Looking for solutions for reinforcing a Prelude's hull

[milkman]

I was out on a creeky summer run yesterday and cracked a Prelude for the third time. All three cracks are in the seat vicinity. Two have been welded. This third one opened up one of the welds and extended the crack. I should add that at 160 pounds, I'm not a heavy guy.

Welding obviously isn't enough for these thin polyethylene bottoms. I'm starting to brainstorm other solutions. One thought I had was to weld the crack then glue a ABS plate on the inside of the hull that would cover all the area around the seat. I would flame treat the Prelude prior to gluing.

Another thought I had was to weld the crack and then apply Patch N Repair (http://geminimaterials.com/patch-n-repair. I had good luck with this on Royalex canoes, both as patches and skid plates. The manufacturer says it will adhere to polyethylene. I could see putting this on the outside of the hull, but that would create a 1/16" lip for rocks to catch on. Not great, but I could probably deal with that. Another thought I had was to use the Patch N Repair on the inside of the hull to cover a 12 x 24 area of the hull and on the outside hull use raft vinyl glued down with g/flex. The vinyl would be mainly so that if the hull cracks inside this sandwich, I don't really have to care.

I'm rather desperate to find a solution since I like the Prelude so much, but they're just not holding up to the rigors of whitewater paddling. I'd be interested to hear what others suggest.

[klund]

I have a Pyranha version that seemed like it was cracking almost everytime I paddled it. After about the 12th or so weld under the seat, I took it to a professional welder and had a 1/4 inch PE plate welded to the bottom, outside of the hull. No more cracks under the seat. I don't really notice the plate when I am paddling - it slides right over rocks just like it's part of the hull. I know several people that did the same thing with Spanish Fly's.

The place I went to is Boulder Boat Works in Boulder, CO. Maybe give them a call and see if they can point you in the right direction for wherever you are located? Or just start calling plastic fabricators in your area and see if any of them do welding.

[milkman]

Klund, that sounds like a good solution. What's the approximate size of the plate you had welded on? And how many paddling trips do you think you now have on it?

Interesting that the Pyranha version is prone to cracking as well. I wonder if that means that the mold is simply designed to produce a hull with too thin of a bottom.

[cheajack]

I G-flexed a full bottom on the inside of a SuperFly. I harvested the "patch" piece from an old kayak hull. I did flame treat both patch and Fly at the time of repair. I put about 300# of weight on the patch to squeeze out all the extra G-flex and let it sit for a week or so. Seemed to do just fine.

[klund]

The plate is about 1.5 x 2 ft. and is right under the saddle area in the middle of the hull. I paddled it pretty hard for about 2 seasons of Colorado mank before switching to a L'edge. I'd say maybe 30-40 trips or so. The plate could separate - that happened to my bud with the spanish fly after a lot of rock bashing elf trips. If I remember correctly, he had a new one welded on slightly bigger.

I don't know about the design aspects v.s. plastic. My lude was bought used. It looked to be in pretty decent condition when I bought it, but I don't know if it was stored outside in full sun or not. The welder did mention he thought the plastic was very thin - but that could be just because i scraped it all off.

[milkman]

I've been thinking of some other ideas to try. Two of them involve gluing down with g/flex a plastic plate on the inside of hull as cheajack suggests. Then for the outer hull I'm debating between:

1. Flame treat, cover a large area with thick G/flex (tube), lay on top of that some really light wire mesh screen that can conform to boat shape. When that dries, apply another layer of g/flex. Extra credit--several layers of g/flex with graphite. Or cover with raft vinyl glued down with g/flex.

2. Flame treat, cover with liquid g/flex (bottle), add fiberglass cloth. Do several layers and then paint on g/flex + graphite or cover with a raft-vinyl patch glued down with g/flex.

Any opinions?

[PAC]

My older Prelude was / is almost worn through... I tried welding with a supporting G-flex lining and it held for a time but gave out with the pounding.

Handed off to Shawn at Fall Line Canoes who added a plate and re-welded and its holding up well. Cost was minimal and craftsmanship matters (and I'm not that bad at welding either). I think he also added some light mini cell to the top of the plate to help absorb some of the hammering under the seat.

[milkman]

So the plate that was added was a polyethylene plate welded to the outside of the hull like Klund recommended?

[klund]

i'm not really sure why the guys welded it to the outside. I was worried that it would negatively affect my paddling, but I really didn't notice and performance hits. Or maybe my paddling is already so poor that it just didn't matter...

[sbroam]

I suspect the plate was added to the outside because that was easier (than pulling out the outfitting...) and that's where the wear is. If the edge is beveled or tapered, it shouldn't cause much problem paddling-wise. If it isn't beveled, it will be soon if it doesn't get knocked off I'm not sure how you would weld a whole plate? Maybe g-Flex in the middle, then weld the edges? The PE should be good in compression (good for the outside) - Maybe add something thin on the inside that's good in tension - g-Flex + cloth (fiberglass, kevlar, ...) or raft material?

[squeakyknee]

Welding plate on inside is key. also, drill 1/2" holes in plate throughout so you can spot weld it to the hull. this is of course after welding what you can on outside. Then plate will be backing for welding thin spots. use zip screw to hold plate in place, as well as holding cracks together then fill screw holes. This has been a great fix on many boats and has revived more than a few.
Shawn
Fall Line Canoes
http://www.falllinecanoes.com" onclick="window.open(this.href);return false;

[sbroam]

Shawn - have you ever bought PE sheet from a plastics supplier? or have you always used scrap boats? I've bought and used sheets to make outfitting (i.e. plate for a conversion) but haven't welded it (to itself or boat). Not sure if there could be any compatibility issues...

[milkman]

Shawn,

Sounds like a great solution, but your post raises some questions:

“Welding plate on inside is key.” Are you saying the plate on the outside is unnecessary or are you suggesting plates on both sides of the hull?

“Use zip screw to hold plate in place, as well as holding cracks together then fill screw holes.” So the screws are temporary--you remove and fill? Fill with what? I'm guessing you would weld them closed?

This made me think of a different idea for a plate inside the hull. Drill the holes in the plate, flame treat both hull and plate, lay down lots of g/flex, apply lots of weight. The glue should come up into the holes and help hold the plate.

[Einar]

John & Matt in Boise use Marine goop to hold abs 1/8 sheets in place as bow plates. They mold them with a heat gun to achieve good fit
i would mold the plate so that it extends up the sidewall interior to distribute the pressure and goop it in place.
e

[milkman]

I don't think marine goop is going to work with polyethylene.