Prop pitch advice

[Bob Kimber]

Hi all,<br /><br />2000 model 90hp Merc, 60hrs running, recommended WOT 5000 - 5500rpm, boat is 17ft fibreglass half cabin estimated weight 2,600lbs normal load.<br /><br />I have been running 13-3/4" x 15" S/S prop from previous motor, inline six Merc, 36mph @5700rpm WOT, in the last 10hrs running WOT has slowly increased to 6200 rpm, tach calibration has been checked and is OK. Borrowed 16" pitch S/S prop and reached 6000rpm at WOT.<br /><br />Tried 19" pitch aluminium prop today, 32mph @ 4600rpm and WOT of 39mph @ 5200rpm, boat came up on plane well and accelerated smoothly to WOT of 5200rpm (normal load for test), generally performed well at all speeds including idle. <br /><br />Alternatives :-<br /> # keep 19" pitch prop, motor is within WOT recommended range and may free up a little more with more hours running?<br /><br /> # swap prop for 17" pitch with possible WOT exceeding recommended rpm range (5700 or higher)?<br /><br />Any comment would be welcome<br /><br />thanks Bob

 

[almost retired again]

Re: Prop pitch advice

Hello Bob,<br />I think that you have found the right combination, I think that I would leave it where it's at. You might try that 17" and try to get it cupped a little more.

 

[sho305]

Re: Prop pitch advice

You're good, take the 19" and file the front edge of each blade sharp for a little more speed/rpm. Depending on the boat you have, a Laser type of prop will let you trim higher than stock props. A light boat will gain some, but only in smooth water.

 

[Dhadley]

Re: Prop pitch advice

I have a couple of new 17" SS Stilettos left at a good price if you would like a new prop. If you need one it's 175.00. List is 377.00.<br /><br />Good luck!

 

[sho305]

Re: Prop pitch advice

I can throw a big rooster with my Laser II SS 19p trimmed up on a '73 Merc 150 and gain 2-3mph with lots of torque steer. But if I hit a wake the whole boat goes airborne at 50-54mph and everything flies around in there. It is a 17' and a stock prop blows out if trimmed much.<br /><br />A guy asked me about one for his boat but he is kind of crass, and I doubt he would know enough to trim down in rougher water as he just hammers it WFO all the way around the lake. I said it runs fine & he ought to leave it be. Hate to see someone get hurt because of an idiot driver.

 

[Bob Kimber]

Re: Prop pitch advice

Thanks to everybody for their input, I did like the way the 19" went but I forgot to mention that all my boating is done in the open sea, we have no freshwater lakes in this part of the world consequently a lot of running is done in fairly choppy and rough conditions (10 to 20 knot wind and waves up to 10 feet). It was because of this I was worried that running at slower speeds in poor sea conditions may have been stressing the motor with the larger pitch.<br /><br />I will try loading the boat up a bit more (2 extra bodies) to see if it drops the rpm below WOT range,if it drops to 5000 I might try the 17".<br /><br />Dhadley if I was closer than 10,000 miles away I would take you up on one of your props, S/S props are very expensive in Australia.<br /><br />Thanks Bob

 

[Bob Kimber]

Re: Prop pitch advice

^ bump