Oakum or Cotton

[tillergirl]

Proceeding onwards with the winter theme of getting the bottom watertight, I've raked out the majority of seam above the garboard which was in poor condition either side. The old caulking is a mixture of oakum and cotton - not together of course, but cotton has been used where part of the seam has been redone. What's the best to put back, cotton or oakum? (already got some cotton of course!)

 

[Peterduck]

If everything is equal, and you have abundant supplies of both, I suppose that the oakum would be the better of the two. However, when you've got cotton and you don't have oakum, the oakum's advantages are not so great that it would be better to ignore the cotton and buy oakum. Go with the cotton. By the time that you have primed the seam before and after running in the cotton, it's going to stay there for a long time to come as long as the plank edges are in good shape.
Peter.

 

[tillergirl]

That's jsut the answer I wanted! Currently letting the empty seams air and contemplating how many other seams I ought to have a serious go at!

 

[seo]

At least over here in benighted former colonies (Maine,) oakum is only used in fairly large boats that are planked with hard wood. So my 60 ft. freight boat that is planked with 2" yellow pine is caulked with a single strand of oakum, with two strands of cotton over.
A larger schooner with 3" oak planking would have two strands of oakum.
My 40' Sparkman and Stephens yawl is planked with 1 1/8" mahogany, and it is caulked with two strands of cotton. A 28' Herreshof ketch planked with 7/8" cypress (which is a lot like cedar) had one strand of cotton.
I also work as a marine surveyor, and look at quite a few boats. The determining factors seem to be: a) are the back seams tight enough so that you can drive cotton without driving it out through the back of the seam? and b) will the plank seams remain perfectly stable. If the planks are moving in and out or back and forth in relation to the plank next to it, the caulk will "crawl" which means that the planks will roll the caulk out as you would roll a bit of clay between your hands.
Not knowing how big your boat is, my advice would be to not use oakum if you don't need it, use cotton over oakum, and drive the caulk hard enough to make a little dent in the planks for the caulk to lie in.
As a final bit of apostasy, I use a plastic ! mechanic's hammer to caulk with. I once had a caulking hammer made of proper osage orange, but its head kept flying off at inopportune moments.
seo

 

[tillergirl]

I think the answers to the questions are (a) yes (b) no - so cotton for me. Grateful for the advice. Currently worrying about the floors as inthe post further up!