Better on one tack than the other upwind

[Spoonie]

The paddlewheel being off-center has a big (negative) affect on the entire instrument system. I have seen up to 1kt difference from tack to tack with an off-centerline paddwheel sensor. Set your instruments to GPS speed, then take data on long tacks to confirm what you are seeing isn't simply a speedo issue.

I think that was my comment in the other thread.  The first rule of instruments is they're probably wrong.  The 2nd rule is...

 

[Pollination]

Just use a gps and check your SOG and COG on both tacks....mark your sheets so that everything is duplicated on each tack. You can also use the Navionics app on your phone. 

 

[SpudH]

What way is your boat moored?

I am tied up on the Southern side of an East/ west orientated marina leg in Ireland.

The difference in marine growth between the south facing side and the north facing side has to be seen to be believed.

Easily a knot between tack speeds when she is fouled up 

Speed differential not marked when she is clean.

 

[Omer]

How about the heel angle. May be your boat carries more weight on one side than the other. May be she is sailing more upright on one tack than the other.

 

[danstanford]

How about the heel angle. May be your boat carries more weight on one side than the other. May be she is sailing more upright on one tack than the other.

I don't have a way yet to measure heel angle but from seat of the pants there wasn't much difference. The biggest reason for me to go down this rabbit hole is the difference in sail shape in the main which indicates something is amiss. 

Dan

 

[Omer]

We sometimes tend to look for a single factor . It is also possible that there is not just one reason but many acting on top of another if you are unlucky enough that they all act negatively in the same direction. If there are four different reasons each causing quarter of a knot difference, you probably would not notice it if the other three was not there. 

 

[danstanford]

If the mast top is plumb and the sail shape is different, then your lowers are the problem.

Your mast shape when loaded is different between tacks.  If the middle of your mast falls to leeward a bit it will hook your main.  If it stays straight or a few mm to windward it will flatten it.  Does not take much and you will not see it at the dock.

Get the spanners out and tweak the lowers till you get the same shape both sides.

I probably should have asked the initial question citing this possible solution as it makes sense to me. I don't want to get too far from standard settings but it does make sense to me that if there is a hook in the mast resulting in asymmetry of sail shape I should be adjusting the lowers to bring back evenness on both tacks. 

I will start with a review of shroud tension and centeredness and work from there.  It is difficult to get all the back stay tension off due to its rigging but I know I should be extra careful there to review mast column. 

 

[danstanford]

Good place to start, but my point was that everything can checkout, apparently, till it's loaded.   I'd sail it and take a photo up the mast on each tack.

Is it a masthead or fractional rig?

Very large fraction, 7/8 or so. 

Great idea about taking a photo, I had even thought about rigging a gopro there to look at how the mast is acting. Due to the way the backstay is rigged, I often think full-on is not enough. 

 

[Mid]

is the rig in the middle ?

 

[Mid]

is the keel on the center line ?

 

[Mid]

is the keel and rudder symmetrical ?

 

[danstanford]

Mid, I am going to give the centeredness one more go round before I proclaim it there but it is reasonably close if you are talking about the top of the mast. If you are talking about the mast base I have never really worked on that so I will look with a measuring tape. As for the keel and rudder, they look fine by eye but I have never attempted to measure them. 

Trying to imagine how to measure these accurately....

 

[slug zitski]

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

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

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 

 

[Mid]

Trying to imagine how to measure these accurately....

 , almost all yachts are asymmetrical , however your discrepancy of a whole knot is extreme .

 

[Mid]

btw , mast base then tune the rig  , bottom up and measure top down .

 

[Mid]

First check your speedo for accuracy 

second check your wind instrument for accuracy

slug has a couple of valid points also , Saints be praised ,  :blink:

it's not unusual for the knot meter to have a favored tack , it's guaranteed to be off center , and a slight bias in the anemometer will also throw things .

 

[terrafirma]

Forget your Speedo FAM and do a proper GPS Speed check on both tacks. 

 

[Delta Dog]

1 knot is a huge difference tack to tack.   Make sure the data you have on performance is correct.   Bring a GPS.   Understand current.   Assume that the data from your instruments is WRONG until you prove it otherwise.   

Once you have correct data, if you really have 1 knot difference tack to tack, look at big stuff.  Are your foils symetric?   Is the rudder straight?   Is the keel on straight?   Are both foils on center line.   Then look at the rig.   Is it on center line and straight?

 

[Gray Skies]

I experienced this on a Peterson 34. It was the sails trimmed differently tack to tack was our clue. After measuring everything including tracks and mast centering that lead to the conclusion the hull and/or chain plates were the culprits. We finally just kept tuning the rig to one side until the sails trimmed equally tack to tack. The difference was about 5/8ths of an inch difference to the mast head.

 

[Lightfoot]

Can’t be said enough. Make sure your on board instruments are accurate first. A lot can throw it off. 
 

the boat I race on has a .3knot difference at 6knots of boat speed between tacks upwind. And the difference gets bigger the faster we go (and smaller the slower) We given up trying to solve it, and just sail it with two sets of polars. 
 

also If you don’t have a hand held gps to get speed, Is there anyone around you with a j99 you can test yourself against? Go pace someone before a race? That would tell you if you are actually slow on one tack.