Boats

Wetted surface area

Definition

Wetted surface area is the total surface area of the hull and appendages below the waterline. It should include both sides of the rudder and keel, and if the boat has multiple daggerboards, the given wetted surface area usually includes as many foils as would be used simultaneously.

Units: Area (usually square metres or square feet).

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Model testing the Almaguin, part 5: Detailed behaviour

In the last few entries, I've covered the construction of the framework and hull for the Almaguin 400 test model, the towing rig, and some videos of the boat's behaviour. In this final episode of the series, we'll take a detailed look at what we've learned about this boat's behaviour from the model tests.

Displacement

Definitions

Displacement is the truest measure of just how much boat you're dealing with. In a nutshell, it's the actual volume or weight of the vessel.

Of course, there are more than a few ways to state displacement, but only two- the volume displacement and the displacement mass, both at the design waterline- are fair points of comparison between different boats. The rest, although important and helpful when used properly, can be deceptive when seen alone. Always ask which weight is really being discussed, and what's included in it!

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