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How to measure wave height

Jun 14, 2010
1,076
Quorning Dragonfly 1200 home
I have heard sailors debate the proper way to measure wave height. I copied the following from the PredictWind "help" guide. It will clarify the significance of professional readings reported by that app and other weather sources:
"The wave height is the mean wave height from trough to crest of the highest third of the waves, which is known as the 'significant wave height'.
The significant wave height is generated from the primary swell and also the local wind wave.
The wave model also takes into account the effect of ocean currents.
As the significant wave height is an average, it is possible you may encounter a wave that is roughly double the significant wave height depending on the conditions."
 
Jun 14, 2010
1,076
Quorning Dragonfly 1200 home
The hard part of wave height measurement for a skipper is having a reference point and when the waves kick up keeping fear out of the observations.
I use my boats beam as a visual reference. My crossbeams are 7’ and beam overall is 28’. The biggest waves I was ever in were 28’ in the Gulf Stream in 30+k winds near a tropical storm, on a “sister boat” of the same model. :eek:
 
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TomY

Alden Forum Moderator
Jun 22, 2004
1,972
Alden 38' Challenger yawl Rockport Harbor
That hard part is exacerbated by darkness.

A few years ago my daughter and I hove to on the Gulf of Maine at midnight, for some much needed rest. With wind topping 40 knots sailing downwind the whole day, the waves were,...big enough.

Once hove to - close reaching a bit due to enough power in the fully reefed main (only) - measuring wave height was all by feel from below in the cabin.

It's hard to tell but from the moment the bow begins to turn up you feel your world begin to climb, and climb,...and climb.

The long waves we had made the climb seem to take forever. At the top, the process is reversed and you go, down,...down,...

I got used to it and actually slept a bit.

One change in this motion was an occasional breaking wave approaching. You'd tense up a bit in the berth as you hear a building soft roar upwind, and wait,...and wait. Then a loud "whomp' from forward followed a second later by buckets of water on the dodger.

In daylight, these conditions would have seemed much different I'm sure, and the wave height in feet, much less than your mental image.
 
Mar 1, 2012
1,891
1961 Rhodes Meridian 25 Texas coast
sailing from Key West to Channel Five on my Cross 35, not waves but swells- smooth, but with an ocasional small break on top. 20 feet at least, maybe more- we could look up from the trough and see fish swimming above us. Sailing in company with another boat, our biggest fear was cresting one and finding the other boat RIGHT THERE!!

We figuredd there had been a storm well offshhore and we were experiencing the left over seas. should have seenn the spray ass each swell hit the inshore reef!!
 
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Sep 22, 2018
768
Hunter 216 Kingston
I have heard sailors debate the proper way to measure wave height. I copied the following from the PredictWind "help" guide. It will clarify the significance of professional readings reported by that app and other weather sources:
"The wave height is the mean wave height from trough to crest of the highest third of the waves, which is known as the 'significant wave height'.
The significant wave height is generated from the primary swell and also the local wind wave.
The wave model also takes into account the effect of ocean currents.
As the significant wave height is an average, it is possible you may encounter a wave that is roughly double the significant wave height depending on the conditions."
A graphic I found to illustrate.

257783B7-F6FE-49BE-9EF9-C46FC1541D8C.jpeg
 
Oct 22, 2014
10,822
CAL 35 Cruiser Portland OR, moored EVERETT WA
I figure if the stern is in the trough as I’m going up a wave and if the bow is out of the water it’s about a 20 footer. HOLD ON.
 
Feb 10, 2004
3,037
Hunter 40.5 East Greenwich, RI
I just make an estimate of the trough to crest of most of the waves. However I once returned from Block Island with a powerboat friend and the waves and spray were quite large. In fact my head sail was wet half-way up!

Upon return I asked him to sign my ship's log and he wrote "Great sail, loved the 1/2 to 1 foot waves." Questioning him about his wave height estimate, he told me that he only counts the wave height as the depth of green water coming over the bow.

Obviously we all have different estimating criteria! :yikes:
 
Jan 19, 2010
326
Catalina 34 Casco Bay
Then there are the ground swells... Add them to the existing waves... yeeee haaaa, more so when quartering and surfing....then fun is in the counter steering at just the right moment..
 
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Sep 22, 2018
768
Hunter 216 Kingston
It is one thing to be bashing into wave in open sea... It is quite different to be docking a ferry in bashing waves...
I get the people rushing to get off the ferry but what are the people that are rushing to get on thinking?? ;) obviously locals, no big deal if you do it on a regular basis!

But then there are people who do this “on purpose”.

C89D9D54-CE0B-42EF-9E96-056237305C99.jpeg
 
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Apr 5, 2009
836
Catalina '88 C30 tr/bs Oak Harbor, WA
I was on this ferry on the upper deck of the Muklitio / Clinton ferry when this series of photos were taken. It was impressive how far the boat can roll and remain stable. The rolls were quick reversing with no linger so it was not near the tipping point. the list was over 20º to each side. The big wave pictured put green water on the upper deck front windows I was standing behind and lots of water over the top of the pilot house.
 
Oct 22, 2014
10,822
CAL 35 Cruiser Portland OR, moored EVERETT WA
That was incredible Hayden. Was that the same event that had waves hitting the Anthony’s Restaurant in Mukilteo?

Here is another Washington State Ferry ride with free salt water cleaning. One of those days when it is better to be last onboard than first in line. Near San Juan Island 3 years ago.