Sunday, May 31, 2009

Setting Up the Strong Back

Building the strong back consists of two parts: making the strong back, the beam on which the forms are mounted; and making the support, which keeps the strong back aligned and solid during construction.

The support consists of 6 inverted T's each made of two layers of 3/4" G1S plywood sandwiching 3/4" Baltic birch in the base, for receiving threaded 1/4" inserts and plastic feet, and a gap at the top where an L will be mounted and height adjusted for receiving the strong back. The adjustment is necessary because the strong back varies in depth from 3", to 4" to 5" and back to 3" as it goes down the boat. As long as the support is rigid and close to being aligned, the fine-tune adjustments can be made with the L pieces as shown below.

The longitudinal and vertical position of the T's are held by 2x6's which are lag-bolted (not shown) and bolted thru with ready-rod.

Here I am fine-tuning the position of an L seat. The red dot is from my laser level to ensure that all the L's were vertically adjusted correctly. The string aligns all the L's down the length of the support. and the spirit level is used to make sure that the seat of the L is parallel with the ground. As each one was set in true position, I clamped it with a spring clamp, then screwed it twice from each side of the support.

Here is the completed support with the L's set as required to receive the strong back with the boat in the upright position.

Note that it is common to build kayaks making the hull first, therefore mounting the strong back upside-down initially. I have a reason to build the top decks first, which I will get into later when we get to that part.

Then, it's a matter of building up the beam portion of the strong back, and sliding the forms on at their 6" intervals. A trick is to rub floor wax generously on the beam to help ease the tight-fitting forms along. I know I broke a couple of forms in my first project. I didn't break any this time. Either I'm more patient now or perhaps just wiser. I'll credit the Baltic Birch.

So, after a 13-hour day, the forms are on the strong back and the whole affair is sitting on a rigid support. Note that the 26ft long boat is fitting diagonally across 2 bays of our carport. This was a great compromise because it left room for Rick to park his BMW motor bike, AND the entire length of my boat is under cover! (see pic below!)

This photo also shows my first boat hanging in the rafters, and the form for it up on a rack on the wall to the right. Hopefully I'll get "My Escape" into the water soon so I can row while the new boat is getting built.

Whew! Just fits! But, not finished the form yet. Each station has to be checked and secured, than the Shearline bracing goes on. Lots to do yet....

Saturday, May 23, 2009

Shearline Bracing

I have decided to install a 1/4" x 3/4" strip along the shearline. Because I intend to use a non-linear layup of strips, I'm going to need somewhere to clamp the strips to when they land between form stations. To do this I needed to scribe and then cut out a notch for the strip on each form.

Here you can see how the shearline bracing starts to define the shape of the boat.

Tiny form!

Cutting the Forms

The first step in transferring the patterns to wood is to check that your photocopier isn't stretching the image. Once I found a copier that was true, I made a copy of the drawing for every form (52 in total).

This time I used 8.5"x11" sticky back labels on Baltic Birch plywood, rather than gluing the forms onto G1S (good one side) plywood. Baltic Birch plywood has very thin laminations that are thoroughly bonded, and the surface is very smooth on both sides. It is sold in 60"x 60" sheets. I purchased 3/8" for the forms and 3/4" for the strong-back. My experience so far is proving that this product is superior to structural plywood by far, and is well worth the cost, especially if you intend to use your form more than once.

Using a bandsaw for cutting out the forms was sheer luxury after the jigsaw method of my last project.

Finally I have all the bow and stern sections cut out. There is something very satisfying about seeing all the forms line up like this!
The end form protrudes from the center of what will become the strongback. I formed the V in the bottom with a power plane, but a belt sander works just as well, especially on Baltic Birch.

Design Stage

I redrew the bow and stern sections making the boat with 10% higher volume than the prototype. I hope this doesn't prove to be a mistake, as I am also decreasing the weight of the boat. Later I added the curve to the top of the bow and stern decks, and changed the shape of the forms after 25'-6".

I want the woodwork on the deck to get away from the long straight lines of the boat by creating the illusion of depth and motion.

I like the idea of a twisted ribbon: red cedar on one side, stripped red/yellow on the other, over a yellow cedar background, twisting loosely around a thin meandering strip of dark hardwood. This is drawn out in full scale on freezer paper.

The method for building this top deck will stray very far from normal strip-kayak building. The decks are each about 10ft long and about 12" at one end, tapering to nothing at the other. I'm hoping I've solved the problem I had last time with glassing the inner seam where the deck meets the hull. It is extremely difficult to reach into a 10ft long tube!

The next big challenge is the rowing deck itself. In my effort to make the boat both light and stiff, I am going to cast the deck in carbon fibre and embed attachments for the rowing hardware. For this I will need to make a form that will look something like this, shown in negative shape and upside down.

Monday, May 18, 2009

Lighter, Faster, Better

In 2005 I launched "My Escape", a 26ft long cedar strip rowing scull. It was the culmination of my dream to build a cedar strip boat and my determination to figure out a challenge, fueled by my love of rowing. I used technology taken from Nick Schade's book "The Strip-Built Sea Kayak" along with research on rowing sculls and rigging. I drew the sections and built the form work then launched into hundreds of hours of building, ripping up bad ideas, re-building and finally launching. I didn't know whether the boat would even float until it hit the water.

Happily, the boat DID float, and it even rowed in a straight line! At 65lbs it was about 20lbs overweight (like the owner!). Despite its flaws, of which there are a few but no too many, I have enjoyed many memorable episodes rowing "My Escape". But the desire to build another boat using the experience I gained on the first round has always been in the back of my mind. This year, I'm going for it.

The new boat is as yet un-named, but the vision is pretty clear. The big goal is lighter, lighter, lighter. Rather than conventional 1/4" cedar-strip with 6oz fibreglass I'm going with 1/8" cedar strip with 2.8oz carbon fiber inside and 3oz glass on the outside. Half the cloth, half the cedar. A rowing scull does not need the durability of a kayak, so I'm trading durability for weight.

The other big change is a much lighter inner structure. I WAY overestimated the amount of strength I needed to build into the boat to convert the force and action of rowing into forward movement. This was a huge challenge because it was a complete departure from kayak design. I overdid it. This time I am going for a rowing deck of Carbon Fiber, and I am going to rely on the rigidity of carbon fiber inside the boat to give it its stiffness. Ya...that should work.

The last big change will be in the artistic beauty of this boat. The last one was a prototype, and in the end I didn't want to spend too much time on fancy wood inlay if the boat wasn't going to even float! I cut a big corner there last time....but won't be this time.

So, the purpose of this blog is to show the steps of this venture, which I hope has a happy ending. I sure hope that fellow boat builders, rowers, or anyone who just wants to see if the risk will pay off enjoys tagging along this ride with me. Cheers!