Gelcoat 'spider' cracks at bulkhead

[tpenfield]

Yea, so as I was looking at the hull of my boat today I noticed vertical spider cracks on both sides of the hull . . . it appears to be right at the point of a forward bulkhead.

Here is a photo I took and note the spider cracks pointed out by the arrows.



They are a bit hard to see because of the light, but they are there nonetheless. They span about 2 feet in total and go across the strake shown in the picture.

I had the boat surveyed about 2 months ago and the cracks were not evident then. They were not there as of a couple of weeks ago. But they are quite noticeable now.

I found a fair amount of water accumulated in front of the forward bulkhead about 2 weeks ago and drained it. So, I am thinking that the 'spider' cracks ( or checking) is a result of the excess moisture penetrating the bulkhead and then drying out. . . causing it to expand and then contract.

I am wondering what you folks think about these spider cracks , cause, effect, treatment, etc.

T.I.A. for you comments.

 

[ondarvr]

Re: Gelcoat 'spider' cracks at bulkhead

The water you found probably has nothing to do with it, if they are right where the bulkhead is, then it's most likely from the hull flexing around the rigid structure, Could be from pounding on the water or on the trailer, maybe even from just one event.

Sometimes cracks are difficult to see until they become dirty, then they stand out and can be easily noticed by just walking past the boat, so having just spotted them doesn't mean they haven't been there for a while.

Is this the boat in your sig, or a different one?

 

[Ike-110722]

Re: Gelcoat 'spider' cracks at bulkhead

Good answer. Spider cracks tend to occur in gelcoat where there is a concentration of stress. If the bulkhead on the inside of the hull is actually pressing against the hull, and has no stress relief, then that's what caused the cracks. The flexing of the hull while the boat is moving causes slight twisting and flexing and pressing against the bulkhead. This is in engineering parlance is called a hard spot. This spider cracks are cosmetic, and yes they probably look like crap (can't tell in the photo) but they do not affect the structural integrity of the boat.

The same thing occurs where there are sharp corners, such as at the transom, chines, corners of windows, where cabin sides meet the hull, and where there are stress concentrations.

 

[tpenfield]

Re: Gelcoat 'spider' cracks at bulkhead

Sometimes cracks are difficult to see until they become dirty, then they stand out and can be easily noticed by just walking past the boat, so having just spotted them doesn't mean they haven't been there for a while.

Is this the boat in your sig, or a different one?

Yes, that is the boat in my sig . . . the interesting thing is that I have been over the hull in great detail many times, having recently acquired the boat and I have not seen them until now. I suspect that they have been there for a while (years), but not visible over the past few months.

The boat has been out of the water since Sept 25th

A couple of weeks ago, I found a hole in the anchor locker that was allowing rain water, etc to accumulate against this bulkhead. I repaired & re-furbished the anchor locker and the bulkhead has remained dry since then. . . now the cracks have become visible.

 

[Bondo]

Re: Gelcoat 'spider' cracks at bulkhead

Yes, that is the boat in my sig . . . the interesting thing is that I have been over the hull in great detail many times, having recently acquired the boat and I have not seen them until now. I suspect that they have been there for a while (years), but not visible over the past few months.

The boat has been out of the water since Sept 25th

A couple of weeks ago, I found a hole in the anchor locker that was allowing rain water, etc to accumulate against this bulkhead. I repaired & re-furbished the anchor locker and the bulkhead has remained dry since then. . . now the cracks have become visible.

Ayuh,.... Does that forward bulkhead have limber holes to drain water back to the pumpable bilge,..??

Shouldn't it,..??

 

[tpenfield]

Re: Gelcoat 'spider' cracks at bulkhead

Ayuh,.... Does that forward bulkhead have limber holes to drain water back to the pumpable bilge,..??

Shouldn't it,..??

No, it doesn't . . . Yes, it should.

I suppose I should add that to "The List" . . .