Fuel Economy

Brian · 16 November 2002, 12:12

Has anyone got any experience of small sib fuel economy?
Specifically I have a Zodiac 3.1m Fastroller with a Selva 6hp 2-stroke engine and a 12l fuel tank.
With one up and a calm sea, how far do you think this will take me? (No rude comments please!).
The more intelligent and perceptive amongst you may have gathered that this is a "testing shot" question prior to an attempt to cross the Pentland Firth next year-consequently currents are an issue.

Charles · 16 November 2002, 12:56

Are you going to be towed again.......har, har, har ?

(Only joking)

Brian · 16 November 2002, 17:50

Blimey. Well let that be a lesson to you all!
You mention intelligence and perception in one sentance, and you get a reply like that!

Garygee · 16 November 2002, 18:27

Hi Brian

We used to have a Caribe 2.8 RIB with a Suzuki 10hp 2 stroke.

We used to go out on Windermere and have a full day of playing, trips to top & bottom of lake, say 20-30 mile in total and still come back with some fuel in a 3.5 gallon tank.

However we always carried a spare gallon !!.

Knows its a bigger engine but also consider it would be at a lower throttle setting for the same speed so may have opperating at a more efficient level.

Think you may have a 6HP WOT most of the time.

Regards Gary

Richard B · 16 November 2002, 20:52

Brian,

I've had much the same experience as Garygee... my SIB has been used mostly on the Thames (4kt speed limit) and has hardly used any fuel at all. Sea use has been limited to short trips, and the 18hp 2-stroke has never got through more than half of the 25-litre tankful - but that's not anything like a full day's trip. The spare gallon's never been in any danger of being used. I'll see if I can find any consumption statistics.

Richard.

Keith Hart · 16 November 2002, 21:14

Same here folks, my 15hp when pottering about seems to make more fuel, never mind use it!

I should think that you'll have no bother getting across the Pentland Firth to Scapa beach Brian. We can also carry spare fuel on the boats. I've never had to use my spare fuel yet and I've a 25l tank.

Keith Hart

Richard B · 16 November 2002, 21:57

This is the best I could find:

http://www.tohatsu-outboards.com/fuel-consumption.htm

It looks realistic - I reckon that 3hrs use at WOT for my 18 sounds about right. And so for a 2-stroke 6hp, I guess the same by the following estimate:

6hp (4-stroke) @6,000rpm = 2.0 litres/hr. (x2 for 2-stroke)

4.0 litres/hr from a 12 litre tank gives three hours.

Some real world testing needed, I reckon!

Brian · 17 November 2002, 09:52

Thanks everybody. That is really helpfull and has put my mind at rest.
So if I said 3 hours at 8-10knots, and then only planned to go 20 nmiles, this should be OK shouldn't it?
PS Not sure that I will do WOT in a 3.1m in the Pentland Firth though!!

Charles · 17 November 2002, 11:16

You're welcome

Richard B · 17 November 2002, 11:21

Quote:

Originally posted by Brian
this should be OK shouldn't it?

"famous last words"

Isn't there supposed to be a support boat? If so, then if said boat had jerrycans of petrol and 2-str oil (and perhaps Wavehumper's siphoning gadget) then passing one's depleted SIB fuel tank up to the support boat for re-filling should be a reasonably safe procedure - sea state permitting!

Brian · 17 November 2002, 15:54

This is all absolutely true Richard.
I have always found though, that God helps those who help themselves.
I am therefore PLANNING to do the trip, with lashings of spare margin, using my own resources.

Richard B · 17 November 2002, 15:56

Quote:

Originally posted by Brian
lashings of spare margin

Can't argue with that.

In fact I'm not arguing at all. Also the "own resources" bit is important.... but you don't need me to tell you this!

DM · 17 November 2002, 16:11

Quote:

Originally posted by Brian

I have always found though, that God helps those who help themselves.

This is probably a very wise maxim, Brian. As I'm taking my rib up, I think Keith sees me as a support boat whereas its usually me that needs supporting. (old age, mental infirmity etc.) I have been having this recurring nightmare of being towed into Scapa Flow by three SIBS, and having to scuttle the boat to lie alongside the German fleet, all the time being photographed by aspiring RIB International reporters. Oh the shame of it!

David.

gavin · 17 November 2002, 23:01

I remember once on a sailing boat coming from Holyhead to Dublin myself and Tim ran my 1979 15hp evinrude at about 3/4 throttle for 9 hours continously on the stern of the sailing boat to give us a bit of a push home, it ran from a 25 litre tank and we topped up the tank with 5 litres as we approached Dun Laoghaire 30 in total .We were left with 2 or 3 litres in the tank so 9 hours 27 litres at 3/4 throttle 3 litres per hour, is this any help gavin

Tiger · 18 November 2002, 17:54

In Chile we had the same problem for our expedition.

We needed to move camp regularly about 15-25 miles with the boats fully loaded (6.5 tons between 7 boats (weight inc boat + engine and the 25 people).

We needed to find out the best speed we could make and fuel consumption so not as to end up adrift in the Pacific.

Answer:

Get GPS set to record trip for average speed over time going into and with the wind in reasonable weather. You need to do both I would say.

Put your fag / candle lamp etc out!

Get an (empty) 1 Ltr plastic coke bottle, rinse with petrol to get worst out. Stick 1 Ltr of petrol in and insert fuel lead into bottle.

Drive off and see how far and at what speed that 1 ltr will get you. Try not to throw the petrol all over you and who-ever is there.

Once you have the results, add a bit extra to be sure.

From experiance before and the experiment, we decided we needed about 4,500 Ltrs over the expedition period, which is approx 4.2 tons I think.

Tiger