05-10-2008, 10:03 AM #1
Delam prevention / tub reinforcement Vern style
I completed the tub reinforcement project yesterday with some help from Dan (RXP'n in MI). Thanks again Dan!!
I pulled the motor and gas tank, cut the 'feet' out entirely, then beveled the edges of the holes where the feet were and sanded the entire tub area with 60 grit on a grinder to rough it up and get it ready for bonding, then cleaned it thoroughly with water, then with lacquer thinner. I put thin styrofoam sheets in the feet holes just as a way to keep the cloth/resin from sagging into the holes and basically re-creating the feet.
I had two yards (x 50 inches) of 5.8 oz carbon fiber, as well as similar quantities of fiberglass mat and fiberglass cloth, and lots of West System 105 epoxy and 205 hardener. I used varying sizes of fiberglass cloth and mat for the first three layers, basically sealing up the holes and building some thickness over the holes, overlapping over most of the tub and up to the sides and top of the tub area. After the 3 layers of 'glass, we switched to carbon fiber, and laid in 4 layers of that, wetting out all layers pretty liberally with the epoxy resin. Each layer of 'glass and CF was a different size and shape ... roughly half of them reached up and over the 'upper shelf' of the tub to help spread the weight and distribute the load over the entire front of the ski. Hopefully you can see in the last pic where I 'anchored' the layers onto the upper shelf, but they anchor between the gas tank brackets, in front of the tank brackets, and in the front middle (big chunk there).
I had cut templates out of plastic sheet for all the different layers of 'glass and CF, then cut the layers of 'glass and CF, trial fit them dry, and re-trimmed as needed, so when we started wetting them out and laying them in we could proceed quite rapidly. I did this so that the entire project would be a 'primary bond' with all the layers chemically bonding due to laying them in on top of each other while still wet. Far faster, far stronger, far easier than laying in, letting it dry, sand it, lay in next layer, etc. Laying in all seven layers took us roughly two hours. We used paint brushes to brush on the epoxy for all the layers, and used brushes and our gloved hands (rubber gloves are a necessity) to smooth out all the layers, and eliminate air and resin bubbles.
In case anyone is curious, the weight of all the materials used is approximately 7 - 8 pounds max, most of which was the 60 ounces of resin/hardener. Approximate cost of materials used was $250; if someone used only fiberglass and typical fiberglass resin the cost would be significantly less (but so would the strength).
In order to do this all in one session I really needed two people ... it would have been extremely difficult to do this by myself, so if you try a project like this, line up a friend to help out.
I will try to attach a few pics ...
Last edited by Vern; 05-10-2008 at 10:52 AM. Reason: added
05-10-2008, 10:15 AM #2
Pics - feet cut out.
Last edited by Vern; 05-10-2008 at 10:31 AM. Reason: added
05-10-2008, 10:18 AM #3
Pic 2 - Sorry for doing these one at a time ... multiple pic uploads don't work for me due to only having cheesy dialup at home ...
The fiberglass cloth and mat layers - dry, just fitting them.
Last edited by Vern; 05-10-2008 at 10:52 AM. Reason: added
05-10-2008, 10:38 AM #4
Done - all layers epoxied in and epoxy now dry.
05-10-2008, 01:09 PM #5
Wow!! Nice job! Should last forever.....
05-10-2008, 09:52 PM #6
Thanks Larry! I forgot to mention the real reason I did it this way ... my opinon is that the feet themselves are the biggest problem with the hull, and that they literally focus all the gas tank weight and pounding on two very small areas and beat the crap out of the outer hull. By eliminating them altogether and trying to spread the weight of the gas tank over the entire tub I think it will eliminate the pounding and potential gelcoat cracking.
11-09-2008, 03:27 PM #7
Pushing this up for EngineerMike ...
One thing I forgot to add in the original post was that I also drilled four holes in the corners of the front tub, down into the gap between the inner and outer hull, then used expanding Foam and 3/8" hard plastic line to inject foam deep into the hull cavity between the inner and outer tub. I pushed foam thru the plastic line, slowly removing the hard plastic line as I injected. Foam was coming up out of all 4 holes for quite awhile after I was done. I let it dry for a couple days, then cut out the excess foam, cleaned it up, sanded it, and put a layer of carbon fiber and epoxy resin over the four holes.
My opinons on delam ... it is due to the feet focusing the weight of the gas tank and pounding those feet on the outer hull. The pounding eventually causes stress cracks in the gelcoat ... that, combined with the dry layer of glass Mike and others have mentioned, results in delams.
When I cut the feet out of the inner tub, the fiberglass of the outer hull under the feet themselves was literally powdered from the pounding of the feet ... it was radically different than the clean, solid, untouched fiberglass of the outer hull anywhere except directly under the feet. I again looked where my outer hull had gelcoat cracks, and it was directly under the inner tub feet ... it was crystal clear what was going on. ** PS - my 'Pics - feet cut out' picture above is AFTER I thoroughly cleaned and vacuumed the hull, AND then painted on a heavy layer of epoxy resin over the powdered/splintered area where the feet had pounded the shit out of the outer hull. I should have taken a pic of what the feet had done before I soaked that area with epoxy resin ... but I did not, oh well.
If you do nothing else, you should carefully drill holes into the inner tub in the four corners (and possibly elsewhere) and inject serious amounts of foam using 3/8" hard plastic line to get it deep into the hull and spread all over. That is a cheap and easy thing to do to help support and spread the weight of the gas tank over a larger area hopefully. IMO, the fix I did is much better, but it is also a PITA. At least doing the foam correctly is a cheap and easy way to TRY to help prevent the delam. I just used the expanding foam from the nearest hardware/home improvement store.
As far as the outer hull, if you already have serious gelcoat cracks, I have also considered getting carbon fiber tape and, using epoxy resin, put a few strips of cf/epoxy resin from the rubrail down past the affected areas. This will be virtually invisible on our black hulls, yet add good protection against a delam starting and tearing gelocat off. I personally would FIRST get after the inner hull work, but both will help prevent delam.
Last edited by Vern; 11-09-2008 at 03:32 PM. Reason: added
11-09-2008, 07:58 PM #8
Vern, thanks for the thread re-bump.
This is one of my biggest concerns on my 04, especially as i try to get past 80 mph.
Something i need to look at this winter for sure.
11-09-2008, 10:36 PM #9
Steven even after all this, my RXP is my favorite water toy ever ... BuRP screwed up on some things, but so did every other mfr with a fast ski. My two GPRs were slower, blew up motors, and needed many other fixes too. The RXP is not bulletrproof from the factory, but no 80++ mph ski ever was ... no other ski has ever ran nearly so fast, sounded so good, or been so much fun for me. Yes, I have had to fix some things, but that is true OF EVERY SKI I HAVE EVER OWNED. I have never had so many screaming chicks on the back of any other ski I have owned ... this POS sounds good, runs good, hauls ass, and impresses all the neighbors on the bayou. Sure, it does not run 100 mph but it will pull 3 big guys to 75 mph, run stable and flat, and scare the shit out of anybody who hops on behind me. Next year it will run 85+ mph and be reliable all sumer.
Yeah, it ain't perfect, but this thing has put more smiles on my face than other toy I have owned ... and for me, that is saying a lot. YES, I wish BuRP had done more engineering on the hull, but ...
07-07-2009, 05:43 PM #10
I really think this should be a sticky in How to! So, while I am buffing the butt of my ski I see these stress cracks that run longitudinally with the ski, but there is one spot right by the fuel tank foot on the port side. I think to myself "damn, I want to build the engine - not itch for a week from fiberglass. I really didn't want to do the project, but in the end I am glad I did. It doesn't take a pedigree to realize that there is no good reason to put the feet in the inner hull. Damn - the inner hull was 3/8" thick in places. That is much thicker than a boat! Very strong and shouldn't flex that much. I might say that the styrofoam they used is very soft. Bascially the feet will take all the impact. There is an older post where the user completely cut out the tub, but I agree with VERN on this one - that reduces the strength too much. BTW - I did not inject foam after removing the feet because I did not believe it was necessary.
Total cost for this project was about $75 and IMO if you have your engine out (like I do) you should do it. Thanks very much to VERN for starting this thread and helping me along the way. The HOW TO is to his credit and not mine. I just went the less expensive route with just epoxy and resin. How to will follow.
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