Swell sailing

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Swell sailing

Postby talbot » Sun Sep 28, 2014 11:39 pm

I was sailing on the Umpqua River in Oregon, and decided to go out to the harbor entrance buoy, just so I could say I had sailed my DS on the Pacific. I checked the bar conditions, weather, tide tables, GPS, and VHF, and hung with a few sport fishermen in small power boats, just in case.

None of which prepared me for the experience of being in the troughs of Pacific swells, with nothing in sight but mountains of water above me. Besides being impressed by the visuals, I realized I was not sure how to safely handle the boat in those hydraulics-- the angle to approach, where to make a tack without getting rolled, etc.

This was not any special day for the coast. The breeze was light enough for me to be under full sail. The fishermen--when our waves and troughs were in sync so I could see them--were pretty laid back, fussing with their lures and lines. But the wind and tide both wanted to take me back in, so I let them.

Anyone out there with ocean experience have any tips?
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Re: Swell sailing

Postby Interim » Mon Sep 29, 2014 10:33 am

Talbot--

Great adventure! Things must have gone ok, or you would have written more. :)

Let me preface by saying I don't have any ocean sailing experience, but if you are looking for a written resource Chapman's has a nice section on handling conditions like you describe.

I look forward to reading what others have to say on this subject.

--jf
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Re: Swell sailing

Postby GreenLake » Mon Sep 29, 2014 12:13 pm

Tallest waves I was in were from a wake of a passing ship. They were a few feet high and probably steeper than your swell. We were ghosting along in a dying wind on otherwise flat water and by the time we realized that the wake of the distant ship was coming in that high we weren't able to turn the boat to meet them head on. We simply had no option but to take the waves from the stern. I was sure we would take some water, but we didn't. The DS just rose and fell with the waves. The distance peak to peak was such that the DS "just fit" in the wave trough - that's the best recollection I have.

I have taken water in situations where wakes came in over the stern quarter (diagonally). Usually just filled the motor well. I attribute the difference to the effect of presenting a corner, which does not have enough buoyancy to lift the boat with the wave.

I imagine swells with their longer period should be gentler, so the DS should be able to float over them without taking water, and unlike chop, I'd expect less "slamming" into waves. Was that your experience?
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Re: Swell sailing

Postby talbot » Mon Sep 29, 2014 2:15 pm

Thanks for the reference to Chapman's.
I don't think this is about riding through a single wave event, but living with wave after wave for as long as you are on the water. I'm used to surface waves that are directly related to local wind. If the boat is into the wind, it is into the waves. But swells are generated by storms on the other side of the ocean. So the boat can be dead to (local) wind, but still be broaching in relating to the swells. I was worried about how I would ride the rollers if I had to put in a reef. And where do you tack? At the top of a swell, like a skier turning at the crest of a bump?

I know, I was only outside the harbor for a short time, and maybe if I stuck around, I would find that nothing much happens except riding up and down. Technically, I was still over the bar, and had I gone out to open ocean, things might have been smoother in deeper water. On the other hand, the news carries stories about capsized fishing boats on our coast several times a year, so I have data, not just paranoia.
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Re: Swell sailing

Postby K.C. Walker » Mon Sep 29, 2014 3:46 pm

I don't have experience sailing Pacific swell. However, I have been in and out of "breach ways" from the salt ponds into the Atlantic in powerboats. It can get pretty bumpy and not something I would want to sail through or be underpowered. I would guess that you were experiencing the worst of it being over the sandbar/Delta. Likely your swell had a wavelength more than twice the depth of the water. This causes the swell to stand up and start to become surf. If it were a standard beach this is the zone where the surfers would hang out waiting to catch the next wave.

As you suspected, had you gone out a bit further it would likely have smoothed out. I've been out on the Atlantic when the surf was supposed to be 4 to 5 feet. I didn't go out through a shallow area that would have been affected, so no intimidating waves. Though it did feel like very big water, and rather exciting, it wasn't scary. The wind was moderate. It is an odd sensation to be out on the water and watch boats disappear in the trough and then reappear. Obviously, you would want to take care but I don't remember needing to be careful about when I tacked, that time.
KC Walker, DS 1 #7002
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Re: Swell sailing

Postby Interim » Mon Sep 29, 2014 4:01 pm

Chapman's refers to things like quartering the waves, and running parallel in the trough to regain speed before taking the next wave. I don't recall how specific they are about sailing in these swells--the book covers powerboats as well as sailing vessels. Worth a read, but I'm sure there are other resources out there too.

Hasn't been an issue on the Great Plains since the pre-historic seas retreated.

--john
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Re: Swell sailing

Postby talbot » Mon Sep 29, 2014 6:37 pm

I still have to look in Chapman's Piloting, but how do you handle intersecting crests, either with swells, wakes, or wind waves? One of the disconcerting things was to be lining up to head into the main swell (which was WNW that day), when I would see the secondary swell coming at me from WSW, with a nasty little peak where the crests met. In the short time I practiced, I hustled to take whichever wave I thought would arrive first, turning off the crest to face the cross swell. I wondered what would happen if I misjudged and went over that pointy intersection. When I realized I didn't know the answer, I headed in. This situation comes up all the time on the lake when powerboats are buzzing around, but it never seemed all that important before.
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Re: Swell sailing

Postby TIM WEBB » Mon Sep 29, 2014 9:34 pm

Never had TRW out on the open ocean, but two years ago on the FL120 we had conditions just inside of Pensacola Pass that may as well have been. Wind and tide conspired to create a 4-6 ft chop that could best be described as a washing machine. Plus, we were beating to weather, which didn't help. There was no choice but to go over crests, through troughs, and everything in between. Some boats handled it better than others. TRW performed well with a single reef in, but took on so much green water spray over the rails that I was forced to stop and bail the bilge, due to the many openings into same (which have since been identified and plugged).

Sounds like you made the right call, to head in when you realized you were in over your head, so to speak ...
Tim Webb
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(I used to be Her "staff", in the way dogs have owners and cats have staff, but alas no longer ... <pout>)
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Re: Swell sailing

Postby GreenLake » Mon Sep 29, 2014 10:06 pm

I believe steepness, which is height relative to wave length, is an important factor. For the same height, I would expect more problems from short, sharp waves (or longer, but breaking waves) than from wider, gently rolling ones.

I gave my experience with a ship wake on purpose. Because the speed of those things, the wavelengths are relatively long to begin with. Because of the distance, the longer wavelength part of the wake has had a chance to run away from any shorter waves, making the wave train smoother. I was in (very) deep water at the time, so no shallow-water effects. Because at its source the bow wave was 6-8 feet high (that's probably a low-ball estimate) there was substantial wave height left when it reached us. Powerboat wakes cannot compete.

My experience before that was from powerboat wakes in a confined channel, with reflections. Talk about criss-crossing waves. Not a pattern like you observed, but just random peaks rising at double the average height and troughs opening at double the average depths. The area has a speed limit, but for some boats that makes the height of the wakes worse. However, the lower speed makes the waves shorter, and therefore steeper, than when the same boats rush by on the open lake.

From that experience, where wakes slam into the hull and I regularly take small amounts of water, I had feared the worst when we first saw that ship's wake following us. When the first wave crest didn't slam into the transom, but lifted us I was beginning to be relieved, until we tipped down in the first trough, which made the second crest look even taller. I was sure that the DS would "dig in" but, as I wrote, it "just fit" into the trough and rose over the next crest as easily as over the first.

In that way this was very different also from wind-driven chop, which, for some angles, does slam into the hull (it's harder to sail backwards into chop, even if on some occasions I have surfed it on a downwind run, so slamming happens when you sail into it). And unlike chop, this did not come in direction that was related to the wind.

So, my question with respect to your swells, Talbot - did you have any issues with the waves being steep to the point that they were slamming into the boat? Or that you were actually taking water? Or were they smooth enough that you were "bobbing" over them like a cork. I think those cases may make for different strategies.

Non-breaking waves have an interior circulation that is based on a circular motion of the water (each tiny volume of water proscribes a circle as the wave passes). Because of that you get a surface current that goes with the wave when you are on the crest, and one that goes against the wave in the troughs. If you sail with the waves, steering can be affected as the wave crests under you, in some conditions, the flow over your foil might even reverse direction. (That's how really big, especially breaking waves, will broach boats). If you hit the wave at an angle, the cresting wave will set you leewards. And in the troughs, you may experience less wind.

Those are the basics and your strategies for sailing would be expected to be making use of that. So, for one, I would expect that if you tack like a skier on a mogul, you would have both the wave circulation and the (extra) wind to contend with. Whether that helps or hurt you would appear depend on what angle to the swells you were sailing. (Having to deal with multiple crossing wave trains is no fun). I think that crossing the bar was the most gutsy move you made...

A boat like the DS behaves differently from a keel boat in one important aspect. On a keelboat, especially a more traditional hull with narrow beam, you would expect that boat to stay closer to the vertical, because the pendulum effect of the keel counteracts the effect of the "tilted" water. On a DS, with no ballast and wide beam, you would expect the boat to tilt immediately to conform to the wave surface (if you sail more or less parallel to the crests).
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Re: Swell sailing

Postby talbot » Tue Sep 30, 2014 5:45 am

No, nothing was slamming into me. I was just not used to sailing uphill. Or to the realization that I had to actively steer indefinitely, whether the wind was blowing or not. Sort of like whitewater boating, except the rapid never ends.

Again, it was just a regular Sunday for everyone except the nervous old man in the daysailer. I kept the radio on from the moment I trailered into the parking lot. There was a securite (safety advisory) for the bar, but it remained open all day. The Coast Guard closed the next harbor north of us, but no one around me seemed to be concerned with anything except fish.
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Re: Swell sailing

Postby jeadstx » Tue Sep 30, 2014 12:49 pm

Only sailing of that type that I have done has been on the Tx200 when the chop gets a bit big. This year we had strong winds (25 to 30 knots) on the first day so the boat did a lot of surfing down the waves which made it hard to hold course. We had the waves coming from the stern starboard quarter. I'm glad we didn't have to tack in those conditions. On the 2011 Tx200 we had to cross one of the large bays with 4 to 6 foot chop and winds above 20 knots and gust to 28 knots (according to NOAA radio). We did a lot of wave surfing that year.

Next year I'm thinking of taking the outside route in the Gulf on the first day of the Tx200. I will be dealing with swells out there I'm sure.

John
1976 Day Sailer II, #8075 - Completed the 2011, 2012, and 2013 Texas 200
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Re: Swell sailing

Postby talbot » Wed Oct 01, 2014 6:31 pm

Six-foot "chop?" I'm trying to imagine what that looks like, but it's too disturbing.
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Re: Swell sailing

Postby GreenLake » Wed Oct 01, 2014 8:23 pm

What John means is six-foot wind-driven waves.

Here is NOAA's estimate for the relation between fetch, wind speed and wave height.

Image

The Tx 200 is a largely downwind event that crosses several basins (lagunas) in their lengthwise direction. As the day goes on, you add to the fetch of the waves.

From the diagram, a 6' wave would need a fetch of 20nm. There is an additional variable, which is the time that the wind has been blowing. For the wave height to reach the maximum size for a give windspeed and fetch there's a minimum time that the wind has to blow from the same direction. Above that, there's no more increase.

This diagram gives some data.
Image

The dark blue likes match the first diagram and give wave height in relation to fetch.
The dashed blue lines show that the wind has to blow for nearly 4 hours at 30kts to result in waves of 6ft with a period of 5.25 seconds (the white lines show the period).

At 25 kts, the wind would have to blow over a fetch of 40nm for six hours.

The lagunas are rather shallow. In some areas, that could lead to the waves piling up, in other areas, I suspect the water isn't deep enough for waves of that height to build. But there are some places along the published route where the conditions would seem to be such that this kind of wind driven wave could build.
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Re: Swell sailing

Postby jeadstx » Thu Oct 02, 2014 2:20 pm

I remember crossing Aransas Bay in 2011. We went straight across the bay where the rougher water is. NOAA radio was reporting 4 to 6 foot chop. I would look at my cousin when we were in the trough of a wave and could see wave tops about 2 feet above his head for the wave behind us. Fortunately we were running downwind (wind off the stern starboard quarter) with a double reefed main. My cousin kept saying "more wind, bigger waves" and I would respond "shut up Bill". My boat felt small out there that day. It was good when we reached the land cut and the waves reduced significantly, even if the wind didn't.

Reading some of the accounts from this year by the "Ducks" (PDRs) sailing the event can give an idea of the conditions on the Texas coast. Here is one from Small Craft Advisor: http://smallcraftadvisor.com/our-blog/?p=4208 The "Duckers" had a rougher time of things this year than the other boats.

John
1976 Day Sailer II, #8075 - Completed the 2011, 2012, and 2013 Texas 200
1952 Beetle Boat Swan Catboat
Early Rhodes 19
1973 Mariner 2+2, #2607 - Completed 2014, 2015 and 2016 Texas 200
1969 Day Sailer I, #3229
Fleet 135; Canyon Lake, Texas
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Re: Swell sailing

Postby GreenLake » Thu Oct 02, 2014 4:10 pm

That's fairly dramatic. How did he get the aerial picture?
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