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Old 07 October 2008, 08:36   #1
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Fuel advice

Hello fellow sibbers!

Would be grateful for some advice. I'm pretty inexperienced having only been out one or twice. I'm planning a trip for later this month which will involve us travelling 12 miles (or more) along the Sound of Mull, Scotland (coastal waters) and it would be useful to know an approximate amount of fuel to take with us. Its a 3.8m bombard with a 25hp engine so would be useful to hear from anyone with the same sort of configuartion and who has more experience. I understand that fuel use has a lot to do with speed and water conditions, knowing Scotland's coastal waters, it may be a bit choppy so plan to just phutt along about 3/4 miles an hour.

Any info/advice/recommendations would be much appreciated.

Cheers
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Old 07 October 2008, 10:13   #2
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bit hard to say but unless its a 4stroke you may use more fuel than you think even at just a few miles an hour, than when on the plane but it depends how much weight there is ,hopefully someone on here may have a similar set up to you ,
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Old 07 October 2008, 10:17   #3
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Originally Posted by Rexmundi View Post
Hello fellow sibbers!

Would be grateful for some advice. I'm pretty inexperienced having only been out one or twice. I'm planning a trip for later this month which will involve us travelling 12 miles (or more) along the Sound of Mull, Scotland (coastal waters) and it would be useful to know an approximate amount of fuel to take with us. Its a 3.8m bombard with a 25hp engine so would be useful to hear from anyone with the same sort of configuartion and who has more experience. I understand that fuel use has a lot to do with speed and water conditions, knowing Scotland's coastal waters, it may be a bit choppy so plan to just phutt along about 3/4 miles an hour.

Any info/advice/recommendations would be much appreciated.

Cheers
Just to have an idea: 2 strokes engines consumes about 10/12% of it's HP, that is 2.5 gal per hour at full throttle, 4 strokes consumes 25/30% less, about 1.75 gal hour at full throttle. In choppy waters cannot run fast, gets to bumpy, if cannot refuel where you will be heading for, take another 6 gal tank, so to have 12 gallons in total. "Better to have more and don't need it than to have less when in the need"

Happy Sibbing
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Old 07 October 2008, 11:33   #4
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Rex,

If we first assume it is a nice day (its unlikely as there was one already this year!):

You will be able to do around 20 knots at full throttle with your set up in good weather. 12 n.m. will therefore take you less than 45 minutes.

Your engine will use roughly 2.5 US Gal/hr at full throttle = just over 7 litres for the trip. The general rule is you want 1/3 of your tank for the outbound trip (which leaves you 1/3 to get home, and 1/3 in reserve). So you would be fine with a standard 25L tank.


Now if its seriously choppy and you are only able to manage 4 knots (actually at that point I probably change my plans or go home!).

12 nm will take you 3 hours.

Your engine isn't going to be working flat out, but as m. chappelow says will not be very efficient and will still use a fair amount of fuel.

If we assume you need half the amount of fuel to maintain 4 knots compared to 20 knots (probably pessimistic - but better to do that than run out!). Then you will need around 14L on the way out. 14L on the way back and ideally another 14L reserve.

My boat and engine are similar-ish to yours (3.9m mid v-hull, with 20HP 2-str engine) and in mixed use I would use no more than 1/2 a tank (12.5L) in 3 hours. So I think that the above estimate is a sensible approximation. If I was planning to make a 12 mile trip (each way) in that part of the world I would be carrying 25L of fuel in my main tank plus at least 10L spare in cans.


OH and of course check your fuel before doing the return leg, and change your plans if you don't have well over 1/2 what you started with.
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Old 07 October 2008, 11:54   #5
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If we first assume it is a nice day (its unlikely as there was one already this year!):
LOL.



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Now if its seriously choppy and you are only able to manage 4 knots (actually at that point I probably change my plans or go home!).
Or stay home.


Quote:
OH and of course check your fuel before doing the return leg, and change your plans if you don't have well over 1/2 what you started with.
There's a good suggestion.

Though 12 miles shouldn't be much of a problem at all. Being relatively new, I doubt Rex will be tempted to bash through heavy weather. Yet. Least, I hope not.

Luck to you, Rex;

jky
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Old 08 October 2008, 15:28   #6
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Originally Posted by Rexmundi View Post

I'm planning a trip for later this month which will involve us travelling 12 miles (or more) along the Sound of Mull, Scotland (coastal waters) and it would be useful to know an approximate amount of fuel to take with us.

Cheers
Are you going solo or in company? - if there is a bigger boat get them to carry fuel. Take 2 25l cans that should be ample for trip and reserve

Will your boat be heavily laiden? - (people, kit etc) if not i'd be carrying the second can at the bow (well strapped in of course)

I have uesed 25hp f/s and struggled to get through a can in a day however an older 2 stroke being 'worked' in a chop can eat the stuff for fun.

More go juice the better
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Old 08 October 2008, 15:35   #7
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Might also be worth checking the tidal stream up that way, that could play a big factor in fuel calculation.
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Old 08 October 2008, 16:08   #8
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I used to have a Bombard with a 2 stroke 30hp Mariner. Left Resipole (Loch Sunart) and crossed to Tobermoray. 2 folk and a big dog on board with just picnic stuff and guddle. It did surprisingly well at about 10mile/gallon. But without fuel you're going nowhere so take plenty to be sure. If it's choppy, make sure your teeth are firmly in place.
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Old 08 October 2008, 16:49   #9
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Might also be worth checking the tidal stream up that way, that could play a big factor in fuel calculation.
Indeed it does Rex.. you'd be surprised at how just a very few knots of tide can throw you out over a distance



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If it's choppy, make sure your teeth are firmly in place.
For the distance you are talking about in that size of boat .. be prepared and have a bail out plan for safe haven if you or your occupants feel like youve had enough 'phutting' as you put it is all very nice when the sun is out , but at the time you want to do your trip, check your forecasts carefully.. since change is seldom an hour or two away round these parts .. dont mean to be pessimistic.. just do your homework first
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Old 08 October 2008, 18:01   #10
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Fuel advice

Thanks for all this info guys. Its much appreciated.

Just to clarify, it's a round trip of 12 miles (cheers Polwart, I'll half that calculation you provided) and there will be 3 adult males with packs and supplies for an overnight trip incl. coal and logs. We have a 12l fuel tank and will back that up with another 10l in a jerry-can (unless you guys recommend any different).


You're right to raise concerns over our inexperience. In August we took a trip across Loch Ailort. We sailed on the Friday, returning on the Sunday and experienced contrasting conditions. But we were prepared with tide tables and weather forecasts so at least we weren't surprised. For this trip, if the weather forecast is going to be windy then we'll have a plan 'B' and go elsewhere, like upstream on Loch Etive.

With regards launching and the tides, what do you recommend? For our last trip it was easier to launch from a rocky shore at high tide, arriving at high tide on a sandy beach. This time we will be (probably) launching from a concrete slipway (so not so important to leave at high tide I presume) and arriving at a rock/sandy beach.

In what way can we use the tide to move us along more efficiently?

Thanks again guys, this information is really useful to us.

Tony
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