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Old 16-03-2015, 13:37   #1
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Is it my electronics or the SF Bay messing with me?

Ahoy!
We recently bought our first large boat, and we keep her in the San Francisco bay. We of course heard that SF is a very challenging place to sail, and we're looking forward to it.

I recently installed a fresh set of raytheon electronics. Wind/depth/speed pack.

We've been out on the bay a a handful of times times now, and I am starting to question the accuracy of these electronics. Wind forecasts for ~10 knots. We routinely see periods of time where the wind is over 20 knots.

Did I maybe not calibrate the wind instruments or something?

It certainly feels windy, but it's never even close to what the forecasts say.

Is there a way to look at historic data for wind at buoys?
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Old 16-03-2015, 13:41   #2
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Re: Is it my electronics or the SF Bay messing with me?

Yep, but why not start in the dock and ask the neighbouring boats what windspeeds they are seeing and adjust to the lowest average. Also I think forecast speeds are at 5m and the mast is at 20m so expect it to be a bit breezier up there...
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Old 16-03-2015, 13:49   #3
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Re: Is it my electronics or the SF Bay messing with me?

are you reading apparent wind or ...?
I think there is a NOAA site where you can read actual bouy readings with a time stamp.
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Old 16-03-2015, 13:52   #4
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Re: Is it my electronics or the SF Bay messing with me?

Read Kimball Livingston's Sailing The Bay. Great book.
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Old 16-03-2015, 14:16   #5
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Re: Is it my electronics or the SF Bay messing with me?

Winds very tremendously depending on where you are in the Bay. On a normal daysail, we usually went from from a full 135% jib and main to a genoa roller reefed down to 100% and double reefed main, back to full sails, down to fully reefed and back to every light air sail we could muster going from Alameda to Angel Island and back. Your anemometer may not be dead accurate but it definitely shows the reality of the difference in wind velocity that you've experienced. Suggest you learn to judge the wind velocity from the way it feels and sea conditions and use the anemometer for bragging rights at the bar when the boat is back in its slip after a day on the Bay.
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Old 16-03-2015, 14:23   #6
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Re: Is it my electronics or the SF Bay messing with me?

LOL, The NOAA Sf Bay wind forecasts and even live data is NOT at all accurate. I've been out with wind howling in the rigging and the live wind speed at a nearby airport, would read 5 to 10 knots , while I'm putting another 50 feet of scope out on the anchor.

The problem with bouy data is wind speed outside the bay can be calm, while it's honking windy in the bay. It's driven by inland heating in the central valley that causes the daily winds on the bay. Average summer winds are almost always 20-25 knots or higher. Just a easy summer sail on the bay.

Of course it can be dead quite east of angel island when it's blowing snot in the slot. (gate to Berkeley). Then there are the currents. Always fun.
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Old 16-03-2015, 14:25   #7
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Re: Is it my electronics or the SF Bay messing with me?

Thanks!
It sounds like my wind transducer is working just fine.

Great advice here
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Old 16-03-2015, 16:38   #8
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Re: Is it my electronics or the SF Bay messing with me?

I was out last Tuesday. Two of us with separate weather forecasts predicted probably no more than 7-8 knots, which is what it was for the first hour. The next couple of hours it was howling steady, probably 18-20 knots (tho the wind meter was not functional yet). You could get a handheld anemometer. I hear the one that hooks onto the Iphone is pretty reliable. But the best is to ask your dock mates what they're reading at the top of the mast, which is going to be different than deck level as others have noted.

The bay is a funny place Have fun!
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Old 16-03-2015, 20:32   #9
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Re: Is it my electronics or the SF Bay messing with me?

Then be prepared for when your depth reads
50 fathoms and next instant it reads 2. Seems
to happen when salt/cold water tide runs over
fresher/warm water or vise versa.
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Old 16-03-2015, 20:40   #10
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Re: Is it my electronics or the SF Bay messing with me?

I have a handheld anenometer for comparison. Have to make allowance for the difference in height, of course.
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Old 17-03-2015, 10:13   #11
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Re: Is it my electronics or the SF Bay messing with me?

Quote:
Originally Posted by jongleur View Post
Then be prepared for when your depth reads
50 fathoms and next instant it reads 2. Seems
to happen when salt/cold water tide runs over
fresher/warm water or vise versa.
Thanks for that Jongleur!
I was about 1/2 mile from Blunt Point approaching Angel Island last Friday afternoon when my depth reading "abruptly" changed from 90+ ft to 4.8 (my keel is 4.5') resulting in a mild heart-attack. Knowing the area and having a chart handy, I figured I was ok and the depth sounder was acting up. As the tide was ebbing, I'm sure the phenomenon you mention was the cause.
- Another mystery solved!
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Old 17-03-2015, 11:59   #12
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Re: Is it my electronics or the SF Bay messing with me?

Knowing SF Bay, I would blame outside variables. If your depth is correct when you are tied up it will be correct when out in the bay. If your wind speed gauge is the same as your neighbors it will be correct, if there mast is the same height. In other words check with your neighbors. The bay is a funny place and the bottom can give you funny readings, as will the mast height will give different readings. Bottom conditions may change over 50 ft as will wind speeds will increase as you go up a mast. Get a rigger or electronic tech to check things out if you are still not sure of what is happening.
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Old 17-03-2015, 12:10   #13
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Re: Is it my electronics or the SF Bay messing with me?

I have the same experience with my instruments - the wind instruments consistently report higher numbers than the forecasts.

One thing to note is that the NOAA instruments are not in the best locations to really measure the effects of the slot. I've found the station at Point Blunt on Angel Island to be the most accurate when it comes to checking central bay conditions. The SailTactics forecast is also pretty good, their model actually takes into account the bay area's detailed topography.
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Old 17-03-2015, 13:37   #14
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Re: Is it my electronics or the SF Bay messing with me?

Sounds like you're new to wind instruments? You need to be sure you are looking at apparent wind or true wind, and then there's the matter of wind height, winds are always higher as you go aloft. Masthead wind speed on a J/24 will be higher than deck wind speeds, but on a 70' tall mast they'll be much higher still. There are standards for that gain-per-foot.


There could be calibration, set-up, simple defect issues but if you checked the manuals and gave Raymarine a call, those should be easily eliminated.


And if you really believe NOAA...we call that broadcaster the "NOAA-nothing man" because the forecasts are so often so unreal. They do the best they can, but you really need to take them with a grain of salt, geographically adjusted, and study up on meteorology to get some idea what's really going to happen.


I've seen forecasts for a "blissful 5mph breeze tomorrow" at sunset, which turned into a "40-knot eight foot seas half the fleet is abandoning the race" by 10am. Yeah, sometimes they goof.


They tend to be most accurate, I think, when the forecast says "A line of squalls is moving through...spawning waterspouts and tornados...mariners are advised to seek shelter" and when you hear that, don't debate it, just make sure you are ready to get clobbered. Just in case they are reporting that based on local spotters, on the ground.
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Old 17-03-2015, 14:28   #15
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Re: Is it my electronics or the SF Bay messing with me?

Quote:
Originally Posted by sailorchic34 View Post
LOL, The NOAA Sf Bay wind forecasts and even live data is NOT at all accurate. I've been out with wind howling in the rigging and the live wind speed at a nearby airport, would read 5 to 10 knots , while I'm putting another 50 feet of scope out on the anchor.

The problem with bouy data is wind speed outside the bay can be calm, while it's honking windy in the bay. It's driven by inland heating in the central valley that causes the daily winds on the bay. Average summer winds are almost always 20-25 knots or higher. Just a easy summer sail on the bay.

Of course it can be dead quite east of angel island when it's blowing snot in the slot. (gate to Berkeley). Then there are the currents. Always fun.
I believe sailorchic has the correct answer. Having spent 15 years sailing and teaching sailing in the bay area, this has been my experience. The gate will funnel the winds into the bay toward Berzerkley. Prepare to reef when entering from the north at Angel Isl and when north bound at the bay bridge.
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