Instruments went goofy

Dr. D

Dr. D

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Nov 3, 2018
273
Beneteau Oceanis 35.1 Herrington Harbour North
Last Wednesday the local sailing association had a race which I participated in. (Did OK.) I went out sailing a couple of hours before the race just to enjoy being out on the water. Everything working fine, pointing as I expected and all.

The race starts. I am on a starboard tack, just off from luffing. I look at the instruments and the TWA is 73 degrees. Heck, no! I know I am closer to a TWA of 45 degrees. After tacking and settling in just off from luffing. Now the instruments show a TWA of 23 degrees. Again, nonsense! I finish the race with the goofy numbers showing.

I stay aboard and the next morning get underway. Sails up and the instruments are showing the normal values. Two hours sailing and all is fine.

Which instrument might have gone goofy resulting in the nonsensical TWA? I'm guessing maybe the Precision-9 compass might have and it just needed to be reset which happened when powered down.

Anyone else experience this goofy behavior?
 
Ron20324

Ron20324

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Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
Dr. D said:
... Anyone else experience this goofy behavior? ...
Click to expand
You mean the instruments? In the Severn River in Annapolis, MD, there is a bridge that, when built, they used metal forms for the footings (caissons?) . The metal forms are still there. If you go too close to them, the comasses and such go whacko-o for maybe 15 seconds. Then, it is back to normal with a mental note to me to use the middle of the span from now on, though it is a good teacher for the newbies on board. Pehaps you have a battleship sunk in the race course path that dictates "local knowledge" required ?
 
mdibella

mdibella

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Jun 10, 2019
56
Beneteau First 36.7 Marina Village, Alameda
TWA and TWS are calculated using the AWA and AWS measurements from the masthead sensors, adjusted for boatspeed from the hull paddlewheel. If your BS reading isn't accurate, TWA and TWS will be wacked.
 
Davidasailor26

Davidasailor26

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May 17, 2004
5,069
Beneteau Oceanis 37 Havre de Grace
mdibella said:
TWA and TWS are calculated using the AWA and AWS measurements from the masthead sensors, adjusted for boatspeed from the hull paddlewheel. If your BS reading isn't accurate, TWA and TWS will be wacked.
Click to expand
:plus:

Compass heading is not used for TWS or TWA. It sounds like either your boat speed or wind speed was reading incorrectly. Did you notice what your AWA, AWS, TWS, and BS readings were when the TWA was wrong?

If something’s gone wrong with your boat speed readings there should be a setting buried in the menus to use SOG for the TWA and TWS calculations. With Simrad/B&G instruments there seems to be a bug where enabling that setting also uses SOG as boat speed, but at least the wind will be accurate.
 
Dr. D

Dr. D

.
Nov 3, 2018
273
Beneteau Oceanis 35.1 Herrington Harbour North
Right, TWD needs compass, not TWA.

BS was good (compared to SOG) and AWS and TWS seemed about right. Sailing upwind was OK, but downwind was a guessing game.
 
Davidasailor26

Davidasailor26

.
May 17, 2004
5,069
Beneteau Oceanis 37 Havre de Grace
Was there a large amount of current relative to the wind strength? I’m guessing not if the BS matched SOG closely.

Also, were the winds relatively light? I’ve had days in lighter wind where the wind direction at the top of the mast was sheared about 20 degrees from what the lower tell tales show.
 
Dr. D

Dr. D

.
Nov 3, 2018
273
Beneteau Oceanis 35.1 Herrington Harbour North
The first upwind leg the winds were 8 to 10 kts. By the downwind leg the winds had dropped to 4 to 5 kts. The goofy readings were consistent. For a while I wondered if an osprey had perched on my mast and bent the wind indicator. Everything OK the next day, so that didn't happen.

I have seen an osprey perching on the mizzenmast of a boat across the fairway. One time even eating a fish while perched there.
 
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