How to measure wave height

[ronacarme]

while at the helm?
I have simply looked at the waves and guessed but I suspect 3' waves look bigger than that to me, like maybe 5', so when I later tell the story even I wonder if I'm exagerating.
I have also watched the horizon "rise" from deck level at the bow, up to the top rail of the bow pulpit (call it height H), or twice that (2H)..... If I am far enuf aft of the bow, would not the actual wave height be H (or 2H in the second example)? If so, is the 22-24' from helm to bow far enuf for rough accuracy as to wave height?
Any suggestions thankfully received....

[ALX357]

edited out.... based on info given below

[Moe]

Measuring wave height

I find it harder to judge absolute height when looking forward, but can at least judge relative size of what's coming. It's a lot easier looking abeam, especially when the wave height puts the top about level with your eyeball to surface distance.

[adm]

ronacarme,

Modern instruments keeps us more in check then before but we all exagerate a bit when telling stories. It is part of tradition of the
storytelling.
Moe remarks mentioning to look abeam are right on the money.
I my opinion the "numbers" are not that important. Knowledge if this is 3 or 6 foot swell does not mean too much. Important is how your boat is affected by waves in particular conditions and what should you do. And this comes from experience.

[Sloop John B]

What's simpler than measuring the height of a wave?

You are descending into the trough and you look down at the bottom of the sea and look up to see where the top of the wave is.

You go home to report that you were in six foot seas and actually survived.

NOAA reports that seas were three feet that afternoon.

Complain about government and it's inaccuracy; you were there!

[moonie]

Tried a tape measure once, but fell overboard.

[Scott]

actually wave height is measured visually at the back. This gives an accurate distance from at rest sea to crest.

The height in the front of a wave can vary greatly depending on the speed and strength of a swell. the wave makes a dip in front of it called the trough as it sucks up water to use for heighth. If the back of a wave is 3' the face or front can be 4-6'.

Ask a surfer.

[Jeff Ritsema]

Ron,
This is an important and relatively difficult question to answer. It's important because of the decisions we make regarding predictions of seas as they will build through the day, relative to our crew and boats ability to stand up under the predicted conditions, in short, whether to venture out and for how long in unprotected waters. To complicate things even more, wave heights and conditions differ greatly among locations. A 3' wave on Lake Michigan, where I sail summers, is a much different wave from the 3' wave in the Carribean, where I've sailed winters, Lk Michigan having much steeper, faster, and closer wave trains than the ocean.

I think the key here is experience and caution when you learn the nuances of this subject and the waters you sail. Rely on local knowledge to some extent. If the fishing boats aren't leaving port and they're similar length, think twice about a long crossing. If the weather forcast for the day was 2-3', and you go out in that, file that in your memory banks for future reference. Do the same for greater wave heights and your tolerence level. Learn your local waters and the daily wind and water patterns; for example, on Lk Mich, there is a strong tendency for the early AM to be calm, for winds to build mid-morning thru late afternoon, and to die in the evening. I have used this advantage if I'm on a long transit to leave late afternoon and enjoy an evening and night sail. Differently, in the Windward Islands, the winds hardly vary in a 24 hr period. Ask other boaters who have boats similar in length, probably the most commonly approached subject in the marina head in the morning, "well, are you going out today?". What direction are they going, upwind or down, how much experience do they have, all of these things factor in.

I have used this guide as rough full of thumb:

Speed Term Observed Stated wave Height

Windspeed: 0 = Calm Mirror Glass
1-3 Light air Ripples, scales Rippled
4-6 Light breeze small wavelets Rippled 0-1'
7-10 Gentle breeze Lg wavelets Wavelets 1-2'
small scattered
whitecaps
11-16 moderate breeze small waves slight waves 2-4'
numerous caps
17-21 Fresh breeze moderate waves moderate waves
some spray 4-8'
22-27 Srong Breeze larger waves rough 8-13'
more spray
28-33 Moderate gale Sea heaps Very rough 13-20'
White foam in streaks YIKES

This, again, is only a guide, but adding windspeed into the equation does help some. The fetch of the water (length over which the waves travel before getting to you) is another important variable, depth of the water, and shoaling of the shorelines, all of these things factor in, (again, local conditions).
Hope this helps some.
Fair winds (we trust),
Jeff

[Jeff Ritsema]

Ron, Sorry, the Beaufort wind scale didn't turn out quite like I typed it. Perhaps this will be more "readable":

Categories: 1:Windspeed 2: Term 3: Conditions observed 4: Stated wave height.

1: 0-1 2: Calm 3: Mirror 4: Glass

1: 1-3 2: light air 3: ripples, scales 4: Rippled

1: 4-6 2: light breeze 3: small wavelets 4: Rippled, 0-1' waves

1: 7-10 2: gentle breeze 3: lg wavelets, small scattered wavelets,
4: Wavelets 1-2'

1: 11-16 2: moderate breeze 3: small waves, numerous caps
4: Slight waves, 2-4'

1: 17-21 2: Fresh breeze 3: moderate waves, some spray
4: moderate waves, 4-8'

1: 22-27 2: Strong breeze 3: larger waves more spray
4: rough, 8-13'

1: 28-33 2: Moderate Gale 3: sea heaps, white foam in streaks
4: 13-20'

[Dimitri-2000X-Tampa]

In Tampa Bay, they don't list the wave height, its either light, moderate, or heavy chop and then goes to rough, extremely rough, etc. But when the winter cold fronts come through and you get a SCA with NE winds blowing 25-35 (rough), the waves down in the SW part of the bay get pretty high, easily 5-6 ft and they are very close together too, probably about 25-30 feet. You can't hardly take them directly on the stern since your bow will run into the next wave as you are going down the last one.

Having learned to sail mostly in Europe, I used to use the Beaufort scale pretty exclusively. Here is my interpretation:

0-1: Very boring
2: good for beginners or when you want to do some extremely relaxing sailing.
3: Nice wind for cruising, good for intermediate sailors
4: Perfect wind for sailing, too much for beginners now
5: Good racing in this wind, but better on a windsurfer when you are in good shape, starts getting hairy if you don't have advanced skills
6: Very hairy sailing by now, only for advanced sailors
7: Big ships start getting tossed around, only crazy small boat sailors out
8-12: Gale through Hurricane - Stay in port...No boating today.

Beaufort Scale LINK

[waternwaves]

<--- greatly agrees with Dimitri, with the following addenda:

0-1 even the in-laws will go out with you
2 Plenty of room to make even big mistakes.
3 call work, your going to be late
4 start calling your crew and friends, you can get somwhere. only little mistakes allowed.
5 Full crew of rail meat required for an exhilarating experience.
6 Margins are too thin to stay this way long, stuff starts ....stretching/breaking... Wisdom declining, next stop safe port.
7 ya better have running room, stay in harbor and protected.
8 On the trailer time