Prop change for merc 115 tower

[IronOutlaw]

Right now I have a 21" quicksilver stainless prop. The boat is a 16' 10" ranger 330v. Engine is an 86 tower of power 115.

I had about 750 pounds worth of people in the boat and it planed out fine. Fast enough to pull up a skier. At wot I'm turning about 6000 rpms with the speedo showing a little over 45. I have no gps to verify speed. I think the speedo is off though because it stops gaining at 45 but the boat is still speeding up.

I'm wanting to drop wot rpm but not lose much if any low rpm torque for planing. I'd like to be aroun. 5500-5800 instead of up around 6000.

Should I step up to a 23". From what I understand that's alot of prop for a 115. I'll get the part number of the prop tomorrow that's on it.
What about if I get my current prop cupped? Will that give me a few more Mphs up top and less rpms?

 

[usskydvr]

Re: Prop change for merc 115 tower

Yeah a 23 is a bit steep for the 115 normally. Make sure your tach is correct. Also get that part # of the current prop. Cupping will only drop the RPM about 100RPM or so. Which model 115 do you have? We need to know the MAX recommended RPM range.

 

[IronOutlaw]

Re: Prop change for merc 115 tower

Alright the engine is a 1986 mercury 115 inline six. Max rpm is rated for 5000-5500 but the 140 horse is rated to 5800 and I think the have the same internals.

Prop is a quicksilver stainless

Quicksilver 48 72500 a5 21p

I just read online that a 330v weighs right at 1000# dry. It's a v hull with a pad. I'm usually gonna have two or three people in it. Last weekend we had four.

The motor is sitting one notch up which is sorta high. Has the ventilation plate even with the transom, not the pad. I trim it up some at high speeds to keep the nose from plowing into the water. With the engine down I still turn over 5000 rpms on the tach.



I like how the boat performs as is but don't like the high rpms it turns at wot. But then again I don't like to run my stuff hard and only hit wot very rarely such as outrunning an incoming storm.

This weekend I'm gonna get a gps to get an accurate speed reading. How do I verify my tach? Will any cheap tach work?how do I hook it up.

I don't want to hurt my motor. If 5800-6000 rpms is ok then I guess I'll
leave it.

 

[usskydvr]

Re: Prop change for merc 115 tower

So that was one of the earlier Lazer II props. I can't remember if that one had the adjustable vent plugs. If so you may want to put in plugs with smaller holes or with no holes at all. Also I would move the engine down so the plate is even with the pad. The other option is just watch your RPM's. I think the 23 is not the way to go. The gray wire on the voltage regulator is the signal for the tach, but you need an outboard tach with a switch to select the # of poles on the stator.

 

[IronOutlaw]

Re: Prop change for merc 115 tower

K I'll try dropping the motor.
I think the tach is close by the sound of the motor, so I don't think I wanna spend the money on a new one.

I'm definitly not going 23".

How do I tell if I have a vented prop?

 

[IronOutlaw]

Re: Prop change for merc 115 tower

Google is my friend. I do have a vented prop and am gonna buy the pop in covers to fill the holes. Right now there's nothing in them.

If that don't work I'm gonna lower the motor.

Along with the two ideas above I'm just gonna watch the rpms. I've been reading of some folks running these things 6000 plus with no problems ad long as the carbs are right and the engines getting enough water.

Thanks for the help man.