Plastic washboards/coaming material

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Andan
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Plastic washboards/coaming material

Post by Andan »

Can anyone definitely confirm the type of plastic used for the older Greenland II coaming? I know the ribs are polycarbonate, but the coaming looks like extruded polyethylene.

Ours are rather badly warped (bowed, not twisted), and the slots for the embedded rope on the edge of the decking are visibly enlarged. As a result, they're very tricky to install, and the rope pops out. I can post photos if that description isn't clear.

Polyethylene being a thermoplastic, I want to try to reshape them. They're otherwise in fine condition. The idea is to strip off the snaps (simply screwed in) and t-bolts, then patiently clamp sections of it between the jaws of a Work-mate, put a bit of tension on it, and carefully work it with a heat gun until it becomes pliable. Then tighten the jaws until it staightens out appropriately and let it cool.

Repeat up and down the pieces until all of the wow is out (understanding that the bow half has a curve), then do something similar to narrow the slot for the rope. The slots are spread so much that the opening is larger than the diameter of the embedded rope in several places (mostly adjacent to the t-bolts).

I've been searching Craigslist globally for Folbot parts without much success but have found a single unit on eBay for a good price. Like everyone else with the plastic coaming, I'd jump at a chance to pick up a set of the aluminum ones, but we'd be happy if the plastic ones weren't warped and would stay put.

Anyone tried something like this?

JohnSand
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Re: Plastic washboards/coaming material

Post by JohnSand »

I haven't, but I like your plan. You might also consider making them of wood.
Good luck, keep us posted.

Andan
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Re: Plastic washboards/coaming material

Post by Andan »

I just spent most of an hour straightening the stern half of the right-hand unit. I love it when I guess right! 😁

There is a bit of a learning curve. I started out focused on the lateral distortion and soon noticed that there was a little vertical sway that wasn't there before. Turned it 90° in the Work-mate and nudged that back straight, then paid closer attention to accurate clamping. The Work-mate is really useful, as you can clamp about 18" of warm material in a straight line to let it cool.

There was quite a warp near the aluminum end piece. I had to clamp vise-grips on to manipulate it when it was hot. I used a stepladder to support the other end. It's really unwieldy with the hinge and the leverage otherwise.

Then it's just a matter of working down the curves. I started out on the low setting on the gun but pretty quickly went to high once I saw the material's behavior. The trick is to clamp it very close to where the bend is and waft the heat all around with some pressure in the direction you want to go. After about 15-20 seconds, it stops immediately springing back when released. Now it's malleable. Pull and twist as needed to get it straight and hold it. I used a big sponge and cold water from a bucket to speed up the cooling. Once it's cool enough to touch. It's setting up. There's a little bit of malleability while it's still warm, so you can still fine-tune the shape.

The groove seems to have a memory. When I went to see how to close it up a bit, it already looked good except for a couple of spots. Re-heat it very quickly (not much material there) and gently use a big screwdriver blade to open or pliers to reduce.

I think it's probably possible to get it perfect with experience and patience. I took photos of before and with one section straightened. I'll post the sequence when I'm done.

BTW, definitely polyethylene. It smelled like repairing P-tex ski bases when it was heating.

HoosierPaddler
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Re: Plastic washboards/coaming material

Post by HoosierPaddler »

Great job.

I still believe these coaming sections would have been sourced from a manufacturer that supplied the sailing world. I've received no tips up to now. Another option, as pointed out earlier, would be wood. I think rather than using a router bit to create the the deck rope/cord groove in a single piece of wood for each section, you make each coaming section in two pieces, with the router used on each side, and then the sides are joined in a such a fashion to come together and provide the appropriate groove to allow the deck cord to slide easily while hopefully withstanding the slight twist and rise near the cockpit nose piece.

HoosierPaddler
GII x3, Kodiak x2, Edisto, and Citibot

mje
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Re: Plastic washboards/coaming material

Post by mje »

The aluminum coamings they switched to also look like they must have been a stock extrusion, as I can’t imagine that Folbot’s volume would have justified a custom one. They were a pretty low-tech firm, using wooden or MDF fixtures to build their frames.
Michael Edelman
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