Thursday 17 June 2010

Forms - backbone of the cedar strip boat.

I received the plans for the Rangeley 17' Lake Boat on A1 sheets.
In total there are 16 forms and a transom, and these must be anchored onto the strongback after they've been cut. These forms form the skeleton around which the cedar strips are aligned. Once all the cedar strips have been placed and attached to each other, the forms can be removed.

The plans for 8 forms are on one sheet. In addition it's only half the plan, as the plans are symmetrical around the centerline.
In order to cut the forms I needed to transfer the plans to 16mm MDF (Medium Density Fibreboard) also known as Supawood.

Taking 8 sheets of A4 carbon paper, I glued the edges together to create a larger sheet (approx A2 size).
I made two of these sheets.
One sheet is placed face down, in order to transfer the plan to the wood when traced over.
The second sheet is placed face up, when doing the original half of the trace, in order to transfer the plan to the back of the original plan.
This original plan can then be flipped over, aligned with the half that's just been traced, and then the second half of the plan can be traced to the wood.
It's tricky to get everything aligned. Be patient and take care in getting everything in place.
Carbon paper is not your friend, it wants to roll up into tight cylinders. Use wooden offcuts to keep the corners flat.

Creating full size plans of the forms, each on a separate sheet paper would be preferable. Glue these sheets to the MDF with normal aerosol spray adhesive. At over R500 for printing costs, I decided I'd stick to tracing.

Subsequent to doing my tracing of the plans, I was told I should have used a tailor's pattern wheel . This leaves small holes in the pattern and in the wood. Coloured chalk on the back of the plan prior to the trace will leave the holes in the wood with a chalk outline, making it more visible. This would probably have been faster than my shaky old hands trying to trace the curve of the hull ... SIXTEEN TIMES !

I used a jigsaw to cut the forms after I completed the tracing.
I cut slightly proud of the lines, leaving approximately 1mm on all edges. This extra was sanded back with a random orbital sander. A bench sander would be good for this job, but I do not have one, so I made a temporary jig to create one. More about that in a later post.

Since the forms are 16mm thick and I have the plans traced to one side, when I sanded I bevel-sanded so that the other face of the form is slanted away from where my strips will touch the form.

Here are two pictures of what the forms will look like once they are attached to the strongback. ( I did not spend the hours required to draw the exact shape of the hull into these forms, but you will get the general idea)

From the rear...
EDIT: - it is interesting to note in the picture above how the forms are not "fair". A “fair” hull is one with no dips or bumps in the longitudinal lines of the hull. As I said earlier, these forms are drawn merely for purposes of giving you a visual of forms on a strongback and do not conform to my hull's shape. I'll post real photo's when I get the forms onto the strongback.

From the side...
I have completed the cutting and sanding of my forms, but not yet attached to the strongback. I need the space.
Tomorrow I will go shopping for lumber to mill the strips needed to build this boat. I have to mill these planks into strips before I can start. That means I need about 4m infeed and 4m outfeed at my table saw to complete the job. It's going to be tight.
I will only attach the forms to the strongback once all that is done.


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