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How a 2:1 halyard works


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The cave experiments, along with a couple too many beers, do line up exactly as WT's pretty picture or there is a serious drinking issue standing in the way of science, possibly both. Nice simple easy drawing, thanks WT.

 

That work for you 'Mr I jump around on a big red Mary' :wink: and the other interested lurkers? Told ya it was simple yet knot as simple as I to explain it nicely.

 

Yes we were talking about a local club racer, but do you really think KMs ross 930 rig is a lamp post? I think not.....
More an al dente noodle than lampost for sure. In fact It's only up there as a sailmaker made a previous owner heavy duty fully battened mainsail I suspect. Very wide stay base and long quite raked spreaders has the noodle.

 

Nice thread people.

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Yes, WT is correct, as is his diagram :D.

However, I stand by my original statement. For a given halyard tension, it is not possible to reduce the compression load on a rig. If you have 100kg on the halyard, you cannot have less than that on the mast.

Halyard load and compression load are related, but not the same. You CAN HAVE MORE compression load than Halyard load, and most boats do- ie a standard 1:1 halyard (worst) 100kg on Halyard, 200KG Compression, or a 2:1 Halyard (better)100 Kg Halyard, 150 Kg Compression. A Halyard lock is best.

 

However;

If your halyard lock is like many, and uses a strop back down the mast a bit after rounding a sheave, then the section of the mast above that sheave takes the full 200KG compression load - same as a 1:1 halyard. The advantage is that only that section of mast between the Sheave and the lock has that load, and it is not transmitted to the mast step or the boat. In WT's diagram with the lock horizontal to the sheave, this compression load is across the masthead, but in my experience it's normal for the locks to be below the sheave.

 

Also, talking about compression loads and stay bases only clouds the halyard compression situation, and is to totally separate issue. It will put heaps more load (compression load I'm talking about) on the mast than than a halyard ever will.

 

KM, pleased to hear you have it sorted. Sorry I could not help last night!

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Im with WT here for sure. Its a fact and a well known fact too.

Having a friction sheeve/ferrule or shackle as the 2:1 block (on the sail attachment )is even better as it further reduces compression when compared to a low friction block.

It all sounds farr fetched but if you actually sat down with someone who could explain it and draw some pictures you would understand and see how simple it actually is.

 

I guess the most simple way I could discribe it is imagine getting your fishing rod, then tying a bit of string to the flexy end of it in addition to the line that runs from the reel out to the end and back with a hook on it.

Now grab the hook end and pull it towards the reel you- can bend the rod easily. Pull the direct 1:1 string that is tied to the end and its much harder to bend the rod. This is the difference in compression between a halyard lock and 1:1 halyard.

 

Correct. The lock system is best followed by 2:1.

 

I was with WT diagram 100% until the chain plate point.

 

Chain plate angel, spreader angle and length on serve to support the mast, pre bend the mast, fore and aft and side ways.

 

Compression of a mast from the stays only come from the loadings we put on the stays.... until we hoist a sail and fill the sails then the forces of wind, keel, wave loadings, stiffness of sail cloth, sail shape, crew weight, rigging and running rigging strenght and stretch comes into play.

 

Maybe mythbusters would be a good demo.

 

if you were trying to open these 50kg cast iron deck hatches by pulling on the red line, which one would take more force to open? where does all that excess force go?

post-10268-14188722512.png

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Nice JH but there is no boat in that world with a stay angle like you're left picture angle

 

Also this is a silly comparison. To compare correctly you need an opposing red line to make the other stay (that is holding the rig in equilibrium and transferring loadings to compression on the mast) that all boats have on every mast except a back stay on a fractional rig.

 

Close but no cigar.

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Yes, WT is correct, as is his diagram :D.

However, I stand by my original statement. For a given halyard tension, it is not possible to reduce the compression load on a rig. If you have 100kg on the halyard, you cannot have less than that on the mast.

Halyard load and compression load are related, but not the same. You CAN HAVE MORE compression load than Halyard load, and most boats do- ie a standard 1:1 halyard (worst) 100kg on Halyard, 200KG Compression, or a 2:1 Halyard (better)100 Kg Halyard, 150 Kg Compression. A Halyard lock is best.

 

However;

If your halyard lock is like many, and uses a strop back down the mast a bit after rounding a sheave, then the section of the mast above that sheave takes the full 200KG compression load - same as a 1:1 halyard. The advantage is that only that section of mast between the Sheave and the lock has that load, and it is not transmitted to the mast step or the boat. In WT's diagram with the lock horizontal to the sheave, this compression load is across the masthead, but in my experience it's normal for the locks to be below the sheave.

 

Also, talking about compression loads and stay bases only clouds the halyard compression situation, and is to totally separate issue. It will put heaps more load (compression load I'm talking about) on the mast than than a halyard ever will.

 

KM, pleased to hear you have it sorted. Sorry I could not help last night!

 

Correct and I don't think anyone was argueing that point?

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Thanks all.

Reports from the lurkers is all positive and grateful for the simple explanation/s. WT's drawing got a special mention from them all.

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Well this thread pretty much sums up Crew.org to me and why I'm spending way less time here.

 

I just read this thread through yesterday and like KM said I did explain the 2:1 to him a while back and very early in the thread both Marshy and WT got it right and were spot on.

Then for what ever reason it got very clouded with some opinions that were just plain wrong.

 

Some valid reasons to fit a 2:1 halyard.

 

Reduce the compression on the mast (if comparing it to a 1:1 halyard).

Halve the load on the rope itself meaning less stretch and less creep, meaning lower load on the Halyard jammer, can possibly use a lighter rope, setup could possibly be lighter, keeping the mainsail head closer to the P band at the top, making the Topmast more effective by increasing leverage at the top (as in when the sail comes down from the top it stiffens up the topmast of the spar)

 

Even the P class has a 2:1 halyard.

i didf this to save the need to tip the boat over when rigging (as had been the norm) as lots realised that Ramp space was tight at some venues and lots tipping over takes up more space and is a bit of a pain.

By engineering the spar correctly the 2:1 halyard does not adversely impact on the boats performance and with the turning at the top around a shackle (not a pulley) and using 4mm Challenge braid (vectran) the sail stays right up at the black band.

I know the 2:1 halyard has been a success on the P class (as well as on my Finn masts) because over all these years no one has ever complained and heaps have poured praise on it!

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Also, Booboo you said "Having a friction sheeve/ferrule or shackle as the 2:1 block (on the sail attachment )is even better as it further reduces compression when compared to a low friction block."

I don't follow how this makes a difference? Could you please explain?

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Its hard to explain...

So effectively you are trying your hardest to make the 2:1 work like a halyard lock and as Tim says to reduce the amount of load going down through the rope/jammers ect.

If you have nice roller bearing blocks, its easier to get up and down but then again its easier for the load to get transferred back down the halyard/jammers.

Having a ferrule or shackle adds friction into the system so it’s harder for the loads to get transferred back down the rope and often even when the halyard is eased right off it takes a good pull to get it to start coming down.

Imagine having so much friction that the sail was actually completely stuck at the top even when the halyard was right off, then having some system to release that friction so you can get it down- that's a halyard lock!

 

Does that make sense?

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No Booboo it does'not.

 

I thought as you did too but whatever attachment to the headboard must surely be loading the masthead and sheave pin the same amount.

 

Sure there is extra friction when the rope is moving thru the shackle but when stopped it is all same.

 

As for the shroud base issue. I understand the width/ loading numbers but when practical assessment is considered to a narrow yacht where the beam differences are so small and the dissection angles of attachment of the stays are so minimal there is bugger all difference in compression calcs.

 

In a cat it would count and yeas on a back stay on a fractional rig it would but with all stays on all boats there is an opposing stay converting the pull into compression.

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If you have a 1:1 halyard leading over a sheave with the deflected angle near enough to 180deg, then the resulting force on the pin is double the halyard load.

 

If you can somehow stop the halyard at the sheave or pin off the halyard to a dead end pin (P class pop top), the resulting force on that pin will be near enough to halyard load.

 

For a 2:1 arrangement, if you're still talking a 180deg deflection around the sheave then the resulting force on the pin is 2(1/2xHL) which ends up being the same resulting pin force as the 100% halyard load, but you have to take into account the 2:1 dead end side of the system which gets you back up to 150% of the induced head load compression on the mast tube.

 

For a lock, mast section between a halyard lock and the hoist sheave there will always be 200% compression. Unless you use a 'lock before sheave' assembly or you have space to put the lock horizontal to the sheave like a drew in the picture. So if space inside the mast tube permits, you have the sheave and the lock in the same assembly. That way the mast tube never sees the 200% load, it's all taken care of in the box.

 

I had the horizontal lock system (as drawn) in WT's last 220 x 90 wing mast. Worked really well, but we had the room up there to do it. I was battling compression at the mastbase as I wanted maximum ease of rotation + as little load on the ball as possible, so we were 2:1's and locks all over. Also had all the halyard jammers on the rig.

 

As for angles etc: Reality is, in an alloy rig you take what you're given cause the tube is what it is. In a carbon rig, for example a V70 where there are a lot of halyards and the small load savings here and there sum to a larger saving at the mastbase. Then you might be able to drop a layer out and save a few kg's.

 

As for chainplate width, it is a big driver of tube weight in a carbon rig becuse the laminate is optimised to suit. Again, with an alloy rig you can't really optimise the tube cause it is what it is. In the case of most cruising boats they go a section size up and be comfortable, on something like a ross 930 the narrow CPW and skinny rig is right on the limit. Chances are if the 930's had their chainplates on the gunnel, a lot of the original rigs would still be standing.

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Oh good golly. All the dude banging Big Red Mary, the other one with the dodgy ticker from watching too much porn and I wanted was someone to put what Tim told me into a nice picture. But it is still interesting with the little bits here and there making a nice overall picture for us dumber viewers.

 

I can test the halyard shackle verse block things. Stand by for a day or so until my new micro sensors arrive and I find a moment to have a play.

 

Don't you just keep saying the sweetest things

Chances are if the 930's had their chainplates on the gunnel, a lot of the original rigs would still be standing.
my chain plates are out on the gunwale. Long live the noodle :thumbup: :lol:
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No Booboo it does'not.

 

I thought as you did too but whatever attachment to the headboard must surely be loading the masthead and sheave pin the same amount.

 

Sure there is extra friction when the rope is moving thru the shackle but when stopped it is all same.

 

As for the shroud base issue. I understand the width/ loading numbers but when practical assessment is considered to a narrow yacht where the beam differences are so small and the dissection angles of attachment of the stays are so minimal there is bugger all difference in compression calcs.

 

In a cat it would count and yeas on a back stay on a fractional rig it would but with all stays on all boats there is an opposing stay converting the pull into compression.

 

Its basic maths that a wider side stay angle will reduce compression for a given side load. Are you retarded?

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No Booboo it does'not.

 

I thought as you did too but whatever attachment to the headboard must surely be loading the masthead and sheave pin the same amount.

 

Sure there is extra friction when the rope is moving thru the shackle but when stopped it is all same.

 

As for the shroud base issue. I understand the width/ loading numbers but when practical assessment is considered to a narrow yacht where the beam differences are so small and the dissection angles of attachment of the stays are so minimal there is bugger all difference in compression calcs.

 

In a cat it would count and yeas on a back stay on a fractional rig it would but with all stays on all boats there is an opposing stay converting the pull into compression.

 

Its basic maths that a wider side stay angle will reduce compression for a given side load. Are you retarded?

 

My god, the question had to be asked Samin!

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The sum total of mast compression is a factor of all its parts and the force vectors. (angles of force).

In halyards the force may only increase by the addition of friction.

In a two to one, you may have additional "purchase" on the down side, but you increase the friction on the sail side, thus increasing the compresion by that small amount.

The "weight" of the sail does not change, whether the halyard is pinned to the top of the mast or the bottom. It is still the same.

Tennsioning the sail beyond the weight of the sail is added compression to the mast. If you release the halyard at the bottom of the mast, and lock it at the top the tension is still the same less the halyard tennsion and friction.

(not much, and really only done to overcome halyard stretch).

As I have said, in standing rigging compression is the sum of the force of the vectors...that is how much is pulling and at what angle.

A mast for example with nothing else but a back stay at 45 degrees ''sees" a force that is pulling backwards at the same force as downwards.

The recistance to that force by the mast however in those differant angles is differant. Beacuse our mast is in line with the downwards force. It is stronger in compression than flex , and for it to have equal force in down and aft, it would have to be angled at the medium of the vector which is 22.5 degrees forwrds.

Because it isnt and we have intermediate stays we get mast bend. A classic example of mast resistance versus force vectors.

It takes more force to bend the mast when the stays are closer to the mast, less when they are at a greater distance.

Because it takes less force the further apart from the mast the stays are, the less tension that is needed. It is transferring more and more to a sideways pull than a pull in line with the mast.

(The optimum would be to have the stays a 90 deg to the top of the mast !)

 

Fractional rigs only change loadings by their relative force vectors. That is the same as cap rig , changed by the deflection resitance of the mast section....and the differant vector angles of the stays. (and of course the amount of tennsion you place on each stay.

 

As a final point, stretch loadings on stays also change things. The longer a given stay of the same material the greater the stretch under load.

This also comes into "modulus of elasticity" of any given material. ......

 

In summary, a 2 to 1 dosnt decrease compression on the mast, in fact by a small amount of added friction (all other runnning gear being the same) it actualy inceases the load and just transfers some of the load to the front of the mast.

 

"Purchase decreases effort, but does not decrease force".....which is the whole point of it.

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