Crouch Constant

From Propeller Handbook

"(See Dave Gerr's Propeller Handbook, pages 15-17)

knots/hour =(hp/pounds)^0.5*C

Dave gives the following constants

150 - average runabouts, cruisers, passenger vessels
190 - high speed runabouts, very light high-speed cruisers
210 - race boat types
220 - three-point hydroplanes, stepped hydroplanes
230 - racing power catamarans and sea sleds"

George Crouch, probably close to a hundred years ago. Still quoted, and apparently still in use. Does anyone know about Crouch's original work or publications? Dave Gerr treats it like gospel, but Propeller Handbook was written long enough ago that there would be some continuity of collective knowledge. But the guys Gerr knew, that knew Crouch, are long gone.

 

The way I use Crouch constant is:

Step 1 - find a prototype - similar size, Fn, shape boat(s), with similar propulsion system, with reliable speed data.
Step 2 - define Crouch's constant
Step 3 - carefully apply it to new the design, for speed estimates at early design stages only.

All other ways are not reliable and misleading.

 

Hi Alik. To be honest, I'm surprised you use it even to that extent. After all, Crouch was beating the world in 1923. The science has advanced since then. But where did you learn it from?

 

If you don't like Crouch's formula,you could always use Keith's.

 

I neither like nor dislike. I'm interested in the history. The Crouch Formula has been superceded by better knowledge. Crouch had been dead for years before Savitsky wrote his seminal work. But for generations it was as good as it got.

Eric Sponberg uploaded a nifty pdf of a guide he wrote, back in 2012. Gives some history for Crouch's Formula.

 

Had a look at Keith's formula. Very dependent on LWL. Savitsky says LWL is irrelevant in a planing boat, since it could easily be 30" in a 30' boat. Or 25' or anything in between.

 

Y'know what else amazes me? Folks been looking at that table of Crouch Constants for a minimum of 70 years, and hardly anyone goes
"230...?! what the heck is a sea sled? I want one of those."

 

This is interesting.
Gerr is into sleds, he designed a modern day spin-off.
The Interdictor:
INTERDICTOR 28 SEA SLED http://www.gerrmarine.com/INTERDICTOR_28_SEA_SLED.html
None built and it appears the plans are not yet finished but for $15 000 USD he'll complete them for you.
That's what he told me in an email last year.