Mercruiser 5.7

[cliffsorge]

Can anyone give me an idea what fuel consumption I should expect with a 5.7 Mercruiser I/O on a 24' boat

 

[ccscott49]

I'm sure there will be people who will know exactly, but it will use a bunch is a ballpark figure! tee hee. IMHO of course.

 

[BarryH]

What you should expect and what you actually get are 2 different things. There was a thread a while ago that gave a formula! as to consuption. If the grey matter remembers rightly, a 4 stoke inboard uses about 7 gals per hour for every 100hp. So as cc says "a whole bunch". but then what did you expect out of a 5.7 V8 yank tank.

 

[ArthurWood]

On a 29ft boat, I got about 19US(~15 Imp) gal/hr at 3200rpm with a Merc 5.7L on a lake which was normally flat water. Close to the formula above, but I think that applies at max hp.

 

[burgundyben]

Have you bought it?

I dont mean to start the many times fought petrol vs dielsel war, but....

I use about 5 gallons an hour in my 225 hp diesel, at about a quid a gallon. She 23ft and I get 31 knots.

If my fuel bill went up by a factor of 4 or 5 it would to some extent take out the joy of using the boat. I get from top of the Hamble to Cowes and back for lunch on about a 5er.

......girls, girls, get back, please, one at a time......

 

[Guest]

Don't bother trying to apply formulas. There are many factores which influence fule consumption - state of the hull and outdrive, number of people being carried, amount of fuel etc. The main thing is that you have a fair amount of grunt for a 24 ft boat. The most fuel is used when getting on the plane, given the power you will get on the plane much quicker than a similar boat with a smaller engine, on reaching planning speed it is then up to you but pulling the power off will be a great fuel saver, as long as you don't keep dropping off the plane and then having to power back up again! Crusing at about 25 knots should give you a fuel consumption of some 7-8 gallons an hour start pushing the power and then you will see the figures really go off the scale 15 gallons + you will need to "feel" the consumption thats best for you, pushing for an extra few knots could double you consumption and just by dropping the revs by 500 can result is very significant savings. BUT the carried by the boat - people, fuel, kit etc all play a signicant part in everthing.

 

[Guest]

Spot on. We had a Maxum 2300SC with a 5.7 Mercruiser. Displaced about 2 tonnes, and coul,d see off 18gph flat out, but more like 8gph if I could ever get SWMBO to stop leaning on the loud stick...

 

[BarryD]

Hi I had a 5.7 in my 25' boat - I saw about 8gph cruising / displacement speeds, and 17gph at at 6/8s throttle. We managed about 17kts in a F5 into wind / tide so a gallon a mile seems to be expected at speed.

The correct phraseology is "Are we insured..." NOT "Were we insured"
(IMHO, BTW, FWIW and NWGOI)

 

[KevL]

Are we talking 25 foot LWL or LOA coz I've got a 2556 which is 25 foot LWL with a 5.7L Mercruiser and if I could get up to 25 knots I'd be happy. 20 knots = about 20GPH, 15 knots = 10 GPH. Mind you this is a flybridge job weighing about 3 tonnes.

Hope that helps


--
Tides - Never there when you need one.
Wind - Always there when you don't.

KevL

 

[MapisM]

Is the boat you are talking about the typical target application of such engine?
Of course flybridges are in a different league - though, I would definitely recommend diesel engines for such applications...
By typical boat I mean a fast planing hull, open bow or with a small cabin, something that with an Alpha drive at the maximum rpm (4600 rpm or so) should reach about 40 kts?
If yes, then I fully agree with the 7-8 gals range (cruising speed, between 25 and 30 kts) which was already mentioned.
If and when used for waterski, add approximately another gallon.

Anyhow, it is also true that every boat/hull can be different.
If you look at the tests on the Mercury site you can get an idea:
http://mncfp.mercurymarine.com/boathousebulletins/default_display.cfm
Though they (even they!) do not report the consumption, the performance differences show you the meaning of that.

 

[dom]

I have same engine in 25 ft Searay, 2.5 tonnes, and calculations over the last 3 years have returned a regular 2 to 2.5 miles per gallon.
Have also established the following.
Cruise at 1000rpm and double the above figure, (but not much fun)
Cruise between 2000 and 3000 and halve the above figure.
The 2.5 mpg applies at 1750 rpm at 7-9mph and 3500rpm at 25-28mph

 

[Chris771]

You could always buy my 23' 6" Skibsplast 700 Hard Top which does about 4 galls/hr at 24 knots or 5 at 27, all with a nice simple shaft on a 140 Yanmar diesel.

As burgundyben said, spending 4 times as much on petrol takes a lot of the pleasure out of boating.

Even for my new boat I am buying an Antares 760 which should do 18 kts at about 5 galls/hr on diesel and only about 9 at 25 kts.

Chris