How much HP?

[djackson99]

I am designing an ambient submersible that I will power with a jet dive when surfaced. The specifics are below. What I need to know is how much horse power will be needed in order to get the boat to plane and at what speed the boat will plane? I am not so interested in going 30 mph but I do want to be sure that the engine selected can obtain planing speed. I have seen a chart in "Boatbuilding with Aluminum" (pg 15) that indicates a 120hp would push 4500 just over 30 knots. Is that realistic for something like a Mercury 120hp Jet Drive? Where can I find additional formulas for calculating planing and maximum speed?

Length 20 feet
Water Line Length: 17 feet
Beam: 50 inches
Hull: 12 degree V-Hull
Draft: Aprox 16 inches
Displacement: Aprox 4400 to 4900 (depending on engine weight)
Design Images: http://members.cox.net/djackson001/s...les/Sub_H7.htm

I certainly appreciate any help!
Doug Jackson