Prop Selection

[Lucky Penny]

I realize that this has to be one of the most posted topics on the board, but after searching this and other sites, I still need help.

The boat: 25' express cruiser; chevy 5.7L (mercruiser) engine; alfa drive with 1.50:1; estimated weight (fully loaded, fuel, water, food the dog and me) approx 6000 pounds.

I am a long distance (for me) cruiser. some trips as much as 1400 miles. with fuel cost doing nothing but going up, I need to consider re-proping. I normally do not throttle up to the point were the secondaries open, so I usually keep my RPM at/below 2800 (it is a cruiser, not a speed boat.)

What I would like to know is what would be the best prop to yeild the best fuel eco? I try to achieve 14-18MPH during transit.

It is not pleasure boating per sa for me. This little cruiser is my home and for 6-8 months a year I travel up and down the ICW for work. I am also a realist, and sooner or later the cost of fuel will be my demise.

I love boating, and the life style. The number of pleasent evenings after work with other boaters is beyond count. The number of times I have been given a "what for" when working late and my dog was not walked "properly" is also beyond counting.

Anyway, I need to be as efficient as possible to continue. Please help

 

[Don S]

Re: Prop Selection

Moving to Prop Questions and Topics forum.

 

[Silvertip]

Re: Prop Selection

If your boat is set up to allow the engine to operate at or near the top of the recommended WOT rpm band, changing props means you now make the engine operate where it does not want to operate. It doesn't matter if you don't go WOT. I'm sure your thinking you should increase pitch to slow the engine down and thus save fuel. By doing that, what you actually do is make the engine lug getting started and also work harder at whatever speed you cruise. Lugging means the throttle is open farther, not less. My suggestion is to make sure you are propped correctly for WOT. Anything less than that will take care of itself. My next suggestion is that you install an inexpensive fuel flow monitor (such as the Northstar 210/Navman 2100). These units allow you to quickly determine where the most economical engine rpm/speed is so you can get the best economy. These units are easy to install and are available for as little as $125.00 depending on where you shop.