Motor Boats - Fuel Economy at Low Speed

[rustybarge]

He is doing around or just above 6 knots, not 7. Numbers verified with both floscan meters and fill up after a longer trip on only one engine.
I am not surprised by the numbers a Ph43 has a longer waterline length than I do. My boat is hitting the wall at about 6,5-6,7 knots so I keep my cruise speed there in calm conditions.

Ok 6kts could work.
I keep on forgetting that every knot has major significance at displ speeds!

 

[sap_2000]

Ok 6kts could work.
I keep on forgetting that every knot has major significance at displ speeds!

Yes. As with my my boat, I doubble the consumption by increasing one knot from 6,5 to 7,5kts. Not worth it at all in calm conditions. I do sacrifice economy sometimes for comfort in beam or choppy seas. The boat gets significantly more planted in the water at 7,5 kts.

 

[No Regrets]

excellent advice.

i would add that all of these boats are twitchy at low speed and will need constant input to the steering, particularly the 'seeker. Some get used to that and forget they are doing it, some find it wearing.

Birchwood 33 twitchy at low speed!?

Seriously dude?

I think not ;-)

 

[Chris_d]

Birchwood 33 twitchy at low speed!?

Seriously dude?

I think not ;-)

I think he is refering to the outdrive powered 330 with a planing hull not the old SD 33, but anyway a 33ft twin outdrive boat is not that bad at slow river speeds.

 

[Anders_P42]

Here's some data I collected, the gap in data from 1700 - 2600rpm is the inefficient zone. Boat is 10.2m with single diesel.

 

[rustybarge]

Here's some data I collected, the gap in data from 1700 - 2600rpm is the inefficient zone. Boat is 10.2m with single diesel.

you have a brand new boat with the latest ecu common rail injection and only weigh about 5 tons......super efficient!

As predicted you chug along at 2gals/hr at 7 kts which is a very good rule of thumb up to 34' and 6-7 tons approx.