Propeller advice

[eyepatrol]

I've got an 18 foot fiberglass boat with a 150 optimax on it. I've got 2 props. One is aluminum 3-blade and the other is stainless steel hi-five prop.

Question....why is it I can do about 56mph with the 3-blade aliminum prop and only 48mph with the hi-five ss prop? I was told the ss prop would get me more speed.

And, along those lines, can anyone recommend a ss prop that could get me a little more speed, yet not be too hard on the motor?

Thanks.

[kjgmh]

The high=five is not a speed prop, it more suited for water sports or keeping hooked up in rough conditions. If you are looking for speed I would try a Mercury Rev4 or Tempest for speed. Mercury also makes a 4 blade aluminum that works great on heavier hulls.

[marine_man]

Before anyone can make an educated suggestion on a new prop it would be helpfull if you can provide your wide open throttle rpm... for both props.

Once you provide that one can make a more educated suggestion...

marine_man

[eyepatrol]

marine man

I guess I've never compared the rpm's between the aluminum and stainless steel props, but I have seen the rpm's at about 5250 with the aluminum.

If I'm not mistaken, the dealer I bought the boat from said the 150 Optimax (which is what I have) has an rpm regulator on it...that it won't let the rpm's exceed 5500. But, the best I can answer your question is to say with the aluminum prop the motor runs at about 5250rpms.

[marine_man]

I would take a look at the recommended RPM range for your outboard, which should be on a sticker on your motor (either on the powerhead, or on the tilt bracket).

Merc's HSOforum shows the recommended RPM range to be 5250 - 5750, but this could be different than your recommended range depending on what year your motor is... again, check the sticker to be sure.

If the recommended range is as I've listed it above the rpm limiter is beyond 5750... it's probably closer to 6,000... HOWEVER, you do NOT want to run the motor beyond the recommended range.. the rev limiters there to prevent any damage from happening, not as an upper limit.

Anyway, I'd try and find a prop that gets you closest to the upper range of the suggested range... you'll want to do that when you have your lightest normally run load on your boat (if you do a lot of fishing by yourself that'll mean you, 1/2 tank or so of fuel and some gear).

If the upper limit is 5750 and you're currently turning 5250 you could probably drop pitch by 2 for sure, maybe 4 depending on what pitch prop you're running right now...

Find out two things: 1) What the RPM range is for your motor) 2) What pitch prop you're running right now. On most mercury propellers (the aluminum ones anyway) you'll find it stamped on the outside hub of the prop (running parallel with the hub.) The two numbers you'll be interested in are the last two, which'll probably say something like 21P.

I'm not real sure where the pitch is on your stainless prop.. it's either in the same spot as the aluminum, or, if you take off the prop on the face of the prop that mates to the thrust washer on the propshaft.

Good Luck!

marine_man