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Fuel economy - Mercury Optimax 115

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    Posted: 28 Nov 2020 at 8:14pm
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Just bought a boat with this on the back....took it for a run on a lake today and was a little surprised to use close on $90 of fuel for an hour cruising around. I was playing around with the trim to see what effects it had on ride, etc. 

What consumption would you expect to get from this outboard? Also, what optimal settings am I looking for in trimming an outboard ......trim appears to be measured in degrees (or am I getting that wrong?) Boat is a 5 and a half metre McLay.

Thanks in advance!!
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Post Options Post Options   Likes (0) Likes(0)   Quote Big -Dave Quote  Post ReplyReply Direct Link To This Post Posted: 28 Nov 2020 at 9:53pm
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There is no abitarty optimum trim.
Trim up when you are cruising until the boat porpoises, or the propeller ventilated. .. then back down a touch to stop whatever just happened. Learn how the boat feels, the ow comes up, steering gets lighter etc.
In rough weather you might want to trim the bow down.

And 45 oddliters in an hour does sound a lot.
you can't fix an idiot with duct tape, but it does muffle them for a while...
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Post Options Post Options   Likes (0) Likes(0)   Quote Nek minnit Quote  Post ReplyReply Direct Link To This Post Posted: 28 Nov 2020 at 10:49pm
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Wow. I went around the hen n chicks from manga and back last week with my opti 125 and would have been lucky to use 20lt. I think you have a fuel problem.
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Post Options Post Options   Likes (0) Likes(0)   Quote bricker Quote  Post ReplyReply Direct Link To This Post Posted: 29 Nov 2020 at 12:05am
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So the gauge that says "trim" and a reading of 6.6 or 7.2, for example, is reading what exactly? Anyone know of an online Operator's Manual for an Optimax 115?

As for the fuel consumption, I'll set the odometer and monitor next time. (when I filled up on the way to the lake, I assumed that when the nozzle clicked 'off' it was full rather than a false click!!)   Assumption is the mother of all cock-ups!!


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Post Options Post Options   Likes (0) Likes(0)   Quote pjc Quote  Post ReplyReply Direct Link To This Post Posted: 29 Nov 2020 at 5:46am
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Originally posted by bricker bricker wrote:

So the gauge that says "trim" and a reading of 6.6 or 7.2, for example, is reading what exactly? Anyone know of an online Operator's Manual for an Optimax 115?

As for the fuel consumption, I'll set the odometer and monitor next time. (when I filled up on the way to the lake, I assumed that when the nozzle clicked 'off' it was full rather than a false click!!)   Assumption is the mother of all cock-ups!!


under flor tank??fuel guage??had a mazada in oz that when clicked off presume full and faulty guage.Turned out niether.Had  to slow fil due to way fuel pipe went into tank as didnt allow air to escape properly.
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 29 Nov 2020 at 10:12am
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Daves post above descibes using trim.
Just adding .. at stop, trim right down, throttle forward to get over the bow wave onto plane, then trim up as he describes.
Every speed and sea combo has its own trim position.
The trim gauge will vary between boats , set up etc

If you took out and was doing a few stop starts , accelerate,  some high , or very fast cruise runs etc, you WILL chew thru fuel quick.
 Get on the plane, trim up (as Dave describes) then just cruise... If proped well will be about the 3800/ 4000 rpms on a well powered boat..
 Think of it like cruise control on a motorway with no towns, hills or traffic Wink

 When I fill up, my fuel tank breather pipe is close toi the filling piont. I put my finger over tyhe vent so the air still flows out. As soon as a bit of fuel is there stop filling. Let the foam in the filler pipe and tank drop and top off.

If the breather/ vent is the stern end of the boat, and boat sits bow up at the pumps, you will get a air lock at the bow end of the tank... I had a 130L under floor.. I could only get around 90L into it.
Even dropping the trailer off the vehicle, wind bow down on jocky wheel the bow end of the tank was still high and estimate then got about 100, maybe 110 into the tank.

 Boat tank gauges are notoriously inaccurate due to9 being a generic sender unit in different sized/ depth tanks.
I have just replaced my 130l tank with a150L that has vents both ends.
The fuel out of the old tank (about 65L) I added back with the trailer hitched to the tow ball.. then filled 10L at a time making pictures of the needle on the fuel gauge...
 Then continued to fill at the pumps, also noting the gauge level (just over 3/4 is full)
 And have also noted level on gauge when back at ramp, still on the water.. then filled the tank.
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Post Options Post Options   Likes (0) Likes(0)   Quote Nickb1 Quote  Post ReplyReply Direct Link To This Post Posted: 29 Nov 2020 at 10:37am
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even with my opti 115 having a **** prop, I went out to the chicks last weekend from marsden, about 40Nm and had the outboard running most of the day chasing work ups and still only used 30L, thats 0.7-0.8L/Nm!
I am really looking forward to seeing the proformance of my new prop next weekend.

as for the trim reading, its just a variable resister sensor, its not really tuned right to read in degrees as such, like with my smart craft gauges, I have to do a calibration on the trim sensor so I tell it where full down is and where full up is and then it divides that into 10 parts.
hope this helps
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Post Options Post Options   Likes (0) Likes(0)   Quote Bounty Hunter Quote  Post ReplyReply Direct Link To This Post Posted: 29 Nov 2020 at 2:23pm
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Originally posted by bricker bricker wrote:

Just bought a boat with this on the back....took it for a run on a lake today and was a little surprised to use close on $90 of fuel for an hour cruising around. I was playing around with the trim to see what effects it had on ride, etc. 

What consumption would you expect to get from this outboard? Also, what optimal settings am I looking for in trimming an outboard ......trim appears to be measured in degrees (or am I getting that wrong?) Boat is a 5 and a half metre McLay.

Thanks in advance!!

sounds like an erroneous measurement on this occasion - no way youre using 40+ litres per hour

make some more notes on fuel and distance next time and get back to us if youre using more than 1litre per nm


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Post Options Post Options   Likes (0) Likes(0)   Quote bricker Quote  Post ReplyReply Direct Link To This Post Posted: 30 Nov 2020 at 7:05am
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sound plan Bounty Hunter........it was a sobering moment at the pumps, all the same!! 

Having come from a Haines v17L + Johnson 120 that chewed fuel via a light Marco + Etec 60 that used nothing to the McLay 566 + Optimax 115, I reckoned I'd be somewhere in between the 2 extremes. I'll pay more attention to distance and run time on the next outing! 
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Post Options Post Options   Likes (0) Likes(0)   Quote Rozboon Quote  Post ReplyReply Direct Link To This Post Posted: 30 Nov 2020 at 9:15am
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That's bonkers fuel usage... a quick google suggests that WoT fuel consumption for that motor is 37.4LPH... I mean, I know it's a fairly arbitrary measure, but you're maybe 25% over that in what shouldn't be a terribly heavy boat?
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Post Options Post Options   Likes (0) Likes(0)   Quote neil_cb125t Quote  Post ReplyReply Direct Link To This Post Posted: 30 Nov 2020 at 10:45am
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Fuelling up can often be the problem not the amount actually used.

I had a good 25-30% discrepancy between my gauge and litres at the pump. Seems it was all about the vent or lack of venting, so the tank would pink the nosel off and have fuel pouring out but there was more gap in the tank.

For me I have to drop the boat off the car hitch so its bow is down - my filler cap is at the back so that helps alot. This makes filling up more accurate.

chap
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 30 Nov 2020 at 11:15am
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what shouldn't be a terribly heavy boat?
 around 1200kg 3 guys bit of gear gross weight on water.
115 hp will give around a WoT speed 38/42 mph if ball parked propped.
Bottom 'edge of well powered so lot of acceleration, star stop , getting over bow waves, a few full on good WoT  or near WoT runs will quickly get above the official 37l/hr.
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Post Options Post Options   Likes (0) Likes(0)   Quote Rozboon Quote  Post ReplyReply Direct Link To This Post Posted: 30 Nov 2020 at 11:18am
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Originally posted by Steps Steps wrote:

what shouldn't be a terribly heavy boat?

 around 1200kg 3 guys bit of gear gross weight on water.
115 hp will give around a WoT speed 38/42 mph if ball parked propped.
Bottom 'edge of well powered so lot of acceleration, star stop , getting over bow waves, a few full on good WoT  or near WoT runs will quickly get above the official 37l/hr.


The current McLay 551 is 900kg BMT... so 1200kg maybe if he went out with the trailer still attached... which would explain the fuel usage
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Post Options Post Options   Likes (0) Likes(0)   Quote bricker Quote  Post ReplyReply Direct Link To This Post Posted: 30 Nov 2020 at 10:11pm
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Lol - the trailer definitely WASN'T attached LOL

The more I dwell on it, the more I think it was a venting issue. As for the gross weight of boat + trailer + outboard + fuel + bits'n'bobs, a weighbridge will never lie!! I'll head down to the local Balance fert store and put it over the scales. 
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 01 Dec 2020 at 8:55am
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Hull weight 900 kg, add another 175/ 200 for engine,2 guys ave say 85 kg .. there is 300kg there.
So 1200 for gross weight on water guesstimate not far off.
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Post Options Post Options   Likes (0) Likes(0)   Quote Rozboon Quote  Post ReplyReply Direct Link To This Post Posted: 01 Dec 2020 at 10:01am
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Originally posted by Steps Steps wrote:

Hull weight 900 kg, add another 175/ 200 for engine,2 guys ave say 85 kg .. there is 300kg there.
So 1200 for gross weight on water guesstimate not far off.


900kg BMT - Boat Motor Trailer - although it wouldn't be the first time a manufacturer fibbed a wee bit.

But yes, put it over a weighbridge for the full truth, or do the Steps thing with the jockey wheel and scales.
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 01 Dec 2020 at 1:44pm
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Yep, they say "hull weight"  then in the description mention hull weight is defined as BMT...
So add 2 guys 160kg
Tank gas 80L approx 70kg
Battery(s) anchor, gear and other optional addons gets up quick to around  200/250 kg thats still not far off "around 1200kg" Gross weight on the water.
 Still not a bad guesstimate off the top of the head back when posted right?
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Post Options Post Options   Likes (2) Likes(2)   Quote Rozboon Quote  Post ReplyReply Direct Link To This Post Posted: 01 Dec 2020 at 3:56pm
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I dunno about you but I'm not loading my trailer boat with a literal half-ton of crap (myself included in said crap!)

I reckon you're out by 20% on this one, but we digress.

My wager is either some sort of inaccuracy in measuring the actual fuel used... from not-actually-full to actually-full would be my guess. Unless you were out there for an hour at WoT or towing a waterskier or something.
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 01 Dec 2020 at 5:44pm
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but I'm not loading my trailer boat with a literal half-ton of crap

 ppl, batteries, anchors, winches , gps, a full fuel tank etc are not crap. to the rest of us boaties
1/2 ton is not 250/300kg..

 And you are the one who brought this up trying to split hairs again wishes to digress with this crap.
 

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Post Options Post Options   Likes (1) Likes(1)   Quote smudge Quote  Post ReplyReply Direct Link To This Post Posted: 01 Dec 2020 at 6:35pm
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