Cracked Fiberglass Shaft Log

[djm284]

Have some pretty big cracks in the shaft log on our 1990 Supra Sunsport and now water trickles in when in the water. Pressing lightly around the cracks it feels somewhat flexible/soft, similar to rotting wood.

I'm comfortable with mechanical and electrical, but have never attempted fiber, so I'll probably have a pro fix this. What are most viable options for fixing this (e.g., repair fiber, replace entire log with fiber, cut out and replace with bronze). Also, what range should a repair like this cost if I have someone else do it (we live in northern VA / DC area).

Thanks - Dave

[rludtke]

I would carve a v into the crack and fill with a cabosil mixture, and then laminate several layers of heavy glass cloth over the top. I don't think that this is a very difficult repair, as there is no molding or critical location required.

[Salty87]

okie's been there and documented it for us....
http://supraboats.com/bbs/showthread...ighlight=shaft

how much you have to repair depends on how much damage there is so there's really no guessing at cost until you have a better idea. fiberglassing isn't hard but it is messy.

[djm284]

Great! I haven't found someone I trust in the area yet (and being the overly frugal do-it-yourselfer with everything, I likely never will), so I'm happy to hear this is doable.

As I mentioned, I'm all too familiar with the engine and electronics on the boat, but as ignorant as can be when it comes to the structural aspects of the boat. So please excuse me for the extensive list of rookie questions...

1. "Carve a v into the crack" -- Is a Dremel and cutting wheel sufficient for this?

2. I'm assuming I want to make the v as small as possible while still ensuring a clean cut?

3. Since water is leaking through, I'm asuming I need to cut and fill all the way through. Can this job be done without removing the shaft, or do I need to apply glass under the repair too? If no glass required underneath, is any other coating required on the bottom or is the epoxy just fine?

4. Will the epoxy drip, and if so, can i just cover the shaft with plastic or do I need something butted up against the inside of the log? If the latter, what type of material should be used so that the epoxy doesnt stick to it?

5. What is the shaft log made of? As I mentioned above, when I push on the crack there is some flex similar to rubber or rotting wood, but shape seems odd for wood. Could it be rubber, or does fiberglass itself get that way with a sufficient crack.

6. I not sure what caused this, but have a few ideas that I'm not proud to admit. Given the nature of the crack, do any of these seem more likely that the others, and if so, anything I should be concerned about for the future. (1) Left plug in while out of town, cover colapsed in, and this area was sitting under at least a couple inches of water for probably a couple weeks. Only engine casulty seemed to be starter motor. (2) ski rope fell off back mid last year and tangle prop enough to stop it. Everything seemed to survive, except the ski rope. (3) New prop + cluttered potomac river after rainy week = old beat up prop.

Did a search for similar issues and the following is very helpful, just need to understand some of the specifics above: https://forum.supraboats.com/showthr...hlight=cabosil

Thanks!

[rludtke]

1. "Carve a v into the crack" -- Is a Dremel and cutting wheel sufficient for this?

The dremel is perfect.

2. I'm assuming I want to make the v as small as possible while still ensuring a clean cut?

I would make the V on the order of a 1/2" wide at the upper surface, give or take, and perhaps 2/3rds of material thickness deep.

3. Since water is leaking through, I'm asuming I need to cut and fill all the way through. Can this job be done without removing the shaft, or do I need to apply glass under the repair too? If no glass required underneath, is any other coating required on the bottom or is the epoxy just fine?

I would avoid grinding all of the way throgh, as I don't know what the log is made of, and do not risk harming anything with the grinder. Filling the upper 2/3rds with cabosil, and then building numerous laminants over the top is intended to restore the strenght and rigidity to the composite structure.

4. Will the epoxy drip, and if so, can i just cover the shaft with plastic or do I need something butted up against the inside of the log? If the latter, what type of material should be used so that the epoxy doesnt stick to it?

If you avoid grinding all of the way through, I think you should be ok.

5. What is the shaft log made of? As I mentioned above, when I push on the crack there is some flex similar to rubber or rotting wood, but shape seems odd for wood. Could it be rubber, or does fiberglass itself get that way with a sufficient crack.

I always thought this was all fiberglass, but I am not sure.

Did a search for similar issues and the following is very helpful, just need to understand some of the specifics above: https://forum.supraboats.com/showthr...hlight=cabosil

Cabosil is a structural thixotropic used in combination with composite resins to create filler material.

[wotan2525]

My shaft log has a visible collar and I believe it's aluminum -- it sure looks like it as you look down the bore. My driveshaft wore a hole through one side and we repaired it first with building up several layers of JB Weld and then resin.

[rludtke]

I would make the V on the order of a 1/2" wide at the upper surface, give or take, and perhaps 2/3rds of material thickness deep.

I would avoid grinding all of the way throgh, as I don't know what the log is made of, and do not risk harming anything with the grinder. Filling the upper 2/3rds with cabosil, and then building numerous laminants over the top is intended to restore the strenght and rigidity to the composite structure.

After looking at Okie's posts on his shaft log repair, I now think that you should go to the effort of grinding away all of the lamainants that hold the shaft cover in place. This means grinding essentially all the way down to the base hull. My concern is that water has probably found its way between layers of glass, and the laminents that wrap over the shaft cover have been comprimised. If you follow Okie's repair, you'll see that he essentially removed everything, so that he could start over like new. This is probably the only way to be gauranteed of sucsess.

[djm284]

Thanks for all the info. I like your first answer better though

So my next question is obviously subject to a million different variables. But any thoughts on about how long option 1 might take vs. option 2?

Looking at Okie's post, it looks like option 2 took about a month of weekend work. Given that it is now July, I'm in the middle of rewiring the entire second floor of my house and semi-finishing the attic, have kitchen cabinets sitting in a friends basement ready for our do-it-yourself kitchen overhaul (free, used, but in great shape - couldnt pass them up), and we have a full basement refinish including new bath on the horizon... a month long boat project probably means no boat until mid next summer (although using the boat has been my excuse for the slow progress, so on the bright side, all those other projects may actually get done!).

What is the risk if I use the first method? Could the water between the layers of glass create significantly more damage requiring a more extensive repair than just the log area, or will the patch just not last very long? Does a half-assed patch create any risk of a big rupture occuring and sinking the boat? (again, I'm as ignorant as can be about fiberglass, but guess I'm gonna learn pretty quick now).

If I'm just looking for a temporary fix to get me through a season and a half, is option 1 the way to go, or is that the best alternative?

I'm rarely one to take the shortcut, but ideally looking for a temporary fix until I have more time. Will want to do it right eventually, ideally in about 16 months, but If I can get by with a $100 and a four hour job to save a season or two, I'm fine with the lost time and re-work. But I dont want to do anything stupid that causes further problems down the road. I'm gueessing these are hard questions to answer, but I'm happy with educated opinions. Is there anything specific I can look for to help answer these questions?

Of course I could just have someone else do it, but if Okie's quotes came in at $1000-$2000, they're probably even worse up here, and who know's if they'll take their own shortcuts that'll come back to bite me in a couple years.

[djm284]

I probably should have put this at the beginning of the last post... If I misinterporeted Okie's thread and this is a job that can reasonably be done in a day as opposed to a month of weekend work, please let me know and disregard the rest of my questions. If it is a month, what is it that takes so much time, grinding? -Thanks!

[rludtke]

This is just guess-work, as I only have Okie's pictures and the recollection of what my boat looks like to go by. I think that the extra grinding is not much more work than the grinding you would have to do to prepare the surface anyway, and the glasswork is about the same. A small electric angle grinder should fit in there, and course sanding discs should make reasonably quick work of the glass that needs to be removed. Okie may disagree, but I would like to think that you could get the area prepared for re-assembly in a weekend. Add a second weekend for reassembly. In fact, I think it is likely that the whole job could be completed in a weekend, but I am trying to be conservative in this estimate. Of course Okie can quote actuals.