Catamaran Hull Speeds

Hi, I'm a long time lurker of the forum and have just finally joined! I have a general understanding of hull speeds for monohulls but I'm a bit confused when it comes to multi hulls. If you calculate hull speed for one hull of a catamaran would that be the boats hull speed since both hulls are the same length? What about a proa or outrigger, would the lower hull speed ama subtract from the higher hull speed of the main hull?

 

...and what about how the wake of each hull interacts and affects the other?

You can search all that here on the Forum!

Welcome aboard!

 

I think you're getting confused with - speed - and - resistance.

If you have 1 hull, and establish its resistance, then split the hull into 2 hulls, it would have a different resistance.

Speed is not the metric, resistance is the unit of measure to compare like for like.

 

Usually, You can get a general idea about it with a search, then come back about specific questions

Catamaran Hull Speed Calculator For Beginners (Table and Free Spreadsheet) - Catamaran Freedom https://www.catamaranfreedom.com/catamaran-hull-speed-calculator-for-beginners-table-and-free-spreadsheet/#google_vignette

 

Hulls with very high length to beam ratios behave significanly different from typical monohulls. At 10:1 there isn't a huge "hump" at the transition to what is usually considered past displacement speed. This means that the shorter ama would not have the huge difference in resistance that two fat monohulls of different lengths would at the "hump".

 

True but it gets tricky for me when working with really slender human powered craft with a balancing outrigger.
For the original poster, @AdHoc is right it's more an issue of drag at a given speed, for twin hulled craft with different lengths and or displacements it's the sum of each hulls resistance at a particular speed. There's some additional consideration for interaction of wakes and the like but it's usually a secondary issue.

 

Interesting ideas about hull resistance and form resistance,

Are Longer Kayaks Really https://guillemot-kayaks.com/sea-kayak-recreational-kayak/petrel-play-petrel/are-longer-kayaks-really-faster?fbclid=IwAR2_2IYYTFuNvpSi4p0I4QVclTaaorowdczF8Mofk10dj9B9-S4hBY4UJtg