Plywood frames?

Okay, that's not the 15' 135 CC class C Flyer, but a 13' warped bottom of a later date. It still has similar issues, but does have better balance at high speed.

For good preformance these need to be light and strong. I think some versions of these had reversed lapped bottoms, which didn't do much but complicate the build and leak.

These structures, if traditionally built, rely heavily on neighboring elements to share loads. If you make some areas stiffer, stronger, weaker or more flexible, it can have a cascade affect across a large area. Simply put a stringer needs adjoining and neighboring structural elements to help transmit and share load bearing duties. If you alter properties in one area, you can expect other areas to benefit or conversely become disadvantaged, depending on what's been done.

Consider carefully the changes you make, particularly just for the sake of making a change, as it can have a dramatic affect in other portions of the structure. We see this frequently when new products and techniques are used, in an attempt to fix or solve perceived problems in traditional structures. An example might be epoxy bonding or tabbing of some joints, in a traditional boat's repairs. The pieces once were permitted a slight bit of movement, but now are locked down with cured goo. The glued structural elements becomes isolated and stress risers form in neighboring pieces, plus load paths change as a result of the new strain transfers and things break and crack well away from the area that may have been repaired, seemingly for no reason.

 

Thanks PAR, well said. Yes the lapped bottom version that I am aware of, was called "Black Arrow" and Crandall makes the statement that its an inprovment of his earlier Flyer Racer Runabout design. Its interesting to see the evolution of bottom design and the attempts to reduce surface drag. Somewhere else, a comment was made about gentlemen's racers that they "were probably never intended to last more than a year or two because of the experimenting that was part of racing, therefore a hull was scrapped in favor of a new build" so perhaps leaks could be tollered for a season and then "we wont do that again". And as "something new is something old", look at the Rascal design, it has a pad on a slight V bottom that achieves much the same as the lapped ply of before.

In this instance, I am smitten with the O/B Flyer profile and its general big brother look reminicent of the GlenL Squirt that I started with. Now, that did not have anti-trip chines and my dad persuaded me to add a trim rail along the chine edge that was shaped to ride up in sharp cornering at the stern and forward of the cockpit the rail actually threw the spray down, making the ride much drier and we picked up a little speed because I think we were trapping some turbulated water and eliminated some surface drag. My first experience with theory, design and testing.

Going back to the original querry about plywood/laminated frames, I do understand the issues presented here. Thats why I came here to ask the question. I have been a fan of the Gougeon Bros. methods of boatbuilding and the aircraft like look with 'nothing extra but what is required' way of dealing with transfering loads. However that said, I think I will stick to what is drawn. I have to keep asking myself, "Are you wanting to build the boat or are you wanting to design a boat?" Have you ever been there?

As an aside, I just got another the Motor Boating volumes (#20) with many J. Atkins designs. One of them, the Rescue Minor, made use of only two 3/8 plywood diaphram bulkheads plus transom for a boat of almost 20 feet and was skinned with 3/4 ply ("new material" as Atkins describes it in 1944)

 

Ian, there are many ways to approach scantlings, the one used on Rescue Minor was a relatively new idea when Atkins drew it up, which was a homogeneous hull shell, with torsional loads contained by athwart stiffeners (bulkheads). The hull skin bear most of the longitudinal stiffness, but also contributes heavily to "webs" portion of a box beam. The bulkheads then only have to maintain the relative hull shell shapes, to insure rigidity. By modern standards a 3/4" plywood skin on a 20', low speed powerboat is well, way over the top and a fairly heavy way of doing things. This hull shell could have been half the wight and thickness with only a modest amount of additional structure, had the build method taken a different engineering approach.

Modernizing these old plans is a good idea, but you do have to have a clue about the engineering involved, or the usual result is an over heavy boat prone to several issues. Getting those 1936 plans brought into the 21st century, doesn't cost much and would produce a lighter, stronger, stiffer and more economical to operate (and build) pocket rocket. I'd recommend a taped seam modernization, to dramatically reduce the parts you have to buy, cut and install (looking much like the Gougeon boys builds) and one that will be inherently more water tight and robust. It's a common request of a designer and you may want to look into this route.

 

No worries, I was pleasently surprised to see an opening gambit with a "new material". I dont know if there are others out there who wonder when something like plywood or a microwave became a common day product, for most of us its always been there.

Atkins, did comment about the envisioned heavy useage of a Rescue Minor and drew up the scantlings to match. And yes, its is a logical stitch and glue project. One can only imagine Atkins' comments