sail(plane)

Square top and plastic mast track

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Hi, I have a question for the experts, didn´t know if I should post it in Multihull, in Fix-It, but since it´s a small boat issue I guess it´s better here.

I have a custom square top main in my weta trimaran. The Weta has a carbon fiber mast with a glued-on PVC mast track for a luff bolt rope. The downhaul tension does what it is supposed to do, curves the top of the mast and flattens the top of the sail. Very effective depowering for high winds. After 2 years since the last track repair, the top of the sail has pried open the mast track and comes out. I need to change the top 30cm section of track with plexus and all that. I can plainly see that when cranking the downhaul hard, the top of the mast curves a lot and the track must be experiencing some pretty big forces, on top of that, when running the top of the sail has a wide open angle, putting even more strain on the track.

Questions:

- Should I accept that the track will eventually give up in the most stressed area, and just accept it as maintenance?

- or is there something wrong with the sail or the battens? (performance wise the sail works just fine)

- or should I put in a stronger track? maybe PVC is not the right material for a curved luff mainsail? How do other similar mainsails work , like 29er etc?

Any comments appreciated, thanks
 

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Hi Downhaul loads should not open the sailtrack up at the top, it should open it more up at the bottom, than the top, because there is more movement.

Possibly the issue is the alignment of the halyard, or your batten pockets are to close to the bolt rope, and when running square they are levering the track open.

Not sure who's plastic track you have, but its a good thing it is plastic other wise you will end up with a X/Y axis in the mast, the fore & aft being significantly bigger than sideways so the mast hangs off to the side, which is not flash.

PVC is also the perfect material to make the track from.   Nylon swells, ABS is very brittle, Acetaly is heavy.

29er, 49er tend to only have track opening issues when the mast is dropped and they smash the track, takes a bit to do it.

Also it is plastic, so heat muck's it up! Flip side, a decent hair dryer and you can close the track again.

I would be looking at Halyard alignment and batten pocket ends.

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We have a similar issue with the Swift masts. A couple things, everyone has had issues with the track. Over time, the PVC hardens and starts to crack and we have had issues with the lamination failing. I haven't had the track open up and let the bolt rope pull out though. We generally hoist with a lot of halyard tension to take the stress off the track at the tip of the mast. Too much tension on the battens will put extra stress on the track. I'd only tension them until the vertical wrinkles are removed. Most of the sail shape comes from the mast bend, not from the battens. They are there to support the roach.

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49 minutes ago, TeamFugu said:

Over time, the PVC hardens and starts to crack

Time and UV, adds the man in FL.

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1 hour ago, JulianB said:

Hi Downhaul loads should not open the sailtrack up at the top, it should open it more up at the bottom, than the top, because there is more movement.

Possibly the issue is the alignment of the halyard, or your batten pockets are to close to the bolt rope, and when running square they are levering the track open.

Not sure who's plastic track you have, but its a good thing it is plastic other wise you will end up with a X/Y axis in the mast, the fore & aft being significantly bigger than sideways so the mast hangs off to the side, which is not flash.

PVC is also the perfect material to make the track from.   Nylon swells, ABS is very brittle, Acetaly is heavy.

29er, 49er tend to only have track opening issues when the mast is dropped and they smash the track, takes a bit to do it.

Also it is plastic, so heat muck's it up! Flip side, a decent hair dryer and you can close the track again.

I would be looking at Halyard alignment and batten pocket ends.

mmm In fact, the halyard is NOT perfectly aligned. Need to re-visit this.

Good to know the material is right. It´s the OEM Weta track.

hair dryer, eh?

thanks Julian! 

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1 hour ago, TeamFugu said:

We have a similar issue with the Swift masts. A couple things, everyone has had issues with the track. Over time, the PVC hardens and starts to crack and we have had issues with the lamination failing. I haven't had the track open up and let the bolt rope pull out though. We generally hoist with a lot of halyard tension to take the stress off the track at the tip of the mast. Too much tension on the battens will put extra stress on the track. I'd only tension them until the vertical wrinkles are removed. Most of the sail shape comes from the mast bend, not from the battens. They are there to support the roach.

TF, also very good tips. The track has some longitudinal cracks on the inside, although I don´t think it could be UV since the boat always sleeps totally covered including the mast.

The Weta has a mainsail halyard lock at the top, so all tension is by way of the downhaul. I guess it´s the same thing but in reverse (luff tension). Does the swift mast bend when you put tension in the halyard? is this why you are "taking stress out of the track"?

 

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1 hour ago, JulianB said:

Hi Downhaul loads should not open the sailtrack up at the top, it should open it more up at the bottom, than the top, because there is more movement.

 

somehow the mast bending suggested the bolt rope trying to get out of the track... but then if I think of the luff curve matching mast bend, suggests an unloaded track...  I can´t picture all the forces at play, it´s too much of a 3D problem with the sail shape, battens, etc

I´ll just take your word for it and go check alignment and batten pockets!!

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There is a shop in Mass. that makes light weight rowing skulls etc that has a polycarbonate (Lexan) extrusion that matches up pretty well with the pvc section. Higher MOE that PVC therefore stiffer & works well with Plexus.  A little heavier than PVC but the extrusion section is so small would make little difference if just using a short piece at the top.

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Going from pinhead to square top the 800s have had some track issues with plastic tracks around the top batten. New masts are fitted with alloy tracks and don't have the cracking issue.

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32 minutes ago, Mozzy Sails said:

Going from pinhead to square top the 800s have had some track issues with plastic tracks around the top batten. New masts are fitted with alloy tracks and don't have the cracking issue.

Thanks. In my case It's got to be plastic, but since it seems it is a specially stressed area, I'll make sure halyard alignment, batten pocket protectors and track wear are all ok

An 800 is a RS800?

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Hi guys, there is plastic track and there is plastic track.

The base is PVC, its whats added to it that makes all the difference.

And if you add say Lexan, as someone suggested you just took the mast from bending symmetrically to having a X-Y axis, so it will lay off to leeward, which aint flash.

My son sails one of these modern 18teen, and they have carbon track, they spend all there time tweaking the cap shrouds so it wont hang out of the boat sideways.

Sideways bend = very poor pointing angles.

I can only talk about the track we use, we go to great extents to make sure its right and we don't have a issue.    We have had issues, and we have dumped a few tonnes of crap track also.

If it aint right, then bitch about it and get it right!

 

                    Jb

 

 

 

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Yes, an RS800. 

Julian, can you explain the laying off to leeward comment? In which dimension are you saying the mast isn't symmetrical? 

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49 minutes ago, JulianB said:

Hi guys, there is plastic track and there is plastic track.

The base is PVC, its whats added to it that makes all the difference.

And if you add say Lexan, as someone suggested you just took the mast from bending symmetrically to having a X-Y axis, so it will lay off to leeward, which aint flash.

My son sails one of these modern 18teen, and they have carbon track, they spend all there time tweaking the cap shrouds so it wont hang out of the boat sideways.

Sideways bend = very poor pointing angles.

I can only talk about the track we use, we go to great extents to make sure its right and we don't have a issue.    We have had issues, and we have dumped a few tonnes of crap track also.

If it aint right, then bitch about it and get it right!

 

                    Jb

 

 

 

Julian, you mean a stronger track would change the section moment of inertia from symmetric ( round carbon mast) to a section that has two different moments depending on the axis?

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Sail Plane,  Absolutely!

Mozzy, If you want to point, then what you want is the masthead to come to windward if you can. 

Most of the time your happy with it straight, and again, go to the 49er, they spend a lot of time getting the caps just so, plus we have the trapeze wires going in above the shrouds, so the trapeze wires are pulling the mast head to windward.

Often, when you exceed cap shroud tension, the windward cap shroud is occasionally loose.   Then with the 49er and I8teen and other hi end skiffs you actually heel the boat to windward when you can, even though this reduces your RM, because the CoB comes to windward of the CL.

Obviously its beneficial [to heel the boat to windward] otherwise they would not do it, and they all do it.

Why, OK, we where staggered by the amount of span-wise drift you get on a rig, and if you think about it, its inevitable, we should not be surprised, especially if your sailing something like a Laser.     All those single handers sail at about 6d heel, mostly to keep the arse out of the water, really dose not matter which one (boat not arse).  So you have a bunch of  pressure on one side, and a great amount of suction on the other.   The air speed is not that great, so going up or down is a real option.   A lot goes down, mostly because the pressure - suction is greatest at max camber and max cord.    This is how we stumbled across the efficiency of the cuff luff, and the more efficient the boat, as in the higher pressure/suction differential, the more you need the cuff luff or the end plate, just look at Moths, the A class and then look at the AC and these new 50ft Cats.    It not a coincidence.

The same happens at the tip, more so on a yacht, which heels, and possibly why the 49er heels to windward, as it virtually stops it.    If you can get the air to flow across the sail, then its a lot more efficient, and the normally means its a lot less draggy.    Also if you have the air flowing across and not up and over, no vortex, what birds have been about for years.

If its less draggy, then you can point higher.

If the mast is hanging out of the boat sideways, because you have put a carbon track on the back, and your cap shrouds are too loose then your going to have a lot of air traveling up the rig and spilling over the tip.    That lead to tip vortexes, and lots and lots of drag, loss of power which all equals pretty poor point angle.

Again, I was on the harbor on Thursday, 2 18teens, one tighten up the caps I hole, and they gained 3-4d in height, just like that.    This was bottom end #2 rig.

I sometimes wonder about our drive to go to less and less stretch, in this case wires.     The problem with tightening the caps if it restricts the movement of the topmast for and aft.    If you replaced say the 2.5mm Dyform, with say 3mm SK78, then you would probably have the topmast "straight" far more often, and when loaded up with the spinnaker, mast head goes fwd and the extra 2mm of stretch you get with dynema would make 2/10 of FA difference.

          Jb

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1 hour ago, JulianB said:

Sail Plane,  Absolutely!

Mozzy, If you want to point, then what you want is the masthead to come to windward if you can. 

Most of the time your happy with it straight, and again, go to the 49er, they spend a lot of time getting the caps just so, plus we have the trapeze wires going in above the shrouds, so the trapeze wires are pulling the mast head to windward.

Often, when you exceed cap shroud tension, the windward cap shroud is occasionally loose.   Then with the 49er and I8teen and other hi end skiffs you actually heel the boat to windward when you can, even though this reduces your RM, because the CoB comes to windward of the CL.

Obviously its beneficial [to heel the boat to windward] otherwise they would not do it, and they all do it.

Why, OK, we where staggered by the amount of span-wise drift you get on a rig, and if you think about it, its inevitable, we should not be surprised, especially if your sailing something like a Laser.     All those single handers sail at about 6d heel, mostly to keep the arse out of the water, really dose not matter which one (boat not arse).  So you have a bunch of  pressure on one side, and a great amount of suction on the other.   The air speed is not that great, so going up or down is a real option.   A lot goes down, mostly because the pressure - suction is greatest at max camber and max cord.    This is how we stumbled across the efficiency of the cuff luff, and the more efficient the boat, as in the higher pressure/suction differential, the more you need the cuff luff or the end plate, just look at Moths, the A class and then look at the AC and these new 50ft Cats.    It not a coincidence.

The same happens at the tip, more so on a yacht, which heels, and possibly why the 49er heels to windward, as it virtually stops it.    If you can get the air to flow across the sail, then its a lot more efficient, and the normally means its a lot less draggy.    Also if you have the air flowing across and not up and over, no vortex, what birds have been about for years.

If its less draggy, then you can point higher.

If the mast is hanging out of the boat sideways, because you have put a carbon track on the back, and your cap shrouds are too loose then your going to have a lot of air traveling up the rig and spilling over the tip.    That lead to tip vortexes, and lots and lots of drag, loss of power which all equals pretty poor point angle.

Again, I was on the harbor on Thursday, 2 18teens, one tighten up the caps I hole, and they gained 3-4d in height, just like that.    This was bottom end #2 rig.

I sometimes wonder about our drive to go to less and less stretch, in this case wires.     The problem with tightening the caps if it restricts the movement of the topmast for and aft.    If you replaced say the 2.5mm Dyform, with say 3mm SK78, then you would probably have the topmast "straight" far more often, and when loaded up with the spinnaker, mast head goes fwd and the extra 2mm of stretch you get with dynema would make 2/10 of FA difference.

          Jb

outstanding, a lot to think about

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I'm here in Milan on Sydney time thinking about pressure differentials at 4am.

One of my earlier 18teen, probably mid 80's, we had flip/flop wings, hinged at the side of the boat, supported by wires, probably weighed 15kgs, think it may have been Bradmill.  Wings would have been 16ft tip to tip, boat was 8ft wide, so 4ft hanging out each side.     At some point in time, we covered them in with Chickapea, that black mess used on cats, mostly.    Falling though the hole was not much fun.

Cut a long story short, going up wind, hit by a gust, probably doing 14 knts, the leeward wing would often simply rotate up into the rigging on the leeward side.

Took a couple of years to work it out!   (we quickly went to Tennis netting, and it stopped happening)

Very simply we where generating enough vacuum/suction on the leewards side of the rig, probably help by the slot of the jib, and reasonably well set mainsail that the wing was sucked up into the rigging, and it stayed there, real bitch when you wanted to tack running into a wall of wing.

Just a interesting tid-bit giving you and idea of how much suction is developed by a reasonable efficient sail.

You can just visualise and roll of air, 1/2 m thick, starting infront of the mast, spiraling of the windward side of the main, going under the boom and spinning off at about 20d of the aft 1/4 of the boat.  

We had another anecdotal experience that reinforced all of this late last (2017) year with a 49er, so its definitely there and the cuff definitely stops most of it, most of the time.  We had a wind device, and on a 49er places to put it are limited, so we hung it off the back of the boom, about 200mm below and 1/2m back.   Going up wind, normal sort of stuff, wind drops, crews squeezes the mainsheet on, wind gauge kicks about 15-20d, ease the mainsheet, new gust comes main is eased, wind gauge goes back to a AWA.

Same wind gauge, on a wand, tied the rudder frame, sitting about 400mm above the boom, on CL, again only 1/2m behind the leach, never flicked, always sat on AWA.

         Jb

 

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The reason for using Lexan is the fact that the Heat Distortion Temperature is about 50% higher than PVC.  80c v 130c.  Turns out that the friction from hoisting and lowering the sails is high enough to melt the PVC if you go too fast or things go wrong.

The carbon fiber mast laminate is enough larger and stiffer than the sail track laminate that the mast doesn't give a shit what thermoplastic you glue to the back.  Start using something like aluminum and you start to see a difference, and also enter the world of pain that was the 49er mast before the sail track was converted to plastic.

Of course it also matters where along the taper you are talking about, because the mast section changes diameter, but the sail track does not.  So whatever effect will be greatest at the very tip, where the two are closest to the same size.

I have the exact same sail track section in PVC and in Lexan, and the only difference I can see is in durability.  Of course I am not as sophisticated as the most.

Fulcrum Speedworks has Lexan sail track.

To Sail(plane)'s issues.   The track wear is most likely a function of the excessive twist when sailing down wind with the sheet eased. He head of the sail is really trying to pry its way out of the track. I an surprised that you haven't seen bites taken out of the track by the inboard batten caps. If I recall correctly the Weta mast does not rotate, so this may be a perfect confluence of conditions where the production set up was pretty good, but the square head was a step beyond what the track will tolerate.  I guess yopu are just going to have to accept the maintenance as payment for the increased performance.   You can try adding some fillet or glass laminate to either side of the track to toughen up the area, I don't know what that does with regard to class rules or whether you care.

SHC

 

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So, Julian, Steve, Steve's point about over twisted off sail seems to make sense to me. One solution might be a short length of carbon track, which could be bonded in really thoroughly, but if it was short enough not to affect mast bend too much would it be too short to protect the rest of the track? Or could one consider bonded on stops where the battens are to minimise leverage? Horrible for sail wear I suppose.

Interesting point on sideways bend. Decades ago I had an untapered over rotating oval section mast on a Cherub which bent to windward like crazy and nothing was ever better for leech control, just a shame about the zero gust response. I've got one of Nicky's old over rotating Cherub masts in the garage roof,and the taper on that is spectacular, I think at the tip the structural element is actually wider than its long. How did they bend in practice? I've used it, but don't recall.

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18 hours ago, Steve Clark said:

Of course I am not as sophisticated as the most.

We won't take your word for it.

18 hours ago, Steve Clark said:

To Sail(plane)'s issues.   The track wear is most likely a function of the excessive twist when sailing down wind with the sheet eased.

I co-own a Weta, along with my UFO. We had several instances of track breakage on it, and I have good reason to believe that the proximate cause had to do with hoisting or dropping the mainsail misaligned with the wind. My fellow co-owners may or may not have been hoisting dropping without due care re wind direction. The root cause was more likely aged / UV-damaged material.

Once the boltrope is under tension, there's reasonable distribution of the batten pressure, so it's not a point load. That means that besides hoist and drop time, the other recommendation is: don't sail the Weta with slack downhaul, as a gybe might break the track.

Our shared Weta hasn't seen breakage since we discovered/discussed the causes above.

Given this discussion, I am intrigued with the Lexan alternative, and with the fillets I've seen on the UFO at the shroud attachment point. I might try Lexan + some strategic fillets on the Weta next time. 

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As I think I said before, there is plastic track and there is plastic track.

From our POV its about keeping it ductile enough so it remains just that and wont break, but not so ductile that the bolt rope pulls out or so britle that the batten pockets make a mess.    We also try and make it non structural, and that's obviously impossible, especially with the 29er pin head rig.

But at the same time handle the heat of the sun, which down here can cook even the best laminates way above their TGi.  (Singapore is possibly the worst place, as you move away from the Equator it gets easier and easier.    Obviously the material is UV stabalised, so sun wont affect it for a long long time.

But heat and elasticity is your friend (re policing an Olympic class) because if someone tries to tension or compress the track to alter the mast bend, first decent day in the sun, and all that work "re-sets" so it just become pointless. 

We rarely have the issue with the 49er, the FX or the 29er.   People break the track, sure, but that's due to misadventure and they will break anything if they try (and they always do)

49er and FX both have square heads, and we rarely see a track issue!!     

So again, go back and bitch and get them to do something.

I know people who have use conduit, of-course carbon tube, but never Lexan, that's the first I have heard about it being used.

From our POV it would completely mess up the luff round, and you would have people pulling tracks on and off to gain a advantage.    Just way to hard to contemplate.

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Is there any advantage to moving the halyard attachment back on the headboard, an inch or so, so the headboard is being forced into the track at the top by luff tension, or does this just break the sheave/masthead?

 

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On 2/12/2019 at 1:38 PM, JulianB said:

  So you have a bunch of  pressure on one side, and a great amount of suction on the other.   The air speed is not that great, so going up or down is a real option.   A lot goes down, mostly because the pressure - suction is greatest at max camber and max cord.    This is how we stumbled across the efficiency of the cuff luff, and the more efficient the boat, as in the higher pressure/suction differential, the more you need the cuff luff or the end plate, just look at Moths, the A class and then look at the AC and these new 50ft Cats.    It not a coincidence.

The same happens at the tip, more so on a yacht, which heels, and possibly why the 49er heels to windward, as it virtually stops it.    If you can get the air to flow across the sail, then its a lot more efficient, and the normally means its a lot less draggy.    Also if you have the air flowing across and not up and over, no vortex, what birds have been about for years.

 

          Jb

like this? check out from 1:30  

 

 

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So the air is being sucked under the boom creating this tip vortex? And the same happens up top and it happens more if the rig bends off or is heeling to leeward?

tip vortext.jpg

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Smoke, love it, so much smarter than what I would have done.

On the top of the sail what we did was attach a fishing rod to the end of batten #2 & #3,

That went up past the top batten, which is the top of the sail,  then put a few tufts there.

GoPro facing backwards captured all the action.

But smoke and a drone, that's pretty cool.

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4 hours ago, Mozzy Sails said:

So the air is being sucked under the boom creating this tip vortex? And the same happens up top and it happens more if the rig bends off or is heeling to leeward?

tip vortext.jpg

I would love to see the same footage but with a deck sweeper

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Where does one buy Lexan sail track?  Asking for a friend. ;) 

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On 2/22/2019 at 8:28 PM, Mozzy Sails said:

So the air is being sucked under the boom creating this tip vortex? And the same happens up top and it happens more if the rig bends off or is heeling to leeward?

tip vortext.jpg

 

How does it look when you have the jib trimmed and the main not oversheeted?

So many variables to make sweeping statements/judgements from...

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On 2/25/2019 at 3:43 AM, Mozzy Sails said:

I wasn't making a statement, I was asking questions. 

Sorry Mozzy - wasn't a shot directed at you! (Although re-reading my comment I can see how it seemed).

My statement was more about the sweeping generalisations being made in this whole thread and being summed up by a somewhat unrelated single image of a completely out of trim proto-foiler with a smoke stream coming off it alluding to all the secrets of the sailing world...

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Meh, it's a forum, people are going to postulate. 

The photo one visualisation which may have represented what Julian was trying to get across in text. Does it prove anything? No. Does it add to the discussion? I think it does. 

The mast tip dropping to leeward does feel bad. But personally my intuition tells me that heeling to windward doesn't correct this, it's actually mast bend to leeward which is damaging. I'm not convinced skiffs healing to windward is evidence of reducing tip loss. I think it's fast for other reasons. 

Re-the photo, the jib is poorly trimmed, but it's very hard to get leech tension at wider sheeting angles due to how close the track is to the clew... probably needs a jib boom. 

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I am sure there are a multitude of reasons that most skiff sailors heel there boat about 5-7° to windward.

Re the smoke, If you trim the jib on, and carried a bit more of the load (with the jib), the swirl will reduce a little, not a lot.

The major contributing factor is the higher pressure on the windward face of the main-sail and the vacuum on the leeward side.   A well placed slot will enhance that Pressure dif and increase the resulting swirl.

As the boat gets higher and higher pressure differentials the swirl (its really a vortex) gets bigger.   With moderate pressure Difs, of a 49er then the cuff we have seems to stop it unless the main is sheet-ed in hard. Given they are driving the boats harder we possibly should now drop the cuff closer to the deck and increase its cord,  A Moth is probably similar to a 49er but I have not done the sums.   On a 18teen you have less of a issue (much lower Pressure Difs), on a A-Class or a AC you have more and the work they put into cleaning it up, shows.

Re the top of the main, I literally have just come back from China, (and Spain, Italy and HK).  In China we where playing with a 29erC rigs, and they have wiglets on the tips of those rigs.   Just tried to dig out a photo, there is a video doing the rounds somewhere.  

   

This is the only photo I have "to hand" of all 3 boats in Longchi, look at the top aft corner of the 29erC.   It works.

And re Heel, just did a real simple dwg of a boat, extended the mast height to exaggerate the effect.

image.png.4b6ad3a147c807f3ed4868554865d124.pngimage.png.887b73094b969c93263df4f9e4f853a9.png

First dwg is side on, pretty simple.  Mast has 7° rack, 3-4% bend, pretty std for a pin head rig (I have drawn square, obviously).

2nd dwg is looking at the rig from 22° to windward from head on, so how the wind see the rig!

Blue is a vertical line, red is the mast, its at 2.36° to windward, if you then add 5-7° windward heel that's not insignificant.

Interestingly the jib luff is at almost 10°.   Had not thought about that before.   Possibly why jib work so well.

It not the only reason people heel the boat to windward, I actually wrote something about it back in the 80's, and others where doing it years before me, but efficiency of the rig is helping, not hurting.

                Jb

       

image.png

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What do you think about cutting notches in the track so it doesn't resist the compression when mast bend is induced?

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Can't help thinking it would greatly increase luff tape wear... I've got the opposite - a Bethwaite wooden wing mast with a balsa wood leading edge, and that has saw cuts through the balsa to stop it succumbing to tensile loads when the mast bends.

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Yeah, I don't think it would be good for the bolt rope, could do some pinching. But then if you pull your mains up with the mast under compression I guess the gaps disappear, if they're doing what they're supposed to be doing. 

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Hi guys, it only really works if you cut right through the track, which is why we went plastic.

But it dose work, my son cut the carbon track on the back of the 18teen and it dose allow the mast to be bend more.

Increased bolt rope wear is pretty trivial, if you do a good job of cleaning up the track after you cut.

           Jb

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On 2/23/2019 at 6:42 PM, WCB said:

Where does one buy Lexan sail track?  Asking for a friend. ;) 

Didn't see if this got answered. Composite Engineering in MA (US) somewhere.

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9 hours ago, Chris Maas said:

Didn't see if this got answered. Composite Engineering in MA (US) somewhere.

Thanks for checking in on this, Chris. Yes, Composite Engineering is who I ended up buying from. I'm stoked. 

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I also have a Weta and have noted the issue with the Square Top sail causing the bolt rope to come out of the track - it does help if you hoist it with the gennaker and jib halyard slack so that the mast is able to bend with the sail. But it also tends to jump out of the bottom - possibly because the bolt rope is slightly thinner.

However, one of our local Weta owners urgently needed to replace his worn sail track and was supplied with a black track used for skiffs and 29er/49ers by a local rigger. The rigger also said that they now only supply the black track because it's more effective and I think I can see why in the images below.

Compare the C-Tech White Track with the Black Track and you can see the that the black track has thicker walls and a bead where the sail exits which helps to keep the sail in the track.

C-Tech Sail Track

sailtrack_end03.jpg

29er/49er sail track

21075_4800x528_2_4.jpg

Finally there is this track supplied by Ovington Boats for the Musto Skiff which not only has the beading but also more sidewall support.
61121_1.jpg

CST marine supply both fibreglass and carbon sail track.
https://cst-marine.com/fibreglass-sail-track/
https://cst-marine.com/carbon-fibre-sail-track/

Hope this helps
Paul
Weta #325 & #1148
Sydney


 

 

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Interesting!

Do you have any info or thoughts on how it compresses when the mast bends when putting cunningham on aggressively? Early iterations of 49er/29er mast tracks reportedly didn't compress/bend with the mast, so the top of the mast would twist/turn sideways a bit.

Edit: I'm not paying attention -- the track bend/compress discussion was brought here by Julian earlier. I still wonder how the different tracks compare in that regard. 

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We're still working through this in the RS800 class. Lots of discussion about the alloy track versus plastic. 

As I said up thread we used to have plastic, then swapped to alloy, solely because the plastic gets brittle and opens up or even snaps. Unfortunatley we never measured our mast before swapping tracks to get a definitive comparison. 

I have though measured  our mast with an alloy track the pre-bend at 5 points up the mast. I then stuck our friends mast on, which had a plastic track on and did the same. OUr theory was the plastic track would show greater pre-bend for the same rig tensions and rake because the plastic track was less stiff. 

Now, there are issues. We have fixed spreaders, however, theirs were fixed in a different position. And, whilst the change in track material was the obvious difference there could be other differences in the lay-up of the bare pole (there should be as they both come out of selden and are supposed to be one design!). 

What were the results? Did the mast with the plastic track have more pre-bend for the same rig tensions? 

Well, no. More tension in the caps and shrouds = more pre-bend. More tension in the lowers = less pre-bend.  But for the same tension the pre-bend on both masts was very similar (despite spreader deflection being different). 

The biggest surprise was how much cap tension affected pre-bend low down. I don;t have the numbers below, but pulling on more caps increased pre-bend significantly throughout the mast, even down to the gooseneck. I was expecting it would predominately change the top 3rd or half. 

Obviously this is static pre-bend. When sailing with Cunningham and kicker on the caps loosen as mast compression is coming from the sail controls. At this point you'll want enough caps to support the upper mast and stop it dropping off to leeward. So, maybe dynamically, on the water, cap tension isn't that critical as it's soon 'over ridden' by sail controls. I'd like to hear some experts opinion on this. 

But, I still came away with the feeling that if the alloy track were making the mast much stiffer forward-aft then we should have seen less pre-bend for the same tension for the alloy track. I still have a nagging feeling the plastic tracks allow more mast bend, but the numbers I have don't back this up.

See below the RS800 rig set up. The numbers don't show our complete measurements, we did lots of other stuff but I'm just including what I think are the most important measurements. Probably the only significant number not in the reduced table below is rake, which was within 2mm for the two masts. Mast bend was measured my holding twine tight from masthead crane to mast foot, then measuring the distance forward to the mast track at selected points on the mast. 

distance in mm, tension in loos. 

image.png.41587dd22e3ac94fff39f82571a6013c.png

image.png.c312d683e6a92b29af0cea4d53255c86.png

IMG-20190629-WA0017[1].jpg

IMG-20190629-WA0038[1].jpg

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Might be easier to check with the mast alone supported by saw horses with a tape measure and weight on end of mast.

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5 hours ago, John D said:

Might be easier to check with the mast alone supported by saw horses with a tape measure and weight on end of mast.

I thought that... but then when we got to do it it's very hard to hold the mast without damaging the track. Also, given the length of the mast you need a huge amount of weight on the mast foot. Quite tricky. Just felt easier to wang on the tension and tip the boat on its side. 

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Sawhorses and weight in middle also works for deflection, 10kg should get you plenty, but those deltas are very small Mozzy.

I've dicked around with changing glass track to carbon track and actually the effect is not massive, and suprisingly not massive at tip, as whilst the track becomes a bigger cross section with respect to mast section, the parallel axis contribution reduces.

I would agree that in twin spreader rigs, the leeward cap slackens once full vang and sailing loads are applied. Windward one will be looser upwind than on the beach.

Until that point it backstays the mast a bit, so can be losing power in light.

I think if caps too loose, mast tip falling to leeward maybe doesn't keep rest of mast in column and maybe reduces forestay tension. And mamybe affects sail further down the rig as a consequence. Doesn't matter re: power as above the hounds is not doing much once twin trapping and easing a litle sheet. Caps deffo affect mast in dock trim i.e. on beach down to lowers attachment.

Loose lowers downwind in breeze is dodgy on masthead rigs.

Some i14 rigs these days predicated on looser lowers and tighter caps (bear in mind in dock trim these work against each other, so redcuing one and tightening the other is magnified in distribution of prebend - hence you will notice when tightening caps that lowers tighten up) not sure if they go slack on leeward side.

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Thanks, that's useful information. I don't know why I didn't think of putting the mast with the track up, ends on benches and weight in the middle! 

One of the additional problems of the caps on the 800 is they are joined to another at the base. As the mast tip is pushed off to leeward the windward cap shroud gets tighter as it resists (so far so good). However, because they are joined at the bottom, this tension in the windward cap shroud and loosening of the leeward cap shroud causes the fitting which both attach to, to rotate about the mast and up to windward. This redistributes the tension between the cap shrouds, effectively the windward cap shroud lengthens and the leeward shortens to redistribute the tension between them. This allows the mast head to drift off to leeward and is exactly what you don't want.   Basically when the fitting to which both the caps are attached moves up to windward at the bottom of the mast, you know the mast tip is doing the opposite. 

It's unlike the 49er (or maybe 14, I dunno, never sailed one) where the cap shrouds are tensioned independently, the leeward cap shroud very rarely goes slack. Which is obviously bad, as no matter how tight you do the cap shrouds up they always are pushed off to leeward quite easily. (i'm not sure if I explained that very well?).  

I read an old thread on here from 2009 when the new 49er rigs and sails came out which was looking at measuring luff curve of the main laid out flat then matching to mast pre-bend to get a proportional curve. Any advances on that or what a method would be for doing this?

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So to get this thread back on track (;)), My Square Top Weta sail was occasionally pulling out of the original white C track at the bottom of the mast - and I had to drop the main it in a hurry to get in to a narrow ramp in a blow which permanently damaged the track.

So I took the opportunity to replace the bottom 30cm with the thicker 29er/49er V track (using Selly's Armourflex adhesive) and I haven't had any problem since, although the V-section of the track means the bolt rope is a bit loose but the reinforced track edges make it harder to pull out. I plan to do the same with the top of the mast. I'm also sending samples to Weta Marine to suggest they switch to the V track - does anyone know who makes it?

Paul
Weta #325 & #1148
Sydney

On 9/23/2019 at 4:33 PM, Pewit said:

 

29er/49er sail track

21075_4800x528_2_4.jpg

 

 

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