Need Help With Re-Prop

[FedUpWithBoatEngines]

Need some help here if possible.

1) My engine over revs.
2) Not sure of prop make. Its stainless though.
3) Best I can measure diameter is 12", I believe its 19 pitch. 3 blade. Numbers on prop are 819K, and a bit further away it has 7732 stamped on it.
4) WOT RPM will exceed reccomended 5250, not sure about speed.
5) Mercury OB, 1990 115 L4
6) Tracker Marine Flats, 1989, 18', fiberglass construction, weight unknown.

Boat seems a bit heavy on the stern while running and I would like to pick it up out of the water a little if possible as well as correct the over rev issue.

 

[trendsetter240]

Re: Need Help With Re-Prop

Is the current prop a 3 blade or 4 blade? The Solas HR Titan 4 blade stainless is a great stern lifting prop. I use one on my boat.


How much above the 5250RPM will your current prop allow?

 

[FedUpWithBoatEngines]

Re: Need Help With Re-Prop

Its a 3 blade prop. Atleast 5600 RPM, I seen that and backed off as I didnt want to blow up the engine I worked so hard on to make run.

 

[trendsetter240]

Re: Need Help With Re-Prop

Its a 3 blade prop. Atleast 5600 RPM, I seen that and backed off as I didnt want to blow up the engine I worked so hard on to make run.

My manual shows the 1990 merc 115 has a recomended RPM range of 5000-5500 RPM. That means you should be aiming for 5500RPM at WOT. Where was it that you heard 5250?

If you're aiming for 5500RPM I would go with a Solas HR Titan 13" X 19P 4 blade stainless. It will give you the lift you want and drop your RPMs a couple hundred while increasing performance. They cost about 300 bucks here on iboats.

A less expensive but very good alternative is the 12.5" X 19 Solas Amita 4 blade aluminium.

 

[FedUpWithBoatEngines]

Re: Need Help With Re-Prop

My manual shows the 1990 merc 115 has a recomended RPM range of 5000-5500 RPM. That means you should be aiming for 5500RPM at WOT. Where was it that you heard 5250?

According to my Mercury Service Manual, Part # 90-13645--2, page 1-2 the Full Throttle RPM Range is 4750 - 5250.

Given that info would you still reccomend the 13" x 19P HR Titan?

 

[trendsetter240]

Re: Need Help With Re-Prop

According to my Mercury Service Manual, Part # 90-13645--2, page 1-2 the Full Throttle RPM Range is 4750 - 5250.

Given that info would you still reccomend the 13" x 19P HR Titan?

As far as RPM range, my range came from a seloc manual so I'd go with the factory numbers you have instead. However, reading posts on here people seem to run those motors above 5500RPM often.

This is a tough one, I really feel that the 19p HR Titan is the right prop for that setup. But we don't even know for certain that your existing prop is a 19p.

Do you have another prop that you can get some test numbers with? Even a stock aluminium 19p would be very helpfull in trying to determine what you'll need.

The HR Titan is an expensive prop so I don't want to tell you to buy it and have your motor still being able to overrev.

 

[FedUpWithBoatEngines]

Re: Need Help With Re-Prop

Even though others may be running their engine over 5500, I will not. I would like to stay right around 5 -5100 at WOT.

Unfortunately the only other prop I have is the same thing with the almost the same numbers. Again with 19K at the end of the string. This one seems to be the same diameter as well.

Even if the one on the boat is a 19" pitch, wouldnt going up to the 13" diameter and adding another blade bring my RPM down? And if so by how much?

 

[trendsetter240]

Re: Need Help With Re-Prop

Even though others may be running their engine over 5500, I will not. I would like to stay right around 5 -5100 at WOT.

Unfortunately the only other prop I have is the same thing with the almost the same numbers. Again with 19K at the end of the string. This one seems to be the same diameter as well.

Even if the one on the boat is a 19" pitch, wouldnt going up to the 13" diameter and adding another blade bring my RPM down? And if so by how much?

Yes, increasing diameter and adding a blade will bring the RPM down. But I'm not sure how much.

The problem is I'm not sure of the make/design and pitch of the current prop. Sometimes there can be as much as 600RPM difference between two props of the same pitch but different blade design.

I just don't see your particular setup as needing a 20p or 21p prop; I still believe the HR Titan 4 blade 19p will be a good choice.

It's your money though, I'm just offering up some advice based upon my experience. Perhaps others will be along with more input.

Cheers!

 

[FedUpWithBoatEngines]

Re: Need Help With Re-Prop

I hear you there. I will just go to one of the local experts and get them to figure out what I have and what I should get.

 

[FedUpWithBoatEngines]

Re: Need Help With Re-Prop

So come to find out I do have a 13 1/4" diameter x 19" pitch prop. It's a Merc. Hi-rake. Part number C-48-72762-A4.

This prop is "right" for the engine. Now I'm not so confident in my tach readings. Is there a way to test a Teleflex tach to verify it's working properly?

Also generally speaking, about how many RPM would I drop going from a 3 blade to a 4 blade while staying with the same pitch and same diameter?