Numbers

BY THE NUMBERS

I ran the numbers on these two versions, here they are,

Version	RMSQ&D	RMS
Displacement	304.89 lbs	266 lbs
Block Coefficient	0.18	0.16
Prismatic Coefficient	0.48	0.53
Area of the waterplane	25.55 sqft	27.78 sqft
Centre of flotation (aft or forward of Station 5)	.4381 ft aft	.4772 ft Aft
Lbs per inch immersion	152.29 lbs	137.49 lbs

So what does that mean exactly?

Well Q&D can carry more weight at the designed waterline by about 40 lbs and it takes more weight to sink it any further into the water.

Skene's sets out that a prismatic coefficient between .49 and .55 is best for sailing vessels, any more than .55 and you have a tub, any less than .49 the vessels is so fine it drags a huge quarter wave. So Q&D is on the fine side and RMS is within the parameters set out by Skene's. However the block coefficient tells us another story, by that coefficient RMS is the finer vessel.

Skene's also sets out that the center of flotation should be between 54 – 59% of the LWL aft of station 0 or in our case, between .48 ft aft of station 5 to 1 ft aft. So Q&D is a bit too far forward and RMS is just about right.

The LWL is 12ft for both these vessels and the beam at the WL is 5ft 4in which is a beam to length ratio of 2.5 which is a little beamy, anything from 3 to 5 is better, but the beamyness in such a small vessel adds to the initial stability.

Next time we'll look at stability.