Advice about fuel consumption for a newbie

claretcass · 31 May 2014, 22:51

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

jyasaki · 31 May 2014, 23:19

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

claretcass · 01 June 2014, 06:39

Thanks will do on next trip

ShinyShoe · 01 June 2014, 07:17

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...

Max... · 01 June 2014, 08:33

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!

http://www.rib.net/forum/f50/what-si...ank-59834.html

willk · 01 June 2014, 08:57

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.

claretcass · 01 June 2014, 10:52

Thanks to you all for the advice

Locozodiac · 01 June 2014, 18:21

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

SIBer · 01 June 2014, 20:02

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

claretcass · 01 June 2014, 22:51

Thanks once again for all the help

beyondhelp · 01 June 2014, 23:35

For comparison: I've a 2.3m Wetline inflatable with a 6hp mercury 4 stroke. Was 4hp, changed the carb to 6hp version - much better) anyway. On its 1.1 litre approx tank, at half throttle it doesn't last for that long, perhaps an hour or two. As for range, it doesn't get me that far, couple of miles? The inflatable will only plane with one person on it but just pushes through the water really inefficiently with two, if trying to make any kind of progress. Its quite frustrating actually, it will push along a 17ft sports boat at about the same speed it would move the sib with more than one person on it!

Locozodiac · 02 June 2014, 00:34

2.30 sib has too much hull drag for that small engine HP. Lacks fast hole shot.. Once on plane will remain there.

Happy Boating

beyondhelp · 02 June 2014, 00:36

Yep totally agree! 4hp out of interest was not enough to get it on plane. 6hp does easily. (both cases with just myself in it) Max speed seems about ~12mph which may be prop limited or just a physical limitation. No RPM gauge to see whats really going on.

claretcass · 02 June 2014, 07:43

Yes i had considered other options but as i am 70 and new to inflatables i had to make practical choices based on weight and the ability to handle everything on my own lifting everything in and out of the small garage on my motorhome.
I chose a SL260 from excel because it is one of the lightest SIB's of that size weighing around 20kg which can take up to a 6hp engine, i chose the 5hp which is a little lighter than the 6 hp. I am always on my own so i do distribute the few fishing and other items I carry evenly across the floor.
Based on advice from this forum (and my age) I have considered safety very carefully and have got the required gear. Weather permitting i go in sheltered bays around New England Bay (Luce Bay) but mainly in lochs around Scotland.
Must say, wish i had started at a much earlier age as I would most definitely have started "Ribbing" reading some of the items published on here but alas its one of the pleasures that slipped me by but at my time of life I enjoy taking my fishing gear, camera and A far more tranquil approach to moving up and down lochs.
If you ever passing an "old codger" in an SL260 with a big smile on his face going quite slow don't worry, i am not in trouble but simply enjoying the peace, tranquility and the ability to do it.
Thanks for all the help

Locozodiac · 02 June 2014, 16:20

Claretcass,

Boating on a sib or rib is fun at any age, the difference, the younger the more reckless boating, the older the more prudent boating. Cruising at very slow speeds is very heartwarming, just you enjoying the unlimited sea, mother nature, birds, sea animals, wind on your face, and above all peace of mind without city stress. Enjoy your boating time at your own pace.

Happy Boating

claretcass · 02 June 2014, 17:38

My little set up