Why is my boat faster on a stbd tack?

[Sailorbob8599]

God, how I hate to ask this question. Do you leave the bumpers hanging over the side?

[zedpassway]

Easy----Your rigging needs adjustment.

[Oceanride007]

I didn't see wind gradient mentioned, the true wind angle is different at different mast height. In such a case having main sheet traveller set the same distance from centre on both tacks is the issue, similar for car position of jib.

[bruce v]

Originally Posted by Dangen

Hi,
This has been going on for quite a while and I just cant figure out why? And if I recall my previous boat was also faster on one tack. My rigging is perfectly square, equal tension on all the shrouds, Head sail always completely unfurled. The boat is leveled at the dock. Last weekend, we had 12 to 14 Knots true wind and consistently 1 to 1.6 Knots faster on Starboard Tack. I'm very curious to getting feedbacks on this!

As mentioned by others, no sailing vessel is perfectly symmetrical. The sails, rigging and sea conditions also come into play (never mind the wind. LOL.). Try creating your sought equality by adjusting your rigging tune until the performance is what you want, Just be forewarned, there is a chance your overall SOG may be less. you will not know until you try and you can always change it back (Just make sure to mark the rigging before adjusting - easier to readjust that way.

[SURV69]

Do most sailboats track straight from bow to stern?

My Bristol 29 tracks about 10 degrees off in calm waters and virtually no wind, under power.

Anytime I try to point the boat via the bow, I have maintain a vigilant eye on the course ... a few seconds of inattention results in the bow going to port ... quickly and substantially.

When I aim for a course between the bow pulpit and the forward shrouds, the boat tracks rather nicely.

The full keel(with a forward cutout), and what appears to be a straight rudder, line up when sighted with the naked eye.

Maybe ... there's an established reason/cause for some sailboats to crab through the water, and maybe, it might be the answer to the OP's issue?

[crazyoldboatguy]

I've noticed this on every vessel I have ever sailed on. A
major variable mentioned by a couple folks is the simple reality that no hull is symmetrical. Account for ALL other variables - you can't do anything about your hull shape.

[markpierce]

Originally Posted by gjorgensen

Make sure you're comparing SOG on each tack vs. speed from a transducer. The paddlewheel transducer being off center can often read differently on different tacks. ...

That's my thought too.

[snokid]

Originally Posted by Oceanride007

I didn't see wind gradient mentioned, the true wind angle is different at different mast height. In such a case having main sheet traveller set the same distance from centre on both tacks is the issue, similar for car position of jib.

I'm pretty new to this sailing thing...

main sheet traveler is set the same distance from center.
and
jib car's in the same position

Seems like you are hinting it's wrong to do.

would you mind explaining how you know where they should be when sailing?

thanks
Bob

[UNCIVILIZED]

On boats with encapsulated keels, it's not uncommon for the builders to pour the ballast/lead with the mold on it's side. Which frequently causes imbalances in righting moment from side to side. And that of course causes a boat to be faster on one tack than the other.

[Pascals Wager]

Assymetry somewhere is the most likely culprit but as previously mentioned eliminate instrument error first. Calibrate as Civilised described then get into the water and look at your log wheel and it's position. The log reads speed through the water at the water and hull boundary. As such it will be effected by hull friction and flow disturbances from thru hull fittings forward of the log. This friction can be different on different tacks due lee way.
Is the rudder offset different on the different tacks? One cause can be gear stowed on deck effecting windage differently on different tacks. Your rig produces forward force as well as lateral, the lateral force is offset by rudder and keel. More rudder = more drag = less boat speed. Whilst this effect may be minor it needs to be eliminated as a source in your search for the answer.

[Sandero]

also check that your rig tension is the same on both sides... The discrepancy may only become visually obvious in stronger winds.

[Stumble]

Originally Posted by SURV69

Do most sailboats track straight from bow to stern?

My Bristol 29 tracks about 10 degrees off in calm waters and virtually no wind, under power.

Anytime I try to point the boat via the bow, I have maintain a vigilant eye on the course ... a few seconds of inattention results in the bow going to port ... quickly and substantially.

When I aim for a course between the bow pulpit and the forward shrouds, the boat tracks rather nicely.

The full keel(with a forward cutout), and what appears to be a straight rudder, line up when sighted with the naked eye.

Maybe ... there's an established reason/cause for some sailboats to crab through the water, and maybe, it might be the answer to the OP's issue?

Most sailboats do not track strait, in fact most sailboats are grotesquely non-symmetrical out of the factory. This is why race boats are typically delivered from the factory to an optimizer who fixes all of the factory defects. Don't get me wrong, most cruisers won't know or care that their boats are lopsided, and a couple of degrees one way or the other just doesn't matter that much unless you are racing, but it isn't just common, it has to be assumed.

Basically what happens is that at every step along the way slight errors can and do compound, and even if each part is inside tolerances a) those tolerances are really to large, and b) when combined they can add up to a major difference.

Taking keel for example...

1) The bolt homes in the keel sump are not generally drilled directly on center line, they are routinely just slightly off. Maybe 1-5mm.

2) then the keel bolts are installed in the keel slightly off center. Again lets say 1-5mm.

3) Then when the keel is cast the mold cools down asymmetrically causing the lead to shrink back more on one side than the other.

4) Finally the keel is mounted to the boat slightly off center, again lets say 1-5mm.

This is why racers first laser center the keels, then template them off of the dead center of the boat, to get rid of this asymmetry. The guys who do this for a living will sometimes just take the keel off and remount it, other times keep it mounted but move lead around, sometimes just reshape it depending on what the plan for the boat is and the budget. But it can be a complicated and expensive thing to fix, and to do it right you need full sized templates cut to test the keel against, a great eye for shape, and a tolerance for slowly sanding away and adding back material to get it just right.


This same process btw also happens to the rudder, the mast, the chainplate location, the spreader attachments... Basically everything.

Basically a boat out of the factory is like a car tire that hasn't been balanced yet. Sure it looks right, and it will roll down the road mostly fine, but you will notice it never feels quite right.

[briendaniel]

Hi,
My understanding is that if you are in the northern hemisphere in 'stable air' then ALL sailboats with mast height greater than 5metres will be faster on starboard tack and slower on port tack. The reverse is true for Southern Hemisphere, where here, port tack is faster. This phenomenon can be exploited by proper sail trim. IE if you twist the top of your main and headsail away from the boat (vang off and traveller up and sheet out so that the boom is just to leeward of the centreline, plus headsail car back). (This won't work on the opposite tack, where the only thing a trimmer can do is "untwist" and flatten the sail and point higher but slower)You should be able to exacerbate the difference by up to 25% to 30%. It will win or lose a sailboat race when one uses this characteristic of the wind. 'In stable air' wind exhibits "wind shear" ,where the direction of the wind at the base of the mast can be 30 degrees 'rotated' to the wind at the top of the mast. The reason is that wind slows down as it gets closer to the water due to friction at the surface. If the air is stable then the coriolis effect 'turns' the direction of the wind as it slows, closer to the surface.
On port tack in the northern hemisphere, the top of the is not effective so your boat is slower on this tack. All boats exhibit this characteristic if their mast is high enough. The opposite to 'stable air' is turbulent air. A good example of turbulent air is wind coming off a large land mass that has been heated by the sun.....wind shear in these conditions is not as predicable as in 'stable air' and will result in similar speeds on both tacks.
Hope this helps.

[Oceanride007]

Originally Posted by snokid

I'm pretty new to this sailing thing...

main sheet traveler is set the same distance from center.
and
jib car's in the same position

Seems like you are hinting it's wrong to do.

would you mind explaining how you know where they should be when sailing?

thanks
Bob

Briendaniel, covered it ^^. The phenomenon is due to friction due at the Earths surface. Its been a while but at height wind follows the direction parallel to the isobars of pressure but is deflected towards the lower pressure area due to friction near the surface. I've heard it said that only very tall masts would see the phenomenon, maybe not.

[mrohr]

Coriolis? curious!......this sounds like horsefeathers ,but i am in no way an expert. Somebody here has to cite some authority on this one,I mean some things are just counter intuiitive. Yup, dry air is heavier than wet air.....but if its moonbeams or some such; I really want to know so I can win a few drinks at the club bar (if I ever find one that will have me).

FWIW: my boat often shows similar traits and I am in the N. hemisphere.(I think)

To muddy these waters further, consider that my speedo is installed on stb so there may very well be more (or less) turbulence when heeled one side vs the other and i would expect that with slightly more turbulence there would be an under reading .

...................luv you all (even if you live in the antipods)....mike..............