I thought you were limited to 'hull speed' with a planing hull
http://www.sailingusa.info/cal__hull_speed.htm no matter what size motor you used unless said motor can plane the boat.
I think that calculation example shown is correct if referring to a “displacement hull”? But, we be talking about very small, light weight, shallow draft, fishing boat, with a planing hull. That really has no need for that additional “thrust” to get it moving. It certainly does need horsepower if one wants to move it faster and if in strong winds even control it. The planning hull and displacement hull would be two completely different animals. Just might need that additional thrust to move a heavy displacement hull.
The “Hull speed” is getting a little off track from the thread? It would take quite a large “kicker” to get his boat to plane; however, it wouldn't take much "horsepower" to increase the boats speed. To plane, it is all about the power-to-weight ratio. If any kicker was to ever plane a boat, I really wouldn’t worry too much about Hull speed:
Hull speed, sometimes referred to as
displacement speed, is the speed of a boat at which the bow and stern waves interfere constructively, creating relatively large waves, and thus a relatively large value of wave drag. Though the term "hull speed" seems to suggest that it is some sort of "speed limit" for a boat, in fact
drag for a displacement hull increases smoothly and at an increasing rate with speed as hull speed is approached and exceeded, with no noticeable inflection at hull speed. Heavy boats with hulls designed for
planing generally cannot exceed hull speed without planing. Light, narrow boats with hulls not designed for planing can easily exceed hull speed without planing; indeed, the unfavorable amplification of wave height due to constructive interference diminishes as speed increases above hull speed. For example, world-class racing kayaks can exceed hull speed by more than 100%[SUP]
[1][/SUP], even though they do not plane. Semi-displacement hulls are intermediate between these two extremes.
http://en.wikipedia.org/wiki/Hull_speed
The concept of
hull speed is not used in modern naval architecture, where considerations of speed-length ratio or
Froude number are considered more helpful.
When it is at rest, a vessel's weight is borne entirely by the buoyant force. At low speeds every hull acts as a displacement hull, meaning that the buoyant force is mainly responsible for supporting the craft. As speed increases, hydrodynamic lift increases as well. In contrast, the buoyant force decreases as the hull lifts out of the water, decreasing the displaced volume. At some speed, lift becomes the predominant upward force on the hull and the vessel is planing.
http://en.wikipedia.org/wiki/Planing_(sailing)#How_planing_works
Displacement;
the hull is supported exclusively or predominantly by buoyancy. They travel through the water at a limited rate which is defined by the waterline length. They are often heavier than planing types, though not always.
Semi-displacement, or semi-planing;
the hull form is capable of developing a moderate amount of dynamic lift, however, most of the vessel's weight is still supported through buoyancy
Planing;
the planing hull form is configured to develop positive dynamic pressure so that its draft decreases with increasing speed. The dynamic lift reduces the wetted surface and therefore also the drag. They are sometimes flat-bottomed, sometimes V-bottomed and sometimes round-bilged. The most common form is to have at least one chine, which makes for more efficient planing and can throw spray down. Planing hulls are more efficient at higher speeds, although they still require more energy to achieve these speeds.
http://en.wikipedia.org/wiki/Hull_(watercraft)
Some might need those "high thrust" kickers, if they have a VERY HEAVY boat with a displacement hull (e.g. sailboat or tug); however, most of us sport fishing boats don't have the need for that extra thrust. What we do or might need is that "horsepower" to either control or move the boat faster.
Other than that, don't get caught (like I did once) and buy a 9.9 "high thrust" kicker just to find out it had the thrust; however, it did NOT have the horsepower to control the boat in the winds and currents!