hull cracks around strut and stern tube

[Gary Mc]

I would definitely take all paint and gel coat off the whole area so you can get a look at the laminate. Even if it appears to be OK I would add at least a couple of layers of fairly heavy biax cloth since there seems to be flexing in that area.

Good luck

[GuyFromTheNorth]

Can't comment on the cracks really, although I suspect it is a heavy layer of fairing compound which would be more brittle than laminate, it's just odd it didn't appear til after on the hard.

What I am curious of is do you have a zinc on your prop shaft? I don't see one, and maybe I'm just spoiled being a freshwater sailor but my 36yr old prop shaft is a bright shiny silver and yours looks corroded to me.

[Hardhead]

Are the cracks somewhat symmetrical to each other, on both sides? It's hard to tell exactly from the photos, but if so, that might be a clue as to what stressor is causing the cracks.

[ArmyDaveNY]

Originally Posted by ferrailleur

yes I could.... but more difficult access and work.... and wouldn't that be an overkill??

In the Army we used to say that overkill is better than underkill. If the cracks are definitely cosmetic then I would think it's not necessary. If they are not cosmetic, or even if you're not sure, then I would attempt it assuming that it's practical.

Could you add a few layers on the outside?

[ferrailleur]

Originally Posted by GuyFromTheNorth

Can't comment on the cracks really, although I suspect it is a heavy layer of fairing compound which would be more brittle than laminate, it's just odd it didn't appear til after on the hard.

What I am curious of is do you have a zinc on your prop shaft? I don't see one, and maybe I'm just spoiled being a freshwater sailor but my 36yr old prop shaft is a bright shiny silver and yours looks corroded to me.

Interesting comment..... I didn't see any anomality at hauling time. The soda blasting took all paint and some gelcoat off and I have been sanding like crazy to prepare the hull for two coats of base epoxy. That's when I notices the cracks. They might have been there all the time, just highlighted big time after blasting plus sanding.
Yes there was a zinc which was half consumed.

[u4ea32]

The good thing is: fiberglass is a composite. This means that hull, now so wonderfully one-piece and waterproof and a monocoque structure, was made from lots of little bits: individual pieces of cloth, roving, and mat, often with core materials, glued with resin and hardener. This means you can fix any damage, no matter how severe, to as-new or even better than new characteristics. And it really is not a highly skilled task: most yards I know use lots of low cost, low skilled labor to do fiberglass work.

On my boat that was built (well!) in 1983, there were cracks around the prop shaft strut. I think this was due to the vibration from the diesel engine. Diesel engine vibrations are relatively severe, and cause car manufactures all sorts of durability problems. Sure, the engine might last a long time, but everything around the engine gets beat to hell.

Fixing the strut did require cleaning up about an inch of soggy (like black peanut butter) balsa core material around the strut, removing material until we had nice dry tan balsa core, and then adding in layers of glass cloth. We used vinyl ester, as that bonds very well to polyester that cured very long ago.

[timeout2]

Originally Posted by ferrailleur

They might have been there all the time, just highlighted big time after blasting plus sanding..

Dremel out the cracks. If bottom paint has penetrated deep into the crack then they have been there a long time. That might indicate cracks are a result of a hard grounding. A severly bent shaft might also cause cracking but vibrations would have been very noticeable. Dremel until you're in solid material. Then epoxy as needed. Note that fairing filler is not waterproof but if you're putting on a barrier coat that may not matter.

[boatpoker]

Originally Posted by timeout2

Dremel out the cracks. If bottom paint has penetrated deep into the crack then they have been there a long time. That would indicate cracks are a result of a hard grounding. Dremel until you're in solid material. Then epoxy as needed. Note that fairing filler is not waterproof but if you're putting on a barrier coat that may not matter.

A proper marine epoxy fairing compound is no less water proof that any other epoxy used in hull repair.

[kapnd]

Originally Posted by u4ea32

The good thing is: fiberglass is a composite. This means that hull, now so wonderfully one-piece and waterproof and a monocoque structure, was made from lots of little bits: individual pieces of cloth, roving, and mat, often with core materials, glued with resin and hardener. This means you can fix any damage, no matter how severe, to as-new or even better than new characteristics. And it really is not a highly skilled task: most yards I know use lots of low cost, low skilled labor to do fiberglass work.

On my boat that was built (well!) in 1983, there were cracks around the prop shaft strut. I think this was due to the vibration from the diesel engine. Diesel engine vibrations are relatively severe, and cause car manufactures all sorts of durability problems. Sure, the engine might last a long time, but everything around the engine gets beat to hell.

Fixing the strut did require cleaning up about an inch of soggy (like black peanut butter) balsa core material around the strut, removing material until we had nice dry tan balsa core, and then adding in layers of glass cloth. We used vinyl ester, as that bonds very well to polyester that cured very long ago.

If the hull is cored, and the strut is mounted through the core, that is a big problem. In order to achieve a solid mounting, core material should be eliminated in the mounting footprint, so that the mount is in solid fiberglass, usually several added layers to strengthen the hull at the mount area.
Your strut is in a recessed pocket, which has been either filled/faired with improper material, or it has had no barrier coat applied to protect the filler from moisture.
It is a common myth that gelcoat is impervious to water!
If there are no corresponding cracks inside the hull, you should be good to just grind out the filler and redo, albeit properly!