Thwarts

[GreenLake]

I found one pair of the bolts that hold the thwarts to the seats sheared off recently. I can't account for any particular reason why this would have happened. Possibly, an impact to the side of the boat could stress them, but I can't recall a recent incident. Is that something that has happened to others?

Also, one of the bolts looks bright yellow where it's sheared off, which to me would seem to indicate that it was made from chromed brass rather than SS. I have seen fittings that are made from that, but never screws (and none of the local stores stock anything like that). Anybody come across anything like that? (They are wood screws with oval heads - they are used with special washers that are contoured to fill the gap between the board and the screw's head - forgotten what they are called).

[rnlivingston]

When I took the thwarts off a 1966 DS1 I was restoring, the hull expanded out a 1/2 inch. I had to pull the hull together to get the thwarts back on. All the original screws were brass which O'day used for fastenings back then. I replaced them all with Stainless Steel. In your case just sitting on the gunnels could have pushed the hull outward.

[GreenLake]

Good to know the brass screw was original. Thing is, this happened during a season where the boat wasn't pushed all that hard and the break discovered after a particularly easy outing (no hiking, as far as I remember).

I'll have to somehow drill out the sheared off part of the screws. Brass would make that easier than SS. Not the best access to the boat right now - it's gone into storage, somewhat early because other commitments will prevent me from going out in the remaining nice days.

[rnlivingston]

One of the other causes of this problem is too much pressure on the keel while on the trailer. If you have bunks and rollers, you need to carefully balance the load between them. The 1966 DS1 I restored had sat on a trailer without moving for 20 plus years.

[GreenLake]

All good points, but the perplexing thing, to me at least, is why now, all of a sudden?

Shouldn't one expect a pair of bolts to withstand the kinds of continuous and static stresses such as from storage either not at all, with relatively immediate failure or indefinitely? Wouldn't the cause for sheared bolts be more likely something sudden or at least something beyond the "normal' load range?

I did not have time to investigate this deeply enough because I noticed it right as I got ready to move the boat. In thinking it over, it occurs to me that it might be significant that the bolts that failed were on the seat side. The significance of that is that tension on the thwarts would affect both sides equally, but in compression, the way the thwarts are fitted, the CB trunk would support one end where it buts against it, while the other side is angled - once the bolts give way, the seat could slide under the thwart, pushing it up.

That might point to a spike in compression, and the first scenario that comes to mind would be if the boat slammed into the dock from a passing wake. I don't remember that happening, but it's a busy dock and I'm always gone for a bit parking or fetching the trailer. Next time I'm at the boat, I'll have to check that side for signs of any impact.

[jeadstx]

It may have been that one of the screws had already failed, but wasn't noticeable. The other one then failed due to increased stress. It's odd what can cause things to fail.

I used to carry my grandfather's pocket watch. The mainspring occasionally would break when there were bad electrical storms. The watchmaker (5th generation) I used when repairs were needed told me that she would check her supply of mainsprings after electrical storms to see if any had broken.

John

[K.C. Walker]

John, that watch spring story is great! The world of weird things.…

I had the same thoughts about one of the screws failing at an earlier time. Also, it seems that they could have had stress cracks from some previous occurrence that weakened them.

[GreenLake]

Drilled out the existing screws. Not too cleanly - in the end, just grabbed the stubs with needle nose pliers. The wood backing is probably disintegrating a bit as well after 50 years. Filled the larger holes with Cold Cure epoxy mixed with wood flour. Getting the hull to close was a challenge. Even a belt with ratchets wasn't enough, in the end I had to prop up the rubrail with a plank - that closed up the last 1/4".

I've upgraded to SS screws, because that's what I had in stock; let's see whether these will hold or whether the other side will now pop.