Sunday, February 22, 2009

Project: Replace the Bowsprit



The continuation of this project is being reported in the weekend project updates. To see them all, search on the label 'bowsprit'


Flash!

We zap back to the present, because I am itching to talk about what is going on right now, in this Project segment. I would like to catch you up to the present so that I can talk about the weekend's ongoing progress on Sunday evenings or Monday mornings.


At the end of August last summer, while at anchor in Port Madison, I noticed that some of the paint immediately ahead of the inner forestay pad eye was flaking up. So I dug at it with a pocket knife. It didn't take long to dig a hole a couple of inches deep, because the mahogany bowsprit had turned into mulch, presumably due to all the water entry into its interior from the originally failed fitting (subject of another post, sometime).

You'll note that the quarter is standing up on its own... it wasn't hard to do. I just pushed it into the mulch. Time for a new bowsprit, before the mast comes down.

First of all, we decided to not try to go thru the winter storms without an effective forestay on the main mast (the forestay attaches to the end of the bowsprit, and keeps the mainmast from falling over backward). So I made up a temporary bowsprit from a pressure treated 6x6. The biggest challenge in this job was getting the three holes for the main mounting bolts (OK, 1/2" stainless all-thread) in exactly the right place so that the tip of the bowsprit ends up in just the right 3D location to keep the forestay tight. It was good practice for when I would have to do the real thing.

In a marathon session, we pulled the old bowsprit and replaced it with the temporary. This was a difficult job, since the multiple pieces of all-thread holding the bowsprit to the deck (3 main mounts, 4 for the anchor windless, 2 for the original inner forestay attachment, 3 running horizontally for the Sampson posts) had to be removed. A few of these came out by double-nutting them and backing them out with a wrench. But most needed a stud puller (rented), or in the case of the two for the original inner forestay attachment, the sawzall was the tool of choice. Boy, the old bowsprit was heavy! It was saturated with water. With a lot of help from the other men on the dock, we got it off the bow and onto a dock cart.

Eolian is happily weathering the winter storms with the temporary. I am certain that there is more sound wood in the temporary than was in the rotted original.

The original bowsprit was made up of two huge pieces of mahogany (approximately 5"x10"x10 feet long) laminated together. The new one is a lamination too, but instead of mahogany, I used pressure treated lumber to try to hold back the rot potential. To reach the size needed, I laminated six 10' pressure treated 2x10s, using glass-filled epoxy resin and a bazillion clamps. Before bonding, both surfaces got a coat of unfilled epoxy brushed on so that the resin would be able to penetrate the surface.

To do everything I could to prevent reversing right for left, or drilling a hole leaning the wrong way, I have kept the original bowsprit on the sawhorses right next to the new one as it is formed.

So next, the blank needed to be trimmed and tapered. After carefully laying out the shape of the sides on the top and bottom of the blank, I rolled it over so that one of the sides was upright. Then I made saw kerfs across it, holding the depth of cut just shy of the line. This required frequent adjustments to the depth of cut, and about 500 cuts (on each side...). Then with a hammer, I broke off the "fins" between the cuts.

Finally, a marathon session with a power planer smoothed the rough surface to the line, and a final pass with a belt sander made it pretty by taking out the planer marks.

Then roll it over and do it all again on the other side.

The bottom cut was last. Matching the original bowsprit, there is no top cut - all the taper is taken off of the bottom.

Unfortunately, the depth of cut needed on the bottom (being about twice that needed on the sides, since it is all on one side) was too much by far for the saw-kerf method. Luckily, I have an Alaskan chainsaw mill (used for making timbers from freshly felled trees). It was the perfect tool for the job.

Then clean up with the power planer and the belt sander, as for the sides.

The original bowsprit was tapered full length on the bottom, and was then mounted on a tapered shim (teak, thankfully - it never rotted) to compensate for the taper. This was apparently a design error, corrected in the field as the boat was constructed. I made the new bowsprit with no taper for the first section to eliminate the need for the shim. Making the transition between the tapered forward section and the straight aft section was tricky. I used a hand chisel for most of it, but ended up using the nose of the belt sander (and a couple of belts) to get a nice swoopy transition contour.

OK, so now I had a blank with the right shape and dimensions. Now all I had to do was drill 19 holes, in exactly the right locations, at exactly the right angles so that when the new bowsprit is mounted, it will be located just like the old one. The original holes were drilled by hand after positioning the bowsprit in the correct location. This technique was fine for an initial installation, but makes it hard to duplicate hole alignment for a replacement.

A lot of careful measurement, layout and templating got me the locations, but I needed a jig to guide the ship auger at the correct angle so that it would come out of the bowsprit 8" away at just the right place. After some thought, I buit this jig. It allows me to set the angle in one plane - which is enough if I rotate the jig properly.

Then I cobbled together a transfer jig to show where the hole will come out when it is drilled. This jig holds two short pieces of tubing in alignment, and allows placement of the upper piece of tubing in direct line with the drillling jig and auger. The lower piece of tubing (out of sight below the old bowsprit here) then acts as a gunsight, showing where the auger will exit. It is ugly, and it takes about an hour to set up for each hole by trial and error, but it works.

The 19 holes are now all drilled. I completed the last of them this weekend.

On this last Saturday, I began the task of fashioning a 4" diameter cylinder on the tip to accommodate the cranse iron. No fancy tooling here. I am using a hammer, wood chisel, sureform plane, belt sander and a palm sander. And a short length of 4" heavy PVC sewer pipe as a gauge to know when to stop removing material. I wish I had the actual cranse iron to do this, but unfortunately it is occupied, holding up Eolian's mast.



The continuation of this project is being reported in the weekend project updates. To see them all, click on the label 'bowsprit' just below.

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2 comments:

middlebaysailing said...

What a gigantic project. The hole drilling would have stymied me. You must have exercised a lot of brain cells to design the jig.

I had to drill two holes straight through my skeg when rebuilding that area to accept a new rudder strap (18" x 3.8" x 3" stainless strap bent in a "U" shape). Drilling the holes was definitely the hardest part. Keeping them going in the right direction, coming out where you intend for them to exit - it was touchy. I filled my mistakes with thickened epoxy...

Rick
Cay of Sea

bob said...

Rick -

I'm pretty sure I burned out a few brain cells...

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