pitch change effect

[bill lee]

Looking to put a new set of props on this spring. Boat is a 2001 bayliner cierra, 3055 with T5.7carb BII. approx wt 12,000. Boat in the Chesapeake bay, cruise at approx 30 knts at 3600rpm. boat comes up on plane fine. has trim tabs.<br />Here is my question. The props that came with the boat are 17 1/2 x 23. When I look in mercruiser they suggest a 17 1/4 x 25 prop. What effect will this have on the boat performance? <br />thanks

 

[QC]

Re: pitch change effect

Bill you're gonna need to post your WOT RPM as it is the only really important spec. See the post at the top of this section for some more info.<br /><br />The simple answer is that your RPM at that cruise speed will probably drop which sounds good, but your ability to get on plane will suffer. Also, the reason for the WOT RPM spec is to verify that you are not already putting the engines into a deep lug condition or if you would over rev at maximum speed. The former would indicate that you might need to go to a 21 inch set. The latter would indicate that you could go to the 25 inch prop set and potentially get better fuel economy at cruise, again the "hole shot" would conversely suffer as compared to the 23's.<br /><br />Looks like you have been here a lttle while but, welcome to iboats!

 

[bill lee]

Re: pitch change effect

Quietcat22, thanks for the response. The WOT is right around 4500-4550 RPM. <br />thanks

 

[Bondo]

Re: pitch change effect

A 25" prop will Over Load your motor,..........<br /><br />At 4500rpms,..... I'd say you're Propped about Right,.... Now.......

 

[QC]

Re: pitch change effect

Yup, the 23's seem perfect to me too . . .<br /><br />I have read numerous times here that the Merc suggestions are usually off. Don't read too much into them.

 

[bill lee]

Re: pitch change effect

Thanks, I have the numbers for the original props, now time to shop around. Plan to put the new ones on this season and have the old props referbished as spares.