A study on boat rolling

[FF]

http://onlinelibrary.wiley.com/doi/1...10.00298.x/pdf

 

[AusCan]

Thanks FF; Very interesting read.

I only took in less than half of the article, and learned a lot. I'm going to read it again spending time to look up a few more terms to get a more complete understanding.

A few musings on bilge keels became clearer and were backed up by proper studies; like the fact that they reduce roll by 40-50% when the boat has zero forward movement, but the roll reduction effect is reduced to 15-25% when underway.

I find it interesting that the paper refers to: "Stabilization of ship rolling, i.e., reduction of the roll amplitudes in irregular sea waves" rather than "regular" sea waves.

I find I have the worst rolling problems with regular (consistent) waves on the beam when their interval is synchronized with the roll time of my boat. (for example: 6 second waves and a 2 second roll are much worse than 5 second waves and a 2 second roll)

So much to learn in this area.

 

[Roger Long]

For an explanation of some rolling issues with a lot less math, see page 143 of this document:

http://www.unols.org/sites/default/files/UNOLS%20Small%20Research%20Vessel%20Compendium.pdf

This later was the basis of an article in "Professional Mariner" and then a version of that became a sidebar in the latest edition of "Passagemaking Under Power".

The focus is primarily on comfort from the viewpoint of people working on but you may still find it interesting.

BTW for a non-math explanation of basic stability concepts:

Stability of Boats and Ships

 

[JDCAVE]

Also, be aware of the "Free Surface Effect" of partially filled tanks. It's been a factor in at least one occasion of a vessel capsizing. It includes but is not limited to fish holds. Partially filled fuel and water tanks can also affect load stability.

The Cap Rouge II, a very sad story. I knew the owner of this boat. He lost his daughter and grand children in this catastrophe.

http://www.tsb.gc.ca/eng/rapports-reports/marine/2002/m02w0147/m02w0147.asp#a3

"2.3 Operational Practices and Awareness of Risks

The TSB has observed that many crews on fishing vessels do not fully appreciate that some of their day-to-day operating procedures may create unsafe conditions. A number of practices were observed that carried risks which were either not fully recognized or were accepted by the skipper. For example, the skipper considered the Cap Rouge II to be a ‘wet boat', indicating that it was not unusual to see water on deck or to have to pump out the lazarette. Water accumulating on the main deck and also downflooding contributes to a free surface effect and thus adversely affects the stability of the vessel. Operation of the vessel with the holds partially filled indicates that, like most commercial fishers, the skipper did not fully understand the risks associated with free surface effect.

A vessel's capability to remain safely upright requires its operator to have a sound understanding of the principles of ship stability and to apply them in a manner which takes into account the constantly changing circumstances both on board a vessel and in the surrounding environment. For example, it is necessary to monitor changes in the quantity and location of liquids held in fish hold tanks, fuel tanks, freshwater tanks and oil tanks. It is also necessary to decide on the safest manner of stowing fish product and fishing gear, including nets, to assess the configuration of standing rigging, such as a boom, and to determine the safest manner of transporting a skiff. Knowledge of existing external factors such as sea state, wind characteristics, and under-keel salinity is also extremely important."


Jim
Sent from my iPad using Trawler Forum

 

[what_barnacles]

Also, be aware of the "Free Surface Effect" of partially filled tanks. It's been a factor in at least one occasion of a vessel capsizing. It includes but is not limited to fish holds. Partially filled fuel and water tanks can also affect load stability.

I was going to say hogwash some time ago to this, as the boat I bought had 2- 100 gallon water tanks built in under the bed. Then I opened the access port and dang if the tanks didnt have 4 baffles each.

 

[stubones99]

I thought about making an iphone or ipad app that would let you set the device on a flat surface and have it record the degrees of rock / roll as well as pitching of the bow under way. That way, we could have a quantitative way of comparing different boats, but no way to measure the seas that caused the rocking / rolling motion. Since iphones (and other smart phones) have onboard GPS chipsets it could record GPS location / speed over ground, etc.

Is that of any value to you guys?

Thanks!
Stu

 

[JDCAVE]

I thought about making an iphone or ipad app that would let you set the device on a flat surface and have it record the degrees of rock / roll as well as pitching of the bow under way. That way, we could have a quantitative way of comparing different boats, but no way to measure the seas that caused the rocking / rolling motion. Since iphones (and other smart phones) have onboard GPS chipsets it could record GPS location / speed over ground, etc.

Is that of any value to you guys?

Thanks!
Stu

I'd buy it for sure, if well rated. Make sure I don't need IOS 8 or + for it please! I have an iPad II and have resisted in upgrading the IOS for a year now. Only have IOS 7.1.2.


Jim
Sent from my iPad using Trawler Forum

 

[Al]

DCave-
Your contribution on the subject is a wizard of information! I doubt that many on the forum are familiar with the conditions you outline as they relate to commercial fishing boats.
You and I and most on the West Coast are familiar with seeing commercial saine boats often belly down with holds full of water to maintained conditions that affect caught fish market conditions. Fresher the better! This modifications to saine boats over the years has often drawing concerns by my observations thinking of the required knowledge to address tankage conditions. weather conditions, and other considerations related to abnormal treatment over that of the original construction limitations addressing stability. There have been some very serious modifications made, some inspected, many not, just flying on the seat of the pants modifications, copying somebody else's efforts. what is interesting is that many of these so equipped boats travel with full holds of water as a normal condition. One has to wonder of the economics of hauling the weight and resulting draft about under power. The condition doesn’t seem to slow the boats down and they do look pretty low and pushing all that water!
However I am aware of three incidents where abnormal tanking has ended up with stellar disasters.
Al-Ketchikan

 

[Off Duty]

I thought about making an iphone or ipad app that would let you set the device on a flat surface and have it record the degrees of rock / roll as well as pitching of the bow under way. That way, we could have a quantitative way of comparing different boats, but no way to measure the seas that caused the rocking / rolling motion. Since iphones (and other smart phones) have onboard GPS chipsets it could record GPS location / speed over ground, etc.

Is that of any value to you guys?

Thanks!
Stu

Stu,

I think the app sounds great!
What about android devices?

OD

 

[stubones99]

As long as the device has the required accellerometers then it should work. My other apps work on androids, IOS, and kindle fire devices.

Let me know what information it should gather.

I had thought about recording headings, peak velocities, degree of motion in all directions, and G shock values. Speeds, lateral motion, etc. Can you active boaters tell me more of what would be needed?

One idea I had was to see if I could pull up the weather for the GPS location and add their data, but suspect that most will need to add the data manually.

 

[psneeld]

Already have apps for that..at least for my Samsung tablet

GPS Status & Toolbox App has a pitch and roll....pretty cool..

I think there are quite a few level apps out there...but this one has some GPS info side benefits.

 

[Roger Long]

If you want to play around with rough stability estimates, use this formula:

GM = (0.45 B / T)^2

B is beam in feet and T is the time for a complete roll while rolling free in calm water. Slack the lines, get the boat rolling by stepping on and off or pushing on the superstructure, then stand back and time as many rolls as you can, dividing by the number of rolls afterwards. The best way is to watch for the brief pause at the end of one roll and start your stopwatch. A complete roll is when the vessel comes back to the same side.

The more freeboard and the greater the angle the vessel can roll to before water can enter, the less the GM can be from an overall safety standpoint. Anything under two feet for a normally configured vessel indicates that a more detailed analysis should be undertaken if exposure to severe conditions is expected.

I would be surprised to find inadequate GM on a production trawler unless it is carrying a lot of boats, motorcycles, etc. on the upper deck that were not envisioned by the designers.

Rolling period underway will be close but not the same as the free rolling in a dockside test. Still, if you start rolling abnormally slowly in a seaway, something may have changed in the vessel's stability such as undetected flooding below.

Free surface of tanks reduces a vessel's GM but but few yachts, or even commercial boats without wet well cargo tanks, have enough tankage for it to be a significant factor.

 

[JDCAVE]

The dragger "Calaldonian" has gone down off the WCVI. 3 men dead, one rescued. Hold stability issues again.


Jim
Sent from my iPad using Trawler Forum

 

[Off Duty]

The dragger "Calaldonian" has gone down off the WCVI. 3 men dead, one rescued. Hold stability issues again.


Jim
Sent from my iPad using Trawler Forum

Hold stability issues again

Did you also read where the only person found alive, was the one crewman wearing a PFD?

Very sad. Prayers for the friends and families of the crew.

OD

 

[Al]

During my 25 year career as a Superintendent of loading cargo ships the subject of rolling period is familiar. The ‘Rolling Period’ became important at the end of normal loading where deck cargo was involved. Basically, during the loading of a log or lumber cargo ship, the volume under deck is approximately twice that on deck. Normal loading where possible and often not as multiply loading ports were involved, the heaver specie of wood would be stowed at the lowest point possible reserving the lighter specie for higher in the hatch and on deck.
During loading a rough draft of weight would be kept confirmed to an actual number daily by the Chief Mate’s draft calculations. When the obvious weights were at a given point, the loading would be stopped and a ‘Rolling Test’ would be performed. The test was a confirmation on the status of the vessel’s departure buoyancy related to all the given calculations used including the fuel/water usage during the normal 14 day voyage to the Far East.
We performed this test much in the manner given by others on this forum. We would secure two or three bundles of logs or lumber and at a given whistle, yard the loads in unison to a given point and then a second whistle would be the signal to drop the loads back into the water or on to the lock loading pallet. This would be done for three cycles then the Chief Mate would time the roll from side to side stopping at the max rolling point. If the roll was over 21 seconds, the Mate would be quite agitated as it indicated a slow roll at the point of departure reflecting the potential for stability problems given the right conditions during the later part of the voyage. Historical weather data was in play often due to typhoon conditions in the Far East seasonally. A roll under 21 seconds had the log/lumber buyer then encouraging continue loading till the 21 second point was achieved.
Interesting times. Pleased to report that in 25 years of cargo ship loading were deck loading was involved, never had a ship incident due to stability.

Al-Ketchikan

 

[Al]

Better example of log loaded ship in distress. AMJ

 

[healhustler]

I don't know where that log dump took place, but it gives one pause to think that each one of those stray logs could hole your boat.

 

[FF]

"I don't know where that log dump took place, but it gives one pause to think that each one of those stray logs could hole your boat."

Most voyaging boats go too slow to be holed , but a twin screw boat could easily loose half the propulsion and steering with solid lumber.