Mercury 150 Fuel Mileage - 1971 20' SF
 

I have a 1971 20' SF with a 2003 150hp Mercury Saltwater hanging on an armstrong bracket. Does anyone have a similiar set up that could tell me expected fuel mileage a cruising speeds, WOT, trolling trips overall, etc.? Any help would be much appreciated. I'm guessing 2 mpg. Any advice on extra fuel storage without doing the obvious?

Thanks in advance!

That's a 2.5L block, so fuel economy is going to be more than a 2.0L 150. Prop the boat to turn 5800 and you should see close to 3mpg. I ran a 2.4L 175, 200 and 225 merc on an 18 and 20. Make sure motor height is perfect, find where you blow out and lower it one hole. Definitely put on tabs. Start with a 17P prop and tweak from there.

That is good news. I have lenco tabs and a four blade prop that I can turn 5800 rpm. Don't know the pitch on the prop though.

Perfect! I'd be willing to bet it's a 17P. Keep the RPM's around 3800 (30 - 31mph) and you'll see the best fuel economy.

I wish I knew my fuel economy I have a Merc XRi EFI 150 with a 19p 3 blade prop on my 20 my rpms dont pass 5100 if i really gun the throttle. With a full load i see speeds of about mid 30's mph on the gps but my fuel burn is just guess work at this point. I need better electronics i guess to help figure it out so I really cant help with exact numbers

Yea, I believe your XRi is a 2.5L as well. Maybe Bigshrimpin will confirm or correct that. If you have gps just run it off a 6 gallon tank and measure your distance for a gallon every 500 rpms from 3000 to 5800 rpms. Then do the math.

First you'll have to change your prop as you appear to be over-propped.

Pitch is only one factor in getting the right prop. What brand, model, and diameter is the prop? Al or stainless? Ask a boat/prop shop or friend to loan you a used aluminum 15 x 17 black max or black diamond Quicksilver # is1912 2X. I am certain you will see improvement in every performance category. That should get you closer to your target rpms and make your motor happier. And contrary to popular belief, you will likely see economy increase with less pitch. and the right prop. perhaps I overestimate that motor but I think you should see mid 40s at 5800 rpm on a 20 with that motor and the right prop.

150 XRi is a 2.5L. You need to prop the boat so that the motors turns 5800 WOT with average load. I suspect you can improve your performance quite a bit by raising the motor a few holes and finding the right prop. 5100rpm with a 19P is lugging the motor down too much and you'll get crappy fuel economy and performance. I could crack 40mph on my 20 MA with a 150xr2 and that's a 2.0L motor. The super long 150 tuner limits the top end on that motor a bit, but you should be low to mid 40's with a 2.5L 150.

I have a Mirage SS prop I am not sure on the diameter though. I dont really know anyone that could loan me a prop but I might just pick one up to test it out see what results i can get. Thank you for you information and sorry if I hi-jacked the thread



With myself and another person a light load and flat water i can hit 41 @ 5100. I didnt know you could run these motors safely beyond 5k. I will look into your other suggestions thanks.

I have seen 41mph on my gps (I think the tide was flying out and the wind was to my back). Usually my max is around 38-40mph though. Should I see better fuel economy and speed with a three blade prop? I know the four blade prop has a better hole shot and increases stern lift. I have one as a spare, just never used it.

What Tim said x 2.

The anti-ventilation plate should be at least an inch above the keel. Mirage is a good prop for that boat, but 19P is too much prop. Try a 17P if you can find a loaner.

Dave

Mercury 2.5L block is still the base for almost all F1 racing outboards.


http://www.youtube.com/watch?feature...&v=9ofyoovc6h8

http://www.youtube.com/watch?v=71pUV...ure=plpp_video

up to 7000rpm in stock form is not a problem . . . The manual for our fishing motors suggests 5800 for the max recommended RPM. You can go to screamandfly and read all you ever cared to know about these motors.

Oh man you should of never linked to the screamandfly site....... New reading addiction lol

I ran a '92 XR4 150 motor on my 20' Seafari for a number of years. Remanufactured by AAA Outboard and Machine and produced 192-194 hp on the hydro-dyno.

I had a prop custom made by Powertech, 15.25" diameter, 16.5" Pitch, fairly aggressive rake progression, 3-blades, polished. I changed my lower from the original small gearcase to a large gearcase off a 225 Merc, 1.65 ratio, with nose-cone and low-water pickup from Bob's (already on the lower when I bought it)

Amazing hole-shot, planing in just about 3 seconds lightly loaded, and still under 6 seconds with 9 people on the boat (4 adults & 5 kids).

Slow cruise was 28 mph at 3300 rpms and achieved 2.7 mpg on a Navman Flow meter. Fast cruise was 34 mph at 4000 rpms, 2.3 mpg. My normal average usage over all as 1.9 mpg.

WOT in the right conditions (45*F, downwind in 8kt breeze, light chop, only 12g fuel on board, was 48kts (53-54) mph at 6050 rpms

BTW, I now get 5.3 mpg with the same hull, at 24 mph, running a 90 Optimax.WOT 33-34 mph.

i have a prop you can try. i get 5700 out of my black max on my 20 sf.

That Mirage is a big prop Dia and aggressive pitch and cup, as mentioned too much - with a 17 Mirage for example you will get right at 400 more, raise the motor and anothe 100/150. I have a similar prop - Stilletto - smaller dia but similar that I just raised mine to 2+ inches above the hull bottom - still can't get it break loose = don't be bashful LOL the marina guy will look at you funny and try and talk you out of it but go 2+ trust me

see my post on the other prop thread for numbers, quite remarkable difference and I was already over an inch above.

BTW - Pipers Marine in Tampa had a used 17 Mirage+ for about 225, might still have it, good props but that makes them hard to find used - tell Ron or Chris the goofy SeaCraft guy sent you