Cradle type boat lift cable unspools when lifting
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 |
Chuck
Aug 12
2006
|
| If the cable has too much "spring" in relation to cradle weight it is
possible to envision something like that happening. Does it happen with a boat on the cradle also? If not, you can probably solve the problem by adding some extra weight
on each side of the bunk boards. An inexpensive way to do that would
be PVC pipe filled with concrete and/or rebar. |
Wayne.B
Aug 14
|
| Thanks to everyone who responded. |
Chuck
Aug 14
|
| With the cradle off the bottom but down does there seem to be a
littler more "wiggle" in a diagonal pair? If one pair are banjo
strings and the other two have some wiggle you have your problem.
Shorten one up a bit. |
gfretwell
Aug 14
|
| They may spin free when unloaded, but not under load. How long have the
sheaves been out in the weather? |
John
Aug 14
|
| What would be the point of lowering any further than that? |
Wayne.B
Aug 13
|
|
Somebody please go back and reread my original post. I know where the
bottom is because I have marked the cables with electrical tape. The
problem is that: THE CABLES GO SLACK ON THE WAY UP. (Sorry... not yelling,
just restating the problem) Chuck |
Chuck
Aug 14
|
| It is not usually intentional but if you don't have a lot of water
under the boat and you are trying to get out you might not know you
are bottomed until the cable slacks up. In this "mile wide and a foot
deep" area where I live it is not uncommon to have days you just can't
get a cradle lift down enough to get off. It won't take much slack to
jump a wrap and grind up the cable
They clamp a 3# to 5# weight a couple feet up the cable to hold it
tight.
I have lift rings on my boat so I just need to get the hull wet to go. |
gfretwell
Aug 13
|
| Unless you have a levitation problem (or too much floatation in your
cradle) the cables were not winding right from the start and you just
noticed it on the way up. If you do have so much wood on the cradle
that it floats the result is the same. Weights on the cables will fix
it. |
gfretwell
Aug 14
|
| One of the first things I did was to carefully and deliberately "bottom out"
the lift and then mark that position on the 4 cables with several wraps of
electrical tape so that when I see the black tape come around and unwind I
stop right there before there is any slack in the cables. As I watch this
problem occur, it definitely only happens on the way up. It acts like a
stuck sheave but remember in my original post I stated that I checked the
sheaves and they spin free. In fact, I actually jacked all four corners up
with a come-along and removed and inspected the sheaves and then put them
back. I can understand where the lift would bloat when still below the waterline
due to the buoyancy of the wooden bunks, but it happens above the waterline
as well. At that point I would think the weight of the cradle itself would
keep the cables taught. Someone said that 5/16 inch cables are known to be
troublesome, have a "memory" and don't like to play well when used with
small sheaves. This is really bugging me. |
Chuck
Aug 14
|
| >Hey Mike, |
gfretwell
Aug 12
|
| Just seems like the weight of the beams should be enough weight. People
talk about adding weights so it must be the right thing to do... |
Chuck
Aug 13
|
|
When the beams hit bottom the cable goes slack. |
gfretwell
Aug 13
|
| 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" <cscholtz@mchsi.com> wrote in message |
MGG
Aug 12
|
| 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. |
Chuck
Aug 12
|
