07-10-2003, 05:34 PM
Hi,
A fairly accurate value for the hull speed of a vessel in terms of waterline length is
hull speed (knots) = square root (2 X length of the waterline) (feet)
This works pretty well over an amazing range of lengths.
For USS Constitution, we have 175 ft on waterline giving about 18 knots hull speed. Her actual top speed was more like 13 knots, about 72% of max. HMS Victory gives 186 ft (lower gundeck) which gives a potential 19 knots hull speed. She was actually capable of 11 knots which was only 57% of max. Both ships were copper clad below the waterline and both ships were capable of flying more sail than conditions usually merited, so their inability to achieve hull speed was a result of compromises to speed made for stability as a gun platform.
To compare this to a similarly sized ship where speed was the prime consideration, consider the Cutty Sark. With 213 ft on waterline she had a hull speed of 20 knots. Her recorded top speed was 17 knots, or 85% of max.
Of course, some modern racing yachts with displacement hulls achieve speeds in excess of 100% of hull speed calculated by the above formula, but not much. And, again of course, hull speed is meaningless when speaking of anything not using a displacement hull (i.e., hydrofoils, planing, etc.)
--Pete
A fairly accurate value for the hull speed of a vessel in terms of waterline length is
hull speed (knots) = square root (2 X length of the waterline) (feet)
This works pretty well over an amazing range of lengths.
For USS Constitution, we have 175 ft on waterline giving about 18 knots hull speed. Her actual top speed was more like 13 knots, about 72% of max. HMS Victory gives 186 ft (lower gundeck) which gives a potential 19 knots hull speed. She was actually capable of 11 knots which was only 57% of max. Both ships were copper clad below the waterline and both ships were capable of flying more sail than conditions usually merited, so their inability to achieve hull speed was a result of compromises to speed made for stability as a gun platform.
To compare this to a similarly sized ship where speed was the prime consideration, consider the Cutty Sark. With 213 ft on waterline she had a hull speed of 20 knots. Her recorded top speed was 17 knots, or 85% of max.
Of course, some modern racing yachts with displacement hulls achieve speeds in excess of 100% of hull speed calculated by the above formula, but not much. And, again of course, hull speed is meaningless when speaking of anything not using a displacement hull (i.e., hydrofoils, planing, etc.)
--Pete
How big was the aquarium in Noah's ark?