Sress Cracks

[Doug13104]

Stress Cracks

Hello again
Just wondering if anyone has had problems with Stress Cracks in their hulls below the water line. I am redoing the bottom on our 1988 Hunter 40 Legend and have found two areas, both Port and Starboard , in line with the companionway and about two feet below the water line. I have ground the gelcoat off and the cracks are through the laminate. The hull in this are is only about 5/16" thick . I will take a few pictures and post.

 

[heart of gold]

Would that be in line with the engine area as well? I wonder if vibration over the years could have anything to do with it.

 

[waternwaves]

Pics please..

enquiring minds and all.



Didn't find any on previous haulouts.

Are your motor mounts still in good shape? Those mounts are located on box beams.......hmmmmm

Are in they in line with your sling lift points? The only non impact cracks I have seen on hunter hulls have been due to lifts in the wrong locations, and a yard accident on stands. (

 

[Doug13104]

I didn't have time today to get the pics but will get them up tomorrow. As for the engine mounts they are in good shape. You would not see these stress cracks under a normal haulout, as I didn't, you have to scape the area down to the gelcoat to see them. The boat has a shoal draft keel and the aft sling location was my first thought as it is well aft of the location of the cracks. I had a boat builder look at the cracks and he said the sling location wasn't the issue. I will tell you what he thinks caused the cracks once I get the pictures up.

 

[Doug13104]

Here are the Pictures of the Stress Cracks on our Hunter 40 Legend. The Starboard Pictures show a hole which I routered into the fiberglass to see how deep the cracks where. I had removed the Through hull fittings on the Port side and the fiberglass was about 3/4" thick so I thought I could router into the fiberglass about 1/2" without going through. I was surprised when I broke through after only 5/16 of an inch. The port side cracks are not as as bad but the cracks are still through the laminate.
As I mentioned in my last post I had a boat builder have a look at the cracks. He told me that the Stress Cracks were caused by Stress and more importantly the way the hull is made. The hull is made up of a thin outer layer. the hull, and a inner layer. the hull liner. He sounded the hull and found that just below the cracks is where the outer and inner liner are joined (glued) together. Above this is hollow. You can see the inner liner through the small hole that I made and there is about 1/4" between the outer and inner layers. He said that as the boat heels the keel is trying to right the boat at the same time the rigging is heeling the boat, hence the stress. This area seems to be the weak link as it is the same on both sides and in the same area. I added a picture of the keel after I removed the fiberglass that a previous owner had put on. As you can see by this picture I have tented the cradle to try and heat the cradle area so I can clean and cover the keel with epoxy and also start working on the cracks. Still not sure how I am going to fix the cracks but I think it will involve $$$$$$$$$$$.

 

[Rick Sylvester]

Cracks

Wow. Bummer. I'd like to chime in with a couple thoughts.

First, I'll disagree with the boat builder. On a traditionally built sailboat what he says would be possible but the H40 isn't traditionally built. The heeling forces of the rig are transferred down through the deck by way of the stainless rods that pass behind the settees in the salon. They are anchored into a mild steel L-beam that is captured by the liner/grid. The keel is also bolted to this same grid. I'm no engineer but I'm reasonably certain the forces generated by the keel and rig are NOT shared by the hull.

Also, the engine mount frames are bolted to the liner so I doubt this would be the culprit.

It would also be helpful if you could supply a pic of the entire side of the boat so we could get a more accurate idea of where these cracks are in relation to other structures. This might be useful to those of us making our wild-ass guesses.

No way should the layup at equivalent places on either side of the hull be off by a factor of two. I agree with you that 5/16" is pretty shocking. My 85 is 5/8" at the waterline. I'd guess that the cracks most likely occurred on the hard. I'd be surprised if those cracks were generated by normal forces while in the water. Improper blocking during a haul out would be a good guess.

It appears you're well underway with a repair. If you can gain access from inside to do additional glassing that might be a bonus. You'll probably be okay once finished but you'll want to be present for any future blockings in order to properly 'sound' the hull to place the stands at bulkhead points to help distribute the point loads of the pads.

Good luck and keep us posted.

 

[Doug13104]

Sling location

Thanks Rick
Is your hunter 40 a shoal draft Keel. If so where do you place the aft sling? The aft sling location, and this is where they have been lifting the boat since new, is inline with the Helm. When I first saw the boat lifted in this location I thought the aft sling was to far aft.

 

[Rick Sylvester]

Yes, Anthem is shoal draft.

We place the aft sling between the prop shaft outlet and the aft end of the keel. It's a tough spot to hit and I always bring a picture of a previous haul-out to aid the Travelift operator. They usually appreciate it. It requires maneuvering the sling behind the aft sweep of the keel and nestling it against the aft end of the keel base. More than once we've lift her just clear of the water and seen that the sling wasn't where we wanted it and dropped it back in to reposition. It's a pain in the ass but there you go.

I prefer this spot because the aft bulkhead is there.

I also mark the toe-rail with blue tape to give us something to shoot for. If I recall it's near the stanchion adjacent to the back end of the deck-house.

When I get home (I'm at work, shhh, don't tell) I'll see if I can find the pic I usually use and post it here.

I agree that behind the prop is too far aft although I'd be surprised if that were the cause of your cracks.

 

[heart of gold]

Here are the Pictures of the Stress Cracks on our Hunter 40 Legend. The Starboard Pictures show a hole which I routered into the fiberglass to see how deep the cracks where. I had removed the Through hull fittings on the Port side and the fiberglass was about 3/4" thick so I thought I could router into the fiberglass about 1/2" without going through. I was surprised when I broke through after only 5/16 of an inch. The port side cracks are not as as bad but the cracks are still through the laminate.
As I mentioned in my last post I had a boat builder have a look at the cracks. He told me that the Stress Cracks were caused by Stress and more importantly the way the hull is made. The hull is made up of a thin outer layer. the hull, and a inner layer. the hull liner. He sounded the hull and found that just below the cracks is where the outer and inner liner are joined (glued) together. Above this is hollow. You can see the inner liner through the small hole that I made and there is about 1/4" between the outer and inner layers. He said that as the boat heels the keel is trying to right the boat at the same time the rigging is heeling the boat, hence the stress. This area seems to be the weak link as it is the same on both sides and in the same area. I added a picture of the keel after I removed the fiberglass that a previous owner had put on. As you can see by this picture I have tented the cradle to try and heat the cradle area so I can clean and cover the keel with epoxy and also start working on the cracks. Still not sure how I am going to fix the cracks but I think it will involve $$$$$$$$$$$.

That rectangle shown next to the hull, is that the bilge cavity? Is this an iron keel? Just curious and good luck with your repair. Thanks, Ian

 

[Rick Sylvester]

Yes and yes.

 

[sandpiper10471]

The Hunters of your era rely on the grid structure to absorb the stress. Check all your tabbing to ensure the grid is still bonded to the skin of the hull. If your grid has fiberglass pans between them, sound the pans with a hammer. If it sounds hollow, then the pans have let go of the hull skin. They will need to be cut out and the grid bonded directly to the skin with tabbing. It could be the grid is transfering the stress out to the skin and causing flexing. Good thing you found it now rather than half way across the Gulf Stream in deteriorating weather!

For repairing the skin, I suggest grinding a much larger area before layering new glass and resin but if the grid structure isn't sound you are just wasting time and materials.

 

[Rick Sylvester]

Here's the pic

I mentioned in the earlier post. If you don't have one of your boat yet feel free to use this one.

You'll notice in the close-up that the strap is actually laying over the 'fillet' on the aft edge of the keel. It shouldn't be a problem as that spot is immensely strong.

Oh yeah, you'll notice no Travelift in the picture. This is at a yard in Pensacola during my purchase survey. The crane had a former life at Cape Kennedy lifting Saturn V boosters. The operator operated the whole thing with a handheld wireless controller that looked like an R/C rig. Very cool and a bit freaky.

 

[waternwaves]

I have found similar damage to boats that were hauled for the winter and and were not properly dried.

freezing water between between the hull and liner split the hull.

I look forward to seeing more pics.
good luck on the repair. The rig forces are not anchored in those locations, and extremely unlikely to have contributed to the splits,

also improper stand location cannot be ruled out from the photos.

 

[Doug13104]

We place the aft sling between the prop shaft outlet and the aft end of the keel. It's a tough spot to hit and I always bring a picture of a previous haul-out to aid the Travelift operator. They usually appreciate it. It requires maneuvering the sling behind the aft sweep of the keel and nestling it against the aft end of the keel base. More than once we've lift her just clear of the water and seen that the sling wasn't where we wanted it and dropped it back in to reposition. It's a pain in the ass but there you go.

I prefer this spot because the aft bulkhead is there.

I also mark the toe-rail with blue tape to give us something to shoot for. If I recall it's near the stanchion adjacent to the back end of the deck-house.

When I get home (I'm at work, shhh, don't tell) I'll see if I can find the pic I usually use and post it here.

I agree that behind the prop is too far aft although I'd be surprised if that were the cause of your cracks.

That looks better. I am going to go a little bit further forward with my aft sling and have it go right under the Keel. I replaced the drive line last spring and your sling position is just to close to the drive shaft for my liking. I had another guy look at the boat and he didn't like the aft sling location either. He is going to do the glass lay up, polyester resign not epoxy resign. I will do the prep-work and the fairing work to keep my costs down.

 

[Doug13104]

The Hunters of your era rely on the grid structure to absorb the stress. Check all your tabbing to ensure the grid is still bonded to the skin of the hull. If your grid has fiberglass pans between them, sound the pans with a hammer. If it sounds hollow, then the pans have let go of the hull skin. They will need to be cut out and the grid bonded directly to the skin with tabbing. It could be the grid is transfering the stress out to the skin and causing flexing. Good thing you found it now rather than half way across the Gulf Stream in deteriorating weather!

For repairing the skin, I suggest grinding a much larger area before layering new glass and resin but if the grid structure isn't sound you are just wasting time and materials.

Thanks for the reply Sandpiper
I know that the bonding between the liners was and issue with the earlier Hunters but thought they had fixed the problems by the late 80's model years. Could you give me a little more detail on how to inspect the bond between the inner liner and the hull. Not sure what you mean when you talk about fiberglass pans.

 

[Canonshooternb]

So how did the repairs turn out ? Were you happy with the results ?

Paul

 

[Doug13104]

Thanks to every one that responded to my post. I repaired the two areas myself and am very pleased wirh the rusults. I still fell that it was the repeated wrong placement of the aft sling that caused the cracks. I used West system and six layers of Stich mat. The only advice I will give is wear a hat when working with resign overhead. I had to get ALL my hair cut off once the job was done!