Vandemere 2012

I knew it was a long shot getting the boat ready for the water by 28 October. I still have a couple of weeks worth of work to go. I am not even certain I will launch the boat before we close up shop in Rhode Island for the winter. Did you notice that I did not use the word finish. I hate to give Gary any fodder but someone once said that a boat is never finished................ until it sinks.

Well the good news is I definitely have a shot at having things ready for 2012.

Before I put the decking on I like to precoat the underside with two or three coats of epoxy. Since epoxy bonds best to either bare wood or green epoxy and bonds less well to fully cured epoxy, I usually leave uncoated the areas under the deck that will bear on framing.

This left an interesting pattern on the last piece of deck that closes up the bow. The large opening is there for the base of the mast to swing through. It make me think of a church and of course it lays just forward of the tabernacle.

This shows the framing under the fore deck. The arch was laminated from several layers of very thin wood. There is a lamp in there to help keep things warm so as to move the curing process along.

Here I have primer on the topsides, but still a long ways from being ready for the water.

Bowsprit

Skorpa sports a removable bowsprit that allows her to fly a 250 square foot asymmetrical spinnaker. This more than doubles her working sail area of 238 sqft.  I had a few questions about the bowsprit tube so I called Graham and he answered my questions and as he often does he also gave me a little trick to make the job go easier.

Getting the hole cut in the hull in the right place, with the right shape is a little tricky.

Here is Graham's helpful tip.

Locate the point 6 feet forward of the bow where the tip of the bowsprit should be.

Determine where on the forward bulkhead the base of the bowsprit sits.

Using your best judgement drill a hole through the hull in line with those two points.

Now run a string from the tip location through the hole to the base.

Move the hole until the string is straight and you have the center of the necessary opening in the hull.

I used the same trick to determine the forward and aft points of the opening.

I used a variety of methods to draw the outline of the opening, but knowing for certain the center point was critical to doing a reasonable job.

The opening came out pretty nicely. The carbon fiber bowsprit tube is laying on the deck.

I reinforced the area around the hull opening with 3/8 ply ' to give it some bearing' as Graham says. The I added some carbon and fiberglass tape. You can see the main mast trying out the tabernacle.

Carbon Fiber and Wood

So why aren't carbon fiber and wood a good match?

Carbon fiber embedded in an epoxy matrix is light, stiff, strong in tension and compression, and expensive.

Wood is not nearly as strong, stiff, or expensive. Wood occurs naturally, is pleasant to work with, it can be beautiful, and wood is resistant to fatigue.

Lets say you designed a spar to resist a load of 600 pounds. You use enough carbon fiber to handle 500 pounds and enough wood to carry 500 pounds total strength 1000 pounds. Nice safety margin.

Now apply a force of 500 pounds to the spar. The carbon will flex very little say an inch. The wood will flex an inch readily resisting with say only 20 pounds.

Apply 550 pounds and you will snap the carbon. Now the entire load falls to the wood which will flex several inches before resisting with its 500 pounds. Then the wood will fail.

You would be better off designing and building the spar entirely of wood or carbon.

I did see an article in Woodenboat Magazine where they built a hollow wooden spar and lined the inside of the wood staves with carbon fiber and carbon rod.. Under load the wood fibers on the outer part of the stave will have to flex a greater distance than the carbon fiber laid on the inside of the stave. By adjusting this distance you could get the carbon and the wood to work more closely together.

But my spars have a carbon braid on the outside. The reason has to do with something called hoop strength.
If you design a hollow wooden spar with walls just thick enough to resist a certain load in tension and compression. The spar may fail prematurely because the walls buckle or splay apart under load. The spar needs more hoop strength.You could make the walls thicker but that would add weight. Or you could surround the hollow wood spar with a carbon braid to keep the wood squeezed into shape. The carbon fibers are running diagonally around the spar using their stiffness to keep the walls from bulging even a smidge. Since the carbon is not running straight up the spar the wood is free to flex and the two radically different materials work together to make a light and strong spar.

Carbon fiber and wood not a good match.

Well not usually anyway.
Here I am coaxing a sleeve of braided carbon fiber onto the mizzen top mast.

 If you pull on the braid it tightens like a Chinese finger trap.As you push the braid on it expands and shortens and then when you pull it out it lengthens and tightens.

Once the sleeve is in place I secured the ends with a hose clamp.

The main top mast is in the upper right waiting its turn to be swallowed by the braided black snake.

Spar Building

The mast support came out very well so it is on to the mizzen mast. The top section of Skorpa'a masts are hollow wooden spars sheathed with carbon fiber braid. The idea is to make them as light as possible. At the top of the mast every ounce makes a difference, both when under sail and when raising and lowering the masts at the boat ramp.

Sitka spruce is light and strong also pricier than the construction grade Douglas Fir I have used for most of the solid wood on the boat.

The hollow mast is made up of 8 staves 10 feet long and tapering from 1 1/4 to 7/8 of an inch. I set up a jig to hold the pieces straight and in place. Graham likes to tack the first stave down to a series of blocks that have been leveled and that is what I decided to do.
Unless you have a lot of extra hands the sections of pvc pipe are needed to hold the staves until they lock together. I cut an octagonal plug for the tip and a piece of plastic tubing holds the base open. I am not using any glue here just practicing. 

Seven staves birdsmouth side up are getting a very light coating of unthickened epoxy.

I made a notched spreader to help apply the thickened epoxy quickly and evenly, and as thinly as possible.

The first few staves go in pretty easily, but as you get past the half way point it is a little trickier.
With a little help form Sally who put down the camera to assist I got the last stave locked in.

Some people use hose clamps or wire ties but I think this idea I got from Charlie Jone on the Mess a Bout forum works great. I cut several old bicycle inner tubes into long strips. They go on quickly and put a gentle squeeze on the spar. The next day I unwrapped the tubes and cleaned up any squeeze out. I had two beautiful octagonal spars.

I drew a series of lines which guided me as I planed down the last two feet to give an additional taper. The I drew some more lines that allowed me to plane down the edges to make a 16 sided polygon. Whatever you call that.

You can see the lines on the mizzen.

By the time you get to 16 sides you are not that far from round so I planed the edges by I until the spar was close to round.

The mizzen is 16 sided.

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Once I got the spars as round as I could with the plane I used sanding blocks made from cardboard or PVC tubing to round them completely.

A Thousand Miles A Thousand Things to do.

Graham is hosting a Mess-a-bout in Vandemere, North Carolina on October 28, 2011. I would really like to be able to take Skorpa. I am not sure if I can have the boat finished. Time seems to be slipping away. I am putting in a lot of hours but progress though steady is still slow.

A few things like the forward deadlight, oar locks, compass, bow sprit, things that can easily added later I am leaving for now. I am still trying to do good quality work.

My mother told me to stop being so fuddy duddy and just finish the boat. She would like to see my work while she is still around.

The top sections of Skorpas masts are hollow wooden spars covered with carbon fiber braid.
Never having done a birdsmouth spar before I thought I would practice on a mast crutch that sits in the mizzen mast step during transport and holds the aft end of the two masts.


That is a view of the top of the mast crutch. It is two inches across. To make those cuts accurately I did a little work on my table saw.

The old metal insert is all bent and banged up and the opening is two large. I tried to straighten it. Then decided to make a new out of some plywood.

I put on a new blade and ran it up through the plywood insert making the cutout no larger than necessary.

When I bought my plywood I also bought some sitka spruce. It is light and strong.

The board on the left is the rough sawn wood I started with. After a lot of work I was down to some staves 9 feet long, 7/16 of an inch thick and tapering from 1 and 3/8 to 7/8 of an inch. All to make a tapered hollow wooden spar.

 One of the staves is running through the saw. Two passes one on either side of the fence makes the birdsmouth cut.

Decking

After Jim helped me get the large forward deck section glued down I worked my way steadily towards the stern.

I precoated the underside of each panel with two coats of epoxy.
I glued in 6mm ply under the butt joints in the deck. Under where the oar locks will go I set in some 5/8 solid wood to help distribute the loads.

At first the coaming structure felt fragile. Graham wanted to keep the weight down as much as possible so there is not a lot of extra in his scantlings. I was amazed and pleased though at how stiff and strong the coaming and side decks felt when everything was glued up.

Here is a view of the coaming before the side deck went on. The solid wood is only 5/8 by 5/8.

Graham told me I would want my oars to be at least 10 feet long. Since I added a lazarette the cockpit is only open for 8 feet or so. The solution is to build some tubes into the lazarette that will let the oars slide in and keep any water out.

I am wrapping some wetted out 6 oz glass onto a section of 3.5 inch aluminum tubing. I first covered the tubing lengthwise with one inch strips of plastic then wrapped that with plastic. When the epoxy sets up I slid the plastic out first then the fiberglass tube slipped off easily.

The tube is very light and was fun to make. I probably did not use enough glass, but what can you do.

The rear deck has its two coats of epoxy on the underside and is waiting to be glued in place.

 All the decking except for a small piece in the bow is in.

Tabernacle

What is a tabernacle doing on a boat? In lay terms a tabernacle is the dwelling place of the sacred.
On a ship a tabernacle is a structure on deck that holds the mast on a pivot that allows the mast to be lowered.
When you want to install the mizzen mast on an EC22 you pick the mast up and insert it through the mast partner and into the mast cup. The main mast is too heavy to install by hand so we are building a tabernacle. I have done some searching online to discover why the word tabernacle has come to be used to indicate this pivoting mast support, but I have not found anything convincing.

Here are the parts laid out.

The tabernacle goes just forward of the forward bulkhead. The mast must pivot through the deck so the forward compartment is always open. The floor slopes forward and there is a little drain near the bow. The forward compartment is a good place to store an anchor and line. I put a layer of 2 oz glass down to resist abrasion and water. The deck is reinforced on either side of the notch where the tabernacle fits.

Some temporary braces are holding the tabernacle while the epoxy sets up.

A little help from my Friend

Our good friends from Virginia Jim and Jerryanne stopped by for a brief visit. While they were here we went for a lovely sail in some gusty winds, and Jim helped me put the foredeck on.

The deck is upside down on the bench. The underside has received two coats of low viscosity epoxy.

Jim is spreading thickened epoxy on the deck beams while I mix up another batch.

If you look closely you can see epoxy spread on the deck beams. I used a notched trowel to even out the coating. In the foreground you can see some of the reinforcement for the tabernacle.

Here comes the deck epoxy still sticky.

Trying for an accurate touchdown so we don't smear the epoxy everywhere.

There she is now let's strap her down.

Cam straps hold the deck down to the curve and steady it. Small adjustments can be made but it is not sliding all over the place.

Foredeck is in place. Temporary screws hold the edges down.



Thanks Jim.