prop size for 150 mercury on scout 192

[spoonbill8]

I have a '98 mercury 150 off shore EFI on an '98 Scout Sport Fish 192. I'm running a 21 pitch 14 diameter ss prop WOT 5200rpm @ 49-52mph. I normaly cruise around 38-40mph @ 4000rpms and looking to get better fuel economy! I mostly use it for pleasure ridding while occasionaly fishing near the jetties. I was curious if anyone could help me pick a better prop size and #of blades to fit my usage?

 

[jestor68]

Re: prop size for 150 mercury on scout 192

If you visit the Mercury Marine web site and view the 150 engine tests, you will note that the 150; no matter what boat it's on, gets it's best mpg at 3000 rpm cruise. The speed varies from 23-30 mph depending on the boat.

A boat very much like your's(except 500 lbs lighter) got 8 mpg at 3K and only 4.6 mpg at 4K.

Speeding up to a 4000 rpm cruise resulted in a drop of 1.5-4 mpg, depending on the boat. That's the price you pay for going a little faster. :facepalm:

Depending upon what brand of prop you're running now, it may be possible to realize a slight improvement by moving to a "better" prop. Your present numbers represent a 10% slip, which is average. Running your numbers through the Mercury prop selector came up with a 21 pitch Tempest Plus.

 

[spoonbill8]

Re: prop size for 150 mercury on scout 192

Ok thanks! I could not come up with any optimal rpms in my search. I will try a run at 3000 to see what I get. On a 65 mile trip at 4-4300 I was getting 2.5. I will post results after my next trip!