Okay now we are getting back into the science of things. Great !





My hulls are

3.66 (12 feet)

250 mm wide
458 mm tall
265 liters volume per hull.

Surface area of hull including bulkheads is 5.038 dsq. mtr. (this includes only 2 ply bulkheads under the beams with a combined area of 0.128 sq. mtr.

Freeboard when sailed by 65 kg crew (65 kg platform) is 458-(188 + 58) mm = 212 mm and I don't want to have less then this as freeboard. I know this from experience on my Taipan that also has its hulls at 450 mm height at max point.


So the question is where do you "loose" 5.038 - 0.128 - 4.15 = 0.76 sq. mtr. surface area per hull ?

From the picture it appears you can only win this by having the keel panel angled upwards at a relatively great angle, but this till really decrease the freeboard when sailing on one hull.



My 3.90 mtr hull (12'10")

236 mm wide
455 mm tall
265 liters volume per hull.

Surface area of hull including bulkheads is 5.214 dsq. mtr. (this includes only 2 ply bulkheads under the beams with a combined area of 0.133 sq. mtr.

Freeboard when sailed by 65 kg crew (65 kg platform) is 455-(189+55) mm = 211 mm and again I don't want to have less then this as freeboard.



As you can see the difference is surface area PER HULL between the two boats is 5.214-5.038 = 0.176 = 3.5 % When done in 4 mm ply this causes a weight difference of 0.45 kg per hull.


The two hull design are so close in length that no additional reinforcements will be necessary to the 3.90 hull in comparison to the 3.66 hull

Additionally my designs now have a 3rd ply bulkhead in the bow, but as the hull is rather narrow they will have a very small surface area of 0.093 sq. mtr.


The picture showing the waterlines is of the 3.66 (12 foot) hull but the 3.90 hull looks exactly the same, including where the waterlines are. As I said earlier I developped both simultaniously.




As can be seen my design has a relatively flat keel. I'm trying to approximate the fat keels of the modern "wave-piercers" as to maximize pitch resistance and hopefully allow some planing at the higher speeds. Also a fat keel line helps keep the freeboard up.

The upper waterline is with a single hull carrying all the weight (flying the other hull) and the lower waterline is when both hulls are flat in the water.

Wouter