What is my hull speed?

[Ziya Gun]

I got a used Hunter 33, 1980 model with 15 hp Yanmar. It was in bad shape and had significant engine and shaft/prop repair done. On my shakedown cruise my boat moved flawlessly, no vibrations to speak of. Since I had used to use the amount of vibration to judge my speed(???), I was at a loss as to how fast I was traveling. As you can guess I do not have speedometer on my boat, but I do have a knotstick, a spring/round disk combination. It measured 5.75 knots at 2000 rpm. This is my full thrutle, any more and black smoke pours out. In neutral I rev at 3500 rpm.My questions are: What is the hull speed for Hunter 33 '80 model ?By having replaced 2 blade prop with a 3 blade prop, I am pushing my engine too hard?Please share your wisdom with me.Thank you in advanceZiya GunDouble Finessemzgun@ieee.org

 

[terry dornan]

yep !

yanmar wants to rev up -- keeps the coke out and the engine lubed. If you are overloading at 2000 rpm, sounds like the prop change was a bad choice.

 

[Dick Carey]

Hull Speed

The Hull Speed is calculated as follows;

 

[Dick Carey]

Hull Speed (really)

The Hull Speed is a calculation and is a function of the boat length. It is calculated as follows:The square root of the LWL(Length of Water Line) time 1.34. Practicully the factor is closer to 1.4 than to 1.34.Dick

 

[Steve Dion]

Site Specs

Ziya:Based on the specs on the web site:The prop should be a 2 blade 14 x 12 and your hull speed should be approx. 7.0. You need to find out what prop they replaced your 2 blade prop with. I think that Justin had mentioned that a three blade prop would need one degree less pitch as an equivalent 3 blade. This is assuming that everthing else is correct. Making that assumption you should have a 14 x 11 3 blade!If you are blowing black smoke it is an indication that you are "probably" over-propped. You may also want to check the mixing elbow just to make sure that it is clean and clear too.