Single Line Slab Reefing Question

[vyv_cox]

Full description of the single line system I have used successfully for years on my website here. Yes, there is friction, as already discussed it can be reduced by substituting Dyneema of a lower diameter.

 

[Stoshak]

I don't understand why the thickness of the lines affect the friction. Surely, if the line is not slipping friction will only be caused by mechanical things like slides and bearings?

 

[maby]

I don't understand why the thickness of the lines affect the friction. Surely, if the line is not slipping friction will only be caused by mechanical things like slides and bearings?

Well, I can't speak for others, but on our previous boat, the reefing lines went through eyes in the sail with no block or pulley, so there was significant friction there.

 

[Stoshak]

Ah! Well ours has blocks fitted to the sail, and there is still lots of friction. Was wondering about ball bearing blocks but each line has 6 bearings of various design.

 

[rickym]

On the last boat we had spectacle eyes at the goosneck and 2 line reefing. Worked really well. No need to go to the mast but lots of string in the cockpit. A bit of friction in the clew end as the lines have to do the 'up/down/along and back'. Tack is much easier and any friction when shaking out the reef is easily taken up when tensioning the main halyard.

I would go for a 2 line system every time.

 

[marchhare]

Had single line reefing in previous boat, double line in this one. Double line better IMO, more control over tension, less friction, easier to let out. Have to go to the mast to attach 3rd reef but do have 3rd reefing pennant line in situ.

 

[Fantasie 19]

The snag can be that there can be a lot of friction in the system as it involves up to 5 blocks.

Willing to bet that's why the neighbours are having to go forward - we had the same problem on a friends boat after he took the sheets home one winter and put them through the washing machine to clean them up - they came back cleaner, but they also expanded slightly - and kept sticking/jamming... in the end he replaced with new (smaller) diameter sheets - no more problems..

 

[rudolph_hart]

Ah! Well ours has blocks fitted to the sail, and there is still lots of friction. Was wondering about ball bearing blocks but each line has 6 bearings of various design.

Using Harken 'bullet' blocks on the leech and Dyneema lines makes a heck of a lot of difference, even when the line has quite a journey before getting back to the winch, as mine has:

Attached to luff ring
Down to sheave on top of goosseneck (90 degrees)
Inside boom to exit sheave on top of boom aft (90)
Up through leech block (180)
Back down through sheave (90)
Inside boom to sheave on bottom of goosseneck (90)
Down to Harken mast foot block (90)
accross coachroof through deck tidy (45)
through s/steel tube under coachroof and cockpit coaming (5 metres)
exits tube, through clutch on coaming alongside wheel to winch

Quite a journey for 20 metres of line! Yet, despite this, I have no problem putting in a reef, or shaking one out on a 35 sq m mainsail, without leaving the wheel.

 

[oldvarnish]

I don't understand why the thickness of the lines affect the friction. Surely, if the line is not slipping friction will only be caused by mechanical things like slides and bearings?

Good question. I looked up the laws of friction and found this:

Law 4
The amount of limiting friction is independent of the area of contact between the two surfaces and of the shape of the surfaces, provided that the Normal reaction is unaltered.

So the thickness of the rope ought to make no difference, providing of course that it can run freely through the ends of the blocks.

However, having put thinner line in my single line reefing, I'd say that getting the reefs in and out was at least 20% less work.

We need an A level physics teacher to sort this out for us.

 

[rotrax]

Good question. I looked up the laws of friction and found this:

Law 4
The amount of limiting friction is independent of the area of contact between the two surfaces and of the shape of the surfaces, provided that the Normal reaction is unaltered.

So the thickness of the rope ought to make no difference, providing of course that it can run freely through the ends of the blocks.

However, having put thinner line in my single line reefing, I'd say that getting the reefs in and out was at least 20% less work.

We need an A level physics teacher to sort this out for us.

The single line reefing system on our boat has plenty of friction,as other posters have stated. It does reef and shake out better with the boat just on the port tack for the first reef and starboard for the second. No idea why, but thats how it is!

 

[maby]

Good question. I looked up the laws of friction and found this:

Law 4
The amount of limiting friction is independent of the area of contact between the two surfaces and of the shape of the surfaces, provided that the Normal reaction is unaltered.

So the thickness of the rope ought to make no difference, providing of course that it can run freely through the ends of the blocks.

However, having put thinner line in my single line reefing, I'd say that getting the reefs in and out was at least 20% less work.

We need an A level physics teacher to sort this out for us.

I don't think that limiting friction is what we are particularly interested in here - that is the force that stops two things that are static relative to each other from starting to move. I think we are really talking about dynamic friction - i.e. the force which makes it difficult to keep something moving - and that is proportional to the areas in contact.

 

[oldvarnish]

I don't think that limiting friction is what we are particularly interested in here - that is the force that stops two things that are static relative to each other from starting to move. I think we are really talking about dynamic friction - i.e. the force which makes it difficult to keep something moving - and that is proportional to the areas in contact.

Understood. Thank you

 

[DaveS]

I don't understand why the thickness of the lines affect the friction. Surely, if the line is not slipping friction will only be caused by mechanical things like slides and bearings?

I think that part of the reason is that it takes more force to bend a thick rope than a thin and if there are lots of blocks in the system then it all adds up.

I have a rather clever 3 / 6 part main sheet, but it used to suffer badly from friction. Replacing the fairly stiff 10mm line with more flexible 8mm completely transformed it! It now happily runs out without overhauling, even at 6:1 ratio. I think it was the most cost effective improvement to the boat I've ever made.