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Author Topic:   OUTRAGE 18, Tohatsu 115-HP TLDI
leadsled posted 03-07-2015 10:17 AM ET (US)   Profile for leadsled   Send Email to leadsled  
I just ordered a new Tohatsu 115-HP TLDI for my [just acquired] 1989 Outrage 18. The dealer asked me what propeller pitch I wanted, and I was not sure. The propeller pitches run from 11 to 21 pitch. The gear ratio is 2.0:1 and the RPM range is 5150 to 5850. I will be running light with no more than three people total. The boat was just soda blasted and bottom painted and will be used in saltwater. My guess is either a 15 or 17 pitch. Anybody have an idea?
jimh posted 03-07-2015 10:36 AM ET (US)     Profile for jimh  Send Email to jimh     
The general method for estimating propeller pitch:

--determine expected maximum speed with weight, horsepower, and hull; you can use my Crouch's Calculator to make this estimate. See

--with the maximum speed estimated, select a propeller pitch based on propeller slip, engine crankshaft speed, and gear ratio; you can use my Propeller Calculator to make this estimate. See

The speed of an OUTRAGE 18 with 115-HP will depend greatly on the total weight. I will use an estimate for total weight of boat, engine, gear, and crew at 2,500-lbs. That is double the hull dry weight, and this is usually a safe estimate. I use a hull constant of 180. Crouch's Calculator says the speed with 115-HP will be 38-MPH.

Using my Propeller Calculator, for 5,850-RPM, 2:1 gear ratio, 10-percent SLIP, and 38-MPH, the propeller pitch will be 15-inches.

leadsled posted 03-07-2015 10:55 AM ET (US)     Profile for leadsled  Send Email to leadsled     
Wow that was quick, Thanks . 15" it will be then.
jimh posted 03-08-2015 11:03 AM ET (US)     Profile for jimh  Send Email to jimh     
My estimate is just that--an estimate. It was based on a heavy load and very conservative speed. You really need to test a propeller on the water with the normal load to see how it will work. By starting with a 15-pitch, you should be quite conservative, and you may find more pitch will be useful.
leadsled posted 03-09-2015 04:34 AM ET (US)     Profile for leadsled  Send Email to leadsled     
Thanks JIMH, I was thinking the same thing.I would rather have it slightly under- [pitched] than over-[pitched]. I can always stay under full speed if it's under- [pitched].

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