Post
by **fredrosse** » Thu Aug 15, 2019 2:29 am

According to the DEFTSHIP hull software, for the Margaret S., the following results show linear functions for propeller horsepower vs displacement. While the Margaret S. is a sidewheeler, the software only considers screw propeller propulsion, so the computer results are comparable to typical steam launch practice.

Margaret S. is a typical Sharpie type hull, flat bottom, hard chine, 19ft-3in LOA, 18ft-6in LWL, 5ft Beam, and 9 inch draft at one long ton displacement, fully loaded with one person aboard. The most displacement I have ever had is about 1.4 tons, six people aboard.

Cruising at a moderate speed of 4 knots, one ton displacement, 0.8 propeller shaft horsepower required, and at 1.4 tons, 1.0 horsepower. The linear function is HP = 0.5*TONS + .3

Steaming at maximum hull speed of 5.5 knots, one ton displacement, 2.1 propeller shaft horsepower required, and at 1.4 tons, 2.6 horsepower. The linear function is HP = 1.3*TONS + .8

These numbers are for calm and deep water, with no wind resistance considered. Note that going from 4 knots to 5.5 knots requires 260% of the slower speed horsepower.