Water propulsion for an amphibious rover?

[Blind Dead McJones]

I wanna put a rover on Laythe, but because it has so much water I want to make something that will be able to move in the water. I made a prototype that floats, but once it gets in the water it cannot move anymore.

I'd rather use something electric so I don't need to worry about fuel once I arrive. I can't figure out a way to do this without a rocket engine which would probably be a very inefficient way to move about the surface. I'm not against using mods, so if you have any suggestions for one feel free to include that.

Edited July 14, 2014 by Blind Dead McJones

[Pecan]

Ion engines then - they're (mostly) electric.

[MockKnizzle]

Try a basic jet engine. It'll give you lots of thrust and it's incredibly efficient. An ion engine would probably work as well, but at only 4kN of thrust it's gonna take a while to get anywhere.

While you're at it, pontoons made of radial intakes float wonderfully (and even look the part!) and have a very high impact tolerance, meaning you can skim along at ~70m/s without fear of explosions.

[orcman]

You could try the Firespitter mod pack. It has electric propellers and some float parts (amongst a whole heap more parts)

[KvickFlygarn87]

You could try the Firespitter mod pack. It has electric propellers and some float parts (amongst a whole heap more parts)

Or the Kerbal Aircraft eXpansion.

[Frank_G]

You should try a hydrofoil design with only a few pylons reaching into the water. The best engine by far is the basic jet engine. It offers decent speed and acceleration at sea level and is very fuel efficient. You can use control surfaces to steer the boat.

[OgreMagi]

not use about using a basic jet engine the air is thinner, I would try a Turbojet think you will get better ISP...

[Geschosskopf]

I wanna put a rover on Laythe, but because it has so much water I want to make something that will be able to move in the water. I made a prototype that floats, but once it gets in the water it cannot move anymore.

I'd rather use something electric so I don't need to worry about fuel once I arrive. I can't figure out a way to do this without a rocket engine which would probably be a very inefficient way to move about the surface. I'm not against using mods, so if you have any suggestions for one feel free to include that.

KSP unfortunately doesn't do boats very well. There are no stock boat parts and the water behaves very strangely. About the only way to do boats with stock parts is to build a hydrofoil that floats on (wait for it) I-beams, structural panels, or radial intakes. With these parts and these parts only touching the water, you can make a boat that will move. If any tank or other round thing like your lab touches the water, then you won't go anywhere even with a Mainsail pushing. But with a hydrofoil, you can zip right along with a jet engine. Maybe an ion, give that a try.

NOTE: the rover wheels can't touch the water either, or they'll break off if you get to any real speed. So you'll either need Infernal Robotics to hinge them up and down, or make a landing craft hydrofoil with a ramp the rover can drive up and down on. See the last 2-3 of Wookie's "Rover Adventures" videos on YouTube for ideas on that.

OK, you've gotten the boat to move. Steering it is another issue. Basically, you can't, no matter how many rudders you put on it above or below the water, unless you're hardly moving at all. Thus, driving a stock boat is a series of sprints in straight lines, followed by a long time to coast down to low speed (no brakes), then pivot in place and off on another straight leg.

That's all with just stock. There are, however, mods that make boats a lot easier. My favorite is Firespitter. Firespitter has pontoons for making seaplanes, but a seaplane with its wings sawed off is a boat. Furthermore, the pontoons have retractable wheels in them that are powered like rover wheels, so you can put a couple of these pontoons on your Mobile Lab and have something that will float easily on water and rover on land without need of extra rover wheels. The pontoons also have built-in rudders so you can steer while moving at speed, although still no brakes. You also still need some form of propulsion to move the thing on water, but Firespitter has you covered there with several electric propeller engines if you want to go all-electric. Of course, having something with pontoons, wheels, and an engine, all you now need is wings and you've got an amphibious seaplane, which is more flexible and faster than a boat/rover. So you might as well do that instead.

NOTE: The Firespitter pontoons blow up if you exceed about 120m/s on the water. Also, they have a right-click menu that allows adjusting their buoyancy. I recommend maxing that out.

[cantab]

Wings work for boat hulls too, since they're reasonably low drag at modest speeds. Just be careful when entering or exiting the water since that's when their fragile impact tolerance will come into play. My Laythe boat (the Magellan in my mission albums) gets up to about 20 m/s on them, with about 150 kN of thrust. It also turns well enough just on the torque of a few reaction wheels, or by shutting down a prop on one side, though it's not advisable to take turns at full speed!

As for propulsion, the go-to option in stock is the jets. I think they might even be more fuel-efficient than the ions, due to the jet engine Isp bug. For mods, Firespitter's the obvious choice with a wide choice of propellers, which seem to work equally well above or below the waterline and many can run in either forward or reverse.

The electric propellers are power-hungry, and you can't use deployable solar panels when underway or they'll break. You could stud your boat with OX-STATs which is fine for a small ship but will spike the part count on a big one. A better option for a large boat could be to provide lots of batteries and plan on stopping for recharges. Or if you're prepared to consider more mods, I powered my boat with a nuclear reactor from Near Future Technologies. I couldn't fully deploy the radiators or they'd break like the solar panels, but even with the rads in the closed position I could run the reactor high enough to power the props.

On land, bear in mind an option is to use thrust for drive, and run on aircraft landing gear which won't give you any drag problems in the water. For a modded electric craft this won't use any fuel. Alternatively, for a purely stock amphibian I might consider something that rolls over, so the wheels are on one side and the floats on the other.