80-81 Merc 50 MPG

[andrewkafp]

What sort of fuel economy should I be getting from a 50hp Merc on a 14.5 ft F/glass boat 2 on board ? Is there an optimum RPM or speed to stick to, to get the best range ? <br />Speed is something I'm not interested in.. just max distance.<br />This is a dual carb 2 stroke, and I reckon she'd be lucky to get 10 Kn P G at the moment at above 4,000 RPM. That's thirstier that a Large pickup with a 454 Chev ...

 

[Clams Canino]

Re: 80-81 Merc 50 MPG

Without knowing the exact ratios. I can tell you that boats have a LOT more resistance to forward movement than a car and require a lot more fuel per mile to keep them moving. Yours doesnt sound unusual at all.<br /><br />-W

 

[ZmOz]

Re: 80-81 Merc 50 MPG

Yeah, my 16' with a 150hp Mercury gets about 3mpg. The best range would probably be the slowest RPMs you can plane at. One of those hydrofoil things you bolt on to the motor is suppost to help fuel mileage...

 

[andrewkafp]

Re: 80-81 Merc 50 MPG

Thanx Clams/ZM<br /><br />Got this from OB Repairs. <br /><br />"The rule of thumb is 1 gallon per hr for every 10 hp at WOT. The boat only affects the speed hence mpg that you get. "<br /><br />My top speed is say about 30 KnPH <br />50 HP motor .. so 30 Nautical miles (34.6 miles)<br />will burn 5 gallons <br />6 Kn per gall or 6.9 mpg at full throttle. <br /><br /> <br />Conclusion.. Go slower, Don't go as far, or get bigger tank.

 

[dilligafda]

Re: 80-81 Merc 50 MPG

I've never seen MPG spec for anything - it's always been gallons per hour. And a good rule of thumb is 10% of the horsepower = gallons per hour.<br /><br />Example: 50HP engine running at wide open throttle rpm of 5500 will use 5 gallons of fuel per hour. <br /><br />Of course this is a rule of thumb and should not be used as fact.

 

[andrewkafp]

Re: 80-81 Merc 50 MPG

Can't say that I have seen Marine fuel economy in MPG either, however it<br />it much more useful when checking how far you've gone and how much fuel is left.<br />Can't believe how thirsty they are.. <br /><br />I hear these are quite economical<br /> http://home.jps.net/~rrloesch/outboard.htm

 

[Greg New Zealand]

Re: 80-81 Merc 50 MPG

Hi Unicorn. Your results seem OK. I have a 13' 2" Fibreglass boat with 1977 Merc 50 hp and my sounder log has been giving me similar figures. Still not bad economy as I can go a long way on a tote tank of gas.

 

[andrewkafp]

Re: 80-81 Merc 50 MPG

Greg<br /><br />Still getting used to this water thing.. <br />You get a small 50hp car and it'll do 30 MPG.<br />Whereas a boat is much less efficient. Suppose there is one upside. The carbies are getting a whole lot of filtered clean fuel through them in a short space of time which would go a long way to keeping them clean.

 

[Greg New Zealand]

Re: 80-81 Merc 50 MPG

I think Clams has the right answer - its about input energy, resistance and created motion. Doesn't take long for my boat to stop from WOT back to idle. Perhaps if we can get the whole hull out of the water then we would get much better economy?!

 

[Clams Canino]

Re: 80-81 Merc 50 MPG

But I'll add this. The best fuel economy is had at "cruise". This is that magic throttle setting where the spark advance is full on, but the carb butterflies have only cracked a bit, right before the 2nd pickup hits them.<br /><br />If you can keep the boat up on a good plane at this throttle setting, that's your best economy.<br /><br />This is why underpowered (and incorrectly propped) boats burn more gas. If you need WOT to keep a good cruise up on plane, your wasting a lot of gas.<br /><br />-W

 

[ZmOz]

Re: 80-81 Merc 50 MPG

Originally posted by Greg New Zealand:<br />I think Clams has the right answer - its about input energy, resistance and created motion. Doesn't take long for my boat to stop from WOT back to idle. Perhaps if we can get the whole hull out of the water then we would get much better economy?!

You mean kinda like this? <br /> http://www.screamandfly.com/home/videos/video_day_9_2003/video_day_9.2003.wmv

 

[Greg New Zealand]

Re: 80-81 Merc 50 MPG

Yep ZmOz that looks pretty efficient to me. May not be suitable for windy days though!

 

[andrewkafp]

Re: 80-81 Merc 50 MPG

ZM<br /><br />You are a true MERChead...

 

[ZmOz]

Re: 80-81 Merc 50 MPG

Hehe...I'm seriously thinking about taking out a loan and getting a hydrostream like that brown one in the video...