friction in blocks

[deep denial]

i want to lead my topping lifts through a tackle to reduce the load. Being a classic boat the blocks should really be tufnol or wood. the tufnol have brass bush bearings. But I would like to know how much difference it would make to the frictional effort if i use instead modern bearing blocks eg Lewmar synchromesh - would I notice the difference? Grateful for any views, thanks.

 

[Seajet]

Yes you would notice a lot of difference, even with the line just going round one block rather than a purchase. My boat has ball bearing blocks throughout, and make everything so much easier inc reefing singlehanded, which can be a pain even on a 22' if there's too much friction.

Unless you're raving keen on the classic look, I'd suggest trying ball blocks; you could always change back, but I don't think you will...

 

[Wooden Boat Fittings]

You can do both. This block has this sort of sheave in it --

With plain sheaves, the old rule of thumb was to allow 10% extra load for each block the line ran around. With roller sheaves you should be able to halve that or better.

Mike

 

[Daydream believer]

Just out of interest where will you put the blocks?
On my Stella I could reach the end of the boom quite easily so I put a small block & tackle at the end of the boom on the end of the topping lift with a clam cleat
It meant I could just reach up, pull the line & raise the boom a bit without going forward to adjust at the mast
It was very handy for reefing etc as it took the load off the boom
I then adjusted the topping lift so that if I let the cleat go by mistake when lowering the sails the boom would not drop so far as to bash me on the head

 

[lw395]

A lot depends on the rope.
Some of the friction comes from bending the rope.
The sharper the bend and the thicker the rope, more friction.
But type of rope makes a difference too.
Also alignment. Some roller blocks can have a lot of friction if they don't align perfectly with the rope.

 

[sailorbenji]

The general rule is use plain bearing blocks for lines which see relatively high static loads and are not tweaked constantly. Blocks with ball races/torlon rollers are better for those lines you constantly adjust. It is simply not true that bearing/roller blocks are better in all applications as they are inherently less resilient to higher loads (flatteninh of the rollers/balls etc if load is on same spot for a long time)

The plain bearing blocks can be very close to full on bearing blocks in terms of efficiency. This is achieved by having a very large sheave to sheave pin diameter ratio.

 

[deep denial]

Just out of interest where will you put the blocks?
On my Stella I could reach the end of the boom quite easily so I put a small block & tackle at the end of the boom on the end of the topping lift with a clam cleat
It meant I could just reach up, pull the line & raise the boom a bit without going forward to adjust at the mast
It was very handy for reefing etc as it took the load off the boom
I then adjusted the topping lift so that if I let the cleat go by mistake when lowering the sails the boom would not drop so far as to bash me on the head

I don't think that will work on my boat. I actually plan to run the lines back to the cockpit, hence the need for minimum friction

 

[Humblebee]

Heresy, perhaps, but a spray with Mr Sheen can make a big difference to the friction in a block. Works well on sail sliders too.

 

[lw395]

Heresy, perhaps, but a spray with Mr Sheen can make a big difference to the friction in a block. Works well on sail sliders too.

Very true.
Also worth dunking them in warm fresh water to get the salt out.