Petrol engines on motor boats.

[capnsensible]

I got a fair bit of experience of diesel engines on motor boats and tons on yachts. But very little with petrol.

My instinct is to back off from volatile petrol and spark plugs on a boat....but I'm probably way too cautious. A friend of mine is looking at a couple of mercruiser powered 6 to 8m speed boats, a Faeton 6.2 and a twin engined Searay 280.

Anyone got any tips about these kind of boats? Look great fun but pricey to operate? I don't want to give him poor advice!

Thanks.

 

[ari]

Becoming ever more popular it seems to me, especially outboard engines. Had both and had no safety/reliability issues, just running costs which is why I have diesel now. But diesel is more expensive to service, so I guess it depends how much you use it.

Bear in mind fuel availability and cost too - dockside petrol is less available than diesel and far dearer typically than road prices.

 

[capnsensible]

We got easy access to petrol on fuel docks.

 

[julians]

I wouldnt worry (and dont - having had a few petrol engined boats) about fire risk/explosions etc. The petrol engined boats will be more expensive to run in terms of fuel costs, but that can be compensated for by reduced maintenance and parts costs - certainly parts costs on mercruiser petrols are orders of magnitude cheaper than VP D series diesel parts costs.And an outboard is a lot cheaper to maintain than an inboard (regardless of fuel type of theinboard)

It will all depend on the number of hours running as to whether the petrol boat works out cheaper than the diesel overall.

In the 6-8m speedboat bracket, you probably dont have much choice, most will be powered by petrol inboards or outboards, very few will be diesel - but there will be a few.

These days I would choose an outboard powered boat over a petrol inboard , all other things being equal, but all things are rarely equal so you have to make a judgement. petrol inboard vs diesel inboard is a harder choice, and comes down to whats available , the number of hours you expect to run, and the purchase cost

 

[westernman]

A lot of boats in the USA have inboard petrol engines.
However, in the UK and Europe it will be very very hard to sell later (which might make it a very attractive purchase now).

A petrol inboard will use more fuel than a similarly powered diesel boat.
A petrol inboard will usually be quieter and smoother than a diesel inboard

As others have said it all comes down to how much fuel you are going to use vs purchase price and servicing costs.

 

[ari]

However, in the UK and Europe it will be very very hard to sell later (which might make it a very attractive purchase now).

Not if it's priced right it won't.

 

[ChromeDome]

Having been onboard one with twin Volvo B20 when it exploded, my mind is firmly set on:

If inboard it must be diesel. If petrol it must be an outboard.

And outboard over sterndrives - every time.

 

[waynes world]

Having been onboard one with twin Volvo B20 when it exploded, my mind is firmly set on:

If inboard it must be diesel. If petrol it must be an outboard.

And outboard over sterndrives - every time.

So why did they explode though ?

 

[capnsensible]

Thanks all, plenty to ponder on. I took this friend out on another friends amt 200 with a 150hp outboard. I really like this boat and friend 1 was smitten!

He can only find similar size inboard petrol boats where we are. From what I'm getting here, could well be worth a look. Ta.

 

[waynes world]

Petrol or diesel does not natter. its what you can afford to run. I cant afford much and at 10gph at 20 knots i am not bothered as its the fun factor. If i could afford same performance in the boat with diesel engines i would go diesel just for ease of filling up the tank.

 

[ChromeDome]

They salvaged the remains and did all kinds of investigations. Authorities, insurance companies and more. They found no reason.

Logically, something must have leaked - but no proof of it. The boat was maintained by the book. It's more than 35 years ago now, but it's still with me. My then 5-year-old son was with me, and throwing him into the sea to get him away from the chaos is an image that stays with me for life.

Everyone on board made it, but it's definitely an experience I would have rather not had.

 

[ontheplane]

I had a 26ft Rinker with a 5.7 Carb V8 Mercruiser. Flat out burned over 20 GALLONS so about 90 litres per hour - even cruising about 14 GAL an hour.

I think up to about 20ft and 1500kg or so petrol is fine - over 25' and 2500kg it's got to be diesel or at least super efficient EFi outboards or inboards if you are going to cruise. If you are going out for an hour it probably doesn't matter so much.

Over 30' gotta be diesels.

 

[DAKA]

Having been onboard one with twin Volvo B20 when it exploded, my mind is firmly set on:

If inboard it must be diesel. If petrol it must be an outboard.

And outboard over sterndrives - every time.

Me too
petrol bayliner
aprox 3 years old max 5 years ( it’s a long time ago now)
aluminium tank at some point had been sat in bilge water and was pitted underneath that could not be seen

arrived one night to find what looked like water in bilge
used a sponge to get it out and filled a plastic bucket
sponge went milky oil on outside

bucket had slight smell of petroleum but looked like water
only odd thing was the greasy sponge

carried bucket what I thought was a safe distance away
I needed to be certain that it was water in the bilge before we slept on it

i decided to run a test on the bucket of “bilge water “

threw a match into bucket , nothing
second match , nothing
third match and umph

plastic bucket melted and wall of fire ran down a river bank towards the boats

lesson learned- sell petrol boat and buy diesel
almost everyone in the boat club had told me that previously
there were just 2 or 3 out of 80 in the club that thought petrol boats were good value

ironically it was the first boat in the club to obtain a British boat safety certificate on First inspection.

I don’t agree outboards are safe
going back a few years there was a fatality in a lock
someone had a gas fridge ( naked flame)
it set fire to a close by boat with a petrol outboard that someone had recently filled and fumes were still around contained in the lock ( somewhere not too far from the M62 / A1. if I recall correctly )

 

[Bouba]

I love modern outboards…smooth, powerful and reliable…I would steer clear of petrol inboards…the fumes…the smell…but mostly because most inboard petrol seems to be mated to outdrives …the devil’s spawn

 

[bowler]

I had a 26ft Rinker with a 5.7 Carb V8 Mercruiser. Flat out burned over 20 GALLONS so about 90 litres per hour - even cruising about 14 GAL an hour.

I think up to about 20ft and 1500kg or so petrol is fine - over 25' and 2500kg it's got to be diesel or at least super efficient EFi outboards or inboards if you are going to cruise. If you are going out for an hour it probably doesn't matter so much.

Over 30' gotta be diesels.

Agree with this. I have 21ft ski/wakeboard boat just shy of 2000kg. It's got a fuel injected V8 inboard. Smooth and powerful it is, but it is plenty thirsty. I can only imagine what two of these, or worse carb versions, would drink on a bigger boat.

 

[simonfraser]

the fuel cost is only a small part of the overall boating cost, in my experience

OB modern petrol, not much to dislike, v reliable, excellent access

 

[paradave]

the fuel cost is only a small part of the overall boating cost, in my experience

Entirely depends on usage, for the people spending £000s to keep a boat in marina and use it as a floating lounge, I agree. Lots use their boats regularly and start to factor in fuel cost.


For me, petrol outboard was a revelation - Albeit on a small boat. It’s quiet, clean, cheap to service. Fuel costs are higher though but the pros outweigh the cons.

 

[julians]

I love modern outboards…smooth, powerful and reliable…I would steer clear of petrol inboards…the fumes…the smell…but mostly because most inboard petrol seems to be mated to outdrives …the devil’s spawn

We've had a few petrol inboards over the decades, from old carb'ed v8s & v6's in the eighties and 90s, through to modern MPI v8s in the 2000's , and never had any fumes or smell from the petrol .....or any explosions, fires or fuel leaks.

These days though I agree that you cant beat a modern petrol outboard (or two!)for a boat of the size the Op is asking about, and would be far preferable over a petrol inboard.

 

[DavidJ]

On this note
Running the engine fan for a few minutes before startup is essential with petrol but do people run their fans with diesel motors in the same way. I don’t see anyone doing this in my marina.

 

[38mess]

A friend runs 3 12mtr ribs with petrol 220hp outboards. They are really quiet on tickover. He has told me that they are better on fuel than a diesel powered rib he used to own.