Wave height vs. period. 2x feet or meters?

[serpa4]

I've been doing some reading on the "general" rule of thumb of not going out when the period in seconds is less than 2x the wave height.
3x is considered more comfortable.
However, I've seen it many times in meters and many times in feet. However, they are pretty different.
What standard do you use?
1.5 meter waves are about 5 foot waves.
1) Period should be 1.5 meters x 2 = 3 seconds or grater to be acceptable boating. I don't think I'd like 1.5meter/5ft waves at 3 second intervals at all.
2) Period should be 5 feet x 2 = 10 seconds or greater to be acceptable boating. This sounds much more acceptable.

 

[BB marine]

2 X the wave hight in foot increments = a choppy sea 4', 8 second period is not fun. 4' 12 second period (X3) better but still in my opinion not something I'm going cruising in.

1 meter wave = 3.3' the period X the foot increment. 1 meter= 6.5 to 7 seconds choppy sea still not fun X3 = 10 seconds better.

As we learn our boats handling characteristics the judgment of what is comfortable and safe to cruise in. Many talk about cruising in 6' seas but leave out the period. 6' sea's in 12 second waves in my C26 is Awful in my opinion. To others it is ok (crazy). 6' sea's in 24 second waves are doable but not something I would start a trip in. Sometimes we make mistakes and that is how we gauge or make judgment calls of what we go out in and what sea's keep us in safe harbor.

When I Purchased my C26 I had high expectation of the sea conditions we could and would cruise in. We boat on Lake Michigan most of our summer cruising. When we bought the boat 4' sea's was our max sea's to go out in. That was ok for a short boat ride out in the lake. It was fun. We took a trip to Chicago from Racine Wis. This is only a 60 mile run. Going down to Chicago we had an easy cruise. 1' with occasional 2' beautiful trip. We spent a few days in Chicago and had to go back. Forecast 2' to 4' out of the east which meant beam sea's. We left and it was choppy 2'. I went out about 5 miles hoping the wave's would spread out and they did. 4' 12 second beam sea's with an occasional 6'. I realized the boat was handling the waves but the boat was slightly under powered. I needed all the throttle a few times as I zigzagged back to Racine. We made it back to Racine with no issues, The boat handled the waves good but I reduced my Max to 2' waves unless they had 4 X wave to period.

Many claim they are comfortable in much higher wave hight. It is all opinion of what your passengers are comfortable being in.

I Have mentioned a trip in the North Channel on TugNuts before. I made a weather condition decision to go. Plan was 60+ mile run. This decision to go was based on no knowledge of weather conditions on the North Channel and lack of weather research for that day. We left the bay and proceeded in to the North Channel (Lake Huron) the waves were larger than expected and the wind was much stronger than expected. It seamed to be 3' and with short periods following sea's and the boat was loaded. This was in my opinion the roughest water my C26 had been in for any length of time . Some of the waves high enough I used all throttle to climb out of the trough so the wave didn't push us. A few did and heeled the boat at what felt like 30 degrees. It was not fun. When we made it to our destination and reviewed our day. I did more weather research and found there was a high wind warning on the channel. The weather buoy was recording wave hight of averages of 1.4 meters 5 second periods .Meaning 4' to 6' with occasional higher. I believe theses occasional higher were the ones that healed the boat to an unconvertible angle. This was beyond my limits. This day reinforced my decision of 2' waves will be the comfortable norm unless the waves have a high second period.

Big swells are fun. There is a big difference of cruising in 5 to 6 foot swells and 6' waves.

I may be considered a fair weather sailor. Thats Ok!

 

[fmstuart]

Big swells are fun. There is a big difference of cruising in 5 to 6 foot swells and 6' waves.


Forrest Stuart
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[fmstuart]

I think the difference between swells and waves is brilliant. I have never thought of that difference, but you are spot on!


Forrest Stuart
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[HookedUp]

It's a bit different for me as I like to get out to the Gulf Stream to go tuna fishing. Here the Gulf Stream is usually about 80 miles offshore, so before heading out I get the buoy data and predicted waves/weather from https://graphical.weather.gov/sectors/akqMarineDay.php. Of course I still get caught in those summer storms occasionally, but as I suspect you'll agree the boat can handle bad weather better than the occupants.

If I'm going out after dawn I also look at the beach cams before heading out as it gives me a good idea of what to expect for those first 10-20 miles. Most times we leave in the dark, so all I have is the buoy data and the graphical weather predictions. Here, the buoy data will tell me if the waves are steep, very steep, average or swell, so I don't have to do the math. If they're over two feet and steep or very steep we plan for a better day as 2 1/2 - 3 hours riding in that kind of mess will ruin your day, especially when you know you have the same ride to face going back.

 

[TexasEye]

Legal or Design Standards verses Personal Standards....

Just because the boat data implies she can handle the conditions should not dictate your final decisions. Most design data is certified with an experienced crew often an expert crew. and...The boat is in perfect condition and loaded correctly.

KSA's apply to Boating Decisions.

 

[dclagett]

One major variable that has not been mentioned is the the size and configuration of the boat. Another that has been touched on is the direction of the waves with respect to the boat direction. These two variables make a significance difference in your comfort. As an example: I have a 25 RT and in 3’ waves on the Chesapeake Bay (I don’t know the period) going into the waves is comfortable, however going with the waves is significant work and not comfortable. The boat tends to dig into the next wave in following seas. I had a 22’ CDory and just the opposite occurred in the same sea conditions. Head waves were extremely uncomfortable and it was hard not to pound the boat no matter what speed. Following seas in the CDory were very comfortable. Another example: I owned a 40’ Motoryacht and for the 6 years I owned it I never felt uncomfortable on the Chesapeake unless the waves were coming from the stern quarter, which increased my work load to keep on course. The boat was build in New Jersey and needed to handle the ocean inlets so the 3’, 4’ and 6’ waves on the Chesapeake were comfortable, however docking in 20 to 30 mph winds was sometimes a challenge.

I suspect my 25 RT is in general not as comfortable as a 41 RT in rough conditions.

 

[Brian98133]

Agreed. 3'+ following seas in tight frequency dictate that I stay on the uphill side of the wave/swell, as trying to overtake following seas that size can create a very dangerous situation.

 

[FWTMD]

Pleasure boating. If it isn't a pleasure, don't boat.

"Every man has got to know his (and his boat's) limitations." You will live longer and have less gray hair if you find out what those are by starting at the small end of the scale and working up, than by experiencing the large end and saying "uncle."

No awards are given for surviving avoidable bad conditions.

 

[Hydraulicjump]

All of us have horror stories to tell. If you don't, well you are either very lucky, exceptionally careful, or you don't use your boat enough.

I know this has been discussed on this site before, but we routinely use windy.com to plot our routes. For weather it you can sample multiple models, which is always a good option. An ensemble approach gives you higher confidence in the forecast. Depending on where you are the European model, the ECWMF is the best long-range/high resolution model and within the states the NAM model does a good job for a few days out. This is vastly better than the NOAA marine forecast or Environment Canada forecast, which are too general to be much help.

the nice part is you can select a time and place on your route and you will have a forecast of wind, wind wave direction and height, and swell direction, height and period. It's pretty slick and free, although you can pay $18 a year for a slicker version.

We use it religiously always checking back to Aquamaps to see what the tide direction and current magnitude is. Despite all that, we still have days where we get a world class beatdown in a 20kt breeze with wind waves built against a ferocious tide. The most dangerous thing on a boat is a schedule.

Jeff

 

[baz]

I sure like windy.com site. 🙂

 

[Bruce Moore]

PredictWind is another excellent multi-model site/application.

Cheers,

Bruce

 

[Danation]

Back to the wave height vs. period question. When out on the ocean (with swells), I have heard of the rule of thumb never to go out when the swells+waves height in feet is equal to or greater than the period. You can look that up on NOAA's forecast. It has held on trips I have made tuna fishing off the coast of Washington.

Within protected waters, there aren't swells, so you are just dealing with wave height. For me, when NOAA says 1-3, it's not fun but can be navigated safely. 2-4, not worth venturing out, and it usually small craft warning.

 

[Annie Time]

We boat out of Half Moon Bay in northern California. All of our boating is done using model predictions from sites like Windy.com. We always have to look at the period to boat safely. We like to use the rule of 3x the period (swell) compared to the height. This gives us margin if things like the wind wave on top of the swell changes in the course of our day. So 3 feet height on a 9 sec period would be a good day. 9 feet on 27 sec period would be a good day. Lots of up and down but safe. When things deteriorate to 2x we are running for cover. If the waves are what we call square, 3x3 or worse we are staying tied up safe in the harbor. I believe the lakes waves are all square as there is not a long enough fetch to generate a swell longer then the height. We would use our rule and not go out in 3x3. That is not pleasure boating - more like victory at sea.

The boats will take more than the passengers can handle, but who wants to risk all the things that can go wrong?

Wind is another factor, we don’t like to go out if the wind is predicted to be 15 knots or higher when you combine wind wave on top of swell height and period, it can add up fast

We have been out when the weather turns, it’s not fun but our boats can get us home safely if you are carful.

My 2 cents


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[tlkenyon]

In the oceanography class I tool a long time ago, I learned that the wave forecasts are for a thing called "Significant Wave Height" which is the "mean wave height of the highest one-third of the waves." This means that larger waves can be expected. For example, if there is a forecast 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. 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 1,000 waves will be greater than 6 feet. The largest wave that might be encountered is twice the forecast wave height, in this case 8 feet. The longer you are exposed to the waves, the higher the likelihood of encountering these statistically-indicated higher waves.

In a place like the Great Lakes, where the shoreline can have a significant effect in wave height and direction through reflection and refraction of the waves, the so-called "rough waves" can form and really wreck your day.

Understanding the forecast is important....be safe our there.

TK

 

[Tumbleweed]

I have a question for dclegett and brian98133 - are your RT's inboard or outboard? I'm wondering if the ability to trim an outboard for bow-up makes a significant difference in handling following seas. Is that the reason the C-Dory Handles following seas better in the conditions discussed?

Does anyone else have experience with inboard vs outboard Ranger Tugs handling following seas?

Thanks,
David

 

[Remedy2]

Within protected waters, there aren't swells, so you are just dealing with wave height. For me, when NOAA says 1-3, it's not fun but can be navigated safely. 2-4, not worth venturing out, and it usually small craft warning.

This is my rule of thumb. I fought 2-4s (seemed bigger) from Des Moines to Elliott Bay and it was brutal. Never again. I'll wait it out.