Petrol Outboards v's Diesel Inboard 8.5m Rib

[Ashton]

Does anyone have any fuel consumption comparisons on single or twin outboards v's inboard diesel.

I am considering twin 150 or 225hp outboards (perhaps four stroke) v's a single diesel sterndrive on an 8.5 m rib.

The rib will be coded and used commercially, thereore I'd be in a position to claim the duty back on the fuel.

Any other thoughts would be appreciated.

[jwalker]

8.5mtr approx 350hp diesel, 2800kg returns about 1 mile/litre. Approximately the same as a 6-6.5mtr rib with medium outboard.
I can't imagine a couple of 200hp petrols can get near that. However, performance will be different.

Availability of petrol and how much you enjoy carrying jerry cans may be more of an issue.

[Ashton]

Do you run commercially? If so, what is your net diesel price £/L currently?

[jwalker]

Originally Posted by Ashton

Do you run commercially?

Nope, I don't. Purchase price of diesel varies daily. For commercial use the duty is 10.07p and vat is 5%. Today it was 36p/lt +vat here. For leisure use it would be the 36p + 42.28 duty + Vat.
But, looking at your profile, I presume you know all this.

[Ashton]

Can any outboard powered operators shed some light on consumption an on fuel purchase? All help/advice welcome, however trivial you may consider it!!

[doggypaddle]

Originally Posted by jwalker

8.5mtr approx 350hp diesel, 2800kg returns about 1 mile/litre. Approximately the same as a 6-6.5mtr rib with medium outboard.
I can't imagine a couple of 200hp petrols can get near that. However, performance will be different.

Availability of petrol and how much you enjoy carrying jerry cans may be more of an issue.

a mile a litre holy crap i dont get that out of the 5.4 with the yam 80.
i knew there was a reason i wanted a bigger boat with a nice turbo diesel V8. i could have a wheel house with a heater too...........

[jwalker]

Originally Posted by doggypaddle

... i could have a wheel house with a heater too...........

Of course you could!


And then you'd be able to buy some cheaper fuel too.

[Brian]

I also use less than 1 litre per mile. This is on an 8.75m with 315hp Yamaha inboard.
I take what JW says as accurate..........but aren't there other arguments if running commercially.
Specifically: availability, you can stop a fisherman miles offshore and ask for some fuel. You can also get it dockside in a very large number of places. I can remember getting some from a tiny, tiny fishdock inside Loch Roag once.
Also, maintainability. You can swap an outboard fast and get back to work v. quickly, especially if you had a spare engine. But the cost and survivabilty of outboards is as nothing compared to a diesel inboard.

All in all, you have got to take all factors into account and make your own decision............and having made it, live with it.

[Andy Gee]

Was burning anywhere around .75-1.15 ltr per mile per engine with the 11m Redbay (twin Yamaha 245hp), With the 9.1m I was about .5 ltr per mile per engine (twin 165hp Yamahas).
It would really depend on what type of work I was going to do with the boat if I went for Inboard or outboard.
Andy

[biffer]

roughly speaking it's probaly about 4 time dearer in fuel terms to run a petrol outboard than the same hp diesel inboard, the v8 yamaha 350hp burns 27gals an hour flat out and you can see from the other posts that aint the case with diesel, you could argue the toss for ever with people saying things like maintainance, power to weight, cost of purchase, installation, space in boat etc, i could go on, but the bottom line is in my own view diesel boats win hands down, i'm not getting into arguments as i have with certain people on this site about this subject, i worked in the rib industry more or less ever since ribs started and have been in countless boats doing sea trials, round britian, deliveries etc and my advice to you is if you can afford a diesel 8.5 buy it. posted a few pics of some bits that might be of interest, my yellow boat burns about 17lts per hour at 42 knots (its roughly that, i dont keep tabs on it a lot) and i've never broken down, it's never failed to start, all i've ever done is change oil, filters, two belts and one impellor in 900hours

[LURCHER]

8.5 Humber with KAD44 duoprop about 1lt per mile at 3000 rpm which is about 24 kn.

[GordyP]

I run two 115 outboards on a 6.7m rib, the Arctic is pretty heavy and we usually have six divers with kit on board. We average about 12-14 gallons an hour running at 35 knots, I make that 1.5 - 1.8 L/mile.

[Andre]

Originally Posted by Ashton

Does anyone have any fuel consumption comparisons on single or twin outboards v's inboard diesel.

I am considering twin 150 or 225hp outboards (perhaps four stroke) v's a single diesel sterndrive on an 8.5 m rib.

The rib will be coded and used commercially, thereore I'd be in a position to claim the duty back on the fuel.

Any other thoughts would be appreciated.

Ashton

Have you a rib in mind cos we would be interested in making you an offer
for a brand new Parker 9 mtr single diesel

we have twin diesel and single diesel 9 mtr Parker ribs coded and used commercially in the UK

[JIY]

I currently own an 8.5m XS with twin 200 Verados. With four on board, a half tank of fuel (300 litres) and smooth seas my total fuel burn is about 58 litres/hour at 30 knots.

My last boat was an 8.5m Tornado with a 250hp Yanmar diesel coupled to a Bravo X drive. With four on board, a full tank of fuel (180 litres) and smooth seas my fuel burn was about 27 litres/hour at 30 knots.

So for a private user the twin outboard RIB fuels costs are almost doubled.

However, when running commercially the difference in fuel burn is not as significant as it might first appear, because most of the duty is reclaimed.

My commercial skippering is mainly on 10m Humbers with twin 200hp ETECs (80 litres/hour at 28 knots with 13 on board), but I do sometimes skipper an 11m cabin Redbay with twin 245hp Yamaha Hydradrives (about 50 lires/hour at 28 knots with 14 on board).

In Scotland finding petrol is always an issue, whereas diesel is available almost everywhere, so in terms of flexibility and long distance cruising, diesel wins hands down. However, diesel reliability can be an issue, I certainly had my own fair share of problems, all related to the engine legs. Servicing can also be quite expensive, but probably not significantly more than servicing two petrol outboards.

I love the handling characteristics and the reliability that a twin rig offers, so I do prefer the twin petrol outboard RIB to the single inboard diesel. A twin diesel also offers all of these advantages, but in my own opinion you need a minimum of a 10m hull to handle all this eatra weight.

[Andy Gee]

Originally Posted by JIY

I currently own an 8.5m XS with twin 200 Verados. .

And what a beauty it is
Andy

[JIY]

[gtflash]

Originally Posted by jwalker

Nope, I don't. Purchase price of diesel varies daily. For commercial use the duty is 10.07p and vat is 5%. Today it was 36p/lt +vat here. For leisure use it would be the 36p + 42.28 duty + Vat.
But, looking at your profile, I presume you know all this.

sorry jw! little lost! how much does it cost private?

[jwalker]

Originally Posted by gtflash

sorry jw! little lost! how much does it cost private?

OK, the rate of duty for leisure use is 52.25p/lt. The rate of duty for commercial use is 10.07p/lt. 5% vat is payable on the total in each case.

For an easy example let's take the diesel cost as 50p/lt.
for commercial use: 50 + 10.07 x 1.05 (5% vat) = 63.07p/lt
for leisure use: 50 + 52.25 x 1.05 = 107.36p/t

However, if you are buying at a marine pump the price quoted will normally contain the 10.07p/lt commercial duty so you only have to add on 42.28p duty to get the leisure rate. Then add the 5% vat, of course.

Apologies for the confusion.