Following Seas and Follow Up Steering

Professional Mariner Forum
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In the recent thread “What the Hell is Good Seamanship” one thing that was repeated a few times as a necessity was the ability to steer in a following sea.

Never having done it, I wasn’t sure what about it would be so difficult.

That all changed really quickly when I bought a 28’ sailboat and motored it from Baltimore down to Norfolk through the Chesapeake last weekend. With winds from the North and the tide ebbing, it was a full time job to hold a course. I had no GPS, just charts and a compass and I was doing a lot of night time sailing so it was important that I stay on track. I certainly have a better understanding of what is necessary to steer in a following sea now. Mainly constant rudder adjustments (often large) to compensate for the yawing of the boat. Correct?

Steering my sailboat I could feel the “wheel’s kick” (…and the wind’s song, and the white sails shaking…) and could steer just by feel while keeping my eyes straight ahead. I automatically knew whether or not my rudder was amidships. But I was trying to think how I would do it on a tugboat. Most of the ones I have sailed on have “non follow up” helms.

What do you guys prefer for steering in a following sea? Seems like a NFU would have you constantly checking you indicators since you can’t keep track of the rudder positions by feel. So what’s better choice? A Full Follow up? A wheel?

Having never had to do it, I can’t say for sure but I feel like I could steer much more efficiently with a wheel. (I’ll admit, I’m also just a sucker for tradition)

Just curious what you guys think is best, especially you older guys.

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Steering by jog stick is just as intuitive. Yes, you’re glancing at the RAI, but your inner ear will tell you when the ship is beginning to yaw in the other direction, and you need to change rudder angle. Experience like anything else. I remember greenhorns who would get seasick trying to steer in a big following sea, because one part of their brain was concentrating on judging the motion of the ship, which it should have, but which also irritated the motion-sickness part of their brain.

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We keep it on the mike as much as possible because hand steering requires calling out a second AB for watch, something we try to avoid as it leads to fatigue and work/rest peroid problems.

The ship autopilot aka the iron mike uses adaptive auto steering, in other words it learns how to steer, the longer its engaged the better it does. If the ship goes off course the “off course” alarm sounds and the normal response is to switch to hand steering to get it back on course and than switch back to auto. The issue with that is the auto-steering “forgets” what it has learned about course-keeping and has to start from scratch. What that leads to in heavy following seas is a constant futile switching back and forth between auto and hand.

It’s sometimes better to input, not the course you want into the autopilot, but to imput a course order that results in maintaining the course you want, and then, as the autopilot starts improving course keeping it will slowly change from the desired course to the input course. As the course-keeping slowly improves the input course is gradully changed to more closely match the desired course.

For example, say your are running south down the U.S. west coast with a big sea/swell running from the NW or NNW. You want to steer course 180 but the ship is yawing around the course of 190. In this case the auto pilot is set on 170, which will result in course-keeping of 180. But as the adaptive steering starts learning to steer it will slowly work from 180 to the ordered 170 so the input is has to be gradually changed as required to maintain 180 (170, then 175 etc).

Other autopilot settings may have to be changed as well, max rudder, off-course alarm.

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[QUOTE=Kennebec Captain;191155]

It’s sometimes better to input, not the course you want into the autopilot, but to imput a course order that results in maintaining the course you want, and then, as the autopilot starts improving course keeping it will slowly change from the desired course to the input course. As the course-keeping slowly improves the input course is gradully changed to more closely match the desired course.
[/QUOTE]

Reminds me of how they taught me to do chemistry: “you don’t know enough chemistry, yet, for us to teach you real chemistry, so use a series of wrong, contradictory models until you do know enough.” if only they told us that’s what they were doing, we wouldn’t have been utterly convinced that “they” were all lieing to us.

1 Like
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[QUOTE=Emrobu;191159]Reminds me of how they taught me to do chemistry: “you don’t know enough chemistry, yet, for us to teach you real chemistry, so use a series of wrong, contradictory models until you do know enough.” if only they told us that’s what they were doing, we wouldn’t have been utterly convinced that “they” were all lying to us.[/QUOTE]

Sometimes two wrongs do make a right. The magnitude and direction of the second wrong has to be adjusted as needed to obtain the desired result.

As far as I know the auto-pilot is unaware that we lie to it.

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[QUOTE=Kennebec Captain;191160]Sometimes two wrongs do make a right. The magnitude and direction of the second wrong has to be adjusted as needed to obtain the desired result.

As far as I know the auto-pilot is unaware that we lie to it.[/QUOTE]

For now, maybe. Iron Mike may be a subtle student. You’re just lucky your transits aren’t long enough for it to learn that it is being lied to, and that it’s learning resets each time it is switched on. If it had a very long voyage, like say, to Jupiter, it might inform you that it’s name is actually HAL 9000. Or Number 5.

“Not malfunction, Stephanie. Number 5 is alive.”

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Another way to “trick” the auto-pilot to give required rudder angle in following seas without losing the steering memory is to enter courses far off the course to be steered.

For example again steering 180 and stbd rudder is wanted a course of say, 220 can be entered, the auto-pilot will put on full stbd rudder (depending on settings) for port rudder 140 etc. For admijndships the current heading can be entered. It’s not a precise method but in a big sea precision is not needed.

[QUOTE=Emrobu;191163]For now, maybe. Iron Mike may be a subtle student.[/QUOTE]

Yeah, I hadn’t thought of that. Maybe Iron Mike is not really “forgetting” anything.

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Sailing in following seas can be tricky business. You can more or less control the driving force produced by the sails by for instance reefing, but not the forces due to the shape of the hull. If the wave face is very steep ultimately a large fraction of the weight of the vessel can get converted into driving force. This force is considerable and often greater than that developed by the sails. If the boat does not accellerate readily the wave keeps catching up with the hull lifting the stern further while the driving component of the weight keeps increasing trying to accelerate the boat anyway.

This compromises course stability and is a key risk factor that can lead to a broach. Furthermore a yaw can be amplified by the instable balance of forces and if the rudder is unable to overcome the yaw moment, the boat will come beam-on to the wave crest and broach. Accidents in following seas happen very quickly and are often violent as boats tend to be thrown forward from the crests.

A drogue is an good way to slow down the ship in bad weather conditions to counteract the driving forces of both the sails and especially the ship’s weight. Towing a suitable drogue can provide considerable benefits for boats that lack the course stability required to run in following seas.

Another thing is that if the speed gets out of control the bow and part of the foredeck can dive into green water which could lead to a disastrous pitchpole.

With a friend of mine we sometime used to ride in the North Sea with a powerboat on a wave slope just behind the crest, riding piggyback you might say. That always was quite a special experience!

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[QUOTE=Dutchie;191213][COLOR=#454545][FONT=UICTFontTextStyleBody]
This compromises course stability and is a key risk factor that can lead to a broach. Furthermore a yaw can be amplified by the instable balance of forces and if the rudder is unable to overcome the yaw moment, the boat will come beam-on to the wave crest and broach. Accidents in following seas happen very quickly and are often violent as boats tend to be thrown forward from the crests.
…
A drogue is an good way to slow down the ship in bad weather conditions to counteract the driving forces of both the sails and especially the ship’s weight. Towing a suitable drogue can provide considerable benefits for boats that lack the course stability required to run in following seas.
[/QUOTE]

They taught us this theory in survival crafts and rescue boats. I hope I don’t need it, ever, as I’m not a helmsman. Still, it would have been fun to find a nice sandy surfy beach and practice it. Maybe someone will send me on a coxswain course someday.

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Ship is one thing longer than the wave crest broaching not as likely . Steering with a following sea comes with experience and not all that difficult. Although my deep sea ship experience was before autopilots.

Small Boat on the other hand can broach quite easily particularly if the wave is breaking . You always want to be on the back of a wave never in front. Slide down the front rudder has very little effect. This means going slow & matching your speed to the wave crest. Poor visibility sometimes it’s hard to judge waves from the back side. Reverse strong is the best way to get control if you get in front of one. Little back off on the throttle before going over the top much better. Sea anchor sounds good but if my engine is running I am not dragging any gear.

Too much speed & poor timing is the most common reason for broaching.

Boats

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[QUOTE=Boats3;191218]Ship is one thing longer than the wave crest broaching not as likely .
[/QUOTE]

In following seas broaching and even capsize is possible for smaller ships. For large ships the more likley hazard from following or seas on the quarter is the possiblity of heavy rolls, particularly when the ship is at full sea speed.

Waves the same length or longer than the ship are common. The NWS marine broadcasts include wave peroid.

Bowditch has a graph (as well as a formula) for converting ocean wave peroid to wave length. A wave with a 10 sec period, which is common in the Pacific, has a length of 500 feet.

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All my sea experience is Atlantic Coast were we don’t see long wave crest. My observation speed the issue though. I spent several tours on a Ex Navy ATF 195 feet. She was real lively to steer most times, downwind screw barely turning you hardly had to touch the wheel. Only time I came close to broaching was on a WPB, 82 feet, going fast. She was doing well then into shallow water the seas starting standing up. The Chef had the wheel and a good thing too. He threw one engine hard astern and got her to answer. That’s were I learned about reverse to get control.

Working ashore around the world in cargo handling have seen significant damage to ships from following seas. Master told me once he experienced thousand feet between crest in the Indian Ocean. One caught him wrong and lost or damaged 70 containers. I asked him about hard astern, told me it’s not effective on large modern container ships with slow speed diesels they don’t answer fast enough. Better to slow her down before trouble .

Boats

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[U][/U]- Boats, for sure what your saying sounds right and you have the experience to back it up. In the movie “The Finest Hours” Bernie backs his boat full when he’s going down the slope of a huge wave. This is been fact checked.

Your answer is on topic as far as the OP, timing and speed, that sums it up.

You are also correct about the limitations of slowing down on a low-speed diesel, in general the better option is to change course, which is why good course keeping is important, but working the margins too close can be a problem if conditions change at night or if the night orders are not clear etc.

The Army FS (176 feet) I was on took a deep roll in the Gulf of Alaska one winter day in big following seas and took water in the engine room. A SeaLand ship was diverted by the CG but they came out OK without assistance. It was a year or two before I was there and I don’t recall/know all the details. I’ve also taken a couple heavy rolls in following seas and have always been wary of having big seas aft.

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For small ships following seas can be dangerous. With insufficient bow buoyancy, a large wave approaching from behind can tend to lift the stern and drive the bow into the water. This can result in a sudden broach and even capsize, also a pitchpole is possible.

For large ships the biggest danger of a broach is when the ship is riding on top of a wave crest especially if the wave length equals the length of the ship. The stability at that instant is reduced dramatically, the ship can start yawing which cannot be corrected by the rudder and if the speed is not taken back, if there is time for that, immediately a broach can follow.

FinnbirchGZcurves.jpg748×516

The influence of the wave length on the GZ curve of the Swedish Ro-Ro vessel Finnbirch, which broached in November 2006 in the Baltic Sea, is clearly shown in the picture. The stability of the ship was found to be ‘sensitive’ which aided to the broach.

The second officer of the Dutch ship Mauritsgracht, who was on an opposite course, saw it happen before his eyes. On the radar he could see that the ship’s speed was abnormally high, over 19 knots while the maximum hull speed for a ship of 156 m is 16.7 knots. He noticed that the ship was yawing heavily from left to right after which it suddenly broached.

As a result of the sudden and violent broach major acceleration forces developed which broke many of the lashings causing the cargo to shift. Later on it was found that the lashings were below standard. The inspecting authorities were aware of this but took no action…

Stunning was that it became evident during the interviews that the ship’s captain was not aware of the ship’s rather special stability characteristics with larger heeling angles under certain cargo conditions nor how the stability curve of the ship should be interpreted. He was not alone among the masters of the shipping company in this respect.

The master of Finnbirch could not remember that the phenomena which can develop with following seas had been presented during his training at the ship officer’s school. According to the minutes of the maritime inquiry following the sinking, he was of the opinion that it was advantageous to proceed at full speed in a following sea and thereby pass the waves and reach a condition which corresponded with meeting a head sea. I rest my case…The report on the accident can be found here.

The master as well as the other masters of the company and the company itself had never heard of the IMO circulaire 1228 named ‘REVISED GUIDANCE TO THE MASTER FOR AVOIDING DANGEROUS SITUATIONS IN ADVERSE WEATHER AND SEA CONDITIONS’ in which also the dangers of followings seas are outlined.

The technical university of Hamburg researched 12 similar incidents, including that of the Finnbirch and published the report.

[video]https://youtu.be/Vx9FmEq5D6A[/video]

The ship in this video is rolling heavily, up to 40°. It sails in following seas at about the same speed as that of the waves, no wonder…

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[QUOTE=Boats3;191284] She was doing well then into shallow water the seas starting standing up. The Chef had the wheel[/QUOTE]

Are you kidding me? This is precisely why Chefs should be confined to the galley.

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Master Chief Boatswain Mate was the OIC, Officer in Charge. . From Hatteras NC, he knew a thing or two about rough weather you don’t learn about in schools.

Boats

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FTFY
Don’t most autopilots have dead band and rudder gain controls? I have had luck with adjusting those with a following sea to get Otto to behave.

[QUOTE=Boats3;191352]Master [B]Chef[/B] Boatswain Mate was the OIC, Officer in Charge. . From Hatteras NC, he knew a thing or two about rough weather you don’t learn about in [B]culinary[/B] schools.

Boats[/QUOTE]

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[QUOTE=Island_Sailor;191387]FTFY
Don’t most autopilots have dead band and rudder gain controls? I have had luck with adjusting those with a following sea to get Otto to behave.[/QUOTE]

The autopilot is adaptive. It learns how to behave on its own. We don’t fiddle with gain or other settings as the system is self-fiddling, those settings are not accessible to the crew. The menu instead give various options, for example course keeping: fuel saving or narrow channels etc.

Off topic a little but I just googled it, adaptive steering can use our old friend the Kalman filter.