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post #21 of 24 Old 01-28-2014
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Re: Top Down Furlers

Quote:
Originally Posted by albanychris View Post
I am trying to build a top down furler for my 8m yacht.
There are 2 things I dont understand.
1. Why is it necessary for the tack to be on a rotating bearing independent of the bottom unit. Could it be stationary but independent of the turning parts?
No.
Quote:
Originally Posted by albanychris View Post
2. What causes the bottom of the sail to start turning at a certain point in the furling process when an independent swivel for the tack is fitted? I have watched the videos over and over and I can't work it out.
Cheers
Top down furlers is used on asymmetric sails that can't be furled around it's luff. To make a mental picture start with the sail unfurled and hoisted.

The furling wheel/drum transfer the rotation to the bottom part of the top swivel by a stiff rope (anti twist rope).

The purpose of the top swivel is to let the bottom part rotate without twisting the halyard.

The head of the sail is attached to the bottom part of the top swivel.
So when you start to furl in, the top of the sail will start to wind onto the anti twist rope at the top.

As you continue to furl more and more of the sail will get wound onto the anti twist rope (top down).
When the whole length of the luff is wound onto the anti twist rope the tack need to rotate with the rest of the sail.

That's the reason for the swivel at the bottom.
  • Without the swivel the sail would start to furl along the full length of the luff at the same time and just make a big knot of the sail.
  • With the tack attached stationary the sail would be ripped in two when the whole luff is onto the anti twist rope and you start to furl in the foot of the sail.

If you are contemplating to make your own, it should be easy to make a Mock-up with an old bed sheet, some rope and a swivel
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post #22 of 24 Old 03-20-2014 Thread Starter
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Re: Top Down Furlers

I said that i would feed back on my experience with the top down furler that i was planning to install on my Oyster 57.5 monohull. So here it is:
I have a short carbon bowsprit made by Formula, a Karver KSF5 top down furler and a Navtec custom stay. I have re-used my cruising chute with no modification other than to change the hard ring at the head with three straps so that it furls more neatly at the head. The most complicated part was drilling a hole in the wall of the stemhead to secure the prodder.
I have to say that i have been delighted with the outcome. I simply attach the sprit to the stemhead with its shoot bolt, attach the furler to the sprit with a shackle, attach the sheets to the clews, haul the furled chute up with the spinnaker halliard and then pull on the sheet to unfurl. Furling is easy too - even under load in 15 knots i was able to do this by hand, although its easier on the primary electric winch. Because the sail is furled around the stay it take s up much less volume in the sail locker although on passage i intend to stow it in its bag on the foredeck.
Lessons that i have learnt are: 1. Lots of people make the furling units but the Navtec stay is the critical part (but expensive). 2. The furler unit on the prodder must be fixed. I had it attached on a 2:1 tack line and it kept twisting so i have fitted a pad eye on the end of the prodder and now its fine. 3. Lots of halliard tension. 4. When unfurling don't be tempted to control the furler or it can overrun and get tangled. Just let it run all the way out.
I have been out and used it with my wife in 15 knots with no concerns at all. We would never have used the old snuffer in those conditions. So i highly recommend it but the real test will come when i use it on our transatlantic planned for November this year.
Thanks everyone for all their helpful comments.
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post #23 of 24 Old 03-20-2014
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Re: Top Down Furlers

Thanks for coming back and filling us in!

Ron

1984 Fast/Nicholson 345 "FastForward"

".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
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post #24 of 24 Old 07-06-2014
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Furler for assymetric - update

I have sailed with my Facnor AFX 2500 since the May 2009.

This spring I decided to do some upgrades.

It has been a tremendous development on the construction of anti torsion rope in these five years.
To the right in this picture is the old rope - three layers
- core
- some rubbery sleeve (only to keep the fibers in a bundle)
- Cover
To the left the new rope - four layers
- core similar to the old
- Inner braid (white) made of some stiff thin fiber
- Intermediate braid (black) made of some stiff thin fiber
- Cover assimilate to outer on the old

The new rope is significantly better to resist torsion (might be unfair compare used to new - but I seem to remember that the old one was almost the same when new)


The endless furling line on the system had increased in diameter since new initially 8 mm now almost 9 mm and the surface had gotten "fluffy".
I decided to replace this, double braid polyester/polyester.
New ropes have been developed for this use also, I bought some Marlow ropes MGP furler 50 MGP Furler 50
It's made of VectranŽ / Polyester blend cover, Polypropylene Core
Here is a picture I took during the splicing, notice the tight braid on the core, will give better form stability.


In a system with endless lines it is important to have as little friction as possible in the system
In my old setup I had to double ball bearing blocks to lead the line back to the cockpit, It worked but the problem with blocks is that they only reduce friction when the rope is running over the wheel.
The block housing will induce friction if/when the rope rubs against it - I found that often my blocks would hang on the rope..
The furling line was/is lead more or less direct aft from the bowsprit along the cabin side to an attachment between my two sheet winches.
I got rid of the two blocks, replaced with
One Selden furling line guide attached to the tubing of my self tacker attachment.
One 50 mm SS ring hanging of the pulpit with a shock cord.
The selden furling line guide, this can be opened with one hand to take the line off.
Hopefully this will make me better at taking the hole furling system off when not in use..



This is a picture of the central furling line used on the Facnor system


The adjustable tack on my bowsprit, the combination of the stiff 10 mm Dyneema tack line and the distance between the two points (attachment and strop with thimble) prevent furler from twisting.
This way it's easy to adjust the tack height and thus the fullness of the sail.
I must pull the tack back down before furling.


The adjustable tack also give me a safe way to use the spinnaker boom on DDW.
I have a guy attached to the bottom of the furler(=tack), by easing the tack line and winching in on the guy I can pull the tack to windward and use it as spinnaker.
The tack is always ready to pull the tack/drum down to gybe or furl the sail.


Video showing the furler in action (no sail)


The tack of the sail


It was a little bit difficult to dismantle the system, it was put togheter using liberal amounts of locktite.
The roller bearing balls are made of delrin so it is important to be carefull with heat.
On assembly I decided to modify the design, replacing the set screw and locktite with a rigging bolt through the whole assembly.

The special clamping tool made to dismantle the top swivel (you can use a spanner on cone, the the other part is round).


From the other side
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