I see what appear to be small crack marks on my hull. Is that common?

It's a '91 sunbird with a 20 feet fiberglass hull. The marks are about
4 inches in length and they run top-to-bottom (not from bow to stern).
They are mostly towards the stern of the boat on both sides of the
hull under the boat's waterline. When I run my hand over them, they
are perfectly smooth and flushed with the surface of the boat; you
can't feel them, one can only see them. They're all under the boat's
water line.

There is no water coming in the boat (or if there is, the bilge pump
sucks it out over night). The boat runs great with no trouble. I
purchased this boat used. It didn't have those marks when I inspected
it. I've been using it for 2 years and I just noticed them last week.

Is it expected to have small cracks when a hull gets old? Is there a
fix short of junking the boat? How would a marine mechanic fix them?
What would one expect to pay for that?

thanks.

Y wrote:
I see what appear to be small crack marks on my hull. Is that common?

On a 13 year old boat it's certainly not *un* common.

What you describe sounds like gelcoat cracks (surface layer of
fiberglass). Most likely they don't leak. You don't say whether or not
these cracks are in a spiderweb pattern, that is fairly common. Also
it's common for cracks to radiate from a corner. This can be due to
flexing of the fiberglass structure (gelcoat is stiffer & more brittle
than fiberglass) or it could be due to thermal stress.

Gelcoat cracks are quite easy to fix, if you can paint a surface you can
fix them yourself. You have to carefully grind away a small amount of
the gelcoat in the cracked area, mix some new gelcoat, and spread it on
smoothly.

OTOH when you grind away some of the gelcoat in the cracked area, if the
crack gets bigger instead of smaller as you grind, and it looks like it
goes all the way through, then you have a bigger problem. It can still
be fixed fairly easily but it's going to need structural fiberglass cloth.

Fair Skies
Doug King

Y wrote:
I see what appear to be small crack marks on my hull. Is that common?

It's a '91 sunbird with a 20 feet fiberglass hull. The marks are about
4 inches in length and they run top-to-bottom (not from bow to stern).
They are mostly towards the stern of the boat on both sides of the
hull under the boat's waterline. When I run my hand over them, they
are perfectly smooth and flushed with the surface of the boat; you
can't feel them, one can only see them. They're all under the boat's
water line.

There is no water coming in the boat (or if there is, the bilge pump
sucks it out over night). The boat runs great with no trouble. I
purchased this boat used. It didn't have those marks when I inspected
it. I've been using it for 2 years and I just noticed them last week.

Is it expected to have small cracks when a hull gets old? Is there a
fix short of junking the boat? How would a marine mechanic fix them?
What would one expect to pay for that?

thanks.

Pounding over waves is like kicking the bottom just in front of the
transom. The gel coat will crack before the hull material. Seal it
with paint and wax it.

Don't go too fast in waves.

Terry K

Thanks for the advise. Your descriptions of this problem put me at
ease. Yes, some of the cracks are in a spiderweb pattern specially on
the transom (close to the stern drive) where they are more numerous.

Allow me to ask you one last question: if the previous owner fixed it
in the manner you describe, how long would you estimate it would take
for the gelcoat cracks to reappear, assuming "normal" use? By normal
use, I mean that the boat is kept in a 10-mile fresh water lake with
minimal wakes and I normally go about 20mph (planning) through any
areas with wakes.

thanks.

DSK wrote in message . ..
Y wrote:
I see what appear to be small crack marks on my hull. Is that common?

On a 13 year old boat it's certainly not *un* common.

What you describe sounds like gelcoat cracks (surface layer of
fiberglass). Most likely they don't leak. You don't say whether or not
these cracks are in a spiderweb pattern, that is fairly common. Also
it's common for cracks to radiate from a corner. This can be due to
flexing of the fiberglass structure (gelcoat is stiffer & more brittle
than fiberglass) or it could be due to thermal stress.

Gelcoat cracks are quite easy to fix, if you can paint a surface you can
fix them yourself. You have to carefully grind away a small amount of
the gelcoat in the cracked area, mix some new gelcoat, and spread it on
smoothly.

OTOH when you grind away some of the gelcoat in the cracked area, if the
crack gets bigger instead of smaller as you grind, and it looks like it
goes all the way through, then you have a bigger problem. It can still
be fixed fairly easily but it's going to need structural fiberglass cloth.

Fair Skies
Doug King

Y wrote:
Thanks for the advise. Your descriptions of this problem put me at
ease.

It's really no biggie. Fiberglass is not perfect (but then, what is?)

... Yes, some of the cracks are in a spiderweb pattern specially on
the transom (close to the stern drive) where they are more numerous.

OK, that sounds like it's due to flexing & stress. I'd recommend putting
a little more "beef" down there instead of just a cosmetic fix.

Instead of writing a long post here, which would only relate to my own
skills & experience, I suggest you check into the newsgroup
rec.boats.building and ask about it. There are a lot of people with a
great deal more knowledge. Don't forget the local library will almost
certainly have a book or two on basic fiberglass work ...kind of old
fashioned in this modern cyber world, but a great resource.

In any event, it's a job that requires a little brains and a little
grunt work, but it's not rocket surgery. If you're at all handy, should
be easy... and fiberglass skills are of value to anybody owning a
fiberglass boat.


Allow me to ask you one last question: if the previous owner fixed it
in the manner you describe, how long would you estimate it would take
for the gelcoat cracks to reappear, assuming "normal" use? By normal
use, I mean that the boat is kept in a 10-mile fresh water lake with
minimal wakes and I normally go about 20mph (planning) through any
areas with wakes.

Could be almost immediate. Gelcoat is brittle, that's why it cracks when
the underlying fiberglass is still fine. Probably two years at absolute
most.

Fair Skies
Doug King