Wave Height Estimation; Differences Between Waves on Various Bodies of Water

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Wave Height Estimation; Differences Between Waves on Various Bodies of Water

Postby Buckda » Tue Aug 30, 2016 8:55 am

Let's tackle the differences in waves on different bodies of water first, as it's easiest:

A four-foot high wave on an inland lake or small body of water can generally only be developed under pretty harsh wind conditions--meaning very closely stacked waves with steep faces, probably--almost surely--whitecapping, and any spray developed by your boat will go soaring off in the wind. This is a nasty situation in ANY classic Boston Whaler boat, and a wet situation in almost any boat as you would be fortunate to ever split the wind perfectly. You're gonna get wet at the helm from the left or the right (or from the front) without canvas or a windshield.

A four-foot high wave on a medium body of water, like the Great Lakes, major bays like San Francisco, Chesapeake, Puget Sound, etc,. can vary from the conditions mentioned above to more like an ocean wave; it depends on conditions. These are weird bodies of water because the fetch of a steady, smooth breeze could be great enough to generate larger waves without the chaos required to generate a four-footer on an inland lake.

A four-foot high wave on the ocean is generally background swell for most of our California members. This is no problem. I have heard these members refer to waves differently: swell v. wind blown chop. It would help our Gulf, Atlantic, and Pacific coast members to remember that midwestern boaters almost never have swell and almost always are describing windblown chop when talking about waves

Wave Estimation

It is clear that there is quite a variance in describing waves. It also seems that there is a tendency to overestimate a wave's height. As an example, I took a few of my summer crew of college students around Marquette Island on Lake Huron earlier this summer. We went straight into an east wind with three to four-foot waves in a Guardian 22. They later estimated the wave height at eight to ten feet. Well, THEY were, in fact, eight to ten feet above the water a few times as we worked our way through the waves, but the wave height never exceeded an occasional six foot monster. Whenever I estimate wave height without buoy data, I tend to give my initial estimate a bit of a trim to keep myself honest.

How do you try to help yourself make an accurate estimation of wave height when you're in the Whaler?

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Re: Wave Height Estimation and Differences between waves on small, medium and large bodies of water

Postby GoldenDaze » Wed Aug 31, 2016 9:57 pm

Great description of how conditions vary. If the wave crests are below the gunwale on my 160 Dauntless, that's less than two feet. Three feet is when the crests look about chest high when I'm in a trough. At five feet the crests are pushing up to the horizon. I've had that happen once on the Chesapeake, and as you said, on small-to-medium water they were steep, close together, and breaking. I felt safe but sure not very comfortable. Taking them on the beam might have been a dangerous choice, and turning around took careful timing!

As I mentioned in another recent thread, I took enough of a pounding a different day on the Chesapeake with four-footers to break the plates in my battery. She ran fine all the way home, but wouldn't start again.
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Re: Wave Height Estimation and Differences between waves on small, medium and large bodies of water

Postby macfam » Thu Sep 01, 2016 9:06 am

I have four categories of waves:

--calm up to rippling chop: hammer down

--steep chop, accompanied by significant wind: half throttle, on plane and bow down

--large waves, steep curling face, stiff wind: too slow to plane, trying to stay dry, long uncomfortable ride

-huge waves, ugly breaking faces, foam trails, spray off crests: "I have no damn business being out here"

These four have served me well for over 40 years.

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Re: Wave Height Estimation and Differences between waves on small, medium and large bodies of water

Postby Phil T » Thu Sep 01, 2016 12:53 pm

For the ocean, I looked at sea conditions two ways. There are swells and there are waves. Each can be a reason to stay home.

It also depends on the size of your boat. Three-foot -breaking waves in a 17-foot boat can lead to swamping. Two good bow stuffings and you are almost there. In a 20-foot boat, the LOA helps you miss the next trough.
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Re: Wave Height Estimation; Differences Between Waves on Various Bodies of Water

Postby jimh » Sat Sep 03, 2016 6:42 am

I consider waves in two categories: waves I can safely go down wind with, and waves I can go upwind against.

Boston Whaler classic hulls can go downwind in rather large waves with very good tracking, a very dry ride, and not too much discomfort. The helmsman will have to be very focused and attentive, steering around really big breaking waves and using a lot of throttle variation to keep the boat speed under control at all times, but heading downwind in large seas can be done.

To go upwind and into waves in a Boston Whaler classic hull is quite a different story. Once wave height is greater than about two feet, travel upwind will be limited to plowing along with a bow-high trim at about 7 to 10-MPH in a very inefficient mode.

I have very little experience in running offshore in the open ocean. I do recall one afternoon when we left Southport, North Carolina, and headed into the open Atlantic. The ocean appeared to be very calm, but I soon discovered that there was a remnant swell with a very long wavelength. Trying to run on-plane into this swell was very uncomfortable. The boat would launch off the top of a swell and land hard in the trough. Despite what looked like calm conditions, we could not make headway into the swell at planing speeds without enduring a jarring ride. This was a surprise to me.

We do see some swell conditions on the Great Lakes but usually the wavelength is not as long. And usually there are wind-waves disguising the swell.

My favorite advice about wave conditions on the Great Lakes comes from the Canadian Coast Guard continuous marine broadcasts that give weather information:

"Wave heights are for offshore and are measured from trough to crest. Winds and waves can vary considerable due to shoreline effects."

The shoreline effect is also known as clapotis.

Regarding a method to estimate wave height, I have thought of an approach. Carry on board a inflated ball of a known diameter and made with a bright red color. Throw the ball overboard. Take a photograph of the ball as it is about to encounter a wave. Then in the photo image you will have a size reference from which you can estimate the wave height. Of course, this is not a very practical method in storm conditions, as you probably won't want to bother trying to retrieve the ball.

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Re: Wave Height Estimation; Differences Between Waves on Various Bodies of Water

Postby Jeff » Thu Sep 08, 2016 9:05 am

After trolling on and boating across the Great Lakes my whole life I can say that the general rule of thumb is, when it's snotty the wave duration is equal to or less than its height. Four-foot-high waves every four seconds; six-foot-high waves every six seconds. Or eight-foot-high waves every six to eight seconds.
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