Fuel usage vs speed

[thylacene]

OK, finally got to have a run at WOT and a few other rev ranges.

WOT 36 Knots fuel 1.0l/km (top speed may be marginally higher but conditions did not allow for any longer)

33 Knots @ 0.8 l/km

30 knots @ 0.6 l/km

25 knots @ 0.6 l/km

20 knots @ 0.5 l/km

13 knots @ 0.8 l/km

9 knots @ 0.7 l/km

7 knots @ 0.5 l/km

6.3 M GRP hull @ 1020 Kg DF175 Suzuki 225Kg plus 3 adults and 90 litres of fuel on board, prop 4 blade Solas 15 1/4 x 20, my guess with gear is about 1700Kg all up. Slight headwind during testing, stronger winds do affect usage rate.

Engine revs to 6000 vs 6100 limiter (did not hit limiter)

Cheers

Thy

[Lancair]

Just a question Thy, why do you use knots for speed and l/km for fuel economy ? Why not just use l/nm ?
I get a similar pattern of useage with my Etec 115.

[kitty_cat]

there is some awsome figures there for a 6.3 mtr boat sure will help your fuel range , the 175 a sweat motor happy boating

ps i do the same l/klm and boat speed in knts just habbit but always work out trip in klms hence the l/klm and water rules in knts eg 6 knt zones ect

[Triple]

What revs were you doing at each of those readings?

[thylacene]

Just a question Thy, why do you use knots for speed and l/km for fuel economy ? Why not just use l/nm ?
I get a similar pattern of useage with my Etec 115.

I set the gps up to show speed in knots so I don't have to convert when in a speed limit area with the rest of it set to metric.

As to revs, I will have to do another set of tests to get that, it is the one annoying limitation of the NMEA display on the Garmin GPS, I can see either speed or revs as both are not available on a single screen.

All up I am happy with the numbers given what is happening with the price of fuel recently.

Cheers

Thy

[fishfeeder]

Why do you need the REVS info when you have Speed and Fuel usage per L/km ???
Isn't the best revs range the one where your using the least amount of fuel to cover a distance in the shortest time ?

Cheers

[Scott nthQld]

Why do you need the REVS info when you have Speed and Fuel usage per L/km ???
Isn't the best revs range the one where your using the least amount of fuel to cover a distance in the shortest time ?

Cheers

Because your revs will change in relation to conditions. In flat clam, no wind you might be doing 3700rpm to acheive 20 knts, in rougher weather, you might need to be doing 4000+ rpm to get the same speed. And generally, more revs, more fuel. Working fuel economy with revs will give you a more accurate result when it comes to trip planning and working out your range

[Skusto]

Why do you need the REVS info when you have Speed and Fuel usage per L/km ???
Isn't the best revs range the one where your using the least amount of fuel to cover a distance in the shortest time ?

Cheers

hi i do the same i go by fuel flow if i can get .5l /k then thats where i sit . good day might be 30 knots bad day might be 12 knots