74 foot waves
- Thread starter jimi
- Start date
bedouin
Well-known member
No nm
.
.
webcraft
Well-known member
In 20 knots of wind on Lake Ontario?
I doubt it.
In the North Sea in Winter, no problem.
- Nick
BlueMoment.Com
http://www.bluemoment.com
I doubt it.
In the North Sea in Winter, no problem.
- Nick
BlueMoment.Com
http://www.bluemoment.com
B
bob_tyler
Guest
Not likely at Hythe either! Suggest reading 1 for 7.
Col
New member
Re: Einstein !!!
National Data Buoy Center
Frequently Asked Questions
How are spectral wave data derived from buoy motion measurements?
NDBC-reported wave measurements are not directly measured by sensors on board the buoys. Instead, the accelerometers or inclinometers on board the buoys measure the heave acceleration or the vertical displacement of the buoy hull during the wave acquisition time. A Fast Fourier Transform (FFT) is applied to the data by the processor on board the buoy to transform the data from the temporal domain into the frequency domain. Note that the raw acceleration or displacement measurements are not transmitted shore-side. Response amplitude operator (RAO) processing is then performed on the transformed data to account for both hull and electronic noise. It is from this transformation that non-directional spectral wave measurements (i.e., wave energies with their associated frequencies) are derived. Along with the spectral energies, measurements such as significant wave height (WVHGT), average wave period (AVGPD), and dominant period (DOMPD) are also derived from the transformation.
Note that the wave measurements contained in the SeaBreeze CD-ROM only include calculations of WVHGT, AVGPD, and DOMPD. To receive spectral wave energy density data, see the Web page about obtaining archived data
For a more detailed explanation on FFT's, see
Brigham, E.O., 1988: The Fast Fourier Transform and its Applications. Prentiss Hall International, 448 pp.
For a detailed description on the applications of Fast Fourier Transforms to wave data, see
Tucker, M.J., 1991: Waves in Ocean Engineering: Measurement, Analysis, and Interpretation. Ellis Horwood, LTD., 431 pp.
For more information about NDBC's wave measuring systems, refer to:
Steele, K.E. and T.R. Mettlach, 1993: NDBC wave data - current and planned. Ocean Wave Measurement and Analysis - Proceedings of the Second International Symposium. ASCE, 198-207.
NDBC also reports directional wave data for selected stations. Besides buoy heave acceleration, measurements of hull azimuth, pitch, and roll are also necessary for directional waves. Two methods exist for the measurement of hull azimuth, pitch, and roll.
The first method includes the use of a Datawell Hippy sensor to measure vertical heave acceleration along with pitch and roll. A second sensor, a triaxial magnetometer, is used to measure hull azimuth.
For a more detailed description, refer to:
Steele, K.E., Teng, C-C., and D. W-C. Wang, 1992: Wave direction measurements using pitch and roll buoys. Ocean Engineering, 19, 4, 349-375.
The second method uses only the triaxial magnetometer to measure hull azimuth, pitch, and roll. Vertical heave acceleration is measured by an accelerometer.
For more information, refer to
Steele, K.E. and M. Earle, 1991: Directional ocean wave spectra using buoy azimuth, pitch, and roll derived from magnetic field components. IEEE Journal of Ocean Engineering, 16, 4, 427-433.
The processing stream as applied to raw, directional measurements is similar to that presented above for non-directional data: RAO's are applied to the acceleration data after all Fourier processing is performed. The main difference between directional and the non-directional wave data is that, for directional data, four frequency-dependent parameters are calculated along with the spectral measurements, WVHGT, AVGPD, and DOMPD. These other parameters are ALPHA1 (mean wave direction), ALPHA2 (principle wave direction), and R1 and R2 (parameters which describe the directional spreading about the main direction).
Explains it all really, doesn't it !!
National Data Buoy Center
Frequently Asked Questions
How are spectral wave data derived from buoy motion measurements?
NDBC-reported wave measurements are not directly measured by sensors on board the buoys. Instead, the accelerometers or inclinometers on board the buoys measure the heave acceleration or the vertical displacement of the buoy hull during the wave acquisition time. A Fast Fourier Transform (FFT) is applied to the data by the processor on board the buoy to transform the data from the temporal domain into the frequency domain. Note that the raw acceleration or displacement measurements are not transmitted shore-side. Response amplitude operator (RAO) processing is then performed on the transformed data to account for both hull and electronic noise. It is from this transformation that non-directional spectral wave measurements (i.e., wave energies with their associated frequencies) are derived. Along with the spectral energies, measurements such as significant wave height (WVHGT), average wave period (AVGPD), and dominant period (DOMPD) are also derived from the transformation.
Note that the wave measurements contained in the SeaBreeze CD-ROM only include calculations of WVHGT, AVGPD, and DOMPD. To receive spectral wave energy density data, see the Web page about obtaining archived data
For a more detailed explanation on FFT's, see
Brigham, E.O., 1988: The Fast Fourier Transform and its Applications. Prentiss Hall International, 448 pp.
For a detailed description on the applications of Fast Fourier Transforms to wave data, see
Tucker, M.J., 1991: Waves in Ocean Engineering: Measurement, Analysis, and Interpretation. Ellis Horwood, LTD., 431 pp.
For more information about NDBC's wave measuring systems, refer to:
Steele, K.E. and T.R. Mettlach, 1993: NDBC wave data - current and planned. Ocean Wave Measurement and Analysis - Proceedings of the Second International Symposium. ASCE, 198-207.
NDBC also reports directional wave data for selected stations. Besides buoy heave acceleration, measurements of hull azimuth, pitch, and roll are also necessary for directional waves. Two methods exist for the measurement of hull azimuth, pitch, and roll.
The first method includes the use of a Datawell Hippy sensor to measure vertical heave acceleration along with pitch and roll. A second sensor, a triaxial magnetometer, is used to measure hull azimuth.
For a more detailed description, refer to:
Steele, K.E., Teng, C-C., and D. W-C. Wang, 1992: Wave direction measurements using pitch and roll buoys. Ocean Engineering, 19, 4, 349-375.
The second method uses only the triaxial magnetometer to measure hull azimuth, pitch, and roll. Vertical heave acceleration is measured by an accelerometer.
For more information, refer to
Steele, K.E. and M. Earle, 1991: Directional ocean wave spectra using buoy azimuth, pitch, and roll derived from magnetic field components. IEEE Journal of Ocean Engineering, 16, 4, 427-433.
The processing stream as applied to raw, directional measurements is similar to that presented above for non-directional data: RAO's are applied to the acceleration data after all Fourier processing is performed. The main difference between directional and the non-directional wave data is that, for directional data, four frequency-dependent parameters are calculated along with the spectral measurements, WVHGT, AVGPD, and DOMPD. These other parameters are ALPHA1 (mean wave direction), ALPHA2 (principle wave direction), and R1 and R2 (parameters which describe the directional spreading about the main direction).
Explains it all really, doesn't it !!
B
bob_tyler
Guest
Re: Einstein !!!
That is the most confusing explanation I have ever read for a misprint.
"Explains it all!!!!! I don't understand a word of it.
That is the most confusing explanation I have ever read for a misprint.
"Explains it all!!!!! I don't understand a word of it.
jimi
Well-known member
Well I do'nt know, you do get the occasional rogue wave quite apart from the odd infrequent Tsunami(sp?). So it is possible even if most unlikely!
Col
New member
Re: Einstein !!!
Cut Pasted from their own web site !!
I think I lost it somwhere in the first sentance.
Contender for the plain English campaign awards ??
<P ID="edit"><FONT SIZE=-1>Edited by Col on Tue Apr 30 14:00:00 2002 (server time).</FONT></P>
Cut Pasted from their own web site !!
I think I lost it somwhere in the first sentance.
Contender for the plain English campaign awards ??
<P ID="edit"><FONT SIZE=-1>Edited by Col on Tue Apr 30 14:00:00 2002 (server time).</FONT></P>
ccscott49
Active member
74 feet, in the north sea in winter, no problem. I don't think so somehow, evry 100 years maybe, platforms out here are built to survive the 100 year wave, said to be 100 feet, but I spend half my life out here, for the last 28 yeaars on and off, I've never seen anything over 50 foot, or heard of it.
G
Guest
Guest
If my memory serves me correctly - Amoco Arbroath Platform - installed June 1995 ish. In January/February following year had a "50-year wave" leave a tide-mark three foot high INSIDE the generator room and scaffolding erected underneath the main-deck disappeared in seconds!!!!!!!
It happens - just not very often - thank God!!!
Best regards
)
Ian D
It happens - just not very often - thank God!!!
Best regards
)Ian D
longjohnsilver
Well-known member
Nah, every now and again these buoys have a funny 5 minutes and give a rogue reading, just check those the hour before and after to see what's really happening.
Chris_Stannard
New member
Both the 'Perfect storm" and the 'Fatal storm quote waves heights of at least this size. In the case of the Fatal storm (the 1998 sidney Hobart race) the wave heights were confirmed by helicopters. it can happen though thank goodness it doesn't often.
Chris Stannard
Chris Stannard
chippie
New member
Yes, absolutley amazing . I saw video footage of a helicopter involved in that Sydney-Hobart rescue and it was hovering well above a stricken yacht, and then a huge wave came through and it seemed the helicopter was only just clear of it.
ccscott49
Active member
But not in the north sea, the fetch just isn't long enough, extreme conditions are seen out here, but there has to be some very unusual circumstances, all happening at the same time, to cause it.
vyv_cox
Well-known member
Years ago on Brent Bravo I experienced Force 12 for a couple of days. Waves built up to what looked like horrendous size. Using the semi-sub alongside as a reference, I estimated the wave height to be something like 36 ft. A day later, landed as a helicopter passenger on an exploration ship to pick someone up. From that relatively low position the wave height appeared enormous! I could easily have believed 74 ft.
