Can you Solve this Mystery.........

[Rob Jones]

Originally Posted by Nos4r2

Is the main tank lower than the 25 litre tanks?

Here's what I think happened-assuming the main tank is lower than the 25 litre tanks.

You were drawing from the main tank 'til the fuel slowly syphoned into the main tank from the 25L tank as the valve wasn't open fully.

You then started drawing air into the lines from the empty reserve tank, creating an illusion of being out of fuel.

<edit> just seen the second page. I think you're right.

Im going with this theory, and in a way its reassuring as I was gutted that my fuel efficient engine was costing 260l to cover 82 miles in what was really flat calm conditions, ok yes we were gunning the engine as much as it would go but I still would like to think it was better than that.
SO now it looks like 150l is more realistic.
And yes the 2 external tanks sit on the deck and the internal is buried somewhere under the console with the pickup being at the bottom. I will dig out the build thread that shows the fuel set up

[Poly]

Originally Posted by willk

Rob & Nos have to be Right!

The 25L tank (not in use) was discovered empty after 3 hours running. Obviously it was slowly releasing SOME fuel to either the engine or the main tank via the switch. Once this fuel was gone, air was then introduced to the fuel lines, stopping the engine. The fuel was later found to be in the main tank..

so where did the 210 L bought in france go... or did they screw over les ros beouf

[Rob Jones]

Some pics of the fuel set up

http://www.rib.net/forum/attachment....9&d=1244666283

[Rob Jones]

Originally Posted by Polwart

so where did the 210 L bought in france go... or did they screw over les ros beouf

some of it went travelling over to Braye from Cherbourg, and mucking around while we were there, Diving etc.
I filled up with MarineBrayce in the morning of departure. Which seen me leave with 260l total on the boat

[bedajim]

I'd get a fuel flow meter and just see what it's drinking at different rpm and boat loads etc so you know for future use

Jim

[Poly]

Originally Posted by Rob Jones

some of it went travelling over to Braye from Cherbourg, and mucking around while we were there, Diving etc.
I filled up with MarineBrayce in the morning of departure. Which seen me leave with 260l total on the boat

My point is - you had 210 L of fuel tank space. You bought 210 L in france, so you were indeed empty in Cherbourg - not only partially empty with air in the fuel line as has been suggested. If you still have 50+L in your main tank but couldn't get it out then you couldn't have bought 210 L in france as you had nowhere for it to go...

[Rob Jones]

Originally Posted by bedajim

I'd get a fuel flow meter and just see what it's drinking at different rpm and boat loads etc so you know for future use

Jim

I had one of those fitted, a Navman job, but it broke on the trip and according to the Ribshop (I just had the boat serviced) its dead and they no longer make that brand. So I have a nice dial that does nothing on my console

[Rob Jones]

Originally Posted by Polwart

My point is - you had 210 L of fuel tank space. You bought 210 L in france, so you were indeed empty in Cherbourg - not only partially empty with air in the fuel line as has been suggested. If you still have 50+L in your main tank but couldn't get it out then you couldn't have bought 210 L in france as you had nowhere for it to go...

Ah no - sorry for the confusion, I am not debating the trip out there, sure as eggs are eggs I ran out.
Where the confusion came from was on the return trip where I had 260l and emptied what I presumed was all fuel, but 3 weeks later I fill the tank up and can only get 50l onboard indicating I still had 110l in

[Boats&Outboards]

Originally Posted by Rob Jones

Ah no - sorry for the confusion, I am not debating the trip out there, sure as eggs are eggs I ran out.
Where the confusion came from was on the return trip where I had 260l and emptied what I presumed was all fuel, but 3 weeks later I fill the tank up and can only get 50l onboard indicating I still had 110l in

Its obvious then. Somebody is filling your tank for you :whistling

Peter ~ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007

[Rob Jones]

Originally Posted by Boats&Outboards

Its obvious then. Somebody is filling your tank for you :whistling

Peter ~ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007

Well they are welcome to keep filling - hopefully they can top it off before the weekend as I might run over to Calais

[Searider]

Rob if you were at sea for about 10 hours and used 260 litres (I think that what's you said) that's 26 litres per hour.

Surely that's about right if you were "gunning it as much as you could" with the boat "super heavy loaded".

For reference my 150 Optimax uses 56 litres per hour flat out according to the Smartcraft gauge.
22 litres per hour for 27 knots when the boat is lightly loaded.
Heavily loaded (8 people and weekend kit) it needs to be almost flat out for high 20 something knots.

[Rob Jones]

Originally Posted by Searider

Rob if you were at sea for about 10 hours and used 260 litres (I think that what's you said) that's 26 litres per hour.

Surely that's about right if you were "gunning it as much as you could" with the boat "super heavy loaded".

For reference my 150 Optimax uses 56 litres per hour flat out according to the Smartcraft gauge.
22 litres per hour for 27 knots when the boat is lightly loaded.
Heavily loaded (8 people and weekend kit) it needs to be almost flat out for high 20 something knots.

Thanks for the reply, and actually its better than that - on the way out I had 210l and ran out 1mile offshore. Therefore its say 22l per hour.
Where I was really concerned was the return trip, as I used 260l for a 5 hour run and was gutted as thats not great consumption. But 3 weeks later I find there is still 110l in the main tank which to me ran out.
So based on those figures
Trip out - Avergage Speed 8 knots
Fuel Consumed - 210l (would really of been 220 had I not had the coastguard pick me up
Travel time = 10 hours
Total 21l per hour

Return Trip
Average Speed - 25knots (WOT for 2.5hours)
Fuel Consumed - 150l
Travel Time - 5 hours
Total - 30l per hour

Like I say the only spanner in the works was the thought that I had actually used 260l for the return and that would equate to a 52l per hour which is a sting in the pocket.

Searider - your speed andfuel figures are very much the same as mine, if I have 8 people on the boat it takes full throttle to get it up to the high 20 knots. But with a couple of light kids and a can of coke she will fly at 38knots.
Do you ever find when your boat is loaded the sea can sometimes "grip" the boat and your speed will drop and struggle, then suddenly it gets released and will surge back up tp speed

[gazb]

How long had the fuel been in there?
Would not run if water contamination
Hence the fill up was so cheap

[BogMonster]

Originally Posted by bedajim

I'd get a fuel flow meter and just see what it's drinking at different rpm and boat loads etc so you know for future use

Jim

I agree - with the Etec having fuel flow / instant fuel consumption and fuel used/remaining, I have a very good feel for what the engine will use at all sorts of speed and sea conditions. I never had much of a clue with the old boat and engine, but I'd not go back to anything without fuel flow information again.

[hobbit555]

Rule of thirds for me....

1/3 to get there,
1/3 to get back
1/3 to play with the weather!!!

[Poly]

Originally Posted by hobbit555

Rule of thirds for me....

1/3 to get there,
1/3 to get back
1/3 to play with the weather!!!

Presumably for a cross channel type trip you wouldn't carry 3x the amount required to get to a refilling point though?

If the OP had done that he would have about 3/4 of a tonne of highly flammable fuel weighing down his boat and taking up masses of deck space, probably in cans which weren't that secure and are a nightmare for refilling at sea anyway.

[Searider]

Originally Posted by Rob Jones

Thanks for the reply, and actually its better than that - on the way out I had 210l and ran out 1mile offshore. Therefore its say 22l per hour.
Where I was really concerned was the return trip, as I used 260l for a 5 hour run and was gutted as thats not great consumption. But 3 weeks later I find there is still 110l in the main tank which to me ran out.
So based on those figures
Trip out - Avergage Speed 8 knots
Fuel Consumed - 210l (would really of been 220 had I not had the coastguard pick me up
Travel time = 10 hours
Total 21l per hour

Return Trip
Average Speed - 25knots (WOT for 2.5hours)
Fuel Consumed - 150l
Travel Time - 5 hours
Total - 30l per hour

Like I say the only spanner in the works was the thought that I had actually used 260l for the return and that would equate to a 52l per hour which is a sting in the pocket.

Searider - your speed andfuel figures are very much the same as mine, if I have 8 people on the boat it takes full throttle to get it up to the high 20 knots. But with a couple of light kids and a can of coke she will fly at 38knots.
Do you ever find when your boat is loaded the sea can sometimes "grip" the boat and your speed will drop and struggle, then suddenly it gets released and will surge back up tp speed

Hi Rob,

Not noticed a surging.

This fun does cost some!

Duncan