Tables for calculating hp

[Aheadslow]

Hi all, I was wondering if anyone knows a source for tables used in calculating how many HP in a steam engine would be necessary to reach hull speed in a given size of boat? Here is where years of experience with Traction and Stationary engines ,begins to fail me. Im used to thinking in terms of geared drives and pulleys. Where as in a Launch it is necessary to think in terms of direct drive systems. So here I am trying to decide on what sort of hull to build and Im still a little foggy about necessary hp for the engine.

So I would love to hear your thoughts. I am also interested in books or articles on low pressure steam in marine applications.

[fredrosse]

Boat speed - horsepower - hull - propeller design can get about as complicated as you could imagine, and educated designers have many parameters to look at. As a very crude and approximate evaluation for displacement hulls:

Maximum "hull speed", in knots, is about 1.3 multiplied by the square root of the waterline boat length, in feet for displacement type hulls.
Speed = 1.3 * SQRT(Waterline Length)
For example, a displacement hull having a waterline length of 16 feet has a hull speed of about 5.2 knots.

Another rule of thumb is that a displacement hull can be driven at "hull speed" with about 1 horsepower per ton of displacement. This rule assumes a reasonably efficient propeller, which translates to a large, low speed propeller. If possible the steamboat propeller diameter should be about 8% of the boat's length, and have a pitch equal to, or somewhat greater than the propeller diameter. Propeller slip is in the range of 20-30%. Smaller propellers, and higher speed propellers, are generally less efficient, unless you are examining a modern speedboat, an entirely different technology.

In general, horsepower vs speed is a cubic function for speeds below "hull speed", meaning you can make about 80% of hull speed with 1/2 horsepower per ton of displacement. Driving a displacement hull above "hull speed" has the relationship where horsepower is a fifth power function of speed, so doubling the horsepower will only get about 15% over "hull speed".

Having a little more than the power required for attaining "hull speed" may be prudent to help deal with wind forces, docking, and relaxed tending of the steam plant while underway.

Note that this information is crude and only approximate, a hull with fine lines can do better, a barge with a wide submerged transom will do worse.

[Aheadslow]

Thanks Fred that was just what I needed, not too technical ,,just enough and not too much.
this information will help a lot with my calculations and hull choices.
Hope to see pics of the paddle steamer all fitted out soon
again thanks.