What size prop?

[hct4all]

First time out with my "new" 81 50 hp merc. Whoo Hoo I never ran anything larger than a 9.9. Am I under propped? Full Throttle 6,300 RPM - Don't worry, I did not run it there. 5500 rmp = 28mph (gps) Prop that came on the motor is a 48-73140-15. What do those numbers tell me about the prop and what size prop should I run. How fast should I be able to go in a 16' Sea Nymph Fishing Machine rated for a 60HP?

 

[roscoe]

Re: What size prop?

So what did the motor turn? 5500 or 6300 ? <br />Was that at WOT ? ( wide open throttle )<br /><br />Your prop is a pretty common Merc prop, used on Merc BF 25hp, Merc and Mariner 40, 50, 60 hp, and Force 70 hp.<br />48-73144-(a40) 17 17 pitch<br />48-73140-15 pitch<br />48-73138-14 pitch<br />48-73136-13 pitch<br />48-73134-12 pitch<br /><br />If at WOT, you were hitting 6300, I would switch to a 17 pitch prop.<br /><br />If at wot, you were only hitting 5500, you could switch to a 13 pitch prop.<br /><br />Either way, you should then be running at 5900-6000 rpm.<br />Neither is going to change the speed much.<br />How is the holeshot?

 

[hct4all]

Re: What size prop?

WOT was 6300. I kicked it back because before I headed out I reat the manual that the WOT rmp range was 5000 - 5500.<br /><br />Holeshot was pretty quick, I did not put on the hydrofoil yet. Will this help with speed. I am hoping to get about 35mph out of her.<br /><br />Thanks,<br /><br />Rick

 

[roscoe]

Re: What size prop?

I think the highest pitch prop you will easily find for that motor is a 17 pitch. That will put you closer to recommended rpm, but still a bit high at about 5900 rpm.<br />Many of us do run these motors close to 6000 rpm, and if your motor is in good condition, it should handle it.<br /><br />Yeah, the hole shot should be pretty quick if you are able to spin that high of rpm.<br /><br />Hydrofoils are used to help the holeshot and it sounds like you don't need any hlep there.<br />They can actually hurt your top speed if not set up properly, or if your motor is mounted a little too low on the transom.<br /><br />I wouldn't install a foil and risk ruining a good thing.<br />I definitely would not install it if your motor does not have hydrolic tilt and trim.

 

[hct4all]

Re: What size prop?

Thank you for your advice. I do not have Tilt and trim. Maybe in the future. Its on my wish list. I love this motor. I can't believe that is quiter than my 9.9. Idles very nice. My wife is going to have a hard time getting me to come ashore this summer!!!

 

[hct4all]

Re: What size prop?

Anyone else!