In the latest issue of Professional Boatbuilder magazine, October/November 2021 – #193, contributor Dan Mielke describes the process he used for establishing a new waterline and boot-stripe on his sailing yacht.

(I’ve included the article in the attachments)

By his own admission he started the process by making it as complex as possible with a combination of 3D modelling his hull from the designers plans and researching the subject of boot-stripe design from both modern and historical perspectives.

I have admit that I was lost before he got to step one of his procedure, which involved a laser and a whole lot of multiple decimal place figures, stations LWL lengths and some mathematical formulas just to make sure you can maximize your time with head scratching.

Okay, to his credit, he is a yacht designer and his process is I’m sure going to produce a fine looking waterline boot-stripe at just the right hight and proportions. He is also producing a result that has both waterline and boot-top sweeping up at the ends. More on that in a bit. There is, in my opinion, a simpler builders solution. It doesn’t require a laser. Just a spirit level, some sticks and some string.

First of all, terminology. The waterline is the intersection of where the hull meets the surface of flat water. We usually want this line to be slightly above the actual intersection for the purpose of antifouling bottom paint to do it’s job of resisting marine growth and destructive creatures like the wood gobbling Toredo worm (toredo navalis). The painted waterline is usually laid straight for convenience.

The boot-top is the stripe above the waterline, usually in a contrasting colour. If laid straight, this line will appear to droop at the ends. This is an optical illusion and one we will overcome by sweeping this line up at the ends by an inch or more. How much more is a question of taste and hull style. A bluff bow might require more sweep for instance.

Where the low point of this sweep exists is one thing to ponder. I would say it should land at about the greatest beam of the waterline shape. Dan says to park it at station 7 out of 10. 0 being at the bow. In most sailing craft I would argue that tends to coincide with the greatest beam of the waterline shape. Herreshoff and Chapelle would probably tell you 3/5ths aft of the bow or something like that. I think that puts us all pretty much in the same general ball park. At least close enough that we shouldn’t be coming to blows over it. If you are really steaming over your position, you can sneak away and let the air out of the tires of the opponents.

The method I showed you here is basically the same one I learned in boat school. and the simplified version that develops a flat waterline is also illustrated in Bud Mackintoshes book “How to Build a Wooden Boat”. (see attachments) In a larger yacht we would tack a wooden batten along that waterline or boot-top and scribe or score a line in the hull that can bee seen through paint for future purposes.