prestige 32- with D4-260 engines

[grannell]

Hi there fellow prestige 32 owners.
can you tell me the most economical speed to cruise at.

matt

[napoleon]

The most economical speed to cruise at is a bit of a variable feast and depends on what you want from the boat.
If you want high speed then the slowest speed at which the boat will plane will be about optimal.
In this case this will equate to somewhere around 15 - 16 knots depending on the load carried.
For max. efficiency the boat needs to be kept within it's hull speed which as you may know is approx. sqr root of the waterline length times 1.4. For the prestige 32 I am not sure of the waterline length but it is probably around 27 feet.
So the square root of 27 is just over 5 x 1.4 = 7 knots.
My own boat is the 36 which works out to about 7.5 knots. In practice if we hold this speed (which in my case is 1400 rpm) then the consumption is about 4.5 mpg.
As diesel engines do not like being run at a constant speed, high or low, then when cruising I alternate between 1400 and 2800 rpm every 15 to 20 minutes. This gives me either 7,5 or 18 knots.
The bottom line doing this is that our average speed on a passage is around 12 knots and fuel consumption over the last four years has averaged 16 litres per hour.
If I ran the boat at 12 knots constant speed it would never climb over the "hump" and would probably burn in the region of 30 - 35 litres/hour.
As an ex sailing man an average speed of 12 knots is excellent for me although I appreciate many people like higher speeds.
Hope this helps.
Napoleon

[grannell]

Many thanks for reply, and sharing your experience with me.
14 to 16 knots are my normal cruising speed .
matt