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Author Topic:   Improving top speed in Outrage
Marc posted 09-26-2002 02:55 PM ET (US)   Profile for Marc   Send Email to Marc  
Here's my issue/problem: I have a 1991 Outrage 17', with a 115 Merc. My top speed based on a paddle wheel type speedometer is about 37 mph. From what I know (little) and what I've read (a lot) I should be getting closer to 45 mph. Here are the details.

13.25 X 20p stainless steel prop.
1991 Merc 115 2-stroke mounted directly to the transom in the second hole from the top.
Boat is bottom painted so I may lose a mph or two.

At WOT, I get about 5000-5100 rpm.
Boat weighs in around 1020lbs, 34 gallons of fuel plus a few hundred more pounds for people and gear.

I know if I go a lower pitched prop, I will gain about 200 rpm per inch lowered. But how much more speed I will get I don't know??

So my bottom line question is: How can I get closer to the "theoretical" speed of 45mph? Any ideas or help is always appreciated! :-)

Thanks, Marc...

Marc posted 09-26-2002 03:10 PM ET (US)     Profile for Marc  Send Email to Marc     

I goofed up...I think this post should be in the Performance Section. :-(

hooter posted 09-26-2002 03:35 PM ET (US)     Profile for hooter    
Yes, you may be able to improve performance with a different prop. But da best bet to start checkin' is by NOT believing dat paddle-wheel. Buy or borry you a GPS and check out yer speed. My rig has three speed-o-meters. Say I'm goin' home up da Atchafalaya river to da landin' at Morgan City. The OMC engine speedo will be readin' 42, while the paddle-wheel on da sonar unit is sayin' 50 and the GPS is readin' 38. Go figure. Goin' agin' the current accounts for some of the differences but not all of it. They NEVER read the same thing nomatter wear Ah'm goin'! Mebbe somebody knows how to calibrate dese tings, but not me. If Ah care to know how fast we flyin', Ah look'it da GPS.
Marc posted 09-27-2002 06:32 PM ET (US)     Profile for Marc  Send Email to Marc     
Thanks for the suggestions Hooter...I used to have a handheld GPS but got rid of it. My mistake!

I wonder if changing the hole, thus lowering or raising the motor would help?????


lhg posted 09-27-2002 06:56 PM ET (US)     Profile for lhg    
Since your engine is redlined at 5250, you're OK on your prop. It sounds like you're running a 20" pitch Merc Laser II. You might want to lift the engine one more hole, so that the bolts are in the middle holes. Laser Props need to be run elevated 1 1/2".

Unless the engine is bad, or you have a rough hull bottom, my guess is that you're getting the proper speed, more like 43 MPH. I doubt if you'll ever get 46 out it with out a non-painted, clean polished hull and a set back bracket. I'll bet your paddle wheel is inaccurate on the slow side. Most units have the ability to calibrate them, either positive or negative, by percent. Absent a GPS, figure out a measured mile course, and run it with a stop watch or digital watch. See what you get. Or have someone run along side you who has a good DGPS.

If none of this works, you could drop your prop pitch to an 18" Vengeance, then top speed will only be 41, and you could be over-revving. I would also have the hull bottom paint sanded smooth and re-coated if necessary.

jimh posted 09-27-2002 08:02 PM ET (US)     Profile for jimh  Send Email to jimh     
It has been mentioned by non-authorative sources that the Mercury 115 4-cylinder engine should not be run above the (relatively slow) red line speed of 5250.

This warning and the low speed limit were attributed to some potential resonance in the engine which could be harmful.

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