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Author Topic:   How Big The Waves

jimh posted 12-09-2013 09:56 AM ET (US)
The sea state is an often remarked upon condition, particularly wave height. Reports of navigating a Boston Whaler boat in waves typically include a description of the wave height. In my experience, there is a wide variation in the accuracy of the wave height reported.
With the integration of accelerometers into mobile devices, we can now obtain a measurement of wave height and period from a mobile device, such as an iPhone. iOS developer Lamventions LLC has produced an iOS application called SEA STATE which will estimate wave height and wave period from your boat motion. It can also be used to measure the height of another boat's wake.
See
http://www.LamVentions.com/seastate.html
for more information. As usual, you can obtain this application from the Apple APP STORE, and the price is a modest $0.99.
The application works only on the iPhone 4, iPad2, or iPod Touch 4th generation (or newer) devices that have a three-axis gyroscope and an accelerometer.
My iOS devices are too old to run this application. If someone has a newer device and can run the application, it will be interesting to hear how it worked.
Chuck Tribolet posted 12-09-2013 10:11 AM ET (US)
But you have to define wave height. There quite a number of
measures. Max. Average. Average of highest 70%. And so on.

Chuck
jimh posted 12-09-2013 10:52 AM ET (US)
I believe the iOS application SEA STATE uses the common definition: the average of the upper one-third. See
http://en.wikipedia.org/wiki/Significant_wave_height

See the developer's page for details of what the application uses to define wave height. The application also applies the accepted statistical predictions for wave heights. Notably, a wave of about twice the significant wave height will occur once in 1,000-waves. A good source for information on wave height and statistics is
OCEANOGRAPHY AND SEAMANSHIP
William Van Dorn
http://www.amazon.com/Oceanography-Seamanship-William-Van-Dorn/dp/ 0870334344
Chuck Tribolet posted 12-10-2013 09:42 AM ET (US)
Van Dorn is pretty dry and technical. I found
Waves and Beaches, Willard Bascom, 1980, ISBN 0-385-14844-5
much more readable, though with still more math than some
would like.

Chuck
jimh posted 12-10-2013 02:11 PM ET (US)
The attraction of using a iOS or mobile device application to measure wave height, disregarding exactly how it does it or which definitions it uses, is the notion of having some consistency in reporting sea state. I have noticed that reports of wave height from participants experiencing the same sea state often vary by a ratio of 0.5 to 2.0. With the wave height reported by SEA STATE, the iOS application, we might have a more consistent measurement.
I don't have an iOS device with the necessary triple-axle gyroscopes, but someone must. Invest the $0.99 in SEA STATE and let us know what it says about wave height.
EJO posted 12-10-2013 02:55 PM ET (US)
The most reliable is still a NOAA buoy. The GPS (3-axis) of an Apple device would not be accurate enough. www.ndbc.noaa.gov/
The problem with the buoys is that they are never exactly at the place where you are.
As a sailor I use www.PredictWind.com which gives me enough general info to determine if I want to take any boat out on the water based on the conditions, the more wind the higher the waves.
20 knts great for sailing, but wet ride in the little BW. 3-5knts great for taking the BW but leave the sailboat in the slip.
jimh posted 12-10-2013 11:57 PM ET (US)

quote:
The problem with the [NOAA] buoys is that they are never exactly at the place where you are.
This is especially true when you are not in the United States.
daveweight posted 12-11-2013 08:17 AM ET (US)
In general anything over 60 feet is sickening.
Dave Weight
Chuck Tribolet posted 12-11-2013 11:20 AM ET (US)
EJO: The recent Apple devices have a 3-axis accelerometer
and a 3-axis gyro which is what Sea State uses, not the GPS
(which not all recent iPads and I don't any iPod touch have).
And my experience is that NOAA buoys are where they are
supposed to be, though in deep water they may have a big
watch circle. But it's close enough.
All: I tried searching the AppStore for Lamventions (found
nothing) and Sea State (found a bunch of free kids games and
a couple of $29.95 sections of the Code of Federal Regulations
(you can download the PDFs for free if you Google a little))
No, I didn't download it. I have an old dumb phone, and don't
take my iPad on the boat.

Chuck
djahncke posted 12-11-2013 12:32 PM ET (US)
Chuck,
Search the AppStore for seastate (no space between sea and state) and you will find it.
-Don
jimh posted 12-11-2013 12:45 PM ET (US)
Chuck--If you visit the website for Lamventions--there is a link to it in the initial article of this thread--they have a direct link to the Apple store for purchasing their application.
That link is
https://itunes.apple.com/us/app/sea-state/id446116651?mt=8
jimh posted 12-11-2013 12:48 PM ET (US)
The height of waves cannot be measured very accurately with a global navigation satellite system device because the dilution of precision in the vertical plane is much too high. See
GNSS Position Fix: Horizontal and Vertical Precision
http://continuouswave.com/ubb/Forum6/HTML/003502.html
Chuck Tribolet posted 12-11-2013 04:44 PM ET (US)
I did find it starting from the Lamventions website.
Chuck

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Author	Topic: How Big The Waves
jimh	posted 12-09-2013 09:56 AM ET (US) The sea state is an often remarked upon condition, particularly wave height. Reports of navigating a Boston Whaler boat in waves typically include a description of the wave height. In my experience, there is a wide variation in the accuracy of the wave height reported. With the integration of accelerometers into mobile devices, we can now obtain a measurement of wave height and period from a mobile device, such as an iPhone. iOS developer Lamventions LLC has produced an iOS application called SEA STATE which will estimate wave height and wave period from your boat motion. It can also be used to measure the height of another boat's wake. See http://www.LamVentions.com/seastate.html for more information. As usual, you can obtain this application from the Apple APP STORE, and the price is a modest $0.99. The application works only on the iPhone 4, iPad2, or iPod Touch 4th generation (or newer) devices that have a three-axis gyroscope and an accelerometer. My iOS devices are too old to run this application. If someone has a newer device and can run the application, it will be interesting to hear how it worked.
Chuck Tribolet	posted 12-09-2013 10:11 AM ET (US) But you have to define wave height. There quite a number of measures. Max. Average. Average of highest 70%. And so on. Chuck
jimh	posted 12-09-2013 10:52 AM ET (US) I believe the iOS application SEA STATE uses the common definition: the average of the upper one-third. See http://en.wikipedia.org/wiki/Significant_wave_height See the developer's page for details of what the application uses to define wave height. The application also applies the accepted statistical predictions for wave heights. Notably, a wave of about twice the significant wave height will occur once in 1,000-waves. A good source for information on wave height and statistics is OCEANOGRAPHY AND SEAMANSHIP William Van Dorn http://www.amazon.com/Oceanography-Seamanship-William-Van-Dorn/dp/ 0870334344
Chuck Tribolet	posted 12-10-2013 09:42 AM ET (US) Van Dorn is pretty dry and technical. I found Waves and Beaches, Willard Bascom, 1980, ISBN 0-385-14844-5 much more readable, though with still more math than some would like. Chuck
jimh	posted 12-10-2013 02:11 PM ET (US) The attraction of using a iOS or mobile device application to measure wave height, disregarding exactly how it does it or which definitions it uses, is the notion of having some consistency in reporting sea state. I have noticed that reports of wave height from participants experiencing the same sea state often vary by a ratio of 0.5 to 2.0. With the wave height reported by SEA STATE, the iOS application, we might have a more consistent measurement. I don't have an iOS device with the necessary triple-axle gyroscopes, but someone must. Invest the $0.99 in SEA STATE and let us know what it says about wave height.
EJO	posted 12-10-2013 02:55 PM ET (US) The most reliable is still a NOAA buoy. The GPS (3-axis) of an Apple device would not be accurate enough. www.ndbc.noaa.gov/ The problem with the buoys is that they are never exactly at the place where you are. As a sailor I use www.PredictWind.com which gives me enough general info to determine if I want to take any boat out on the water based on the conditions, the more wind the higher the waves. 20 knts great for sailing, but wet ride in the little BW. 3-5knts great for taking the BW but leave the sailboat in the slip.
jimh	posted 12-10-2013 11:57 PM ET (US) quote: The problem with the [NOAA] buoys is that they are never exactly at the place where you are. This is especially true when you are not in the United States.
daveweight	posted 12-11-2013 08:17 AM ET (US) In general anything over 60 feet is sickening. Dave Weight
Chuck Tribolet	posted 12-11-2013 11:20 AM ET (US) EJO: The recent Apple devices have a 3-axis accelerometer and a 3-axis gyro which is what Sea State uses, not the GPS (which not all recent iPads and I don't any iPod touch have). And my experience is that NOAA buoys are where they are supposed to be, though in deep water they may have a big watch circle. But it's close enough. All: I tried searching the AppStore for Lamventions (found nothing) and Sea State (found a bunch of free kids games and a couple of $29.95 sections of the Code of Federal Regulations (you can download the PDFs for free if you Google a little)) No, I didn't download it. I have an old dumb phone, and don't take my iPad on the boat. Chuck
djahncke	posted 12-11-2013 12:32 PM ET (US) Chuck, Search the AppStore for seastate (no space between sea and state) and you will find it. -Don
jimh	posted 12-11-2013 12:45 PM ET (US) Chuck--If you visit the website for Lamventions--there is a link to it in the initial article of this thread--they have a direct link to the Apple store for purchasing their application. That link is https://itunes.apple.com/us/app/sea-state/id446116651?mt=8
jimh	posted 12-11-2013 12:48 PM ET (US) The height of waves cannot be measured very accurately with a global navigation satellite system device because the dilution of precision in the vertical plane is much too high. See GNSS Position Fix: Horizontal and Vertical Precision http://continuouswave.com/ubb/Forum6/HTML/003502.html
Chuck Tribolet	posted 12-11-2013 04:44 PM ET (US) I did find it starting from the Lamventions website. Chuck