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Old 31 May 2014, 18:51   #1
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Advice about fuel consumption for a newbie

I have an Excel 2.6m inflatable, 5hp Vector engine and with a 12l external tank.
How long will the 12 ltr tank run before empty. I know any answers will be estimates but i am trying to calculate the amount of fuel to take on my 3/4 day fishing trips to different lochs.
I operate the engine on low to mid throttle the majority of the time and rarely run with the throttle in the mid to high range.
Thanks for any advice received
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Old 31 May 2014, 19:19   #2
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Best advice would be to fill the tank (or at least note where the level is), run for a set amount of time (an hour is best but a fraction will do if you can't spend the time), and see how much you burned. Then add a third again as a fudge factor to whatever you think you need.

jky
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Old 01 June 2014, 02:39   #3
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Thanks will do on next trip
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Old 01 June 2014, 03:17   #4
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You will probably find some rib net rules of thumb if you search too.

Something like 1US gal per hour per 10hp at WOT.

But at cruising speed 1litre per NM but the varies from 0.7 to 1.3 aand more depending on the number of gee gees, the boat, weight of passengers kit etc. I think that's a rib value rather than a sib value.

Suspect the sea state will have more influence on Sib performance...
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Old 01 June 2014, 04:33   #5
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Some tips below from a few days ago. 10% of HP in UK gallons (ie 4.5 litres) per hour at WOT is a good rule and gives a very safe margin indeed. Pootling will be much less.

So for you 2 and a bit litres per hour at MAX throttle but as you say you go low to mid throttle you could realistically half this...

SIBs do a lot more than 1 NM per litre!

what size fuel tank??
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Old 01 June 2014, 04:57   #6
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To answer your question from a different perspective, a 12L tank of petrol will run your rig all day. There appears to be a 1.3L internal tank on your motor as well, an ideal reserve that would take you MANY miles. I would run on the main for the earlier part of the day and then switch to the internal tank for the return trip - it's best not to leave petrol sit more than a few months. As you have an internal reserve, you could use this to test your consumption for an hour to get a better picture of your typical usage. But believe me, you'll be pleasantly surprised at how little you use.
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Old 01 June 2014, 06:52   #7
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Thanks to you all for the advice
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Old 01 June 2014, 14:21   #8
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One thing is consumption at plane at wot, maintaining plane at 1/2 to 3/4 throtttle, than at just fast displacement boring speeds...

Things to have into account for best fuel usage : sib is properly inflated, well weight ballanced, engine well height seated, trimmed, water conditions.. A 2.70 sib which has more hull drag compared to a larger size, will plane and perform much better with a larger engine than with a 5 HP.

Assume you have tested that combo already ? Does it plane well and fast ? takes its time ? Its a pig on water ?

Happy Boating
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Old 01 June 2014, 16:02   #9
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A 5hp I'd estimate 2 litres an hour at WOT max.
Rule of thirds says
A thrid out
A third back
A third in reserve
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Old 01 June 2014, 18:51   #10
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Thanks once again for all the help
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