Replacing rotten speedboat floor

[Rodg98133]

Here is exactly what i was thinking of doing in step by step, i have plenty of access from the inside. I was going to grove out the inside of the cut. Then using fibreglass matting and starting with a thin strip to go in the middle gradually building up to the width of the groove and then add a few full sheets over the top to join up to the exisiting glass. Then once this has set use some epxoy marine filler the fill the gap. Im not fussed about what it looks like as it will be below the water line. Does this sound sufficient? What resin shall i use on the fibreglass mat? And is marine epoxy filler ok to fill the crack?

 

[prv]

What resin shall i use on the fibreglass mat? And is marine epoxy filler ok to fill the crack?

I would use epoxy resin. If you do, be aware that standard cheapo fibreglass mat is not compatible with epoxy, it's held together with a binder that dissolves away in polyester but doesn't in epoxy. The right stuff for epoxy is usually woven like cloth rather than the mish-mash of fibres used with polyester.

I would grind out and repair on the outside as well as the inside, not just stick filler in the hole. When you're slamming the thing over waves at speed you need to have confidence that the hull isn't going to open up, sink, and drown you and whoever else you invited along.

Make sure you grind out a nice wide area for the repair to adhere to, don't just stick stuff to the virgin fibreglass around the hole. A mate of mine repaired a similar sort of crack (smaller than yours) on a RIB without really knowing what he was doing and just sticking polyester and mat over the top. The next time out it came apart, the crack spread, and the whole front of the RIB opened up like the toe of an old shoe. RIBs have a buoyancy tube so he didn't sink - your ski-boat doesn't and will.

EDIT: here's a much bigger hole being beautifully repaired: http://www.ybw.com/forums/showthread.php?t=324429 . Anything is possible (albeit at a price in that case!)

Pete

 

[Rodg98133]

Ok so im guessing that inside and outside is the best option so...


Grind out inside and out to a v on each side (about 4" wide?)
Epoxy resin and matting to gradually build up from the inside until level then a few over the top then once set the same on the bottom. (How far below the surface of the existing gelcoat shall i stop building it up?)

Then how do i go about finishing it on the outside as gelcoat doesnt stick to epoxy does it?

 

[prv]

Grind out inside and out to a v on each side (about 4" wide?)
Epoxy resin and matting to gradually build up from the inside until level then a few over the top then once set the same on the bottom.

Sounds good to me. I might skip the "few over the top" though - if you've filled the V properly it will be as strong as the original hull, and making one place stiffer than the rest (with extra thickness) can lead to cracks at the edges of the stiff part instead of the whole lot flexing equally. More of a consideration on thinner GRP than your hull, perhaps.

Then how do i go about finishing it on the outside as gelcoat doesnt stick to epoxy does it?

I think it does, if the epoxy has had any amine blush washed off it. I have certainly used polyester gelcoat over epoxy with no signs of it coming off, though that was just "cosmetic" painting of a joint internally, rather than hull work.

For gelcoat that's not being laid in a mould, like yours will be, you need to exclude all air from the surface as it cures. Two ways of doing this, you either slap some clingfilm or similar plastic over it, or you mix in 2% "wax in styrene" which you can buy along with the gelcoat itself. The wax migrates to the surface during the cure and forms an invisible film that keeps the air away, then it polishes off.

Pete

 

[Rodg98133]

Ok was just looking at ordering the resin and theres loads of different types of epoxy? Also the only mat they have on the site that was recomended earlier in this thread is 400 thickness. That ok? How much resin am i going to need? And how much matting?
Does the gelcoat just roll on? As my boat is white i wont need to add any colouring will i?

When im doing the outside how much before the surface of the existing gelcoat do i need to stop to allow for the new gelcoat?

Sorry for all the questions ive just never done this before and dont want to make it even worse than i already have lol.

 

[oldsaltoz]

Ok was just looking at ordering the resin and theres loads of different types of epoxy? Also the only mat they have on the site that was recomended earlier in this thread is 400 thickness. That ok? How much resin am i going to need? And how much matting?
Does the gelcoat just roll on? As my boat is white i wont need to add any colouring will i?

When im doing the outside how much before the surface of the existing gelcoat do i need to stop to allow for the new gelcoat?

Sorry for all the questions ive just never done this before and dont want to make it even worse than i already have lol.

I would use West System epoxy resin. You should only a litre of resin and perhaps a bit more for the filler/fairing.

You can 400, but make sure it's properly wetted out.

If you use flow-coat (and I would) you can roll in with a standard 80mm wide domestic roller, but do it quickly before the roller falls apart, you can tip off with a foam or standard brush. You can add pigment to get an exact match if needed, but I would not bother.

You need to stop appling glass on the outside just a mm or so, leaving space for the filler and fairing.

See my post above re epoxy primer over the outside repair.

Good luck and fair winds.

 

[Rodg98133]

I am rather confused over all this. Everyone talking about different fillers and primers and rollers??

Anyone localish to notts want to give me a hand? Dont mind paying. I will put in as much work myself as i can. Just want someone there that knows what their doing to watch over me and tell me what to do if nothing else?

 

[D12ty]

Morning all, just following on from this thread I was after a bit of general advice, I have a Fletcher GTO which I've recently adopted and am giving it a once over before joining the waterways! I have taken up the carpet due to it being soaked and found the ply on top was sodden so removed it fortunately in one lump which will make for a perfect template when I lay a new sheet down.
under the initial sheet of Ply I found more plywood which was also soaked so requires replacement also. From reading the comments above I believe I am best to cut along the edge 1/2" inch from the sides and lay another piece of ply down which I will template from cardboard.
Can anyone share any further repair methods and recommendations including what thickness of ply to use? I have attached some pic below to give you a visual of what i'm up against