rpms at the tops of the throttles.... suggestions?

[pelagic2530]

ok guys, im not going to pretend that i know really anything about engine operation, props, and all that stuff. ive been doing some reading up on the subject, but im still pretty confused. i was hoping some of the prop gods here could help me out heres my situation. we hauled the boat this weekend, but before we did, we took her for a burn out in the bay. the water was calm, and we pegged the throttles, which we rarely get to do. doing so, i noticed that the top inch or two of throttle produced no effect in rpm or speed. the engines wound to about 4900 rpm right near the top, and then there were two more inches where nothing happened. the engines are twin Yamaha saltwater series 150 2 strokes wearing the stock yammie 3 blades that came with the boat. the props are a bit beat up, but nothing major. any suggestions for what i should do here before we launch for next season? :?

 

[DaleH]

Wow ... my God that's too low.

What boat, hull? FWIW my bro runs twin '87 Yam 150hp 2-strokes on his 8'6" beam, heavy 23' W/A Grady White. His props are tuned to turn ~5700 RPMs (max = 6K) with 2 people, std gear that stays on boat, and 1/2-fuel.

He too was akin to your predicament when he bought, luckily we have an AWESOME prop place here near Boston. They told him to provide them with ALL details about the boat ... and they dialed them in on the 1st water test.

I'd bet he's about 17" pitch ... :?: but I am NOT sure ...

 

[grouperjim]

is 4900 the best its ever done? not sure what a "stock pitch" is.

pretty much for the type of boats we have, the 3 blades are "offshore" style props. a given pitch with normal slip will yield a particular speed range. for your boat, a 17 pitch would ball park speed-wise. take your props to a prop shop and for $75 a piece, they will tune them up. meaning they will look like new, be balanced and blades sharpened. if that doesn't get you in the rpm range, then take them back to the prop shop and tell them what your rpms are, and they will repitch them, or suggest a new prop if out of parameters for repitching.

 

[B-Faithful]

rule of thumb according to my old Merc mechanic, who I trust, is to try to be within 200rpms of the max operating range. This will give max engine life.

 

[pelagic2530]

thanks guys, the boats a 1995 2530, 9'6 beam, with no fishing equipment, but a fair amount of standard gear and half a tank of gas (~90 gals). ive never seen it spin more than 5000 rpm. i think were going to get the props serviced, probably ship them up somewhere in jersey unless someone knows of a place in DE. any other input is much appreciated.

 

[grouperjim]

.......forgot.......instead of repitching, a prop shop can also adjust cup (cheaper than repitching) which can make a 200 rpm difference as well.

 

[Capt Bill Welder]

If you have never seen over 5000 with a half tank of fuel and a light load something is not right. I would not be surprised if your dealer had no clue or just put on what he had available.

Before I spent any money on tuning a prop I would want to know if it was a good prop.

Are your props SS or aluminum?
What pitch?

 

[pelagic2530]

the props are stainless, dont know off the top of my head what the pitch is. ill check. like i said, i really dont know much about this. thanks guys.

 

[Megabyte]

At the beginning of a season, my 225 OX66 will turn 5200 rpm on a clean bottom and run 35 kts at WOT.
At the end of the season, 5000 max is not unusual at 33 kts.

On a clean bottom and in cold water/weather she will run a bit faster than she will later in the season with some slime and in warm weather. I think that is pretty normal for most folks.

As far the throttle goes... mine is the same. There is a point at WOT that the throttle can be pushed a little further, but the motor is already firewalled at max rpm. I just figured it was a linkage thing. The fact that there is a bit more travel in the throttle than there are engine rpm's has never bothered me.

 

[sparky]

Wow ... my God that's too low.

What boat, hull? FWIW my bro runs twin '87 Yam 150hp 2-strokes on his 8'6" beam, heavy 23' W/A Grady White. His props are tuned to turn ~5700 RPMs (max = 6K) with 2 people, std gear that stays on boat, and 1/2-fuel.

He too was akin to your predicament when he bought, luckily we have an AWESOME prop place here near Boston. They told him to provide them with ALL details about the boat ... and they dialed them in on the 1st water test.

I'd bet he's about 17" pitch ... :?: but I am NOT sure ...

What is this awesome prop place? We've got prop issues with our landing craft, and would love to talk to someone about it.

 

[DaleH]

On a clean bottom and in cold water/weather she will run a bit faster than she will later in the season with some slime and in warm weather. I think that is pretty normal for most folks.

So true! I find that also and ANY normally aspirated motor; car, boat, or plane - will lose ~200-300 RPMs in the heat of the Summer.

Maybe his OBs are 5.5K MAX RPM motors, and if so, I'd still would prefer to see him just a few hundred off MAX.

What is this awesome prop place? We've got prop issues with our landing craft, and would love to talk to someone about it.

New England Propeller, right off Expressway just south of Boston.

New England Propeller
68 Von Hillern St, Dorchester, MA 02125
(617) 288-3132