consumption question

[robyonfrome]

What mileage would you expect to get from a twin 200hp diesel engine at 6/8 knots on a 30' boat. consumption

 

[Bandit]

Assuming a semi displacement boat 35ft 7.5 ton that tops out at say 20 knots, then at 6 to 8 knots the consumption is minimal say 20 to 25% of cruising consumption.

 

[neale]

On a 30 ft boat with a waterline length of say 27 ft, you will probably get very different mileages at 6 and 8 knots. 6 will almost certainly be fully displacement and will use very little fuel, 8 will probably be above the hull speed and will be burning more fuel for little extra benefit, and therefore producing a worse mpg. Stay below hull speed and you should be able to happily run on one engine for best economy.

 

[Chris_d]

We do these sort of speeds reguarly on the river and tidal bits, its an awkward speed range for a 30' planing boat.
With 2 x 150hp diesels I reckon 5mpg at up to 6knts and 2mpg at 8knts, so either stay at around 6 knts or get it up on the plane.

 

[robyonfrome]

Thanks Neale that's very interesting.