Welcome! Log In Create A New Profile



Posted by Sandy 
April 10, 2016 10:43AM
We've been thinking about Plascore all wrong. Boat building in general. Even plywood boats. I had an idea about plywood boats last night that lead to thinking about Plascore differently.

In old fashioned framed boats the weak spots in the hull are all next to the frames. Next to the ribs. If you hit a rock too close to a rib the plywood can't bend so it fractures. The ideal boat is one that is stiff enough NOT to bend or flex during normal use--that will flex a lot if impacted severely. When you hit something flex is good. It's a shock absorber mechanism that keeps the hull from fracturing.

Too many of us have been using thin Plascore as a convenient panel to build on top of. But thin Plascore has too much flex so you have to add a ton of fiberglass weight to make it stiff. Thick Plascore holds its shape better. A hull made with thick Plascore would only need a thin skin of some kind. Fiberglass is brittle. A soft flexy skin over top of thick Plascore would be the ideal boat. It would be stiff enough to hold its shape as you row. But soft enough to give when you smack a mid-river boulder at ten miles per hour.

Thick Plascore covered with a thin skin of traditional fiberglass would be better than what we do now. Build it up at the chine but leave it thinner everywhere else. If the skin fractures so what? It's easy to repair and moisture will not migrate sideways from the fracture point. So you can take your time about fixing it.

If you replaced the thin brittle and easily fractured fiberglass with soft flexy polypropylene fabric like Olefin you'd really have something. Now the skin is like a thin rubber sheet. Stiff enough to paint but flexible enough to bend without breaking. The skin would provide no stiffness to the hull. That comes from 1" thick Plascore. Or even thicker if need be.

I haven't done much for months on my decked 17' foot boat project. I knew I wanted to do something new but I didn't know what it was. Now it's gradually coming into focus. Once I have this idea a little more sharply defined, in my mind's eye, I can start building again.
Re: Cntrl-alt-delete
April 10, 2016 10:53AM
The above idea about a boat built with a thick Plascore hull started by thinking about plywood. You could build an all wooden boat with plywood only. No ribs. No fiberglass. Just oil the plywood twice a year the way AJ does.

No gunwales either. Stiffness at the top edge of the side panels would come from a ledge top gunwale. I've built a few of those. Mike Edmondson has too. This is Mike's boat here. If that ledge top was a few inches wider that (open) boat would be have no gunwale and be totally stiff, and yet it wouldn't have any ribs. And no wood strip gunwale. It would have the ledge top instead. To attach ledge top to sides and sides to bottom panel (in an all plywood boat with no ribs) you wood still need a long angled chine strip, and a similar fastening strip at the top edge of the side panels, to attach sides to ledge top. Those could be cut from boards but they could be made from thicker plywood too.

In this all-plywood boat, at regular front to back layout intervals on 1/4" plywood side panels, where an old fashioned woody would have a rib you could sandwich on a flat piece of 3/8" x 2" wide plywood, to stiffen things up a bit and to provide fastening points for lockers and passenger and rower seat rails.

There would be no gunwale. The bottom panel would screw on to a chine strip. The ledge top gunwale would be like a decked boat with all but 6" inches of the deck cut out, Now you have all the stiffness you need and there are no ribs. Slobber it with oil and go rowing. If any panel breaks it's all screwed together so just replace it.

Somebody needs to make an all plywood no ribs and no fiberglass ledge top boat. Woody Hindman could have built that way. He used ribs but he didn't have to.

I had that idea and then I realized it could morph into thick Plascore, as per the post above.
Re: Cntrl-alt-delete
April 10, 2016 11:10AM
Ok. Back to thick Plascore again. The all plywood boat was just a diversion. Ryan Pearl makes decked white water boats down in Utah. They're a bit skinny but he has figured an ingenious way to build on top of 1/2" thick Plascore with epoxy infusion vacuum bagging. What Ryan is making is a predominantly fiberglass hull. Larry Hedrick built his Chilli Verde boat with 1/2" Plascore too I think. Ah. It was the Rio Verde. I like that boat. I've rowed it. Good boat. But it too is predominantly fiberglass.

If you increased the thickness of the Plascore and reduced the amount of fiberglass you'd end with a boat that wasn't so brittle. It would be stiff enough not to flex under normal load but it would flex--rather than break--when you smacked. That's the concept.
Re: Cntrl-alt-delete
April 10, 2016 02:34PM
RE> "toughness"

Anything but glass. I mentioned Olefin (polypropylene fabric). It's hard to find. I used to get it from a now defunct company named Tech-on. It was amazing stuff. Bends after resin. It did soak up a lot of resin so bagging would be a requirement. Kevlar and Syntech bend without fracturing too. Glass fabric is by far the most. brittle.

Toughness is perhaps not so easy to define. When I had my boat shop out in Gallatin Gateway back in the early 1980s I got one or two Lavros to repair every year (ClackaCraft came along after I went belly up). Lavros are heavy. They have a ton of glass at the chine. But if you let a fully loaded boat water-mellon sideways onto a rock in fast water something breaks, because fiberglass is strong but brittle. Fiberglass has a bending threshold beyond which you cannot go.

Other fabrics are less brittle. I stick by the original theoretical goal as the ideal river drift boat: what ever it is made from you want it to be just stiff enough not to bend under normal load. But when accidents happen you want to have a lot of bend to work with. No bend means break. Bend means all is well.

How best to achieve that ideal trade off is perhaps a debate. But I don't think the goal is.
Re: Cntrl-alt-delete
April 10, 2016 03:03PM
Who is it who makes the roto-molded drift boats? I've forgotten the trade name. Roto-molded kayaks are the norm. They're stiff enough to paddle well enough and yet they bend like crazy when smacked.

Roto-molded drift boats are an interesting idea but they do have problems. They are way too heavy. A little white water kayak is one thing but those roto-molded drift boats weigh a ton. They're very tough but they do (occasionally) get damaged and then they're hard to repair. Impossible on the river.

The good thing about roto molded drift boats is that they are hard to damage. And stiff enough they (almost) row fairly well. And if you do smack a rock they bend and smile about it. If you could somehow combine the good parts of roto-molding (flex when impacted) with less overall weight and with a little more stiffness and with "not so hard to repair" then you'd really have something.
Re: Cntrl-alt-delete
April 11, 2016 08:01PM
Who is it who makes the roto-molded drift boats?

Hog Island. My cousin has one, rows exactly like that, a pig. Very heavy. I can literally row circles around it with my raft.

Re: Cntrl-alt-delete
April 11, 2016 09:36PM
Yes. Hog Island is the roto-molded trade name. They are heavy and too flexible. When you pull hard on the oars the whole boat deforms a little. That's lost motion. That's you the rower busting your ass to deform the boat rather than make it move. That's why you need a boat to be "stiff enough not to bend under normal load."

Perhaps there is no such boat. But if someone could make a boat that did NOT bend or deform at all, under normal load, but that did bend a lot if severely impacted, that would be one hell of a boat.
Re: Cntrl-alt-delete
April 14, 2016 05:23AM
An interesting thought. What about adding a heavy layer or two of fiberglass just around the gunwale area which should offer increased rigidity and less flex for rowing while still allowing you to limit the amount of glass or other material on the boat. you could also consider building a wall (sorry I'm not sure of the technical term) in your decked dory that ran directly between the oar rights and even some other support structures underneath the deck. Unless the boat is just a wet noodle all the power and control come primarily from the boatmens connection to the oars and the strength of the rigidity of the boat where the oars connect. As for the durability of plascore with only a thin layer over it I'd love to see some testing.
Re: Cntrl-alt-delete
April 14, 2016 11:28AM
Absolutely. The boat cannot flex while rowing, else it's a turd. What ever it takes. I'm just thinking a bit thicker Plascore might translate to less glass overall.

You would need plenty of glass in a few critical spots like the chine and around the gunwale. I'm over it with smooth automotive fiberglass finishes too. It's way too much work and it doesn't accomplish anything beyond appearance. Hand laid glass ground down to almost flat and painted looks just fine. Especially if you splatter it with a blots of a contrasting color, by opening up the nozzle on the spray gun.

The other part of this idea is a more flexible laminate fabric. Kevlar is too expensive for me. Haven't been able to find Syntex. Olefin (polypropelyne) is impossible to find. Dynel (polyester) sounds good but it has to be vacuum bagged. Maybe that's the way to go: vacuum bagging Dynel over top of thick Plascore.
Re: Cntrl-alt-delete
April 30, 2016 03:55AM
Cool Sandy, I'm nearing completion on a traditional 'fletcher' Hindeman double ender w/ transom. After Mike's boat I couldn't bear to work with glass/epoxy exclusively anymore. That stuff sux. Maybe someday I'll do it again on a racing sailboat, but old-timey ply is fun and fast to build. I debated with Mike a lot: de-luxe petro-chem and glass or cheap-o ply, and finally thought that boat safety really relied in numbers: build 2+ boats out of anything that could be nested on the same trailer. Sink one, oh well, grab the oars and jump in the other (or a raft). The damn fletcher boats fly together, are functional and beautiful, and I've enjoyed every second building mine. I don't know how it will pan out, really. I'm on serial no. 1 for myself, so could be a raving plascore lunatic by next year. I'll keep you posted! pics next post, they're on my phone. And I've had some brandy. Cheers!
Re: Cntrl-alt-delete
April 30, 2016 11:49AM
I'm working on my last all glass boat now. I have no complaints I just like change. My next boat--when ever that happens--will be all wood with no ribs. 3/8" plywood sides with 1/2" thick ledge top gunwale to keep it stiff. With optional--bolt-down-onto-a-gasket white water deck. Slobbered with oil. No varnish no paint. 1" thick ash chine and gunwale strips, laminated in place from two 1/2" strips (1" thick ash is too hard to bend). No glue just caulk of some kind, so everything can be rapidly replaced.

I like my boat bottoms wider than 48" inches. That will just require a little side scarfing. Wear the bottom out? No problemmo. Back out the torx screws and replace it.
Re: Cntrl-alt-delete
May 02, 2016 11:11PM
I built this boat with a 1" thick Plascore bottom. The sides and interior pieces are the plywood. The bottom is wrapped in Kevlar.
Sorry, only registered users may post in this forum.

Click here to login