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Crack and Water Leak at Prop Shaft Strut

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Oldskidude View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldskidude Quote  Post ReplyReply Direct Link To This Post Topic: Crack and Water Leak at Prop Shaft Strut
    Posted: April-05-2020 at 9:36pm
My son posted the below topic on another forum. I wanted to copy it here to see if there were any additional responses.

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This is my first post. I was wondering if anyone could add some insight on best practice to perform a DIY fiberglass repair.

I purchased a 1990 Ski Nautique right at a year ago. I spent the spring and most of the summer rewiring the dash and a multitude of other things to seemingly get it water worthy, so I really only had it on the water a hand full of times last year. I noticed the bilge filling up with water... not a terrible amount, but more than what I thought was reasonable. I didn't want to leave it on the water overnight, as I wasn't sure if it would be floating in the morning. Now that the weather has broke, I filled the bilge with water to see where it might leak out, and located some cracks at the prop shaft strut. Photos are attached.

Based on some internet research, my plan is to grind out the cracks from the bilge, and do the bulk of the repair from the top side. I was thinking of using West System epoxy, but am unsure on whether to use mat or some other fabric, or some specific combination of the two, or how thick to make the repair. I was then going to do a thin repair on the bottom side, again with West System epoxy, and some sort of filler, and the touch up the gelcoat.

Does the above sound reasonable? Should I consider a poly resin, especially on the underside? Any pointers on glass material to use? All help and information is welcomed.

Thanks,

Dan
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SNobsessed Quote  Post ReplyReply Direct Link To This Post Posted: April-05-2020 at 11:30pm
Dan - you will want to remove the strut & do as you planned, grind the crack to a 8:1 slant angle. Then begin adding layers, each an inch wider.

Epoxy resin is the best to use, even on bottom side. They sell E-glass cloth made for epoxy. You can apply many layers at once (on top anyways).

The layup should end up larger than the footprint of the strut.

You most likely will find cracks under the strut base too.   

You may have to use washers when you realign the strut & engine.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldskidude Quote  Post ReplyReply Direct Link To This Post Posted: April-06-2020 at 12:25am
Thank you SNobsessed! Just what he was looking for. He removed the strut today, and it looks like someone tried to do some fiberglass work already -> slight mismatch of the gel coat. Not sure how hard marine sealant at the strut is, but what was on there was the consistency of bathroom silicon, and the strut came off much easier than planned.

The repair appears to be much of what was cracking out. Probing with a screw driver, some more of the material just cracked right out. So the plan is to probably do more work on the underside now digging out what has delaminated, and adding new material.   It looks like all of the previous repair was done to the bottom side.

For faring, use the epoxy with a filler? Is Spectrum Color the preferred gel coat? Is there a block of wood or something in the strut base to grind to, or that may require more evaluation? Many thanks in advance!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SNobsessed Quote  Post ReplyReply Direct Link To This Post Posted: April-06-2020 at 10:25am
I used materials from US composites. Visit their website to get info on fillers.

I personally just cut cloth into small bits but I am a driveway hacker.

I made similar repair on my 2001 SN, there was no wood in the strut mount area. Yours may be different.

I built up the whole area so it was thicker & stronger than original. Overkill didn't cost much since I had the materials anyway.

Epoxy doesn't stick to plastic much, so if you want to get a flat surface (as molded) you can place plastic sheet over the wet layup & then a pc of plywood or such.

For bottom work, I have used a floor jack, plywood, soft foam, plastic sheet in various combinations to support the layup against gravity.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: April-06-2020 at 10:51am
Dan,
I suggest doing some grinding around the recessed area for the strut base. Here's why, in one of your pictures, it looks like there may be some delamination (or as Tim calls it, dis bonding ) between the layers of glass. If there is, then more repair would be needed rather than just laying up more glass from the top in the bilge.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldskidude Quote  Post ReplyReply Direct Link To This Post Posted: April-06-2020 at 12:47pm
Thank you all very much. He needs to collect materials next. Hopefully we can keep you updated on the progress. All of the above is very helpful!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: April-06-2020 at 12:57pm
I don’t see any damage significant enough to indicate a major structural problem that requires a fiberglass repair. Are there cracks all the way through the hull that you can see in the bilge?

If not, I’d be inclined to think that the exterior gel cracks are probably cosmetic and the leaking is coming from the bolts and dried out sealant.

Fiberglass repair isn’t a big deal if it really needs it but I just don’t see it from those pics.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldskidude Quote  Post ReplyReply Direct Link To This Post Posted: April-06-2020 at 3:13pm
TRBenj,

That's an interesting perspective. Water was clearly coming out of a crack, but as you said, it very well could have come from the bolt hole, and traveled through the disbonded crack. That could very well be worth investigating further. There is no line of sight crack in the bilge, though there are cracks in the general vicinity in the bilge. Thank you!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: April-06-2020 at 3:45pm
I’d clean both sides of the strut mount area pretty thoroughly with acetone and do an up close inspection. If there isn’t any more damage than indicated in your earlier pics, I’d be inclined to reinstall with new sealant (4200 or similar) and go boating.

If more damage becomes obvious, walking you through a glass repair would be straightforward too- but I suspect it may be fine. A little superficial cracking in the gel around the recess and bolt holes is not that uncommon and is not worrisome in and of itself.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: April-06-2020 at 4:29pm
The area that looks like there's some disbanding is in this picture. Far center next to the brown area. I'm not referring to gel cracks.

Originally posted by Oldskidude Oldskidude wrote:



After cleaning one the pocket, take a real close look.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: April-06-2020 at 6:16pm
All these different opinions............if it were me, I'd clean everything up and use 4 bolts, 8 washers and 4 nuts along with some easy to remove later plain old RTV and seal those 4 holes up without the strut in place.

Then put some water in the bilge and see if or where it leaks from and go from there with the appropriate solution from the ones mentioned above

You should be able to see/feel any delamination as you're tightening the bolts if things feel a little "squishy" as you tighten
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