Originally Posted by Maj_Overdrive
Snowmobiles can do it because of their great power to weight ratio and also because on water they use a cleated track that acts as a paddle. That cleated track provides a pretty efficient way to put the power down and keep it moving. The variable transmission also keeps the engine in the powerband. The forward momentum and angle of the track is actually what keeps them from sinking, not the front ski's. If the ski's are in or touching the water it's just slowing the sled down as they aren't even needed for turning.
I've seen some videos of rc cars going across water. You definitely have the tires but I think you're a bit short on power and more importantly speed. Yes you can achieve 33mph on land but you won't be able to put the power down to the water to maintain it and possibly not minimum speed either. A tire on land moves the vehicle forward a distance equal to the tires circumference. On water you're relying on just each paddle to move the vehicle forward. So the space between paddles is like the tire is "slipping" and not moving the vehicle forward. Paddle wheel also isn't the most efficient and needs to spin faster than the vehicle is moving. If I had to guess I'd say 33mph gearing would be the bare minimum to maintain 20mph actual speed meaning you're cutting it real close. I personally wouldn't take the chance unless I knew I had the power and gearing for 45-50mph on land. I'd think an 8lb buggy sinks pretty good
For the most part, you are right about sleds.I've ran open water a few times (not on purpose).
That being said, HP to weight isn't what make sleds on water possible.
The first sled I had on water was an 1985 SRV 540cc. I don't remember the weight and HP of it, but saying 600lb with me on it and 50hp shouldn't be too far off. On a good day, it would do just over 100mph. The last sled I hit open water with was a 1996 Formula 3 600cc with about 115hp and about 750lb with me on it.
Compare that to my current buggy setup at say 9lb and 1.6hp and 33mph....
What makes sleds and water possible is the surface area of the track, shape and speed. You can accelerate on water with a sled, just don't go wide open throttle as soon as you hit the water or you'll drowned it.
I used barefoot skiing as it was the only formula I could find and the surface area to weight was a lot higher.
I think the key will be the surface area, weight and speed.