If you can use a calculator
you can design a boat…

by Morten Olesen

Part 2

Part 1 - Part 3

The Line Drawing

(click image above to enlarge)

The most useful tool when designing boats is the line drawing. The line drawing clearly defines the hull geometry. Furthermore it is used when calculating hydrostatic properties for the hull you are designing.

(click image above to enlarge)

If you have followed the steps in part 1 of this article series you will already have the start of the line drawing. But there is more drawing to do before it is finished. Start with drawing your design water line (DWL). The design water line is the waterline you expect your hull will float at. Later on it may show up that the hull does not float at exactly this waterline but don’t worry about that at the moment. Next you divide your waterline in 10 equal lengthen pieces making 11 stations. In the profile plane the stations 0 and 10 are made where the profile of the hull is cut by the DWL. Now you have a grid to start with. The next thing to do is to begin constructing the stations. The stations cut the hull in the same way as the frames will be placed in the boat later on. But the stations have in principle nothing to do with the frames in the boat.

(click image above to enlarge)

Now with the grid started it is time to draw some more stations in the body plane. As an example you can see above how it is done. In the profile plane the intersections between the hull and the stations are continued into the body plane. Then the ‘Dist 1’ and ‘Dist 2’ from the half breadth plane are set out from the centreline in the body plane. In the body plane you now have 3 points that define the section. In the example there is used a chine hull so the 3 points are sufficient for defining the section. Continue with section 1, 7 and 9. You can fill in the rest later. If you are designing a traditional hull the 3 points will not be enough to define the entire section so you will need some waterlines and buttocks as well.

(click image above to enlarge)

You can add as many waterlines (WL) and buttocks (B) as you want. They have the purpose of helping you define the hull shape more accurately. When you add the waterlines and buttocks you make more intersection points so you will have more points helping you to define your curves. Normally waterlines and buttocks are made with an equivalent distance between them, but you can place them at any distance you choose.

(click image above to enlarge)

The rest of the line drawing is now made. Normally curves should be smooth but since the example is a chine hull you can see some bends where the waterline cuts the chine. Making a line drawing is hard work. It is not unusual for a designer to spend days working on one, so don’t expect to make yours in an hour or so. You must also be aware that the lines may have to be changed many times during the work. Even lines you thought were right may later need to be altered. This is normal and there is no shortcut to that.

Drawing tools

Beside a ruler, pencil and eraser some tools for making curves are necessary when making the line drawing. If your drawing is large you can use a thin batten held with weights, but if your drawing is smaller or there is large curvature some curved rulers are necessary. It is possible to get a large variety of curved rulers but they are not all well suited for the purpose of drawing hull curves.

The most complete set of ship curves is the Copenhagen ship curves. The ship curves are produced by Linex (www.linex.dk). The set of curves are outstanding but unfortunately it will also be quite expensive to buy them all. I can recommend that if this is the solution you want you can buy curves A1, A2, A11/15 and A11/29. They will fit most needs.

If you want to spend less on curves you can use 3 curves from the ‘103DT Burmester Set’. The curves can be used for making hull curves but they are not outstanding. I have often seen the curve set in bookstores for $15-20.


In this article series cad for hull design is not described but there are many cad applications available for hull design. They range in price from free to many thousand dollars. So all the sketching and drawing on paper can be avoided and instead you can do all the work on your computer. It shall be said at once that using cad for hull design is great, it saves a lot of the hard work for you get results quickly. But there are problems when designing with cad programs. First of all, are you sure that the hull you designed with the cad program is the hull you wanted in the first place? Many times, if you are not careful the hull you get is the hull the cad program or the limits in the cad program designs for you. So you sort of loose control over your hull design process. Anyway it can never give you any problems knowing the old fashion way of doing the design process. It might even give you an advantage when using a design software.

Be sure to visit Mr. Olsen's website: www.boatplans.dk