Screwing things to timber spars

[TradewindSailor]

Surely most of the problems with rot around fasteners in wood are due to the fastener being overloaded resulting in crushed wood around the fastener and the varnish seal being damaged? Since the material that the fastener is made from, silcone bronze or s/s, is much stronger than the surrounding wood it would be advantageous to increase fastener size or drill the hole out and fill with hardwood or epoxy to decrease the bearing stress on the wood.

 

[maxcampbell]

I've been squirting a drop of Sealtack (ie Sikaflex lookalike) into the pilot hole and picking up a bit on the screw - it looks OK, with the sealtack forming a flexible gasket around the screw head, or under the fixing. This hasn't been tested by more than a season's use, but looks good so far. Epoxy seems a bit brittle to me, especially in the small amounts everyone except oldsaltoz is using.

 

[Deleted member 36384]

..... Epoxy seems a bit brittle to me, especially in the small amounts everyone except oldsaltoz is using.

If you get a chance to look at the book referred to in my post above, it has a very interesting section on fastenings in wood and using Epoxy resin. The authors have done many tests to validate their suggestions.

The method I quote from the book relies on the Epoxy soaking into the grain and cell structure of the wood. Hence, the shear strength is increased in a similar manner as resin and GRP cloth strands.

This method is not as strong as an epoxy plug. The epoxy plug achieves superior strength by spreading the shear loads over a much larger surface area of wood.

In soft woods where a fastener may be subject to many cyclic loads, for example hinges, it can make the hole very strong and avoid the problems of the fastener enlarging the hole over time.

 

[prv]

The old boat builders method was simply to dip the screw in varnish before finally driving it home.

Now that sounds like an appropriate level of effort for the size of job (it's only a weeny cleat to hook two bits of string over), and I have tins of varnish on the shelf. Cheers.

Pete

 

[prv]

Of course you could always make a proper job of it and have a varnished pin-rail surrounding the mast. Supported on cast bronze dolphins and with highly polished belaying pins and a bell.

Where's my coat?

Not as daft as you think - the bronze dolphins would be a bit OTT, but a pinrail wouldn't look out of place on my boat. I was actually contemplating adding such a thing for the mizzen, as the halyards currently interfere with the mast hoops a little, but there isn't really space. On the mainmast there's a kind of quasi-pinrail with blocks instead of pins, but the lead is the same.

Pete