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Old 11-24-2010, 09:20 PM   #41
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RE: Filling the keel with cement

Quote:
RickB wrote:



The difference in it being a hold rather than a tank is that, except for fishing vessels that use a refrigerated seawater fish hold like you see on the Bering crab boats, the boat is not designed to operate with the hold completely full of water and "batter boards" are used to prevent fish and ice from causing a free surface effect.
Okay, I could look this up but being inherently lazy I'll ask here instead.* It sounds like my description of the sloshing of a liquid in a tank, hold, etc. can be a stability*problem but it's NOT the definition of Free Surface Effect.* If fish and ice can cause a Free Surface Effect the definition must be different than my assumption since fish and ice don't really*"slosh."

So I'd be interested to learn what Free Surface Effect actually is.

*
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Old 11-24-2010, 09:36 PM   #42
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Filling the keel with cement

From Wikipedia........


The free surface effect is one of several mechanisms where a craft can become unstable and roll-over (capsize). It refers to the tendency of liquids and of aggregates of small solid objects, like seeds, gravel, or crushed ore which can act as liquids to slosh about: to move in response to changes in the attitude of a craft's cargo holds, decks, or liquid tanks in reaction to operator-induced motions (or sea states caused by waves & wind acting upon the craft).

In a normally laden vessel any rolling from perpendicular is countered by a righting moment generated from the increased volume of water displaced by the hull on the lowered side. This assumes the center of gravity of the vessel is relatively constant. If a moving mass inside the vessel moves in the direction of the roll, this counters the righting effect by moving the center of gravity towards the lowered side. The free surface effect can become a problem in a craft with large partially-full bulk cargo compartments, fuel or water tanks, (especially if they are located spanning its fore to aft centerline), or from accidental flooding, such as has occurred in several accidents involving RORO type ferries. If a compartment or tank is either empty or full, there is no change in the craft's center of mass as it rolls from side to side (in strong winds, heavy seas, or on sharp motions or turns). However, if the compartment is only partially full, the liquid in the compartment will respond to the vessel's heave, pitch, roll, surge, sway or yaw. For example, as a vessel rolls to the left, liquid will displace to the left side of a compartment, and this will move the vessel's center of mass towards the left. This has the effect of slowing the vessel's return to vertical. Also, the momentum of large volumes of moving liquids cause significant dynamic forces, which act against the righting effect. When the vessel returns to vertical the roll continues and the effect is repeated on the opposite side. In heavy sea states, this can become a positive feedback loop, causing each roll to become more and more extreme, eventually overcoming the righting effect leading to a capsize.

The higher up these fluid motions occur, especially above either the craft's center of moment (buoyancy) or center of mass, the more pronounced the instabilities.

To mitigate this hazard, cargo vessels use multiple smaller bulk compartments or liquid tanks, instead of fewer larger ones, and possibly baffling within bulk compartments or liquid tanks to minimize the free surface effects on the craft as a whole. Keeping individual bulk compartments or liquid tanks either relatively empty or full is another way to minimize the effect and its attendant problems. Tanks or compartments that do not straddle the vessel's centerline are somewhat less prone to destabilising oscillations. Similarly, narrow compartments (aligned bow to stern) and compartments at the extremes away from the centerline, are less prone to cause instability.

Flooding, liquid cargo leakage, or unintended water (from precipitation or waves) in any compartments or on any decks of watercraft, and the resulting free surface effect are often a contributing cause of accidents, capsizes, and casualties e.g. the loss of TEV Wahine (Wellington, New Zealand, April 1968), the MS Herald of Free Enterprise (Zeebrugge, Belgium, March 1987), and MS Estonia (Baltic Sea, September 1994). In the case of the RORO ferry MS al-Salam Boccaccio 98 (Red Sea, February 2006) improper fire-fighting procedures caused flooding leading directly to instability and capsize, which resulted in over a thousand fatalities.

Free surface effect can affect any kind of craft: ranging from watercraft (where it is most common), to bulk cargo or liquid tanker semi-trailers and trucks (causing either jackknifing or roll-overs), or aircraft (especially fire-fighting water-drop and refueling tankers where baffles mitigate but do not eliminate the effects). The term "free surface effect" implies a liquid under the influence of gravity. Slosh dynamics is the overarching field which covers both free surface effects and situations such as space vehicles, where gravity is inconsequential, but inertia and momentum interact with complex fluid mechanics to cause vehicle instability.

-- Edited by Capn Chuck on Wednesday 24th of November 2010 10:36:41 PM
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Old 11-24-2010, 09:43 PM   #43
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RE: Filling the keel with cement

Thanks for taking the time to post this.
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Old 11-24-2010, 09:47 PM   #44
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RE: Filling the keel with cement

No, I think you have it right Marin.* If the tank isn't full and battened down, then the center of gravity changes as the liquid, or fish, or ice move from side to side (the free surface effect) which can have a serious effect on stability.* If the hold can be battened down and is watertight, then you could fill it up eliminating the "free surface" effect.* Since the vessel was presumably designed to allow one to fill up the fish hold, the absence of this designed weight allowance may be contributing to the current tenderness of Skipperdude's boat.* However, adding weight down low probably wouldn't solve the tenderness problem he describes.* For example, take the mast off of a sailboat and not withstanding all the weight in the keel, it rolls a lot, and quickly.* Read 'Fastnet Force 10' for a great description of just how miserable a sailboat is once dismasted.* Weight up higher decreases ultimate stability but increases stiffness and resistance to roll, at the risk of decreasing ultimate stability.* The best example of how weight distribtuion on the vertical axis affects roll period, look at a metronome.* Move the weight higher, the metronome period decreases.* Move it down, it increases.
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Old 11-25-2010, 04:38 AM   #45
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RE: Filling the keel with cement

"Its the way and manner that RickB says things. Most of us moved from PMM because of RickB crass inappropriate replies. A person can make their point with out flaming and being so negative."

Ricky B is a classic ILLEBERAL , and truely believes

"The masses are asses" , so must talk down to his inferiors.
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Old 11-25-2010, 09:24 AM   #46
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RE: Filling the keel with cement

Free surface effect is alive and well. In my business we transport ore concentrates*(copper, zinc, or lead primarily), coal and iron ore in ships up to 80,000 dwt. Each product must meet specific % moisture tests to insure it is "stable" in a rolling sea. If the hold covers become dislodged, seas can enter and render the "dry" products wet and subject to liquid like behavior*with real potential for capsize.

Water as ballast, in specifically designed tanks, *is common for offshore sail boat racing, Dashew's and some other's yachts and water ski craft. Oil tankers and ohter cargo vessels for years have partially filled their*tanks for stability - but in a pre-planned manner to avoid undue movement of thousands of tons of seawater. Environmental controls were put in effect years ago to minimize this practice unless proper discharge mechanisms are in place.

Reputable yacht designers, seldom if at all, use water ballast for our types of vessels. They normally use lead. What happened in a yard 30 years ago in Taiwan regarding "concrete" (there are many different types) does not mean it is acceptable. Sloshing water in the bilge or keel*of a yacht is a sign of careless design or poor owner maintenance IMHO. Sand is not a good product unless it is graded as specific for immersion purposes - few are. Metals leach out of virtually all damp dirt and common sand adding to corrosion issues.
*
The deadliest capsizes have involved human ballast - picture the SE Asia ferries rolling as passengers rush to the docking side. I am not one bit bothered by RickB's statements. Picture your teachers or profs of yesteryear rising to the moment.*I am puzzled though as to why Ancora never weighs in on*this stuff - does he really exist or is he just afraid to get pinned down on tech issues?*
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Old 11-25-2010, 09:43 AM   #47
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RE: Filling the keel with cement

Quote:
sunchaser wrote:

*I am not one bit bothered by RickB's statements. Picture your teachers or profs of yesteryear rising to the moment.*I am puzzled though as to why Ancora never weighs in on*this stuff - does he really exist or is he just afraid to get pinned down on tech issues?*
RickB is RickB but I trust his answers above most others folks PC or not.

It's funny that he is railed against for how he answers folks but then some folks can just call him*names and that's OK.

Mr. Ancora has over 600 posts of which 85% or more are on the DE.* So that must be where his expertise is.* What was*Prissy's line from "Gone with the Wind"? *" I don't know nothin' 'bout birthin' babies. ".* Maybe "I don't know nothin' 'bout boats." fits.



*
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Old 11-25-2010, 10:32 AM   #48
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Filling the keel with cement

Back to my original question about adding cement as ballast to my boat.

Am I on the right track?

The engine Set's almost dead center on the boat.
What would more weight below the engine do to*make the boat less tippy.

When someone heavy steps aboard from the dock she really rolls over to the side the weight is on.*
*
When underway she rides straight and true. When taking a beam sea or a boat wake *she can really start to rocking.

*I have found *if I put one of my Para vanes out this problem in cut cold.*Two out she is as stable as dry land.

If the center of gravity is lowered by adding weight.
*How does that effect the center of*boyancy?*

Would it make her less tippy?

*

-- Edited by skipperdude on Thursday 25th of November 2010 11:33:10 AM
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Old 11-25-2010, 10:54 AM   #49
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RE: Filling the keel with cement

SD, I doubt this will solve your problem or make the motion less. What you will do is simply sit lower in the water. What you describe is a characteristic of all of our boats of this type. I think IMO you will be throwing time and money at a solution that provides little results. Your solution will be more in the traditional approach of either stabilizers or modifications to the hull itself to slow down the roll. I have to ask, your icon, is this a photo of your boat now? The tower in the picture will certainly exacerbate the issue. Chuck
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Old 11-25-2010, 11:10 AM   #50
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Filling the keel with cement

Yes this is how she looks now.

The tower doesn't weigh that much.
I recently removed it to put a new top on and was able to re erect it myself.

The only real purpose it serves other than a place to climb up on , is a place to suspend the Para vanes from.*

I have considered removing it in favor of a mast and boom arrangement.
*For hoisting the dingy and perhaps a stay sail.

This has got me thinking about the metronome thing.
*Raising the height of the metronome slows the roll?

SD



*

-- Edited by skipperdude on Thursday 25th of November 2010 12:10:48 PM
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Old 11-25-2010, 11:14 AM   #51
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RE: Filling the keel with cement

"Would it make her less tippy?"

Initially only a tiny bit , but the price will be an inferior ride in a seaway.

Not a choice I would be happy with, so you might contemplate making it removable if you plan on selling the boat.

Bolting in lead night be easiest.
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Old 11-25-2010, 11:24 AM   #52
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RE: Filling the keel with cement

SD, yes, raising the CG reduces roll period.* Just ask any sailboater who has been dismasted on the effect of moving it lower.* However, it also reduces ultimate stability since the more weight higher up, the happier the vessel is upside down.* Adding weight below might help reduce 'tippiness' at the dock, but resistance to roll underway on small boats is as much a function of hull form as mass.* Is your boat round hulled?* This will be a more tender hull form than one with flatter sections.* I doubt the difference will be worth the effort, and concrete ballast has enough going against it you might want to think carefully before committing to that.

Bottom line, your boat was designed for one purpose and one weight distribution, and you are using it for another purpose with different weight characteristics.* With the vanes, you neutralize most or all of the issues, and I doubt there is much else you could do that would have a dramatic enough effect to make a difference.* To settle the question, even at the risk of my being criminally negligent and you being criminally stupid, replicating the design weight as originally intended would help answer the question for you.
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Old 11-25-2010, 11:46 AM   #53
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Filling the keel with cement

Quote:
sunchaser wrote:

Free surface effect is alive and well. In my business we transport ore concentrates*(copper, zinc, or lead primarily), coal and iron ore in ships up to 80,000 dwt. Each product must meet specific % moisture tests to insure it is "stable" in a rolling sea. If the hold covers become dislodged, seas can enter and render the "dry" products wet and subject to liquid like behavior*with real potential for capsize.

I am puzzled though as to why Ancora never weighs in on*this stuff - does he really exist or is he just afraid to get pinned down on tech issues?
I recently read a very interesting book about the Edmund Fitzgerald called Mighty Fitz by Michael Schumacher.* As I recall from my reading there were two main contributors to the loss of the ship.* The biggie was the ship's brief grounding on Six Fathom Sound which momentarily hogged the ship and split bottom plates apart if not actually breaking the ship's back.

The second was the destruction of some of the ship's hatches which were only partially dogged down which allowed tons of water to enter at least some of the holds.* The cargo was taconite pellets. So while I don't recall the author stating this specifically, based on Tom's statement above I suppose the addition of all that water could have rendered the ship's dry cargo wet and more likely to shift as the waves rolled the ship.

As to Ancora, while others have said they know him and state that he is an actual boater, I believe the only real interest forums like this have for people like him is the access they provide to an audience for their political and social beliefs.* You will note that they never actually enter into discussions in any relevant or intelligent way, and they rarely answer questions about their position.* In the case of Ancora, he simply posts non-stop anti-Obama, anti-liberal and pro extreme-right views.* He obviously has an extreme fascination with Obama.* A fetish, almost, it seems.* I have no idea why--- it's something a psychologist or behaviorist could explain perhaps, but it's far beyond my ability to comprehend.*

But in terms of his participation in this forum, he's what used to be called on the web a "troll," thowing things out there to see what happens.* There are people similar to Ancora on other forums I look at.

Strictly in my opinion, people like this are totally irrelevant to society and the easiest and smartest thing to do is ignore them and leave them to their rantings.* Rational dialogue is impossible and their entire approach to life is negative.* A fabrication that supports their position is far more valid (to them) than a truth that doesn't.

And of course, posts like this are what they want since the mere fact that people talk about them validates (in their minds) their importance.

If you have occasion to visit Hyde Park or Trafalgar Square in London, or Times Square in New York City, you will see all sorts of "ancoras."* They are there, spouting their close-minded, ignorant ideas and theories to anyone who will listen.* And, as becomes readily apparent, nobody listens.



-- Edited by Marin on Thursday 25th of November 2010 01:55:13 PM
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Old 11-25-2010, 12:43 PM   #54
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RE: Filling the keel with cement

Hiya,
** Speak for yourself Phil/Fill.* I moved from PMM because of YOU!!
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Old 11-25-2010, 01:31 PM   #55
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Filling the keel with cement

Quote:
skipperdude wrote:If the center of gravity is lowered by adding weight.

How does that effect the center of*boyancy?*

Would it make her less tippy?

What I know about vessel stability and how to determine or correct it wouldn't fit on the head of a pin.* But I can mention something I've read that may have relevance to your situation.* A number of years ago I read a book called Lost at Sea. An American Tragedy by Patrick Dillon.* It is the story of two of the "A" boats owned by the same company in Anacortes, WA, the crabbers Americus and Adair, that were both lost on Valentine's Day in 1983 in relatively calm seas in Alaska.* (All their boats' names started with the letter "A", hence the term A-boat.)

While the book itself received lukewarm reviews, the reason for the capsizing that was eventually determined by the investigation was an interesting one to me.

Both boats left port (IIRC Dutch Harbor) heavily loaded down with extra crab pots.* Both boats were floating extremely low in the water.* Both boats turned over in fairly calm seas within a very short period of time.* The reason was the piles of extra gear on the aft deck, which while they raised the weight of the boats and thus made them float lower, also made the boats very unstable.*

Prior to reading this book I, like a lot of people I suspect, believed that the lower in the water a boat floats the more stable it will be.* This is wrong, of course, but it was not until I read this book that I learned this.* The Americus and Adair had so much extra weight piled high, the stability of the boats was pushed over the edge and it didn't take much in the way of wave action to roll them over even though they were floating extremely low in the water.

So based on this, it would seem that it's not the addition of weight that can adversely effect buoyancy, it's where you put it.* You seem to be aware of this but I thought I'd mention what I learned.* Based on my obviously extremely limited knowledge of boat stability, I believe that changing the stability of a boat for any reason should be left to professionals who truly understand this stuff and have the experience and knowledge of the formulas, calculations, or whatever to determine what can be done safely.* I don't think it's something I'd want to experiment with by filling spaces in the boat with water to see what will happen.

Vessel stability is not something that I think should be messed around with.* The Americus and Altair crews thought they were just fine with how they'd loaded their boats.* Or at least their captains did.* But as they soon found out, they weren't.* As I recall, there were no survivors from either boat.

There have been commercial fishboats rolled over in little, five-mile-diameter Bellngham Bay on a windy day with steep waves.* A rough passage across Prince William Sound or whatever your home waters are up there is not where you want to find out that a home-grown change in weight and stability to get a better ride has reduced stability, not improved it.



-- Edited by Marin on Thursday 25th of November 2010 02:39:03 PM
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Old 11-25-2010, 02:57 PM   #56
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RE: Filling the keel with cement

I'll try one more time before hanging myself steel leader.

A fish hold is supposed to be filled up with ice (90% the weight of water), plus fish (heavier than water).* It's kind of the whole point in building a fishing boat in the first place.* If the suggestion is that putting an equivalent amount of weight into a space designed to hold this amount of weight requires the supervision of a naval architect, the Chief Engineer of the Navy, or another self-appointed stability expert so that poor Skipperdude's boat doesn't immediately turn turtle with loss of all hands - well that suggestion is just plain silly.

Now I'm going to go hang myself.
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Old 11-26-2010, 03:52 AM   #57
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RE: Filling the keel with cement

The "A Boats" Saga was ultimately solved by talking to the painters in the shipyard. Investigators couldn't figure out why they rolled when clearly they should have been able to handle the loads imposed on them.
After several years the shipyard workers were interviewed and it was determined that the painted waterline was not where it was supposed to be. The waterlines were raised on those boats
on the orders ( architects unaware) of the owners.
Pictures of them leaving port with full load of gear were in fact overloaded and not as they appear.
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Old 11-26-2010, 11:09 AM   #58
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RE: Filling the keel with cement

Quote:
Sailor of Fortune wrote:
After several years the shipyard workers were interviewed and it was determined that the painted waterline was not where it was supposed to be. The waterlines were raised on those boats
on the orders ( architects unaware) of the owners.
Sounds similar to the story about the King of Denmark who ordered that another deck be added to a ship about to be launched.* The deck was added and when the ship was lanched it turned turtle and sank in the harbor.

Any idea as to why the owners of the A boats*had the waterlines painted high?


Delfin wrote:


*"A fish hold is supposed to be filled up with ice (90% the weight of water), plus fish (heavier than water).* It's kind of the whole point in building a fishing boat in the first place."
*
It appears to me*when I watch Deadliest Catch that the holds start out full of water and the water is displaced with crabs as the catch progresses.*
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Old 11-26-2010, 11:11 AM   #59
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RE: Filling the keel with cement

Quote:
Delfin wrote:, replicating the design weight as originally intended would help answer the question for you.
I think that is what the P.O. did by filling the fish hold with tubs of sand.

When I rebuilt the deck, that is when I removed the sand. My initial thought was that all that sand, about a thousand pounds. Would decrease performance and increase fuel consumption.
It seems I was wrong on both counts.

Although I can't be certain as the extra weight just pushed the hull lower into the water



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Old 11-26-2010, 11:28 AM   #60
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Filling the keel with cement

You guys argue about the craziest s#!t.

-- Edited by GonzoF1 on Friday 26th of November 2010 12:29:40 PM
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