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Fast on port, slow on starboard


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I've been able to achieve my target polars consistently when on port tack but once I flip over I stall out about 15 - 20 degrees below where my target wind angle should be. If I poke up once I get within 10 degrees of where I should be I'm about 40% of the boat speed I should be hitting at that angle.

I suspect my mast is not straight and that it could be favoring to the starboard side of the boat. But before I start to redo the rigging I wanted to get some thoughts.

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What are you using to measure speed and point?  If the Speedo isn't centered and calibrated, it can read different from side to side!  Compass off?  Windex Handlebars skewed?  I had one club member tell me a similar malady.  I walked up to his boat and noticed that his Windex handlebars were skewed about 20 degrees.  Centered them up, and everything was better!   

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I have B&G equipment. Precision 9 compass. I've calibrated it twice this season. Calibration seems simple enough with doing the circle so I'm not sure how else I could be improving that, unless it needs calibration every time I kill the power on the boat.

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If not one-design, and you don't have a well-tuned sistership to trial against, then as Silent Bob says calibrate calibrate calibrate.

Meanwhile, it won't hurt to do basic tuning checks on the mast. Check that the mast head is centered, sight up the track to make sure it's in column, measure the rake, measure the prebend. Write it all down.

If you can, give some attention to underwater too. It's possible that the keel is off-kilter or asymmetric. I've also see twisted rudder blades (transom mount) do the same thing. A mass of barnacles on one side of the keel.

If the effect is as large as you say, it's likely to be something pretty noticeable.

FB- Doug

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23 minutes ago, Steam Flyer said:

[  .  .  .  ]   It's possible that the keel is off-kilter or asymmetric.  [  .  .  .  ]

Indeed and that's a hard one to spot.  Raced for a few years on a 52 footer and it definitely was slower on one tack.  Pointed 3° lower to achieve boatspeed targets.  The B&G pros, riggers and sailmakers checked everything out and couldn't find anything wrong.  Two years later during a haul to install an elliptical keel it was discovered the original keel had been bolted to the hull with a 2" skew.

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This is generally an instrument issue. Either speedos off side to side or twa is off. It takes a lot of time to get twa right and is easy to have all f*cked up. 

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26 minutes ago, IMR said:

This is generally an instrument issue.

^^^^^This^^^^^

I mean real simple question from this, have you used an independent hand held GPS to measure SOG on both tacks?  is the difference more pronounced when the boat is healing (upwind) vs not (downwind)?  When you are sailing against other boats, do you get disproportionately smoked on starboard tack?  40% off is a lot.  If that was real, you would certainly know about it as other boats whizzed past you.

First rule of instrument based systems is they're probably wrong.

Second rule of instrument based systems is... well you get the idea.

IMHO People get too fixated on what their instruments are telling them anyway.... (see rules 1 and 2 above)

 

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Seems to me that simply sailing the boat on a nice day with all the instruments covered would clarify the situation. Even better if along side a similar known good boat (like someone suggested above). Rig and hull asymmetries have very little effect and are rare.

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This is a 24' boat, and you're relying on instruments to tell you how the performance is? How does it feel on each tack. Center the windex and go sailing. Screw the instruments except the windex  and GPS speed. 

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A key question is whether the helm is the same on both tacks.  Had a customer back in the day with a C&C27 complaining about different performance on opposite tacks.  Went for a sail with him and there was nothing obvious above the water line, but had weather helm on one tack and neutral to lee helm on the other.  Didn't need any instruments to tell the difference.  I offered the opinion that it could be the keel but more likely the rudder was bent or otherwise deformed.  Owner bit the bullet and did a haul out and sure enough the rudder was misshapen.

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12 hours ago, bcardarella said:

I've been able to achieve my target polars consistently when on port tack but once I flip over I stall out about 15 - 20 degrees below where my target wind angle should be. If I poke up once I get within 10 degrees of where I should be I'm about 40% of the boat speed I should be hitting at that angle.

I suspect my mast is not straight and that it could be favoring to the starboard side of the boat. But before I start to redo the rigging I wanted to get some thoughts.

Lets assume that you are not sailing in waves that would legitimately give you different performance all by themselves.

Does your boat heel differently on each tack?

Are you right handed ? Do you sit in same position on each tack? or do you sit further outboard on port and inboard on starboard?

Your masthead wind sensor may be reading differently, due to offset angle at installation, or asymmetric disturbance from masthead crap if it's too close to it.

Speedo offset to one side may be reading differently, but COG and SOG will be independent of heel, leeway etc.

Measuring your mast;

  • Centered to your hull at deck without loading
  • Centered to your hull at various points on height (put a line on the main halyard, and a loose sail track slider and measure at several heights)
  • Symmetric under loading (Take photos of the mast shot from the gooseneck, measure with an auxilliary halyard)
  • Is your back stay tension centered

Are you sheeted at the same trim angle, NOT just the same hole on the track ?

  • Jib Car
    • Thwartships
    • Fore and aft
    • Height of block
  • Traveller for Main
    • Position vs centerline
    • Sheet tension if not all blocks on traveller
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I'm gonna jump here for ideas/advice since I'm having a similar problem.  pretty sure I know why 

big cruiser old fat cruiser 37' probably close to 18K lbs when provisioned.  Stbd tack is slower than port confirmed by two different instruments (navionics on a cell phone and raymarine st60+)  yeah I know navionics on a cell phone is hardly an "instrument"  but .5 to .75 kts difference....

same day similar conditions each tack. letting otto take the helm slaved to the wind instrument and also sailing by hand.   

In my situation  the port side side of the boat is heavy.  Genset, galley, refer, liquor, food, and holding tank, are all on the port side of the boat.  and the boat has a port list while in the slip. the only heavy things on the stb side are the house batteries

My assumption, in my case that i've got more "meat" on the rail by virtue of my unbalanced loads.   Seat of the pants feels better and more planted on port tack vs stbd.  accelerated out of the tack much better.   sails are similarly trimmed, jib cars in the same spots (counted holes, did not measure)

I should run the tape measure up the mast and check for squareness as well...

In the mean time  i think I'll spend some time moving things around that can be moved.  move the liquid refreshment to the stbd side.  move my tools, pump out the holding tank, etc.  but  not much I can do about genset, refer, or galley...

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As far as weight difference in the boat goes, yes there is some additional weight to starboard. I have a 6hp engine mounted on the transom that weighs bout 60lb and a gas tank that is about 10lb. The anchor is also low in the midsection of the boat but on the starboard side and that weight about another 60lb. The boat itself weight just under 1T so the additional 120lb - 140lb would account for just 7% additional weight. The crew itself on the day that I was recording the difference was about 350lb - 370lb so after the crew weight added t the boat weight as that would be swapping on each tack the static weight on the starboard side is a little under 6% additional. I don't think this amount would result is the effects that I'm seeing.

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This is unscientific and probably incorrect, and no offense intended, but..

Are you steering with a tiller?  So on port tack you steer with your right hand.  And left hand on starboard.  Is maybe one arm/hand "better" than the other?

Goofy idea I know, but the upside would be you don't have to spend money or change your rig.

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4 minutes ago, bcardarella said:

Yes I am steering with a tiller but if I am steering to the instruments what difference would it make?

Maybe none, just a thought.  And if it happens the same with someone else at the helm, please shitcan my question.

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1 hour ago, bcardarella said:

... but if I am steering to the instruments...

If your instruments are telling you you are 40% off and 10-20deg down, you need to stop doing that.  Go back to basics and sail the boat. Get some other reference point; an analog compass, other competitors, hand held GPS. 

Without sog and cog numbers, I'm willing to bet you're sailing your boat into oblivion because your instruments are telling you to.  

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On 6/20/2021 at 5:34 PM, silent bob said:

What are you using to measure speed and point?  If the Speedo isn't centered and calibrated, it can read different from side to side!  Compass off?  Windex Handlebars skewed?  I had one club member tell me a similar malady.  I walked up to his boat and noticed that his Windex handlebars were skewed about 20 degrees.  Centered them up, and everything was better!   

lol this was my first thought too. Couldnt figure out why we werent pointing as high on stbd until i took a closer look at the windex and it was about 10 degrees off.

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Center your rig and tune it to spec, make absolutely sure your windex tabs are centered. Cover your instruments and sail in consistent breeze and flat water preferably on a slack tide. Use GPS to guage your speed and your windex your height. 

Do a quick windshot(note your compass heading), sail briefly on both boards and note your headings. This will give you a pretty good idea how close or far off you are. 

I don't believe your instruments one bit. If your speed and point are down 40% and 20degrees respectively on one tack, your competition would sail right by you on that board. Those are HUGE deltas to be off. 

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I was able to get out to the boat this AM. I could sight up the mast that it was visibly hooking to starboard. I re-tuned the mast got it as center as I could and measured to within a few milimeters.

While looking up the mast I did notice that my wind instrument was twisted a few degrees off to starboard. I suspect my apparent wind readings may be askew and this would affect my true wind and VMG calculations. I could go up the mast and try to make an adjustment but I think it would be easier to just offset it on the instrument calibration. I've never done that but I imagine it would mean pointing upwind then setting the apparent wind angle to the compass heading?

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17 minutes ago, bcardarella said:

While looking up the mast I did notice that my wind instrument was twisted a few degrees off to starboard. I suspect my apparent wind readings may be askew and this would affect my true wind and VMG calculations. I could go up the mast and try to make an adjustment but I think it would be easier to just offset it on the instrument calibration. I've never done that but I imagine it would mean pointing upwind then setting the apparent wind angle to the compass heading?

Depends on your instruments, some allow you to enter a correction table for different speeds, some just an offset angle.

if you simply weathervaned, or motored dead up wind, do you see an angle other than 0 +/- 2 degrees correct that out first.

Given you have straightened your mast at the dock, recheck it after a few tacks when the hull & rigging settles., sight up it, and take photos.

Is the mast base centered (deck or keel step? ) is it centered and then stays centered under load at partners, if keel stepped (are your wedges same thickness &  hardness)

If you can, remeasure while loaded. A tension gauge is better than none, to assess rig tension, and if you apply more tension, realize that the hull will flex and settle 

 

regarding right vs left hand, consider a tiller extension, may allow you to sit with feet braced and use one hand on both tacks...

 

 

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Setting aside that TWD and VMG values are relatively useless to a sailor — Your apparent instrument value can be easily calibrated by simply tacking up a course on a nice day. Thru many tacks watch the instrument as the bow and headsail pass thru the wind. Even pause at the helm when the headsail and main seem centered. Also compare P & S close-hauled values. Tweak the correction up and down until the readings seem best.

Keep in mind that unless your sensor is a meter or two above and ahead of both sails it is not in the actual wind flow but rather in a flow bending around the sails. Makes the actual numeric value somewhat useless for fancy calculations while still being valuable to the sailor for optimizing sailing performance.

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My instruments can calculate target boat speed and target wind angle from my polars and produce a VMG performance %. So while the actual TWD and VMG values alone aren't helpful they are useful for those other calculations which are helping me isolate and diagnose some of these issues.

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The way I would do it :

  1. Find a nice and flat piece of water with some offshore breeze
  2. Sail on starboard tack close hauled, note the compass heading
  3. tack slowly, note the wind direction.
  4. Sail on port tack close hauled, note the compass heading
  5. Make the mean between the startboard and portside heading and compare to the wind direction

20º is a gigantic difference so something is really wrong, my bet is that it is the instruments, if not it is really bad and I can't imagine anything apart from a twisted keel or rudder doing this. I don't think that a completely out of plumb mast would have such an effect.

The pros will roll their eyes but IME the easiest way to calibrate TWA is by sailing the boat on a steady day and tweak things until the instruments tell you what you expect.

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5 hours ago, Panoramix said:

The pros will roll their eyes but IME the easiest way to calibrate TWA is by sailing the boat on a steady day and tweak things until the instruments tell you what you expect.

On a 24' 1T boat, I think the pros would have looked at the numbers and turned the instruments off by now.  Fundamental rule of computational systems though, always compare what the computer is telling you against reality.  Plenty of plane crashes (and the odd shipwreck) have happened because the pilots believed their instruments first and reality second.

 

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