Settee-Hull Joint Cracks

[wfraser]

Hope I can impose with a question. I don't know the terminology so bear with me.

The part of the settee seats on both sides of the cabin that meet the hull where your ankles are when seated has developed cracks in the filler used to fair it with the hull. In fact, this is happening at the chart table and storage lockers in the galley. I'm not sure why this is happening, except that the benches and chart table were loaded with heavy gear when I did my refit. But then again, these are storage areas, so the loads should have been okay.

I've checked bulkhead and other tabbing to see if it's parting, and can find fault only with the tabbing under the chart table. It's lifted quite a bit, perhaps an inch or a bit more.

Would the fix be to grind out the fill, reapply and fair? What fill would you recommend for this type of job?

My concern is that the problem is more systemic and the cracks would reappear. Am I looking at possibly reinforcing the tabbing?

I've attached an image showing the area of concern before the problem started.

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[Quetzalsailor]

You'll have to tell us a bit more: Kind and age of boat? Is there a liner (interior component of fiberglass which is intended to provide stiffness and finish) throughout?

Pretty normal, but undesirable, for a boat to have changed shape under load and over time. Many boats get deeper and narrower as the mast foot presses down and the shrouds pull up. Tabbing tears loose along bulkheads under the mast and the doors no longer fit.

Also, find websites specific to your boat make and/or model; others will be having similar issues.

[bcooke]

Fiberglass boat structures move. Not like a wooden boat perhaps but they are still not rigid structures. Fiberglass also (very very slowly) breaks down and the shape can/will change a bit.

Given the location you describe, I expect the hull is flexing (slightly) and the settee front is not. The filler is probably too rigid and brittle for the difference in movement which is pretty typical of fillers.

I am not sure there is much you can do about it. If the boat is old then maybe you can chalk it up to old age, grind out and replace the filler, and have a good expectation that the cracks will not return for many years. The automotive industry has 'flexible fillers' that might absorb the stress better but I don't really know much about them. Other than that, you can try to minimize the visual impact with paint.

Its hard to say from the description as to whether its a widespread problem or a local issue. More pictures might help but it might still take an on-site visual inspection to make a determination that the hull is indeed moving around excessively. The diagnosis may be beyond the internet forum kind of thing.

[Rachel]

As has been mentioned, it's really hard to say anything definitive without at least seeing photos.

A couple of factors:

1) Fiberglass is relatively "floppy," and in general it relies on bulkheads and other structural "boxes" to make it stiff.

2) A boat in the water is supported more-or-less equally over every square inch of immersed hull, whereas one on the hard is often only resting on the bottom of the keel, and offered supplementary support by six or eight 1-foot-square pads. Also, land supports can shift.

If it were me - and if you have what I imagine is happening, happening - I would probably check that the blocking and stands were basically proper, then wait until the boat was back in its element (water) and subsequently see how the cracked areas behave. I would then consider fiberglass tabbing that vertical "ankle piece" to the hull to make a one-piece support; but that depends on how the boat is constructed and what it going on specifically.

Rachel