Re: All Plascore boats and plugs

This started out as a response to Henrysfork's post about a group purchase for Plascore. I didn't want to highjack attention away from his original question about a possible group purchase so I just now made this a separate thread--now a thread about the concept of building over a temporary form or plug. Plugs are highly optional. They can be seen as a big extra-step pain in the butt. They can also be seen as a handy convenience. Plugs do not cost much. The only extra expense is two sheets of 1/4" inch AC construction plywood. Read on if interested.

I'll post a few photos eventually. I just rolled out of bed. I have a coffee responsibility to work on right now.

Larry Hedrick has built a cool all Plascore boat. His is a standard 15' foot Honky Dory with an extra 2' feet added to the middle. So it still has a 56" inch bottom but the gunwales are 18' feet long instead of the original 16' feet. It's also a decked white water boat. It's been down the Grand Canyon more than once. Larry did not build a plug. He cut out the pieces and glassed one side only and treated it like plywood, attaching those "glassed on one side only" panels directly onto temporary chip board or 1x6 scrap rib like formers.

I have built only one all Plascore boat, which was my one and only Dayak. I'm 72 and in poor health right now (that's not necessarily permanent, I'm still trying to get over Covid, now a year later). If I finish my current project my next one will be aluminum. Anyway plugs are the big question for building all Plascore. To plug or not to plug? That is the question.

I like the plug method but it's obviously not required. Larry built without a plug, treating Plascore as if it was plywood, and he has a fine boat. Plugs are mainly a tool for working out the dimensions of a new design. But they do also make it easier to deal with somewhat floppy Plascore. I just thought I'd mention it.

When I piece sections of Plascore together to make a larger panel I like to use a biscuit joiner at the edges. The biscuits add no strength but they do help to keep the edges aligned while piecing everything together, and while waiting for (a small amount or resin putty) to set up. Biscuits are not required. But if you do not use them you will have to put Visqueen over the wet joints, with plywood over that, with tools and paint cans over the plywood, to weight everything down, so the edges are held in alignment as the glue sets.

If you treat Plascore like plywood I recommend piecing together the two side panels, over a flat floor over Visqueen, as two separate pieces not yet glassed. Then fiberglass the inside surfaces only. Now you can treat it like two big funny-looking pieces of plywood. When it comes time to fasten those side pieces to temporary rib formers, use drywall screws that go through a piece of 1/4" inch plywood 2" inches by 2" inches square. That will hold the plascore in place without the screw head imploding through the soft outer surface of the Plascore. Once all the edges (side to bottom and transom, etc) are glued together you can remove the all the 1/4" inch plywood squares.

The closest Meranti Hydrotech is out on the Northwest Coast. Montana/Idaho/Wyoming boat builders can pay a ton of money for freight, or take a drift boat trailer with them on a Steelhead fishing trip, so they can bring plywood back. Plascore is made in Michigan. They have Steelhead there too. Odd ones anyway, that live in the Great Lakes.

If you do build with a plug the only extra material expense is two sheets of 1/4" AC construction plywood (a plug is temporary sides temporary ribs, temporary stem, temporary transom, no bottom). For building all Plascore over a plug I'd probably go with no permanent stem at all. Once the plug is in place I'd piace the Plascore pieces on top and vaguely miter the front stem edges of the side panels, so they can be glued together with not too much resin putty. Then, in a later step, putty and fillet thickly on the inside of the stem, before covering with 6" glass tape.

Most commercially molded all fiberglass boats are built inside an expensive, highly-polished female mold. A plug is a quick and dirty male mold, covered with thin 4mil Visqueen, then covered with Plascore. Then glassed. Once the Plascore hull comes off the plug it's still a bit floppy. You have to build a cradle to hold it right side up and square and not twisted so you can glass up the inside. That sounds more complex than it really is. I just jerryrig that step with what ever is on hand. Once the inside is glassed (it's already glassed, you're just taping up the seams) it's a boat hull, needing only a few finishing touches. Like gunwales and seats.

Another thought about building over an optional plug. I know of at least two MRBoats customers who have built aluminum boats. One Buffalo Boat and one Honky Dory. both of those boats were built without a plug, with aluminum sheeting side panel stock temporarily attached to chip board formers--just long enough to weld up the edges.

My next project will be an aluminum hull. I'll build over a plug. That's mostly because I will also be building a new experimental hull design (that's all I ever build now) and the plug doubles as a temporary full size model that can be adjusted at great length without worrying about dinging expensive marine grade plywood.

I also have a hunch it will make dealing with the aluminum sheeting easier and more convenient, with a few ledges built here and there, to keep the aluminum in place while I fiddle with it.

The late Derald Stewart was the only guy I know of who built (decked white water) wooden boats inside a female jig. Which is a bit like a female mold.



The following is the Coconino, one of Derald's legendary boats. In action on the Colorado. In the Grand Canyon.


Like the Briggs Derald put two passengers up front and two behind the rower. I'm making a big decked white water boat now. I'll make two rows of two seats in front of the rower, and slide the rower back a bit, so the boat's payload is centered in the middle of the boat--at the boat's center of gravity--rather than pushed out to the ends.

When passengers are placed near the ends of a high rocker boat that puts them higher up rather than lower down, which makes the boat subject to sudden lurching and tipping. Putting the payload in the middle of a boat results in a much more stable hull. Weight out at the ends is harder to turn too. A long and skinny profile sinks further into the water than a wider bottom. That too makes a boat harder to turn.

You want that rocker but you (well me anyway) want the weight in the middle rather than out at the ends. I like wider better than narrow too. I hate side-to-side tippy boats.

I'll find some "mold mold or plug" photos soon too.