Scarf Joint in a Wooden Mast

CatfishSoup · #1 (**permalink**) 11-23-2008

Anybody know what sort of scarf joint i would use on a wooden mast? i just need to replace the bottom three feet or so. Also, what sort of strength am i losing in a scarf joint? should i just get a whole new spar?

davidpm · #2 (**permalink**) 11-23-2008

How big is the mast?
how is it constructed. Solid, stave's, box etc.
What kind of wood.
What is wrong with the bottom 3 feet?

Pictures?

The answer will be different depending on your situation.

CatfishSoup · #3 (**permalink**) 11-23-2008

Quote:

Originally Posted by davidpm

How big is the mast?
how is it constructed. Solid, stave's, box etc.
What kind of wood.
What is wrong with the bottom 3 feet?

No pictures. I don't actually own the boat, it's an impending purchase. The boat is on the other side of the state from me so its hard to get info that I forgot to check out last time I was there. The spar is solid and rectangular shaped. I'm no expert, but it will probably be doug fir. The boat is a 31 foot gaff ketch, so you can guess the length; I never measured. The bottom three feet is a little rotten.

CatfishSoup · #4 (**permalink**) 11-23-2008

I just spoke with a schooner captain who told me a half-lap with through-bolts or screws would be fine.

davidpm · #5 (**permalink**) 11-23-2008

Quote:

Originally Posted by CatfishSoup

I'm no expert, but it will probably be doug fir. The boat is a 31 foot gaff ketch, so you can guess the length; I never measured. The bottom three feet is a little rotten.

The kind of glue is very important.
Epoxy has been said to not be the best in this application.
resorcinol is the old standby but it does leave a glue line and needs a good fitting joint.
If you are putting bolts in I doubt if a glue line is a problem.
Sitka Spruce is considered very good.

Depending on the nature of the rot some properly scarfed in Dutchman may be stronger than chopping off the bottom. And can look cool too.

A half lap is going to loose some strength but may be OK since most of the force will be compressive near the bottom of the mast.

A fancy scarf joint will be stronger but harder to do right.
Traditional Tools » Forums » Tools & Woodworking » Woodworking » SCARF JOINT

sailingdog · #6 (**permalink**) 11-23-2008

I think a 8-to-1 scarf would be a better solution IMHO... but as davidpm said, harder to do right.

CatfishSoup · #7 (**permalink**) 11-23-2008

Im no expert woodworker, but it seems to me a half-lap would be very effective because most of the force would be, as DavidPM said, compressive because of the shrouds, and for the same reason, just a plain diagonal 8:1 scarf (I don't know what that is called) would be not as strong. It seems like the half lap would be pressing wood butt to butt, whereas the latter would not. Hope that makes sense.

badsanta · #8 (**permalink**) 11-23-2008

If the bottom is rotted, I would e very concerned about the rest of the boat. I love wooden boats, I also know they are a lot of work. If you have the time and skill, go for it. If is your first one, this may be more than you can handle if this is going to be done by your self, I hope you have lots of time of money either way. Even a free boat can cost you a fortune. Not trying to talk you out of this, you need to do what you want. But having tried to rebuild one, it was more than I imagined. Don't forget to add the price of repairing sails, rigging, plumbing and electronics. The list will go on for ever. best of luck.

okawbow · #9 (**permalink**) 11-23-2008

A well fit half lap joint would be strong enough for a mast base. If it were higher up; a finger joint would be better. Half lap joints are used in post construction in buildings for compressive loads.

davidpm · #10 (**permalink**) 11-23-2008

Quote:

Originally Posted by badsanta

If the bottom is rotted, I would e very concerned about the rest of the boat. I love wooden boats, I also know they are a lot of work. If you have the time and skill, go for it.

I second what badsanta said. You may be on your third wooden boat restoration and anything I say is obvious. If not I'll make a couple of comments.

The rules for wooden boat survey are radically different than for glass boats and not everyone knows them anymore ever all surveyors.
Removing a few fasteners is a pretty common request. A plank, fastener and rib can look perfect and be completely gone inside. Removing a fastener or 6 is the minimum that is considered prudent.
Removing a plank is even better.
Pulling a keel bolt is not considered excessive.
So that means just doing a proper survey is not for the cost conscious buyer. Take if from someone who is still traumatized from the experience and is wiser for it.
If maintenance is let slip for even a few months a wooden boat can be seriously damaged. If it is let go for a couple of years it can be fatal.
If it is stored out of the water it can be even worse.