What would you guys do?

kwluis · #1 05-26-2005, 11:06 AM

I just took delivery of a SC 23 with 225 opti.
The boat with 140 gal of gas and 2 people would only hit 5010 rpm max and just over 35 knots. The manual says that recommended full throttle range is 5000-5750 rpm and suggest that it runs WOT in the upper half of that range. The prop that the dealer put on there is the Mirage 17P. I am on the low end of the WOT rpm range that the manual suggests, I just don't know if that is good. I just can't go to the dealer and ask for a new prop either...they are located approximately 4 hours away.

My question for you guys is what would you do? Would you change the prop for an extra 700 or so rpm or just leave it alone? A new stainless prop is pricey and I am happy with the speed, performance and hole shot. I figured since they have sent out so many of these engines propped like this, that it would have the correct prop from the get go. Is the mirage 17P about the right prop? Is it possible that all I need to do is check the throttle adjustment in the engine? Is it bad for the engine though leaving it the way it is? Am I making the engine work harder? Am I taking the life away? I don't want to hurt the engine.

Thanks,
Luis

sailcat · #2 05-26-2005, 11:37 AM

Luis, One of the worst things you can do to an outboard is to lug it. Follow your owners manual. Dropping your pitch is going to give you a better hole shot, and the RPM that you gain will keep you if the same MPH range WOT. Call your dealer and express your concerns. Let them be responsible for your new motor.

ocuyler · #3 05-26-2005, 12:01 PM

Luis,

Bob gives good advice. I would suggest you see what RPM you get with a 1/4 tank of fuel and one guy on board. Under those conditions, I'd like to see at least 5500 RPM at WOT. I think sheding almost 1000 pounds will give you that.

If that works out, I'd probably leave it alone. If the RPM is still low, I'd buy another to get up where you should be. I think it's always good policy to have a spare prop...

FELLOW-SHIP · #4 05-26-2005, 12:17 PM

I’m with Otto on this one with the ¼ tank and one guy and trim it up as high as possible. If that doesn’t do it something is wrong. That Merc. of yours with a 17” should show around 5500 rpm’s. That’s the right prop. And 5500 is the right rpm’s.
Fellowship [img]/images/graemlins/cool.gif[/img]

kwluis · #5 05-26-2005, 12:30 PM

Thanks for the input guys. I now have about 80 gallons in there...I will run her either today or tomorrow and see if there is any increase.

The only other things that I could figure for lack of RPM was either the engine was mounted too low (merc XXL shaft)or the throttle wasn't adjusted right. I'm going to play around with it a little and see what we find. Thanks again.

Abe's Rocket · #6 05-26-2005, 12:38 PM

What kind of tach are you using? The tach itself could be off as well.

A Merc tech can plug directly into the motor while you are running and give an accurate RPM and then prop out based on that. But 35knots doesn't sound right with a 225.

kwluis · #7 06-02-2005, 09:01 PM

Ok...I had the boat out the other day. Approximately 50 gallons of fuel, no fishing gear, and one other buddy. I had the engine trimmed up and the tabs trimmed...top RPM was 5200. I called the local Merc guy, but he was out this week having surgery. I am going to call him next week when he returns. I think the engine does need to be raised after looking at it. I will keep reporting in. Thanks for the advice.

kwluis · #8 06-28-2005, 03:47 PM

Update:
I just replaced the prop this morning with a 15 pitch Mirage. Trimmed out, I hit right around 5500 rpm and just over 37 knots. This was with me and just over 1/2 tank of gas. The low end and mid range RPMs seemed smoother...if that is anyway to explain it. The engine sounded a lot quiter and felt better...the prop just doesn't seem to grab as much on sharp turns as the other prop did...but that's ok.

This prop seems to be a better fit for what I was looking for. Thanks fol all of the suggestions!

Luis

Bigshrimpin · #9 06-28-2005, 05:42 PM

Are those mirage props heavily cupped?

37 knots is theoretically impossible for a 15 pitch prop, 1.86 gear ratio, turning 5500 . . . 37mph would be right on the money.

http://www.continuouswave.com/whaler.../propCalc.html

kwluis · #10 06-28-2005, 10:01 PM

37 KNOTS according to my Raymarine C-80. I will be running it more tomorrow. I was actually hoping for more top end speed. I don't know about the amount of cupping on that prop. I was told by a guy who has the same set up that he was getting 46-48 MPH. Maybe I will get more speed later...the engine only has 25 hours.