Fuel economy seemed bloody excessive!!!

[gazza2006au]

Last night 4 of us drive the Silverline 4.6m glass boat from grays point boat ramp to lilli pilly and back, we had put 10L in the tank i had previously put 10L in the tank, this afternoon i flushed the engine and to my surpize there was only 4L left in the tank

The trip is only around 6-7kms :O 50hp 3 cylinder mariner rebadged mercury

With evaporation and testing there would have been atlease 15L how could it use 11L to travel 6-7kms?

[NAGG]

Assuming that the motor is running ok - my first bet would be on an underpowered boat …… 50hp for a 4.6m glass half cabin would be at the bottom of the recommended HP ……. add 4 blokes & it's a big ask

Did the boat plane OK ?

Chris

[Vromme]

I get around 1l per km with approx 2.5t boat loaded - 300yam (not the most economical motor in its class) doing 27knots.

Id say that fuel econ is terrible!

[stevej]

vrome your boat is powered correctly though


gaz
timing not done properly when you did it
under powered defiantly, most likely wasnt planing just pushing water in front of it (my 4.2 tinny with a 50 4 stroke would be half the weight of what you had in boat people and gear)
motor is just shagged

[gazza2006au]

I used this distance app last night to calculate my trip and it came out to 4.5km's each way or 9km trip we are using something like 1L per 1km which is shocking for a 50hp engine, we were doing around 40kph most defiantly on the plane boat planed around 25kph 28kph we were at around 3/4th throttle but never actually needed full throttle, timing is set perfect because its max advanced timing if it were incorrect i would have killed the engine

The little 50hp engine had plenty of power to power this size boat with 4 on board, i guess a previous owner put the oz plate hydrofoil in it to reduce its fuel usage i took it off and dont need it the boat leveled out really well

[stevej]

the hydrofoil was put on because its under powered.
1l per km seems about right for that load and boat size with a small engine, the 90hp johnson on the 500 cruisecraft i had used 1l per km offshore


its a 2 stroke what are you expecting it to use

[gazza2006au]

Steve its not under powered we got up on the plane shit easy and it was cruzing along without using full throttle, i think this engine may have been upgraded to the 60hp but geez shes thirsty

[stevej]

its not thirsty and yes its under powered as you would be holding more revs to maintain the speed

if someone came along side you you would see water being pushed up in a bulge and not planing as well as you think

[gazza2006au]

Steve lol i have been boating for 20 years mate i have owned over 15 boats i am a experienced boater... the boat is not under powered and it gets in the plane easy with plenty of power left over, the boat is not bogging down into the water i dont know how u come to that conclusion when the boat is doing 40kph

[Crocodile]

Hello Gazza,
My 60hp 2/ gets 1 nautical mile per litre (or 1.85 km/litre) on a 4.3 Webster Twinfisher.
You have a problem.
How sure are you that you started out with 20 litres in the tank?
Is it possible that something is amiss with the motor, eg. sticking float or weak spark to one cylinder. It would probably run OK and hide the problem.
I would try it again and be more precise with the starting fuel amount.

[bluefin59]

You have a major problem my 60 hp 3 cyl 2 stroke merc used to get 130 k out of a 60 lt tank loaded with 2 blokes and fishing gear and I had full floors and casting decks . Matt

[swof63]

Far too much fuel. My 150 4/ merc gets 1.2nm /l at that speed. You most definitely on the plane, no 4.6 will do 40kph in displacement or semi displacement mode with that horsepower. Something very wrong with that motor or it’s tune. Or you have a leak in your tank.


Sent from my iPad using Ausfish forums

[stevej]

Steve lol i have been boating for 20 years mate i have owned over 15 boats i am a experienced boater... the boat is not under powered and it gets in the plane easy with plenty of power left over, the boat is not bogging down into the water i dont know how u come to that conclusion when the boat is doing 40kph

have owned enough properly powered boats to know that's not enough ,guys complain 50s on 4.2m tinnys isnt enough with 4 guys on board

there are guys been boating for 50 years and still dont have a clue

whats your tacho say at 40

never wondered why the previous owner fitted a foill

[catshark]

if my adding is correct, gazza should have used 4.5 litres to gain the 9klm trip, instead the assumption is that it used 11 litres for the 9klm round trip ?

[tunaticer]

It would be impossible to pour 15 litres of fuel down the throat of a 60 in 9km and have it still run.
Either you are incorrect in the fuel amount, you have a leak in the fuel system or you are bullshitting.
Which one is correct?

[Paul071978]

At that rate electric would seem very affordable. I would have to agree with above 60hp not possible to guzzle that much juice. 25L per hour at WOT

[gazza2006au]

Think one or two of you need to reread my posts before saying i am talking shit!

1-2 weeks ago i had filled up 10 litres in the tank i had only done some idle and fast idle testing from then to now

We went to the servo and my cousin put another 10 litres into the tank just assuming we still had 10 litres roughly (the boat sat in the drive way other than to set the timing on the trailer)

We than went and done the distance mentioned than the next day while flushing the engine i had lift the tank and only had 4 litres if that left

Going by the hp it should use 5 gallons per hour at wot that is about 25L

The timing is sone right but i just dont know where the fuel has gone i mentioned to my cousin someone may have takin petrol from the boat but if that were the case they would have takin the whole tank

[NAGG]

By the look of it everyone thinks there is a problem with either the numbers or the story ……

Here is something I dug up on a 50 Merc 2 stroke

www.tradeboats.com.au/tradeaboat-reviews/engines/1505/mercury-50-two-stroke-outboard-motor-review

[gazza2006au]

Nag where do i benifit from talking shit?

[NAGG]

Nag where do i benifit from talking shit?

Did I say that ? …… I just said "or" a problem with the story - eg how much fuel , leakage …… hence why I put up the link for you. You're welcome !

Chris

[shakey55]

gazza - you yourself can’t believe the results in you testing.

Before you go any further empty the tank, refill with exactly 20 litres and do the test again over same distance.

If result is again as bad then start scratching your head because something is terribly wrong.

Maybe even do the test with only you onboard and then the same test with the extra bodies onboard.

A little bit of messing around but you will eventually get test results and go from there.


Sent from my iPhone using Ausfish forums

[Cape Crusader]

G'day
Perhaps best to check the usage on the next couple of outings and see how it goes?
Cheers
Rod

[scottar]

Any chance someone pinched some fuel?

[gazza2006au]

I'm hopefully taking it out on the weekend if good weather i will fill the tank and take an extra 10L, I'm not exactly sure where the fuel went i ran it for probably 30mins max at idle while testing i thought someone could have taking some fuel but than they would have just taking the whole fuel tank

that 9km trip was half 8 knot zone but i can't see the engine using more in a 8 not zone than 3/4th throttle its the first outing so i will have to check again i will fill up this time and i will check our usage after the day to make sure

there was no excessive smell of fuel either to suggest a leak other than the fuel hose connection on the tank was sucking air and i had to remove it and shove the hose into the tank

[Muzza]

Just to be funny, your cousin didn't put the 10 litres in the car and not the boat, what you have left sounds like it didn't get the extra 10 litres?
And funnier things have happened, I've seen people pour fuel into rod holders before.

Cheers
Muz

[gazza2006au]

Muzza we used two pumps mate so not possible just wish my cousin had lift the tank instead of dragging it up side the boat, we asked him how much petrol was already in the tank he said donno

I might head out now for a quick one and be back by 9 or something trying to get some mates to come out

[Moonlighter]

The only way to test actual fuel used is to start with a full tank, do the trip, and refill again on the way home.

This starting with a guesstimate of what is in the tank caper is what inevitably leads to incorrect results. As youve discovered.

Most likely, the problem is that your estimate of what was in the tank must have been way off. Regardless - that is history - as above, start with a full tank and redo your figures.

I had a 70 2 stroke Yammy on a 4.8m plate cuddy, a quite heavily built boat for its size, and consistently got around 2.2kms/litre.

[Crocodile]

Hello Gazza,
the information about the 8 knot zone may be the key.
At 8 knots the motor will guzzle fuel.
The actual km/litre figures will blow out.
If you look at all of the motor tests there is a major bulge in the graph at about 8 knots.
I like your idea of starting with a full tank and carrying a reserve
Also test the boat somewhere without a lengthy 8 knot zone..

[scottar]

Yes, the 8 knot zone, assuming you were at 8 knots and if the bow is starting to lift but the hull is only pushing water, could make a huge difference. At these hull attitudes on my rig my fuel consumption is literally double what it is when on a clean plane. Proper testing will reveal all though. If it's calm enough - take one of your scales with you. Weigh your empty tank, add 20 litres and weigh full. A bit of maths and recorded weights you can then do some tests at various revs and roughly work out how much is being burnt at various RPM's. It will need to be calm so the scales steady though.

[gazza2006au]

Thanks for the suggestions the scales would be a good idea, do u perhaps filling the tank on the gunnel has anything to do with it, 5 foot off the ground as that is where my cousin sat the fuel tank

[Triple]

If the boat has sat in the sun with the heat we have had lately with an open breather you may of lost a heap to evaporation too...

[gazza2006au]

Triple i always leave the breather open and the tank was sitting in the sun but it couldn't evaporate 7 to 8 litres in 1 week or just over i dont think so anyway

i didn't get out tonight so i will reply on the weekend as to fuel usage going to head outside and chase some big calamari or some decent arrows in the deeper water

[SUPERDAFF]

I'm hopefully taking it out on the weekend if good weather i will fill the tank and take an extra 10L, I'm not exactly sure where the fuel went i ran it for probably 30mins max at idle while testing i thought someone could have taking some fuel but than they would have just taking the whole fuel tank

that 9km trip was half 8 knot zone but i can't see the engine using more in a 8 not zone than 3/4th throttle its the first outing so i will have to check again i will fill up this time and i will check our usage after the day to make sure

there was no excessive smell of fuel either to suggest a leak other than the fuel hose connection on the tank was sucking air and i had to remove it and shove the hose into the tank

Gazza - the 8 knots is the killer. My 625 with 175hp HPDI only goes 1.1 km per litre when trolling - at 7 or 8 knots. At 45km/h (or 24 knots) travelling with more gear and more people, I get 1.7km per litre. So in your case, to think you will get better economy at 8 knots than 3/4 throttle could be a very wrong assumption. Add in some error factor for your 'estimates' instead of the 'actuals' and you may have an explanation.

[ericcs]

if this is the same boat you mentioned you were fixing up to sell, don't bother about the fuel consumption. as long as it run's well and is reliable for the next owner, leave it alone. Don't think there will be a magical cure, as you seem to have tuned it right.

[Funchy]

Gazza you say there was 4L left. Did you measure it or was it “about 4L left” ?

[gazza2006au]

Was about 4L Left we put 20L in today at the pump and it was a full tank we than went and done 10-11kms in botany bay late this afternoon/tonight now i eye balled our fuel usage and we used around 6L much better fuel economy than the other day so it leads me to believe the fuel was either pinched from the boat or the pump at the servo wasnt working correctly

Tonight i was using mostly 2/3rd throttle to full throttle but backed off

Love how a glass boat can actually over take a following sea where as a tinny is sketchy

[stevej]

would not have been the servo pump, eyeballing is not a accurate measuring device and is just wasting peoples time

and plenty of tinys can over take a following sea

[catshark]

didnt your anchor get pinched from the boat too recently, might have a rogue neighbor nearby.

[Paul071978]

Depends who’s eye is doing the balling

[Volvo]

Thank Gawd fer that !!! , was starting to run out of fuel reading through it all lol..

[gazza2006au]

Fuel economy seems to be around the 1.5km/1L I'm ok with that that is without using the hydrofoil i feel the boat doesn't need the foil

went for a fish last night with a mate and boat kept leaking so i need to fix the bungs than maybe repair the bow chips and various other underwater chips on the hull, can u mix tints in with just resin as a sealing coat once u putty the chips? i am not up to this stage on the big boat so i have never done it before

[gazza2006au]

Yeah Cat its likely someone has flogged the petrol from the tank, on the morning i noticed my anchor gone i woke up at 4am as i smelt a really strong petrol smell coming thru my bedroom window which the boat is next to and it woke me up, i checked the previous hour on my CCTV but i only showed the bow of the boat so i don't know i can only assume someone was in the boat pinching the fuel and my anchor while at it

2 days before this the neighbour alerted me to someone trying to break into his kitchen window which is just 20 meters from my boat the fly screen was damaged with a screw driver or jimmy bar i again checked the CCTV but seen no one come in the street so its likely this person or persons are jumping the fence in the vacant lot, at 4am my dogs are sleeping in the kennels so wouldn't have heard anything

btw i bought a new anchor and received 1 meter of tiny chain bloody shocking parcel got lost in transit too so i bought another anchor from BCF which was much better 3 to 4 meters of chain i had to make one decent anchor from the two anchor kits and it held bottom at the Hawkesbury River last night that has massive tide flowing waters (as in strength and flow)

i can't believe a 4lb anchor with 4 meters of tiny chain actually held bottom on my glass 4.six meter boat