Mast Mainsail halyard bottom sheave box

[xeitosaphil]

In an effort to reduce friction and aid mainsail dropping, I have taken the double inline sheave box out of the bottom of the mast with the idea of refurbishing the sheaves. The old aluminium sheaves have started to disintegrate and have become tired and sloppy, causing vibration and friction when lowering mainsail due to age - 40years old this year.
I wondered why these may have been fitted in the first place. Could the mast manufacturer not have used halyard exit plates instead, as I would have thought that these have no friction at all. I wonder if they could have been used as an aid when the main halyard was hoisted by a winch at the mast?

I should add that all my halyards etc go aft at the bottom of the mast via turning blocks back to the cockpit, just for reference.

Is there any benefit by having these double sheaves to exit the main halyard now, if so I will try to find some ball bearing sheaves as suitable replacements?
If I go this route will I have to try and calculate the halyard load and how will I go about that.
How do others halyards exit the mast with my present arrangement - via sheaves or just exit plates.

Do you think Bearing sheaves would be ok, or should I try to replace with Delrin or similar, or Ali with original Tufnol inserts - or just try and find some exit plates which will cover the original sheave box slots?

As usual thanks for any comments in advance, Philip

 

[bbg]

Is the boat old enough that it was built before the widespread introduction of exit plates? I would be surprised if an exit plate would not work, unless there is some strange routing inside the mast.

How high above the deck-level turning block is the exit from the mast?

 

[xeitosaphil]

not sure date widespread availability of exit plates but boat was built 1974

Original sheave box is about 700mm above old halyard winches which are still on the mast, and also approx. 1750mm above turning block. I assume halyard comes down straight from top masthead sheave

 

[merlin3688]

This type of box was used in the 70s and 80s possibly before the exits plates were about, Proctor, Sailspar and ss spars all used to use them. Fitting a exit plate is fine and will not need to be replaced like the sheaves! As long as the lead goes to the bottom of the mast and is turned by a block at the base.

 

[Daydream believer]

My plastic exit box liner split so i used the SS one that you show. However it was a bit narrow to get 4 pop rivets in - 2 each side- so i put it at the bottom of the slot to get 2 rivets in the bottom & tilted it sideways to get a third rivet in, The remaining hole has no rivet.
The point being- check the width suits your slot first

 

[xeitosaphil]

My plastic exit box liner split so i used the SS one that you show. However it was a bit narrow to get 4 pop rivets in - 2 each side- so i put it at the bottom of the slot to get 2 rivets in the bottom & tilted it sideways to get a third rivet in, The remaining hole has no rivet.
The point being- check the width suits your slot first

Thanks for the pointer, if I do use an exit plate I will probably have to mount it on a S/S backing plate first as the exit plates probably won't be long enough to cover the existing slot?

Unless of course I can find one that's long enough and a direct replacement change over, but I very much doubt it.

Thanks chaps for your input :encouragement:

Philip

 

[Daydream believer]

Thanks for the pointer, if I do use an exit plate I will probably have to mount it on a S/S backing plate first as the exit plates probably won't be long enough to cover the existing slot?

Philip

Mine is not as long as the slot either so there is a gap- no problem at all ,so if you want to save some work you can leave it
bear in mind the plate only makes a smooth exit to stop the mast cut out cutting the halliard or a wire halliard cutting the aluminium
so there is no weight on the insert. That is why mast manufacturers use a simple plastic insert ( although it can break from time to time)

 

[xeitosaphil]

Mine is not as long as the slot either so there is a gap- no problem at all ,so if you want to save some work you can leave it
bear in mind the plate only makes a smooth exit to stop the mast cut out cutting the halliard or a wire halliard cutting the aluminium
so there is no weight on the insert. That is why mast manufacturers use a simple plastic insert ( although it can break from time to time)

The reason for the back plate is two fold, my existing sheave boxes are about 28mm wide with a mast cut out of 22mm. Chances are the new ones will be narrower, and the exit plates could be as small in length as 90mm where my existing ones are 210mm.

I would like to fit a new backing plate to cover the existing slot hole and also stop water getting into the mast and collecting at the base, it will also cover the scar and form a more acceptable appearance to me, as I am a bit of a fuss pot- it goes with my occupation unfortunately.