The keel crane:
One of the most overlooked items on the SB20 is the Keel crane…..once the keel is down it is often thrown on the dock and forgotten…but a failure of the keel crane or any of its components can be both dangerous…and expensive!
First we will have a look at the numbers…
The keel itself weighs 327kgs…
The keel crane structure has been tested to withstand 800kgs (you can see the stamp on the head of the crane itself)
Then we have the components…..the winch, the sheave box, a block and shackle, a further shackle and of course the rope itself.
Large safety margins are built in to all of these items when they are new but after and during use things may start to change which will effect the safe use of your keel crane.
These issues can occur when the keel is dropped into the boat and the sailors, very keen to ensure the keel will not move in the box, pack it to within an inch of its life and can only manage to get it fully down by either dropping it from a controlled distance and or jumping up and down on it!
Perfect for sailing….but when you come to pull it out at the end of the day you are no longer lifting 327kg…you are trying to winch the keel out of a tapered keel box which has had a huge load applied to get it in!
This is where it is possible to break stuff…and if you do not break it at east weaken it incrementally for the next time…..
So…here are a few top tips to prevent issues:
- Renew the line regularly, UV will weaken the rope over time, so will frequent use!Finally the bit of rope…..we use 5mm dynex which has a breaking strain of 3200kg…but this does get point loaded at the sheave and of course the splice on to the shackle. Whilst Dynex does have good UV and abrasion properties resistance it does fail over time…..make sure you replace it before it needs replacing!
- Check the sheave box in the crane is running smoothly…if it is not that is a good sign the pin is bent. Renew the sheave!
- Shackles…a 5mm shackle actually has a load bearing capability well in excess of the 800kg of the crane (1000kg in some cases)….however, if you point load it, they will bend. We have recently changed our standard new boat offering to a 6mm shackle….(available soon!) this has a break load of 1500kg…bent shackles are not easy to get off with cold fingers at the best of times.
- The block is also an area for close attention. If a block explodes it would be fairly dangerous! Look for the lower tech blocks, no ball bearings required here…and check the load that it is designed for! We are now using a block with a 1100kg load.
- The winch….can go rusty and the spring return on the ratchet may fail. It goes without saying that if you let go of the winch handle whilst the keel is up..stand clear to ensure you do not hurt yourself and cross your fingers you do not cause damage to the keel or keel box!