Tuesday, August 20, 2013

Drawing out the next major Zip part

At first glance, the Zip has some rather odd frame designations.... Specifically, frame number "5-1/2".

It seems odd until you understand that the designations are logically based on boat design drawings. If you look at a cross-section drawing of the boat, there are several vertical lines that divide the hull into sub-sections. Each one of these vertical lines is called a "station." The numbering starts at zero (the transom), and ends at "F.P." (which stands for "Forward Perpendicular") at the foremost tip of the boat. In the case of the Zip, there are 8 stations including "F.P.", dividing the hull into 7 sub-sections of about 24-1/2" each. Frame # "5-1/2" is the frame placed between stations 5 and 6. It is located near the base of the stem.

Frame number 5-1/2 is a very important part. As the instructions indicate, the horizontal line formed by the floor member of frame # 5-1/2 is the plane from which the rest of the boat is set up. The instructions specifically state to take extra care to ensure that this part is accurately measured and constructed.

I just finished drawing this part, and I thought it would make a good blog post to illustrate how the Glen-L plans are copied to the wood.

First of all, you fold the carbon paper in half, so that the lines you trace through it are transferred to both the wood AND the back of the actual plans. Then you place the plans on the wood, and flatten them down securely. Push pins help for this.

Secondly, trace the plans for the part you want to build. As I mentioned in an earlier post, the centerline is THE crucial reference point for the boat. ALWAYS carefully draw the centerline. Make sure you extend your traced centerline beyond the needed dimensions of the part, for this reason:

Third, draw "sight holes" that are centered on the extended part of the traced centerline. I like to trace a small coin for this purpose. Use an exacto knife to cut your sight holes through the paper. You'll need these holes to align the plans after you flip them over.

Here I've traced out the floor timber, and have cut sight holes on the centerline.
Next, remove your push pins, plans, and carbon paper from the wood. The half-width of your part should be clearly visible.

Half-width of the floor timber drawn onto 3/4" Douglas Fir marine plywood.
Now, un-fold the carbon paper, and place it normally onto the wood where the second half of your part is to be drawn. Flip the plans over, and you'll see the carbon-copy you made on the back of the plans. Carefully and accurately align the sight holes on the extended centerline that is traced onto the wood. Again flatten the paper down securely. Now you're ready to trace the second half.

Plans flipped & aligned. Ready to draw the second half of the floor timber.
Trace the carbon-copied lines onto the wood, just like you did the first side. When you're done, the full part will be drawn onto the wood.

The full floor timber drawn onto the wood, waiting to be cut out.

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