Building an electric propulsion hydroplane?

Discussion in 'Projects & Proposals' started by Piggy, Jul 1, 2019.

  1. Yellowjacket
    Joined: May 2009
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    Yellowjacket Senior Member

    Hydros look cooler but aren't that much faster than runabouts in a straight line. Hydros work by getting most of the boat out of the water and are riding pretty much on a cushion of air. Hydros work the way they do because they're really light relative to their bottom surface area. That is, the air pressure under the hull is roughly equal to the stagnation pressure for the speed you are running. You can calculate the stagnation pressure vs speed ( p = .00002222 * v^2) so at 60 mph you get about .08 psi... That's not a lot of pressure, but over a 3 foot x 10 foot bottom you end up with about 350 pounds of lift. So a light boat can support most of its weight on the air cushion and this is why they call riding most of the way out of the water as "airing out'. Now add another 150 pounds and you are basically going to be riding much more heavily on the sponsons and the back of the hull is much more heavily in the water. In that case the speed is going to fall off very quickly The problem is if you don't get it up on the air the boat isn't working as a Hydro, it's working as a conventional planing hull. In short "you're gonna need a bigger boat".. Or at least a boat with more bottom area to carry the extra weight.

    Hydros are pretty much set up to turn left. All the time... What happens in a Hydro is that the forward skid fin pulls the boat to the left. The driver at high speed moves his weight aft to get the skid fin out of the water to a significant extent so it can go (somewhat) straight on the straight parts of the oval. When you want to corner you lift off the throttle, move your weight forward at the same time. Both of these actions put the skid fin deeper in the water and along with some steering input you go around the corner like you're on a tether. If you don't get your weight back on the straight you'll just keep turning left.. Which is what will happen if you put another 150 pounds in the boat.. You could try to straighten out the skid fin, but then the boat won't turn very well.. The problem you have is that you can't shift that extra weight that you're putting in the boat. Hydros are really weight sensitive, from a speed and from a handling standpoint.

    As to what size boat, first of all, forget about an "A" class boat. That's way too small. With a heavy person (like over 150 pounds) makes it almost impossible to get on a plane with the "A" class motor. An A class runabout is about 8 feet long and 4 feet at the beam and a B is only a bit bigger, lots of boats were built at the time as A/B boats, the only difference being that you put an 18 HP motor on the boat to change classes. Runabouts have a lot more floatation than hydros. You'd never float another 150 pounds in an A or B hydro, you'd swamp it just trying to get in it. It's easy enough to swamp a "C" class boat when sitting still, saw that happen a couple of years ago when a driver wasn't watching what he was doing. You might get away with a "C" runabout but what you really should be looking as is a "D" class boat to support that kind of weight. If you put that 35kW motor on "D" hydro and then add an additional 150 or 200 pounds of batteries you're not going to run 70 mph, since it won't ever get on an air cushion. A "D" runabout is 13 1/2 feet long and about 58 inches wide at the transom. There's a lot more buoyancy in that bigger boat.

    Another issue you will have to consider is where are you going to put the extra weight. All ABPA boats (both runabouts and hydros) struggle to get on a plane. They have a lot of weight aft and to get on a plane the driver generally has go get most of his weight ahead of the steering wheel. More weight aft really hurts the ability to plane off. But more weight forward will hurt speed. So your speed potential for the boat isn't going to be as good as a conventional rig.

    One thing you could consider if you went with a hydro is to design the boat with more area forward. That is bring the lifting surface further forward and fill in the area between the "pickle forks" to get more lifting area. Back in the old days hydros had a "shovel nose" design. Shovel nose boats went away because they had a tendency to blow over when the technology pushed the speeds into the higher ranges, because they had a lot more lift forward. There was an interim design that were called "cab over" boats that had a conventional shovel nose but had the driver moved forward so they wouldn't blow over as easily. As speeds went up the area needed to provide enough lift got smaller and the lifting area got cut back, which is where we are with the "pickle fork" boats of today.

    If you look at the electric powered boat in the video, its wider both at the transom and between the sponsons than a typical hydro. That's necessary to float the batteries and to get more lifting area to get the boat out of the water and into the air. You're going to have to do the same thing to offset the battery weight. What I'm saying here is that to go with a hydro you're going to have to design it to carry that extra weight and you'll have to have it custom built, or you're going to have to build it yourself. Unless you have a complete wood working shop and a lot of hydro design experience you can end up hurting yourself. Don't think you can just put an extra 150 pounds in an existing hydro and have it work at all. That's not going to happen.

    I still think that a runabout is a lot more safe and would handle he weight better than a hydro and you can set them up to turn both ways which is also a plus. A "D" class runabout with maybe a 40 hp motor running 45 mph would be a pretty stable ride. If you put a 35kW motor on it you might hit 55 or so, but that would also be a very stable ride at those speeds. You could also buy an existing "D" boat and with some reasonable modifications to house the batteries, have something that would work pretty well.

    If you want to learn a bit more about race boats you might think about coming down to Constantine Michigan the weekend of the 13 and 14th of this month, a week after this coming weekend. The AOMCI has a meet and they have a oval race course set up. A lot of racers will be there using it as a two day test session in addition to some antique race boats. I'll be there with my rig and there will be a lot that you could learn. It's not far at all from Ann Arbor and you'd get a feel of what goes into a race boat. Friday is for "putt putt" boats, Saturday and Sunday the race boats are on the lake most of the day. Constantine is about 2 hrs from Ann Arbor, it's as close as you're going to get to a APBA race boat any time soon.
    kerosene, BlueBell and alan craig like this.
  2. Piggy
    Joined: Jul 2019
    Posts: 8
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    Location: Texas

    Piggy Junior Member

    So a Class D runabout seems to be the choice here if I want to make a boat that can meet our requirements. I would love to go to Constantine, but I actually live in Texas (where I am now) and will be attending UMich as an out-of-state student (move-in day is Aug 28). I think making a custom boat is within the realm of possibility considering we'll have a whole team of students and an engineering project building at our disposal. However, turning both ways does sound kinda nice, so a runabout still sounds like the way to go here. Now I just have to figure out how to sell this project to the University and/or sponsors to get enough funding.

  3. Christian Lucas
    Joined: Dec 2018
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    Location: Munich

    Christian Lucas Junior Member

    there is no problem to design a electric hydroplane. As it it easy possible to get on plane with a electric powered wake foil.
    Home of the eFoils, Hydrofoils and Classic Foils | Lift Foils like in the linke. A water foil does nothing other that producing lift like an airfoil to lift a hydroplane.
    So the basics are that you have to look for the right design of an wing in ground effect. For such low speed the reversed triangle wing with big stabiliser is a good way and wy not run such plane with surface pircing propeller. Russian have done it with succses. Also the normal Hydroplane layout with higher air compersion will get the lift to fly, but it fly not so stable like wing in groundeffect aircraft do. An other option are the wing in groundeffect Ekranoplanes with straight wing and big stabiliser wing . About power, Do you know the Lampuga electric surfbord. The profesional racing surfbord run up to 60 km/h with a motor from Lehner Motorentechnik in Germany . Lampuga - Premium Electric Surfboards Made in Germany .
    This motors are brushless and powered by Lihium batteries. They can do 18 kw and are water cooled. And the surfbord has for safty the impeller jet drive that is less efficancy than a real propeller. Highest efficancy you will get with a an airpropeller like the human powered Decavitator used , but much moore dangerus.
    This are very light powerfull drives . If you like moore information aske .

    Happy Amps Christian
    Last edited: Aug 28, 2019
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