Mahogany splice in spruce mast

[SchoonerScotty]

Hi Sailing and Rigging Whizards,


My boatwright said he can use mahogany to slice a foot to two foot section, using epoxy and a thickener, to replace rotted spruce at the top of my 28' box sectioned Sitka Spruce mast. Will this work OK structurally?

Just want to be sure... he then will put on nine coats of varnish, sanded between coats and said the wood should be protected. Also, at the mast head, there is a sheeve box inside so the wood is not thicker on the port and starboard side more than about a half to 3/4 of an inch on each side....

Thanks,

SchoonerScotty

[Ian McColgin]

I presume that by slice, you mean splice as in scarf - basicly 8:1 to 12:1 bevel for the glue surfaces, viz ==//==. A "cloths pin" scarf takes up half the liniar length, viz: ==>>==. If your boatwright does not know the clothspin scarff, he or she is not a boatwright. I suspect that he is and that the confusion is your use of terms more than his, but answering is still hedged with uncertainty.

The truck, like the butt, takes mostly compression strain and a short length means that the wood type is not so critical as if you were replacing wood around the spreaders, to take another spot where rot is common enough that you really ought to look there quite closely before determining on this repair. While at it, check at the partners and at the butt. These are places where compression blocks are not uncommon inside a hollow box mast and thus are places where the natural condensation inside the mast could pool to detrimental effect.

Anyway, survey of the mast aside and we hope it's already been done, the truck is not the most dynamic place on the mast and using a wood somewhat different from the Sitka spruce is something you can get away with. I'd personally still prefer spruce, even if not sitka, or fir. There's a lot of stuff about these days marketed as mahogony about which I'd be not so very confident. I think it easier to judge firs and spruces.

Finally, thickened epoxy. End grain soaks up lots of epoxy. The scarf should be cut to excellent tolerances anyway. So, in mast repairs I've undertaken, I put a slow curing mix of unthickened epoxy on the surfaces, reapplying as needed to be sure that all the epoxy that would take up took up. Then I put in the very least thickening material (not microballons! something structural but not for this so hard as colloidal silica) that is consistant with filling such very minor gaps as were left by my workmanship and consistant with the glue not running out.

G'luck

Ian