Fuel Hazards

[Guest]

Which poses the lower risk from fire/explosion, a boat with inboard petrol engine and tanks, a boat with inboard diesel and tanks or a boat with outboard petrol engine and inboard tanks?. What safety features should each have to mitigate the risk

 

[andy_wilson]

Lowest risk diesel.
Then Petrol outboard (no hot engine compartment, no need to vent).
Worst inboard petrol.
Petrol has a far lower flash point, and vaporises more easily than diesel, and the vapour is heavier than air, so collects in the bottom of the boat.

 

[Guest]

Received wisdom is that diesel is safer than petrol. Inboard petrol engines are safer than outboard since the fuel lines/tanks are fixed installations. Or outboard petrol engines are safer than inboards because there's no engine bay for petrol fumes to collect in, along with sources of sparks to make them go bang.

From personal experience lighting barbies, petrol is not something to dick around with, whereas, you've got to work quite hard to get diesel to burn...

 

[Chris_d]

This sort of question always brings a out the anti-petrol brigade, trying to justify the extortionate price of their diesel powered boat. Then they all drive home in their petrol cars!
Although it is true to say that petrol has a lower flash point, and the vapour is very dangerous, it is also foolish to think that diesel doesn't burn. If your boat catches fire and is burning around the fuel tank, the diesel will ignite due to heat transfer through the tank sides, a petrol tank will not unless the fuel sees a naked flame.
So if the fuel system and all the lines are up to standard and correctly installed, the actual risk is probably equal for both, unless you have a leak.
If you are considering a petrol vs diesel boat, the biggest factor is how much it will cost to run, and where to obtain fuel, not safety, that will be down to the condition and quality of the actual boat.
I have seen a few burnt out petrol boats which have ignited due to fuel leaks and its a scary sight, but I have also seen many burnt out cars, but I still drive petrol powered car.

 

[sonarbell]

But you need to turbo charge diesels to get the same performance, cos they aint as powerful as petrols, nice red hot turbos and a split high pressure fuel line spraying fuel everywhere in the warm dark depths of an engine compartment= Same effect i think!!!!!

 

[Guest]

I have had all sorts of boats including large outboard powered, twin petrol outdrives and currently twin diesels on shafts. Basically any fossil fuel is potentially dangerous but petrol and/or petrol fumes is more likely to explode than diesel as a result of stray sparks, naked flame etc. Diesel can as has been pointed out behave just as badly. The key is to ensure that whatever your installation is, it is properly maintained and you don't take liberties with it. Both fuels are perfectly safe properly installed and maintained.

On the points about the economics of petrol v diesel, there are arguments about the lower initial capital cost of a petrol boat balancing the extra cost of the fuel but you have to bear in mind that the diesel boat will hold its value better and, over the period of ownership you are unlikely to take as much depreciation on a diesel boat.

As far as actual fuel costs are concerned, my own twin 200hp diesel boat averages around 10/11 gal per hour over a season. A comparable petrol installation would use maybe 18/20 gal per hour for the same relatively gentle use (obviously both boats would use much more driven flat out). The difference is that my fuel costs around £13 per hour whereas the petrol boat is about £80 per hour. In a hundred hour season that's a difference of somewhere about £6500.

There are some other advantages the main one of which is availability. You can get diesel virtually anywhere but petrol is much more limited at the waterside.

I do not wish to criticise petrol boat owners - I've been one myself but I think the economic argument for diesels is pretty compelling and will continue to be so until the EU finally force harmonisation of taxing on us (currently deferred for about five years we are told).

Nick

 

[chrisbrown]

Every one is right as far as I see this but I would like to add that where the risk of a fault in gas oil is fire, the same fault in petrol produces a potential explosion. Fire fighting on board a small vessel is a poor option to exacuation but at least you might get the choice on a gas oil boat, ( unless the cooking gas goes up instead).

 

[andy_wilson]

???????

"If your boat catches fire and is burning around the fuel tank, the diesel will ignite due to heat transfer through the tank sides, a petrol tank will not unless the fuel sees a naked flame."

The petrol tank will be venting explosive vapour long before the diesel one.

I suggest that if there is fire lapping around the fuel tank in a petrol boat you should jump over the side and swim like hell!

If it's diesel, try and put it out first, if unable, send appropriate message on VHF, launch the raft, and organise an orderly evacuation.

 

[Guest]

Any fire on any boat is a very serious situation, once a fire gets a good hold, the structure of the boat itself provides the fuel, GRP burns very nicely. The answer lies in prevention of the fire in the first place. Whether the fuel is Diesel, Petrol or LPG the design, installation and maintenance of all fuel systems needs to take into account the relevant hazards. By and large, fire prevention on larger petrol engined boats is taken very seriously with flame traps on intakes, metal fuel lines and automatic extinguishers as standard.

Insurance companies do not seem to penalise petrol or LPG installations providing they are up to standard, which would tend to indicate they assume no greater risk is indicated.

We are all quite comfortable with gas cookers / boilers in our homes and petrol tanks in our cars. We fly in planes that have wings full of fuel yet express horror at the thought of petrol in boats.

I personally believe gas installations for cookers etc present a far greater risk.

KL

 

[peterb]

He\'s right, though.

Surprisingly, it's very difficult to make tanks of either petrol or diesel explode at room temperature. For any flammable gas there is a range of concentrations within which it can explode; either weaker or richer and it won't.

The vapour pressure of petrol at normal temperatures is above the flammable range, so a tank with liquid petrol in it won't explode. If you want to make it explode then you need to either remove the liquid petrol and then dilute the vapour, or reduce the temperature. The first method is the reason that the tanks of abandoned cars sometimes explode; the petrol has all evaporated and the vapour slowly leaked away until the remaining mixture comes in to the flammable range. The second method is the reason that petrol engined aircraft during WWII were sometimes fitted with nitrogen purged fuel tanks; aircraft fly at high altitude, where it's cold, and the lower temperature reduces the vapour pressure down to the point at which it can explode.

With diesel, though, the room temperature vapour pressure is too low for an explosion. But if you heat the diesel up (somewhere about 100 deg C, I believe) then the vapour pressure moves into the flammable range and the tank can explode.

So a fire burning round a petrol tank is unlikely to cause an explosion, unless of course the tank is unvented so that expansion of the contents causes it to burst. I've stood within 25 yards of sixteen 100 ton petrol tankers and watched them all burn out without exploding. But a fire burning round a diesel tank is very likely to lead to an explosion once the diesel has heated up a bit. Talk to any knowledgible fireman; he won't mind standing near a burning petrol tank, but if it's diesel, and if he can't keep it cool, then he'll be off.

 

[Seadog]

Re: He\'s right, though.

After reading that last post all i can say is... Blimy!
id be off toward the hills whatever was in them

 

[Guest]

A vast aray of arguments for petrol verses diesel engined boats. My advice to you would be to buy what ever boat suits your needs and pocket. In this day and age don't be put of by thinking Diesel engines are less powerfull than Petrol engines, it's codswalop! Make sure the boat and istilation is up to correct standards, if new it should be CE marked and up to ISO standards. If second hand then have it serveyed and checked to conform with the boat saftey scheme. This will ensure adaquate instilation and fire prevention, Making sure the engine room is fitted with auto fire extinguishires to the correct capacity. By the way Halon fire extinguishires are no longer allowed to be fitted on new instilations due to their distructive power on the environment, however the alternitive is just as good. If still indoubt have a gas detector installed!!
I hope this helped.

 

[Guest]

Re: He\'s right, though.

Do you suggest I remove the immersion heater from the diesel tank then? I fitted because the boat doesn't have glow plugs, and it seemed to make it easier to start.

 

[Chris_d]

Re: A diesel bomb!!.

Blimey, if your thermostat fails your history mate, a typical imersion heater thermostat costs £2.50, would put your lift in the hands of such a cheap component.
As I think another poster explained you have raised the temperature to nearer to the flash point hence it's easier to start. normaly the glow plugs will do this for you
within the safe confines of the combustion chamber or inlet port.
I have seen truckers light a fire under their fuel tanks in very cold weather to achieve the same effect, but its very risky.

Please put pride aside and remove it fast, then thump the idiot who recomended
it!

 

[Scubadoo]

Re: He\'s right, though.

Graham,

If this is not a windup, from what I have read and learned I would remove the immersion heater asap - you might even invalidate your insurance!

Why don't you preheat your engines using shore power, not sure what is involved. The work generators (volvo penta engines) are always warm from the 240v mains. I guess their is a kit to so this.

RM.

 

[Scubadoo]

Well said and just to add one further point you also have almost double the range.

But it is all down to how much boating you intend to do, if you do less than 70hours petrol may seem the best option. I prefer diesel and will alway have diesel even if the prices go up in the future, like you Nick have tried both petrol and diesel.

RM.

RM.

 

[Guest]

Re: He\'s right, though.

This must be wind up surely? If not can you tell me which marina you are in so I can avoid visiting.

I once inadvertantly left the boat with the calorifier immerser switched on. The thermostat failed and the hot water tank boiled dry. The tank then got so hot that it melted all the connecting pipes and burned the insulation off the tank. The wooden plinth on which the tank sat and the bulkhead next to it were scorched and the only thing that saved the boat was that the shorepower supply tripped because of burnt wires.

If that happened in your boat you would be picking up bits of it + surrounding boats in the next county.

I would get rid of it if I were you.

Nick

 

[peterb]

Good advice, Graham

Heating the fuel up will certainly make the engine easier to start. But it's not the fuel in the tank that you need to heat; it's the fuel that's going into the cylinder. I suspect that you will need to turn the engine over for quite a long time before the warmed fuel from the tank reaches the engine.

As has already been said, thermostats are not totally reliable, and a failure could result in quite a nasty situation. Why not use a glowplug?

 

[Guest]

Re: He\'s right, though.

I fitted the immersion myself - just epoxied a domestic one into a hole I made with a tin opener. It leaks a bit, but the bilge pump gets rid of the spillage. I should really get round to putting some insulating tape on those bare wires, I suppose, and put a proper fuse in, not just that old nail. Still, it's a lot safer than the old way of stuffing a burning rag in the air intake.

For a small fee, I'll publish my summer cruising itinerary, so you know where to avoid...

;-)

 

[Guest]

Re: Good advice, Graham

What thermostat? I just leave it on the mains till I hear it bubble...