does fiberglass rot?

[madstories]

I am currently replacing a transom on a 1975 16 foot fiberglass boat. As I was sanding the inside, there is some spots in the corners where I could not sand down to the fiberglass. It looked like just resin. Instead I sounded straight through to the outside of the boat. I did not see any fiberglass in these areas.. All that seemed to be there was resin but I am unsure of that. I was thinking that maybe somebody put a few holes in it and repaired it without using any fiberglass material in that spot and I just happen to find it while sanding. But then I got to thinking what if the fiberglass has been too wet and somehow broke down or rotted for lack of a better term.
This is really making me wonder if the whole hull could be full of these weak spots. Does this fiberglass look normal, or is therr something wrong?
My plan is to reinforce the back with a layer of chop strand then woven roving then a final layer of chop strand which will cover the entire transom 8" past all corners. Does this sound good?
The first picture shows a small area where I could not sand down and find any woven roving I'm sure if I continue to little further it would come through to the outside like the other spots. Does anybody have any idea what I'm looking at here?

 

[ondarvr]

Nothing odd looking there, just thin glass and you sanded through.

 

[tpenfield]

fiberglass/resin does not rot, and as stated is just probably thin in those corner areas where you sanded through. It does, however, absorb water to some extent.

 

[Flukinicehole]

Yeah, nothing odd there. It happens.

 

[kcassells]

450 years



Different kinds of plastic can degrade at different times, but the average time for a plastic bottle to completely degrade is at least 450 years. It can even take some bottles 1000 years to biodegrade! That's a long time for even the smallest

It's not the glass it's the way it was put in. Water pockets,air pockets etc.

 

[madstories]

Before I epoxy the apply wood to the transom, I thought I should reinforce the corners that I have grinded through. Instead of just glassing the corners I figured I should do a solid piece from one corner all the way across the transom and then through the other Corner. This will keep the surface area of where the wood is glued on even.
I bought chop Strand and 18 Oz woven roving. How many layers of this would I need to stiffen up the corners?
Would it be enough just to put a layer of chops strand with one layer of woven roving and another layer of chop strand on top?

 

[Tnstratofam]

What type of drive does your boat have? If it's an outboard or inboard reinforcing the transom with extra cloth and resin is not to big of a deal. However if it is an inboard/outboard or sterndrive your keyhole thickness comes into play. To much glass combined with your transom wood will cause the gimbal assembly not to bolt up corectly. I can't tell from the pics you posted above what you're working on.

Reinforcing the corners is doable with a sterndrive transom so long as the keyhole thickness doesn't change.

 

[madstories]

What type of drive does your boat have? If it's an outboard or inboard reinforcing the transom with extra cloth and resin is not to big of a deal. However if it is an inboard/outboard or sterndrive your keyhole thickness comes into play. To much glass combined with your transom wood will cause the gimbal assembly not to bolt up corectly. I can't tell from the pics you posted above what you're working on.

Reinforcing the corners is doable with a sterndrive transom so long as the keyhole thickness doesn't change.

Its an I/O, a Volvo AQ130C.
Somebody who does this for a living warned me about this a while ago. I put a lot of thought into it and I cannot see why it would make any difference. I understand that the area needs to be flat to make a seal but I do not see how the thickness comes into play. I'm simply taking it and bolting it on from the back. the bolt stick through the transom and the bolts are long enough that I could probably add a whole inch and they will still bolt on as long as the back is flat so it can make a seal what could possibly go wrong? The engine stick straight into the gimbal assembly and does not touch the inside of the transom at all it is completely independent of it. What am I missing? What could go wrong if I made this part too thick?

 

[madstories]

Double post

 

[madstories]

Here are a few pics of what Im talking about. The gymbal housing bolts onto the back. There is no inner plate. The engine is mounted into the housing from the inside of the boat. It mounts directly to the gimbal housing. The 6 bolts holding the engine to it is shown in the last pic. The only difference I see in this circumstance it would make if the transom where to be thicker, is I might need to buy a longer bolts. Of course if I made it way too thick, it would get in the way of the engine installation, but that is not going to happen. That is to say, the thickness of the transom would have zero effect on the relationship between the engine and gimbal housing. I just personally cannot see how it will make a difference, but, two people now have brought this to my attention maybe I am missing something. If I am please help me out. I do not have the patience to build my transom twice!

 

[Tnstratofam]

The thickness of the transom at the gimbal housing to engine connection matters because your drive splines will not fully engage the motor coupling. If you have the Volvo service manual it should give you the minimum and maximum transom thickness. This should include the gel coat, wood core, and any fiberglass layers. This is true of all stern drives including Mercruiser, OMC, and Volvo Penta I believe. I could be wrong in this case but I don't think I am.

Think of it this way your gimbal housing and motor may bolt up because the bolts are long enough, but if there is to large of a gap when you install your drive housing the drive shaft wont fully seat in the coupling. Your driveshaft is a set length and cannot be shortened or lengthened.

 

[madstories]

The thickness of the transom at the gimbal housing to engine connection matters because your drive splines will not fully engage the motor coupling. If you have the Volvo service manual it should give you the minimum and maximum transom thickness. This should include the gel coat, wood core, and any fiberglass layers. This is true of all stern drives including Mercruiser, OMC, and Volvo Penta I believe. I could be wrong in this case but I don't think I am.

Think of it this way your gimbal housing and motor may bolt up because the bolts are long enough, but if there is to large of a gap when you install your drive housing the drive shaft wont fully seat in the coupling. Your driveshaft is a set length and cannot be shortened or lengthened.

Well, it looks like in my case, that distance couldnt change. The gimbal housing is attached from the back, and protrudes through the transom. The engine attaches here. There is no transom plate on the inside. If the transom were thickened, I cant see the engine moving. So if the issue is the drive shaft splines, it's not the case in my aq130c.

 

[Tnstratofam]

My mistake. Just thought it might have a minimum or maximum thickness like most do.

 

[crabbingcake]

On the resin, how thin is too thin?

 

[JASinIL2006]

On the resin, how thin is too thin?

Noticed you are heading into your own restoration... you'll do much better starting your own topic rather than piggybacking on others' threads.

Also, we like pictures te see what you're facing!