prop question

[wiskerchaser]

I had originally posted about being under proped and ventalating. I had nice fellow help out with that," greatly appreciate it". I now have a 12 3/4 x 21 cupped prop on a 15' shallow v astroglass.Boat and motor is 1050lb + me, wife = 300. gear, and 15gallons fuel.Boat runs 30mph at 5900 rpm. Motor is rated 5500-6000. Is it possible i can use more pitch? Figured it should run around 40mph at wot, am i crazy or is it still not right? ANY ONE KNOW.

 

[JB]

Re: prop question

Howdy, Whiskerchaser.<br /><br />I don't think you are going to gain any more with prop changes. You are very near ideal for the mystery engine. <br /><br />If you will tell us what engine you have we can estimate maximum speed with ideal prop and rigging. That should tell us if there is potential for more speed.

 

[wiskerchaser]

Re: prop question

sorry, I didnt relise i left motor out. 1979 70hp johnson

 

[walleyehed]

Re: prop question

I have a funny feeling either your tach or speedo is off... at 5900 with the 21", you should be cookin' right along...about 45MPH would match up if your tach is right.

 

[JB]

Re: prop question

I agree with walleyehed.<br /><br />I calculate 43.6mph as theoretical maximum speed for your rig with a well tuned, ideally rigged and propped 70hp engine, Whiskerchaser.<br /><br />That assumes 1500lb total, on the water weight.<br /><br />I think you are very overpropped for that load with a 70. I think 17"to 19" would be close to best pitch for 70hp on a 1500lb load<br /><br />Something, tach or speedometer, is giving you very wrong numbers.

 

[wiskerchaser]

Re: prop question

O.K. guys, do you think my motor might be to low and dragging water then? Because, I can make a corner at wot and the motor does not ventilate and boat does not slow down or skip. Motor is curentlt all the way down on transom and running in middle tilt hole. If i tilt up or down one hole boat slows down. I dont know if it maters but my boat has one of thoose funny rear ends were the v stops about a foot shy of transom and raises an inch or so.

 

[Bondo]

Re: prop question

You Might want to Try Something .?.?.?.?.?<br />I Believe the "Standard" for an "Efficent" boat set-up is 10% slippage factor....<br />I haven't run your #s, But off the top of my head, I can see you're Well Over That.......