15' McKee... gas hog?

[NEStriper]

Hey guys.

I'm running a 1977 15ft McKee craft, tri hull. I'm quite certain it has a fair amount of extra water weight, but I have never weighed it, so I have no idea how bad the problem is. She sits maybe an inch lower than you'd expect for a boat this size, but this is just a guess.

It's got a 2stroke 50hp Mercy on the back, 1980's era.

From my very rough calculations, she's getting around 3-4mpg, which includes some idling and time spent not on plane. I usually go near wide-open to get her on plane, which is less than 5 seconds, then throttle back until she's just on plane to save on gas. This assumes no chop on the water, for which she needs a little more gas to stay on plane. The outboard has treated me great, idles well (will every once in awhile stop mid-idle), accelerates without a hitch, doesn't seem to struggle at all back there. I run 89, but I doubt that would make a lick of difference in efficiency.

This seems low for such a small boat and outboard. Are these old Merc 2 strokes just gas hogs? Is it the extra weight in the boat? I don't have my tach installed yet, so I cannot comment on RPMs. The prop is very slightly chewed up from the previous owner. No clue on pitch.

Looking forward to the responses.

 

[SigSaurP229]

Re: 15' McKee... gas hog?

To calculate rough gas mileage,

You will burn 10% of the maximum horspower in gallons per hour.

So a 50 hp will burn roughly 5 gallons per hour at wot

 

[airshot]

Re: 15' McKee... gas hog?

Sounds about right, OB are not fuel efficient critters especially the older 2 stroke.

Airshot

 

[H20Rat]

Re: 15' McKee... gas hog?

So the OP's boat probably does about 30 mph at WOT. If he is estimating 3-4 mpg, that 7.75-10 gallons per hour. If you go by the 10%/hp rule, you are using quite a bit more fuel than you should.

OP, instead of estimating mpg's, which is a car measurement, go for gph, gallons per hour. The best is with a fuel flow gauge, but those are $$$. Instead you could rig up a gallon tank and hold her wide open and time it. All in all, I'm guessing you probably are using pretty much exactly what you should be. Older 2 strokes, irregardless of brands, are not exactly fuel efficient.

 

[NEStriper]

Re: 15' McKee... gas hog?

Does a gas tank get more or less sucked dry? Could I put a gallon in my 6gal fuel tank and run her till she sputters, using that time as a benchmark?

Thanks.

 

[crabby captain john]

Re: 15' McKee... gas hog?

I had a 17' McKee and the minimum suggested HP was 90. My GUESS is the 50 is the minimum on the 15'. Your hull is built like a tank! It is heavy and a tri-hull has more resistance in the water than a mono-hull. What makes you think there is water intrusion? Blisters? Intrusion in a hull that old would not be a shock as it could come from screw holes where the fasteners worked lose. It is just as likely a 20 - 25 year old Merc is tired. Enjoy the boat from one of the best builders ever.