Does 2:1 halyard lessen load on mast head sheave?

[mrybas]

Originally Posted by estarzinger

I found the best things to do were #1 'lock' the head block so it cannot swivel and #2 move the masthead dead end as far from the sheave as practical to create separation which causes the rope to 'untwist' when it gets up there, and

#1 What do you mean by 'lock' the head block? The swivel below the block has to swivel or the sail won't furl.
#2 If the sheave is just port/starboard of centerline, where is the best place to move the deadend? My dead end is off to port, so when on port tack the block/swivel chafe the mast.

[mrybas]

Originally Posted by UNCIVILIZED

What's the story with using knots to attach the ends of the halyards at the masthead? Not an ideal method for high modulus cordage.

PO's doing. I tried to splice them, but the cover is too stiff to work with.

[UNCIVILIZED]

Originally Posted by mrybas

PO's doing. I tried to splice them, but the cover is too stiff to work with.

Since I'm guessing the lines aren't new, it's likely safe to wash them. Which in addition to adding to their lifespan, makes them easier to splice (& to handle). Also, you can end for end them, as I doublt that the tails have seen much load, therefore making them easier to splice. Plus T900 (white with blue & red flecks), & V100 (red with yellow blazes & orange flecks) are both spliced using core to core splices. So the condition of the cover isn't critical in this, as you don't have to include it in the splice itself. You can either leave a short piece of cover overtop of the core in the loop formed by the splice, or leave it off entirely in the region of the splice. And optionally paint the splice with Maxi Jacket II to increase it's UV & chafe resistance. Also, using thimbles, in order to prevent point loading the line around small radii like shackles, is an option in addition to the above. Helps the line to live longer, & carry higher loads more easily.

[sailjumanji]

To answer the initial question, the tang is taking up part of the load. Remove it, and the sheave load increases. As does the tension on the deck clutch. I know all of this from personal experience, having converted many 1:1 to 2:1. I am obviously not qualified to calculate static or dynamic loads.

[Benz]

Mike, you should fabricate a crane to replace the tang, one that reaches out forward of the masthead far enough that the block can comfortably fit between the deadend at the end of the crane and the masthead sheave. This will do a lot to alleviate the twist and the block harshing on the mast. You can't lock the block, as Evans suggested, because of the swivel, though unless it's on a furler, I don't see what you have a swivel for.
Last dodge to try when the deadend is twisting is to put a swivel at the deadend, so all the twist that goes up there turns right out. Facnor and Equiplite make some Very Expensive high-load swivels that will do this.

What I wonder in regards to the unending engineering argument is, if adding another leg of line increases the load on the sheave by 50%, how much load are we adding to each sheave if we make it an 8-leg system? And why, after all the gassing about the superiority of the metric system, are they now trying to switch from kg to n? If anyone can answer my question in good, sensible pounds, I'll be grateful.

[mrybas]

Originally Posted by UNCIVILIZED

Since I'm guessing the lines aren't new, it's likely safe to wash them.

Haha, funny you should mention washing lines. I started washing all of the running rigging last week. While it might be safe for the lines, the washing machine didn't like it. Oh well, washing machine drums make nice fire pits!

[UNCIVILIZED]

Originally Posted by Benz

Mike, you should fabricate a crane to replace the tang, one that reaches out forward of the masthead far enough that the block can comfortably fit between the deadend at the end of the crane and the masthead sheave. This will do a lot to alleviate the twist and the block harshing on the mast. You can't lock the block, as Evans suggested, because of the swivel, though unless it's on a furler, I don't see what you have a swivel for.
Last dodge to try when the deadend is twisting is to put a swivel at the deadend, so all the twist that goes up there turns right out. Facnor and Equiplite make some Very Expensive high-load swivels that will do this.

Are you saying that it's impossible to put a non-swiveling block up there, or rather that it's unwise to? As doing the former isn't that tough.

The issue of twisted halyards in 2:1 systems, & the lines in dinghy davits has been addressed dozens of times here on CF. So I won't repeat their content, as they're easy enough to find by searching.

Note. As to cranes in this context, sometimes it can be a challenge structurally to build one that's long enough to do be able to locate the attachment points on it in the ideal location for a block, or the end of a 2:1 halyard. Since the lever arm may need to be (relatively) long, & we're talking about a significant amount of load acting upon the crane.
It is possible, I'm just saying that it may not be simple nor cheap.

To that end it might be wise to ask others to post pics or sketches of their crane & masthead setups, in order to get some ideas that'll be workable for the OP.

[mrybas]

Originally Posted by Benz

Mike, you should fabricate a crane to replace the tang, one that reaches out forward of the masthead far enough that the block can comfortably fit between the deadend at the end of the crane and the masthead sheave. This will do a lot to alleviate the twist and the block harshing on the mast. You can't lock the block, as Evans suggested, because of the swivel, though unless it's on a furler, I don't see what you have a swivel for.
Last dodge to try when the deadend is twisting is to put a swivel at the deadend, so all the twist that goes up there turns right out. Facnor and Equiplite make some Very Expensive high-load swivels that will do this.

I'm not having twisting issues, just the block/swivel are chafing a hole in the mast.
I fly the screecher off this halyard which is a furling sail. Here's a picture of the block and swivel.
The equiplite has a sweet 2:1 top swivel that would do less damage when contacting the mast, but $$$$$$.
I agree a crane that gets the dead end farther from the mast sounds like the best solution.

[estarzinger]

Originally Posted by mrybas

#1 What do you mean by 'lock' the head block? The swivel below the block has to swivel or the sail won't furl.

Yea, I was responding to Privilege, who was commenting about a 2:1 mainsail halyard. It is useful to have the block locked/non-swiveling there and on a fixed head stay furler. But, on your 'free flying' sail, as you point our, because you have the furler swivel on the head of the sail, the block swiveling does not matter much either way (except in theory a fixed one can be lighter/stronger).


#2 If the sheave is just port/starboard of centerline, where is the best place to move the deadend? My dead end is off to port, so when on port tack the block/swivel chafe the mast.

Our three 2:1 halyards had different arrangements. On our (fractional) headstay jib halyard we had the sheave below the stay tang and the deadend the same distance above so that the load was triangulated right up the stay, and increased halyard tension did not pull on the stay. On our code zero (masthead) halyard we had the deadend on one crane and the halyard block on another crane. The cranes were each angled out a bit (as they usually are) so the separation was pretty decent. That caused a pretty good 'pull' to untwist the sail when it was hoisted. On our mainsail the halyard sheave was in its normal place and we dead ended at the end of the backstay crane.

Originally Posted by UNCIVILIZED

spliced using core to core splices.

That is certainly the tidiest, and 'highest strength when new', approach. But a quick aside - both T900 and V100 have fibers that are more UV sensitive than dyneema (V is vectran, and T has a Technora/dyneema blend). So it is prudent to try to protect the core to core splice from UV. It can be done pretty easily (like wrap with tape) . . . .

but see comments below and their somewhat complicated implications if you are really looking to maximize longer term strength with UV sensitive fibers.

As an aside, I will comment that I tied knots on these deadends for practical reasons - because I found it easier to shorten them when a bit of wear showed, and to end for end them, and to put them in place while up at the masthead (hated fiddling with shackle pins up there) and because they were way over strength already. Not what I would do on a finely rigged/tuned race boat, but seemed practical on a cruising boat.

Originally Posted by Benz

UV

Just answering a question you asked on another thread following a comment by SL on UV. I am aware of three studies on the amount of UV protection a braided cover provides. One by Samson concluded that the most damaging UV frequency will penetrate at fiber damaging intensity thru 4mm thick of polyester. That implies it will penetrate most 'yachting' covers and cause damage to the core. The downside was this study was focused specifically on large ship lines which were braided differently than 'yachting' line and did not comment on cover color. NER did a study of their dyneema covered/dyneema cored line designed for lifelines, and concluded that the cover provided significant chafe protection but less than expected UV protection. But that was a test of a very specific line for a very specific safety application, so difficult to know how much generalization can be made from it. And I did a test of a number of different brands and sizes of 'used' line - testing the strength of the core alone vs the strength of the core alone of identical new line. The cores were very significantly weaker, but we don't know exactly how much of that can be attributed to UV penetration vs other factors. Bottom line, none of these individual studies are perfect science, but I think it is fair to say that none provide a ringing enforcement that braided covers provide a massive amount of UV protection.

.........

[UNCIVILIZED]

Originally Posted by mrybas

I'm not having twisting issues, just the block/swivel are chafing a hole in the mast.
I fly the screecher off this halyard which is a furling sail. Here's a picture of the block and swivel. Attachment 156864
The equiplite has a sweet 2:1 top swivel that would do less damage when contacting the mast, but $$$$$$.
I agree a crane that gets the dead end farther from the mast sounds like the best solution.
Attachment 156865

For the issue of chafe on the mast tube, why not bond some UHMWPE to the mast in that area. Or in a pinch use a couple of layers of 2-liter plastic soda bottles attached with Sika or 5200. And if you want to go overkill, add a layer of 3mm aluminum or 1mm stainless plate.
Similar skid plates are commonly added onto boat's bows to protect them from the anchor, for the 1st/last meter of it's hoist/drop.

estarzinger, I'm aware of the UV vulnerability of the lines in question. About which, do you feel that the cover on such lines needs to be fully included in the splice as when doing so in double braid lines such as polyester, & if so, why?

I ask as it's seemingly much easier to do a core to core splice with things like Vectran, & to leave just enough line jacket in place to cover the loop formed by the splice. This, or perhaps a fraction more, so that the tail of this bit of cover can be tucked into the standing section of cover right at the end of the spliced loop. And then, either way, stitched in place, along with painting it with a UV preventative like Maxi Jacket II.

Part of my asking is that for things like Code 0 halyards, where they're under huge amounts of tension, tying them might be problematic from the standpoint of having the knot slip. Along with the knot weakening the line. Which, if the lines are being tensioned near their max working load, then knots might present something of an issue. Though if the cordage isn't seeing strain akin to this, then odds are knots won't be nearly so much of a problem, if at all.

[jmschmidt]

As usual half of the respondents strayed from the original question which was, Does 2:1 halyard lessen load on mast head sheave?" No The load on the masthead sheave is the total of the weight of the sail, attachments, blocks and lines. It doesn't mater if you have a ten-part halyard or a 1:1. The entire weight is on the masthead sheave. In the ten-part example that would include the nine lines from the attach point running through two multi sheave blocks and the single line running back to the deck that you would hoist the sail with. What else would be supporting all that weight? A skyhook?

[Uncle Bob]

Originally Posted by jmschmidt

As usual half of the respondents strayed from the original question which was, Does 2:1 halyard lessen load on mast head sheave?" No The load on the masthead sheave is the total of the weight of the sail, attachments, blocks and lines. It doesn't mater if you have a ten-part halyard or a 1:1. The entire weight is on the masthead sheave. In the ten-part example that would include the nine lines from the attach point running through two multi sheave blocks and the single line running back to the deck that you would hoist the sail with. What else would be supporting all that weight? A skyhook?

Ahh, got it, the line end fastened to the tang does nothing.

[Adelie]

Originally Posted by jmschmidt

As usual half of the respondents strayed from the original question which was, Does 2:1 halyard lessen load on mast head sheave?" No The load on the masthead sheave is the total of the weight of the sail, attachments, blocks and lines. It doesn't mater if you have a ten-part halyard or a 1:1. The entire weight is on the masthead sheave. In the ten-part example that would include the nine lines from the attach point running through two multi sheave blocks and the single line running back to the deck that you would hoist the sail with. What else would be supporting all that weight? A skyhook?

The answer for the 10 part block question depends on how the sheaves are laid out. Lets say that there is one sheave carrying line thru the top of the mast with and a 4-block pack with a bail hanging from the tang. That means there is a 5-block attached to the top of the sail. So if the sail load is 10lb and there is a 10-part block system then the load in the line is 1lb.

We are only concerned with the load on the sheave thru the mast, not the load on the tang that is carrying the 4-block with bail.

Let's assume the sail is pulling straight down and not at all forward. Let's also assume the sheave diameter is the same as the fore and aft dimension of the mast so the tail side down the the deck is also vertical. So the sail side of the halyard is pulling down 1lb and the tail side is also pulling down 1 lb. Both loads are in the same direction so you can sum them. 1lb + 1lb = 2lb.

Lets change our assumption about the sheave diameter and make it less than half the original diameter. That means there will now be 2 sheaves at the masthead, 1 at the front and 1 at the back. In between the 2 sheaves the line is horizontal. Let's look at the forward sheave. There are now 2 loads on the sheave that are 90* to each other and both are still 1lb. 1 lb pulling down towards the sail and 1lb pulling aft towards the aft sheave. For the net load on the sheave you would vector sum the 2 loads. The direction of the net load is down and aft at a 45* angle from the vertical and the net load is root 2lb which is 1.41lb.

Let's assume the sail load actually pulls forward at some angle which is how it works in reality. Lets continue to assume 2 sheaves at the masthead. That means on the sail side there is some force forward that will be counteracting the pull aft on the tail side and the sail load in the down direction will be less than 1lb. When the sail load is somewhere around 30* forward of vertical, the net load on the sheave will drop to 1 lb. The net load on the aft sheave will stay at 1.41lb because the sail loads on it are still horizontal and the tail load is still vertical.

Remember the sail load is still 10lb. Where is the other 9lb supported? By the Tang. The load is still going into the masthead, but it is not all on the sheave or the pin that supports it.

The actual load on the masthead as a whole is 11lb, 10lb for the sail weight plus 1lb for the tail load.

[savoir]

Originally Posted by Pizzazz

Not correct. The tension in the line is the same throughout the line. There is one line pulling on the tang, but there are two lines (one going to the sail, the other going to the winch) pulling on the sheave. Hence, the load on the sheave is 2x the load on the tang.

If you remove the tang and dead-end the line to the sail, the force on the sheave will be 2x the weight of the sail (split between the sail and the winch). If you dead end the winch end of the line to the sail as well, then the load will be 1x the weight of the sail but you will not be able to raise it. Think about it again. It is a little non-intuitive.

One more way, when using a 1:1 halyard, you have to pull hard when raising the sail. This bends the mast slightly. When using a 2:1 halyard, you pull less. Therefore, the force on the mast will be intuitively less. The only time the force on the mast will be equal to the weight of the sail is if you are actually sitting on top of the mast and pulling the sale up. Now may be it is clearer.

I'm sure glad you weren't my math teacher.

[rhubstuff]

Anyone who claims that the sheave takes 100% of the load of a 2:1 halyard purchase must also admit that the tang end takes 0%. This is clearly impossible. The tang takes 1/2 the load, the sheave the other half, regardless of wind loading, weight of the sail, etc. If this were not true, the tang could be removed without consequence. But it obviously can't. It is absolutely wrong to confuse the issue with halyard winches, turning blocks, wind loads, dynamic loads, and other elements that do not directly bear on the question of direct sheave vs. tang loading. I think I'll use this as a test question when interviewing crew. I might not want to sail with someone who clearly doesn't know basic high-school level physics and fails to see what is patently obvious.