Maximum Horsepower

[Stoisy]

Hey all,

Just curious if anyone knows the reason for a boat's maximum horsepower rating? We are looking at re-powering a 2007 Grady 228 that has a max hp of 250. However this was rated during a time that the current 300hp Yammy weighs less than the 2005 225hp Yammy that is currently hanging on the back.

Are the Max hp ratings set for weight? or for torque caused by the motor?

Any advice is greatly appreciated! Cheers!

Steve

 

[trophywife]

insurance reasons....

 

[chris73]

Engine weight is only one factor. Stress on the hull and structural parts the main. Pushing plastic or alu sheets with 50 MPH against water requires some strength.

 

[Sr SQ]

While there are many variables, I believe cost to be the #1 reason…….
The associated costs are many, litigation claims, insurance claims, construction costs and market demographics

 

[Olde School]

Also, you DO NOT want enough power to push the speed past the hull's limits. Chine walking is no fun.

 

[sly_karma]

Max power rating is calculated by a formula that uses simple hull geometry. Has nothing to do with transom strength or stiffness. Transport Canada has it all defined here if you want to do your own math:
https://www.tc.gc.ca/eng/marinesafety/tp-tp1332-section4-1346.htm

 

[pescador]

Isn't the hull design of the new 228 same as the 07? If so, why wouldn't the 300 work? The new one is rated for a 300 HP. Weight of the 300 i believe is same as the 250. Why not call Grady and ask?

 

[Derby]

e-mail them..they have been good to deal with for me.... custserv@gradywhite.com

 

[Capt_Ed]

Derby clear your PM box

 

[Sr SQ]

Max power rating is calculated by a formula that uses simple hull geometry. Has nothing to do with transom strength or stiffness. Transport Canada has it all defined here if you want to do your own math:
https://www.tc.gc.ca/eng/marinesafety/tp-tp1332-section4-1346.htm

Correct, however those are only recommendations
If companies want to pay more for higher assumed liabilities they can rate for whatever they want.
Some fishing boat purchasers put speed at the top of their criteria ( the bass boat crowd) some dont, market demographics decide.
Thats why you will find 20' hulls that weigh 1500lbs rated for 250hp and go over 70mph, the market wants it, the market gets it……if they are willing pay the higher associated costs.