Prop ( I know it's a dead horse)but trying to understand)

[edandq]

Okay, recently I changed my 1970 Starcraft from a 1970 Johnson '85 to a 2003 Suzuki DF70. The boat does sit a little lower in back end. I can tell the difference in the weight, however, I love this engine. It's quiet, strong, and very reliable. But.... I don't think it's propped right. At WOT it's running over 6000 RPM. According to my book, the optimum range is 55-58. It has a 3 blade 13.25 x 13. I've read I should increase pitch if I want to bring down my RPM. So, that being said, I'm thinking of going with a 17 pitch. Is that out to lunch? I want to increase my hole shot as well, as the boat runs great on plane, but takes a bit to get there. Any thoughts would be appreciated.

 

[JB]

Re: Prop ( I know it's a dead horse)but trying to understand)

Howdy, EDandQ.<br /><br />If you are getting over 6,000rpm you need more pitch, but jumping all the way to 17" might be too much.<br /><br />I have a DF70 on my Boston Whaler Montauk 17' and it does well with a 17" SS prop. 37mph at 5800rpm WOT. The boat weighs 950 bare and is well loaded. Probably about 1300-1400lb on the water.<br /><br />You don't mention the size or weight of your boat. That is important in guessing where to start in selecting a prop. Your 13" prop seems to be too little, but if you can borrow a 15" prop and try that before going to a 17" you might save yourself some frustration.<br /><br />Good luck.

 

[LubeDude]

Re: Prop ( I know it's a dead horse)but trying to understand)

Originally posted by edandq:<br /> I want to increase my hole shot as well, as the boat runs great on plane, but takes a bit to get there. Any thoughts would be appreciated.

I think JBs right about the 17P.<br /><br />Any time you raise the pitch, your hole shot is goung to suffer, thats just the way it is. You may concider the 15P, and a set of Smart Tabs for the hole shot problem.

 

[edandq]

Re: Prop ( I know it's a dead horse)but trying to understand)

Oh, sorry, my boat is a 16'. I'll try to figure out the weight, but not sure except to take it and weight it.

 

[Dhadley]

Re: Prop ( I know it's a dead horse)but trying to understand)

If you dont lose drag, just changing the prop will usually improve only one end of the range or the other -- as stated above. <br /><br />Reducing drag will generally improve your overall performance. Whether you reduce drag from the motor or reduce the wetted surface of the hull or both.<br /><br />Its possible to have two identical boats with identical motors and the one with the larger pitch prop can be quicker and faster than the other.

 

[edandq]

Re: Prop ( I know it's a dead horse)but trying to understand)

Dhadley, I see your point, but I really don't have a choice but to change props, correct? I mean, if I'm running above the mfg suggest RPM, aren't I just asking for trouble? I did find a 13 3/4 x 15 laying around the house from my old engine, and that lowered my RPM and didn't seem to affect the boat too much one way or the other, which leads me to believe I need to go one step further to the 17. I'm now down around 6,000 at WOT.