Bulkhead Stress Crack Repair

Hey all, we have a new to us 2007 Cobalt 282 with twin 6.2s. The interior is in great shape but the hull has some wear and tear that needs attention. I have done some gelcoat and fiberglass repairs on our other boat but this issue is new to me. On the hull in the same spot on both sides there are stress cracks. Directly behind them are a bulk head that runs across the back of the boat in front if the engine compartment. I am 99% sure that the bulkhead is sitting on the hull causing stress cracks. What is the best way to fix this? My initial plan was to cut back the bulk head 1/2” on each end where its making contact, leaving the tabbed glass behind it and fill the gap I cut out with 5200 or PL and reglass and gelcoat over everthing. This would be from inside the engine compartment. Any thoughts or a better way to do it? TIA!

 

Here are a couple of pics from when we bought the boat

 

I see what appears to be adjacent scratches in both photos, could the cracks have been caused by impact other than normal pressures from running? Perhaps damaged from forklifting into storage? Banging into a pier or other vessels in bad weather?
I’d be interested to find out what the manufacturers layup schedule was.
A quick Google turned up a Facebook owners group.

 

If it is a structural bulkhead, that would be a bad idea. It is difficult to see the location on the photo. However, the direction of the cracks would indicate there might have been an impact.

 

The pictures are pretty bad. For any diagnosis we need pics that are farther away and then get closer. A cause of gelcoat flaws related to a bulkhead might mean the bulkhead creates a stress risor on the hull or deck because the bulkhead is too rigid next to too weak a deck or hull. The way to fix this is to make the strength vary less by using glass tabbing. Weakening the bulkhead bond to structures is not a good solution. If you were building from zero, bulkheads may be padded to the hull. Padding is basically something like 12mm thick foam glued to the hull 2” wide with a 45 or 30 degree angle to hull and then the bulkhead and tabbing goes over it all. This reduces areas of weakness near strong areas.

Otherwise, the stresses find the weak zone.

The proper repair is on the inside and requires removing paint and gelcoat and going down to raw glass and adding glass tapes to the bulkhead and hull or deck. The fix the gelcoat damage on the outside. Massive pita.

This probably happened because someone was beating the hell out of her in high seastate vs slowing down, but a lot of conjecture here. A good surveyor may be able to diagnose the issue. Basically, they will push on the hull near the bh and if it moves easily; then the problem is transistion to BH is too fast..

 

I agree with gonzo,we need an indication of exactly where the bulkhead is located.From the fairly scant information that is presented,I'd agree that the damage looks like the sort of thing that would happen if a piling was given a tap,perhaps while docking in a cross wind.

 

I appreciate all the comments, This boat has spent its life at Lake of the Ozarks based on all the paperwork which can get rough in the summer for sure. I will get more pics later this week and do a better job identifying the bulkhead location.

 

I finally made it back to the boat for some pics....there is a definite high spot on the stbd side at the cracks. The bulkhead is located direcy behind the high spot in the hull (center of the cracks)

 

That is typical impact damage.

 

Thanks Gonzo, would damage create a high spot?

 

I can’t see anything in the new pics, even less than the initial ones.
Lay a straightedge over the perceived high spot to check, or have an expert evaluate the damage.

 

The impact crushes and delaminates the tabbing of the glass to the bulkhead or the interlaminar structures. When the striking object departs, the laminates open up, for lack of a better way to describe it. So, I would expect an impact to do one of two things. Completely crush in, or less an impact would result in the interlaminar damage and the hull gets thicker and raises up.

 

Thanks for all the input guys, my apologies on the poor pics. If its impact damage I feel comfortable grinding out all the cracks and filling with thickened gelcoat ensuring the damage does not extend into the glass. For my own education, If it is the bulk head creating the cracks how is that repaired?? My thought would be that you have to get to the bulkhead from the back side, cut back the tabbing that attaches it to the hull on one side in the area of the high spot (leaving it tabbed on the opposite side to maintain the hull integrity during the repair, trim the bulkhead back off the hull creating a 1/4"ish gap off the hull, then fill the gap with epoxy peanut butter or PL construction adhesive, then retab the bulkhead to the hull?

 

If the bulkhead is showing as a high spot, gelcoat is not going to repair that.
It’s much more likely that the hull side is pushed in adjacent to the bulkhead.
Cutting the tabbing may relieve it some, but it may need a much more invasive repair entailing removal of the damaged hull laminate, grinding back a long taper and reglassing the area.
I’d find an owner’s group where there may be some discussion about hull layup and strength.