Wave Height

[ontherocks83]

Originally Posted by DefinitelyMe

It's very important to make the distinction between 12-foot seas and 12-foot waves, and it surprises me that so many posters on here seem to be confusing the two. if a forecast says 12-foot seas, they are telling you the amplitude of the waves, which is the height from the mean amplitude to the maximum, i.e. half of the total height of the wave. A 15-foot sea is a very big sea, with 30-foot waves. DO NOT CONFUSE THE TWO, as you could very well get into a lot of trouble if you look at a forecast and it says '10-foot seas' and you think 'that's fine, i can handle 10-foot waves'!!!

Ok that makes sense now. Thank you! Now as an annoying follow up question. Why? Is there a reason for the disparity between waves and seas or is it one of those that's just how its always been?

[Delancey]

I like it when you get on top of a really big wave and feel like you are looking DOWN at the horizon.

[thinwater]

Often a fish finder that runs a trace will give a good estimate, if you are over a flat bottom. The trace will mimic the wave train, depending on speed and how you are taking the waves. Mostly useful in a long swell.

[Dsanduril]

At least in the US (NOAA) "seas" and "waves" are the same thing and measured trough to crest:

Significant Wave Height
Commonly referred to as Seas in the Marine Forecast

This is the average of the highest one-third (33%) of waves (measured from trough to crest) that occur in a given period. This is measured because the larger waves are usually more significant than the smaller waves. For instance, the larger waves in a storm cause the most beach erosion, or the larger waves can cause navigation problems for mariners. Since the Significant Wave Height (Seas) is an average of the largest waves, you should be aware that many individual waves will probably be higher.

If we take a sample forecast of Seas Beyond the Reef of 2 to 4 feet, this implies that the average of the highest one-third waves will have a Significant Wave Height of 2 to 4 feet. But mariners need to keep in mind that roughly one of every ten waves will be greater than 4 feet; one in every one hundred waves will be greater than 5 feet; and one in every 1000 waves will be greater than 6 feet.

As a general rule, the largest individual wave one may encounter is approximately twice as high as the Significant Wave Height (or Seas).

Note: Seas can refers to the combination or interaction of wind waves and swells (combined seas) in which the separate components are not distinguished. This includes the case when swells are negligible or are not
considered in describing sea state.

Significant Wave Height

[DefinitelyMe]

Originally Posted by ontherocks83

Ok that makes sense now. Thank you! Now as an annoying follow up question. Why? Is there a reason for the disparity between waves and seas or is it one of those that's just how its always been?

Hmmm, having hastily written that post i've done a bit of research online and it seems that different forecasters will use different systems depending on where you are in the world. So, the average height of the top 1/3 is true for some, the amplitude is true for others and the total average wave height is true for others.......... so my original statement may not be true depending on where you are....... I guess you just have to be really careful about figuring out exactly what they mean!

The reason it is expressed like that comes from the mathematicians and physicists. The classical wave formulas for modelling behaviour use amplitude almost exclusively, hence it is the number that is spat out by the models, and the one that is reported on forecasts.

As a side note, i personally find estimates of sea state according to the Beaufort scale to be more useful than wave height per se, and possibly more accurate. I wouldn't mind 300-foot waves provided they were long enough, but a sea state of 10 is always going to be bad news!

[Nord Sal]

Copy and paste my link to see it if interested. It will work with then with the "waves.pdf" included at the end of the link. Not sure why it posted that way

[barnakiel]

@ DefinitelyMe

Definitely I am glad you did 'some more research'.

National Weather Service Marine Forecasts - FAQ

You have done now you are forgiven and forgotten. Man, you got me puzzled for a moment.

Please quote the other scientists who hold the opposite view. I want to earmark them for future use ;-)

Love,
b.

[Steadman Uhlich]

Language of the Sea and Sailors:
Wave Height has been a matter of discussion for sailors ever since men and boys and women started going to sea.

There is a long established language for describing the heights of waves, along with some acronyms that may be familiar (perhaps from use in non-nautical situations and text messages on sat phones and in ship's logs). I will post a few acronyms with examples of usage:

HUUUGE
"That freakin wave was HUUUGE!"

BFW
"That was a BIG Freakin Wave!

GTSPDD
"That wave was Greener Than St. Patricks Day in Dublin!"

SDICSB
"The trough of that wave was So Deep I Could See Bottom!"

OMG
"Oh My God!"

HSFB
"Holy Ship! That wave was Freakin Big!"

MBITS
"My Boat Is Too Small!"

Of course most salty sailors know the proper response to any of these terms is to simply say: "That was nothing, I once…"

[Rustic Charm]

Originally Posted by Steady Hand

Language of the Sea and Sailors:
Wave Height has been a matter of discussion for sailors ever since men and boys and women started going to sea.

There is a long established language for describing the heights of waves, along with some acronyms that may be familiar (perhaps from use in non-nautical situations and text messages on sat phones and in ship's logs). I will post a few acronyms with examples of usage:

HUUUGE
"That freakin wave was HUUUGE!"

BFW
"That was a BIG Freakin Wave!

GTSPDD
"That wave was Greener Than St. Patricks Day in Dublin!"

SDICSB
"The trough of that wave was So Deep I Could See Bottom!"

OMG
"Oh My God!"

HSFB
"Holy Ship! That wave was Freakin Big!"

MBITS
"My Boat Is Too Small!"

Of course most salty sailors know the proper response to any of these terms is to simply say: "That was nothing, I once…"

Now that's getting very technical.. you forgot, 'WTF' which seems to be the latest technical term over this way.

[annsni]

Originally Posted by Steady Hand

Language of the Sea and Sailors:
Wave Height has been a matter of discussion for sailors ever since men and boys and women started going to sea.

There is a long established language for describing the heights of waves, along with some acronyms that may be familiar (perhaps from use in non-nautical situations and text messages on sat phones and in ship's logs). I will post a few acronyms with examples of usage:

HUUUGE
"That freakin wave was HUUUGE!"

BFW
"That was a BIG Freakin Wave!

GTSPDD
"That wave was Greener Than St. Patricks Day in Dublin!"

SDICSB
"The trough of that wave was So Deep I Could See Bottom!"

OMG
"Oh My God!"

HSFB
"Holy Ship! That wave was Freakin Big!"

MBITS
"My Boat Is Too Small!"

Of course most salty sailors know the proper response to any of these terms is to simply say: "That was nothing, I once…"

Yep - regularly heard around the yacht club bar.

[ontherocks83]

Sounds like wave stories are like fishing stories.

[Zzmeyer]

3 meter wave height is very small during daylight and very large after dark.


Sent from my iPhone using Cruisers Sailing Forum

[DefinitelyMe]

Originally Posted by barnakiel

@ DefinitelyMe

Definitely I am glad you did 'some more research'.

National Weather Service Marine Forecasts - FAQ

You have done now you are forgiven and forgotten. Man, you got me puzzled for a moment.

Please quote the other scientists who hold the opposite view. I want to earmark them for future use ;-)

Love,
b.

Ha ha! Cheers! Well, i wouldn't say it's an 'opposite' view, just different. 'builder dan' (post #25 in this thread) gives an example of using this method to report wave height when he was reporting to weather stations from his trawler.

I'm pretty sure Bermuda Weather for one uses this method to report and forecast seas, however, having been so assertive (and erroneous) in my initial post i am hesitant to be so over-confidently assertive this time round! At any rate, since max. wave height can be about twice that of 'significant wave height', 'mean of the biggest 1/3' and more than twice average amplitude i think it's safe to take all of these forecasts conservatively with a grain of salt, and i think we've explained why they look so much bigger to us out on the ocean than the reported or forecast heights given by weather stations.