Mariner outboard fuel consumption

bobdoughty

bobdoughty

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Hi. Does anyone have any idea what the fuel consumption of a two-stroke Mariner 8hp saildrive outboard engine might be? I'm taking my newly acquired boat to its mooring (about 35 miles) and just in case there's no wind I want to make sure I've got enough fuel. Thanks for any pointers.
 
This will also depend on the boat in question, i.ee how easily driven the hull shape is. From my experience in small sportsboats with 4hp 2 strokes, the sea state makes a great difference. I used less fuel in calm weather but in a chop, since the speed was lower, used more fuel due to longer running time (usually on full throttle!). Sorry can't be more helpful, but would certainly take a spare can!
 
Take it easy, and 2 gph would be a safe 'worst way' estimate as it should do 1gph on the river on a 20 footer.

IMHO.
 
I'd plan on no more than about 4 knots so if thats all at sea, and if you can do it all with the tide in your favour you should be able to do it practically all on one tide and take only little more than 6 hours. Unless you are battling against a strong wind and a rough sea I would say you should do at least an hour to the gallon (I reckon about 1/2 gallon per hour with a 6hp on a 19 footer in calm conditions.) But take plenty with you & dont forget the oil.

Very important to work with the tide or you can stand still, just burning fuel.

Warning it can be b.......y cold at this time of year. Have gloves!
 
My Mariner 8 two stroke on a Dockrell 22 uses about three quarters of a gallon an hour, I have a high thrust prop, and there is a mark on the twist grip that indicates the fuel consumption, up to a certain point it is ok, then it rises very sharply, on mine at the point before the sharp rise I am doing about 4 knots and three quarters of a gallon, to open it to full throttle it only increases to 4.5 – 5 knots makes a lot of noise, and does not like running for long periods. Mine coughs after about 15 mins at full throttle but runs happily all day at the mark I mentioned.

Vic's comment about the tide is very valid.
 
[ QUOTE ]
Mine coughs after about 15 mins at full throttle

[/ QUOTE ] That sounds as though it might be suffering from fuel starvation, Could be for any of many reasons eg tank vent, air in-leakage into fuel line, dirty filter, or a restriction somehwere, poor pump performance, dirty jet, incorrectly adjusted mixture etc. It really should run at WOT but I agree that the fuel consumption will increase dramtically.
 
There's a rough rule of thumb for the fuel consumption of two-stroke outboards. It is one gallon per hour per 10hp. So your 8hp should burn about 0.8 gallon per hour. Which seems to tie in with the advice given by the other posters.

Work on the basis of having at least a third over of what you need. Four knots is probably a fair estimate of speed so I would say 9 hrs running at 4 knots is a 7.2 gallons plus a third more comes to 9.5 gallons say ten gallons.

But remembering that you won't get all the fuel out of the tank then I would be super cautious and add another couple of gallons and, of course, there will be some time when you will be going against the tide - so I would take 13 gallons.

It sounds alot doesn't it. Maybe I'm being over-cautious - what do others think?

Shorn
 
[ QUOTE ]
what do others think

[/ QUOTE ] Working the tides could save a couple of hours worth and any time with a foul tide should only be with a weak foul tide.

It could be argued that the trip should only be undertaken when there is a reasonably good chance of completeing it under sail.

The RNLI are always happy to give anyone who has run out of fuel a tow /forums/images/graemlins/laugh.gif
 
The 10 hp per gallon per hour is for US gallons not our Imp gallons so should help privde an added safety margin.

Pete
 
Thanks everyone, very useful. I shall sail and use the tide as much as possible and err very much on the side of caution with extra fuel - don't fancy calling up Dover Coastguard to report out of fuel! /forums/images/graemlins/blush.gif
 
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