HOT BOAT speed calculations

[burtandnancy]

The current issue of Hot Boat gives Bob Brown's and Tyler Crockett's methods of calculating boat speeds based on propeller & rpms. Bob taught me a slightly different formula years ago that works on both V-drives and outdrives;
rpm x pitch x ratio x .00094697 = optimal speed. Then you must find your efficiency factor. Tylers formula missed a zero in the final multiplier. Remember, V-drive boats will almost always have a ratio of more than 1, and outdrive boats will always have a ratio of less than 1, ie, 1.36:1 will have a multiplier of .735
To all you proof readers, did I get it right?

[Flashwave]

Actually this yields the same result, but, much simpler:
Theoretical top speed=(Pitch*rpm)/(Gear Ratio*1056)
To calculate Prop slip use the following;
Prop slip=(((Pitch*rpm)/(Gear Ratio*1056))-Actual Speed)/actual speed
Jim
[ March 15, 2003, 09:26 AM: Message edited by: Flashwave ]

[Kilrtoy]

Alright the manufacture lied to me. According to this calculation, my boat should do 142MPH with the 454MPI 310 HP bravo 1 22 4 blade. I think I did something WRONG eek!

[Flashwave]

A 22 pitch with a 1.5 gear ratio at 4500 RPM has a theoretical speed of 63 mph. With 12% slip you should see 55 mph.
If you have a 1.36 ratio drive, your theoritical speed at 4500 rpm is 69 and at 12% slip 61 MPH.
J

[Kilrtoy]

Thats pretty awesome, That is exactly what the boat runs 63MPH jawdrop