Maths challenge…..

[AntarcticPilot]

The maths is far from simple, because all simple approaches make unrealistic assumptions about how the line will stack on the drum. Even if the line stacked perfectly on the drum, with nice even layers, do the successive layers match the dips between rows on the preceding layer or not? It makes a big difference. As reefing drums don't include a feed mechanism to ensure the line is laid in a particular pattern, it will probably vary every time the line is wound in.

Realistic stacking problems are a research topic! I've seen stuff about the analogous problem of filling an arbitrary volume with as many uniform spheres as possible, and it isn't at all simple. There are simple solutions for unbounded spaces (e.g. atoms in crystals) but not for bounded spaces (like the drum of reefing gear, or a jar of marbles). This is even worse in that you're filling space with a cylindrical object of unbounded length.

As stated by @Refueler above, the only good answer is to use line of the diameter and length recommended by the manufacturer.

 

[Sea-Fever]

I think the diameter of the bare drum is irrelevant. If you have a massive or tiny drum it won’t change how many turns you need to furl and unfurl…..that’s dictated by the sail and foil size.

It may effect how easy it is to furl, and how much furling line is required, but not the number of turns on the drum.

What affects the depth of the wound line is, I believe, the furling line diameter and the ‘length’ of the drum (because a longer drum can accommodate a greater number of turns before it rides up).

Of course it is never uniformly wound, this is just a bit of fun…..but the practical effect of a thicker furling line is undeniable - better on the hands, and more turning moment for a given number of turns.

 

[Sea-Fever]

Sorry I should have said the radius of the bare drum is relevant only to the extent that you need to work out the available area which could be expressed as drum length x (max drum radius - bare drum radius)

 

[Refueler]

I think the diameter of the bare drum is irrelevant. If you have a massive or tiny drum it won’t change how many turns you need to furl and unfurl…..that’s dictated by the sail and foil size.

It may effect how easy it is to furl, and how much furling line is required, but not the number of turns on the drum.

What affects the depth of the wound line is, I believe, the furling line diameter and the ‘length’ of the drum (because a longer drum can accommodate a greater number of turns before it rides up).

Of course it is never uniformly wound, this is just a bit of fun…..but the practical effect of a thicker furling line is undeniable - better on the hands, and more turning moment for a given number of turns.

Of course the number of turns are same for sail / line.

But the length of line in each turn is greater than the length of sail in each turn.

 

[boomerangben]

The maths is far from simple, because all simple approaches make unrealistic assumptions about how the line will stack on the drum. Even if the line stacked perfectly on the drum, with nice even layers, do the successive layers match the dips between rows on the preceding layer or not? It makes a big difference. As reefing drums don't include a feed mechanism to ensure the line is laid in a particular pattern, it will probably vary every time the line is wound in.

Realistic stacking problems are a research topic! I've seen stuff about the analogous problem of filling an arbitrary volume with as many uniform spheres as possible, and it isn't at all simple. There are simple solutions for unbounded spaces (e.g. atoms in crystals) but not for bounded spaces (like the drum of reefing gear, or a jar of marbles). This is even worse in that you're filling space with a cylindrical object of unbounded length.

As stated by @Refueler above, the only good answer is to use line of the diameter and length recommended by the manufacturer.

I agree it far from simple, but you have to start somewhere.

The manufacturer’s recommendation I suppose would be start, but they would need to know details of the sail if they were to give you a recommended line diameter. I suspect the marketing department would want to maximise the size of sail their product could handle and therefore recommend a smaller diameter line. But I don’t know, I’ve never bought a brand new furler.

Moreover the ability of a line to fleet correctly on to a drum depends on the position of the last eye/block the line goes through which the manufacturer would have no control over.

Having said all that, I did up the diameter of my furling line on my boat, although I don’t remember doing any maths, but looking at how the line goes onto the drum, it would seem that I consistently get a reasonably well packed drum. Hence my original suggestion of an 80% volume factor

I’m not sure the dips between the rows helps since the line in each successive layer lies (ideally) diagonally across the one below. Certainly when loading wire rope on winches, we never accounted for that dip. However synthetic rope will tend to deform slightly so not a true cylinder. As you say, it’s not a simple problem, but one we can have a stab at with simple maths and a few reasonable assumptions.

 

[GHA]

Thicker furling lines are easier to handle and also provide a greater turning moment at the drum but you can’t exceed the max diameter of the reel….so how do you work out the max size of line for your setup?

I spliced some 5mm dyneema D12 into the furling line. Works well here anyway, lots room on the drum & it sits well.

 

[Refueler]

I seem to remember a few various brands of Furling Gear I've fitted for people - some manuals gave a max figure of nominal xx diameter pre-stretched line drum could accommodate.

 

[Slowtack]

Is this a wind-up?

 

[greeny]

Is this a wind-up?

Yes, it's just going round in ever increasing circles and...............................

 

[LadyInBed]

If you have a massive or tiny drum it won’t change how many turns you need to furl and unfurl…..that’s dictated by the sail and foil size.

Unfortunately not exactly true.
Furl in a strong wind and the sail rolls in tight so the drum takes up more turns to fully furl the sail.
Furl the sail in light winds and the sail rolls in loose so the diameter of each roll is larger, so less turns are required.

 

[Refueler]

Unfortunately not exactly true.
Furl in a strong wind and the sail rolls in tight so the drum takes up more turns to fully furl the sail.
Furl the sail in light winds and the sail rolls in loose so the diameter of each roll is larger, so less turns are required.

True ... but at least the sail and line will make same number of turns in relation to each other.

 

[Daydream believer]

I think it should be possible to get round it with a spreadsheet, using a row for each layer. The number of turns per layer (t) is the width of the drum divided by the diameter of the line (d). The number of layers (l) is the height of the drum sides divided by d.

May I suggest that is wrong for a start.; because you are assuming (& we all know what assumtion leads to) that each line sits vertically above the one below it. However, it could (& will do) in the groove of the 2 below it ,thus the height of 2 tightly wound rows is not 2 * the diameter
Edit: possibly already said but I have not seen it

 

[Refueler]

May I suggest that is wrong for a start.; because you are assuming (& we all know what assumtion leads to) that each line sits vertically above the one below it. However, it could (& will do) in the groove of the 2 below it ,thus the height of 2 tightly wound rows is not 2 * the diameter
Edit: possibly already said but I have not seen it

If you get a riding turn that decides to go diagonal across existing turns ... then its totally whacked out.

 

[Daydream believer]

If you get a riding turn that decides to go diagonal across existing turns ... then its totally whacked out.

I was referring to the calculations suggested in Stenmar's post. Of course, If the overiding turn went at an angle that would make the calculations he suggests even less relevant. However, I did fail to go into such detail.
Quite honestly the sensible thing for any owner would be to get an old length of line & roll it on the furler & see how much it fills the drum & if it meets the required number of turns. It need only be long enough to do the turns. It does not have to go back to the cockpit for this investigation. Most owners have a suitable offcut. If not then make some friends & borrow a piece. Thus, armed with that info one can go & purchase a new line of the correct length
I do never sail with a partly furled sail,so do not load up the furler to any extent. But If I did, I doubt that I would want to over fill the drum, as it might lead to line getting nipped between layers below the current one. It may lead to line heaping up on one side then falling over on top of other layers causing a jam. Not a desireable feature. Others may say that this is not a possibility. But I do hear stories of jammed furlers.

 

[boomerangben]

Are riding turns a common thing on furlers? I don’t think I’ve ever had one. I would have thought that since the rope goes onto the drum at a low nominal tension and the tension in the line when furling will be dissipated in the first 2 or 3 turns, riding turns are quite unlikely. A rope digging in might be more of a risk if there’s has been little/no back tension when the sail is unfurled.

I like the maths challenge, but I think the best answer is to take the core out the line that goes onto the drum. Would it work as well or better if you took the outer sheath off and let the core be the only part on the drum?

 

[AntarcticPilot]

Are riding turns a common thing on furlers? I don’t think I’ve ever had one. I would have thought that since the rope goes onto the drum at a low nominal tension and the tension in the line when furling will be dissipated in the first 2 or 3 turns, riding turns are quite unlikely. A rope digging in might be more of a risk if there’s has been little/no back tension when the sail is unfurled.

I like the maths challenge, but I think the best answer is to take the core out the line that goes onto the drum. Would it work as well or better if you took the outer sheath off and let the core be the only part on the drum?

Well, I've had my furler jam several times because of a riding turn. You end up having to go to the foredeck and turn the furler by hand to get past the riding turn. And yes, I do know you're supposed to keep a slight tension on the reefing line while setting the sail - but when I'm single-handed, that doesn't always happen, or in a bit of a breeze, the sail can unfurl itself a bit quicker than the tension on the sheets would suggest. I know, again I should be controlling it with the reefing line! But the reefing line is a relatively small diameter (8mm on mine) and is hard to hold when the wind catches the sail.

 

[Daydream believer]

Are riding turns a common thing on furlers? I don’t think I’ve ever had one. I would have thought that since the rope goes onto the drum at a low nominal tension and the tension in the line when furling will be dissipated in the first 2 or 3 turns, riding turns are quite unlikely. A rope digging in might be more of a risk if there’s has been little/no back tension when the sail is unfurled.

I like the maths challenge, but I think the best answer is to take the core out the line that goes onto the drum. Would it work as well or better if you took the outer sheath off and let the core be the only part on the drum?

I do not think that taking the core out is so good. At some point the outer will have to be whipped to the inner. This will rarely be a nice even taper because it will not splice nicely into the inner core. .. More a step. That has to run through the fairleads on the deck. Or rollers etc that one has leading the line to the furler. That might lead to the outer getting caught & eventually bunching.That might prevent it passing through the fairleads. The inner core has to be braided otherwise it will open out. It will be devoid of its designed protection.
Changing to dynema for this purpose would seem an expensive waste of money for a simple furling line unless on a very large sail.

I sail SH . I do not need a particularly large diameter line. I wear fingerless gloves for rope handling so do not need thicker ropes than necessary for the loading. I simply place the first few furls on the winch to get it started. I make sure that the sail is free to start with. Then I can pull the rest by hand. I can tell from experience if anything is stuck. So I have no qualms about using winches for any line on the boat. All the ropes on my boat are of a smaller diameter where possible. I think that thick ropes cause needless friction & are usually unnecessarily over specified.

 

[Refueler]

I have had odd occasions of riding turn ... not often but it happens.

The line feed tio the drum does not traverse the width of drum - so the line is feeding in at same point. The only reason it lays turn by turn is by virtue of it wanting to sit by side of preceding turn.

 

[Sea-Fever]

Unfortunately not exactly true.
Furl in a strong wind and the sail rolls in tight so the drum takes up more turns to fully furl the sail.
Furl the sail in light winds and the sail rolls in loose so the diameter of each roll is larger, so less turns are required.

Yes, you’re right, although I’m not sure the difference would be that great.

The line on my furler is thin, circa 6mm (haven’t measured it). In a blow it’s does somewhat cut into the hand when furling…..maybe I should service the whole lot rather than gloss over the fact that it is stiff by putting a bigger line on it.

10m boat, standard genoa…..is 6mm about average across all manufacturers?

 

[Refueler]

6mm sounds about right.