I recently purchased a home on the water that included what I call a
cradle-type boat lift. Simply put, it's 4 pilings with an aluminum cradle
mounted between them, and the boat is lifted from the water on this cradle
via two electric motors. There are blue plastic pulleys (sheaves) at the end
of each beam and a few other places. The cradle has 2 long, carpeted bunk
boards that run the length of the cradle. It has 5/16" cables and is rated
for 10,000 pounds.

I haven't moved my pontoon boat to the lift yet, and when I run the empty
lift up and down I noticed the following problem when the lift comes up (not
down). The two bunks appear even and level but the problem is that when
there is no pontoon boat weight on the lift and I raise it up, the sheaves
on one side nearest the dock where the controls are lose cable tension and
the cables then windup unevenly on the spool. If I push down slightly on
the nearest plastic PVC upright used as a guide bumper the cables get tight
and all is well. Said in another way, if there is even a slight amount of
weight on the lift like from my foot pressure on the inboard (dockside) bunk
board there is no problem. This is not a buoyancy problem from floating
bunks because the bunks are already out of the water. This is not a bound
or frozen sheave problem because I used a come-along to take the weight off
of each of the pulleys and they spin freely. Going down is no problem at
all.

I suppose I could just add some solid cinder blocks to the center of the
cradle I-beams, but I really want to know is the physics of why it's acting
like this? Someone please help me diagnose this.

Chuck

By chance are the cables that are not winding properly, newer than the
others? I'm guessing that may be the case, since newer=stiffer (usually).
Let me ask this: if it works fine with the boat on the lift, why would you
run it up without the boat on the lift? Just checking operation, I
understand, but the lift was designed to, you know, lift a boat. It would
seem like a drag to have to lower the lift first, then drive the boat on it,
to lift it out...if you know what I mean.

--Mike

"Chuck" wrote in message
news:7QaDg.86278$FQ1.35449@attbi_s71...
I recently purchased a home on the water that included what I call a
cradle-type boat lift. Simply put, it's 4 pilings with an aluminum cradle
mounted between them, and the boat is lifted from the water on this cradle
via two electric motors. There are blue plastic pulleys (sheaves) at the
end of each beam and a few other places. The cradle has 2 long, carpeted
bunk boards that run the length of the cradle. It has 5/16" cables and is
rated for 10,000 pounds.

I haven't moved my pontoon boat to the lift yet, and when I run the empty
lift up and down I noticed the following problem when the lift comes up
(not down). The two bunks appear even and level but the problem is that
when there is no pontoon boat weight on the lift and I raise it up, the
sheaves on one side nearest the dock where the controls are lose cable
tension and the cables then windup unevenly on the spool. If I push down
slightly on the nearest plastic PVC upright used as a guide bumper the
cables get tight and all is well. Said in another way, if there is even a
slight amount of weight on the lift like from my foot pressure on the
inboard (dockside) bunk board there is no problem. This is not a buoyancy
problem from floating bunks because the bunks are already out of the
water. This is not a bound or frozen sheave problem because I used a
come-along to take the weight off of each of the pulleys and they spin
freely. Going down is no problem at all.

I suppose I could just add some solid cinder blocks to the center of the
cradle I-beams, but I really want to know is the physics of why it's
acting like this? Someone please help me diagnose this.

Chuck

Hey Mike,

Thanks for the response. Since the boat wasn't on the lift I was just
checking things out, letting it down to the bottom to see where the bottom
was so I could mark the cables with red electrical tape. Also looking for
cable frays etc. From what I found out the cables are the original from
about 4 years ago. All I am thinking is that when the lift is all the way
down and the boat is above it, there wont be any weight on the lift for a
few feet and I will have to be careful not to wind the cables crooked on the
uptake winding spools. It just seems like it is binding a bit even though I
checked the sheaves and the roll fine. Most a curiosity at this point
because it makes no sense to me why the cables on one particular spool get
looser as the lift comes up? Someone must have figured this out in the
past.

"MGG" wrote in message
t...
By chance are the cables that are not winding properly, newer than the
others? I'm guessing that may be the case, since newer=stiffer (usually).
Let me ask this: if it works fine with the boat on the lift, why would you
run it up without the boat on the lift? Just checking operation, I
understand, but the lift was designed to, you know, lift a boat. It would
seem like a drag to have to lower the lift first, then drive the boat on
it, to lift it out...if you know what I mean.

--Mike

"Chuck" wrote in message
news:7QaDg.86278$FQ1.35449@attbi_s71...
I recently purchased a home on the water that included what I call a
cradle-type boat lift. Simply put, it's 4 pilings with an aluminum cradle
mounted between them, and the boat is lifted from the water on this cradle
via two electric motors. There are blue plastic pulleys (sheaves) at the
end of each beam and a few other places. The cradle has 2 long, carpeted
bunk boards that run the length of the cradle. It has 5/16" cables and is
rated for 10,000 pounds.

I haven't moved my pontoon boat to the lift yet, and when I run the empty
lift up and down I noticed the following problem when the lift comes up
(not down). The two bunks appear even and level but the problem is that
when there is no pontoon boat weight on the lift and I raise it up, the
sheaves on one side nearest the dock where the controls are lose cable
tension and the cables then windup unevenly on the spool. If I push down
slightly on the nearest plastic PVC upright used as a guide bumper the
cables get tight and all is well. Said in another way, if there is even
a slight amount of weight on the lift like from my foot pressure on the
inboard (dockside) bunk board there is no problem. This is not a
buoyancy problem from floating bunks because the bunks are already out of
the water. This is not a bound or frozen sheave problem because I used a
come-along to take the weight off of each of the pulleys and they spin
freely. Going down is no problem at all.

I suppose I could just add some solid cinder blocks to the center of the
cradle I-beams, but I really want to know is the physics of why it's
acting like this? Someone please help me diagnose this.

Chuck