Fuel consumption

[Charles]

What is the range of Blue Ice, Rich and/or Louise, under 'normal' cruising circumstances.

[Richard B]

About 180 nautical miles is safe, 200 miles if conditions good and careful on the throttle. We have a capacity of 270 litres.

[Charles]

Thats pretty good! I'm about the same, although my tank capacity is 420 litres with 2 x 225Hp. I have a big problem with trying to keep it down to a sensible speed though, what a difference a few knots make in fuel consumption!?

[brucehawsker]

Been thinking of range issues for Farfetched in last 24 hours. The global average figure off the smartcraft gauge (to date since new, now 54 hours) is 1.1 - I think that is nm/l.

Tank is a nominal 160 ltres, although Kev at Solent told me that I should assume 20 l are effectively inaccessible.

So how do I calculate a safe figure? Lots of the usage so far has been blasting around having fun at close to WOT. I unfortunately did not take the numbers before and after Littlehampton cruise.

Bruce

[Jimbob]

The best way is to try e.g

1) find out what you average comsumption is
2) leave 25- 20% of your tank for sefety - so if you get in a jam, e.g tide against you ++++++, then you will be OK

[Alan]

Originally Posted by brucehawsker

Been thinking of range issues for Farfetched in last 24 hours. The global average figure off the smartcraft gauge (to date since new, now 54 hours) is 1.1 - I think that is nm/l.

Tank is a nominal 160 ltres, although Kev at Solent told me that I should assume 20 l are effectively inaccessible.

So how do I calculate a safe figure? Lots of the usage so far has been blasting around having fun at close to WOT. I unfortunately did not take the numbers before and after Littlehampton cruise.

Bruce

Bruce,

Firstly look at the manual for the smartcraft guages and establish whether your 1.1 figure is nm/l or l/nm. It makes a 10% difference & you need to know.

Secondly, a fair assumption is that 20l of your tank is not useable.

Thirdly, calculating a safe range should be based on cruising rather than blatting around. Its the distance travellign where its more important anyway.
Assuming you have 140l of useable capacity and do 1.1nm per l. In theory you have a range of 154nm. However a 20% reserve is a sensible precaution so a range of 123 nm is more realistic. But, and heres the important bit, be sure to factor in weather and seastate when planning trips. You will burn significantly more fuel in bad weather - working the throttle more to maintain a comfortable ride as you burn fuel to lift the bow, accelerate down waves etc etc. Think about it this way, you have many more humps to get over than when the sea is flat so you are travelling further to go the same distance if you see what I mean!

You should also do some fuel burn tests at a comfortable cruising speed. Unless conditions are dead calm and your wallet is bursting, you are not going to be travelling any significant distance at WOT. If you did your range is probably going to be 70nm not 123 nm! If you cruise at a comfortable speed say 25-30kts you will probably get max range. The smartcraft guages can help you with this IIRC. You can look at litres burned per hour and range at different speeds and set your speed and trim to maximise fuel economy.

HTH, Nice article in RIBLINES btw. I rather suspect I was one of those that told you to just get on a buy a bloody boat. Glad you are enjoying her now!

Alan

[Seaharrier]

Bruce,

We have a 220l tank + 2 jerry cans of 22l. I put a low fuel alarm at 40l. That means we have 80l spare fuel on board when the low fuel alarm goes off. Most people calculate there fuel consumptions and the a amount of spare fuel needed in almost optimal conditions. Our engine (250HP ) burns 25 - 30l at 25kn but with a heavy sea we will burn much more!

Once we had engine problems although there was still 50 l of fuel left in the tank. Due to the (very) big waves the engine sucked air and died. That was our first scary experience . At that moment we were very happy to have 2 jerry cans of fuel!

So it’s good to know the fuel consumption of your engine in different circumstances but take margins!

[Richard B]

Originally Posted by Alan

establish whether your 1.1 figure is nm/l or l/nm. It makes a 10% difference & you need to know.

You sure do, but it's 20% difference... think about it!

Also remember that arriving at your destination with exactly zero in your tank probably isn't acceptable - you may find that the fuel pontoon has moved!

[jwalker]

Originally Posted by brucehawsker

.....although Kev at Solent told me that I should assume 20 l are effectively inaccessible.

Bruce, why would that be?

[Pete7]

Jeff,

Whilst I wouldn't dream of comparing a Tohatsu and a Solent Rib against each other , I think the fuel tanks are a very similar shape. They are very long and shallow so even with baffles the last bit of fuel could be beyond reach.

The important question though for a Solent based Rib is can it make it across the channel to France or Alderney and I think Alan answered that.

Pete

[gavin]

I have thought about this aswell Jwalker, I wonder does the fuel draw off pipe in the tank, stop say an inch from the bottom, we have a 440 ltr tank I dont know if the draw off pipe hits the bottom, or is pipeed all the way back

[jwalker]

There is no way I would have a tank with the pickup pipe above the lowest point of the fuel. I reckon any contamination needs to be sucked out as it happens and caught in a filter. Not for me the potential of having 20lts of gloop in the bottom of my tank. A big problem waiting to happen.

Any reasonably designed tank would have a fitment inside, similar to a swirl chamber, which holds fuel at the pickup pipe while the rest of the fuel is slopping about. For a boat, to me, it makes no sense to have otherwise.

[Pete7]

I am almost certain that the Tohatsu fit flat bottomed tanks with the pick up 1/4 " above the bottom of the tank.

Pete

[eupa]

About 180 nautical miles is safe, 200 miles if conditions good and careful on the throttle. We have a capacity of 270 litres.

At 2000 rpm - what speed are you doing( normal conditions) and how many liters/hr please- info needed whne I do Niewport /New York direct
Jonatahn

[Richard B]

Originally Posted by eupa

info needed whne I do Niewport /New York direct
Jonatahn

On which planet are you doing that?

[eupa]

dont mock it Richard - I need some 3000 liters of fuel even in a force 6 - which should give me 70 hours running+ a top off on the scilly isles. It can be done.

jONATHAN

[Richard B]

Originally Posted by eupa

I need some 3000 liters of fuel...

I was right - you're not on this planet! I make it approximately 3500miles, so if your burn rate is 2 litres per mile per engine (remember you're going to be seriously loaded down) - you'll need about 7000 litres PER ENGINE!

[Nick Hearne]

I smell mackerel!

[Richard B]

Indeed!

[eupa]

dont mock it Richard - I need some 3000 liters of fuel even in a force 6

Oh sorry - I forgot to tell you -am going to be refuelled at sea- 3000 liters was to my waypoint.

Jonathan