How do the boat lifts that use air work? If they have a check
valve to let water out the bottom when they force air in, how
do they let the water back in to sink it? I thought maybe a
solenoid valve, but don't see any wires running to the float
tanks...only what appears to be an air hose. Is HydroHoist
the only lift that uses air? I read that they have a patent,
but they can't have a patent on the concept of using air
to lift a boat can they?

Just a guess:

The float tanks have a drain fitting on the bottom which is always open to
the water. To lift, you pump air in from the top to force the water out. To
lower, you vent the air pressure to allow water to fill the tank.

David
dh@. wrote in message ...
How do the boat lifts that use air work? If they have a check
valve to let water out the bottom when they force air in, how
do they let the water back in to sink it? I thought maybe a
solenoid valve, but don't see any wires running to the float
tanks...only what appears to be an air hose. Is HydroHoist
the only lift that uses air? I read that they have a patent,
but they can't have a patent on the concept of using air
to lift a boat can they?

No Valves or solenoids. There are holes in the bottom of the tanks.
Many brands use air to lift the boats.

On Sat, 15 Oct 2005 13:47:27 -0400, dh@. wrote:

How do the boat lifts that use air work? If they have a check
valve to let water out the bottom when they force air in, how
do they let the water back in to sink it? I thought maybe a
solenoid valve, but don't see any wires running to the float
tanks...only what appears to be an air hose. Is HydroHoist
the only lift that uses air? I read that they have a patent,
but they can't have a patent on the concept of using air
to lift a boat can they?


I am speaking out of turn - because I don't know how the model works
that you are talking about.
But if *I* had to do a lift, an air line connected to the float and
selectable for a pressure source, or an atmospheric vent would work
perfectly well would it not?

Brian Whatcott altus OK

Hydro-Hoist is one of several...Boat Floater, Econo Lift and others.

A motor with a blower attached about the size of a vacuum cleaner motor
blows the air out of the tanks. Each tank has a hole at the opposite end of
the tank of where the hose attaches, on the bottom that is about 4 inches in
diameter.

Two controls are in the enclosure that houses the blower, an electric switch
to turn on the blower and a valve. To raise the boat lift the valve is
opened and the blower motor turned on. It can be left on until air bubbles
out of the 4 inch holes and this is the maximum lift that can be obtained.
Once the boat is lifted to the desired height of to the lifting limit the
valve is manually closed and all the air is retained in the tanks. When the
boat is to be launched the valve is opened but the motor is NOT turned on,
the captured air from the rank escapes past the blower and the lift settles
into the lake.

I made a lift for my personal watercraft using 2 plastic 55 gallon drums,
some channel steel some 2X6's for the bolsters, a gate valve and an old
vacuum cleaner. My total cost was under $20. A purchased PWC is about a
thou!

Don Dando

Don Dando








dh@. wrote in message ...
How do the boat lifts that use air work? If they have a check
valve to let water out the bottom when they force air in, how
do they let the water back in to sink it? I thought maybe a
solenoid valve, but don't see any wires running to the float
tanks...only what appears to be an air hose. Is HydroHoist
the only lift that uses air? I read that they have a patent,
but they can't have a patent on the concept of using air
to lift a boat can they?

On Mon, 17 Oct 2005 02:09:25 GMT, "Don Dando"
wrote:

Hydro-Hoist is one of several...Boat Floater, Econo Lift and others.

A motor with a blower attached about the size of a vacuum cleaner motor
blows the air out of the tanks. Each tank has a hole at the opposite end of
the tank of where the hose attaches, on the bottom that is about 4 inches in
diameter.

Two controls are in the enclosure that houses the blower, an electric switch
to turn on the blower and a valve. To raise the boat lift the valve is
opened and the blower motor turned on. It can be left on until air bubbles
out of the 4 inch holes and this is the maximum lift that can be obtained.
Once the boat is lifted to the desired height of to the lifting limit the
valve is manually closed and all the air is retained in the tanks. When the
boat is to be launched the valve is opened but the motor is NOT turned on,
the captured air from the rank escapes past the blower and the lift settles
into the lake.

I made a lift for my personal watercraft using 2 plastic 55 gallon drums,
some channel steel some 2X6's for the bolsters, a gate valve and an old
vacuum cleaner. My total cost was under $20. A purchased PWC is about a
thou!

Don Dando

I was surprised by the mention of the gate valve - they have the
reputation of always leaking slightly. I would have thought a ball
valve would have fit the bill?

Brian W

Not commenting about all the other replies, but chiming in with another
option, not knowing if you were just curious or were wanting to have
one:

I'm a personal (well, was, as I've sold my home) user of Air-Dock, and
happy enough about them to become a dealer (spam warning: I earn
something for each one I sell; the price is the same to the user - if
you're interested in buying, please let me know).

The principle on which I personally was enthused was that it doesn't
have any hard points. It's basically a pillow for your boat.

Now, if you have a sailboat, the task gets virtually impossible without
some heroics in any air lift, due to the keel. OTOH, nearly any size V
or flat-ish bottom boat can use either the Hydrohoist model (tanks and
trailer bunks, practically speaking) or the Air-Dock.

However, in shallow water situations, the reason I first bought the
Air-Dock, you can use any level water which will float your boat, plus
about 6". Try that with a Hydro-Hoist!

Another bonus is that the end price is usually about half of what the
commercial hard-point floats will cost.

As to raising it, the others are correct except that ball, not gate,
valves, are typical. And, yes, it's basically a vacuum cleaner motor
in a water-resistant housing. Drawing about 600 watts, I've done
installations with an inverter (750W, under 75 at Wallyworld, but I
redo the connections to fit the battery, usually replacing the wire to
allow a more convenient location for the box) connected to the battery.
As little draw as they use in a lift (or many, for that matter), each
time the boat's started, the alternator will bring the boat back up to
full charge and they're ready for the next lift when they come home.

In this case, you have a sealed system - the bag never takes on water
(unless you puncture it - which you could, same as you could puncture a
very heavy duty inflatable dink - but the repair process is way simple,
and each comes with a kit for such eventualities), but instead just
inflates and deflates. Pushing air requires somewhat less effort than
water, so it doesn't take as much horsepower. However, in either case,
the ambient pressure inside, once it's up, is never more than about
3PSI if it's sized correctly.

If you're interested, go to http://www.justpickone.org/skip/gallery/
and click on "airdock" for an installation I did from my boat, as well
as my personal installation. And, if you're interested enough (spam
warning) to pursue it, please do it through me :{))

L8R

Skip, rehabbing, about to enter active PT (currently passive) and
itching to get back to the boat

Morgan 461 #2
SV Flying Pig
http://tinyurl.com/384p2 The vessel as Tehamana, as we bought her

"Twenty years from now you will be more disappointed by the things you
didn't do than by the ones you did do. So throw off the bowlines. Sail
away from the safe harbor. Catch the trade winds in your sails.
Explore.
Dream. Discover." - Mark Twain

Oops - sorry - the airdock gallery is a subgallery in the guestki
folder. Click on guestki and then airdock is in the upper left corner.

L8R

Skip