Fuel Consumption for twin V8

[subra]

Hi, Sorry that my first post is so ambiguous.

Im looking to buy my first boat in the next few weeks.

One that looks suitable for what i need is fitted with twin Mercruiser 5ltr V8 petrol engines. Its a 30ft hull.

I am hoping to get a lot of time out on this boat (i bet thats what we all say) so fuel consumption is something i want to pay attention to.

Does anyone know a rough GPH or MPG figure for this set up?

I have done a lot of google research and it looks like im looking at 10-15 GPH per side which seems high to me?

Thanks for the help and advice, i hope to contribute myself here over the coming years.

 

[BruceK]

Seems a bit low to me unless you plan on just keeping on the plane. I'd expect more than 15 gallon per hour per engine if you plan on being ambitious. here is a link you may find useful. note US gallons not imperial

http://www.boat-fuel-economy.com/mercury-mercruiser-twin-engine.html

 

[oGaryo]

I used to own a 25ft boat with a single V8 merc and recall it requiring go juice regularly which involved emptying my wallet somewhat.. 2 x would make me shudder a little. Sorry I cannot be more specific, I am somewhat head in the sand when it comes to this aspect of boating considering the extent of other expenditures (berthing costs, maintenance, keeping the fridges full of booze .. Hopefully someone will be along with real experience advice of owning a 30ft boat with twin V8's.

p.s. 30 something ft is getting pretty close to the magical 10m LOA mark, magical because it usually triggers a significant hike in cost per metre berthing. I would also ask yourself whether you need the additional LOA when for your money you may be able to come down a metre or so in LOA to fund purchasing boat that meets your needs with diesel engine(s)

 

[kashurst]

wise words from previous posters - you might want to check just how much petrol your potential purchase will get through. Also depends where you are in the world. If your in the Gulf or Venezuela then go for it. If your in Western Europe you might want to rethink. Another thing not every marina sells petrol either so this can be an issue too. Check out any potential destinations.

 

[subra]

Thanks for the replies,

Bruce the link you directed me to is very useful thanks. Its telling me that i may be looking at a consumption of 37 gallons per hour. Converted this works out to be around 140 litres burned per hour.

So am i correct in thinking at the running cost for this boat will be around £155 per hour? Ouch!

Gary, the berthing for this boat stands around £1700 which i think is ok, there was no mention of any price hike, perhaps im inside the threshold.

Thanks

 

[[2068]]

30 gallons per hour for two 5.0 MPI's at a fast cruise won't be far off.

.

 

[BruceK]

I would also ask yourself whether you need the additional LOA when for your money you may be able to come down a metre or so in LOA to fund purchasing boat that meets your needs with diesel engine(s)

Having just come out of the market searching for boats of this size I was initially very pro petrol engined examples. The reasons being that the boat I could afford (35k) would be old to start off with and if the engines died petrol would be by far cheaper to re-engine if neccessary. And I understand petrol engines intimately, not so diesels. All the diesels in my price bracket were so ropey that I simply couldn't take the risk and would live with the added fuel cost of petrol. Diesel boats were significantly more expensive than their petrol counterparts like for like or for my pound equivalency I got a better boat with petrol engined examples. So petrol it was. Then I looked around extensively and spoke to a lot of sellers of petrols about their consumption, did the math of per annum cost using the 50hr p.a. average and the cost for petrols simply scared me into buying diesels. Finding the right diesel for my limited budget was another matter entirely. Loads of miles, even more dissapointment. But I got there in the end....touch wood. The figures the OP posted are very realistic erring on the optimistic side but I hope I am proved wrong. My 34 foot hull on twin diesels will do 8 Imp Gal per engine per hour

 

[lynall]

23 ft with the v6 4.3 ltr version full chat 30 knots 13 gph, so add a bit for the extra 2 cylinders then double it, then run away very very fast!
1/2 gallon per minute
Got to be almost impossible to sell on?
Pottering along 6/7 knots 1.5/2 gph, 4.3 v6
Just on the plane which from memory was 20 knots give or take and throttle back so it just held it 7/8 gph, 4.3 v6

 

[Flynnbarr]

This thread reminds me of when I did my VHF course many moons ago and on the course were a very nice couple,new to boating who had just bought their 1st boat and were v.excited to say the least to expand their horizons and go round Britain,Europe,visit basically everywhere once they'd done all their courses.
When I asked them what boat they'd bought and they replied a twin v8 Searay,I asked if they knew how juicy they could be,obviously being diplomatic,not wanting to shatter dreams.
Oh no it's fine,the broker has assured us she is really economical.....

 

[epervier]

Your boat will probably have an extra gauge fitted on the helm console, it should look something like this,

 

[darrenw]

Converted this works out to be around 140 litres burned per hour.

So am i correct in thinking at the running cost for this boat will be around £155 per hour? Ouch!

Thanks

I think you're basing your calculations on garage forecourt prices, as you're suggesting £1.10 per litre.

I'm relatively new to boating and one of my first reality checks was that marina fuel is priced differently, with diesel being offered at less than petrol and the latter at significantly more than forecourt prices.

Just as an example, here's an excert from Cowes Harbour Fuels website...

Marine Fuel (per litre)
Diesel - Commercial £0.72
Diesel at 60/40 - Propulsion/Domestic £1.02
Petrol £1.37
Prices correct as of 23rd April 2015

So your 140 ltrs ph is more likely to cost circa £190 rather than £155.

The ruse with diesel being cheaper is that 40% of the tank is used for onboard heating, so VAT isnt applicable.

So you've a double whammy with petrol engines.

V8s do sound good though !

 

[[2068]]

Contrast the above figures to a similar sized boat (mine) with twin diesel engines.
Top speed 34kts.
Each engine burns something like 20-25 litres per hour when cruising.
So maybe £50 per hour in total.

Petrol engines sound amazing: they are fine when there's just one of them, in a smaller boat (e.g. up to 24ft), and when you're not going too far.

 

[Spi D]

For the scientifically interested fuel consumption relates to the work performed by the engines. RPM alone tells you nothing without this parameter.

A classic petrol engine will burn approx. 250 grams of fuel pr. kW per hour. Factor in the density of fuel and kW/hp ratio to get a result.
http://en.wikipedia.org/wiki/Brake_specific_fuel_consumption

Planing boats will return best mpg at just above idle or at the lowest speed where it stays on a stable plane - which is notably less than full throttle on boats with a fair amount of power. At the end of the day the cost is in the hand of the driver. Of course all the wonderful times anchored or berthed does not count in this regard

 

[Greenheart]

Prices correct as of 23rd April 2015...So your 140 ltrs ph is more likely to cost circa £190...

What's that...slightly over a tenner, every three minutes? Hmm...must be like traveling everywhere in three Bentleys. :hopeless:

 

[zapcat]

I have 2 x new 5.7s running through dp290 drives running in a 25ft deep V hull, a Triana Tropica. We used her last year for the first time after the rebuild, and didn't consume as much fuel as I anticipated. I had a temporary 96 ltr tank in the saloon at the time which when full wept fuel, and when about 1/4 full surged as there were no baffles.

I think it depends on what you are planning to do, and how far you intend to go. Our typical 'day out' last year was motor for about half an hour (30-35kts) anchor up and then motor back later with some diversions on the way etc. This would be something like St Just in Roseland to Helford, and back via Falmouth, and fuel used would be around 70 - 80 ltrs. Critical to our consumption was not opening second chokes! We were running in to start so keeping the revs low and due to incorrect prop size max we could do was 45knots which was on redline but not WOT - as we redlined the chokes were just opening. I have new larger props and fuel tank for this season so when we launch Monday (yay) we will see what we have achieved.

We spent a whole day out for the start of the Tall Ships, did the entire circuit a couple of times and a lot of motoring in between, came back from the start line at full tilt and then up to the Pandora in Restronguet and used a total of 160ltrs. This is an accurate figure as we had a total of 196 litres on board (main tank and 4x jerry cans) and ended up with just under half the main tank at the end. We always refuel from cans and at £1.20 ish, thats about £200 - and on that occasion it was split with friends.

I will update and try to put more accurate figures on this later this month, but for us and our useage, this is an affordable guilty pleasure!

 

[julians]

I had a single mercruiser 5.0v8 in a 21 foot sea ray, and it used about 30-35litre per hour at abot 20-25mph and about 55-60litres per hour at full throttle(about 45mph)

I now have 25foot boat with a volvo d4 diesel which uses about 20-25litres per hour at 25-30mph, no idea what it uses at full throttle. The new boat is noticably cheaper on fuel ,but seems to make up for it in increased maintenance costs.

 

[oldgit]

Run Away...Now.
Suprised they can even give that boat away.!
At some point you may well want to move upmarket.Fuel prices will rise again from the temporary low at the moment.Until recently petrol could have cost you £1.60 + at some marinas.....Think about trying to sell it on then.
During my boat buying escapes could never work out why certain boats were absolutely immaculate,very underused and seemed to represent extremely good value for money...Bargains in fact.
Then it dawns on you at some point the previous owners (usually lots of them) could never afford to use the blimming things and were desperate to unload the thing onto the next mug.
Dont let people kid you you can use supermarket petrol,the amount they guzzle will be nightmare to carry around and if the cashier catches you trying t0 fill cans,they will run out and stop you.

 

[zapcat]

I disagree totally (with the exception that fuel will rise, and not just petrol) - I have never been stopped from filling up 4 cans, and also have never had to fill more than four in one go - and I am talking from experience!

 

[lynall]

Sainsburys Allington guy came out and said I could not fill up my 20 litre jerry can, as he was telling me I was still filling it up!
But never had any issues anywhere else, but the 20 litre ones are pita to carry around especially 2, the 10 litre ones much easier.
I filled up car yesterday and noticed fuel prices are on the way back up again!
I can remember Gillingham marina petrol was over 1.50 a litre 2 years ago.

 

[skipmac]

Owned a 25' deep V boat with twin 4.5L V8s. Average was about 4 liters per mile. This was a smallish boat without a bridge and no real cabin. My son in law has a 25' cabin cruiser with head, small galley, etc, very heavy boat. Has a single 7 Liter V8 and burns a good bit more than my twin engine rig and doesn't go nearly as fast.