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Masthead halyard blocks

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Graham W:
Does anyone know of any reason why I should not replace my existing standard fiddle block for the jib and spinnaker halyards (picture below) with a double (side by side) block? As can be seen from the photo, the fiddle block leads to the halyards slightly fouling each other.  In addition, a new double block with a becket would allow me to install a second block on the jib halyard, making it easier to tension than I find at the moment.

Anthony Huggett:
Sorry for asking the obvious, but why not swap the jib and spinnaker halyards in the existing block?

The problem with a double parallel block is that they are designed for use in a tackle where there is an even loading. If only one sheave is loaded, they tend to sit a little sideways, which could lead to wear on the cheeks of the block over time.

Anthony

Graham W:

--- Quote from: Anthony Huggett on 20 Jun 2011, 13:27 ---Sorry for asking the obvious, but why not swap the jib and spinnaker halyards in the existing block?

--- End quote ---
Anthony
I wondered that as well.  To quote from a caption to a photo of the fiddle block in the BR manual "The jib halyard is threaded through the head block. This boat is equipped for a spinnaker, the halyard of which would be threaded through the empty lower block." 

I thought it might be because the top part can cope with bigger loads (and is used more) but I am unable to find any evidence for this.

Thanks for the advice about imbalance on double blocks.
Graham

Craic:
I have been using double blocks there for years, even triple in order to have a balanced distribution.
When you use a double block, you may want to look out for a block with an asymmetric or horizontally adjustable shackle so you can adjust the balance there. I never had any noticeable friction or wear from using a horizontal block up there. But do not oversize it, the weight up there matters.
BTW I did not know they recommend a big violin block up there, and even recommend the jib halyard to go over the main wheel, I find that surprising.

Anthony Huggett:
Ultimately all the shear load goes through the pin, regardless of the size of the wheel. So I'd say that if the pins are the same diameter then the ultimate strength is the same. The bigger pulley makes for less friction as the sail is hoisted, and less bend on the halyard as it goes around.

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