fuel consumption?

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silverdawn

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Hi all, I have a 20hp beta engine with 3 blade prop all new in 2003 prior to me buying the boat. Iam very please with the
performance, it pushes the boat with ease and plenty of power to spare. it uses 4/5 litres an hour which seems excessive, the boat is a finesse 24ft / 3500kg is this right.
 
With a Sadler 32, and a Bukh 20hp, if I am light on the throttle, I will easily get 1.5 litres/hour.

A slighly more heavy use of the throttle, with actually no major extra speed, the consumption will go to 2 or so litres per hour.

4 or 5 litre/hour does seem to be a lot.

Cannot give you any reason why your consumption is almost double what it should be.

Mj
 
I have the Beta 622, the 17hp predecessor of your engine. With a 34ft boat, at about 2500rpm I reckon <1.5 l/hr. There is something very amiss with your consumption, especially with that size of boat. Have you checked it over a reasonable period of time? It's so high, I can't suggest what it might be, leakage on that scale would be very obvious.
 
On a 31' of about the same weight, I'm getting 1.5-1.8 litres/hour.

prop is a 3-blade Autoprop, cruise @ 1800rpm is 5.7kts in still conditions. Engine is a Yanmar 3YSM20, comparable with your Beta.

Mind you the Kubota industrial engine has a reputation for thirst.
 
G'day Stuart,

We run twin 40HP Volvo sail drives with 3 blade stainless props at 3 litres an hour and that's the total for both.

You have a leak or a slick behind you, failing that it's black smoke, if not that bad maths.

Avagoodweekend......
 
A 20 HP engine at max output will use around 4 litres per hour. It doesn't matter what size the diesel engine is the consumption is pretty standard at roughly 4 l/h per 20 HP. So if your engine is working flat out you could have that consumption but with a 3.5 tonne boat you should need nothing like 20HP to push it along at 5 or 6 knots unless the prop is very badly matched to the gearbox/engine setup and you are having to run at near max rpm to achieve that speed.

Another thing to check is that you are not just measuring fuel draw from the tank (or day tank) without taking into account the fuel return (which may go back into the main tank if you use a day tank). On many engines the return fuel flow is many times the fuel actually used.
 
You have a leak or a slick behind you, failing that it's black smoke, if not that bad maths.

I think that about covers it! /forums/images/graemlins/smile.gif
 
Just a thought, do you have 3 foot of weed growing on the bottom, a couple of buckets hanging off the stern or is the handbrake still on?
Stan
 
Hi all, from your your comments it would seem that the fuel consumption is high, how I arrived at my calculation, 1st I dip the tank prior to leaving the marina and note the mark, on returning after an hours motoring within the river(calm water
I fill the tank from a 5 litre can up to the noted mark it always takes about 4 litres give or take an amount not to make a great deal of difference
The boat bottom is clean and the engine when running is checked always for leaks etc before leaving, the above calculation is based on about 70% throttle, the one thing that Iam doubtful of is the tickover speed which should be 850 revs a minute, it seems higher for when on tickover and in gear the boat moves at about half a knot, i cannot creep forward nice and slowly when needed, I intend to check the tickover next visit this might be contributing to the problem.
 
I used to have a GK29 with this engine with a 2 bladed prop and got about 1/3gph, which seems to be of the same order as your other replies. Are you motoring at (or above) hull speed? (Probably about 6Kn for 24' LOA???). What happens if you slow down? Does it improve significantly?
 
Crikey! That consumption will drain Kuwait dry /forums/images/graemlins/smile.gif

With a petrol outboard pushing a 9.2m trimaran at 5.5 knots I'm only using 1.5 litres per hour. So something's amiss.
 
My 19 HP Volvo 2020 on a 2 fixed blades saildrive, pushing a 4 tonne empty weight 32 footer, with a Coppercoat bottom, at an ordinary sea, at about 1400 revs, at about 4 knots, uses between 0.7 and 1 litre an hour.

That is notionally 1 horsepower at the prop according to Volvo information. The rest of the diesel is used to overcome internal losses.
 
I don't think that a high tick-over speed will contribute to your excessive fuel consumption. An easily driven hull will move forward at an appreciable at tick-over, when in gear.
 
[ QUOTE ]
Rule of thumb with us over many years and boats, 1 gallon per 20hp per hour, you seem to be not far off that, maybe a little fine tuning needed.

[/ QUOTE ]

OK if you mean you are actually making use of 20hp, but I think the thread was talking about the typical consumption of a 20hp rated engine on an average boat. That being the case I agree with the consensus that 2 to 3 hours per gallon is typical at 5kt for a yacht motoring into an average sea.

Vic

(mixed and assorted units-of-measure keep the brain active /forums/images/graemlins/cool.gif )
 
I too have a 20 hp Beta driving a 3 bladed prop on my 32 ft sailboat. Fuel consumption at about 5 knots is 1.5. litres /hour. That's 15 nautical mpg which isnt wonderful.
I cannot believe you should have such a high consumption. Are you running the engine at full power?
Can you see a lot of pollution (black or blue smoke behind you)?
Is your exhaust system properly designed or are you getting high pressures in the exhaust?
Is the engine warm enough or perhaps the thermostat is stuck at open?
 
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