Wave height vs period

Didn’t see a thread on this in the archives, so:

I understand that, as a rule of thumb, wave period should be about two times the height for “comfort” in open water. And I know that comfort is a relative term.

Just wondering what sea conditions most you in 40-ish sized boats would consider comfortable?

When we lived in SoCal and often cruised to Catalina Island for the weekend, my personal rule of thumb was a forecast of 5' seas or less. Once or twice we got into 6'+ and regretted it. It wasn't unsafe but uncomfortable at that level.


Can't say what the period was at 6' but I would guess less than 12 seconds. Would 15 seconds have been more comfortable. Maybe but not much.


David

When I crossed over from the Bahamas we were in 5-6’ (I think, I never know for sure) on the stern quarter, and it pretty much sucked. Had the sails out but we were pretty much running with the wind and motorsailing so I think the apparent wind was very low so the sails didn’t help with stability.

So, 5-6’ may be my limit, unless it’s a long period, which it never seems to be.

Lots of valuables in determining comfort.

Direction plays a big roll. Going head on into seas and quartering is very different from traveling in beams seas or taking them on your stern, depending on your speed. As previously mentioned, period has a great deal to do with comfort. Duration of exposure is also a big factor. Have been in 7'+ seas a couple of times, but only for a few hours before moving into the lee of the land.

3 to 4' is my general go. Above 4', period, duration of exposure and importance of moving today, become factors. I try my best to keep stuff from sliding around. While stuff is generally stowed well, I'm not interested in cruising with a seatbelt on as my coffee cup and cellphone slide back and forth at the helm. We're out here to have fun aren't we?

Ted

angus99 said:

Didn’t see a thread on this in the archives, so:

I understand that, as a rule of thumb, wave period should be about two times the height for “comfort” in open water. And I know that comfort is a relative term.

Just wondering what sea conditions most you in 40-ish sized boats would consider comfortable?

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Not a bad rule of thumb for starters. However your route vs the waves is an extremely important factor as well. Also in a lot of areas, wind waves on top of inherent swell come into play. Likewise, wave direction vs any current that may be present.

We look at the period just as much as the height. We also look at the direction.

5’ x 7 Seconds is not an issue as long as they are not straight abeam, but even then they are doable, we just hit the throttle to dampen roll.

5’ X 10 seconds is no problem at all

8’ X 7 seconds is OK but “wet” as a head sea, but we don’t generally go out in those conditions. Abeam they can be extremely unplesant, requiring a quartering angle of attack.

Here is a video of us in 5’ x 7-8 second seas a couple weeks ago. These were bouy measured.

https://youtu.be/lX36WQJuEUE

sorry, unable to view, for some unknown reason

ksanders said:

We look at the period just as much as the height. We also look at the direction.

5’ x 7 Seconds is not an issue as long as they are not straight abeam, but even then they are doable, we just hit the throttle to dampen roll.

5’ X 10 seconds is no problem at all

8’ X 7 seconds is OK but “wet” as a head sea, but we don’t generally go out in those conditions. Abeam they can be extremely unplesant, requiring a quartering angle of attack.

Here is a video of us in 5’ x 7-8 second seas a couple weeks ago. These were bouy measured.

Click to expand...

Nothing comes up but voice over, but no pics.

Keep in mind that boating on the Pacific is different than the east coast or the Great Lakes. We have been in 18’ waves on the Pacific and the period was long enough so that it was exciting but we were not in fear for our lives. 18’ on the Great Lakes I would definitely be in fear for my life. Lake Erie in particular is so shallow that the waves are steeper and the period is usually short. We crossed Lake Ontario a couple of years ago in 6’ quartering waves and it was uncomfortable but not dangerous. The auto pilot worked very hard trying to keep us on course. I believe that a lot of it depends on where you are and what your comfort level is.

On our top heavy 40' Nova, we can do 5' swells with long intervals all day, provided they're not on the beam, which is sometimes the case during a Predicted Log contest.

Gordon J said:

Nothing comes up but voice over, but no pics.

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Here is a link to the youtube video

https://youtu.be/lX36WQJuEUE

We just had a bout with really short period 4 footers on Delaware bay. It was very unpleasant. Not dangerous but we'd rather avoid it when they're that close together.

For our typical cruising (here in the NE), 3-4 is about the max I "want" to cruise in. Above that, it becomes a matter of what direction, for how long and how badly do we want to make the next port today? Then there's also the very real matter of forecast vs reality. I find its always better (and often closer to reality) to add at least 1 extra foot to whatever is forecast.

Ken

So many variables.

I've been out in a 10+ foot swell where with a 20 second interval and it was a pleasure to boat in. The water was almost glassy with no wind.
I've also experienced ugly 4 foot conditions with mixed up swell swell against current that was horrid.

The comfort limit also depends on the crew. I don't mind rough water, but often I don't go out if I suspect the others aboard would not enjoy themselves. My wife is more adventurous than most, but still prefers not to have to hold on to stay seated. There's a couple fishing buddies that are willing to tackle anything for a big snapper.

As far as boat handling characteristics, my boat probably likes the swell on the stern more than most. It rolls like a sausage in a beam sea with out the sails; and hobby horses into a head sea like any 30 footer. Usually there's an angle thats fairly comfortable, but it doesn't always lead to where I want to go.

I don't think of it as height vs period, but height and period. It's also important to recognize what makes up the "wave." Is it wind or swell or both or multiple swells.

The Pacific is much different than the Atlantic because of the normal prevalence of swells which may be very high but very long periods.

The period double height rule of thumb is mainly for low wind waves. 2'@4 seconds, 3'@6 seconds. I think more in terms of period at least 2 greater than height and preferably 3 greater. 4' wave at 6 seconds is fine and at 7 seconds better.

There's also the separate issue of bars or inlets. You might have 3'@6 seconds outside as you cruise but find you have very large, confused waves at the inlet as they break over the bar, so that's always a separate consideration.

Waves I'll cruise on depend on so many other factors in addition to the wave itself. What boat? Experience? Guests? How long? For instance, I might be very comfortable with an hour and half run to Bimini with just my wife and myself and maybe another experienced boater in rough conditions that I would never do an 8 hour cruise off shore in with inexperienced boaters aboard.

After my first round of steep 6 footers in a 3 second period, I'll be doing my best to avoid that battle next time! Ouch!

http://www.trawlerforum.com/forums/s3/holy-crap-what-39536.html

I don’t get swell in the waters that I boat in except when crossing the Strait of Juan de Fuca. Most of the time we deal with wind waves. Height vs period are key. Most of the time we don’t get good forecasts on wind waves. Also, because of the variable currents, the conditions can vary wildly over a small area.

The trawler doesn’t handle the rough water nearly as well as the sailboats. Or maybe I should say that the boat handles it fine but the passengers don’t handle it as well in my trawler vs my past sailboats.

Gulf Coast off Al and Fl panhandle.... a 5 second period is rare. Mostly choppy disorganized and steep.

hjorgan said:

Gulf Coast off Al and Fl panhandle.... a 5 second period is rare. Mostly choppy disorganized and steep.

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You mean something like this?

Yeah, that's it.

I call that "washing machine chop"
Remember, the only thing worse than being at the dock wishing to be out on the water is to be out on the water wishing to be back at the dock!

I can't remember the last time we saw a 5 or longer period down here. When it's 4 x 4, you'll see me at the slip. The boat is way tougher than the skipper. I'd like to borrow "washing machine chop" Steve. Very descriptive.

Steve said:

Remember, the only thing worse than being at the dock wishing to be out on the water is to be out on the water wishing to be back at the dock!

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That's a good adage to remember!

We were just in Tahiti a couple weeks ago on a Bali 45-foot catamaran. On the 24-mile passage from Tahaa to Bora Bora we were quartering reported 6-7 meter seas (20-23 feet!), but the period was generally 8-10 seconds. It was quite a ride! Never felt in danger, but you certainly had serious focus while at the helm...

O C Diver said:

Lots of valuables in determining comfort.

Direction plays a big roll. Going head on into seas and quartering is very different from traveling in beams seas or taking them on your stern, depending on your speed. As previously mentioned, period has a great deal to do with comfort. Duration of exposure is also a big factor. Have been in 7'+ seas a couple of times, but only for a few hours before moving into the lee of the land.

3 to 4' is my general go. Above 4', period, duration of exposure and importance of moving today, become factors. I try my best to keep stuff from sliding around. While stuff is generally stowed well, I'm not interested in cruising with a seatbelt on as my coffee cup and cellphone slide back and forth at the helm. We're out here to have fun aren't we?

Ted

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Well said, Ted!

In our area there is no swell, but islands, connecting channels, and near vertical shorelines which can cause refracting and rebounding.

We were in fully loaded sea kayaks in Devastation Channel when a strong north wind came up suddenly with no place for us to hide. There were wave sets coming from around the island and from over the island (45 degree difference) which then bounced off a cliff making waves coming from four directions.

There was no rhyme or reason to them...they combined into 'haystacks' maybe seven or eight feet high which exploded at the tops when they couldn't hold together any longer.

It was like a rodeo ride, but with most of the weight below the waterline a fully loaded sea kayak is amazingly sea worthy. Would have been desperate in our current boat

There are so many local variations in sea conditions such as what Murray experienced, that a standard wave height limit is somewhat useless.

My biggest concern is breaking waves. A large, long interval swell which is usually benign can break unexpectedly, if there is a small rise on the sea floor. This can occur even in 100+ foot water. I learned this the hard way.

When I was young I had 13'3" Boston Whaler with 40 HP Johnson and two 6 gal red fuel tanks. Family had 38' raised deck, SD hull, single 180 hp. Perkins powered fly bridge sedan cruiser. We boated on weekends year after year... spring, summer fall. Took long jaunts up New England coast during dad's four week vacations. All year I kept the Whaler in water and used her often in the winter too. 38'er was hauled for bottom paint etc during winter months.

Some times on jaunts from NY to Maine and back again we towed the Whaler. Often I'd simply take off and meet our family cruiser in the next port. Some times on lesser duration distance cruises we'd leave the Whaler at dock.


More than a few times we'd get caught in some pretty snotty conditions. Have seen conditions that tested my dad's handling abilities and the 38' cruiser's capabilities. There was one time I was not aboard that really rattled my dad, mom and younger brother. Afterward mom forced sale of the cruiser "Never to go out again with dad" - It was beyond severe unexpected conditions... my brother was 14 yrs at the time and has become pale when recounting to me what occurred. Boat needed immediate hauling and bottom plank repairs at Block Island. Boat was bujilt to take anything... dad ran into something unexpected that nearly sunk that stout craft. Dad sometimes pushed things to the limit - remnants of his love for daring activities gained from piloting RCAF Spitfire reconnaissance planes in WWII - Shat happens!


With the Whaler, employing cues from dad's daring nature, I would go out Short Beach Inlet in mid winter storms. Have been in some really hairy wave conditions. My youth [that still has close semblances continuing today at... 66 yrs young] had a strong sense of no matter what I can do it! So far, I'm not dead!!


Sooo... reason I related the above to contents in this thread: Every type of sea. Every type of boat. And, every type of a boat's Captain experience then and there interacting degrees of capabilities.


I can say - having owned and piloted many different size and type boats, as well as being aboard many boats with good captains - Short of tall "surfer-type" heavily breaking waves... That 13.3" Whaler with 40 hp Johnson, leaving rear scupper drain open and full weather gear on as well as gas tanks battened down tightly is the boat that can handle nearly sea thrown at it. I have even broken upward through some not too tall breakers off Jones Beach during storms; that use-type is not recommended... but in my teens with courage burning brightly that is an incorrect chance I took.


Happy Boat-Handling Daze - Art

Very well written, Art. Daring nature and good judgement often don't go together. Just because we can do something safely doesn't mean we should do it or that we can do it comfortably. You mentioned the one trip that ruined boating for your family. I think back to the Nordhavn Atlantic Rally of 2004 and it proved all those boats could make it. However, the part that doesn't get publicized is how unwise it was for a couple of the smaller boats and even ruined boating for at least one couple.

We're currently on a long trip and one of our guests is our wonderful, nearly four years old, niece, Aurora. We want her to boat with us forever and enjoy it as much as we do. We have been and are very conscious of conditions and any that might make boating somehow less of a joy for her. Right now she absolutely loves being on a boat of any size. She's never been scared on one. It's part of our job to make sure that we don't put her in conditions that might scare her.

Every time you go out on the water, you create memories for yourself and anyone else with you. They can be very special memories or very traumatic ones. Often the traumatic ones are never overcome.

BandB said:

We're currently on a long trip and one of our guests is our wonderful, nearly four years old, niece, Aurora. We want her to boat with us forever and enjoy it as much as we do. We have been and are very conscious of conditions and any that might make boating somehow less of a joy for her. Right now she absolutely loves being on a boat of any size. She's never been scared on one. It's part of our job to make sure that we don't put her in conditions that might scare her.

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That's an excellent approach, whether your guest is young or even an older newbie to boating.

It's easy when you are old enough to never want to go over another wave more than 6 inches high...

Reminds me of one of the many boating truisms I like to relate regularly:

"The main characteristic of a captain with superior seamanship skills is his always avoiding putting himself in the position of having to use them"