Safe sea state?

[David in Sandusky]

In my experience, a swell is usually smooth enough to be a minimal issue. Wind becomes uncomfortable between 25 and 35 knots. So wind driven waves are the big issue for us. Sailing close hauled, things get uncomfortable around 5 footers. But most of our cruising is on a reach, and we have been quite comfortable in 6 footers if they are not breaking. If the waves come abaft the beam, surfing begins, the ride is fine, but the helm will work hard, since the waves try to steer the boat. So we stay out of open water when the forecast is 6-8 foot wind driven waves. (With depths of 30 to 60 feet, waves on Lake Erie tend to be more "square" than those in deeper waters.)

We could probably give more pointed advice if you told us your home port. The Chesapeake and Albemarle Sound are very different than sailing in the open waters of the Atlantic, for instance. Also, "coastal" sailing often means that you have some protection from windward shores, depending on the wind direction. This reduces waves substantially compared with open water.

 

[jibes138]

Read the book "Waves" it is all about waves and is a very good book.

 

[shemandr]

It might seem obvious but do waves travel at different speeds? I think I read somewhere - maybe as accurate as the wave height source - that the speed of a wave in governed by the density of the water it travels through. But, it seems to me that a chop with square waves comes at me faster. So do all waves in the same density of water travel at the same rate? How much variation is there between water at 35 degrees and 70 degrees?

 

[Kings Gambit]

Travel velocity of ocean waves is directly proportional to their wavelengths, assuming there is deep water under them (i.e., no bottom effects). Velocity of sound waves in water varies with water density--velocity goes up with increasing seawater density. Seawater density is a function of temperature, salinity, and pressure (depth).

 

[shemandr]

Velocity of sound waves in water varies with water density

That's what I was thinking of. Years ago there were studies done with sound waves in the Pacific to try to quantify ocean warming.
So if the the period of waves determines velocity, what determines the period? I think I'm going to end up reading Jibes138's book Waves. Hopefully on Kindle 'cause I have some flight time coming up.

 

[Jwhy]

"Waves" sounds like a must read.

I did some more research on the NOAA site and found a nice overview map to go along with the coastal zone maps.
http://www.weather.gov

Part of my question was stimulated by the recent large swell predictions with a long period for the west coast that didn't sound that bad until I read-
http://forecast.weather.gov/wwamap/wwatxtget.php?cwa=usa&wwa=Small Craft Advisory For Rough Bar

The note for San Francisco explained it.

 

[FastOlson]

There is a lot of interesting wave info you can study and learn, but for everyday boating there are some "shorthand" guides. Main guide is avoiding being out when the ratio of wave period vs wave height approaches "Square". i.e. when the seas are averaging 7' and the period shortens up to about 7 or 8 seconds, stay home.

Even in so-called protected waters where you might have chop that is 3' by 3 seconds, the rapid collisions with seas will halt a small boat and make it hard to get back up to speed.
In the open sea, you can have a nice day of watching horizon appear and disappear ... even in bigger seas IF the crests are a long way apart.
Once those seas start breaking, you do need a new game plan!
I had one memorable delivery offshore where we spent 36 hours running in 19' seas that had a lot of breakers. Fast boat and we only got pooped once. Exciting and scary. Sunny day and moon-lit night. Beautiful to look at, but it did get us all contemplating our relationship with fate and God....
That was one long sleepless night, of just hanging on until your watch started (or ended), and listening to the thump and whoosh of big seas passing under (wind was steady 39+) , but the boat was rocketing along with a scrap of head sail at 9 to 10+ kts. A shot of green water over the cabin top would launch a spray of water thru a "closed" ventilator every so often.
Good news is that the Sea takes no personal interest in your discomfort.... it is totally indifferent.

Regards,
Loren

 

[jssailem]

In the early 70's I was sailing downwind on the Chesapeake towards Norfolk. We had a following sea. Wind driven waves from the long fetch were 6-8 feet. Aboard the 28 footer with a canoe stern some 2.5 feet above the water the waves looked like giants about to fall and fill my cockpit. But as the waves approached, the boat slid up the wave, we began surfing the crest, then it slid away and we settled down ready for the next ride. It was a first time experience that scared me at first, then was accepted as ok, even a kick in the pants. As was said it is a personal level of comfort you need to develop with your boat. You can be the judge. Take baby steps and build you skill. As Capt Ron says: "If it's going to happen, it's going to happen out theres..."

 

[Captn Scotty]

Another consideration to watch for is the direction of swell vs wind direction, if the lump is coming from the west and you have a sustained wind over a long fetch from the southwest it can be uncomfortable. However, if it is directly opposing it will tend to knock the lump down. You always have to be on the watch for backing or veering winds.