On another thread a forum member scoffs at the idea “feel” matters when figuring stability. I really don’t want to see that thread ran too much off course but think it’s an interesting topic. How often do Masters disregard their stability letters & programs to do what they feel is right? On some vessels I worked the stability programs were a complete joke & strictly following them would have ended in doom. I assumed everyone had worked on such vessels with such programs & bewildered with the protagonist from the other thread.
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The vessel is it’s own best stability instrument.
But you need to actually do the math using the variables the vessel gives you. Feel doesn’t mean shit unless you’re regularly inclining to severe angles at which point it’s too late.
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Static stability calculations are a starting point.
Once underway dynamic stability is what really matters. The feel, rolling period too long, deep rolls in turns, etc. warn that something is wrong.
I’ve seen some vessels that are really scary when loaded to the load line and oversteered or in certain sea conditions. Usually, less of a load is indicated.
I’ve also seen some vessels that are much better with the load line submerged. Particularly tugs.
I cannot quote a reg and I don’t have enough bandwidth to look for it, but it is common practice to fuel over the load line inland for loadline level at the sea bouy.
It’s common to load barges over the loadline on inland” routes, but only go to loadline if going coastwise. Cargo surveyors have no objection.
There are a few barges around that cannot pass loadline inspection, but are still in use on “inland” routes.
There is a huge difference between what the reg consider “inland in the US. In the South it tends to be inside the jetties.
The Inside Passage from Puget Sound (Seattle) through Canada and Southeast Alaska is considered “Inland”. Parts of it are quite inland, parts are more of an inland sea, and other parts are really an exposed coastwise route.
It’s not news to any of us that government regulations often don’t make much sense.
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A good example of this would be on an ATB i sailed on. Like most (if not all) vessels, the stability letter required no more than one set of slack fuel tanks at any time. To avoid flying out of the the notch when un-pinning after our transit, we would cross-burn…pull from a fwd set and aft set, alternating. Another theory was burning fuel by this method it would create less stress on the pins (side load.)
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I recall doing the same thing when I worked on ATB’s. Ballasting the bow down before coming out of the notch helped too after a long trip. But I’m curious about excel & other 3D stability programs that are a little or completely off & the crew needs to improvise on a regular basis. IMO, I think some shipyards & marine architects develope stability programs for their drawings or for the 1st vessel built in a certain line of vessels but the program doesn’t work for anything afterwards. I’ve worked with all types. I remember one older Mexican Chief Mate that I sailed with who was obsessed over every ton of water in each tank like our electronic tank sounding sensors were anywhere close to being accurate. On the other extreme I’ve worked with guys who would guesstimate on stability based on how much the vessel rolled, sea conditions & how much speed we were making. If I had to choose between the two extremes I would prefer the guesser because I don’t completely trust some math nerds 4,000 miles away who’s never been to sea. But I rather work with a captain in the middle who could do both as needed. I think “feeling” stability is a real thing.
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So become your own math nerd. It’s not as hard as it looks.
There’s a good comparison to electronic navigation tools. People don’t want to trust some computer or satellite but those things are easy to verify with a 5 second glance once you know how.
Similarly the information in the spreadsheet will tell you how the vessel should be behaving under certain conditions and then you can verify - either one of your input variables is incorrect or the static data is. Most of the time the errors are variable input based. The static data errors are often input errors as well and they’re often easy to spot especially if you can extract the data and plot the curve. After a few times you can spot where somebody fucked up the spreadsheet pretty quickly.
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With the introduction of computerised stability programs we have quick answers but dynamic stability and understanding ones ship is still vitally important. A feeder container vessel with fine lines has a different and much more violent roll period when the wavelength is similar to the vessel’s length. In the past the list induced by lifting a weight or timing the roll period were all seat of the pants stuff to check that our calculations were an accurate picture of the ship’s stability.
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There is that…but on this boat in question the forepeak was small, didn’t make much a difference in this case.
Of course there was ballast on the barge that could be played with sometimes but that’s a different jumble of logistical pitfalls. I’m getting a headache again already remembering it…
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Knowing the “feel” or behavior of one’s vessel- especially for the Senior Deck and Engine Officers is of paramount importance. I have personally experienced (on more than one instance) where the vessel was taking on a large amount of water- it turned out that by the time I ran up to the Capt’s Office and told him (I was in my office compiling the departure figures for his report- on the deck below) we had already shipped about 800 tons. this was due to an error in a storm ballast line up in one of the OBO holds- we were in ballast, 90,000 DWT San Clemente OBO.
I instantly felt something going haywire… Another time- when I was engineering manager for one of the oil majors- large (2700T Displacement) ocean going salvage/towing/ship assist tug) was absolutely lightship to cross the sill going into the DIANCA drydock- the Capt was nervous- knowing how tender the vessel was- I only permitted a scant crew to get her in- the engine torque moment of the vessel in lightship heeled her over very slowly to about 10 degrees…just by clutching in the starboard engine…
On one of my last ships- the Captain and I could recognize the synchronicity and gaining amplitude of heel when parametric rolling events started- usually in the first or second set… This comes from knowing the feel of the vessel.
Respectfully and reverently- one major loss at sea- in my opinion might have been lessened (or avoided actually) if the deck and engine officers recognized the effect of vessel movement when flooding started… It’s nearly unfathomable to me that someone didn’t recognize that somewhere around 1000 tons of sea water had shipped aboard- and no one recognized it until it was too late…
The again- another calamity comes to mind- the Derbyshire- and the progressive flooding of the bow spaces might easily of been overlooked because of the pitching and heaving during the typhoon… unfortunately- later when the bow was “diving under” the sinking sequence took less than 3 minutes from the #1 hatch failing… God Help them.
So, (forgive my verbosity) it is of MAJOR IMPORTANCE that the Mates and Engineers aboard any vessel be situationally aware of their surroundings at all times- this includes knowing the way the vessel feels…
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I know that feeling. A general cargo ship I was mate of back in the past had a negative GM light ship.
To get into the floating dock I had to ballast the minimum amount to keep our shoes dry, my skives good for the rest of the day, and remain within the lifting capacity of the dock.
We had a cold move and the tugs were ordered to be very gentle. It was a near thing with the undergarments.
The responsible naval architect never made it to my Christmas card list.
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In the NTSB report on the tug Valour sinking a mate who had worked a few years on her said he wasn’t aware of the vessels unnatural/common starboard list even though it was commonly known to exist to those who worked on that vessel & sisterships of that vessel. On another ongoing thread a forum member ridiculed the idea that a person could “feel” a vessels stability. Unfortunately I believe not everyone can feel a vessels stability or perhaps some have a better knack for it than others? Definitely something mariners who don’t have it should be conscious of & ensure they work with those who they trust that do.
I don’t think it’s so much a matter of “if” a mariner can develop a “feel” for a ship but rather a matter of how quickly and how well.
Comparing direct observations against instrument measurements and the result of calculations is going to be the quickest most efficient way to gain proficiency. All methods have errors.
A deep-sea chief mate has the experience and access to all the information required. The characteristics of a tender ship vs a stiff ship is described in books on stability. In La Dage & Gemert it’s in chapter one, page one.
The stability booklet has a section where the rolling period vs GM is given in tabular form. As @Hogsnort mentioned this can be checked by timing the rolls. The NWS observation form requires sea height and wave/swell period.
Once the basics are understood by using the instruments (watch, inclinometer, anemometer (for wind heel), draft marks / gauges) and calculations; then by being observant other methods of estimating will be discovered and developed.
In time intuitions will become improved.
I’ve posted about this a few times, for example here. Seamanship, Navigation, Piloting, Metis Techne
And it’s possible to go too far the other way:
The Seaman’s Eye Fallacy
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Blockquote
I’ve seen some vessels that are really scary when loaded to the load line and oversteered or in certain sea conditions. Usually, less of a load is indicated.
You are looking at Article 12 of the International Convention on Load Lines, and 46 CFR 42.07-10(d).
Another example wrt to “feel” is when lifting the ramp on a ro/ro. Normally the ship will heel over about 1-1/2 degree or so. The Hoegh Osaka reportedly rolled about 7 degrees when the ramp was lifted.
That observation might not have worked in the case of the Golden Ray however because that ship had good initial stability , she wouldn’t have heeled over much while lifting the ramp, but it lacked sufficient righting arm at large angles of heel.
In that case only looking at the numbers would have reveled the problem.
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Specifically wrt the question in the thread title - “feel” matters when there is a mismatch between the way the ship behaves and the way it’s expected to behave. For example if the ship’s calculated gm is good but the ship seems to hang too long at the end of a roll or has excessive wind heel then time to dig in and investigate the cause of the mismatch.
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Maybe just lucky - but have never been on a ship where the static stability programs had any kind of significant error. Surprised so many had, and could get out of the shipyard like that.
I’ve never had any reason to doubt the calculations. Far more common to have entered the data wrong or loose track of which stability file is the correct one when dealing the multiple ports and/or last minute changes in condition. - or bad weights.
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agree
I think it’s more common on fishing vessels because they are often conversions of conversions and that complicates things. Also, to our shame that is often the last time someone will look at those numbers and that probably affects the effort put in.
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“Feel” is very important to decide any ship’s stability. Basic intact stability is easy to calculate and feel.But if suddenly your ship rolls slowly and doesn’t feel stable? What’s wrong? Probably a leak in/between the double bottom tanks or a hull leak and free water sloshing around in the bottom of your ship! Sound all tanks in the DB, etc. You’ll soon find the defect.
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