Safe sea state?

vhoisington · Oct 30, 2016

I've been out in 30 waves, even broadsided by a 45' wave, the good news was we were on a 110' schooner but it still threw people around. During one day of my basic sail training (5 guys) on a j-24, one reef in the main and the 90 % jib up, we did just fine, even with an offshore breeze clocked at the sail club at 60+. But no waves just wind.

If you are comfortable with your boat, and how she handles you can sail in most anything. Now on the other hand, if you or the admiral isn't comfortable with whitecaps on the bay, it's probably better to stay in and have another beer.

Read the stories, people and boats survive major hurricanes, and I've seen them sink in a small gale. Preparation, know your boat and how she handles, preparation, keep everything in tip top shape, did I say preparation, and planning and you'll soon learn what is comfortable and what is just not worth the stress.

Good question, I'm interested to see what others have to say.

Victor

capta · Oct 30, 2016

I guess it really depends on the boat and one's skill set.
If you want a sailing vacation in the Eastern Caribbean around Christmas time, you'd better be prepared to sail in winds as strong as 35 knots and seas to around 10 feet in the channels, or you are never going anywhere. If that's not your comfort zone then try after March through October and if there are no tropical systems passing through, it's usually 10 to 15 with 3 to 5 foot seas or less.
I don't think anyone else is capable of saying what conditions are suitable for you and your boat. Stick your bow out there and if it's unsuitable, turn around and spend another day in the marina/anchorage. What else can you do?

Kings Gambit · Oct 30, 2016

Jwhy said:
I'm looking at coastal conditions and trying to picture how rough the water is from the predictions of swell height, period and direction, wind wave height and direction, and wind velocity.
I know what 30kt wind feels like and I've been in 10 ft swell with 15kt winds, but what combination makes it wise to spend another day in port before starting the next leg of a trip?

Need more information. 1) Your point of sail to destination; 2) wind speed; 3) significant wave height; 4) shape of waves (steep versus not steep); 5) period of waves; 6) the degree of mixed swell; 7) principal swell direction relative to your point of sail/heading, etc. For example, steep waves, > 12-15 ft, on the beam, might be dangerous in your boat; decidedly so if breaking occasionally.

shemandr · Oct 31, 2016

It's a good question. There should be some kind of index that compares wave height to period to give a relative index of roughness. I don't know of one. This data is available from buoys and other sources. It's not wave height alone - many of us have passed over swells of 10 feet or more and barely notice them. In my case my 35 boat has been stopped and turned around by waves which weren't 4 feet but were extremely steep and close together.

JamesG161 · Oct 31, 2016

shemandr said:
There should be some kind of index that compares wave height to period to give a relative index of roughness. I don't know of one.

Most professional meteorologist use the Beaufort Scale...
https://en.wikipedia.org/wiki/Beaufort_scale

Make mine Beaufort 5 or less for fun, but my boat is ready for 8 or less.
Jim...

capta · Oct 31, 2016

shemandr said:
index of roughness.

It's still an individual thing. What one person might consider a 'rough' day is probably someone else's 'grand old fun' day. There can't be a one size fits all sort of thing in this.

Ron20324 · Oct 31, 2016

FWIW, my B323 2006 came with CE Certification the boat was rated to waves of 4 meters, wind force of < B 8. It's an "offshore rating".

Kings Gambit · Oct 31, 2016

A sea state is what it is--that's not a matter of opinion except perhaps as expressed by one's skill in assigning Beaufort numbers. The OP was asking about safety in his boat, a Cat 30, under various conditions of sea state. Small boats are generally more vulnerable to big conditions than large ones; especially if the small boat was not designed and constructed with the expectation that it would be sailed in high seas or in rough conditions for extended periods--such as days to weeks at a time. A old Cat 30 and an old Tartan 30 might not feel the same nor offer the same security in the same rough conditions.

markwbird · Oct 31, 2016

If you are in doubt maybe you should wait. That said, you will never gain experience unless you get out there and try it. Just make sure you have a good plan and a good backup plan and that all your safety gear is in good working order.

shemandr · Oct 31, 2016

I thought about the Beaufort scale before posting. I guess it is the operational gauge of record. But I still think there could be something better. After all the Beaufort scale uses a fair amount of vague terminology such as "Large waves." BTW can we agree that a 2 foot wave means that there is two feet of height between mid wave and the crest and not 2 feet from trough to crest?

Kings Gambit · Oct 31, 2016

shemandr said:
BTW can we agree that a 2 foot wave means that there is two feet of height between mid wave and the crest and not 2 feet from trough to crest?

If you wish to alter the definition of a couple of hundred years of oceanography!

What you're talking about is effectively the "amplitude", as also used to describe a sine wave, etc. I think you must stick to the actual definition. If a boat slides down the face of a wave, it's going all the way to the trough-- a drop of, say, 8 ft. Not 4 ft. Or, if you're topping a wave heading into it the bow will crash into the trough following the wave. That's the stress the boat "sees", so that's what we must refer to.

leghyker · Oct 31, 2016

I have heard the thumb rule. If the wave period is the same as the wave height, its choppy. If the wave period is 1.5 times the wave height its moderately choppy. If the wave period is double or more the wave height its nice. As the wind picks up the chop picks up.

Parsons · Oct 31, 2016

shemandr said:
... BTW can we agree that a 2 foot wave means that there is two feet of height between mid wave and the crest and not 2 feet from trough to crest?

I think that you are referring to "amplitude", and that height is the difference between corresponding crests and troughs.
https://en.wikipedia.org/wiki/Wave_height
FYI: When the US National Weather Service refers to "significant wave height" in their forecasts and measurements, it's the measure of the largest third of observed waves to eliminate some of the variation we naturally see in waves. These big boys are the ones that cause damage, and make my coffee mug skip off the nav station.

shemandr · Oct 31, 2016

OK, I guess we didn't agree. But we do now. So long as when I read a wave prediction, or look at buoy data, I know what it means.

MrBill_FLL · Oct 31, 2016

for me it really depends on wind direction. 25knts from west is not much wave action.

i like to view a ocean web cam. after seeing the NWS forecast.

-ymmv

Johnb · Oct 31, 2016

Amplitude in the electrical or mathematical sense is the difference between peak and middle.

Wave height in the marine sense is from trough to peak. In the electrical sense that would be referred to as peak to peak, the peaks in that context being the max positive and max negative excursions.

rgranger · Oct 31, 2016

leghyker said:
I have heard the thumb rule. If the wave period is the same as the wave height, its choppy. If the wave period is 1.5 times the wave height its moderately choppy. If the wave period is double or more the wave height its nice. As the wind picks up the chop picks up.

Chop can also be affected by currents. If the wind is against the current, the waves "pile up". This can be a significant factor if you are coastal cruising in estuaries or other bodies of water where rivers empty... and/or tidal changes cause significant current. I remember a very uncomfortable sail to Tangier Island three summers ago... the wind was out of the south, the tide was going out adding to the normal current and I was sailing north. The wind was only about 10 kt but it was not a comfortable ride and we all got a little queasy. I've also sailed in 25 kt winds double reefed on an inland lake with no problems.

JohnShannon · Oct 31, 2016

Breaking waves are the big problem, otherwise it is just up up up followed by down down down, and your personal tolerance for seasickness and gear breakage. If you are leaving the bay you want to avoid the potato patch where the water is shallow. To be on the safe side you want to be in water deeper that 4x the significant wave height. Google "low speed chase" also "Fastnet race"

Stu Jackson · Oct 31, 2016

Height is very important and so is period and direction. Sometimes you have to add wind waves on top of the swell. You MUST get out and try different conditions and sail directions to find out what works for you.

Safe sea state?

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SBO Weather and Forecasting Forum Jim & John

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