Re: [Electric Boats] Knots to Watts

 

On 07/11/2012 09:32 PM, Ned Farinholt wrote:

Here are my numbers for a 1967 Starcraft aluminum utility, 15' x 5' [14.2' water line], 800 lb displacement, Torqeedo 4.0R outboard, Torqeedo high performance prop, 8 kwh LiFePO4 [16 x 160 Ah].

0.2 kw 3.0 kn

0.4 3.9

1.0 5.5

2.0 7.4

3.0 9.1

4.0 10.4

These are averages of multiple runs, no current, little wind during Sept. 2011. The boat was running in a semi-planing state. That is why you do not see the sharp knee at hull speed, 5.1kn. 

Ned

Ned,
your hull with a sinked transom stern is poor at low boat speeds. This is why the hull speed kink is not seen in your data. Low speed kW data for a corresponding displacement hull with raised transom stern should be about:
0.055 kW    3.0 kn
0.15 kW      3.9 kn
At speeds lower than 3 kn speeds the sinked transom stern hull would show really bad drag figures in comparison with a not sinked transom hull. Ref. rowing boat hull small drag at low speeds. Well, propeller efficiency was not considered here, as the reference data were derived from a hull drag simulation software.

redu

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