I would like to mention that making a boat significantly lighter while keeping it at 20 foot is not an optimal thing to do. Reducing its hull length makes it noticeable faster again.

To give rough mathematical an example

180 kg + 150 kg crew on 20 foot => drag ratio wetted surface = 100 %
130 kg + 150 kg crew on 20 foot => drag ratio wetted surface = 92 %

compare to

130 kg + 150 kg on 18 foot => drag ratio wetted surface = 87 %

For this reason I never understood why Marstrom and even Eagle remained at the 20 foot hull length. Some extra 5 % on top of the original 8 % reduction can be had by making the hulls shorter. Dive stability is not that much of a problem as the reduction in drag causes the sailforce to reduce as well and in in this example a 19 foot hull on the lighter boat will still have exactly the same dive resistance as the heavier 20 foot hulls when running the numbers on the complete boat while sailing.

Wave making drag then ? Look at prismatic ratio's

180 kg + 150 kg crew on 20 foot => Rough Prismatic ratio = 100 %
130 kg + 150 kg crew on 20 foot => Rough Prismatic ratio = 85 %

compare to

130 kg + 150 kg on 18 foot => Rough Prismatic ratio = 94 %

See the shorter 18 foot hull of the lighter boat also has a lower wave making drag coefficient then a 20 foot hulled boat of the original weight. This is an example of how looking only at waterlength can be very misleading.

By now it is well understood that wetted surface drag is a larger portion of the overall drag than wave making drag while the later is still significant enough to not be neglected. So If one has to choose between a lower prismatic ratio of a lower wetted suface ratio one is wisest to choose the lowest wetted surface ratio.

In short at 130 kg boat is best build at 18 foot length (within the limits of this example) instead of at 20 foot. The difference in speed CAN WELL BE significant. Another 5% can easily be gained this way.

So unless some designer comes out with such a platform and doesn't f*ck up the rig at the same time I think we will see the lightweight boats being (very) limited in their gains. Simply because their designers don't take the time to do the basic math and ratio research.

Wouter