Split Backstay Tensioner on a Ketch

[osirissail]

The tensioner in Post 10 is elegant except for a few small details. You have to find a block that will work with the psi loads on that backstay and it has to accept the size wire you are using and has to have a radius that will work with the wire without kinking/damaging the wire due to perpendicular loading on the wire instead of axial loading. Rigging wire is not all that flexible and doesn't like side loads.
- - And an additional question is - Is your mast designed to be bent? Ketch boats are not really racing boats and standing rigging is normally permanently fixed with periodic "tuning" needed as the wire ages and stretches. If the mast is not designed to be bent and unbent you could get into more troubles than you want with a mast failure.

[IdoraKeeper]

If you put a sheave that far above deck, how are you going to grease it? It's going to be a high load item and will require attention. Two sheaves mounted on the deck would be accessed more easily. All the working parts would be at deck level. In the DC9 and the MD80 the slats are controlled by multiple cables wound on the a common drum. Works good lasts a long time.

Hurry up and finish that boat and go sailing!!!!
Todd

[Stillraining]

Idora...Draw me a picture please ..I cant visualize it.

How often would it need lubed...Im thinking self lubricating delrin bearings myself...no?

[IdoraKeeper]

Sorry, I am on the road and don't have all the tools I need. I will try words instead.
Imagine the current attach points on the deck as sheaves which lead the wire to a winch drum mounted vertical on the centerline of the boat. One wire winds across the top on one end and the other across the bottom on opposite sides of the drum. (Like a windlass) When the drum rotates both are tensioned equally. Come to think of it you could use a vertical windless and brake and it would be safe.

Can Delrin take the shock loads? Just trying to keep the parts down where you can get at them.

Sorry if I am unclear (that's what I am told at home)

Todd

[Stillraining]

Ah!...I get it now....too much deck clutter.

Was just researching the derlin thing...cant find a wire shived one any way so its a moot point probably.

Realistically how often would that shiv need attention anyway...Its not like it will get but a couple 180 to 360 degree revolutions per sail.

[daddle]

The sheave is not a problem. The sheave will not need grease as it runs very little, maybe 4 inches. And it probably has a plain bearing anyway.

If I recall, marine wire comes in 1x19 (19 single strands) which is seen in standing rigging, and 7x7 (seven strands of 7 wires each) which is for running around blocks. Your block will be for "wire". It will have a solid, large diameter, probably metal, sheave and steel cheeks. You will probably need to get the block from a serious rig shop rather than the usual retail sources.

This is a common way to set it up. As some poster said you can also use synthetic line for this but it's mainly a weight saving technique which I'd guess you're not too keen on. And a pro rigger should be consulted for designing that trick.

[Dockhead]

Originally Posted by Stillraining

I would like a way to adjust my back-stay tension on the main mast of my Ketch .

Is this accomplished the same way as a split back-stay on a sloop?...with some sort of car and block and tackle?

I dont see how this would not be a real mess to contain, as the split in my back-stay is at least 1/3 the way up the leach of my Main sail...it has to be to clear the mizzen shrouds.

Red circle shows split location

Entirely off topic, but that's a pretty boat.

[Stillraining]

Originally Posted by osirissail

The tensioner in Post 10 is elegant except for a few small details. You have to find a block that will work with the psi loads on that backstay and it has to accept the size wire you are using and has to have a radius that will work with the wire without kinking/damaging the wire due to perpendicular loading on the wire instead of axial loading. Rigging wire is not all that flexible and doesn't like side loads.
- - And an additional question is - Is your mast designed to be bent? Ketch boats are not really racing boats and standing rigging is normally permanently fixed with periodic "tuning" needed as the wire ages and stretches. If the mast is not designed to be bent and unbent you could get into more troubles than you want with a mast failure.

Orisssail:

Somehow I missed this post...all very good points...

1) I am going to consult a rigger for the block issues..and have thought of all this wire bending tight radius already...Im still considering twin hydraulic application due to that as it would leave everything the same except shorting the two legs to accommodate the cylinder...Its just expensive is all. Am-steal is still an option but I have stated my concerns with that already.

2) Im not fractionally rigged as you already know so its not like Im bending the mast so much as tightening the forestay...I love wind...If it isint a SC waring or greater its not a very good day for sailing IMHO......so I need a way to consistently increase and decrease my forestay tension for proper sail trim yet relieve it at the dock...its just to hard on the boat IMO ...at least an old one like mine to leave everything that tight all the time.

Originally Posted by daddle

The sheave is not a problem. The sheave will not need grease as it runs very little, maybe 4 inches. And it probably has a plain bearing anyway.

If I recall, marine wire comes in 1x19 (19 single strands) which is seen in standing rigging, and 7x7 (seven strands of 7 wires each) which is for running around blocks. Your block will be for "wire". It will have a solid, large diameter, probably metal, sheave and steel cheeks. You will probably need to get the block from a serious rig shop rather than the usual retail sources.

This is a common way to set it up. As some poster said you can also use synthetic line for this but it's mainly a weight saving technique which I'd guess you're not too keen on. And a pro rigger should be consulted for designing that trick.

Agreed...I don't see a lube issue myself either but always open to others experience and will listen...This old dog learns new tricks pretty easily.....so Im not closing the door on synthetics or other ideas either but am very Leary of errant knifes, sharp things of any kind around them..especially in this aplication...Also the UV thing has its own issues..

If I used twin hydraulics the rigging would be 10 to 12 years like every other piece on the boat...start to bend that around shivs or switch to synthetics and you through that out the window.

Originally Posted by Dockhead

Entirely off topic, but that's a pretty boat.

Thanks!...After almost two years in the yard... she isnt quite as charming but will be again...................................someday... .I want to go sailing....

[Sailmonkey]

I've never greased the blocks on the runners........they have plain bearings, and they don't move quickly.
As for the block, they're already made off the shelf items. Harken can match a tensioner with a block for you, all you need to do is add the 7X19 wire (done with mechanical terminals like hayn hi-mods), shake and add water.

on a side. Have you already played around with pre-tensioning the backstay for beating in heavy air?

[barnakiel]

Dyneema's good. Then again why so much hassle tensioning. Why not pre-tension properly and let it be?

Racing? A lot of heavy weather upwind work?

I found it that on a cutter rig it is much easier to fly the inner sail (staysail I think) than to tension the furled, or shortened genoa. Sort of like the shorter the string the less curve in the jib given the same tension of the stay.

We have a tensioner but do not really remember ever needing it badly. It is there so I will use it, but I could do just as well without it (top rigged sloop, double backs).

b.

[Sailmonkey]

Originally Posted by barnakiel

We have a tensioner but do not really remember ever needing it badly. It is there so I will use it, but I could do just as well without it (top rigged sloop, double backs).

b.

I added a tensioner to my pearson vanguard. While it was nice to be able to tune like the boats I crewed on with other peoples money, it was nothing really other than cosmetic shape for the headsail(the boat would only go so fast or point so high anyway).

[Stillraining]

Originally Posted by Sailmonkey

I've never greased the blocks on the runners........they have plain bearings, and they don't move quickly.
As for the block, they're already made off the shelf items. Harken can match a tensioner with a block for you, all you need to do is add the 7X19 wire (done with mechanical terminals like hayn hi-mods), shake and add water.

on a side. Have you already played around with pre-tensioning the backstay for beating in heavy air?

Im thinking the same way about the lube issue.

Yes I put some pre bend in the mast last time but it wasn't enough in the snot....so if I crank more on I want to be able to releave it when done playing.

Originally Posted by barnakiel

Racing? A lot of heavy weather upwind work?

I found it that on a cutter rig it is much easier to fly the inner sail (staysail I think) than to tension the furled, or shortened genoa. Sort of like the shorter the string the less curve in the jib given the same tension of the stay.

b.

The latter.

I have an inter forestay as well but I sill want the adjustment...Hydrolics with a guage is also a way to actually see what kind of tension is on it.

Originally Posted by Sailmonkey

I added a tensioner to my pearson vanguard. While it was nice to be able to tune like the boats I crewed on with other peoples money, it was nothing really other than cosmetic shape for the headsail(the boat would only go so fast or point so high anyway).

Probably true...see previous answer.

[Portobello]

Originally Posted by Stillraining

So you just keep adjusting your turnbuckles all the time?....or just set it and forget it?

My understanding is normal turn buckles do not have the thread design
for constant adjustment all the time....that's not their purpose.

Mine is similar to the one here:


http://www.harken.com/images/back3.gif

Cheers