Crack in joint of two piece hull...

[ErikG]

Hi guys and gals, a repair question if I may...
Background:
I have a 26 foot sailboat from 1979 built in two halves.
Late last year I noticed that some water was gathering in the bilge.
I could locate that the water entered forward of the keel, as it trickled slowly from further ahead. Unfortunately a fixed part of the GRP interior is in that area so I can't see any problem from the inside. This is also where the internal mast support is located (mast on deck).
There is (was until I removed the gelcoat joint) a crack in the geloat filled area between the hull haves under the hull, 10-25 inches in front of the keel, just below the mast support.
So it seems that excessive force, to much rig tension or slamming, might have caused the gelcoat to crack, no big deal. But since water enters I do worry.
When looking at the joint between the hull halves from below the GRP is poorly wetted out, the reinforcment looks dryish. From the inside it all looks fine in the areas that are "inspectable".

So here are my questions...
Is there a risk with a joint like this?
Should I just fill the the joint with gelcoat again or should I indeed worry about the looks of the laminate from below?
Should I make a thourogh repair from below, "angling" the outside laminate with a grinder and building up an external joint from below and then fairing it?
Or should rip apart my fixed molded interior in that area to inspect/replace the joining GRP? That would indeed take a lot of work, and since the basic interior is a part of the stiffening members in my small boat building it up again is no easy thing, and then I'll have to paint the interior, I won't be done for a long time... So racing the first part of the season...

questions, suggestions and fixes appreciated.
If any yard workers are around they'll surely have done stuff like this so how should I go about it?

Thanks

Erik

[Guest20100203]

Fixing the gel coat will not be a long term repair, though may look good for a while. You're on the right track, but there isn't a short cut to a easy repair.

You'll need to grind back to and area where you're sure the laminate is sound, dramatically bevel the area, fill with material and finish with gel coat or epoxy.

This is assuming the tabbing or joint area is solid enough to handle the loading asked of it. This may be a small area that a worker didn't get a roller or brush worked into as well as could be. It also could be indicative of the rest of the layup. Yanking the liner isn't fun, nor ripping it up for a good go at it. Try the good repair from out side, it'll save your liner and can be done with minimal disassembly.

If you feel the step area isn't transmitting the loads to the hull because of design or poor layup, then you can install some addition support, by way of a floor or two, maybe a partial bulkhead, all well tabbed into the hull. Every hull can use some additional support in areas the loading has exceeded what was expected.

In the areas you have access, look at the other tabbing and joining areas to see if there are more signs of breaking away, delaminating, poor wet out, etc. If so, you know the story, if not, you got lucky and the outside repair will last for as good as your workmanship will permit.

[gonzo]

The laminate might be dry, or what you are seeing is crumbled resin. It looks very similar. The repair should idealy be from the inside. Is there a bulkhead under the mast step or a post?

[ErikG]

Originally Posted by gonzo

The laminate might be dry, or what you are seeing is crumbled resin. It looks very similar. The repair should idealy be from the inside. Is there a bulkhead under the mast step or a post?

Nope. This is an extremely simple construction from th 70's, It uses the egg concept of strength. Pretty ok for tension but not as good for slamming loads.

The fixed molded interior floor (not as in FLOORS but as in the floor u walk on) which is about an inch above the hull bottom, this space is PROBABLY filled with polyester an "talk" (white stuff, don't know the english word for it, 70's cheapass filler). The mastpost endpiece is small and therefore only has a small surface to spread the force. These last boats in the series (around 170 boats) was made lighter and probably just using less material than the old ones. At least one other late series boat suffered from the same problem some years ago.

The idea at the moment is to remove the mastsupport. Make a hole in the interior floor, grind away the filler, and when I reach the laminate, I'll build it all up again (Polyester+mat), that should make for a stronger base. After that I'll replace the old small base of the mastsupport with a larger one that will be able to spred the load over a larger area. And finally I'll grind away the outermost part of the laminate in the cracked area with say 5-6" on each side of the joint, building up a new stronger joint from below (Epoxi, biax+stiched mat).

Sheez lots of work, but if it's worth doing... Do it well!

Adding a floor could have been a good idea if there was any space for it, I don't fancy tripping over a raised floor that much.

I'll post som pics in a day or tweo when I've been at the boat again.

Sounds good to you, or should I do something differently or simpler?

[gonzo]

With only an inch of space your options are limited. I think that cutting away a section of plywood floor, strengthening the laminate and repairing the floor will work.

[ErikG]

Originally Posted by gonzo

With only an inch of space your options are limited. I think that cutting away a section of plywood floor, strengthening the laminate and repairing the floor will work.

The direction I'm going, and I think I'll include a build up from below as well.
But no Plywood floor... It' a fixed GRP interior floor.