6-8 foot swells! Whats the danger? - SailNet Community

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Old 11-14-2011
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6-8 foot swells! Whats the danger?

Went out for a sail and to my surprise I encountered 6-8 foot swells. It was the first time I have been in those conditions. I am more used to to 2-3 foot waves that are choppy. These were rolling 6-8 footers and to be honest other than the visual intimidation, the boat handled them quite easily and it was actually not rough at all. The boat just glided over them where the smaller waves seem to smack the hull. The winds were about 10 knots and other than the swells it was great. I didn't stay in it long and sailed back into the harbor and enjoyed sailing there. I would have stayed in the swells but the wife was bit nervous as neither of us had been in those conditions. Asking a seasoned sailor about it and he said it wasn't too dangerous as long as the wind didn't get too heavy. He said if it gets harder than say 20 knots then the swells can start to break and then it gets a bit more challenging. I just want to know what I should be aware of if I encounter them again.
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Old 11-14-2011
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The period of the swells determines how comfortable the are in deep water. A 12 second interval for an 8 ft swell will mean it is smooth, while a 6 second interval will mean its rough. Regardless of period, there is danger in shallow water, where the swells may break--if the channel into your marina is only 10 feet deep, it will be impassable.
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Old 11-14-2011
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The swell can come from hundreds of miles away. There are few better feelings to me than to get out of Lake Champlain and back in the swell of the ocean. It can be an indicator, depending on its direction, of some impending weather to be aware of. Coming from the deeps onto shallower water, it can create some interesting effects such as in Block Island Sound and off Martha's Vineyard and Nantucket.
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Old 11-14-2011
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I'd take 8 foot swells over our 4 foot chop, any day. Just make your tacks nice and smooth, and avoid presenting your broadside to the sea any longer than necessary (without any way on, at least).
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Old 11-14-2011
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Here in hawaii 6-8 foot wind swell is typical with a 25 knot wind. I was out Saturday and had 30 knots gust to 35 with 7 foot swell and at times a 10 footer would rool through- these were wind swell and on top of that there was a 4 foot ground swell from storms near alaska. I had two reefs in the main and a roller jib about 1/2 out. I was single handing and the boat handled all fine (S&S 34).

Actually the boat handles things better when fully powered up, but not overpowered. A proper reef makes all the difference. I have been out in equal wave conditions with winds 25-30 knots with full sail, got overpowered and could not steer the boat due to the weather helm. Rolled the fuller in about 1/2 and all was great again. Better to have to little sail up than too much. It is amazing how calmer everything gets when properly reefed. The boat heels less, less force on all your standing and running gear, easier to steer and less chance of things breaking. The other thing is make sure everything is secured down below and on deck. You don't want things flying around when going through waves. Secure your anchor well, have your jack lines set up. Know you boat well so if somthing does break, you know what and how to fix, and you have some spares parts to improvise a fix- I am still working on that one.

Thing is too learn how to steer around waves to get a better ride and less pounding of the boat. Look for big waves coming (or breaking waves and steer to lessen the impact. Thing to try to avoid is a wave hitting you beam. It can fill your cockpit with water and knock your boat down. They say any breaking wave more than 1/3 the lenght of your boat is dangerous as it can lead to a knockdown- so beware.

http://www.passageweather.com/

BTW, above site is great for wind and swell conditions/predictions
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Last edited by casey1999; 11-14-2011 at 01:42 PM.
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Old 11-14-2011
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Quote:
They say any breaking wave more than 1/3 the lenght of your boat is dangerous as it can lead to a knockdown- so beware.
But, if I understand correctly, it is just the portion that is breaking that is dangerous. So, if you are on the beach, the whole height of the wave is breaking. If you are on the ocean, with a large swell, but only the top few feet breaks, then you are not in much danger.
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Old 11-14-2011
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Swells and breaking waves at the beach are different creatures. Swells on a nice sailing day don't usually break unless there's something happening on the bottom like a quick rise over a shallow area a la the Potato Patch just outside of the Golden Gate Bridge in SF. Yesterday we had small swells (4' ish) and wind generated white caps and counter swells close to shore. A little lumpy, but nice full on surfing when the wave pattern was right!

Last edited by puddinlegs; 11-14-2011 at 03:39 PM.
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Old 11-14-2011
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Newport,

The swells along the SoCal Coast are dramatically effected by depth of the bottom. It is reasonably deep outside of Newport, so the swells are gentle. Up by Seal Beach, the bottom is shallow and the swells will tend to be short and steep(er)


The S30 is designed to be an offshore champ, so it should handle big swells with ease.

One of the posters mentioned that the period of swells is usually the key variable. Wide spaced swells are usually easy to manage.......and fun to surf downwide


BTW - when applying sail repair tape, best practice is to round the corners of the tape to not have a sharp corner which (supposedly) will catch easier. I have no idea if the round corner adage is true, because since I have never seen anything but rounded corners on sail patches.

Last edited by WDS123; 11-14-2011 at 03:41 PM.
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Old 11-14-2011
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Quote:
Originally Posted by Barquito View Post
But, if I understand correctly, it is just the portion that is breaking that is dangerous. So, if you are on the beach, the whole height of the wave is breaking. If you are on the ocean, with a large swell, but only the top few feet breaks, then you are not in much danger.
At sea, you are not concerned about a wave breaking on the shore line (a wave normally starts to break when the depth is about 1/3 its height as I remember) unless you are getting to close to the shore or have to cross a sand bar or shallow water to get into/out of your harbor (and that is another issue). When at sea, a wave is considered breaking when you see white water on its crests and it actually starts to curl. This should not be confused with a white cap which is not dangerous. A breaking sea can be caused by many things: a current moving in the opposite direction as the wave train, very steep waves due to very high winds, two wave trains meeting each other and combining (rouge waves)- these breaking waves when the wave height is 1/3 your boat length is what can knock you down.

Last edited by casey1999; 11-14-2011 at 03:50 PM.
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Dangerous wave heights

It's always been my understanding that when the wave height is equal or greater than the beam of your vessel, you run the danger of a knockdown if you take those waves beam on. If the wave height is greater than or equal to the length of the boat you could get pitchpoled if the period is short enough and you catch the wave the wrong way (like heading down the wave face too steeply to where the bow gets buried to deep at the bottom of the trough).
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