Need help and advice on Prop

[UnWired]

I installed a new Yammie LF225 on my boat 2520 MVSC, (Left hand rot) and called my local prop shop here in California. They recommended using a 15.5" x 15p LH Mercury Mirage II prop. I broke the engine in over a month ago and it runs GREAT... very happy with the fuel burn figures and mostly happy with the fuel mileage, etc. In fact, more than happy.

I am able to get up to 5700 - 5800 RPM WOT. 38-39 MPH (Statute) but I never run it that fast except a couple of times during the break in procedure and very rarely coming back from a long trip in the bay.

My burn figures for the prop combo are as follows:
Yamaha fuel management burn.

4400 RPM - 9 GPH - 25 MPH (statute) (2.7MPG)
4700 RPM - 11GPH - 28-29 MPH (Statute) (2.6 MPG)
Tuna troll speeds - 8 MPH - 1700 RPM - 2.7 GPH burn

I have bottom paint on the boat and these figures are will a completely full load. 4 people, 120 gallons of fuel, 300-400 pounds of ice full gear, full everything. A lot of weight.

While the figures look excellent, I'm not sure if I should get another prop. The Mercury calculator suggests the following for Medium cruise speed, or Best overall Performance.

I am looking at getting a Stainless prop and keeping my existing 15p as a backup or heavy load prop. The figures are for RH rote... So I will have to do a LH, but not available on their calculator.

When we were running hard from the Oregon Tuna Classic tournament pushing it hard in heavy seas 9-10 ft combined at 25-28 MPH at 5000 - 5100 RPM and the boat honestly took the big stuff great. I buried the 9 x 24 Lenco Trims and stuffed the bow hard. I heard some people talking about the MV hull not being that good on heavy seas and I'm sure a DV would have been better because we did take some water over the bow, but all in all, for how we fish, the MV is great and the fuel mileage is good now with the new motor. I included the last part to explain how we use the boat and what performance we need, so mostly we're in 4-8 foot swells and 2-4 foot wind waves (Calm) water and occassionally we're in the bad stuff, which requires more torque when I stuff the bow down hard, thus maybe stick with the 15p prop... not sure.

Any ideas or any suggestions would be great. Maybe a 4 blade 16 or 17p?

 

[BradV]

I wouldnt change pitch if you are turning 5800 with that motor anymore pitch and a heavy load you will be bogged down. Sounds like you are getting good all around performance. No prop will truly make that much of a difference in performance. Maybe handling and ride and a .1 mph difference up or down. You will however notice a bad prop in a hurry. Maybe you can take the prop to a local shop and have them cup it if you want to try to squeak out a little more performance. I have my motors so i can turn 6100 rpm and i have the Rev 4 19's on my twin 225 yamaha 4 strokes

 

[hwsiii]

UnWired, the only real way to know how well your prop is doing at ruising speed is to run a true analysis of how your prop is doing at all RPM from about 3,000 RPM to WOT RPM in inrements of 250 RPM. With this information you an see how muh prop slip you are having throughout your whole RPM range and run an anaylsis so you an see what eah different prop is doing. To do it right you also need to run it in the approximate seas you normally enounter with the loads that you normally arry. Numbers that look good on paper for one prop but are in alm water are not always the same in truly formed seas where the boat is being pushed around by the water, and a prop an start ventilating easily beause of not having enough blade surfae area and/or the orret blade geometry beause of the extra loads and drag plaed on the boat beause of formed seas.


H

 

[captbone]

I used to run a 15pitch Mirage Plus on my 25ft with a single 225hp. I switched to the 15pitch Enertia and gained 200 rpm and almost 2mph. I am much happier with the Enertia over the Mirage Plus.

I would highly recommend it. Your application is exactly what it is designed for. A heavy single engine application.

Just my 2 cent.