Please try to help further diagnose what is causing this. There is more
information this time to work with.

We have an 8,000# Magnum 'HD' piling-mount cradle boat lift with what I
think appears to be a slight "bunk buoyancy" problem. When the lift is down
in the water near the bottom of its travel with no boat weight on it yet and
I start to bring the lift up, the cables on both inboard sheaves (pulleys)
start to get a bit slack (especially bad on the right inboard side) while
the outboard cables stay nice and taught. As a result, the inboard (1/4"
cables) don't always windup on the winder spool without a bit of
"criss-cross" unless I keep some downward pressure on the PVC upright pipes.
We operate in sal****er and have a pontoon boat on the lift with 3"x12"x20'
wooden bunks.

I experimented once while the boat was away from the lift just to see what
was going on and the problem definitely goes away the moment the wooden
bunks get above the waterline. The inboard cables get tight again and
everything spools fine.

Checked by lowering the beams down just to the waterline, the lift is very
nearly level (only one inch higher one the inboard side) from an
inboard/outboard perspective. I have checked and none of the sheaves are
stuck. I added 80 pounds of weight nearest the pulley/sheave on the right
inboard side which has "band-aided" the problem some, but has not "cured"
the problem. I am seeking the CAUSE of this problem.

Two Questions: 1. Why do just the inboard cables get slack? 2. Why does
just primarily the right-hand inboard cable get even more slack than the
left inboard-cable??

Your help appreciated.

Chuck

Lift installation diagram for reference:
http://www.lunmar.com/commerce/asset...de/maghd-1.htm

I just now noticed that the below instructions say that when installed, the
outboard end of the lifting beams should be 3 INCHES higher than the inboard
end. Why is that and is this related to the inboard cable slack problem??

http://www.lunmar.com/commerce/asset...de/maghd-1.htm

Chuck wrote:
Please try to help further diagnose what is causing this. There is more
information this time to work with.

We have an 8,000# Magnum 'HD' piling-mount cradle boat lift with what I
think appears to be a slight "bunk buoyancy" problem. When the lift is down
in the water near the bottom of its travel with no boat weight on it yet and
I start to bring the lift up, the cables on both inboard sheaves (pulleys)
start to get a bit slack (especially bad on the right inboard side) while
the outboard cables stay nice and taught. As a result, the inboard (1/4"
cables) don't always windup on the winder spool without a bit of
"criss-cross" unless I keep some downward pressure on the PVC upright pipes.
We operate in sal****er and have a pontoon boat on the lift with 3"x12"x20'
wooden bunks.

I experimented once while the boat was away from the lift just to see what
was going on and the problem definitely goes away the moment the wooden
bunks get above the waterline. The inboard cables get tight again and
everything spools fine.

Checked by lowering the beams down just to the waterline, the lift is very
nearly level (only one inch higher one the inboard side) from an
inboard/outboard perspective. I have checked and none of the sheaves are
stuck. I added 80 pounds of weight nearest the pulley/sheave on the right
inboard side which has "band-aided" the problem some, but has not "cured"
the problem. I am seeking the CAUSE of this problem.

Two Questions: 1. Why do just the inboard cables get slack? 2. Why does
just primarily the right-hand inboard cable get even more slack than the
left inboard-cable??

Your help appreciated.

Chuck

Lift installation diagram for reference:
http://www.lunmar.com/commerce/asset...de/maghd-1.htm

IMHO!!! What a bizaar design. I live on the water in Florida and
have worked on many of my neighbors lifts but have never seen this
design. After studing the design of your lift I can easily see why
your having this problem when you have no load on the beams. It is
easier to see if you take a look at the drawing in your link titled
INBOARD AND OUTBOARD CABLE RUN. When you start to raise your lift, the
cable going to the outboard side has to lift first on the inboard pully
before it can get any lift on the outboard main beam. I know, you
think both cables are lifting at the same time so there should never be
any slace on the inboard cable, but because the inboard beam is being
lifted by the inboard cable - the outboard cable also has to lift the
inboard cable just go get tension on it so that it can lift the
outboard end of the beam. This looks to be an inherent design flaw. I
say flaw because even if you are lifting your boat, when you first
start to lift your boat it is floating and the inboard cable is going
to do this all the time. Just grab the outboard cable and try to lift
the outboard end of the beam and you will see what I mean. I see this
very clearly but don't know if I've explained it properly. All the
boat lifts in my area have a motor mounted of the outboard and the
inboard side and each motor lifts one side of the boat or the other.
Your lift keeps both motors on the inboard "land" side and lifts either
the bow or the stern. Looks good on paper. I think the only way to
defeat this design flaw is to add whatever weight is required to the
inboard end of the main beams to stop the outboard cable from lifting
the inboard side of the beam.


Again, this is IMHO!

ELDON