Filling the keel with cement

[Delfin]

SD, if you didn't see any difference in tenderness with the sand on, then adding weight lower probably wouldn't help.* If you did add weight, adding it as low as possible enhances stability, but won't have much of an effect on the rocking and rolling.* I think I mentioned it before, but if you read the book Fastnet Force 10, there were a few boats that rolled and were dis-masted.* Some crews then took to the life rafts because they just couldn't handle the motion of the boat after the weight of mast was removed - the metronome effect.* Many lost their lives when their rafts inverted, or died trying to make the transfer from boat to raft, while their abandoned boats survived just fine.* With the dis-masting, the center of gravity had been lowered, but it sure didn't make the boat motion better.

Sounds like the answer is the one you have already come up with - paravanes while underway.

 

[skipperdude]

GonzoF1 wrote:

You guys argue about the craziest s#!t.

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

Would you not consider it more of a discussion?

Is it s#!t or shinola.

SD

SD

*

 

[Tom.B]

skipperdude wrote:

Is it s#!t or shinola.

I don't know the difference.

 

[skipperdude]

GonzoF1 wrote:



I don't know the difference.

That cracked me up.

SD

*

 

[RT Firefly]

Hiya,
** Mr. SD.* This may help answer some of your questions.
http://en.wikipedia.org/wiki/Metacentric_height

 

[RickB]

" 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."

Assumptions about stability without documentation of real data has sunk a lot of boats. The only thing I can think of that is riskier is to advise someone based on those assumptions.
"Weight up higher decreases ultimate stability but increases stiffness and resistance to roll, at the risk of decreasing ultimate stability. "

Weight moved higher on a boat raises the CG, it decreases the GM, it slows the roll. A slower roll is exactly the opposite of how a "stiff" boat performs.

"If you did add weight, adding it as low as possible enhances stability, but won't have much of an effect on the rocking and rolling."

What???* Please go get a book on stability. Are you getting this stuff from P/F?

Now do you see why I think your providing advice to anyone about stability is dangerous? You are filling in for the role Phil/Fill used to provide over on the PM site, the source of outrageuosly distorted and just plain wrong "information."

*


-- Edited by RickB on Saturday 27th of November 2010 06:00:50 AM

 

[RickB]

"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.'"

Long past this but I was out of town having a real life so missed the fun here.

Sloshing is the fore and aft movement in tank. In certain seaways, a ship will "surge" fore and aft and the tank contents follow this motion, sometimes out of phase and it puts a very large structural load on the bulkheads.

This can happen to a tank truck and the force can cause steering or braking problems.

It is a phenomenon associated with free surface because if the tank was pressed it could not happen.

Anything that is capable of becoming fluid in a tank or hold will create a free surface effect. Another post here talks about solids getting wet. Sugar is one of those cargoes that is extremely dangerous if it gets soaked. A leak in a cargo hold can make the sugar flow like water and then become solid again after it flows to one side.

The CG shifts to the side, the CB shifts to the same side and the ship can stay "stuck" at that "angle of loll" and not return to an upright position. Any force that then creates a roll to the down side can easily capsize the ship. There is a classic example of that exact situation used in stability classes:

http://www.uscg.mil/hq/cg5/docs/boards/silverdove.pdf

It's also a great example of why the instinctive means to correct the problem can actually make it far worse. Something to think about when considering a stability problem or giving advice to someone with a boat you know nothing about.

 

[RickB]

skipperdude wrote:

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

If you want to know exactly what you have, follow the directions here:

[url]http://tinyurl.com/2fgdj6s[/url]

If you want to know if your boat is within safe limits, contact these people:

http://www.npfvoa.org/

or the Valdex CG marine safety unit and ask them about fishing vessel stability. They have done a huge amount of work to teach the operators of boats like yours about what is safe and what isn't. They got tired of seeing fishermen die every year because of lack of information and bad advice from amateurs.

There is no one on this site who can tell you if your boat is safe or not or what the ultimate effect of adding or removing weight from it will be.

*

<a href="http://tinyurl.com/2fgdj6s">
</a>

*

 

[Delfin]

<blockquote style="padding-left:30px;">RickB wrote:"If you did add weight, adding it as low as possible enhances stability, but won't have much of an effect on the rocking and rolling."
What???* Please go get a book on stability. Are you getting this stuff from P/F?
Now do you see why I think your providing advice to anyone about stability is dangerous? You are filling in for the role Phil/Fill used to provide over on the PM site, the source of outrageuosly distorted and just plain wrong "information."

From a technical article on stability:* "Heavy displacement helps dynamic stability, but the most important factor is the boats roll moment of inertia. The roll moment of inertia is calculated by multiplying the weight of each piece of the boat by the square of its distance from the center of gravity. The "squared" term makes the calculation very sensitive to how far heavy objects are from the center of gravity. For example, a dingy with two people sitting fore and aft on the centerline has a smaller roll moment of inertia than the same dingy with the people sitting side by side. Both boats weight the same, have the same center of gravity, and the same center of buoyancy (exactly the same static stability), but moving the people off the centerline greatly increases the roll moment of inertia. If two identical boats are hit by a gust, the one with the largest roll moment of inertia will roll the least. Deep draft, heavy displacement hulls, with long heavy masts will have the largest roll moment of inertia."

Frequently Rick, you are a source of great information and your obvious passion for weighing in as an expert many times helps people understand complex issues.* However, you also weigh in with equal passion when offering up errant nonsense about as frequently.* Since you'll defend your point of view with a pathological determination to be right even when wrong, you make it harder for people to benefit from your obvious experience.* Turning personal and nasty when disagreed with doesn't help much either, and makes it less likely that people can learn something form you when you do know what you're talking about.

*

 

[RickB]

You really ought to just quit Delphin, you're only getting worse by learning a few new terms.

"Moment of inertia" is a measure of the resistance to a roll induced by an external force. It is not a measure of how much a boat will roll, how far it can roll before capsizing, or (by itself) its period of roll.





-- Edited by RickB on Saturday 27th of November 2010 11:06:12 AM

 

[FF]

"Turning personal and nasty when disagreed with doesn't help much either, and makes it less likely that people can learn something form you when you do know what you're talking about."

But he is an ILLEBERAL, and when the reality s does not fit ATTACK the other person, not his point of view is the standard, Cloward & Pivin.

 

[skipperdude]

I don't know about the rest of you but*I have learned things with this thread.

I know I can just go ahead and drive the boat and deal with challenges as they come up.
With me it's not enough to just accept the way things work.

I like to know why.

Does it make me* a better boater, safer boater?*I don't know.

*If Rick B sometimes comes off a little short that is fine with me.

He possesses Knowledge I don't have.*
On all accounts i have found his statements to be concise and true.

*If i have to weed*through*the debates and follow along in order to extract the desired information. So be it.
Those proven wrong also benefit as they are forced to engage in research to at least hold up an end to a debate.
*
I have received some of*the best*lessons from a few gruff teachers.
Some I liked some*I didn't. But if you paid attention you learned something

When it rolls from the facts and numbers* to opinions .* Every one has one.

If you want an argument have at it. If you have a question. I don't think Mr. RickB will steer you wrong. Especially if it is within his line of expertise.

Thanks for all the input everyone. Most enjoyable.

SD*
**

 

[RickB]

skipperdude wrote:I don't know about the rest of you but*I have learned things with this thread.

Thanks for your feedback, SD. I am glad you got something positive out of this.

The USCG and the fishing vessel association has done a huge amount of work to provide useful information abuot stability for fishing vessel owners. All you have to do is ask and they will bend over backwards to help you with good information and safe advice.

Good luck and keep the ice off the rigging.