Mercury 135, How thirsty?

[diver]

I am considering the purchase of a signature 540F (17.6ft ) which has a 1997 Mercury 135 carburetted outboard. Can anyone with this motor on a 17 to 18 foot rig tell me how much fuel it uses in cruise mode which would be about 20knots at 3500rpm on this size hull in average conditions As its not working as hard as a similar boat with a 90hp engine I would be interested to know what this size engine would use.I do know a 90 uses about 1litre per natuical mile at4200rpm for the same speed

[Oldyella]

General rule for 2 strokes is 10% HP at WOT in USA gallons used per hour.
135hp will use 13.5 US Gallons in 1HR at WOT.
If the boat can reach say 30knots at WOT it will use 13.5 US Gallons or 11.5 AUS Gallons to cover 30 Nautical miles. 35 miles.
This is around #3-4 miles to the gallon..2 strokes are thirsty little mothers.. At cruising speed I would say 5-6 MPG

[Oldyella]

[AaronF]

I'm not sure about the mercury but owned a 17' Seafarer Viking with a 1996 140hp Suzuki 2 stroke (Carburetted). The Haines I guess would be around the same weight from what I know. Fuel usage really varied depending upon conditions and load. The dealer claimed the engine should be using about 18 - 20 litres/hour at cruising speed. I found the most economical rev range to be about 4000 rpm which gave us about 21 - 24 knots depending upon trim and water conditions. I figured about 22 - 25 litres/hour at cruise. An "average" trip would entail us heading from Scarborough to Hutchies in as straight a line as possible via Comb point. Trolling lures for 4 - 6 hours at a SOG of 6-8 knots and then maybe a bit of stop start bottom bashing around there and a trip home is weather not usually as kind as the trip out but not terrible. Fuel would be 135 - 150 litres on average. I always packed 20 litres in a spare tank that would get me to land in a worst case scenario anyway or home if you were at Comb point in most conditions. It really used fuel (more than at cruising speed) when trollong hex heads at 10-14 knots so I gave it away after not catching any more fish than the slower trolling. Usual crew was 3 - 4 + gear and 160-180 litres of fuel (140 tank + 20 or 40 spare for a big day out). I think you will find that 3500 rpm is not your most economical rev range as with a heavy hull it tends to want to slow down into a swell and you have to keep gassing it. I'd buy a fule flow meter and check it out for sure so then you really know and can charge your mates for the right amount of fuel if that's your thing. Have Fun. Aaron

[Spot_X]

G'day Diver I have a 135 1996 mod merc on a 1850L signature. I cruise at 4000 rpm this gives me a speed of 50kmh over ground. Fuel usage at this speed is 1.4km per 1litre of fuel. I work on a safety margin of 1km per litre of fuel.eg (rough seas)Roy.