Why is my boat faster on a stbd tack?

[Dangen]

Originally Posted by belizesailor

Ive also sailed boats with notable performance differences with no obvious reason. Different performance on different tacks is surprisingly common.

What make/model boat?

Aside from rigging anomalies, hull fairness differences, etc...one rather pedestrian cause is uneven hull fouling. Quite often boats get more growth on one side than the other due to angle relative to sun. Take a peak below the waterline too.

I once had dock crew clean the bottom of a small boat before I took it out to teach a class. Performance was DRAMATICALLY different on one tack versus the other. Jumped in and checked at lunch...dipstick had only cleaned one side!

Its a CS 36

[Dangen]

Originally Posted by Sandero

If so this is rubbish GPS and shows there is current... good catch Jim... I suspected the same... He obviously is repeating from his ray MFD. Can it display speed???? Who knows...



On my dash you can see the 3rd instrument from the left is a GPS repeater (from ray MFD) and reads SOG of 7.2 and the center instrument is the B&G boat speed and it read 6.72.... so it looks like I had some fair tide of about .5 knots. Not bad for 9,5 knots true and apparent 13.5 wind speed.

On the displays, there is SOG and also actual speed coming from the transducer that is located about a foot ahed of the keel and a foot to the port side.

[Dangen]

Originally Posted by thomm225

Tide / Current ?

About 1 knot steady current

[Sandero]

Steady current from which direction? What was the wave direction? You likely are getting this disparity because of the direction of the current and the direction of the waves.

Where were the tests conducted?

[Dangen]

Originally Posted by Sandero

where is the speed transducer? Is it angled properly?

Do not use GPS speed it is useless for comparing speed on port and starboard tacks.

Is this discrepancy for all points of sail or just when wind is forward or the beam?

The transducer is accurate, it cross references SOG in the currents.

The Discrepency is upwind , beam reach and up. The gap reduces as wind increases

[Dangen]

Originally Posted by Sandero

Steady current from which direction? What was the wave direction? You likely are getting this disparity because of the direction of the current and the direction of the waves.

Where were the tests conducted?

I'm sailing on the St Lawrence,

[Sandero]

OK... I am sure there are eddies and the current is not a laminar flow...

[sv.antea]

My yankee 30 sailed better on one tack when I bought her. The PO told me, too. Two things I noticed when hauled out: The keel was not straight, when you looked at the foil from astern with one eye and centered it so the trailing edge appeared in the middle of the bulk of the keel, your eye wasn't under the center line. The error appeared huge. But when I did careful measurements, it only came out few tenths of a degree.
The other thing was the leading edge of the keel was sharp. Not what a proper foil design would call for. I guess the keel was bolted on crooked or was crooked from casting and the factory shaved off some led on one side of the leading edge to make the error less apparent. I then added fiberglas to the leading and trailing edges of the keel a/ to make it symmetrical and b/ to optimise the foils to NACA standards as per recipe by my guru Marchaj. The boat has sailed same on both tacks since.

[belizesailor]

Originally Posted by Dangen

Its a CS 36

Any other owners or those knowledgeable of this boat here?

[Sailmonkey]

Originally Posted by belizesailor

Any other owners or those knowledgeable of this boat here?

I believe Mainesail owns a cs36

[UNCIVILIZED]

It's an asymetry somewhere; the rig, the hull, the keel, the rudder. Or any combination of these.


First check your instruments, & GPS by motoring in both directions over a sheltered patch of water at slack tide. So that you're fairly certain they're not way out of calibration. And then try sailing on both tacks in sheltered water at slack tide.
If nothing else it'll give you a better sense of what's truly going on, since you will have removed some of the possible errors from your testing. And as stated, there's a reason racers template their foils. And those times when the keel comes off, you make damn sure that it's 100% vertical when it goes back on. Even though that likely means rebedding it once or twice to get it right.

[barnakiel]

Yep. If on gps then likely some current under you.

b.

[Jorge M]

[QUOTE=Sandero;2443717]where is the speed transducer? Is it angled properly?

Do not use GPS speed it is useless for comparing speed on port and starboard tacks.

Is this discrepancy for all points of sail or just when wind is forward or the beam?[/QUOTE
Why useless?

[Sandero]

[QUOTE=Jorge M;2444119]

Originally Posted by Sandero

where is the speed transducer? Is it angled properly?

Do not use GPS speed it is useless for comparing speed on port and starboard tacks.

Is this discrepancy for all points of sail or just when wind is forward or the beam?[/QUOTE
Why useless?

Because GPS is speed over ground.... not speed through the water. The OP said his boat sails at different speeds on opposite tacks presuming the same conditions....

I can be sailing at 7 knots against a 3 knot current and boat speed is 7 and the GPS SOG will read 4 knots. Or reverse the course and the GPS SOG will tell me I am sailing 10 knots...

[kas_1611]

All things on a boat are never equal across the beam. Even a can of beans extra in a cupboard can have an impact on the healing forces when you get down to the fractions of a knot and micro level forces.

OK that's a bit extreme but have you considered the volume of fuel and water in your tanks? Remember that a gallon (US) of oil weighs about 7 pounds but a gallon of water weighs 8.4 pounds so an equal volume of each will weigh a different amount. Then think about all the stuff in your cockpit lockers, in the aft cabins, under the galley, under the saloon seats and I bet you will find one side of your boat is heavier than the other which will present itself in a difference in speed from one side to the other.

At least that is what I reckon on ours especially if we have a full tank of water and only a half tank of diesel.