Another FUEL CONSUMPTION question for you boating gurus

[No Fear]

Hi Guys, This might be a bit of a repeat question but I am very intrigued to find and answer.
Myself and a mate went to the barwon Banks a fortnight a go (44 km out), me in a yalta 21foot half cab with 2 foot pod (probably makes no difference) powered by a 150hp 2000 model Johnson with 175 carbs (again don't know if this is important) and my mate headed out in a 19 and a half foot Allison powered by an Merc Optimax 135 hp '99 model. Both boats similar in weight (Allison slightly heavier if anything) and we burnt approximately 160 litres of fuel compared with his 76 litres of fuel..... How can this be? Is there a possibility that one has a problem. I realise the Allison's hull is better designed being a new shaped hull but surely that would result in such a reduction in fuel consumption.
Last weekend the Allison ran around Tipplers for about 5 km buggering around and only burnt 5 litres...what the???
Both boats are burning the correct amount of oil per litre of fuel but it seems a little strange to me.......
Let me know if something seems fishy to you gurus

Cheers in advance,

[blaze]

carbie versus fuel injection, its a for gone conclusion. The carbi is a simplistic fuel metering device and the injection is a very accurate metering device with micro tolerences. I know what repair bill I would rather have of the 2 systems.
cheers
blaze

[saurian]

No Fear , optimaxs figures sound about right , but the johno 3.3 odd litres per
per nautical mile.( approx on figures given)
I get 1.8 litres per nautical mile with 2x90 2 banger mercs so the johno is sucking
nearly twice the fuel as 2 x 90hp motors.
Your boats making me feel good, all these " figures are approximate".
Apart from oversize carbies and old generation design , props and driving style would really effect your outcome as well as different hulls.
Ocean conditions I presume where the same , maybe your boat is just not as slippery as the other one !!!!
I had a freind who had a 175 johno , and it used 2 lt/nm at 20 knots unsure of his revs , but heaven forbid if he opened it up, That was on a 7m platey.
I don't know much about glass hulls so can't comment there.
I'm sure a few others will but.
I think I'd be going out and buying an optimax , pay it off quick 100lt a trip.
Ta.

[Noelm]

right on, with carby compared to injection, they cannot be compared, two entirely different motors. but you do SEEM to be using a tad too much.

[gone_fishing]

hard to beat technology

[Vitamin Sea]

I had a 1991 carb Johnson on the back of my 19C Haines, it used about the figures you are quoting.

Have just put a 200 Opti on the back, at this stage seems to be useing about 1/2 of what the Johnson did, there's a post here about it.

Cheers

Bill

[MADKEEN]

NO FEAR

i run a 90 optimax on a cc 6mtr and a mate runs a 115 johno on a 5.5 bowrider and he uses double the fuel for ex same trip these fugires were over a weeks running

david

[Ron173]

Why 175 carbs on a 150?

Could be helping you to chew more juice than absolutely necessary, for a small if anything power gain.

[whiteman]

Sounds like you are towing a parachute with those figures. You should be getting 1km/1lr at worse. Buy a digital fuel guage (Navman?) and use this to trim the boat and monitor fuel usage. It will pay for itself in a couple of trips the way you are going.

[jeffrey_h]

Is there an inline fuel meter gauge (that you can buy) that can be used on any engine? Mine's a 1990 Johnson 90.

Jeffrey

[saurian]

Jeff the navman unit whities talking about can be calibrated to most motors, but I think you still have to buy a chartplotter to use as the screen ????????
Ta

[Angla]

I have a 5.75 metre cruise craft outsider with a 2003, 135 Optimax.

I left Mooloolabah and went to Coolum then sunshine reefs and then went northern banks. Travelled down the banks to southern banks and the returned to Mooloolabah. 139 Km for 84 litres.
The trip out was at around 4000 rpm and 21 knotts but the trip back in was at 5300 rpm at 31 knotts. Took around 40 minutes to get back. Yahoo.
I was solo though and had an empty esky so to speak.
Make your own judgement

Chris

[snelly1971]

Maybe so Blaze..??? my Mercury 200 EFI seems to burn more bloody fuel than my old carbi 200 Yammie..??...proped the same so i am not quite sure if the the older EFI models are any better than there carbi counter parts..There is not a great deal of difference but it is noticeable .

[Noelm]

yep, from the first question, I am not too sure of the benefits of having the 175 carbies, unless he was thinking along the lines of converting it to a 175, if so it is entirely wrong, and will probably increase fuel consumption, as there is quite a few differences in the two motors! if you still have the old carbies, get them rebuilt by someone who knows what they are doing, and refit them, try again on fuel consumption.

[Greg P]

100% on that Noel - those 175 carbies would probably have bigger jets and wont be helping with fuel consumption but it still won't allow the engine come within a bulls roar of new gen dfi 2 strokes and multi-point efi 4 banger's fuel consumption.


I went from about 130l for a day of trolling in my old Sportfish with 115 Yammie 2 to about 65l with the DF140 zuke. The new electronic (2 or 4st) engines can pay themselves off quickly in the right applications.


Cheers

Greg

[Smithy]

My experience of the 115 size OMC Oceanpros is 1km/litre. The old 90 degree block Johnrude series 85-90-115-120-130-140s and the newer OMC 150-175-225 Oceanpro series only get worse from there.

[wessel]

In my opinion, every boat has a sweet spot. That area where you are burning optimum fuel for the speed being travelled versus the sea conditions and lastly your inner childhood hooligan tendencies.

A drop in rpm by as little as 500 can have a dramatic effect on your fuel consumption figures. The gain in speed is just not worth the extra petrol required to have that magical little number appear on the GPS screen. So, you are doing 47 km/h. Why do we always listen to that little inner hooligan voice and open the throttle that little bit more just to see the dial reading 50 km/h?

Have fun

Wessel

[whiteman]

Jeff the navman unit whities talking about can be calibrated to most motors, but I think you still have to buy a chartplotter to use as the screen ????????
Ta
Navman sell a model that includes the readout module.
http://www.navman.com/Navman/Templates/productinformation____28780.aspx

[SgBFish]

No Fear I hope you catch a lot of fish!
160L of juice for a trip is a lot.
My F115 Yamaha DFI 4 stroke gets 10% better fuel economy than the 115 optimax. Around 16L /hr @ 4000 rpm.

[rockstar]

i have a 6.3m whitley with a 175 johnson (2000) and at worst it does 1km per 1l and that is on about 4000rpm and at best it can get around 1.5-2km per 1l. the fuel flow meter are a great investment to get they tell you how much fuel you are burning and with a few adjustments you can save a fear bit of fuel. so i reacken you should get one of them

cheers

rocky

[jeffrey_h]

Thanks Saurian & Whiteman,
I have a Lowrance 339 df iGPS that will take the fuel sensor and tank guage.
I checked their site today and built the system on their test screen that you can use. Will visit Bias at Tingalpa soon to get them. I know that it will pay for itself in a short time.


Jeffrey