Curriosity. What is a cat's MPG?

[rabbi]

The figure we use for the no wind motoring our 36ft Mahe with 2x Volvopenta D1-20 and 18hp each:
Running one engine at 2100 gives just over 5kn in flat water and no wind, consuming about 1.3 liter per hour. 2500rpm gives 6kn at 1.7 liter
Any wind or chop changes this dramatically in both directions.

We almost never use both engines for any longer period so i have no figures.

[a64pilot]

Odd, you guy's numbers are very similar to a mono hull's.
I would have though due to the lighter weight, a Cat would burn less fuel, but guess that the wetted area sort of cancels out the weight?

[Mirage Gecko]

Originally Posted by a64pilot

Odd, you guy's numbers are very similar to a mono hull's.
I would have though due to the lighter weight, a Cat would burn less fuel, but guess that the wetted area sort of cancels out the weight?

In my experience I don't think it makes much difference if it's a multi or mono as most of the diesel motors used give a fuel consumption commensurate with the revs used and don't seem to be affected greatly by weight or weather conditions however performance is greatly affected by sea and weather conditions.In other words they perform similar to a stationary engine if kept at constant revs.
Like others I keep an eye on the consumption but in fact unless using flow gauges calcs of fuel burnt ,unless you are extremely particular in recording hours and actual litres or gallons put in relevant to those hours can be way out.

[Factor]

Used about 100 litres a year on my Seawind 1000xl. And we cruised a lot, still our boat was a sail boat, so fuel economy was never a problem

[dirkdig]

Lagoon 440
5 litres per hour per side.
One engine only 6 knots at 2200 rpm
Two engines 7.5 to 8 knots at 2200 rpm
Gori 18 inch props.

One engine only 5 knots at 2000rpm uses about 3.8 litres an hour.

350 litres a tank each side.

Going low revs 1500 rpm one side at a time you could get 1100 nm.

We also carry 160 litres in cans which gives us another 192 miles extra.


Sent from my iPad using Cruisers Sailing Forum

[valhalla360]

Keep in mind, while 6-8kts doesn't sound like much difference if 8kts is hull speed, it can make a huge difference.

We are a little smaller at 34' but with a 25hp 4stroke outboard we plan on around 6mpg at 6kts. If we drop back to around 5kts, it jumps to around 10-12mpg. If we push up to 7kts (hull speed), well I've never left it there long enough to measure but I'm sure it probably drops to something on the order of 2mpg.

And yes, you can certainly measure efficency in MPG and it makes just as much sense as in a car.

[svinvictus2]

Originally Posted by serpa4

What kind of fuel efficiency does a catamaran get in the 40-45 foot range at 6-8 knots and not full throttle? 4mpg, 8mpg, I have no idea.

It all depends on the CAT however you will have 2x the engines......

[kas_1611]

I know we have a monohull but over the last 5 years I have been tracking fuel used (bought) against miles logged and engine hours as that's the kind of geek I am

So far we have a rolling average of 1.98 litres per hour which is 0.44 Imperial Gallons per hour. At cruising revs, on our D2-40 & 3 blade prop, of about 1850 (which is ~6kts) that works out as 13.8mpg or 11.6mpg(US).

I compare that to a goods vehicle of a similar weight (8 tonnes) doing 56mph on a motorway/freeway/autoroute getting approximately 128 miles per gallon (imp). Not that you can really compare like for like but it gives an idea of relative fuel economies.

Keiron

[Sailshabby]

Mine doesn't get nearly the mileage yours do, but he's a Maine Coon and about as lazy as they come...

[Olde Chief]

It all depends on how hard you run your engine(s). I would hope you would get 10 mpg or 1 gal. per hour. You will have to make a trial run and do the math. Let us know how it figures out.....

[Toys_with_time]

Originally Posted by serpa4

What kind of fuel efficiency does a catamaran get in the 40-45 foot range at 6-8 knots and not full throttle? 4mpg, 8mpg, I have no idea.

Over the past 4 years I have averaged consistently between 1.1 and 1.3 litres per engine hour. When I have tried tracking it in more detail have found that I am averaging around 0.3 to 0.4 litres per NM travelled but this can be seriously impacted by wind / waves and I have only been assessing litres per NM in conditions when I am motoring for lack of wind. The overall average reflects all conditions including engine idling time (I virtually never run an engine to charge batteries but I do motor sail when conditions dictate)

Running 2 x 30 HP Volvos with Volvo 3 blade folding props on a Lipari 40' cruising cat, approx 9,750kg laden. With 1 motor in flat sea figures are:

1600 rpm 4.8 knots, ~ 0.9 lph
1800 rpm 5.3 knots, ~ 1.5 lph
2200 rpm 6.3 knots, ~ 2.5 lph
2600 rpm 7.1 knots, ~ 3.6 lph
2800 rpm 7.5 knots, ~ 4.4 lph

Below 2000 rpm using second engine adds approx. 0.6 - 0.8 knots to boat speed. Above 2,000 rpm adds approx. 1 knot to boat speed.

(do I spend too much time doing stats and not enough sailing?)

TwT

[model 10]

Originally Posted by valhalla360

And yes, you can certainly measure efficency in MPG and it makes just as much sense as in a car.

It does not make just as much sense as in a car. A car is little affected by current Wind is apples and oranges. If you can figure out your mileage on a particular trip from gph great.

[Cheechako]

Lagoon 42 about 7- 8 KMPG n flat water.
ie: 2 engines burning about 1/2 gal per hour each at 7- 8 knots.

[contrail]

leopard 45, 7.2 knots at 1 1/3 gph, or 5.4 kmpg, using one engine. 8.1 knots at 2.4 gph, or 3.33 kmpg with two engines. Yanmar 4JH3E's with Max-Props. One engine at 2750 rpm goes as fast as two engines at around 2100, by the way. All of this with no wind and flat seas.

[doublewide]

we have twin 29 HP Yanmars. Each burns a gallon an hour. we make 5 knots with one engine and 7 knots with 2. These are round numbers, but close enough for your purposes.