Saturday, September 10, 2016

Slow but steady progress on the Zip transom

If any one thing characterizes THIS build over the Utility, it's that I'm striving to be much more meticulous with each part of the process. 

When I started building the Utility, I admit, I wasn't fully confident in myself that I would or could finish it. 

Well, I did. 

Along with that has come a great deal of positive growth and change. With the Zip, I want to make a much nicer boat. I'm not necessarily shooting for a "showpiece," but I do want to make it as fine a boat as I can.

With all that said, let's take a look at the work on the transom so far:

What I learned from William Jackson and the Sande Ace

I will be building this transom differently than what is described in the Glen-L plans.

First of all, the transom is constructed of 1" mahogany framing that is attached to 3/4" plywood backing. In the plans, Mr. Witt calls for only the mahogany frame parts to be notched for battens, keel, etc... NOT the plywood. The main reason for that, I assume, is more aesthetic than structural.

1-inch mahogany framing and motor board for the Zip transom

In this detail shot from the Utility transom's construction, you can see how only the frame is notched for the keel, NOT the 3/4" plywood transom. Many Glen-L plans specify this method for building a transom, but it's not the only way.

That is all fine and good. However, during my Utility build, I found that fitting the battens, keel, etc into these notches was a bit "tricky," particularly with my limited woodworking skills. 

I learned a different way to build a transom, by studying William Jackson's "Ace" runabout design. Basically, you cut the notches through both the mahogany framing AND the plywood. Then later, you cover the ends of the battens, etc with another piece of wood or plywood across the width of the transom. On the ACE, the "cap" is only used across the bottom area of the transom.

This photo, from an ACE restoration project, shows how batten notches are cut through both the framing and the plywood section of the transom. Battens are run all the way through the back, then trimmed to fit.

This photo of an ACE transom shows the full-width "cap" that is placed over the ends of the battens. NOTE: I did not take either of these two photos. They were sent to me by a very helpful gentleman who has restored several ACE boats made by the Sande Boatworks company in Washington state in the 1950s-60s. I HIGHLY recommend learning about the Sande ACE, and this fine piece of post-war Americana. Please explore the website, and see for yourself this rich snapshot of American history. Thank You, to the community for preserving and sharing these boats and this slice of history on your website.

My plan is to combine this method along with my own experience from building the Utility transom. I will start with a 1/2" plywood transom, framed in 1" mahogany. I'll cut the notches all the way through both parts. Then, after installing the keel, battens, etc, I will cap the entire transom with two additional sheets of 1/4" plywood.

I believe this method will allow for easier fitting of the battens, and consequently result in a stronger overall joint.

What I've learned from thickened epoxy

I will need to use thickened epoxy on the transom, because over time, I will build up its full 1" thickness by laminating multiple layers of 1/4" marine plywood.

During the course of the Utility build, I used quite a bit of thickened epoxy. Some was thickened with #2 silica. Some was thickened with mahogany sawdust.

I also had to sand, file, and chip away at some cured globs of the stuff. What I found was that epoxy thickened with the silica tended to be more brittle, whereas epoxy thickened with the sawdust tended to be more resilient.

However, I also learned that using sawdust brought its own problems. Basically, sawing the wood leaves larger grains and chips of the wood than sanding. When mixed with epoxy, these larger grains and chips created a "clumpier" mixture that was both more difficult to use, and also tended to leave gaps and air pockets.

Still, I believe that epoxy thickened with wood dust IS more resilient than epoxy thickened with silica. So, moving forward, I decided to collect as much wood dust as possible from sanding the mahogany. Sanding leaves a much, much finer wood dust. That leads to better, more consistent mixtures of thickened epoxy.

The frame parts, including the motor board, are all made from rough-cut 4/4 mahogany. I have been doing a LOT of hand-sanding of these parts, to shape them and smooth out the rough sides. While sanding, I have also been meticulously collecting the mahogany sanding dust.

These are the upper frame pieces for the transom. The one in the foreground has been sanded smooth. The one in the background still has the rough-cut side from the lumber yard. As I go, I've been "sweeping up" the sanding dust with a paint brush, and collecting it in a ziploc bag for later use.

I'm trying to keep all the parts as symmetrical as possible. So, when working on sister parts like these, I clamp them together while sanding them to shape.

Aligning the transom parts

Transom frame parts laid out on the first 1/4" plywood cutout.

My motor board is 1/4" wider than specified on the plans, so it extends into the area where the upper frame parts go. 

I plan to trim 1/8" off of these narrow points of the top frame parts to fit them to the wider motor board. I prefer to maintain the width of the motor board as-is, just for that extra little bit of strength on the transom.

The upper frame parts (L) are cut to size. This leaves a slight step between these parts and the transom side frame parts (R), which are extended for fairing. Since the finished transom is supposed to have a 10° outward bevel, I may have to add a small shim, just to have enough material to bevel the upper part.

The First Lamination

Finally, the time came to laminate my initial 1/4" transom cutout onto a second layer of 1/4" Meranti. I cut out a large enough rectangular piece, and laid it out on my work bench. In order to keep from gluing the transom to the work bench, I covered the bench with sheets of wax paper.

Then, I mixed 120ml of System Three Silvertip epoxy, and thickened it with some of the mahogany wood dust. I planned to coat both mating surfaces with this mixture. However, I ran out of epoxy while coating the first piece. So, I quickly mixed another batch. After thickening it with the wood dust, I coated the second surface.

Then I carefully mated them together.

Some people will use cinderblocks, or weights, to press plywood sheets together. I decided that I needed to get my money's worth out of that expensive Raptor stapler I bought 2 years ago.

And, just as before, once the plastic staples were trimmed and sanded, they virtually disappeared.

Two 1/4" plywood sections, glued and stapled together.

Here, you can see the wax paper that kept me from gluing the transom to the bench.

Close-up of the laminated plywood sheets and the Raptor staples.

The trimmed 1/2" plywood transom. It only took minutes to snip and sand the Raptor staples, and they virtually vanish.

Close-up of the trimmed, laminated plywood edge.
So, where do we go from here?

Currently, I'm drawing and measuring the plan lines onto the back of the newly-laminated plywood. I want to make sure that everything is shaped as symmetrically and precise as I am able.

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