What is a MKII?

[CBinRI]

Originally Posted by SailinJay

Rousmaniere's "Annapolis Book of Seamanship" uses 1.34.

My understanding is that it is the same for all boats unless they are able to plane.

[SailinJay]

It applies only to displacement hulls such as keel boats or heavy centerboard boats, not to multi-hulls or, as you mention, planing hulls.

[SteveCox]

1.34 is not an absolute. If you look at a graph of speed vs power required it goes up a fairly slow slope until it reaches the area of 1.34 times sq root LWL and then takes a very steep pitch upwards. What it means is that for a small increase in speed it requires a very large increase in power. The example of a 25' boat being towed by a destroyer is a good example. There is plenty of power from the destroyer to overcome the increasing drag of the small hull but it can't carry a large enough powerplant to do so by itself. So yes, somes boat can't reach 1.34 and some that have different hulls can reach 1.5 or so.

[stlcat22]

One last thing about hull speed. Remember that it depends on the LWL while sailing, i.e. heeled and with perhaps the stern wave wetting more of the over hang, and not just the LWL at the dock.