Pendulums effects?? CB, CG....

[Wynand N]

Maybe everything I learned and practice about boat design was a waste of time.....

The following from a boating forum. Tell me what is wrong with what you are to read. I had a smile or two

Well, the nice thing about the round bilge with a keel, it's like a pendulum and it's EZ to lower the COG (center of gravity). Unlike a hard chine where most of the weight is spread over a wider area, in effect, raising the COG when it heels over. No pivot point.

If we have the technology to make them round, I would do it.
I do not think there are any hard chined fish.

But there are some things for sure!!!

If you take a weighted keel sailboat and put it in a calm harbor, WITH DECK HATCHES SEALED, then list it up on it's side, then let go, it'll right it's self. The COG remains constant above the waterline. Round bilge!

As well, and upside down power boat or cat will stay upside down in most cases due to their beam and/or hard chine. Even a sail boat, as discribed above, will right itself if inverted. There is NO PENDULUM EFFECT in hard chines and cats. This is why mono sailboats are the choice of world cruisers.
I'll bet this guy below had a round bilge or at least a displacement hull. "PENDULUM EFFECT" Otherwise, he'd be at the bottom of the ocean.

And while the center of gravity will be fixed for any loading, and even assuming nothing shifts (like fuel and water in the tanks or supplies and gear in lockers) the CG will move vertically and horizonatally relative to the center of bouyancy or to the water even if it does not move relative the boat itself.

Typically hard chine boats 'roll up' meaning that the center of gravity rises relative to the surface of the water as the boat heels, while round bottom and vee bottom boats tend to 'roll down' as they heel.

[sorenfdk]

Originally Posted by Wynand N

Maybe everything I learned and practice about boat design was a waste of time.....

The following from a boating forum. Tell me what is wrong with what you are to read. I had a smile or two

Was it signed "Mighetto"?

[Robert Gainer]

Wynand, the first thing that jumps out at me is the fact the he comes from Puget Sound, in WA, the home of several other misguided individuals. Doesn’t mighetto come from that neighborhood also? The second thing is that he said in his profile that he is a “Blue-blood Americain back to 1625 A.D” He can’t even spell American let alone have a history that goes back that far. I was following the thread when it started and was surprised that you got involved at all. It must be a slow day for you.
Robert Gainer

[Wynand N]

Soren & Bob,

No, I wish it was mighetto, then I could fathom this ramble for what it is.

Actually, the last two quotes are from a chap who is also a member here at Boatdesign.net. I will keep his name secret to save him some red face.
I always thought that CG is fixed and CB changes with boat heel....and what can one say about raising CG when a boat heels and all that Pendulum effect. I agree, it smacks of Mighetto thought

This gentleman also answered my reply

Wynand N. Sorry to burst your bubble. A few basics in boat design.

[D'ARTOIS]

Help, did I drink that much? LOL

[MikeJohns]

People with opinions who are convinced that they and only they have a true knowledgeable insight.
They inhabit every boatyard, haulout facility (and now we can add forum) and are the bane of an engineers life, you either smile and nod idiotically waiting for them to go away or spend an hour explaing (or arguing ) some absolute basics that they have completely failed to grasp.

[marshmat]

I suspect whoever the poster was is talking about the position of the CG relative to the CB, taking the CB as fixed relative to the water surface... kind of an odd way of looking at things, but some of the statements seem a bit less strange in this context. Still somewhat contradictory and weird, of course.

[gonzo]

Would a multichine screw up their arguments? I think those boat concepts came from a Disney cartoon

[MikeJohns]

Originally Posted by marshmat

I suspect whoever the poster was is talking about the position of the CG relative to the CB, taking the CB as fixed relative to the water surface... kind of an odd way of looking at things, but some of the statements seem a bit less strange in this context. Still somewhat contradictory and weird, of course.

But as Gonzo also says above chined boats do not suffer from this imagined malaise and obey the laws of physics along with their round bilge cousins.

[sharpii2]

It seems like this guy is almost getting it. But not quite. Makes for some good comic relief!

How come every time someone (me too, at times) tries to show how 'learned' they are, they usually end up doing the opposite?

[h_zwakenberg]

Hallo Wynand, hello all others,

when heeling, CB moves mainly to lee, and hardly upwards (depending on hull shape). What changes a lot with heel is the position of the metacenter, which actually will be lower with heel. Perhaps the original author mixed up metacenter and CB?

As to hard chined hulls: when such hulls are rolling, the chine trips the partly lateral flow to locally separate and form a vortex. This creates extra resistance, which in turn dampens rolling somewhat. So, there is just a little merit in what he wrote, HOWEVER: when conditions are such, that round bilge hulls are in danger of a capsize, roll damping will not be so large that chined hulls aren't in danger as well....

just my 2 €-cents....

take care and keep those masts pointing upward,

[Wynand N]

Exactly. I tried to explain that CG is mass/weight and geometrically fixed. CB moves according to heel and change of submerged hull shape and that GM changes as well.

I believe my friend had it the wrong way around and I kindly did point this out to him.

However, the first four quotes are from a very confused gentleman

[Guillermo]

Originally Posted by MikeJohns

People with opinions who are convinced that they and only they have a true knowledgeable insight.
They inhabit every boatyard, haulout facility (and now we can add forum) and are the bane of an engineers life, you either smile and nod idiotically waiting for them to go away or spend an hour explaing (or arguing ) some absolute basics that they have completely failed to grasp.

I agree. Absolutely. Forums seem to be now a preferred place for that kind of people.