Double, side by side, sheave blocks

[Neeves]

I recall decades ago seeing back stays with a side by side block. Triangular face plates, two bearings and 2 sheaves. I actually recall some of them having 3 sheaves - but cannot imagine how they were used. They were seriously big units, slim but a large area. Easy to get double sheaved blocks - but the sheaves are one on top of the other and only one shaft. Does anyone know of a source of the sort to which I refer? Why did they become unfashionable?

Jonathan

 

[westernman]

I recall decades ago seeing back stays with a side by side block. Triangular face plates, two bearings and 2 sheaves. I actually recall some of them having 3 sheaves - but cannot imagine how they were used. They were seriously big units, slim but a large area. Easy to get double sheaved blocks - but the sheaves are one on top of the other and only one shaft. Does anyone know of a source of the sort to which I refer? Why did they become unfashionable?

Jonathan

DAVEY fiddle block
https://www.amazon.com/HARKEN-Premi...2?keywords=fiddle+block&qid=1663043164&sr=8-2

 

[Neeves]

DAVEY fiddle block
https://www.amazon.com/HARKEN-Premi...2?keywords=fiddle+block&qid=1663043164&sr=8-2

Thanks - but not like that, on the link. The link is a fiddle block?

The type I am thinking of, sorry no picture, are 2 triangular face plates, a sheave in each of the bottom corners and a shackle at the apex.

J

 

[DanTribe]

Your description sounds a bit like tensioner for twin backstage. Thw sheaves fit over the stays and it is pulled down with a block and tackle. Can't find an illustration at the moment.

 

[davidmh]

Agree with DanTribe, used a lot in the 70's
David MH

 

[Neeves]

Thanks to you both

I can see how they work, very simple.

Why did they go out of fashion?

Jonathan

 

[AntarcticPilot]

Weren't blocks like that sometimes used so a mainsheet could be led to both sides of the cockpit? A vague recollection of having seen something like that.

 

[steve1963]

Westerly Storms have this system. Maybe it is to make space for boarding from the stern?

 

[Martin_J]

Not exactly the triangle I remember either but looks like Barton still make them...

 

[Neeves]

Application for use from either side seems how I recall seeing them - but why did they disappear, abruptly.

Maybe I should have posted on the racing section of the forum?

Jonathan

Not exactly the triangle I remember either but looks like Barton still make them...

View attachment 142918

Not quite what I recall either - but if that was the RRP price I understand why they lost popularity

Jonathan

 

[Tranona]

Not exactly the triangle I remember either but looks like Barton still make them...

View attachment 142918

Do you have a link to the supplier please?

 

[Plum]

Do you have a link to the supplier please?

Barton Size 2 Plain Block Backstay Tensioner System (BAN02740)

www.solocoastalsailing.co.uk

 

[Refueler]

If its the system I remember .... then it was usually in league with a fractional rig where mast top section could be made to 'bend' rearwards to alter mainsail shape ..... without altering foresail. The use of blocks because of the tension required.

There may haver been other uses of course.

 

[William_H]

Typically used around here for mast head rig where single back stay splits to 2 legs about 2m above transom. (this enables a transom mounted rudder tiller) The adjuster squeezes the 2 legs together when pulled down from the join point. So shortening back stay and applying more tension.
OP could fashion one out of a triangle of metal with a single block shackled to each top corner and a block for multi purchase tackle down to deck. Usually one sided because it is not adjusted often but could easily be made with adjustment each side.
This system has limited range of shortening back stay ok for masthead rig but not really suitable for bendy mast fractional rig wheree large amounts of back stay shortening is used. ol'will

 

[Neeves]

Typically used around here for mast head rig where single back stay splits to 2 legs about 2m above transom. (this enables a transom mounted rudder tiller) The adjuster squeezes the 2 legs together when pulled down from the join point. So shortening back stay and applying more tension.
OP could fashion one out of a triangle of metal with a single block shackled to each top corner and a block for multi purchase tackle down to deck. Usually one sided because it is not adjusted often but could easily be made with adjustment each side.
This system has limited range of shortening back stay ok for masthead rig but not really suitable for bendy mast fractional rig wheree large amounts of back stay shortening is used. ol'will

Thanks

Coincidentally I had tried your suggestion, its easy to rig, using two (single) blocks. You can join the 2 blocks with a single shackle - or a custom made triangular plate (though triangular plates are available commercially, used by arborists and rock climbers). Its a bit clumsy and having the whole unit as 'one piece' would be neater. I had made a search from the 'common' suppliers. Lewmar, Harken et al (as I do recall seeing them) but I could find nothing available today. Obviously the device I recall did not stand the test of time.

Jonathan

 

[Martin_J]

There's one with two sheaves each side that seems to reduce the bend on each backstay...

JOHNSON #38-203, SPLIT BACKSTAY ADJUSTER. The Chandlery

 

[Martin_J]

Catalonia seem to use a 2" ring instead of a shackle for joining three sheaves..

 

[Neeves]

Catalonia seem to use a 2" ring instead of a shackle for joining three sheaves..

View attachment 142961

Yes, that's the sort of assembly I had envisaged - in the absence of a single unit incorporating the 2 blocks/sheaves. Looking at the captions on the drawing the yacht seems quite small (for such a complicated system). I'd thought it was for bigger yachts, with higher tensions (though the clevis pins on the tang plate are pretty hefty).

Jonathan

 

[Martin_J]

Think yourself lucky you're not setting up a 48:1 system...



Although they do look neat with the block and tackle all under deck..

Backstays » Olson 30 Class Association

 

[Neeves]

Think yourself lucky you're not setting up a 48:1 system...

View attachment 142976

Although they do look neat with the block and tackle all under deck..

Backstays » Olson 30 Class Association

It makes me shudder (and my wallet squeal) - but interesting none the less

Thanks

Jonathan