Most efficent propulsion?

[Jeremy Harris]

Bubble "lubrication" works, primarily by reducing viscous drag (it effectively dramatically reduces wetted area). The snag is the power need to get a layer of bubbles under the hull, as they need to be at a fairly high pressure to work. Low pressure bubbles have the opposite effect and cause the vessel to sit lower in the water. It's how some old torpedo and depth charge explosions used to sink ships, they'd great a large gas bubble under the centre of the hull, leaving it unsupported by the water, so the ship would then only be supported at the ends and would break in half. The same effect has caused big ships to sink when large undersea gas deposits have been suddenly released.

The golf ball dimpling effect does work if you can get it right. Some fast swimming fish (sharks, for example) use the surface roughness of their skin to reduce drag by creating a thin turbulent flow layer that effectively "lubricates" the area immediately around them, reducing the energy they need to expend on swimming. Dolphins go one better, by having semi-active control of surface flow over their bodies. They have flexible skin, with an elastic layer underneath it that deforms with local dynamic pressure. This acts to constantly move the skin surface in and out as they swim, optimising local flow conditions at the micro level and reducing the energy they use when swimming fast.

[edited for typo]

[The fingers]

"Whitewater" being mostly air, will not float you but you can't breathe it. Surfers usually find this out the hard way!

[Drunkskunk]

The textured surface idea works. the boat I mentioned in my first post was painted with a non glossy paint. I'm not sure what sort of micro surface it might have had, it was 80's tech, but that reportadly gave it a few seconds faster time. My friend promptly painted it glossy blue.

Making the paddlewheel efficent I can understand, as I've seen one in action. The propeller I can't. I can know that it is because people who know said so, but I don't understand it, something hasn't clicked in my head yet.

How can a prop reach that efficancy while it has to travel so far through the water? Since the tips of the blades have to move several feet through the water (and displace that water) for every inch forward the boat moves, how can they be efficent? I don't dispute it, I just don't understand it yet.

[The fingers]

Can a type of oil or grease make the hull slide through water with less drag without polluting the lake or violating the rules? I have used vegetable shortening to waterproof my work boots when I went out in wet conditions, and the traction soles were dangerously slippery upon returning to smooth surfaces. It needed to be reapplied often to remain effective; but it is edible, inexpensive, practically odorless (unless rancid), and readily available.

[spinningmagnets]

As outrageous as a kayak hydrofoil may sound, I believe an ultra-light carbon-fiber version might be well worth some consideration. Of course there would have to be a certain minimum speed to maintain elevation above the water.

An inverted V-wing seems as though it would be the easiest to experiment with, and I also think a V-hull would be optimum (Rinspeed Splash shown below in pic). As you begin accelerating, every inch of elevation you attain would remove more of a V-hull out of the water. As to what type of propeller (pedal-driven?), I have no idea what would be best.

Jeremy, I am intrigued by your efforts using a semi-hydrofoil...

[Jeremy Harris]

The textured surface idea works. the boat I mentioned in my first post was painted with a non glossy paint. I'm not sure what sort of micro surface it might have had, it was 80's tech, but that reportadly gave it a few seconds faster time. My friend promptly painted it glossy blue.

Making the paddlewheel efficent I can understand, as I've seen one in action. The propeller I can't. I can know that it is because people who know said so, but I don't understand it, something hasn't clicked in my head yet.

How can a prop reach that efficancy while it has to travel so far through the water? Since the tips of the blades have to move several feet through the water (and displace that water) for every inch forward the boat moves, how can they be efficent? I don't dispute it, I just don't understand it yet.

Propellers are just rotating wings, and just like wings they work most efficiently when they are long and thin (like a glider or sailplane wing). The math required to understand them gets complex pretty quickly though, as each bit of a prop is working with at a different speed and different inflow angle, making performance analysis complicated.

[lpbman]

Take a "mini submarine"
increase the size of the dive plane

tether to your boat (thoughtfully)

as it dives, dive planes produce forward thrust. blow ballast, same thrust,
repeat.

No idea how efficient it would be, it just seems low power. It wouldn't be fast, but there is no limit to how large you could make a concrete tube.