Better on one tack than the other upwind

NicoW

New member
2
1
Hi,

as others here I do not trust speedo so much. I had the same problem a while back, and I will pass over the advice they gave me: look for something else than the speedo to measure the assymetry.

Do you see anything different from tack to tack if you look somewhere else than your speedometer? Try to look from different angles. I could tell you where I looked, but I am sure you know better where to look: it is your boat.

Generally, I find that I do too much pronostics (actions), and too little diagnostics (measurements).

 

danstanford

Anarchist
610
151
Lake Ontario
Hi,

as others here I do not trust speedo so much. I had the same problem a while back, and I will pass over the advice they gave me: look for something else than the speedo to measure the assymetry.

Do you see anything different from tack to tack if you look somewhere else than your speedometer? Try to look from different angles. I could tell you where I looked, but I am sure you know better where to look: it is your boat.

Generally, I find that I do too much pronostics (actions), and too little diagnostics (measurements).
Nico, it has been the inability to trim the main properly on port while easy on starboard combined with the speed difference that has prompted the questions.

 

DickDastardly

Super Anarchist
3,867
255
Syderney
Assuming your mast is in the middle of the boat , your keel is symmetric and weight distribution is equal 

First check your speedo for accuracy 

second check your wind instrument for accuracy

third check for wind sheer 

forth record your rudder angle ....tack to tack 
fifth, learn to spell fourth

 

Spoonie

Anarchist
742
91
Sydney
This is another one of those "a good coach in a coach boat would probably see the problem in about 15mins"  type problems.

Let's assume the performance difference is real.  And that when trimming both sails, exactly the same way on one tack over the other,  and sailing the boat exactly the same way on both tacks, you get a bubble in the front of the main on one tack and not on the other.  

This means one of two things:

1) the pressure at the front of the main is higher on one tack than the other

2) the angle of attack of the main sail is different on one tack than the other

If it is 1) then the mostly likely causes are:

  • Your jib is not sheeted the same way on both tacks. 
  • The sheeting positions, relative to the main are different on both tacks
  • The position of the main relative to the jib is different on both tacks (that is the mast is moving disproportionately on one tack to the other.)

If it is 2) then the most likely causes are:

  • The main is not sheeted the same way on both tacks
  • The sheeting positions, relative to the mast are different on both tacks
  • The position of the tack and luff of the main is different on both tacks. 
  • The tension on the luff is different between tacks.

The last two points might occur if say the tack is not in the middle of the mast, or say the cunningham pulls the tack to one side.

In lieu of a coach or coach boat.  Mount a go-pro to your spinnaker pole ring looking straight up the mast, then go do a couple of tacks.  Also, take some photos at the gooseneck looking to the top of the mast on each tack.  

Another option is to tie a piece of string to the clew of your main.  Run it to the clew of your jib and mark it.  then tack and repeat.  If it gets longer or shorter then the trim of the main compared to the jib is different.  

Other possibilities are you're pinching on one tack more than the other, or something really wonky with your boat.

We are comfortably hitting our polar target on the weaker tack though perhaps not able to point as high as we might like, especially at higher wind speeds where we are managing the traveller to keep the heel in range and the rudder engaged. 
Not pointing as high compared to what?  do you hold the lane on what tack but not the other?  If you're hitting your polar then is there a problem?  Are you subconsciously creating a problem?  How much faster than polar are you on the other tack then?  1 knot up?  You recently stepped the mast, was there a problem before you stepped the mast?

My gut feel is a few things:

1) your speedo is reading differently on one tack than the other

2) you're subconciously or unknowingly sheeting sails differently on one tack to the other.  Either because of the way you're sailing the boat or because gear is not in the same position on both tacks.

3) your mid mast is sagging between the hounds on one tack more than the other.  I would have thought it'd have to do that a lot to make such a big difference.  But I could be wrong.

4) some combination of all the above

There are a lot of controls that can affect the way your boat is sailing from one tack to the other, and especially the way alu masts are manufactured (if it's Alu) plenty of reasons why it might be stiffer on one tack than the other.  Without pictures or video, if we as a group happen to stumble on an answer in this way I'll be amazed.  

But IMHO start with " what is the angle of attack of this main on one tack to the other"  and " what might be causing increased pressure on the leeward side for one tack than the other"  or even "is the difference real and measurable outside of the boat" and go from there.  

 

danstanford

Anarchist
610
151
Lake Ontario
This is another one of those "a good coach in a coach boat would probably see the problem in about 15mins"  type problems.

Let's assume the performance difference is real.  And that when trimming both sails, exactly the same way on one tack over the other,  and sailing the boat exactly the same way on both tacks, you get a bubble in the front of the main on one tack and not on the other.  

This means one of two things:

1) the pressure at the front of the main is higher on one tack than the other

2) the angle of attack of the main sail is different on one tack than the other

If it is 1) then the mostly likely causes are:

  • Your jib is not sheeted the same way on both tacks. 
  • The sheeting positions, relative to the main are different on both tacks
  • The position of the main relative to the jib is different on both tacks (that is the mast is moving disproportionately on one tack to the other.)

If it is 2) then the most likely causes are:

  • The main is not sheeted the same way on both tacks
  • The sheeting positions, relative to the mast are different on both tacks
  • The position of the tack and luff of the main is different on both tacks. 
  • The tension on the luff is different between tacks.

The last two points might occur if say the tack is not in the middle of the mast, or say the cunningham pulls the tack to one side.

In lieu of a coach or coach boat.  Mount a go-pro to your spinnaker pole ring looking straight up the mast, then go do a couple of tacks.  Also, take some photos at the gooseneck looking to the top of the mast on each tack.  

Another option is to tie a piece of string to the clew of your main.  Run it to the clew of your jib and mark it.  then tack and repeat.  If it gets longer or shorter then the trim of the main compared to the jib is different.  

Other possibilities are you're pinching on one tack more than the other, or something really wonky with your boat.

Not pointing as high compared to what?  do you hold the lane on what tack but not the other?  If you're hitting your polar then is there a problem?  Are you subconsciously creating a problem?  How much faster than polar are you on the other tack then?  1 knot up?  You recently stepped the mast, was there a problem before you stepped the mast?

My gut feel is a few things:

1) your speedo is reading differently on one tack than the other

2) you're subconciously or unknowingly sheeting sails differently on one tack to the other.  Either because of the way you're sailing the boat or because gear is not in the same position on both tacks.

3) your mid mast is sagging between the hounds on one tack more than the other.  I would have thought it'd have to do that a lot to make such a big difference.  But I could be wrong.

4) some combination of all the above

There are a lot of controls that can affect the way your boat is sailing from one tack to the other, and especially the way alu masts are manufactured (if it's Alu) plenty of reasons why it might be stiffer on one tack than the other.  Without pictures or video, if we as a group happen to stumble on an answer in this way I'll be amazed.  

But IMHO start with " what is the angle of attack of this main on one tack to the other"  and " what might be causing increased pressure on the leeward side for one tack than the other"  or even "is the difference real and measurable outside of the boat" and go from there.  
What a great piece of writing and loads of things to think about. 

Thanks for your very reasoned response and please know I will spend the time to get through all of these and report back.

Dan

 

lyvet

New member
26
6
Is the keel true? (i.e. properly aligned along the centre line of the boat) and is it vertical?

Don't laugh:- I've seen instances when this hasn't been the case.

 

Gouvernail

Lottsa people don’t know I’m famous
37,677
5,243
Austin Texas
Measure EVERYTHING. Invent stuff to measure:

Measurement suggestions  I didn’t notice while skimming through the posts:

* bow chainplate to jib sheet leads

* side shrouds to jib leads 

* spreaders to deck

* spreader sweep

* standing behind boat. Sight over a level held crosswise ..  are the spreaders symmetrical?

* put an long foot lEvel across the deck and see if the chainplates and jib leads are at symmetrical heights below said level

***I am not suggesting below the water keel and rudder measuring because the sail shapes are different. The keel and rudder may be out of whack but that has zero to do with asymmetrical tack to tack sail shapes

*maybe the boat is bending, or an important bulkhead is lifting under load

Maybe you can measure whether the chainplate is riding with respect to the mast and deck and other chainplate?? Maybe put a straight edge across the boat and go sailing. Do the numbers change?

* simple at dock measurement :

On many boats with “sick” compression posts or loose bulkheads I can feel the movement at the dock. I reach out and grab the lower shrouds. If the deck goes up and down when I pull them together, we have a problem 

**
cracking or loose keel cross braces ( floors)? If the keel is bending to weather and lifting the entire weather side of the hull or pulling the leeward side down inappropriately the parts above it could be thrown out of whack

* are the deck chocks letting the mast move only one sideways direction? Is the deck soft right next to the hole where the mast goes through?? Maybe it takes more load to push the mast sideways than is noticeable standing at the dock

* maybe you need to measure distances like bow chainplate to jib leads, mast to jib leads, and spreader tip to jib leads out on the water. It might take a couple thousand pounds to deflect whatever is moving. 
 

….. 

Sorry if I am suggesting a lot of time at the boat and sailing.  Perhaps if you drink beer while doing all of the above you will feel better

 

G-Shack

New member
12
0
UK
One whole knot!! Are you sure you aren't dragging your outboard along on one tack? 

In all seriousness what kind of boat is it? I would check:

  • Jib tracks from CL
  • Keel alignment 
  • double check mainsheet car is the same distance from CL on both tacks
  • double check the backstay is on the CL (forestay, mast base and Backstay must all be on CL (or at least symmetrical if using runners)

Then it's into the rig setup which isn't always as simple as the guide. 

  • Assume rake is OK (it may not be but isn't a tack to tack issue) 
  • Check chain plates are same distance from Forestay both sides
  • Check spreaders are same length and same angle 


    Length with a tape measure
  • angle by tying a string between the tips and between the shrouds near the deck - sight up (or down) and make sure lines are parallel 

[*]Take all tension off lowers (or D1s and D2s - can't remember what boat type

[*]Tension main shrouds 

[*]measure if the hounds are in the middle of the boat (fish scale technique above is a good one) 

[*]if mast step is not on CL then do some head scratching but ultimately get it on the CL 

[*]if spreaders are square and hounds are on CL the mast should be straight sideways 



Next go to your D1's

  • Tighten them evenly so they are a little tighter than the guide (a higher tension makes one turn more sensitive) 
  • Adjust them so that the mast is straight side to side 
  • Now do the same with your D2's (if you have them) 

Now you can adjust shrouds and D's to your tuning guide but make sure you do even turns on port and starboard - small D tension variation side to side can make your main look different tack to tack. The fact you have a bubble at the luff means the main is either to deep or the jib is sheeted closer to CL or firmer in the leech on one tack. 

Failing all this then bend test your mast. It is possible that the wall thickness isn't even on port and starboard which would cause a difference but that's pretty unlikely. 

Also the only real way to know if you are fast is to line up against other boats on both tacks. Who cares what the speed says. That's a whole other problem on instrument calibration. 

Hope that gives you some ideas. I would check the keel alignment as the other factors won't make a knot of difference. 

 

G-Shack

New member
12
0
UK
Reason keel would make a big difference is that if it's 1 degree off the rig will effectively be 2 degrees more open or closed to the wind from one tack to the other. Imagine if you are always footing one degree on one tack and pinching one degree on the other. It's going to be a significant factor. 

Also the jib would effectively be sheeted closer to AWA on one tack than the other even if the deck is symmetrical so this may explain your luffing main on one tack even if the rig is perfectly aligned with the deck. 

 

Knut Grotzki

Anarchist
502
159
Germany
We are finding the boat a full knot quicker on port than we are on starboard and for sure we have a fairer shape to the main on port with quite the bubble in the luff of the main on Port. 

We tuned the mast using the North Guide and a Loos Gauge when we stepped the mast and I plan to go back to review it now in pursuit of a solution. Looking at the sail it occurred to me that a hook in the middle of the mast might cause this but sighting up the mast one is not obvious. 

Where would you Folks look first for a solution? We are comfortably hitting our polar target on the weaker tack though perhaps not able to point as high as we might like, especially at higher wind speeds where we are managing the traveller to keep the heel in range and the rudder engaged. 

Dan
You might consider the coriolis force.

"Cruising and the Coriolis Force

Wind shear: Due to the Coriolis force, the angle of the wind turns from the mast top downwards, counterclockwise, i.e. to the left (shears). Consequence: The pressure point is different depending on which bow you are sailing on. Wind shear reaches values of up to 20 percent.

On starboard tack (i.e. with wind from starboard) the wind at the masthead comes more aft, the boat heels more strongly. The helmsman lets himself be tempted by the failure of the clicker to steer a little higher, but this leads to greater drift and the speed drops.

Remedy: trim more twist on the starboard tack and flatter on the port tack.

Nevertheless: With the wind from starboard you can point higher due to the wind-shear effect.

Incidentally, the neglected wind shear is usually the reason why boats sail at different speeds depending on the bow. The true angle of incidence of the wind is different on the starboard and port tack.

windvonstbtable50.gif
  
windvonbbtable50.gif


(edited translation from https://www.sailpress.com/richtigkreuzen/index.html  as port and starboard "tacks" are the other way around in Germany).

Discussion started...

 

danstanford

Anarchist
610
151
Lake Ontario
Took the great advice from this thread to the boat and did some review for a few minutes yesterday. I found a couple of things which might be a start and perhaps when combined with the speedo would get me most of the way there. The lowers D1 were much tighter than spec'd and a bit asymmetric plus I found the starboard inhauler jammed up which probably means it was set in when it should not have been which was likely the cause of the bubble. The breeze was quite heavy for the canvas we had up so everyone was on the rail and nobody went to check the jib sheet angle....won't happen again. 

The tuning guide calls for 7 on the Loos 2 gauge for the D1's and the Euro version of the tuning guide calls for these to be 28! 7 is so loose as to be floppy, why would they be so loose? 

Sailing Wednesday and will report back.

Dan  

 

Spoonie

Anarchist
742
91
Sydney
The tuning guide calls for 7 on the Loos 2 gauge for the D1's and the Euro version of the tuning guide calls for these to be 28! 7 is so loose as to be floppy, why would they be so loose? 
Depends on what the other settings are.  Someone is trying to induce bend lower down the mast.  Typically that results in a straighter mast from the spreaders upwards.   Means a flatter main at the bottom but fuller mid and top sections.  Also might result in less forestay tension as the mast compresses so your jib knuckles up.  

Where as tight D1's result in a more rigid lower section pushing the bend further up the mast.  That means the mid/head of the main is likely to flatten more and the forestay remains tighter, so a flatter jib.

I'd say, and I could be wrong, the 7 setting is medium to light air in sloppy water and the 28 setting is heavier air/flatter water setting.  

With two very different settings between two different tuning guides, I'd say the respective authors have different philosophies on how to sail your particular boat.  The 7 guy is probably fatter and likes to sail low "bow down" in the groove while vang sheeting.  The the 28 guy is probably lighter and likes to pinch.

Someone is surely going to come along and tell me I'm wrong though I'm sure... 

 

danstanford

Anarchist
610
151
Lake Ontario
Depends on what the other settings are.  Someone is trying to induce bend lower down the mast.  Typically that results in a straighter mast from the spreaders upwards.   Means a flatter main at the bottom but fuller mid and top sections.  Also might result in less forestay tension as the mast compresses so your jib knuckles up.  

Where as tight D1's result in a more rigid lower section pushing the bend further up the mast.  That means the mid/head of the main is likely to flatten more and the forestay remains tighter, so a flatter jib.

I'd say, and I could be wrong, the 7 setting is medium to light air in sloppy water and the 28 setting is heavier air/flatter water setting.  

With two very different settings between two different tuning guides, I'd say the respective authors have different philosophies on how to sail your particular boat.  The 7 guy is probably fatter and likes to sail low "bow down" in the groove while vang sheeting.  The the 28 guy is probably lighter and likes to pinch.

Someone is surely going to come along and tell me I'm wrong though I'm sure... 
Spoonie, the 28 came from the European Tuning Guide from North and the 7 from the North American one. The other settings are different but not so drastically. 

I wondered if the D1's might be so loose as to allow more mast bend from the back stay tightening.

This is the base setting for 10 knots of wind.

Dan 

 

Spoonie

Anarchist
742
91
Sydney
North says North American made mast and European mast are very different stiffness and this is why the shroud tensions are different. 
Well there you go.  that makes sense.

the way I think about this is to imagine bending a batten.   If you take a batten and bend it , it forms a fair curve.   If you push that curve one side or the other, one side becomes more round, and the other becomes more straight.  If you bend the batten more the distance between the two ends gets shorter.

 

WHK

Super Anarchist
1,645
97
Newport, RI
quod umbra said:
...

The other thing I would suggest to you, people all the time sight up the main track and try and determine if the mast is in column. Uhhhhhh....okay.
What I do is establish a reference point both port and starboard as discussed above I do believe. Then take a sail slug. run that up the mast on the halyard and tape measure and measure at the termination of the uppers, intermediates and lowers from side to side.... adjust as necessary.
Here is another tip to check the mast in column.  Make sure the halyards, vang and backstay are slack so only the standing rigging is positioning the mast.  Stand about 10 feet behind the mast in the center (on my J/109 I stand in the companionway) and take a picture up the mast so you can see the top of the mast and as low on the mast as you can get.  Drop the picture in PowerPoint and draw a straight line up the mast track.  Easiest if you drop the two end points, then blow up the picture and position each end point on the mast center.  It will become very apparent if you have any curves in the column when you expand the view and go up the drawn line.

 
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