Fuel Consumption

[markanddawn]

Hi Forum

I have recently joined the forum and have found browsing the topics very interesting, thank you.

As a converted raggie, I am wondering what the consumption of my petrol engine is likely to be during an average weekending. The boat is a Maxum 2300 SC running a 5.0 Mercruiser on carbs through an Alpha 1 Gen 2 stern drive. The specs I can google say up to 22 gallons per hour flat out but of course, we all know that you do not run flat out all the time.

Just a ball park figure, cruising ground is Bristol Channel from Penarth, South Wales.

Heres hoping a motor boat will allow more flexibility, not having to consider the notoriously fast channel tidal flow as much as when relying on a stick and rag.

Thanks all.

[Rinker]

That's a fair size engine in your boat and it is not stressed so it will be relatively economical when cruising. I should imagine that you should be able to cruise across to Weston on a couple of gallons at 20 knots or thereabouts. Open the throttle and it's a different story.

[baasboat1]

Hi MarkandDawn

I have had a look on www.boattest.com to see if yours is listed, the exact model isnt, but they do have a 2200 with an efi engine as the nearest one. The figures they publish for my searay are pretty accurate so this would be a good guide for you.

http://www.boattest.com/boats/Boat_video.aspx?ID=597

Their figures are:
Maxum 2200 SR3 (2009-) Test Result Highlights
•Top speed for the Maxum 2200 SR3 (2009-) is 49.9 mph (80.3 kph), burning 19.3 gallons per hour (gph) or 73.05 liters per hour (lph).


•Best cruise for the Maxum 2200 SR3 (2009-) is 35.6 mph (57.3 kph), and the boat gets 3.42 miles per gallon (mpg) or 1.45 kilometers per liter (kpl), giving the boat a cruising range of 154 miles (247.84 kilometers).


•Tested power is 1 x 220-hp MerCruiser 5.0L EFI.

hope that helps

regards

Baasboat1

[markanddawn]

Thanks again for the information. Scary stuff, fuel prices when you are used to a sail and 7hp diesel!

[cobraphil69]

Yes scary!! just keep putting it in fun factor that matters ,plenty off time when it runs out or too old to fly about .Then think about how much we all spend on the stuff

[baasboat1]

I don't consider my carbon footprint, its more of a carbon crater anyway!

[Centaur]

As an educated guess, I would expect that you will achieve 2.0-2.5mpg as an average. You might get close to 3.0mpg if you do a lot of cruising at or around the sweet spot - about 26-29mph. Gallons per hour is a bit misleading as it clearly depends on how fast you are going! Flat out you might use 80-100 litres per hour but I would expect that you would only use about 15 litres per hour with a mix of cruising and trundling at displacement speeds.

The average boat only does about 50 hours per year, so at 20 litres per hour this would still only be 1,000 litres. Therefore, the fuel cost probably won't be the single largest cost of ownership - not insignificant but, in comparison with any other hobby, not collossal...!

[baasboat1]

I filled my boat up at the weekend - it was only half full but it was quiet on Fri morning so thought I would beat the mad Saturday rush (106 litres of unleaded from the marina at £1.40 per litre...ouch.

I have worked out that over the last year I have run the engine for 34 hours at an average cost of £11.93 per hour for a 5 litre V8 in a 22ft searay. To be fair, I dont go hurtling round skiing and spend most time at 3,000rpm pulling 28 to 30 mph which is very comfortable cruising, i do have the occasional mad half hour going fast but most of the time I just cruise, so overall £12 per hour in fuel is less than I thought it was going to be - which is a nice surprise.

Baasboat1

[JORIDAPILOT]

I have worked out that over the last year I have run the engine for 34 hours at an average cost of £11.93 per hour for a 5 litre V8 in a 22ft searay. To be fair, I dont go hurtling round skiing and spend most time at 3,000rpm pulling 28 to 30 mph which is very comfortable cruising, i do have the occasional mad half hour going fast but most of the time I just cruise, so overall £12 per hour in fuel is less than I thought it was going to be - which is a nice surprise.
Baasboat1

Last year we averaged 3.6 gallons per hour at a cost of £18.40 per hour. Not too bad, I guess. We have the Mercruiser 5.0litre MPI V8 pushing a 24foot boat probably close to 3 tons loaded.
We always have 20 -25 minutes at 6 knots at the start and finish of the day and this can easily be 20% of the days engine hours so it is a case of mixed revs, I like to cruise at 20 - 25 knots as the boat doesn't have a tendency to drop off the plane too easily then.

Would I be right in assuming that the best fuel consumption is at maximum torqe of the engine or are there too many other factors to take account of in a boat?
I always like to drive a car at max torque, then the blue lights can't catch me.

[Ed]

The engine itself is most efficient around max torque. However the boat won't be. From fuel data it seems that slow displacement speeds at pretty much idle is the most efficient way to get about! I think the most efficient on plane speed is one just where you're cleanly on plane with as little power as you can get away with.

[baasboat1]

ok, should have put it as litres per hour as well as cost, so it works out as 9.07 litres per hour or 2 gallons per hour

[Centaur]

9lph with a 5.0 V8 - wow! The best I got out of a 3.0L 4 cylinder Mercruiser in an 18' bowrider was 10lph and averaged 13.7lph...!!!

I do use my boats for watersports though... towing must cost more than you think!

[dpb101]

Her, if it works is a fuel economy graph for my boat:

G is mph
H is mpg

Bayliner 652 with 3.0L 135hp engine

[Ed]

Thats a detailed plot. Did you do this yourself with data picked up from the engine etc?

[baasboat1]

I know when I was changing boats, my old Fletcher 18 had a 4.3L V6 and the dealer told me that by moving to a 5.0L V8 even on a bigger boat I wouldnt use much more fuel. My V6 had carbs and the V8 has fuel injection, even with a much larger and heavier boat it didnt really go up.
When I moved from a Fletcher 15 with a 90HP Mercury to the V6 my fule consumption went down, which I really couldnt get my head round at all, how does going from a 1.3L 3 cylinder to a 4.3L V6 cause the fuel burn to drop even with a heavier boat. Well a mechanic explained it to me that the outboard was a two stroke and I was probably running at much higher revs (from memory I used to run at 4,500rpm normally), then the V6 only needed 3,500 rpm to cruise, then the V8 only needs 3,000rpm, so the engine is running slower and burning less fuel. The two stroke was a 1988 so quite old in fule technology terms and not that efficient (though dam good fun at the time!), the V8's fuel injection is substantially better than the V6 carb's. Strange but true I know.
So working on the principle, my next boat needs to be a pair of 8.2L V8's and I will be sipping the unleaded at a miserley rate....not!

regards

Baasboat1