how much roll is too much?

[Bill V]

In November 1964 while a crew member aboard the USS Boxer LPH4 (Essex class carrier) in a north Atlantic storm we experienced a 44* roll. I can only tell you that every crewman of the 888' ship thought that roll was too much. Virtually every last marine onboard felt they were "goners". Wave heights exceeded 100' on a regular basis.

 

[Hippocampus]

One thing not discussed in Kasten’s excellent article is the biology of people and the brains vestibular system. USN and NASA otoneurologists have done extensive research in this subject. Puking in a spacesuit or crew performance degradation is of great concern. In simple terms everyone can get motion sick. Thresholds may vary. But of interest most people fit into one of three groups. Those more sensitive to low frequency oscillations. Those to high frequency. And those to both equally. Although the amplitude of the motion is relevant so is the frequency. Both Kasten’s discussion and some of the above doesn’t discuss this biology. So depending upon the biology of the crew slowing or speeding up the frequency of the oscillation may have deleterious impact of crew comfort aside from amplitude of the motion. Some may find the snap roll of a boat depending upon form stability (multihull or hard chine light planing hull) uncomfortable and be fine with the slow roll of a FD heavy boat even if large. Many find corkscrewing with motion in two axis more uncomfortable than pure roll even if amplitude of motion less. Antiroll is just that. Reduction in one axis. Fins, fish, gyros, bilge keels and rolling chocks address one axis. Wave penetrating bows, displacement/lwl, gyradius and reserved buoyancy may impact acceleration of heave and degree of pitchpoling. Frontal plane, prismatic coefficient and other features of design may impact frequency, acceleration/deceleration in response to wave action. In the past NAs have proposed a calculated comfort quotient in an attempt to quantify all these factors but now it’s generally accepted that the comfort quotient is flawed. Fortunately computor analysis allows multifactorial analysis so the behavior of a hull, it’s appendages and add on stabilization can be predicted with some accuracy. In some respects roll is the easiest to address. When looking at crew comfort would suggest you consider the other axises as well. Please note this post has absolutely nothing to do with AVS, Gz or safety. Only with comfort.

 

[psneeld]

In November 1964 while a crew member aboard the USS Boxer LPH4 (Essex class carrier) in a north Atlantic storm we experienced a 44* roll. I can only tell you that every crewman of the 888' ship thought that roll was too much. Virtually every last marine onboard felt they were "goners". Wave heights exceeded 100' on a regular basis.

They thought they were goners because carriers are so big and fast...it's probably rare they roll even 1/4 that much....I remember watching the USS America launch aircraft east of Hatteras while out USCG icebreaker was probably rolling 30+ degrees with the weather deck secured from traffic.

Even the USCG's biggest icebreakers back in the 1980's had hulls that rolled like crazy...one week while transiting from Seattle to Dutch Harbor, AK....we were in 60 some foot seas at one point and rolling better than 30 degrees up to 60 degrees for days....more foot prints on the bulkheads than on the decks. 2/3 of the crew was sick for days...even the gally was limited and didn't cook for at least several meals....just dumped miscellaneous food on the tables and it was fend for yourselves.

Here's a picture of the bridge window on the USCG Icebreaker Polar Star 399 feet, broken out by a wave.... 80 feet above the waterline..... 4th bridge window from the right is plywood maybe covered in ice.

Also if curious...look at the amount of ice on the forward crane cables.

 

[Roger Long]

I did a lot of study of roll and heel perception back when I was doing forensic investigations of sailing vessel losses for USCG rule making and as expert witness and consultant for the British government in a wreck inquiry.

If you stand near an inclinometer and ask people how much they think a roll or heel is, they will almost universally think it is twice what it actually is. Same thing if you ask people to estimate wave height.


Chuckle: My co-owner (and love) expressed concern about rolling over on a rough day. I assured her that our high freeboard trawler was safe. She wasn't convinced. I said, "You know, not many people in your situation get to have that question answered by an internationally recognized expert in sailing ship stability who ..(see above)"

 

[long-cours.62]

Our former Long-cours 62, normally, was self righting boat.
With 2.4T of lead ballast, great stability but in another hand a short roll period.
The period was more uncomfortable than the angle, but after added the mast and 2 small "bilge keel" the boat totally change, and my stomach was happy !

 

[Hippocampus]

RL totally agree with you. Think even the ambient temperature effects peoples perception. My wife won’t comment on the same degree of roll in the tropics as she would when traveling in the damp cold when down east. I’m much less perceptive when focused on racing then when stressed and tired trying to fix something down below.
I’ve always been in awe what commercial fishing men and the military will put up with. So many things go into peoples perception and tolerance. Think habituation is a major factor as well. Brains will habituate to some extent to most sensory inputs be it smell, touch, sound or motion. Although the action potentials from the saccules and semicircular canals remain nearly unchanged the processing at midbrain and then a cortical level is damped over time. Those sensory organs feed the cerebellum. Coordination between visual, vestibular and proprioceptive inputs is complex but the brain does get better over time in dealing with the conflicts between those systems.
Personally think tolerance and perception of the seastate is different if you’re on the boat at rare intervals or constantly or even frequently. Did you formally study if that’s true or just my misguided belief. I’m aware of literature concerning this habituation but not of the particulars of people subjective perceptions.

 

[FWT]

Chuckle: My co-owner (and love) expressed concern about rolling over on a rough day. I assured her that our high freeboard trawler was safe. She wasn't convinced. I said, "You know, not many people in your situation get to have that question answered by an internationally recognized expert in sailing ship stability who ..(see above)"

ROFLMAO

Hence the age-old expression: "No man is a hero to his wife."

 

[Marco Flamingo]

do you have experience with anti roll tank system?

No, but I've been thinking about it for the last several days now that I'm snowed in. Given that limited amount of time, here are my thoughts.

Somebody posted about a relatively new small boat gyro system. I was all excited when I saw that it was 365 pounds. Turns out that is the weight of the gyro, not the cost. It is 16,000 U.S.D., not including installation, so figure $20K. It requires power, prime space, and time to spin up, but it is the price tag that gives pause. The stabilizing force for the gyro is given in the advertisements, and the videos are impressive. I haven't really compared the gyro to that of a passive anti-roll tank. However, if a passive DIY system cost 2% of the gyro ($1000), but had 18% of the stabilizing force, would it be worth it?

I'm going to leave out the naval architect calculations for the moment, both because I haven't done them and because I think that the simplest system could use valves that can be fine tuned after construction. I'd use trial and error more than calculator and prayer.

My interior beam in the engine room is about 11 feet. During a healthy roll of 15 degrees, one side would be 2.5 feet higher than the other. I might need to keep that in mind for the shape of my tanks, probably making them about that height. My boat has enough space to easily fit 20 gallon tanks on each side right behind the fuel tanks. Once my generator is removed, it would be clear from side to side across the engine room.

Let's say my hypothetical system is two 20 gallon tanks connected by 6 inch (maybe 8) PVC pipe. The PVC has a ball valve for future fine tuning. One of the tanks has a fill (either fresh or salt given that everything will be PVC) to allow fine tuning the right amount. To start, the tanks are less than half filled, say 7 gallons. The 6 inch connecting pipe contains 1.5 gallons per foot, say 10 gallons. But at a 15 degree roll, one tank and half of the pipe (12 gallons) would run into the other tank, filling it to 19 gallons.

The problem has always been that the changing mass of the shifting water is too fast. Putting baffles in the crossover helps, and maybe the ball valve can help with that. It seems to me that a better approach might be to connect the top of the tanks with an air vent (as is usually done) and control the flow that way. Control it passively, as avoiding pumps and electronically controlled valves would be a large part of the appeal.

Say the air vent is a 2 inch PVC pipe that contains a simple throttle valve. On the throttle valve is a rare earth magnet. Outside the pipe is another magnet that is adjustable such that it can hold the throttle shut, but allows instant opening at various degrees of vacuum by varying the distance between the two magnets. As the water tries to shift from upper to lower tank, a vacuum builds in the upper tank because of the closed throttle valve, partially holding back the water until the vacuum is sufficient to overcome the magnetic attraction and pop, the valve flips open, allowing the water to surge into the lower tank moments later than a free flowing connection.

From what I've seen on the web, the "hold back" time required is less than 1 second for small boats. That seems possible based on my experience with rare earth magnets. I use them some in repairing dented saxophones (another hobby). When I first had a rare earth magnet on my workbench, I opened a drawer only to find all of my jeweler's screwdrivers had disappeared. It turned out that the magnet pulled them up out of the drawer and they were stuck to the underneath of the workbench. Holding back a little vacuum shouldn't be a problem.

As to calculating the amount of effect an anti-roll tank could have with such small amounts of water, the secret seems to be in timing the small amount of water. In my hypothetical, I'm only shifting 12 gallons of water (100 pounds) from beam to beam, so the key would be getting the timing perfect. I know that a 100# weight, if shifted perfectly from beam to beam every 1.725 seconds (or whatever my roll rate is) would really have a surprising effect after a few cycles. Question is would it have the same cancelling effect?

 

[psneeld]

I don't think shifting 100 pond is gonna be worth the effort.

More calculations might be required....or some brilliant backyard engineering.....

But what I have gathered....the right amount of weight has to be shifted and held the right amount or all you will do is aggravate the rolling.

I too have played with the concept for my boat.

 

[Lepke]

The best low cost roll inhibitors are flopper stoppers. But most yacht owners don't want the booms and rigging needed to make them work.

 

[Roger Long]

As to calculating the amount of effect an anti-roll tank could have with such small amounts of water, the secret seems to be in timing the small amount of water.

It does take a considerable amount of water and the timing is critical. A fellow had a patent on the "flume tank" in which an hourglass shape to the tank controlled the timing. I was VP of a company which wanted to include anti-roll tanks on our fishing vessel designs. We (well, my partner) got around the patent by figuring out that a breaking wave could only travel a certain speed. We installed simple rectangular tanks on the pilot house top. With the right amount of water in them, they were very effective in reducing roll. Then came the problem.


The less stability a boat has, the slower it will roll. The slowest roll, after all, is one in which it just goes over and doesn't come back. Captains in this small fleet of vessels discovered that, the more they filled the tanks, the more comfortable the boat. However, they were damn near to capsizing. Written instructions and lectures didn't work so the tank plumbing was disabled. I figured out an overflow but it didn't allow the fine tuning for different loading conditions easily and bankruptcy made the whole thing moot shortly after.


Tanks only work on boats with less stability than you really want. I went on in my career to figure out how to make boats with oodles of stability good working platforms by incorporating high hull damping and careful roll period tuning. Among other things, that got me the invitation to write the sidebar on rolling in the latest "Passage Making Under Power."

 

[Marco Flamingo]

I don't think shifting 100 pond is gonna be worth the effort.

The amount of water moved in passive tanks is surprisingly small when the timing is right. In this YouTube video using an open anti-roll tank, the total amount of water poured in to the model tank seems like a lot (even though less than 10 ounces). In the final few seconds of the video you can see the little wave going back and forth in the tank. The wave height shows the actual volume needing to change sides and stabilize the hull. Maybe 1/10th of the water volume is actually doing the work, i.e, one ounce of water moving at the right time stabilized the model.

The rest of the water mass in the model tank, even were it stationary, would have some effect, just like the stationary mast of the sailboat slows the roll. The little tank in the video is well above the model's center of gravity and that would also slow the roll even if the water wasn't allowed to move. Too bad the model tank wasn't level with the CG so that only the effect of the water changing CB was shown. I know that a passive tank on the flying bridge is more effective, but no thanks.

It would also be nice to know the weight of the model. Is one ounce of well timed water shifting back and forth damping the roll of a 2 pound model? A 5 pound model? 10 pound model? Of course, the weight distribution on the model would also effect the damping effect of 1 ounce of water, but if one ounce can dampen a 5 pound (80 ounces) model hull, then a 1/80 ratio using 100 pounds of water could dampen an 8,000 pound boat. I would need 200 pounds or 24 gallons of shifting water for my boat.

All of this would depend on how much stabilization is required. Is a 50% improvement worth it? Or a system that isn't really effective until the boat rocks over 5 degrees?

I had a weird feeling when looking at the gyro stabilizer videos. A big wave came and the boat stayed absolutely level. Just not natural. Watching it made me a bit queasy.

 

[psneeld]

Tell you what... my back yard mechanic mentality would tell me to go out on a day of normal conditions and turn beam to...put the boat on autopilot or have someone steer... then go to the back deck and walk/run towards the high side of the roll and act like I was the water in an antirolling tank....

If 200 pounds had the desired effect...great. If I accentuated the roll then maybe your 100 pounds might be better....if 200 pounds had little effect...then my guess was right and try it again with 2 5 gallon buckets of water or another friend of equal weight.

Simple, cheap and gives one the idea of the upcoming engineering requirements. For a lot more money, hire a NA.

 

[markpierce]

Roll is excessive when your bowl of cereal slides/spills onto your lap. Happened to me on a 900-plus-foot cruise ship.

 

[North Baltic sea]

Hi,

thanks for the reply anti roll tank. I understand that this link Trawler is installed in a passive anti roll tank designed by Kasten and it would have worked well?

https://www.trawlerforum.com/forums/s9/m-v-cygnus-sale-60485.html

NBs

 

[Portage_Bay]

I'm happy to see that Roger Long has joined in this discussion. For those who have not studied stability I suggest a visit to Roger's discussion of Stability of Boats and Ships. He does an outstanding job of explaining the concept without a lot of technical jargon and almost no math.

You'll come away understanding the reasoning behind why he says in post #71

The less stability a boat has, the slower it will roll. The slowest roll, after all, is one in which it just goes over and doesn't come back. Captains in this small fleet of vessels discovered that, the more they filled the tanks, the more comfortable the boat. However, they were damn near to capsizing.

.
You'll also learn that moving, adding or subtracting any weight on the boat is changing the center of gravity and how that change affects stability.

 

[FF]

"The best low cost roll inhibitors are flopper stoppers. But most yacht owners don't want the booms and rigging needed to make them work."

True dat!

Some folks have discovered the lever arm of big poles are not needed all the time.

So mounting the FS to the rail works , especially in harbors have enough depth.

 

[rslifkin]

"The best low cost roll inhibitors are flopper stoppers. But most yacht owners don't want the booms and rigging needed to make them work."

True dat!

Some folks have discovered the lever arm of big poles are not needed all the time.

So mounting the FS to the rail works , especially in harbors have enough depth.

At anchor, yeah, off the spring cleats is still a significant improvement. Not sure you could drag fish that way though, I think that would require the poles.



For paravane rigging on some boats, it's not just a matter of looks, but on plenty of boats, there's just not a good way to install them at all. I can't think of a high enough, strong enough point to anchor the upper stays to on my boat, for example.

 

[Capn Bob]

We have just returned from moving our boat, a Hartman Palmer Offshore 38, from Kingston NY to her new homeport in Murrells Inlet, SC a trip of over 900 miles. The boat is 38' long with a 13' beam, has a so-called semi-displacement hull with a full-length box keel filled with concrete. Displacement unloaded is 23,000 lbs.


Part of the trip was "outside" on the ocean, and the boat was very comfortable in moderate sea conditions. But while sailing in Chesapeake Bay from Annapolis to Deltaville in poor weather (windy and very choppy) off Smith Point, just S of the Potomac, a large motor yacht roared very close by and waked us, all while we sailed in very choppy, confused seas. Our boat was rolled onto its port side about 45 degrees, possibly as much as 50 degrees. Everything aboard that wasn't tied down went flying about the cabin, flybridge and afterdeck. I was at the upper helm on the flybridge, trying to outguess the confused seas, and found myself looking DOWN at the bay through the isinglass of the canvas, I was thrown out of the helmsman's chair and wound up with my left foot on the flybridge coaming and my right foot still on the flybridge; I was unable to stand upright on the flybridge deck. The boat hesitated for a moment but came back up smoothly. I can't say that my level of freaking-out came down as quick or as smooth.


I had estimated that the roll was around 40 degrees (at least), until I noticed the following day a stain on the white fiberglass coaming of the flybridge. It was brown and sticky, and I realized it was the remains of a partly-filled bottle of iced tea which had been sitting in a cupholder to the left of the helm. In order for the iced tea to have left the bottle and pour onto the tilted side of the coaming, I calculated that the bottle had to be tilted at least 45 degrees.


It was a chilling moment that I never want to repeat. We are sailors and are used to the heel of a sailboat, but to have our trawler heel at such a sharp angle, to the point where things flew off the deck and into the sea was a terrible feeling.


As if that wasn't enough, my starboard engine began to lose power. The nearest port was a tiny fishing community, Reedville VA, which I attempted to reach, but I would have to take the seas on my starboard beam to reach the safety of the port, which between the wind and waves was once again trying to lay us over on our port side. Instead of heading directly for the port, I waited for a lull in the waves and turned into the waves, taking them on my starboard bow. After a while, I would turn to port and then take the seas on my starboard quarter. I repeated this over and over, tacking the trawler like a sailboat. It was the only way to avoid exposing my boat to another roll onto our port side.


When I reached port, every fisherman that I spoke in the area with said that Smith Point was notorious for very confused and/or choppy seas in certain conditions, with wave periods very short. And strong winds made conditions much worse.


After repairs (lift pump was leaky on one Lehman), we met another trawler on the ICW who had passed Smith Point the day after our encounter. The skipper of that boat said it was quite smooth on that day...just my luck!


After that experience, I had more confidence in our boat's ability to "take it". She's a sturdy little ship, built by the same shipyard which builds Flemings. She's overbuilt in many areas, and I especially appreciated the ballasted keel. BUT I swore that I NEVER want to experience that again!

 

[Vandeusen]

Do you put that up or to steady the Trawler in choppy conditions

 

[Vandeusen]

Very similar after the calm sees became rough seas we broke anchor in the middle of the night between the winds the waves and the current and the fact that it was pitch Black outside I couldn't get the anchor set again so we ditched to a bend which was near markers we we're in my Silverton at the time it was the crack of dawn when a boat probably doing 15 knots realized there was a bend he didn't have much choice but to take that bend at that speed and he not just rocked my boat he knocked me right out of the bed everything in the boat was being thrown around I rolled myself over to the radio to give him a quick piece of my mind and of course he acted dumb later that day I caught up with him at a marina I so wanted to beat his you know what but the wife dragged me the other way I noticed being out here as a liverboard whether I'm anchoring or at a marina there's some people with great boat etiquacy and there's others that Mama probably should have put them over her knee and gave them a good spanking

 

[Marco Flamingo]

She's a sturdy little ship, built by the same shipyard which builds Flemings. She's overbuilt in many areas, and I especially appreciated the ballasted keel.

Tung Hwa. Same yard that built my pocket trawler.

I don't know whether there is ballast in my keel. The old sales brochure that is online is sketchy on details. My bilge appears to be filled in and heavily glassed over, but what's underneath is a mystery. Presumably, there are materials cheaper (and heavier) than fiberglass and resin, but what? I think that I should do more web searching before any exploratory drilling.

 

[Lepke]

Roll is excessive when your bowl of cereal slides/spills onto your lap.

On destroyers where 45° rolls are common, we placed a paper napkin on the table, dampened it, and put food tray, bowl, on top and it didn't slide.

 

[long-cours.62]

Luckily

On destroyers where 45° rolls are common, we placed a paper napkin on the table, dampened it, and put food tray, bowl, on top and it didn't slide.

On all merchant ship (cargo or tanker) we never reach 45° !!!
Even in big swell of south Indian sea or in south Atlantic

 

[Hippocampus]

Although angle of heel is of course important believe degree of acceleration is also important as regards comfort. Sailing one isn’t discomforted by severe heel angles. It’s not uncommon to put a rail down and the side decks awash with house wet on a beat. You know you have an AVS of 130+ and wind will dump off the top of your sails if you go over further. Personally have been more uncomfortable with more troubles moving around with much less heel angles but much more acceleration of the movement. Raced a Chris White tri. Long period ocean swell with moderate 2-4’ wind waves on top. Long amas so very stable boat but on a beat in those conditions you felt nearly airborne at times. There seems to be no rhythm to the motion. Reason was boat floated on the water not in the water and sail loading varied with whether you were in a trough or not. Degree of motion maybe 5 to 10 degrees but really uncomfortable. Degree of heel compared to wave face minimal.
Recreational trawlers usually have a AVS of around 90 or less. Sometimes much less. Now you get real nervous at modest degrees of heel just like you would on any boat dependent upon form stability like a multi. Still even at modest heel angles it’s the acceleration of the movement that makes life miserable. Comfort is totally distinct from safety. Unsafe degrees of heel terrify you. What’s an unsafe degree of heel depends upon the factors Roger discusses Rapid accelerations make you a unhappy camper and subject to bumps and falls. The original post seemed to be aimed at comfort.
The ex monohull sailors among us may have experienced a true knockdown with tip of mast wet. If things stored correctly and companionway closed an oh well keep calm sail on. Suspect there’s very few of us trawler owners whose boats could tolerate such an occurrence. Few would self right and fewer wouldn’t downflood. It’s a different activity with different parameters. There’s no chance I would take my current boat knowingly into circumstances where a knockdown was possibly in the offing. There’s every chance I will take her into situations where things could get uncomfortable.