Calculating my range with Beta BD722 20hp

[Badger]

I am fitting a Beta Marine BD722 3 cylinder 20hp diesel. I have a 10 Gallon fuel tank. I am told the engine uses 1.5 Litres of fuel an hour at 2800 rev's and doing 5.5knts. If 10 Gallons is 45.5 Litres, then is 30 hours at 5.5knts giving me 165 miles range about right ? If I do 5knts at 2500 revs will I use 1.0 Litre an hour and get 225 miles range ? What's the best way to work it out accurately ? Thanks.

 

[aslabend]

Most accurate way is to use it but keep accurate records of how much you put v's how much you use it. Over a time of different conditions and usage you should build up an accurate picture of how long a tankful will last.

With my beta I found that the figures in the beta data on the web were reasonable if on the optimistic side but then I have a long keeler so bigger wetted area to push along. A lot will depend on your hull, prop and how much weed you carry on both.

 

[reeac]

range under power

I don't believe that you can calculate the range at various boat speeds - you need the benefit of some actual fuel consumption data either from someone with a similar boat or from your own boat. The 1.5 litres per hour sounds about right to me and I think that you might attain 1.0 litre per hour under benign conditions at around 2200 rpm.. It all comes down to how much power you extract from your engine. The former consumption corresponds to about 7 bhp. and the latter to about 5 bhp. If you extract the full 20 bhp [i.e. max revs.] you'll use 4.5 litres per hour. The difficulty is to translate these data into boat speeds - that's where you need experimental observations.

 

[MoodySabre]

Fit an hours run meter - not expensive and easy to wire into the ignition switch (ignition usually being on only when engine is running). I use this method to work out how much fuel I have left. I keep a fuel log of amounts and meter reading and work out consumption each time. Your figures sound right but you will only work it out accurately with an hours meter.

 

[macd]

It very much depends on the type of boat and how easily driven. I agree that practical testing and measuring is the only reliable guide. I have your engine's 28hp big brother; Beta's consumption graph is a very lose guide.

Bear in mind, too, that of those 10 gallons, maybe a gallon will be below the fuel take-off (or ought to be). And depending to a degree on the baffling and shape of tank, you won't want to be using the crud at the bottom through your fuel system.

 

[bazobeleza]

It very much depends on the type of boat and how easily driven. I agree that practical testing and measuring is the only reliable guide. I have your engine's 28hp big brother; Beta's consumption graph is a very lose guide.

Bear in mind, too, that of those 10 gallons, maybe a gallon will be below the fuel take-off (or ought to be). And depending to a degree on the baffling and shape of tank, you won't want to be using the crud at the bottom through your fuel system.

I'd allow about 20 -30% for reserve or at least have a spare 20l drum of fuel aboard if you're planning passages that push you theoretical limit of fuel use.

I recently crossed biscay from vivero to cameret in a big mobo whose range at a given speed was the distance between the two points, I loaded up an extra 500l in drums. We had a jammed rudder from the midway point of the crossing and that effected the consumtion, we got to cameret on fumes. if we hadn't shipped the 25% extra we'd have been in serious doo-doo