Theoretical Hull Speed - Cat's

If the approximate theoretical hull speed of a monohull displacement sailboat can be calculated:
HS = Root LWL x 1.34
What would be the equivilent formula for a Catamaran?
Thanks,

 

drag specified would get you there but havent seen that cat formula yet...

eventho two hulls have more WSA than a single, its not the WSA but the WAVE resistance determining hullspeed. in HS = Root LWL x 1.34 this is not specified. displacement cats use sharp small beams and encouter less wave resistance. a calculation of those variables times two gives a cats hullspeed i would think?

yipster

 

Water will behave the same wether it's a mono or two monos built as a cat.
You can run a cat at very low power up to hullspeed. But due to the shape of the two hulls it doesn't need a lot of additinal power to exed hullspeed.... A mono with the same design will behave the same..... but you'll not make a fotune selling them....

 

The multiplier, in your case 1.34 depends on many variables. For example, block coeficient, fineness of entry, displacement/length ratio and type of shape. It is not a fixed number for all hulls. There is no difference in calculations between mono and multi hulls.

 

"Hull speed" is just a rule of thumb and doesn't mean much for either cats or monohulls. ULDB monohulls and dinghies routinely exceed "hull speed" by a lot.

 

Catamaran hull speed

If you're speaking about power catamarans....hull speed is a function of many variables. Check out Secrets of Tunnel Boat Design book.