Diesel v Petrol - at what premium marine petrol engines sensible?

jonnybuoy

jonnybuoy

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The following chart shows how the wholesale (ie by the shipload before any tax) price DIFFERENTIAL between diesel and unleaded gasoline has moved over the past 18 months


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DieselvNolead.jpg
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You have noticed the difference at the pump (which gets magnified as tax is a (large!) multiplier of the wholesale price). Reasons for this fundemental shift include car fleet dieselisation & diesel for power but most significantly a fall in the RELATIVE value of gasoline due to one of the world's most idiotic decisions - that of turning food into fuel (biggest of which is ethanol into gasoline pool).

Is there a price differential at which large marine petrol engines become viable? Seems a balance between lower petrol engine costs vs. lower petrol engine mpg and lower petrol engine lifespan (and probably a bunch of other factors I know nothing about). Anyone any idea?

Jon.
 
I think we have probably reached the balance point and passed it for anything under 28feet.

28-30 ft is probably a bit of a grey area, over that then for a petrol engines to generate the torque needed to get a heavy boat going you need a big one - or big ones.

If you look at the states they are using 7lt plus engines doubled up in mid sized cruisers for this reason.

The other issue you have is range. Most bods who buy a 30ft plus boat are looking to do some cruising and spend some time on board. Generally this means a trip somewhere. I cant find it now, but I did a little range comparison about 2 weeks ago on here and it highlights the problem.

Your average mid 30's cruiser probably holds 400-500 litres of juice. With diesel engines on board you will be looking at a range of 300nm with a 10% reserve. the same boat with a couple of 6.2lt V8's is probably going to be lucky to get 180nm out of the same tank.

It doesnt leave much room for error on the petrol boat if you fancy going to Guernsey for example, and if the weather kicks up on the way you could double your consumption quickly and come close to getting caught. While there is a point that the financials may start to make sense, I think there is a way to go before the practicalities do...
 
Agreed, you cant underestimate the amount of petrol that gets burnt up.

I know of a Carver Flybridge that couldnt get out the thames estuary, it simply ran out of fuel.

I tried to do some cruising with a single V8 petrol in a 24ft boat.

110 nm , I had to fit an auxiliary fuel tank and still ran out,can be very dangerous.

I calculated how far I could get on worst case scenario but still got it wrong.

Most petrol boats really have no idea how much they use.

A 20 mile return trip to Studland bay includes 15 miles at tick over and only 5 miles at cruising speed, hence it is assumed the Petrol boat is 4 times as economic as it really is.
Add to that a few waves and usable safe range is 50 nm, a picnic day boat with accommodation.
 
Got to agree with what you say. My 25ft boat used to have V8 petrol. I once went from Lymington to Cherbourg. (80ish nm) I have a 45g tank and I ran out of juice just off Cherbourg entrance. Luckily I also had LPG at the time so switched over and carried on.

Same boat now has diesel. In October I went from St Peter Port to Brighton (125ish nm) and arrived with loads of fuel spare.

I reckon my range is now nearly double. So even with petrol and diesel both at road prices, diesel will still be sooooo much more economical. Plus, and it's a big plus, I can get fuel just about anywhere. With petrol, fuel planning was just as important as weather and tides, and usually involved jerry cans and aching arms!
 
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If you look at the states they are using 7lt plus engines doubled up in mid sized cruisers for this reason.

The other issue you have is range. Most bods who buy a 30ft plus boat are looking to do some cruising and spend some time on board.

Your average mid 30's cruiser probably holds 400-500 litres of juice. With diesel engines on board you will be looking at a range of 300nm with a 10% reserve. the same boat with a couple of 6.2lt V8's is probably going to be lucky to get 180nm out of the same tank.

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I frequent the Regal boat forum, where 95% of the posters are US based. I'm quite surprised at just how few of them have dismal engines in their boats, it really is all petrol, right up to the big cruisers and they're starting to be concerned about fuel prices, paying ~$4 a gallon. Chap there quoted a flat water run he did in his 3560 cruiser (so 36ft ish) with twin 8.1lt V8 petrols where he burnt through 500 litres of fuel in 3 1/2 hrs at a cruise of 3100rpm / 31 knts, so that's not much of a range.

Impressive fossil fuel reduction though /forums/images/graemlins/tongue.gif
 
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Chap there quoted a flat water run he did in his 3560 cruiser (so 36ft ish) with twin 8.1lt V8 petrols where he burnt through 500 litres of fuel in 3 1/2 hrs at a cruise of 3100rpm / 31 knts, so that's not much of a range.


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That sort of says it all.

3.5 hours at 31knts is a distance of 108.5nm
500 litres is 110.13 gallon, so his consumption is 0.98mpg!!!!

A modern 36ft diesel boat with D4's will give a similar cruise and return more like 2.5mpg /forums/images/graemlins/blush.gif

Even better, go for a big single diesel and get closer to 4 mpg /forums/images/graemlins/grin.gif
 
Yup

Just wait until they get fuel costs like ours, then they'll start squeaking. At least it only cost £300 to do that, rather than the £600+ it would've been here.

It's certainly an interesting discussion though. Given that our next boat would probably be in the 25-28ft range, I'd have to question buying one with dismal engines as by then, the fuel costs will be the opposite way round to now and for our usage, I think the petrol would still win. I couldn't see us paying out the extra to buy the diesel engined boat, albeit that *might* limit the resale.
 
I had a 21ft petrol boat based in Penarth, problem is you can't go anywhere in the BC as petrol isn't avaialble at most places you want to stop. We moved up to a diesel on a 27ft and the difference in fuel consumption is amazing as Westline says and we still take the 27ft our water skiing etc. If you do move up you'll want to go further and petrol is almost impossible to get in the BC.
 
I think in the 24-28ft range you are right as the accomodation for long range cruising just isnt there on those sized boats. OK, I know some who do very well on S25's etc, but the norm for these boats is fairly local (sub 50 mile) weekending and for that purpose a petrol engine is worth considering.

Take our 24, I cant remeber the figures exactly here, but from memory a D3-190 (Diesel, 190Hp) powered boat manages around 0.75l per mile when fully on the plane at cruising speed. The V6 boat (Petrol, 225Hp) manages around 1.1l per mile for the same sort of speed.

If you look at it in raw % terms, the petrol boat uses 46% more fuel than the diesel boat. However, if you look at it in costs terms with the fuels at equal money (lets assume £1.35/l?) and consider most boats of this size will do less than 70 hours on the plane the actual yearly cost difference for those 70 hours (assuming a mid speed of about 25knts) is

((1.1x25x70) - (0.75x25x70)) x 1.35 = £826.89

Thats how much extra it costs to run the Petrol boat per year.

A diesel boat costs around £8k more than the equivalent petrol boat. Depreciation is likely to be the same for both boats assuming everything else is equal, so the cost of the £8k additon is how much of that will you get back, and what is the cost of either financing that amount or loosing the interest on the money had you not spent it.

Working on the old basis of 20%, 15%, 10%, 5% for the first 4 years of depreciation on a boat, your 8K diesel option is likely to be worth around £5k more than the petrol boat after 4 years.

So, the extra cost of the diesel boat over 4 years is 5% of the £8k cost per year in interest or lost earnings, plus the £3000 of depreciation. In other words, £4,600 or £1,150 per year.

Compared to the extra running costs of the petrol at £826

Not a big difference, so as always it comes down to use...
 
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...Add to that a few waves and usable safe range is 50 nm, a picnic day boat with accommodation.

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Yup, that's what ours is /forums/images/graemlins/grin.gif
I have no regrets about buying a 26' petrol boat. I wouldn't fancy doing any real distance on it anyway because it's too small.
Until I can afford a 50' flybridge I will ring P&O when I want to cruise anywhere.
Besides, you gotta love the sound of a small block V8!
 
Very interesting thread. I currently have a Mercruiser 165 diesel in a 25’ sports boat and have been considering an investment of a new diesel in the 250hp range which would roughly cost about £14k, trouble is I can get a 5.7ltr V8 bobtail for about 5K! Although these prices don’t include a host of sundries or fitting, it does make you think whether it’s worth it. If you calculate a 9k differential, plus I might get 4k for my engine, then that leaves 5k. And 5k can buy an awful lot of petrol - possibly 5 years worth!

But I worry that if I went down the petrol route, by boat may become virtually worthless in 5 years, whereas diesel would make her far more an attractive buy.

But of course the other factor not mentioned here is the 60/40 duty split. Petrol at the forecourt pumps maybe about 1.35 but at the marina depot it’s about 1.85 whereas diesel must be still be about £1.25 with the 60/40 split. So once you calculate the difference in fuel costs, it starts to make diesel more attractive again. I suppose it’s all about upfront/capital investment over operating/running costs.

And although only a 25 footer, I still intend to travel further distances such as the CI's next year and some longer coastal runs, so again, diesel wins here too.

What a dilemma!!!!
 
Yes, I just noticed that - doh!
But it was on the first page for some reason else I'd not have seen it.

But my dilemma is still relevant and the data in the thread is still relevant, so adding the two together should make for some interesting comments.
 
Here on the east coast its availability of petrol that's the problem. I can get it at my home berth (Crouch)-Bradwell & then only Medway.Nothing going north,unless SYH at an enormous price if at all! Going up the Thames is a no no so diesel is really a very positive option around here!For day boating its OK but that about all really.I now have a diesel boat!:D
 
I had a 25' petrol that was fine on the River Thames.

Now, just sold a 30' Broom which did 5mpg average, and up to a 32' Scand, which will probably do 3mpg, must agree, there is no place for Petrol engines above 25 odd ft...:eek:
 
The problem is that petrol and diesel aren't the same price at marinas.

Parkstone Bay in Poole, last time I looked was £1.25 for diesel on the 60:40 split, and petrol was £1.75 per litre.

So not only do you burn more, you're paying 50p a litre more!

I run a 25' Monterey and when looking, waited until the right diesel boat came along. For me, it was more a case of not wanting to be scared to use it for fear of the massive fuel costs so it had to be a diesel.
 
rhino_mac said:
For me, it was more a case of not wanting to be scared to use it for fear of the massive fuel costs so it had to be a diesel.
Click to expand...

I think that sums up my feelings too. I feel less concerned with a larger investment that'll add value to the boat than I do about constant refuelling costs. So I'm leaning towards diesel again. But why are they soooo expensive!
 
Very interesting thread. There are so many arguments most of which are intertwined. The literal running cost differential i.e. cost per mile or cost per hour, the absolute range given by both power options etc etc. I think perhaps the most relevant argument for diesel now days is more of a consumer psychology one. Like rhino_mac said, he waited around for a monteray with a diesel. It’s that fear of running something that consumes a lot of fuel that will swing people towards diesel every time. I don;t know what it's like n the UK but in Ireland if you went into your local BMW/Audi/Merc etc. dealer and tried to buy any petrol car let alone 6 or 8 cylinder petrol’s the salesman will almost not sell it to you!

I run a 5.7L v8 wakeboard boat which is relatively economical up to about 21mph on the gps. This is perfect for wakeboarding but push it over 30mph for skiing or fast cruising and the boat is not worth running at this speed. I can't imagine using the same or two of the same engines in a cruiser >30ft.

As for the idea of when will it be more economical to have petrol engines over diesel. Well take two of the same car models with roughly the same power output (say a 2007 model BMW 523i petrol and a 520 diesel of the same model, both of which produce about 170 or so hp) one with a diesel and one petrol. Diesel would probably have to be >1.5 times the price of petrol before the petrol starts to make sense.
 
Also another factor is where you keep your boat. I berth at MDL as an outlook member and this helps substantially with the fuel costs as you get the fuel at cost to them which works out about the same as at the forecourt. In that time I have had 2 petrol boats and the fuel prices/consumption hasn't been as horrific as I first thought but then I'm a dayboater really. I'm sure my next boat will be a diesel though as the family grows and we look to do longer passages.
 
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