Halyard loads - how to estimate

[wiekeith]

I’m about to change my wire/rope halyards to all-rope, a subject that’s been well covered in a recent interesting and informative post. However, the problem I have is estimating the loads that the halyards may be subject too.

I’ve purchased, as a replacement, 8mm Dyneema Cruise Melange rope, which, according to the manufacturer is “a high tenacity Polyester braided cover and braided Dyneema® core”, with “a minimum spliced breaking load” of 2,100Kg.

But, is that going to be strong enough in extreme conditions? My logic says less, but hey, what do I know, it’s just guesswork on my part. My logic was/is as follows.

Main halyard: There will obviously be a static halyard load due to the weight of the sail and the tension I introduce when winching it up, which remains after jamming it off. But, what would be the additional load if I had full sail up and it was subject to, say, 50kt winds (heaven forbid I’d ever be in that situation), if any at all? I know for a fact that when dropping the sail I don't need to be too far off head-to-wind for the friction of the cars in the mast track to prevent the sail from dropping under its own weight, which indicates to me that there is no load whatsoever on the halyard at that time. But, would the affect of a 50kt (or greater) wind on the sail overcome this friction and indeed add a significant load to the halyard, or would it increase the friction, hence adding very little additional load, if any?

The furling genoa halyard: The main loads would be on the stay, which is wire. So again, what additional halyard loads could be introduced other than the sail weight and static halyard tension? In reality, the sail would be furled somewhat in higher wind conditions, which, I would think, would introduce enough friction to further reduce halyard loads and even prevent the sail from dropping even if the halyard broke. But the worst conditions need to be considered - what if there was a 50kt (or greater) wind on a fully unfurled sail?

There are resources on the web for estimating sheet loads etc., but I’ve not been able to find one that deals with furler or main halyards. If anyone, by chance, has the knowledge to do the calculations, or even make an educated guess, here are some details.

Boat - 12m, mono, P=15.4m, E=4.8m, I=16.3m, J=4.4m
Main - 42 m2, 27Kg
Genoa - 42 m2, 25Kg

I guess what I’m really looking for is comfort that I’ve not made the wrong decision in purchasing the 8mm rope, because I do have doubts, but I will be willing to accept it if I was wrong. Oh, and would have 75m of unused rope for sale

[UNCIVILIZED]

Sorry, but any rope with an MBL of 2.1t is more than a little underwhelming. Say for example you have a winch with a 50:1 power ratio, & that you can input 50lbs of force into a winch handle. So 2,500lbs of force, but due to frictional losses & such we'll call it 2,000lbs. Right there you're already at almost half of the rope's MBL.

Or if you input the sail area into one of the calculators by which to determine the loads on your sheets, with 42sqm of sail at 25kts, the load on the sheet is 552kg. This is without any knots to weaken the line, ditto on sheaves, etc.

Rarely, if ever do you want to have a piece of cordage operating at or above 25% of it's MBL. Which while the specified lines aren't to be used as sheets, the numbers give you something of a feel for the realities of things.

Aside from the Harken load calculators, there's reference info on cordage, & what size & type is suitable per boat, here http://samsonrope.com/Documents/Broc..._Guide_WEB.pdf

And some more info here RM_Choosing the Best Line for the Job

You also might get in touch with the folks at www.APSltd.com they've seemed to both be friendly, & know their stuff when I've spoken with them.

[Stumble]

To the best of my knowledge there is not a good way to calculate from first principles halyard loads on a boat. They are just to variable to make accurate predictions. It isn't just wind strength and size that that you need to know to even begin... also important are track friction, head angle, leech tension, mastbend, main sheet stretch, Cunningham stretch, sail luff stretch, mast deflection... worse as any of those change they interrelate and change the rest of the equation. It quickly gets to a FEA mess requiring super computers to crunch the numbers.

That's why all the reputable line manufacturers have calculators... they really don't calculate much, they just turn a large book of anecdotal evidence into a recommendation. With that recommendation the important take away is the mbl of the line they recommend. Buy something with that strength or higher and that stretch or less and you will be fine.

[thinwater]

Check the data. I think that is 4000 kg BS.

That is less than the polyester for that size rope, but on a working load and stretch basis I think you are close. Many choices out there.

It varies by manufacturer, but generally the practice is to rate strength by breaking spliced dogbones, which in this case would be core-only. You should check the core-only strength.

[fallingeggs]

You purchased rope with a dyneema core. It's more than strong enough!

My boat is of a similar size. Your 8mm rope appears to be just about the same strength as my 3/8" (10mm) partial-dyneema core rope (Samson MLX). Mine is plenty strong and low stretch.

I'd be a little concern on the line feel and how your winches and clutches grip it. My 3/8" feels small in my hand. I bet 8mm would hurt to pull. The Samson MLX has a pretty slick cover that just barely seems to work in my winches. Clutches are for 5/16" (8mm) to 3/8", and hold great; but not sure if they would with a 8mm line.

[fallingeggs]

Playing with the Harken mainsheet load calculator, you can get some estimates. With your E (4.8m) and P (15.4) plugged in, 50 knots of wind and assuming boom end sheeting (zero for X), you are close to 4000kg, the breaking limit of the rope.

First, this assumes the approximate boom end sheeting load is about the halyard load, which I would think is roughly correct, but perhaps an engineer will correct.

Second, who carries a full main in 50 knots of wind? Not I. Dropping the wind speed to 20 produces only 600kg of load, well within the working limit of the rope. Any higher (apparent) wind speeds and you'll be reefing, which reduces the load. If you have a deep reef that is only 1/2 of the full main (divide E and P by 2), the load in 50 knots is still only 900kg. (In addition, you'd also heel in gusts, which spills the wind, reducing the load. I suppose there is an initial load that is high, but it won't last long.)

[UNCIVILIZED]

Originally Posted by thinwater

Check the data. I think that is 4000 kg BS.

That is less than the polyester for that size rope, but on a working load and stretch basis I think you are close. Many choices out there.

It varies by manufacturer, but generally the practice is to rate strength by breaking spliced dogbones, which in this case would be core-only. You should check the core-only strength.

According to their website Dyneema Cruise : Cruising Ropes : Kingfisher Yacht Ropes 2,100kg BL is correct. Which means there's only enough Dyneema in the line to allow them to use the word, in order to sell more cordage. AKA Name Recognition = Better Sales, at least amongst some who skipped the fine print.
Either that or their website got it WAY wrong. Regardless, the core is a blend. Although a blend of Dyneema & what else we'll likely nver know. But whatever the bulk of the core's made of, it's not what you'd call strong.


fallingeggs, please check you numbers, including what units you're using, & recalculate. Also, as mentioned, using any cordage at or near 25% of it's MBL could very well necessitate it's needing replacement, due to failure, before lunch time tomorrow. So perhaps a redaction or three is needed.

[Stumble]

Originally Posted by fallingeggs

Playing with the Harken mainsheet load calculator, you can get some estimates. With your E (4.8m) and P (15.4) plugged in, 50 knots of wind and assuming boom end sheeting (zero for X), you are close to 4000kg, the breaking limit of the rope.

First, this assumes the approximate boom end sheeting load is about the halyard load, which I would think is roughly correct, but perhaps an engineer will correct.

Second, who carries a full main in 50 knots of wind? Not I. Dropping the wind speed to 20 produces only 600kg of load, well within the working limit of the rope. Any higher (apparent) wind speeds and you'll be reefing, which reduces the load. If you have a deep reef that is only 1/2 of the full main (divide E and P by 2), the load in 50 knots is still only 900kg. (In addition, you'd also heel in gusts, which spills the wind, reducing the load. I suppose there is an initial load that is high, but it won't last long.)

Sheet load is a completely different variable than halyard loads. In any given day of sailing you can routinely expect sheet loads to vary from more than the halyard load, to 1/100th of it.

Typically the main halyard should be substantially stronger than the main sheet in order to control stretch. Since the mainsheet is going to be constantly trimmed while the halyard is generally left alone. As a very rough guide main halyards tend to be about twice as strong as the sheet, but this does vary a lot based on line material.

If you are only going to have one high tech line then the main halyard is where it is most critical. The stretch reduction is critical not really the strength.

On this boat normal a recommendation would be a line with 7-8,000lb mbl.

[fallingeggs]

Originally Posted by UNCIVILIZED

fallingeggs, please check you numbers, including what units you're using, & recalculate. Also, as mentioned, using any cordage at or near 25% of it's MBL could very well necessitate it's needing replacement, due to failure, before lunch time tomorrow. So perhaps a redaction or three is needed.

Those are just hit numbers inputted into the Harken website.

But it doesn't matter if the rope really has a breaking strength of 2100kg (thought it was 4000kg!) because that seems a bit low for my taste.

What is a good safe working load limit? I thought many consider a 1 to 5 margin good enough, so 20% of breaking strength?

IF Harken calculator works for halyard loads (and, I suppose, I entered in the three numbers correctly), then, roughly speaking, the OP requires a rope with a breaking strength of at least 3000kg based on a 600kg working load.

[Hard A Lee]

The dynema core does seem a little misleading. An 8mm straight dynema line (Amsteel or similar) has a minimum breaking strength of 12,300lbs (5,600kg) so they aren't using very much. Of course, dyneama on its own is very slippery and doesn't cleat well or work very well in a rope clutch. Seems like maybe a 1/8" line inside the cover at most and the cover is just for easy of handling.

One thing to consider also is that an 8mm line is a little small in hand. I like a larger line to make it easier to handle. Just my opinion...

[thinwater]

Originally Posted by UNCIVILIZED

According to their website Dyneema Cruise : Cruising Ropes : Kingfisher Yacht Ropes 2,100kg BL is correct. Which means there's only enough Dyneema in the line to allow them to use the word, in order to sell more cordage....

Ouch. That is just plain lame. I did not look to the source, my bad.

Yes, that is too weak for that boat, consistent with long life.

[wiekeith]

Many thanks for all the responses, pointers and calculations, they've been really helpful and appreciated, even if the end result is me accepting I've cocked up - grrr

There does appear to be some discrepancy between the loads stated on the manufacturers spec sheet and those stated on some of the resellers' web sites. 2,100kg verses 4,00kg is a significant discrepancy, so I've emailed the manufacturer directly to clear that up, but wouldn't expect a response until tomorrow - it's evening here - but will post it here when it comes.

Assuming for now that the manufactures spec sheet is correct, then the rope I bought is similar in characteristics to 3/8 Sta-set or 3/8 XLS, and I'm sure I've read reports of those being used to replace wire halyards on boats of a similar size to mine, which was a factor in my decision, although I did later have my doubts, hence the post. But I have to confess that I was unaware of the rule-of-thumb relating to a ropes strength being 5 time that of the anticipated loads. So, would I really want to use a rope that's probably (possibly), in the worst case, OK, or one that's five times OK?

[wiekeith]

Originally Posted by wiekeith

There does appear to be some discrepancy between the loads stated on the manufacturers spec sheet and those stated on some of the resellers' web sites. 2,100kg verses 4,00kg is a significant discrepancy, so I've emailed the manufacturer directly to clear that up, but wouldn't expect a response until tomorrow - it's evening here - but will post it here when it comes.

:

Wow, the manufacturer just got back to me at this time of night - the figures on their web site and spec sheet are correct.

[fallingeggs]

Originally Posted by wiekeith

Many thanks for all the responses, pointers and calculations, they've been really helpful and appreciated, even if the end result is me accepting I've cocked up - grrr

There does appear to be some discrepancy between the loads stated on the manufacturers spec sheet and those stated on some of the resellers' web sites. 2,100kg verses 4,00kg is a significant discrepancy, so I've emailed the manufacturer directly to clear that up, but wouldn't expect a response until tomorrow - it's evening here - but will post it here when it comes.

Assuming for now that the manufactures spec sheet is correct, then the rope I bought is similar in characteristics to 3/8 Sta-set or 3/8 XLS, and I'm sure I've read reports of those being used to replace wire halyards on boats of a similar size to mine, which was a factor in my decision, although I did later have my doubts, hence the post. But I have to confess that I was unaware of the rule-of-thumb relating to a ropes strength being 5 time that of the anticipated loads. So, would I really want to use a rope that's probably (possibly), in the worst case, OK, or one that's five times OK?

Good luck there!

PS - Let me also mention that you may want/need to change the sheave at the top of the mast. I haven't personally seen this myself, but I hear that the sheaves used for wire halyards have a smaller groove (or something like a double groove) that may chafe rope halyards. I know this has been discussed on this forum in the past, so a quick search should tell you want to look for on your set up. Stumble or Uncivilized may even have a shorter answer for this.

[Hard A Lee]

Just some other food for thought...Not sure how you're planning on attaching the line to the shackle, but if you use a knot, you can estimate a 50% reduction in strength. It may not always be quite that much, but in pull tests I've definitely seen even greater reductions depending on the knot and how it is dressed.