Fuel burn question.

[CHANCE1234]

Denny, again an awesome reply. It will take me many reads to digest all the info you provided but I will do it. My av plate is 1 inch above the keel. I'll take a look tomorrow while running and also try to set a trip gauge on my gps and monitor cruising rpms and knots. I swing a 13 3/4 X 15 merc prop from,west marine. I'll look through the book tonight for wot and optimal.

[Bushwacker]

That's the same size prop I ran on my 115; it was an OMC SST and was perfect for heavy loads - used to turn up to about 5400-5500 with a 2:1 gear ratio. Your boat is probably lighter and that more modern motor is rated at the prop instead of the powerhead, so if your gear ratio is the same I would think you could turn a little more rpm. If it overrevs, a good prop shop could put a little more cup in the blades to knock it down by 100-200 rpm which would also help efficiency, but you need to the motor height right and check the tach before fooling with the prop.

I used to figure about 8 gallons/hr at 4500 rpm and 20 kts. We didn't stop much on those trips, running for at least 3 hours at a stretch, so that may be why my gas mileage was a little better than Gillie's. Stopping often and climbing up on plane again burns lotsa gas!

[McGillicuddy]

Originally Posted by CHANCE1234

Denny, again an awesome reply. It will take me many reads to digest all the info you provided but I will do it. My av plate is 1 inch above the keel. I'll take a look tomorrow while running and also try to set a trip gauge on my gps and monitor cruising rpms and knots. I swing a 13 3/4 X 15 merc prop from,west marine. I'll look through the book tonight for wot and optimal.

If you're running the Quicksilver Black Diamond, I think that's about as good as its going to get unless you ante-up for the stainless version, the PowerTech MQF3 or 4. I may be mistaken but I believe yourl motor was known a 2+2. Designed for bass fishing circuit, it used a funky cylinder/carb deactivation where in idle it would burn on top 2 cyls, and when it hit around 1800 rpm, the lower 2 would kick in and it would take off. Kinda no mid-range slow putting - slooow or GO! Sloppy idle but nice at cruise. It's very possible that the carbs could be re-jetted for better efficiency with modern fuel. 2.07 gear ratio I think, 5200 rpm target should be about right w that prop.

Glad you got good insight on the vent burping issue -- good call, y'all.

I use a Navman fuel meter, very similar to Lowrances current version to keep me in the loop on fuel, but a 6 gallon portable tank should get you to P'town easy. Might be worth rigging just to see if your motor is burning right. I think you should see over 3 mpg overall as that idle burn with 2 cyls. should be much better than what I could ever hope to see in my I-6.

Lots of god stuff coming out of this post. Thanks, and good luck

[CHANCE1234]

Thanks for all the replies on this and I agree, there a lot of good info on this. Today I started with a full tank, 49 gallons. Cruised to ptown at 4200 rpms, bout 18 knots cause of some slop up to ptown which is 18 miles away. Cruised around trying different spots, trolled for a few hours drifted for a few more hours, ran up to peaked hill bar and trolled spreader bar at slack, ran 20 miles back to Barnstable at 4400 rpm at 23 knots. Trolled around the channel there for an hour and cruised back to the pier. Best I can figure is 50 miles, mostly running pretty good. Tank still above half. I put new spark plugs in yesterday and it was good I did cause they were bad. Now she starts a lot easier and prob helps my fuel a little.

My engine does go from slow to fast with not much I between, just thought that was a quirky 23 year old engine thing. Great info everyone. So I'm guessing I burned 23 gallons over at least 50 miles. I can live with that...

[CHANCE1234]

I forgot to mention how awesome the ride was this morning when it was sloppy out there up to ptown. I found myself saying any other boat would turn around or slow down to 10 knots. Didn't even feel em when I took them head on. It's only when I took em off the starboard bow did I notice it was rough when I noticed a lot of water hitting me in the face. Great ridding hull, a little wet, yes but what a ride! Can't wait till my buddy puts his 23 Parker in the water and runs next to me in my 20 in some cop. I'm curios how we will compare