Thread: Composite PDRacers

You'd be very hard pressed to build a foam cored hull to rival the strength, stiffness and weight of the plywood design Mik has developed. This is typically true of all taped seam small craft, as you'd need to turn towards exotic materials (carbon, Kevlar, Spectra, etc.) to gain the strength and stiffness requirements, given the weight restraints.

If you really want to get hairy, then use 2 or 3 mm plywood on each side of 1/2" foam and see how light this works out. Naturally, you'll want to work out the material weights before actually gluing sheets of plywood, but not a difficult process. I'd recommend a minimum of 5 pound foam for the hull shell and 1/2" would be the minimum thickness, though 3/4" would produce a much stronger panel. Tape only the seams.

The bottom will be about 20 pounds, the sides, 10 pounds each, with internal partitions and seating adding another 15 pounds, producing a 45 pound hull. If you used 2 mm plywood the weight would be about 35 pounds all up. Of course, this assumes Okoume throughout and only a few pounds of foam and tape. No external sheathing, no hardwoods (kiss the bamboo goodbye), just white spruce where necessary or possibly a cedar and sparing use of goo.

Frankly I don't see much of an advantage in this route, as the PDR has a relatively limited preformance envelop, if raced under reasonable guidelines. On the other hand, if raced where you can get away with just about anything, then maybe you'll gain a fraction of a knot over the competition, with a super light version.

PAR,

Thanks for your response and insights. I've tried a number of these material combinations earlier in building PDRacers (See my article 18 Small Scows [now 20] on my website at White Polytarp Sails ) but failed to achieve a target hull weight of less than 60 lb. except with an all-foam hull. I agree with you that a light hull does not necessarily offer much competitive advantage in racing PDRacers, particularly in a chop such as we had this year in the Worlds, where heavier PDRacers with big rigs seemed to fare best. In this case, though, I am more interested in the light hull for a couple of reasons. First, I'm getting old enough that I don't like dragging around hulls that weigh very much. They are hard on the hemorrhoids. Second, I've recently mailed out a couple of prototype mailable PDRacer Kits to a couple of families who were more interested in assembling their boats than building from scratch. Weight (and length + girth size) is very much an issue when packaging up parts to mail here in the US. Third, I'm a little jealous of one of the builders over on the west coast of Florida who has reputedly built a foam composite 38 lb. PDRacer hull of foam and fiberglass. A fellow builder was allowed to take a swing at the foam/fiberglass hull with a hammer, and according to his story, the hammer simply bounced off. There is a photo of this PDRacer about 3/4 of the way through this very nicely presented set of photos of boats that attended the Cedar Key, FL Messabout this year Untitled Document You will note a couple of MIK's Goats, too, as you work through these professional quality photos assembled from members of the West Coast Trailer Sailing Squadron by their founder Rod Hoddinott. I hope to schedule a trip over to that side of the state to try to verify this story in a couple of weeks. I will gladly post any findings if anyone has an interest.

Dave Gray

Hi Dave,

Sorry, I'm very late here!

I would contact John Wright and see what he did with his ultralight PDRacer. It was ply and foam sandwich. But he also cut down every aspect of the boat to minimise surface area. That's probably where most of the weight saving was.

MIK