The "Extremely Light Boat" or "Cowmaran"

You won't reach hull speed on any but a very short boat with that engine, but what you can get is high average speeds. To do this you want to go as long and light as you can, something like a 30' cargo canoe for instance would work very well. But if it's something you want to build, the bigger the boat the more time consuming and expensive.

It just depends on where your priorities are.

 

Have you considered a planing quadmaran design? For a light 24' boat, the individual hull lengths could be about 8' and the short hulls would start planing at speeds as low as 6-7 knots.

 

Horsepower

For a skinny (streamlined) hull you can get hull speed with less than 1.5 horsepower per ton, and from what it looks like you want, about 1/2 ton is your all-in displacement, so 3/4 horsepower will do.

You should be turning a bigger prop though, maybe 14 x 17 three blade at about 500 ROM

 

Did you look at;

http://www.electric-boat-association.org.uk/

Huge, well documented, real examples.

 

If you want it light, then you are correct, foam is the way to go. The method requiring least expertise and equipment is Intelligent Infusion http://harryproa.com/?page_id=1327

Infusion is one of those things where you make a test piece and are an instant expert, wondering a) why you were worried and b) why would anyone build a boat any other way? The Intelligent part is the removal of most of the boatbuilding skills, hard work and mess from the process. There are almost no tools required. All the cutting is done with scissors and a utility knife. There is no sanding or grinding or cutting of cured laminates. The mould and the table are built from rectangular pieces of mdf. Neither of them need sanding or polishing. Not quite buildable in the living room, but not far off it. A pump for a boat like this would be less than $150. The plumbing is a few bucks from the hardware and is reusable. The bag and the sealing tape can be scrimped on, but for the first few times, use the correct materials to ensure you have it right.

The boat in the animation is the T60, a 25' power cat, solidly built as it will have a hard life with a big outboard and lots of gear exploring the Amazon and then Tierra del Fuego. Ex outboard and fuel, it weighs 190 kgs/418 lbs and carries 420 kgs/900 lbs for each 100mm/4" of draft.

It could be built much lighter (<300 lbs) if it was looked after and not as heavily powered. And lighter again without the console and seat backs. It would easily meet your speed criteria with a small motor.

 

Why don't I associate being extremely light with anything having "cow" in its name?

Or is cowmaran a typo?

 

It was dubbed the "Cowmaran" because it was built in someone's cow barn.