Big petrol engines at river speeds

[perry84]

Hello all.

I currently own a diesel boat on the Norfolk broads. It is great, I can go hours on a couple of gallons so very cheap.

I am looking at getting something which is capable of going out to sea as well as using on the broads and rivers. Most of the boats which I fancy all come with petrol engines - most of which are 5 - 5.7 litre V8s. I don't mind paying the fuel premium when I am out at sea having a blast but obviously for sitting at the permitted speed on the rivers (4 - 6 MPH) I don't want to be using 10 gallons an hour!

Does anyone know what consumption I should expect from say a 24ft Searay with a 5.7 V8 petrol going along a river at tick over? I'm obviously not expecting it to be great but will it be bearable? Does anyone have any experiance with these types of boats/engines on rivers?

 

[alahol2]

No experience of that type of boat/engine but perhaps the answer is to use your emergency outboard to pootle about inland. I'd have thought 8-10Hp would be ample.

 

[ricky_s]

Hello all.

I currently own a diesel boat on the Norfolk broads. It is great, I can go hours on a couple of gallons so very cheap.

I am looking at getting something which is capable of going out to sea as well as using on the broads and rivers. Most of the boats which I fancy all come with petrol engines - most of which are 5 - 5.7 litre V8s. I don't mind paying the fuel premium when I am out at sea having a blast but obviously for sitting at the permitted speed on the rivers (4 - 6 MPH) I don't want to be using 10 gallons an hour!

Does anyone know what consumption I should expect from say a 24ft Searay with a 5.7 V8 petrol going along a river at tick over? I'm obviously not expecting it to be great but will it be bearable? Does anyone have any experiance with these types of boats/engines on rivers?

It will use a fraction of 10 gallons an hour at 4mph. I had a 24 ft with 5 litre V8 and it probably used a litre an hour when going that slow.

 

[whisper]

Hello all.

I currently own a diesel boat on the Norfolk broads. It is great, I can go hours on a couple of gallons so very cheap.

I am looking at getting something which is capable of going out to sea as well as using on the broads and rivers. Most of the boats which I fancy all come with petrol engines - most of which are 5 - 5.7 litre V8s. I don't mind paying the fuel premium when I am out at sea having a blast but obviously for sitting at the permitted speed on the rivers (4 - 6 MPH) I don't want to be using 10 gallons an hour!

Does anyone know what consumption I should expect from say a 24ft Searay with a 5.7 V8 petrol going along a river at tick over? I'm obviously not expecting it to be great but will it be bearable? Does anyone have any experiance with these types of boats/engines on rivers?

Hi,
You'll probably get more replies if you move this post to the Motorboat forum.

 

[perry84]

Thanks

Thankyou for your suggestions/answers.

The outboard idea sounds good although I haven't seen many which come with them but its worth looking at.

It makes sense that the engine is likely to use much less on what will be pretty much tickover. Even if its a gallon or two an hour, I could live with that. A small price to pay to have a nice quiet petrol engine with a huge reserve of power.

I guess there is only one way to find out - get the cheque book out and buy one!

Thanks again,
Lee.

 

[perry84]

Thanks for the advise. Much appreciated.

I have been reading other threads and 1 GPH seems to be the average opinion.

As long as its under 2 - I can live with that.

I guess i better get the cheque book out and go and buy a new boat. Then I will know for sure!

Thanks again,
Lee.

 

[gsturgeon]

Hi there

I have just run up a 5.0 litre Mercruiser with a carb and checked the consumption on a fuel monitor. These results were taken with the engine in gear.

Tickover 0.5 gph
800 rpm 0.8 gph
1000 rpm 1.1 gph

Some years ago, I had a 24ft boat on the Thames, with a Volvo 4.2, the cruising revs were 800 rpm.

The good thing about petrol is that at these speeds, the engine is much quieter than the blower and you dont ruin it by running at low power. My abiding memory of river cruising is the clouds of smoke following the older diesel boats.

 

[perry84]

Thanks for the info. Much apprecaiated. The 1 GPH sounds reasonable, even if it were 2 GPH it would be bearable. Like you say, a petrol will be much quieter and are not so likely to get clogged up running at low speeds compared with diesel.

Cheers.

 

[landlockedpirate]

I can confirm the above figures, just spent a week on the Thames with my 5.7l V8 and it used around 5lph at 5mph (Just over tickover).

 

[perry84]

Thanks

Cheers everyone for the info. It is good to know a petrol will be affordable on the rivers and it will be nice to have a quiet petrol engine over diesel.

Thanks again.

 

[Fire99]

My Shetland Black Prince with a 5.0 V8 used to use 1 gallon per hour at river speed and would happily do it all day every day but still able to give it the 'beans' on the coast.
Was still on her original 1982 engine when I sold her 5 years ago and was apparently the quietest the surveyor had ever heard.

 

[Andrew M]

Yep, I agree with all the above, I don't think it will be any shock to you in consumption. Our previous Searay 270 had 1x Mercruiser 350 and the current Sealine 360 has 2x 5.7 Mercruisers. Both kept on the Thames and fuel usage was ,we have always thought, very reasonable on both.

We did deprop this boat to bring the revs up a bit to ensure water/oils got to temp, and also to slow her down to make manouvering in locks etc easier.

I think, without scientific backing, it sort of seems that a petrol version will drink roughly about the same as a diesel for river use as both are only at or around idle so there can't be that much difference, you would only notice it if you had a 3hr blast at speed out at sea.

And yes you might notice that the petrol boat has a nice quiet,smooth and smoke free gait when doing river speeds.

Not wishing to hijack the thread but could I ask Gsturgeon what type of fuel metering you were using ? I am looking to fit a system to show just that.

 

[gsturgeon]

Fuel Monitor

Not wishing to hijack the thread but could I ask Gsturgeon what type of fuel metering you were using ? I am looking to fit a system to show just that.

Hi Andrew

It's a Navman 3100 also sold by Northstar, I think they are now now no longer made but there are a number for sale on the web. With two engines you will need a twin engine kit.

One thing I did was to power it up when the ignition switch for either engine is turned on. It is necessary to fit a diode in the feed wire from each switch or else you can't switch off one engine at a time.

 

[rafiki_]

I had a 25ft Sunbird on the Broads a few years ago (similar ilk to the Sea Ray). She used 1 gph on the rivers.

Worst thing for me was the strong exhaust smell, much worse than my current diesels, and I became a bit worried about the dangers of carcinagens in the exhaust. As a carb 5.7litre, she generally ran rich at low speeds, and smelt like an old petrol car with the choke out.

Other than that we had a great time on her on the Broads. my favorite inland waterways.