Cruising Range... for Dummies

Northern Pike

New Member
Mar 12, 2007
7
Montreal, Quebec, Canada
Hi All,

OK, so I'm finally admitting power is more practical then sailing up here on the St Laurence...

I'm trying to figure out the cruising range on a 250 Sundancer.

Mercruiser 5.7 engine, 70 gallon tank
3000 RPM produces around 23.5 MPH

Assuming no wind, no current, no waves... how far do you think I can get on 1 tank of gas?

Thanks!
 
How do you currently track your usage, hours or miles on a GPS?

I am going to assume miles on a GPS but you can convert to hours using the below described information if necessary.

Fill your tank to the top. Set your GPS trip odometer to 0. Run until you are in need of a refuel. Take how many miles you went per the GPS and divide by the gallons to refill your tank.

I am going to estimate that when you do this you will come out to close to 2.3 state miles per gallon. Of course this is a my estimate based on my experience around boats of various size and various engines. Too many variables to get you an exact without doing the above exercise. One person that is a pack rat that has a full crew and a ton of supplies versus another person all alone with minimal items on board will get different results. Ditto on one boat with bottom paint and another with none.

So given your 70 gallon tank your maximum range is about 70 x 2.3 (or what you come up with) or 161 state miles.

Now at this point you run out of fuel. After you determine your actual MPG the real question is what is your risk tolerance.

A conservative estimate is the rule of 3rds. The means you use no more then 1/3rd of your range to get out, 1/3rd to get back and have 1/3rd in reserve.

Using a more aggressive calculation you take 90% of the calculated range to empty. So using the above estimate of 161 miles x .9 = 144.9 state miles range. This assume there is a place to get fuel at the other end and you have no bad weather, don’t get lost, every thing is perfect.
 
That could vary depending on which 5.7L. What's the horse power of yours?


chazaroo
 
I am still working on the purchase price itself... meantime trying to "sell" my wife on how far we can cruise up the St Laurence!

So I don't have the boat (nor the GPS) yet, but the engine is a Mercruiser 5.7LX 250HP Bravo III
 
There are a whole lot of variables, which is why it's so difficult to come up with an accurate number. Having said that, our boat has gotten 2gph when cruising at 5-6 knots. We just got the boat in mid December and have spent a lot of time cruising slowly (in Florida). At that speed, your cruising range is 175- 210 miles. But it will take you a heck of a long time to get there.

Having said that, I think the calculations made by Presentation are probably a good indication of what you can expect.

Regarding convincing the wife:
My wife and I discussed getting a boat for three years AFTER putting in a dock. She finally OKd the deal and we both love it. She now says we should have done it years ago.

Chazaroo
 
chazaroo said:
Regarding convincing the wife:
My wife and I discussed getting a boat for three years AFTER putting in a dock. She finally OKd the deal and we both love it. She now says we should have done it years ago.
Chazaroo

Hey... sounds like your wife and my wife should talk!

Thanks Chaz
 
Presentation said:
A conservative estimate is the rule of 3rds. The means you use no more then 1/3rd of your range to get out, 1/3rd to get back and have 1/3rd in reserve.


I like this one. Your boat probably burns around 12 Gals per hour at cruise. That's just under 6 hours. So 2 hours out 2 hours back and slighly under that for battling the wind, waves or tide (although it looks like your on a lake...
 
The critical dimension here isn't the size of the boat, engine, tank, wind, current or waves!! It's the size of your CREDIT CARD!!! The other factor is the location of fuel docks. If there is a fuel dock every 10 to 15 miles, don't sweat it! Just note the prices on the way up and stop at the cheaper places on the way back. You'll get better mileage per gallon with only half a tank on board anyway. Just think 35 fewer gallons is the equivalent of one extra 210 lb person on board. So if you are concerned about mileage, throw everything off the boat! :grin:

Our 250 gets just over 1 mpg. There isn't much difference between running at 1000 rpm or 3200 rpm mileage wise. I keep telling myself that is just HAS to be better 1,100, but I'm pushing all that water out of the way. At planing speeds, I'm pushing less water but more wind. I quit worrying about mileage and I have a whole lot more fun on the boat. If it were me and I had to travel a long distance, I'd use diesel and get around 13 miles per gallon with the boat going around 60 MPH three feet off the ground. :thumbsup:
 
Sundancer said:
......Our 250 gets just over 1 mpg......

Northern Pike, please do not let this scare you off.

Like so many things in life, fuel usage is a bell curve.

Sundancer has a big engine however even given this his stated usage of 1 mpg would be at the very high usage side of the curve. Given this I have to assume there is more to the story like a poorly tuned engine or he’s pulling a wake boarder or is boating up a hill or his slip neighbor has a siphon hose. :smt043

Another ‘rule of thumb’ and this is a very ruff one, only to get you in the ball park, is assume a gas engine, running at normal cruising speeds you take 14,500 divided by your total weight in pounds of your boat + everything on board and this is about what your MPG would be.

A 1996 250DA is 5,200 dry. Adding a reasonable 1,100 lbs for fuel, water, gear + passengers and you are at 6,300 lbs. 14,500 / 6300 = 2.3 Miler per gallon. Again it’s a ruff estimate.
 
I have a 250. I have to agree with the 2.3 number. I haven't done scientific research, but after 10 years on this boat, I've always thought that it was around 2.5, but the charts lean more toward 2.25, so 2.3 is probably a good number.
 
1.2, 1.7 whatever it takes!! Four people on board, loaded to the gills, dogs, sinks, kayaks, a cooler full of ice big enough that you can sleep on and enough canned food to live for a month! I can't get my wife to just buy it as we need it. Nope, she loads that sucker to the gills! I probably picked up a good 1 mpg when I leave the trailer attached to the truck instead of the boat when I leave the dock. :smt101 Seems to go MUCH faster! We usually turn between 3,000 and 3,300 rpm which is a 24-28 mph cruise speed depending on conditions and my calculator doesn't do tenths, what can I say? :cool:

It does sit on the trailer all week and I don't recall EVER seeing the neighbor put gas in his lawnmower? Hmmmm.... Maybe we're onto something here? :smt017

I did replace the original plugs, wires, cap, rotor and all the rest when we bought the boat in 2000? Doesn't that count as a tuneup? Only 220 hours on it back then. We're just a tad over 400 now! It is a little annoying when I gun it to get on plane and my neighbor starts counting slowly, $1, $2, $3! It is ready for another tune up. The 454's eat plug wires! I just figured that was par for the course mileage wise at 3,000 feet above sea level. Our old outboard, was much better, but much smaller and lighter. It seemed reasonable based on all the other folks I talked too, so I never gave it a second thought. I still haven't!
 

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