[Fr. Frank]

Originally Posted by pelican

I watched that video...i'm sure you're a real good dude...but.....
no way was that a 5' head sea ! no way !! 2-3' max,that's it...
...a tight 3'-5' sea - with a wave period of 3 - 4 seconds is a tight chop,a long period 3-5' sea,no problem...again,tighten that up,and you've got problems...

The rule of thumb for wave to sea height is 5/9 or 9/5. In other words, if the waves are 9' feet from trough to crest, the sea height is 5'.

So if the WAVES are between 3' and 5' high, the SEAS are between 1.6' and 2.7 feet.

If the SEAS are 3' to 5', then the WAVES are 5.4' to 9' high from trough to crest.
Similarly, 4'-7' seas have waves that are from 7' - 12' high.

Most people think Wave height and Seas are the same thing, they are not. The problem is also that many TV "meteorologists" don't know the difference, either. I've listened to a TV forecast for "waves" to be 2'-4', and gone out only to find out the waves were 4'-7', because the talking head on TV didn't know the difference. I'll go out in a 20' Seafari if the seas are LESS than 3'-5'.

I've been stupid and got caught out off the Juno Ball in a 25' Robalo when the seas were 4'-6', (waves 7'-10') and forecast to fall to 2'-4', (waves 3.6'-7') and instead they INCREASED to 6'-9', (waves 10'-16') and we could no longer safely run back in Jupiter Inlet. We first ran south to Lake Worth Inlet, and then sat offshore for over 4 hours riding into the seas waiting for them to die down before shooting the inlet behind a small freighter.

If NOAA says the SEAS are 3'-5', you need to be aware that the WAVES are significantly higher than that.

In 5' seas, the wave crest is 9' high - usually higher than the the top of your T-top when you're in the bottom of the trough.

Multiply wave height by 5/9 to get seas. Multiply seas by 9/5 to get wave height.