Hovercraft - Experimental Skirt Project

Discussion in 'Boat Design' started by kach22i, May 30, 2006.

  1. kroberts
    Joined: Mar 2009
    Posts: 318
    Likes: 12, Points: 18, Legacy Rep: 210
    Location: Chicago area

    kroberts Senior Member

    OK,

    You will be a bit heavy, but if you are very strict about weight from here forward then you can probably make it fly.

    Things you need to make sure of:
    1. Get some plow planes on there.
    2. Get some landing skids that keep the craft sitting an inch off the ground, and that will slide over the dirt if you lose lift while going over land. Nothing that will catch a stick or rock or cable. Some folks use a green treat 2x4 sitting on edge and rounded on the bottom so as to not catch.
    3. Make sure it's waterproof. What sort of wood are you using? Exterior or marine grade? Make sure you thoroughly paint it with a waterproof paint no matter what.
    4. Are you using epoxy or similar to glue the joints? NO NAILS. The frame needs to have a good glue holding every piece together, and the skin/plywood needs to be glassed to the frame. Staples or screws or nails or whatever can be used to hold things until the epoxy cures, but count on that rusting away before long leaving just the epoxy and glass.
    5. I still say try it without the duct. Paint your prop white, and then paint the tips fluorescent orange for about 6" or so from the end.

    I'm deliberately not telling you how to do some things because this is obviously your design project and I don't want to take over on you.

    One thing about prop safety: If you put a duct or similar around a prop, people assume it is safe even when it's not. When they see an open, spinning prop, though, they assume it is NOT safe even when it has adequate guards to keep everyone away. When your craft is sitting on the ramp idling, some joker will go up and lean against the thrust duct probably not even knowing that there could be a problem. Start the one with no duct though, and everyone steps back instinctively.

    Transitions: This is more an issue with the transition than with the hovercraft. You'll need a lot of space on the other side where you can turn, slow down and avoid junk that might be in the way. Like people. I recommend that you not get too frisky with it until you learn to drive. Hitting almost any transition at 45 mph can be exciting.

    You may not fully appreciate just how fast 45 mph is on water. Most boat speedometers read artificially high. Use a GPS instead, and then don't just take the highest number you got on the whole trip, because wind gusts or other oddities can cause you to read higher than the true ability of the craft.

    There are a few speed demons out there, but not many. I'm one of them. Most hovercraft builders start talking about speed, and then when they get their craft done they have toned the hype down quite a bit. Driving at 50+ mph, you will give the water your undivided attention, or you will be sorry.

    <soapbox>
    Water is not a highway. It has waves, logs floating in it, canoes, swimmers out in the middle of the lane, cable stretched across or some piece of junk just barely piercing the surface. It has rocks, mud, a bridge pylon from a century before. A piece of rebar sticking up just enough to tear your skirt completely off. A really big fish can jump out of the water right in front of you and knock you over. A goose can take off and be unable to overtake you, and go through the prop. Or, he can (and will) drop a bomb on you after he gets 20 feet in the air. They WILL ALL do that, it's instinctive or something.

    Edit: Another category of water hazard is inexperienced or drunk boaters. Most people manage to buy or build a boat and even use it for a few years without ever knowing that there are laws regarding conduct on the water. They are drunk, or driving in restricted areas, or pulling a water skier crosswise through traffic, or being obnoxious with a jet ski. Assuming that they know the rules or even how to drive their boat is a very, very bad mistake to make. Assuming that they INTEND to drive it properly and courteously can be an even worse mistake, especially on crowded water during holidays.

    You can get in serious trouble when going at speed on water. You can be running along fine, and the whole world turns to crap in a heart beat. You can see one problem and then, concentrating on that, miss the other problem until it's too late.
    </soapbox>

    If you get your craft to plane out, it will probably be able to get close to 45 mph. Be sure you take it easy when learning to drive though. Turning and stopping are not intuitive on a hovercraft.

    I do NOT intend to scare you off. I intend to make you think twice before you do anything, make sure you have the right ideas.
     
  2. kach22i
    Joined: Feb 2005
    Posts: 2,418
    Likes: 111, Points: 63, Legacy Rep: 1222
    Location: Michigan

    kach22i Architect

  3. kroberts
    Joined: Mar 2009
    Posts: 318
    Likes: 12, Points: 18, Legacy Rep: 210
    Location: Chicago area

    kroberts Senior Member

    To put things in perspective, my old UH-12r was supposed to weigh 375 lbs total, ready to fly. That was similar in size to what you are building, and while mine was overweight most of that extra weight was engine. It was rated for 90 hp thrust, I had approximately 120 hp on it. I'm guessing that I was around 450 ready-to-fly.

    I strongly recommend that you get some modern, popular plans that look appealing to you and study them. I respect George for doing his own thing, but his craft is a work in progress. I think that's cool, but if you are trying to make your craft work I recommend that you study known-to-work plans or pictures of fully functional, well performing crafts.

    I also use a lot of artistic license in building or modifying my craft. I'm not an engineer, I'm a computer programmer. I used to post pictures of my latest idea, and describe my optimism on how well it would work along with the postings. Then I would finish the project and it would work horribly, or not at all. So I would scrap it, try something else and then show up at the next hovercraft event, where somebody who saw my picture and duplicated my bad design, and now they want me to help them make it work.

    The problem with projects like my experiments or George's skirt is that you don't know how it will work until it's done. We are both in this for the joy of building something in a way that has nothing to do with our professions. We would both rather it work wonderfully, but I don't think either of us is horribly disappointed when it doesn't.

    I mean no disrespect for George, whom I admire for his drive to experiment with skirts. Nor do I disrespect you for wanting to build your own design and make it go. I simply want you to realize that, before you copy the design, you should find out if it works, and how well.
     

  4. kach22i
    Joined: Feb 2005
    Posts: 2,418
    Likes: 111, Points: 63, Legacy Rep: 1222
    Location: Michigan

    kach22i Architect

    I strongly agree.

    Like the Click & Clack brothers on NPR say; don't be like my brother.:D

    The weight is in line, but watch what you do from now on.
     
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