The Tricky bit

The Tricky Bit

When we left off we had our boat in plan and profile. The job now is to see if those lines will match up in the third dimension and still have fair curves. This is done by drawing the sections.

In the cartoon the sections are drawn in the middle of the drawing about station 5 which is used to represent the centreline (CL). You can in fact draw it any where, the reason I chose that particular position was that I was doing this without most of the tools and no drawing board. So to lay off the sections I was using tick strips. You can read more about this method here (http://www.lackeysailing.com/daysailor/sidebars/tickstrip.htm)

In that application the person is using a large piece of wood as he is doing it full size, however you can use strips of paper to do the same thing on your scale drawing. In order to do this you must first draw in a waterline (WL) where you are going to put your sections drawing, in this case I put it mid way between the profile drawing and the plan.

In the following picture a small slip of paper is laid along Station 5 and ticks are made at the WL, the chine (the curve of he bottom) and the sheer.

This then transferred to the new WL and CL by lining the strip along the CL with the WL tick at the WL. Then the strip is laid out on the plan to take off the widths and the widths laid out in the same way along the WL. Lines are drawn from the ticks parallel to the WL and CL and where they intersect are the sheer and chine points. You draw lines through those points and you have a section. This is time consuming and prone to error.

There is another way. To the right, or if you prefer left, of the drawing extend the WL and draw an new CL perpendicular to the WL. Extend the plan CL to intersect with the new CL and from that intersection draw two 45 degree angles.

Then using your triangles transfer the plan and profile measurements. First the plan,

You will probably have to extend the line of the second triangle using a ruler, make a tick mark on the diagonal slide your triangle down and do the same for the chine line in plan.

Then slide your triangle along the yard stick and draw two perpendicular lines through the marks.

Now go to the profile and draw Two lines parallel to the WL from station 5 at the sheer and chine.

Join the intersections, erase all the unneeded lines and you have the half section at station 5.

Now do that for all the other stations with stations 0 to 5 on one side of the CL and 6 to 10 on the other. Draw a line parallel to the baseline from the bow to the CL. You end up with this,

And now for the tricky bit. Join the ends of the section lines at the chine and at the sheer to see if you have a fair curve. In most instances, when drawing by hand, you won't on the first try and will have to alter the lines in plan and profile to make the curves fall fair. That can be exceedingly time consuming.

Once that's done you have this,

In this case the curves fell fair on the first go and there is a reason for that, we'll discuss that next time.