Powering

Having, in previous discussions, introduced the concepts of our differing approach to the hull design we now look at the effects on powering of these changes. The illustrations below are for 57’ narrowboats of equal proportions and both operating at 3.6 knots (4mph)

above: wake of traditional 57 narrowboat with conventional swim     

below: wake of Floating Ohm 57 narrowboat with improved swim

Note the marked difference immediately aft of the stern. The Floating Ohm stern creates much less in the way of stern waves and in particular a completely flat wake behind the boat. This illustrates the clean water flow into the propeller disc on the Floating Ohm design.

Powering of traditional 57 narrowboat with conventional swim

Powering of Floating Ohm 57 narrowboat with improved bow and swim

The pertinent drag and power figures are, at 3.6 knots and 0.69m draft,

Conventional hull

3.6 Knots

Fn 0.143

Resistance 411.20N

Power 1.692 kW

Wetted area 55.755 m^2

Floating Ohm hull

3.6 knots,

Fn  0.146,

Resistance  382.15N

Power 1.415kW

Wetted area 53.143 m^2

This equates to a reduction in power of 16%

The difference in Fn is caused by the Floating Ohm hull having a slightly shorter waterline length.