Foam between CF reinforment and hull?

sharkcus

Breakin' the atmosphere.
Joined
May 18, 2007
Likes
16
Location
Strongsville, OH
#1
Bought a hull with "visual carbon fiber" engine bay, which is just a kevlar/carbon fiber mat. For brevity I'll just call it "cf". 2 years of riding and my bpipe wore through the cf. Didn't notice until I pulled it last weekend. I have no problem patching it up with some cf but I noticed something odd. Whomever did the work ground off the "ribs" on the actual hull, which is fine, then put some kind of a thin foam or something down, then put the cf down.

What is that "foam" layer? It can't be more than 1/8in thick. But it's probably why my bpipe was rubbing, as they are alright really close to the stock hull.

Even though it is super thin, it appears to be waterlogged (from the broken/worn through cf hole by bpipe).

I was going to cut a few inches around the problem area because it feels squishy. Maybe get some decadent packets to see if I can dry out the "foam" layer? Do I just lay the cf right over the hole on to the external hull? or do I need to replace that foam layer? I have no idea what that is there for. I'll post pictures tonight.
 
Joined
Jan 23, 2006
Likes
414
Location
Midland, Ontario, Canada
#2
Someone likely filled the bond line with foam too smooth it out than laid the CF over it. Not the proper way imo, I’d try and rip it all out and do it properly...cabosil and micro balloons to a peanut butter consistency to fill bond line than glass over it.
 

sharkcus

Breakin' the atmosphere.
Joined
May 18, 2007
Likes
16
Location
Strongsville, OH
#3
It wasn't the bond line, also wasn't 2 part foam. I don't think I was describing it right. Its like a super thin foam backing across the whole area. like a thin (like 1/8th or 1/16th) foam sheet or lining to decouple the cf from the hull. I'm tempted to rip it out, but the rest seems to be okay. I think pics will give you a better idea of what I mean, I'll get them in a few hours. I'm pretty comfortable with glassing, I just have never seen a "backing" put down before laying cf.
 
Joined
Jan 28, 2018
Likes
151
Location
California
#7
What kind of ski is this?

Sure looks like they used foam to level the ribs instead of just grinding them down.

Here’s mine, I ground them mostly down but am going to level them with epoxy resin and cabosil instead of foam.
 

sharkcus

Breakin' the atmosphere.
Joined
May 18, 2007
Likes
16
Location
Strongsville, OH
#8
I'll have to go double check, I thought the ribs were ground down but you're right, looks like they aren't. So people use foam to level it out if they don't grind them? Not sure I understand how that's reinforcing the hull if the mat is barely touhing the hull because of foam. It very well could be just for aesthetics. It's a stock sj RN hull.
 
Last edited:
Joined
May 22, 2017
Likes
186
Location
SW Tenn
#9
I'll have to go double check, I thought the ribs were ground down but you're right, looks like they aren't. So people use foam to level it out if they don't grind them? Not sure I understand how that's reinforcing the hull if the mat is barely touhing the hull because of foam. It very well could be just for anesthetics. It's a stock sj RN hull.
As far as Im concerned its a hack way to do it. Useless if you ask me. Grind the ribs.
 

sharkcus

Breakin' the atmosphere.
Joined
May 18, 2007
Likes
16
Location
Strongsville, OH
#11
Yeah the bond gap with foam makes sense. But the rest... I don't see how it even added any strength without being connected to the hull. Ugh. Guess it's coming out then. Probably save me a few lbs anyway. I don't care how pretty my engine bay walls are anyway.
 

sharkcus

Breakin' the atmosphere.
Joined
May 18, 2007
Likes
16
Location
Strongsville, OH
#12
Thanks for your help clearing this up. @Req I agree. If I would have known, I would have torn it out years ago. I've been riding around with all this extra weight (and water soaked foam in between) for years. I should have known better. I also ordered a crane scale so I can beat myself up even more when I weigh it and see it's like 100000lbs.

My shop is too cold right now, even with heat, for glassing. So I'll wait until spring. Now I can spend more time trying to figure out how to keep my RIP hull from sinking. Everything is wide open all the way back. Ping pong balls or poly insulation or something. idk. Fun times though. The kicker is, I do mostly surf on lake Erie so IDK what I'm even doing with this flatwater ski. I'm too shy to ask someone to borrow theirs to try, so I just built one lol.
 
Joined
Jan 12, 2013
Likes
1,997
Location
the jetski grave yard
#13
the ribs are there for strength, but they don't solve the problem of coming up short on rolls. unless side reinforcement is thick and done right , its not protecting the side from cave in. I caved in my first SJ after 1 weekend. I fixed it by using a drill bit cardboard case, glassed in right under the hood opening lip and top to bottom on the side. if some knucklehead just grinds the ribs and slaps on glass or carbon, its a joke. unless you plan on trying and failing rolls, you don't need to do anything with whats there.
 

sharkcus

Breakin' the atmosphere.
Joined
May 18, 2007
Likes
16
Location
Strongsville, OH
#14
So it's way worse than I thought. I'll post some pics tonight. The "foam" was over 1/2in thick at parts. totally water soaked. I removed part of the side and there was 1/4in of water covering the bottom of the engine bay, just from that. Also realized, there's foam under the CF on the bottom too. It was just a giant sponge.
Also - bondo effering everywhere under it.

Man. I always thought this thing seemed heavier than my others. Guess it was.
 

Sanoman

Slowbutgood
Joined
Jun 23, 2009
Likes
1,653
Location
NE Tenn
#18
No,it was just a stupid use of time and materials.Whoever did it,had all the stuff they needed to do it right.
Have you checked it under the tray? More than likely it is also full of water

Looks like a good winter project
 

sharkcus

Breakin' the atmosphere.
Joined
May 18, 2007
Likes
16
Location
Strongsville, OH
#19
So ya. Almost an inch above the bottom of engine bay. More fun. @Sanoman you're right. They clearly had everything needed to do it right but didn't. This ski is going to be so much lighter. 41754.jpeg
 

hornedogg79

dodgin' bass boats
Joined
Jul 9, 2009
Likes
599
#20
That's one of them insulated hulls for riding up north. Curious what the R factor is on this one. ....... whiskey tango foxtrot! This is worse than swapmeet's "really" hull.

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