How to fix cracks in hull to stern tube?

[sailor_ed]

Eastward Ho

You have certainly gotten a wide spectrum of advice and here is some more! :-)

I would do nothing until you have more facts. You need to understand how this was built and what has been done to it since. First, you seem to have ground through the filler: is the area behind a void or does it connect directly to the interior? Probing with a thin rod might tell. Or a strong light outside while examining from the inside.8

Also note that the bolts undoubtedly go through a flange that is probably 1/4 inch or so thick. When was this buried in filler? Is it original? What do the bolts fasten into? Some Mototool work on the lower crack might tell.

Fiberglass boats were built in halves for ease of laying up the keel and then pieced together. They would probably have pressed strips of wet cloth down into the keel and the possibility for voids is real. Other boats have had stern tube problems due to the difficulties getting a proper layup in this area.

Don't be afraid to drill small holes (1/8") to figure out what is going on (look closely at the chips) they will be easily filled later on.

If you can't make sense of it or feel you are in over your head find a good independent surveyor to take a look at it.

I suspect after all this archeological investigation you will find that the easiest and best way to deal with this is to leave all the filler as support and lay up several layers of biaxial and mat over both sides extending beyond the filled area to good laminate with a generous overlap. Essentially create new structural hull in this area. I would use epoxy for layup and vinylester fairing compound to finish.

But I would "do my homework" first! And don't worry, there can be worse things to happen in this world of boating!

Ed

[rognvald]

To add to sailor Ed's good advice, why not rent/buy a borescope to alleviate any guesswork. I've owned one for over 10 years and it has saved me more time and money that I could possibly count. Good luck and safe sailing . . .Rognvald

[Eastward ho 24]

Borescope great idea!!

[jimbunyard]

Originally Posted by Eastward ho 24

It's not an impact crack, or anything hitting from being Tangled in the prop. For lack of a better description looks like how mud cracks when dries. Almost as if the fairing was put on so thick that when it dried it cracked. But couldn't see that being the case since epoxy doesn't "dry". The boat has sat on the hard for a few years, then was in the slip through the freeze of winter for a season or 2. I'd say over the last 8 yrs it hasn't moved other then back and fourth to the lift and when the mechanic took it out to keep the motor up. Maybe some moisture froze in there or that's how the PO put the shaft log in there. Or vibration issues....

I don't think anyone here thinks that the 'current' cracks were caused by an impact or prop fouling, but that the reason for the repair and subsquent cracking was something wrapped in the prop, a chain or steel cable. I agree with those people.

On second inspection of the pictures, the cracks appear to be more than just surface damage to fairing compound.

For a permanent repair here, you cannot just 'glass over' the whole thing and hope for the best; the inability to seal the previous 'repair' from the elements (one can't permanently bond epoxy or polyester resin to bronze (in my opinion) because of their different expansion coefficients. That is what got the boat to this position in the first place.

In the picture below are circled some 'areas of concern'.

The yellow shows fairing over bottom paint. Until established to the contrary, let's assume that the fairing is automotive bondo; the varying shades of 'pink' in the different layers tend to support this. Bondo should not be used under constant immersion; it is hydrophilic enough to cause problems.

The red shows that the cracks are deep; they appear to propagate upwards from underneath, not downwards through the fairing material, as would be expected if they were resulting from too heavy or too rapid application of fairing.

The blue shows application of repair materials over gelcoat; hard to say for sure visually, but it looks alot like standard boat yard resin over roughened gelcoat, followed by multiple skims of bondo, a standard quick and dirty, cost-effective-from-some-viewpoints, boatyard repair.

It may be possible that the cracks are in fact only surface flaws; the only, and quickest, way to tell for sure is to remove the fairing compound and previous repair down to the original glass layup of the hull. If there are no cracks there, you can heave a sigh of relief and just fair everything back up, seal and repaint.

If not, and the cracks go into the original layup, a proper repair will likely involve removal of the stern bearing housing, grinding out the damaged area around the cracks enough to laminate layers of glass sufficient to duplicate the original schedule in a scarf appropriate for the application.

Due to strength and adhesion issues in this area, epoxy is the preferred resin.

Of course, depending on your planned usage for the boat, since you're aware of the problem, it is entirely acceptable to fill the cracks with something, even marinetex, sand (though marinetex sands horribly), paint and go. From your pictures it doesn't appear that there are leaks around the bearing housing, you might get several years of (local, bay) service with no problems at all.

I wouldn't be planning any circumnavigations with it like that though...