Petrol vs diesel

[beancounter]

Hi chaps (and chapesses) - I'm afraid it's another new boy asking questions...

I'm in the early stages of researching the purchase of a sailing cruiser, & I would welcome thoughts from Scuttlebutters on the subject of auxiliary propulsion.

Given my budget (under £10k), and the type of sailing I would be likely to do (day/weekend sailing on the East Coast), I guess I'm looking at craft up to about 26 foot, probably bilge or lifting keel. This seems to be the size of vessel where some types have petrol (outboard) and and some have diesels. Are there any relative merits/demerits of each which I should consider - economy/ease of maintenance/safety etc.?

cheers

John

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[colvic]

The size of boat youy are looking at would take an outboard as an aux. very easily. If to be used mainly for leaving and approaching your mooring then this would be adequate, but if considering a few hours motoring at a time then I think an inboard diesel would be better. However they are often located in small compartments making access and servicing difficult, and need a good healthy battery to start them.

You ca take an outboard off for servicing and if you run it in a fresh water cleaning tank every so often, the marina should have one somewhere on the hard, then it should last a long time.


Phil

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[extravert]

There are lots of pros and cons, so I'll just give one pro and one con, and others can give more.

Pro petrol outboard...

If you need to replace an old engine that has expired one day, a new diesel inboard will cost about 3 times as much as an equivalent power petrol outboard for the type of boat you are considering. This assumes that you could fit an outboard yourself but would have an inboard diesel professionally fitted.

Pro diesel inboard...

Diesel fuel costs are about 25% of the cost of petrol, because it is lower tax and you use less.


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[Twister_Ken]

As you say, the choice is between petrol outboards and diesel inboards. Almost nobody wants a petrol inboard nowadays, and diesel outboards are big, expensive and too heavy for small boats. So here goes:

Outboard pros
Cheap (relatively)
No installation problems
Take them off, take them home to service
Works as a steerable engine, upping manouverability in tight spaces
Doesn't take up room inside the boat - making more general stowage available under the cockpit, for example
Doesn't make holes in the boat for cooling water inlet, exhaust outlet, prop shaft gland, so better hull integrity.

Inboard cons
Vulnerable to knocks
Vulnerable to theft (entire thing, or components)
Uses petrol which is more flammable and more explosive than diesel, therefore requiring more careful, drains-overboard stowage
Marine petrol much more expensive than marine (red) diesel
Fewer mpg than diesel
Prop can come out of water when boat pitching
Puts a lot of weight right aft, which can affect trim on a smaller boat.
Can cause turbulence when sailing if not well clear of water.

Diesel inboard has more or less the opposite pros and cons.

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[vyv_cox]

No doubt users of outboards will rise to defend the advantages of this form of propulsion but for me a diesel engine has all the advantages but very few disadvantages. Here are a few:

* Fuel safety
* Far greater reliability
* Longer lasting
* Easier operation, especially alongside manouevring
* Prop deeper in the water, so better power in rough conditions. This is a very big consideration
* Considerably better economy
* Better weight distribution

Within your budget it should be relatively easy to find a boat fitted with a diesel engine.

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[Trevor_swfyc]

John,
It all depends on how far you intend to go, while an outboard running on petrol is ok for river get you home. It will soon be obvious when you go to "sea" that an inboard diesel is the best option by far.
<pre> (1) Diesel is far safer will not flash off at room temp.
(2) Diesel tank will give a bigger range.
(3) Diesel red is cheaper.
(4) Outboard prop will tend to leave the water in choppy water.
(5) Diesel in general is far more reliable.</pre>

I have a bilge keeler which is a good choice for the shallow east coast.

Trevor


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[Trevor_swfyc]

The exception proves the rule, take a look at the Mariner 5 <A target="_blank" HREF=http://www.bbc.co.uk/science/space/exploration/missiontimeline/mariner5.shtml>HERE</A> /forums/images/icons/smile.gif

Trevor

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[billmacfarlane]

Diesel has many advantages already listed on other replies and I'd guess that in the size range you're looking at the majority will have a diesel. Looking at your budget , £10,000 , the boats you'll be inspecting will have been around a bit and the diesel might have a limited life left in it depending on how it's been looked after. To re-engine will cost you the best part of £3000. It's something to take into account when you're looking.

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[yoda]

Ah my favorite subject. You can of course have the benifits and sortcomings of both and everything is a compromise. I am one of the inboard owning types who is very happy with having the benifits of a petrol engine (light weight, good power, small size) together with the safety worries that go with it. (and safe use of petrol is just about the only concern). While I would hate to tar all owners with the same brush and interesting survey would be to find out howmany owners place a cheap plastic fuel can for the dinghy engine in the stern locker rather than a stowage that drains over the side. With petrol like gas care and common sence must be taken in good measure however do not rule petrol out on the basis of safety alone. Hands up all car drivers who have petrol engines. While diesel is harder to ignite it will go up if for instance an injector pipe splits and fuel is sprayed at high pressure on to a hot part of the engine. In looking for a new boat you will have hundreds of things to consider but in my opinion you should buy a boat that sails well and the engine is jsut what it is supposed to be - an auxilliary

Yoda

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[charles_reed]

On a £10K boat I'd look at the boat first and the auxiliary second.

Outboards have a low capital cost, high running costs, and restricted range, but are easy(ish) to service.

A diesel will give you much greater range, better drive in broken water, have a longer life and cost a lot more if it breaks.

The relative safety of the fuels is, IMHO, academic

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[Cornishman]

Petrol engines, inboard or outboard, require an electric spark for the ignition stroke and the usual cause of marine petrol engines failing to start is to be found in the electrical system.
Diesels use the heat generated by the higher compression ratio, and electrics with all their difficulties of timing, HT insulation etc don't enter the argument
That would be enough for me to go diesel.
I don't know about the prices of marine diesels, but some cars are cheaper with diesel engines than with petrol nowadays (see the Skoda Octavia)

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[BrendanS]

I liked your comment about hands up all car drivers with petrol engines.

This isn't a wind up, but a serious comment. There are a vast numbers of 'stinkies' like myself who use petrol engined boats, and huge numbers in the US where apart from petrol being cheaper, the litigation culture is such that no boat manufacturer would dare to sell an inherently unsafe system.

Don't have any numbers to hand, but from experience, I don't hear many Mayday calls for petrol engines in flames, compared to engines that have conked out, or boats that have gone aground, etc, etc.

Stinkies don't seem particularly worried about having petrol engines. Is it a culture thing?

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[Sybarite]

The day you dismast in a Force 8 with a lee shore in the vicinity, cost differentials don't seem quite so important.

Go diesel.

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[beancounter]

Re: Mariner

Erm - I think it's a tad over-specified for my requirements. Unless, of course, it could survey the hull....

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[saturn]

well,for diesel to spray at high pressure all over the engine,the bolts have to come loose ,the injector to fall out and the engine to keep running!!.
if an injector pipe brakes you will get spurts of fuel (little psi) out at n degees before tdc.
also on all the boats i have been on there has been no surface hot enough that would ignite diesel without the aid of other combustible material ,rags, paper or wood.
if you want a petrol engine ok but why put down the diesel.
pm me if you want more debate.

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[extravert]

Posters are talking about the boating risks here of outboards compared to inboards (exploding petrol vapours, unreliable electrics and lee shores in force 8s). What no one has really talked about is the financial risk. A boat costing £10k is going to be old. If it has an inboard, that is going to be old as well. With an old diesel (>15 years), however well you maintain it, you just cannot tell if it is going to last for another 15 years, or if it is going to go pop tomorrow, like mine did last year. If there is only £10k to spend, then I would say an inboard diesel is going to be a real financial risk with a possible crippling bill appearing at any time. An outboard may limit sailing somewhat, having to avoid bad weather and long motoring trips, but for someone on a low budget considering their first boat to be used on unambitious coastal trips in fair weather, financially an outboard is the obvious choice.

As an example in the financial risk beancounter may face with an old inboard diesel, my inboard of 14 years vintage died last year. It was a 10hp Bukh. Bukhs are the best small marine engines, they said. They last for ever. They can always be repaired. Two major compinents failed on mine. The costs of the parts alone was £2k, without the labour (including engine removal for repair). A repair was uneconomic, so I went for a new one. The final bill came to £5k. Could beancounter take a bill like that?

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[snowleopard]

one more for the list...

in my distressingly extensive experience, outboards, which live in a very hostile environment and rely on electrics, are far less reliable than diesels.

before breakerless ignition they were the work of the devil but even recent ones have let me down too often for comfort.

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[Aeolus_IV]

While our boat was never intended to take an outboard aux engine, and has a internal diesel, I can express an opinion.

We have been sailing her only since summer last year, but we have already had one wave sweep cleanly over the stern, round the cockpit coaming and down the side decks on entering our home harbour! Would an outboard engine continued working while under water? Possibly not, it would have left us powerless, in a narrowest part of the entrance. The weather was not bad (F5/6), but the direction was unfortunate. To be fair, at least one yacht coming in on that day does use an outboard auxiliary and did get in with out trouble.

My vote is for diesel, I feel safer for a number of reasons all mentioned before.

Jeff.

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[tcm]

Not sure if it's a culture thing. If a boat has a diesel option it seems best to go for that from a resale point of view. Also, not all places in UK have petrol at quayside in volumes likley to be consumed by a large stinkpot if at all. Spose safety-wise the US is much better at the safety gear of pumps etc whilst taking on the fuel whereas we just have an open pipe.

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[beancounter]

Thanks....

...very much for all the input. Plenty of food for thought.

John

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