A Shipwright in Training

As the ship’s carpenter on the Aurora I get to fix all manner of wooden things.  A few weeks ago, we realized that some rather important parts of the boat had been made of red oak.  It’s not a good idea to use red oak in a marine environment because of the difference in porosity between the species.  Red oak (at least in the eastern US) grows faster than white oak, and the pores of the wood stay open, unlike the pores of many white oak species which are filled with a cell structure called tyloses that effectively seal them. These 2 cross sections show the difference well.

Red oak on top, white oak on the bottom.  Here’s a close up of the red oak.

And a close up of white oak

You can see that the larger pores are filled with tyloses in the white oak. 

The point of all this is that water gets into the red oak, stays there, and makes a wonderful environment for mold to grow.  The fellow that retrofitted the Aurora from a diesel-powered fishing boat to a 2-masted schooner used red oak for a number of parts that he really shouldn’t have.  My guess is that he had a pile of red oak that he got for cheap and was looking for places to use it. 

One place that he used red on on the Aurora was in the mast wedges.  These wedges go in between the mast and the mast partner (the reinforced hole in the deck where the mast passes through) and help to hold the mast exactly vertical.  They need to be strong and very rot resistant.  They are oriented with their open grain facing up, and water makes its way down the mast onto them (even if you cover them with a flexible boot).  So, to do these fellows properly, you first need to have a tough, rot-resistant wood.  I was able to buy some excellent live oak from the folks down in Mystic.

Live oak is the bomb.  It grows very slowly, has tiny rings and interlocked grain.  You can’t split it with an ax because of the interlocked grain.  It’s exceedingly tough and rot resistant.  You can’t harvest it legally (I think this is true) from live trees, but you can harvest it from trees that have blown down.  After Hurricane Katrina, there were lots of live oaks available, and we got piles of them shipped up to the seaport. 

We needed 32 new mast wedges because the old ones were starting to fall apart with mold.  I set up a little assembly line one night at the shop and whipped them all out in a couple of hours.  Here’s the set up.

I started by milling the wood down to 2″ wide x 3″ high lengths.  Next, set up a stop block on the radial arm saw to cut these into 12″ lengths.

zip zip zip.  On to the table saw to make a 3/4″ cheek cut.

Then using a taper jig that I made up for these wedges, cut the taper in each block on the band saw.

Which leaves you with this shape.

Next, cove the face of the wedge that will fit against the mast using another table saw.  This set up yields a slightly elliptical cove cut, but it’s close enough for our purposes.  I determined the amount of cove to cut by drawing out a cross section of the mast full size and bisecting the circle to represent the width of a typical mast wedge.  This gave me the height to set the blade.  After that, it’s just a matter of trial and error to set up a fence that will have the blade make a centered cut just to the sides of the wedge.  You end up running the piece across the blade at an angle.  It looks like this:

If you’ve never coved wood this way, it’s easier than you might think, and not nearly as scary as it looks.  The end result is a cove like this:

And that’s just enough cove to fit snugly against the mast. 

I then took a couple of these guys to the boat, wedged them in, and marked where they snugged up against the mast partner.  What I want is a very small wedge angle from this point up to the cheek of the wedge.  That way I can drive these wedges down between the mast and the partner more than I could with a constant wedge angle and they’ll fit more securely.  It looks like this:

After that, soak these puppies in a 50/50 gum turps / linseed oil mixture to help waterproof them and you’re done.  Beware though, if you use this mixture make sure you have someplace where they can dry that you don’t have to work in for a while… way stinky.

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This entry was posted on Monday, January 14th, 2008 at 11:32 am and is filed under Classes. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.