floating boat lift

Discussion in 'Boat Design' started by gregs, May 16, 2007.

  1. gregs
    Joined: May 2007
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    gregs Junior Member

    I am interested in building an affordable floating boat lift. Something similar to a lift like this http://www.econolift.com/ or http://www.boatfloater.com/index.asp . I have a 18' v-hull power boat that weighs approx 2200#'s. My design concept is using 55 gallon plastic barrels for the chambers lined up like pontoons connected together with a wood or steel frame similar to a floating dock. Then build a manifold from pvc pipe to connect the barrels together and to a blower, check valve and a valve to release the air. Next cut holes in the bottom side of the barrel (not sure how big) to let the water in to sink it and get the boat off of the lift. So the idea is to lower the lift you open the air valve and water fills the barrels pushing air out and the lift sinks, to raise you close the air valve and turn on the blower and air pressure displaces the water in the barrels and it floats again. The barrels should support about 400#'s each and I am thinking about using 10 total (5 each side) but may have to increase that with a row in the center once I determine what the framing will be made of and the weight. I think I would build the main frame work with PT lumber and steel brackets to reinforce the connections. I would appreciate any thoughts, ideas or experience. I have more ideas on the details but didn't want to get into all of that at this time until I see if this is a viable project. I think I am going to build a scaled test model using plastic 5 gallon buckets and a shop vac for the blower, and I can weight it with sand bags to check its capacity. Thanks, Greg
     
  2. Frosty

    Frosty Previous Member

    Its a good idea. I had thought about something like that myself ,trouble is my boat is 14 tons so--.


    Any way I think it is perfectly do-able.

    Theres is one here in the marina with a 22 footer with a mercruiser in it,--not a light boat but it comes up out onto the floating dock with ease.

    It is just 2 long (big) PVC pipes welded up with PVC frames, and a massive hair dryer to blow the water out.

    I would love to get my boat out of the water and keep it nice and clean with no antifouling schedule --plus electrolisis elimination.

    The thing I find most impressive is its simplicity.
     
  3. gregs
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    gregs Junior Member

    I got some info from a company that makes the floats most builders use. They are simple with having a 4" or 6" hole in the bottom and 1" bungs in the top. The simplicity is what has driven me to test and build one as I think it certainlly will work. I may change the design and put the floats more under the center like the commercial units instead of in a pontoon style. I am thinking of using electric leaf blowers but not sure if I will need one or two to power it. I am going to make a scaled unit with 2 5-gal buckets to test how much weight they can handle at different water levels and figure on using the blower side of a shop-vac for testing. I see this as something an average diy can build and afford. I am not sure if I have this in the correct forum, even though its not a boat a lot of the same principles apply.
     
  4. gregs
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    gregs Junior Member

    I had the opportunity to do some initial testing this past weekend with good results. I built a wooden frame and attached 2- 5 gallon buckets on there sides. I cut a 2" hole in the bottom side and made a manifold with 3/4" pvc pipe and a ball valve with an adapter for a shop vac hose. Its main problem was it was very unstable wanting to turn over. If I let a little water in for ballast it was better but still not very stable. The theroy worked great, open the valve and let the air out and water in and it sank to the surface with no weight on it. Turn on the blower and it raised back up very quickly. I weighted it with another 5 gallon bucket of water (approx 40#'s) and it stayed about half in and half out of the water. So I think the idea of using 55 gallon barrells for the floats will work, I just need to work on the design of there placement to make it stable. I want to attach it to a concrete seawall with a hinged gangway and stability pipes at the corners just like a floating dock. I am still leaning towards a pontoon style with maybe a few extras in the rear area where more weight seems to be.
     
  5. Dave-Fethiye
    Joined: Jun 2007
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    Dave-Fethiye Junior Member

    Hi Gregs,
    I am also wanting to build a pontoon type boat lifter and I am also considering using plastic barrels.

    Did you build your boat-lifter ?

    Any photos or advice for me :)
     
  6. gregs
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    gregs Junior Member

    Not yet. I have not had the time to work on it.
     
  7. Jongscx
    Joined: Oct 2007
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    Jongscx Junior Member

    I've been thinking about a similar design, with 55gal drums... but I'm not really raising or lowering mine. I'm setting it on fire.

    However, my question/suggestion was this:

    How are you going to make sure that they all have the same amount of air inside them? or will this not be an issue?

    I would suggest that instead of drilling a hole at the top of the drum and forcing the air in that way, would it be easier to have the pipe reach to the bottom and curve around? so that the drum will catch the air on its way up? Also, you'd be saved from having to worry about leaks.
    Letting the air out, to lower it, no ideas here, other than to put valves at the top. But, if you used electric solenoid driven ones, you could release them all and not have to worry about it listing to one side because of differences in release rates.
     
  8. Dave-Fethiye
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    Dave-Fethiye Junior Member

    Some good thoughts there.

    I also don't like the idea of making holes in the top of the barrels because of possible leaks and the maintenance to prevent them.

    The idea of the bent pipe to feed in the air is a good one - could that not also work for releasing the air ?
    I mean: have another pipe that starts right at the top od the barrel and goes down, out one of the holes at the bottom and up again way above the water level to a nice dry valve. Identical pipes could be gathered from each barrel, tee'd together and put through just one valve.

    I am not sure if we could rely on the fact that there is roughly equal pressure on all barrels to ensure that they all emty at the same rate ? As you point out we dont want the boat listing over !

    Is there such a thing as a valve that lets out air but not water ?
    That would be helpful in order to prevent water getting up into the pipes,
    but maybe that not needed because once the air is out the water will stay at sea level (of lake level) anyway. However such a valve may help in keeping the air escape equal - I dont know ?

    What do you think ?
    Are we getting closer to a working design?
    Anyone have any answer to the above ?

    Dave
     
  9. Jongscx
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    Jongscx Junior Member

    Well, the water level in the barrel won't be the same as it is outside, since there will be weight on it, compressing it and whatnot.
    So basically, you'd have a pocket of compressed air trapped at the top of the barrel. How to release that air is a problem. It may be best to have two sets of pipes. You can have a high-volume, low pressure pipe that goes under the barrels, to feed the air. Then have a high-pressure small diameter pipe to release it. The small diameter would also work to restrict the air-flow too, making it more controllable. Plus, I would think it would be cheaper to get small diameter, high-pressure pipes than large diameter ones.
    I guess we'd need to figure out the pressures inside a loaded barrel first, to be safe, but it's a start.

    I don't think it would really be important to keep water out of the air-supply lines, plus it would add a lot of complexity to the design. The only thing I can think of would be an up-side-down P-trap, but the difference in water pressure alone would negate that if the pipe extends to the surface. One may be able to make one that is based on a floating stopper, not really sure.
    I guess I see your point on having empty pipes, especially the supply ones, since you'd need a blower that could force the water out of them first before it could put air in the pipes... Would a pair of gas-powered leaf-blowers be enough?

    I would have at least 2 valves, one for each side, if not 4, one for each corner. Then you'd have control of the 2 axises (axes?) that the structure could pitch in. (side to side, and front to back) Again, electrical valves would simplify things, but 4 reliable buddies that you can trust to follow instructions would work too.
     
  10. Dave-Fethiye
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    Dave-Fethiye Junior Member

    Yes, I was wondering about the air pressure inside those barrels.

    The boat I want to lift is 8 tonnes.
    It is 13 meters (about 43') and 3.75m wide

    I am going to buy a compressor for paint spaying so I can use that to put the air in. It is rated at 6.3 cfm with working pressure of 110psi.

    That amount of air displacement seems a bit low. Maybe a leafblower would be better as the high pressure is not going to be necassary.

    After all to raise the boat I am going to need at least 9 cubic meters of air - a cubic meter must contain about 30 cubic feet. So 30x9 = 270.

    At 6.3 cfm. 270/6.3 = 42.8 minutes. Well I suppose 3/4 of an hour isn't too bad - wouldn't want to rush the job anyway. Plus I will need some pressure to lift the 8 tonnes - but I am not too sure how to work out the pressure.

    Lets assume I am going to use 20x460 litre barrels (= 9.2 cubic meters or 9.2 tonnes of water) The barrels are round with hieght of 93cm and diameter of 80cm. They will be positioned apporox 1m beneath the surface before air goes in and then hopefully rise to be close to the surface and hence lift the boat quite a lot out of the water - doesn't have to be completely dry although that would be nice.

    Can anyone help with the maths on this project ?

    Thanks
     
  11. Jongscx
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    Jongscx Junior Member

    Yeah, only reason I'm suggesting a leaf-blower is because it moves a lot of air quickly... It may be advantagous, albiet slow to use the compressor instead.

    Oh, and all that math definitely made my head hurt...
     
  12. 3card
    Joined: Apr 2008
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    Location: Montana

    3card Junior Member

    Boat Lift

    Gregs and all others,
    Hello, Greg I know it was a year ago when you made this post about building a floating boat lift. I just wanted to let you and everyone else know that I successfully built one for my 18-1/2 foot Glastron using a boat trailer!
    I have since developed a websit and e-book on how to build one, as like you, I couldn't find any information on how to do it.
    My website is Liftnlaunch.com Check it out!
     
  13. Jongscx
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    Jongscx Junior Member

    ummm.... link?
     
  14. gregs
    Joined: May 2007
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    gregs Junior Member

    I took a look at your site and it looks pretty nice. I think its a great idea to use the trailer as well. Do you have any pictures of it in action? I am like you, trying to build something affordable.
     

  15. 3card
    Joined: Apr 2008
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    3card Junior Member

    liftnlaunch

    I do not have any pictures or video of the lift in action as of yet. I just got it operational on Labor day weekend last year, the day I had to take my boat out of the water for the season. I am planning to make a video this spring or summer. I would like to put a video on youtube as part of my marketing strategy. Hopefully this link will work liftnlaunch.com
    I spent about two years dreaming this up(and many sleepless nights), rounding up components, and building the lift. Hopefully this e-book will help you and others save time and money. Mine cost me about $2800.00
    Thanks for your interest!!!
    3card
     
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