Quote
-5- Wave-making drag on cats, in an absolute sense, is not very dependent on hull length beyond a certain min prismatic hull ratio.

In this case the wetted surface drag is by far the most dominant factor and it is this aspects that will favour shorter extreme lightweight hulls over longer lightweight hulls and this is due mainly to the wave drag.


Sorry,

Wouter


Here is the drag of a 5m 300kg (150kg boat+150kg crew on one hull) catamaran hull. Predicted using Michlet.
[Linked Image]

Blue Rw is wave drag, Red Rv is Wetted surface drag, speed is in m/s so double it to get knots. Drag is in kN.

As you can clearly see wave drag is far from insignificant, and is in fact larger than WS drag up to around 9 knots.

The next plot is the total drag (wave + WS) of a 5m hull compared to a 6m hull, both at 300kg and both optimised for minimum wetted surface area for there length.
[Linked Image]

The Blue hull1 is the 5m hull and the green hull2 is the 6m hull. Again you can clearly see
that there is no speed which favours the shorter extreme lightweight hull up to 20knots.

When I talk of wave drag at low speed I was talking about under 10knots not under the hull speed perhaps this is what is confusing you.

Gareth
www.fourhulls.com