Designing a Portable Lift

Discussion in 'Boat Design' started by Floater12, Feb 6, 2024.

  1. Floater12
    Joined: Feb 2024
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    Location: USA

    Floater12 Junior Member


    It was a great response and i’ve already gone through the math, but it was nice to see it revisited. However, apart from the math, you’re missing a lot:

    1) the bags are not custom manufactured and come in an assortment of sizes, shapes and buoyancy ratings in pounds. no need for the “great unit of measure”. they are commonly made and used here in the states, i even mentioned the brand of bag i’m buying if i go that way. how do you think they raise sunken boats and vehicles? they use these very same bags

    2) you must not be familiar with the laws of the States. please direct me to the law that says you can’t float a boat on bags and do some work to it. also, please show me where spud barges are outlawed. i see them all the time so maybe i can collect some bounty money and just pay ludicrous yard fees and have them do all my work

    I will check into commercial fishing yards but I'm only aware of one. in Providence, RI. however there must be other in commercial fishing hotspots like new Bedford, MA
     
  2. Floater12
    Joined: Feb 2024
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    Floater12 Junior Member

    and the RI yard is gone
     
  3. Rumars
    Joined: Mar 2013
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    Location: Germany

    Rumars Senior Member

    1. Lifting bags aren't designed to keep their shape abovewater with a load on top. You want what is essentially an air jack, it needs to stay in shape regardless of how the load is applied. That's why inflatable SUP's and boat floors have an internal structure and are high pressure, so they don't fold when you stand on them. Try standing up on a cheap pool mattress of the same volume as an SUP and tell me how you liked it. Anyway, you don't have to believe me, ask the manufacturer of the bags how high your hull will ride above the water. The only way to use normal lift bags for what you want is to place a plywood sheet on top as big as the bag, then a 30in high cradle over it. If instead of plywood you use beams like in your sketch, the bags will fold around them and your cradle legs will have to become longer to compensate the lenght.
    There are ready made inflatable docks that you could use like for example this one Standard Inflatable 6×9′ x 8″ Floating Swim Dock | Cottage Docks https://www.cottagedocks.com/product/standard-inflatable-6x9%E2%80%B2-x-8%E2%80%B3-floating-swim-dock/ 8 of them will float your hull without bending like bananas, and you can jack up your hull on top of them, but as I said, you won't like the price or weight.

    2. If you're so sure about the law invite the EPA to watch you work.

    Edit: I just looked and Subsalve actually has a product for you, the 12t aircraft lift bag. Weighs 185lbs and right now it's on sale, $6,694.50 instead of $8,926.00 plus shipping. Subsalve Pneumatic Aircraft Lifting Bag 12 Tons https://www.americandivingsupply.com/Subsalve-Pneumatic-Aircraft-Lifting-Bag-12-Tons-p/aclb-12-3c.htm

    Goodbye and good luck.
     
    Last edited: Feb 7, 2024
  4. willy13
    Joined: Jan 2022
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    Location: Canandaigua NY

    willy13 Senior Member

    Interesting problem for which I currently don't have much to offer, sorry. But it did make me think of the old movie Airport 1977.
     
  5. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Using lift bags in the USA does not violate any EPA regulations. If they leak is only air. Spuds are not allowed in some areas, like coral reefs in Florida. Other than that there is no problem.
     
  6. Rumars
    Joined: Mar 2013
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    Rumars Senior Member

    You're right of course. There's just this little detail concerning the goal of the exercise, wich isn't to admire the underwater shape. After all, why go trough all the expense when you can just use the tide to beach the boat. If driftwood blocks are to work intensive all he has to do is borrow some used tires. 20$ to the tire place and the cost of the ride to the dinghy dock and back is all it takes and there's no added weight to the mothership, not even for a chainsaw or axe.
     
  7. gonzo
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    gonzo Senior Member

    It is only necessary to lift one hull at a time. That will help with stability too.
     
    Will Gilmore likes this.
  8. Will Gilmore
    Joined: Aug 2017
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    Location: Littleton, nh

    Will Gilmore Senior Member

    Cleaning the bottom shouldn't cause the EPA to raise an eyebrow. People hire divers to do that all the time. Painting the bottom will only be a problem if there is significant sanding or spillage of raw paint into the water. Don't let that happen. A drop-tarp should work for that. Of course, if you are counting on the tide, you have to be pretty quick to wrap up and clean up.

    There are any number of shoals along the coast of Maine where you can strand a boat during low tide. Bar Harbor comes immediately to mind.

    If you go the block under the keel route, you can slip two 6×6 or 8×8 blocks under your hull just forward and aft of midships. Then, once the tide has receded, weigh down one end until the hull lifts above the far block. Take that opportunity to fill the gap and move the weights to the other end. Repeat. Eventually, you can even jack the boat above the high tide mark by as much as you want. Hardly any cost at all.

    The tires and a few carpet remnants sound like a good idea.

    -Will
     
    Last edited: Feb 8, 2024
  9. Squidly-Diddly
    Joined: Sep 2007
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    Squidly-Diddly Senior Member

    since its a cat can you just lift one hull at a time? find a sea wall of some sort and crane one hull out of the water at a time.

    Lay some beams on deck cantilevered and instead of using bags of air to lift a hull, fill the bags with water until the opposite hull clears water.
     

  10. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Floater
    You are not the only one facthis problem.
    I suggest building a stout structure that could be trailered to cheap inshore storage.
    Other tooners will want to use it. Rental income could be greater than storage.
     
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