Need 2 props for 2 boats

[roger3645]

Okay here goes. I’ve have two boats and yes the wife says one has to go, but I only have one old 2 blade bronze prop (13.5 x 19p) to share between them and the pitch is low for both boats.<br /><br />#1 1977 16’ Tri-hull fiberglass bass boat 850 lbs dry weight. Powered by a 1975 850 85hp merc. Now if this motor has a rev limiter I’m hitting it as the motor will shut right off if I try to get WOT. I don’t have a tach in this boat but as I try WOT the rpms sound very high. At 3/4 throttle it’ll only run about 28 mph by gps. I believe the max rpm for this motor is 5300 rpm.<br /><br />#2 1972 15’ Deep V, fiberbglass, Mark Twain V Sonic runabout, 850 dry weight. Powered by a 1973 850, 85hp, Merc. I don’t believe this motor has a rev limiter in it as I’m hitting 6000 rpm @ 31 mph with a little throttle left. I think max rpm is also 5300 rpm.<br /><br />I’m not looking to turn these boats in to speed demons but if I can get them both near 40 mph I’ll be happy. I know these boats and motors are older than some of the folks who’ll read this but they both run good and have good compression. What size prop and pitch should I try?

 

[walleyehed]

Re: Need 2 props for 2 boats

Max "Rated" I believe, is 5800...<br />6000 won't hurt a thing but, I believe you could go to a 19P 3-blade and have good results.<br />Your first engine sounds as though it may have some other issues...power pack maybe...I don't believe there is a Rev limiter on either engine.

 

[roger3645]

Re: Need 2 props for 2 boats

Okay checked a web site and found the Max rate to be 4800-5500 for the motors. In the prop guide it listed a 13 x 23p 3 bladed prop for boats 1000 to 1800 lbs up to 17', and a 3 bladed 13 x 21p for boats 1200 - 2200 lbs, 15' to 18'. Does the 21p sound about right? Or do you think the 3 bladed 19p to be the best bet? Also I'll switch out the power pack of the 2nd motor to the 1st to check it out. Thanks.

 

[walleyehed]

Re: Need 2 props for 2 boats

The "Highest" pitch I would recommend would be the 21..we have to take into account the 3rd blade we're adding.<br />The tach will tell the best, but I think going from a 2 to 3-blade, and with it at 6000, I'd stay at 19 pitch.<br />Also, the specs may say "5500" max, but remember, that was also when we had good fuel..on todays gas, we try and get the older engines up some from that rating, and I think 6000 is fine.

 

[roger3645]

Re: Need 2 props for 2 boats

Okay Thanks Kenny I'll go with the 19P.