Hull speed

[Gary]

I have a 1986 catalina 27 and was asked what the theoredical hull speed was. Does anyone know how I calculate what the maximum speed my boat should be able to achieve? does sail size come into play?

 

[dan]

save this one

to your favorites http://image-ination.com/sailcalc.html

 

[J. Tesoriero]

Theoretical Hull Speed

Theoretical hull spped is a function of the waterline length. It is traditionally calculated according to the formula:Hull speed= 1.34 times the square root of the waterline length.

 

[Terry Dannar]

Calculating hull speed

I think the basic formula is 1.34 times the square root of the length of the water line. That gives you the theoretical hull speed for any displacement hull.TD

 

[dan]

how does PHRF

numbers relate to hull speed? Im not a racer so I have never really thought to much about it?? but, if you have two boats with the same hull speed where do you come up with the PHRF handicap?

 

[michael]

Theoretical hull speed is equal to the square root of (1.34 times the length of the water line). As far as sail size, in five knots of wind you will probaly not achieve hull speed. In 50 kts of wind with a storm tri-sial you could hit hull speed. The correct amount of sail will get you to hull speed with minimum helm and a balanced boat. Please note that hull speed is dependant on more than just sails, theory assumes a perfect bottom, perfectly trimmed sails and no more than the specified amount of ballast.

 

[joe]

maximum theoretical hull speed

for a Catalina 27 - any year- is 6.25 kts. Theoretical Hull speed has very little to do with sails or sailboat performance. But it can offer insight as to why larger boats are generally faster than smaller ones. Displacement hulls only, of course.

 

[RonD]

Theoretical Hull Speed

The equation often cited is 1.34 x SQRT(LWL). It is related to the ability of a well-shaped displacement hull to push through the water until it's speed creates a standing wave equal to the waterline length (LWL). Beyond that speed, it would take very much more energy to push past that standing wave in a fluid - water.The equation & the constant (1.34) is an approximation that incorporates many factors. Fluid density is certainly a factor included here -- sea water is more dense than salt.This is the nautical equivalent to breaking the sound barrier with an aircraft. To efficiently fly faster than the sound barrier (standing wave in a fluid - air) required different hull shape (streamlining), different wing shape (sweepback), and much, much more energy (powerful engines).Planing hull boat designs use different hull shapes to ride up over the standing waves, and these boats have a lot of HP to help push over it, too.--RonD