a few outboard powered). The box lets them track like a freight train in reverse and don't even think about steering against your prop walk. Even "backing and filling" is difficult with these.

Basically it's a V bottom boat that's backed over a canoe, which then was wedged in place, from midship aft. At low to just over displacement speeds, it's very efficient, though it does run into a drag wall as you try to push it's speed up. Atkins developed a hook to counter the bow up trim, but this is only effective up to the mid 20's, where the drag wall becomes overwhelming. Some have been pushed faster, usually small and light versions and I've seen other designers use a wider box to improve bearing area at speed, but then the hull starts to become something else, with these changes. Even Atkins reversed the V in the after portions on some of these designs (Rescue Minor for example) and with the hook, could get a relatively small engine to push them pretty well.

 

Great history lesson Paul! Thanks.

 

The original boat built to these plans, from the website of Atkin & Co.: http://atkinboatplans.com/Utilities/SallieHyde.html

It's bigger than I imagined from just following the thread.

 

I finally received my study plans. This thing is a beast. 3/4 inch sides and bottom. The flat bottom is 1 1/4 white oak. The high speed option (16 mph whoo-hoo) has an inboard rudder and less upsweep on the rear of the chine. I ordered the plans today.

 

You can have a boat that will do everything that Atkins will do, but it'll weigh half as much, cost half in materials as a result, be easier to build and you'll go twice as fast too. It's often wise to research the designs that address your needs, as you can have hundreds of choices and many of these will not be antique designs with their relayed costs and handling attributes.

 

I've purchased more study plans than I can count. I purchased full plans for the Simmons Skiff, the Glen-l Atlantic skiff and True Grit. I've crossed all of them off as too expensive or not appropriate for my waters. I'm looking for a boat I can go out in rough seas every other day or so after I retire and not drive me to the poor house. Salmon are usually over 15 miles out. I'd love to go for tuna, but they are often over 35 miles out. I haven't seen an economical boat that would be comfortable that far out. I've plugged in numbers for at least 30 boats. The Sallie-Hyde looks really good from a trip cost/time viewpoint. It isn't much on comfort. I want a simple, solid somewhat pretty boat I can be proud of. I don't want to waste time building a huge cruiser with features I'll never use. I also don't want to have to buy a huge truck to tow it the 300 yards to the harbor. Any suggestions?