What is a MKII?

42ndstreet · #1 (**permalink**) 12-06-2006

Sorry for the newbie question, what is a MKII?
Also, can someone also explain the term "hull speed" please.
Thanks again.

Gary M · #2 (**permalink**) 12-06-2006

Many manufacturers made upgraded or modified versions of the same boat. A C & C 27 for instance had 5 variations starting with a MK I on up to V.

Hull speed is the theorectical maxium speed that a displacement hull can go. It is based on the water line length, the formula is the square root of LWL times 1.34.
A boat with a water line length of 25 feet will have a hull speed of 6.7 knots. Basically the fastest it will go unless surfing etc. Not all sailboats can attain their hull speed reaching or beating.

42ndstreet · #3 (**permalink**) 12-06-2006

Thanks Gary

SailinJay · #4 (**permalink**) 12-06-2006

MKII translates to "Mark 2." It signifies the second edition of something, such as an airplane or a boat. It was originated by the British. The U.S. used to use "dashes" to denote the same thing, i.e. "-2".

Hull speed is usually described as maximum theoretical hull speed, which, for a displacement boat such as a keel boat, is calculated by taking the square root of the waterline length of the boat in feet and multiplying it by 1.34. This is the theoretical fastest speed at which the hull should be able to go through the water, although in reality such hulls can go faster. Wind, waves, and sail trim all factor into the speed.

SailinJay · #5 (**permalink**) 12-06-2006

Must have been typing my message when Gary was sending his.

captlar · #6 (**permalink**) 12-06-2006

Some of the changes from model to model were dramatic. For example, a C&C30 - MK1 has a PHRF (rating for racing - the lower the number, the faster the boat) of 174. The C&C 30 - MK2 has a PHRF of 144. Obviously the newer boat is much faster, but that does not necessarily make it better for you intended use. When looking at boats, it is important to know the variations of each model.

sailingdog · #7 (**permalink**) 12-06-2006

Of course hull speed is only calculated that way for displacement monohulls... not planing hulls, hydrofoils or multi-hulls.

nolatom · #8 (**permalink**) 12-07-2006

Quote:

Originally Posted by Gary M

Many manufacturers made upgraded or modified versions of the same boat. A C & C 27 for instance had 5 variations starting with a MK I on up to V.

Hull speed is the theorectical maxium speed that a displacement hull can go. It is based on the water line length, the formula is the square root of LWL times 1.34.
A boat with a water line length of 25 feet will have a hull speed of 6.7 knots. Basically the fastest it will go unless surfing etc. Not all sailboats can attain their hull speed reaching or beating.

I recall being told the multiplier was about 1.3 for a "slow" boat, up to 1.5 for a "fast" one, leaving us to figure out which was which (though we pretty much knew). Nowadays boats have the Polar diagrams which supposedly figure this out for us.

I was also told that rather than being an absolute limit (in displacement mode), hull speed was the point at which any additional speed required way too much additional energy to be practical. For example, if a 20-knot destroyer took that 25-footer in tow, the hull would be going more than 7 knots (somehow), it wouldn't be practical under one's own power.

SailinJay · #9 (**permalink**) 12-07-2006

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

42ndstreet · #10 (**permalink**) 12-07-2006

Thanks again for the information. You guys are all a big help.