More tools of the trade

More tools of the trade

In the last post I said to make a line parallel to the yardstick 6” up, that was six real world inches not scale inches and the same for the center line. All other measurements were to scale 1/2”=1'. In this post all measurements are scale unless otherwise specified.

We ended the last post with the following grid,

On this grid we will construct the lines in plan using the centerline (CL) marked in red and in profile using the waterline (WL) in green. From the cartoon we know that the proposed draft is 6”, and it appears halfway between station 5 and station 4. Measure down from the waterline 1' on stations 4 & 5. Draw a line from the intersection of the WL and station 4 to the mark on station 5 and vice versa, that will establish the point of maximum draft thusly.

Now we need to construct a fair curve from the intersection of Station 10 and WL through the point of maximum draft to the intersection of station 0 and WL.

This brings into play new tools, french curves, ship curves and splines and ducks otherwise known as spline weights. The basic drafting set contains french curves but in order to get long fair curves you really need ship curves or a spline and ducks.

A spline is a narrow sectional piece of wood or plastic which can be bent through several points to construct a curve. The spline is held in place by lead ducks,

These things are hard to find and when you do find them they are expensive. When I was doing the Westlawn course I carved two male molds and took then to a local foundry and had them cast ten for me which was way cheaper than trying to buy them, Or you can try to make them yourself, there is a good article at Duckworks on how to do this. (http://www.duckworksmagazine.com/06/howto/splineweights/index.htm)

Once you have all your ducks in a row then you can use the spline to draw the curve of the bottom.

And then remove the X from between stations 4 and 5. Which brings up another tool the eraser, get a good one you'll be using it a lot and you'll also need an eraser shield to protect the parts of your drawing you don't want erased and a drafting brush to sweep all the eraser bits off the drawing so it doesn't smudge.

Once the bottom curve is drawn turn your attention to the bow and stern. From the cartoon we know that the top of the transom is 1' aft of station 10 and 2' above WL, using dividers mark out those points.

Problem! The cartoon length over all (LOA) is 17' but we only want 16'. If we whack 1' off the LOA will we still get the sheer (the curve of the gunwale in profile) that we wanted? The only way to find out is to draw it in and look at it. So, again using the dividers, mark out a point forward of station 0 3' up from WL and 2' forward of station 0. Then draw a line from the mark aft of station 10 to the intersection of station 10 and WL. Do the same at the bow.

From the cartoon we know that the sheer is at it's lowest point at station 7, 1' 9” above WL so using the spline and ducks we'll construct a curve from the bow to the stern through that point on station 7.

Now take a good look at that line from all directions, is it fair, does it look good. I think so, in fact I think it looks better than the cartoon. So 16' is good.

Using the same process of taking measurements off the cartoon and using our spline and ducks we can draw in the sheer and bottom line in plan.

So far so good but the real test of all this will come when you draw the lines in section like the center portion of the cartoon. We'll discuss that next time.