Cable for a Boat Lift

[pckeen]

Hi,

The 5/16" steel cable on my boatlift was rusted on the part that rests most often it the water. It broke tonight when lifting the boat, dropping the boat but fortunately, doing no damage. I need to replace the cable with about 32' of new cable. I see from ebay and other sites that there are different kinds of stainless steel cable - 1x19 and 7x19 for example.

What kind of cable should I use?

If you have any general information on steel cable, I would appreciate it.

Here's a photo of the boat lift and boat.

 

[Chris1956]

Re: Cable for a Boat Lift

You should replace it with Stainless Steel cable. I used 1/4" SS cable on my lift and my boat is 1200#. The kinds of cable you have mentioned seem to be the style of cable. Not sure that is important. Get twisted SS cable of the correct diameter, and you should be fine. Stainless steel is identified by a number like 304, 303 etc. There are lots of kinds.

 

[RotaryRacer]

Re: Cable for a Boat Lift

Steel cable, more correctly, "wire rope" comes in many different styles. The 7x19 type of designation defines how many wires there are and how many bundles of wires are brought together to form the rope.

It's been a long time, but I once worked as an engineer designing overhead industrial cranes. The wire rope specifications and the type of construction was/is very important.

I'd be very careful just assuming that you can switch to stainless of the same diameter. In the overhead lifting applications if we used SS rope instead of regular steel we often times had to up the size to meet our safety factors. As a simple rule of thumb we always worked with a 5:1 safety factor for regular steel and bumped up to 8:1 when we used SS.

If you already had a regular steel cable break, that is an indication that the cable is probably near the safe working load limit and the corrosion you mentioned weakened it just enough to cause it to fail. While the corrosion issue will be mitigated with SS you will have a weaker cable to begin with. Also SS is much more susceptible to work hardening so, every time it is bent around a pulley/sheave you will be stressing it and reducing it's strength little by little.

 

[Bondo]

Re: Cable for a Boat Lift

Steel cable, more correctly, "wire rope" comes in many different styles. The 7x19 type of designation defines how many wires there are and how many bundles of wires are brought together to form the rope.

It's been a long time, but I once worked as an engineer designing overhead industrial cranes. The wire rope specifications and the type of construction was/is very important.

I'd be very careful just assuming that you can switch to stainless of the same diameter. In the overhead lifting applications if we used SS rope instead of regular steel we often times had to up the size to meet our safety factors. As a simple rule of thumb we always worked with a 5:1 safety factor for regular steel and bumped up to 8:1 when we used SS.

If you already had a regular steel cable break, that is an indication that the cable is probably near the safe working load limit and the corrosion you mentioned weakened it just enough to cause it to fail. While the corrosion issue will be mitigated with SS you will have a weaker cable to begin with. Also SS is much more susceptible to work hardening so, every time it is bent around a pulley/sheave you will be stressing it and reducing it's strength little by little.

Ayuh,... For those reasons, Galvanized steel cable is a Great option for boat lifts,...

Most any large Supply House should carry it,...

Generally, the higher the number X number, the less stiff it gets,...

 

[pckeen]

Re: Cable for a Boat Lift

Thanks for all this - very helpful. I ended up finding out who the lift manufacturer was, and finding out about the model boat lift. Turns out I have a 2400 or 2500 lb boat lift, which should be fine for my '68 18 foot holiday. The 5/16 inch cable was probably galvanized, and a local dealer told me to use galvanized, rather than stainless steel. It also turns out that the 5/16 inch cable I had on the lift was too thick for the model of boat lift I had....and too thick for the pulleys that it was wrapped around. So I'm going to drop down to 1/4 inch galvanized cable, which should be the right thickness for the boat lift.

 

[Chris1956]

Re: Cable for a Boat Lift

Gee, it is good to be in fresh water. Here in the salty world, the last galvanized cable I used lasted a month, before the rust got it....

 

[pckeen]

Re: Cable for a Boat Lift

Ok - Installed the 1/4 inch cable - it moved through the pulleys much better and smoother than the old 5/16. I had checked out prices and breaking strains for galvanized steel 1/4 inch, and found breaking strains as low as 1400lbs. The stuff I installed has a breaking strain of 7000lbs. I asked the dealer why the wide difference in breaking strains, and he advised me that the grade of steel has a major impact on its breaking strain.

So anyone with the same issue I had - make sure that the cable you are buying is of the right type, thickness, and grade/load capacity to hold your boat! Don't just buy of the 'net' and assume it will work.