How "easy" -- or difficult -- is it for boats with flybridge to tip over?

BlueStar,
dont worry, I am learning some big words out of this post.

I only wish they had YF when I took the SATs 30 yrs ago....


RT

LOLOLOL, I'm not going offshore in 12 foot seas in any yacht under 150'. It just isn't worth breaking stuff and beating yourself up......On a delivery, I'll take the inside on anything 6' above on a boat 80' and under. If I have to cross the Gulfstream than probably 8' at most. Then again I was in 20' swells, 200 nm offshore in a 75' Hatteras, yet they were so farly spaced it was totally comfortable and felt like riding in a slow elevator.

Blue star. Shame on you for teasing us. Why wouldn't you have asked that question BEFORE you bought the boat?

I really like it when "experienced" Yachtsmen venture out in a 60 ft W/L power boat and sit in beam seas of 12 ft and have "no worries mate" I think I have a few stories where "loss of life" followed...

I have a 95 355 aft motor yacht and I have had 7and 8 packed on my flybridge in the bay and cruising through other wakes of big boats that rocked it a little but very happy with how she handled

Let's have some Phun:

Phun Physics - Topics

Phun Physics - Demonstrations

P.S.- All I remember is some mention of the mass of the ass.

Yeah, "no worries mate", that's an Aussie anthem…..right?
I would guess many/most of those running boats (I am not a qualified Captain, so won’t use that title) for many hours offshore fishing or moving a boat to another port, will find themselves in bigger seas than can be planned for.
I have never put my boat and passengers into a dangerous situation due to a “no worries” attitude. I never stated I go out to “sit in 12 foot beam sea”.
12 foot seas and swell are not that rare where I fish. I try to avoid big seas whenever possible, but a good forecast does not guarantee that sometime during that day there will be a rough patch.
This does not mean I am gung-ho about going offshore, it’s just part of what you prepare for.

That doesn't completely work either because you're still approaching the matter as if the boat is a freely spinning object about an axis. It's not. It's acting more like a pendulum or a metronome, with the axis at the center of gravity, but it has forces acting on it that prevent it from spinning in most circumstances just as the metronome and pendulum do.

I'm not a naval architect but you needn't be one for this discussion since phsyics doesn't care if the floating object you're discussing is a boat or a log or a foam cup or even a bar of Ivory soap. A floating object is a floating object and the essential theory remains the same. The math involved is very relevant to the specific boat, but not to the theoretical conversation.

For the most elemental description, it's a simple matter of gravity vs. buoyancy - as long as the parallel forces are acting equally, things are generally happy.

Imagine looking at the bow of the boat. Now imagine a vertical line down the center of the boat (we'll call it a centerline). In an ideal world, the centerline is also where you find the center of gravity, at about the waterline or at least low down on the hull. When the boat is level, this line will also describe the center of buoyancy. At some point above the center of gravity on this line will be another point, called the metacenter. For the purpose of this discussion, imagine this as the end of the pendulum and the CG as the axis. If you have a high metacenter (long distance from cg to metacenter) you get a boat that's stable, but when it rocks & rolls, it does so quickly (short period). If you have a low metacenter, the boat will roll and right more slowly (long period).

Adding mass (people) to the flybridge will raise the center of gravity, thereby shortening the metacentric height. The boat will roll and recover more slowly, but it will still recover provided the force of buoyancy is acting on a metacenter that is higher above the water than the force of gravity which acts on the center of gravity. The point at which the metacentric height goes to zero and then negative is called the angle of loll. Once you reach that angle, the floating object cannot self-right unless acted on by an outside force. Once the metacentric height goes negative, the object cannot self right - and in the case of boats, openings will begin to take on water, prompting a capsize and/or sinking.

Even with seven people on the flybridge, the angle of loll of a cruiser should be far beyond what wave action or turn banking should reach. If anything, passenger discomfort will prevent you from pushing those limits just as it might when driving on a twisting road. This would be centripetal force acting to send you and your passengers in a straight line - as the boat deck describes an arc. You'd toss your friends and yourself around and make for an unpleasant voyage. Even if they remained your friends, it would be unlikely they'd be passengers again anytime soon.

The bottom line is, as long as long as the metacenter remains above the center of gravity the boat will naturally right itself. You will not drive the boat to 10/10ths and therefore the answers to your original questions are "very difficult" and "beyond your limits" in almost every conceivable circumstance in which a prudent sailor would venture forth in a Carver.

In order:

Why? Because Marmot tends to bray like an ass at any given opportunity, puffing his chest out as though he has some monopoly on knowledge, belittling the weekend boaters who come here to learn something. I find his type a necessary nuisance, a talent to be rented when needed and kept at least at arm's length. He comes across as the boorish lout at the party, whom everyone takes great pains to avoid.

Centrifugal force is not fictional "to me." Centrifugal force is fictional to physics.

"Qualifications" are issued by standards bureaus that are derided and "qualified" people likewise in thread such as http://www.yachtforums.com/forums/chris-craft-roamer-discussion/12598-whole-story-4.html

So either qualifications either make one an expert, or they do not.

I know I've had Harvard MBA grads who weren't worth peeing on if they were on fire, and C-students from state schools who are creative, industrious, and skillful. I'd rather have someone who doesn't have all of the papers but has all of the goods.

Paper qualifications often aren't worth the effort to wipe with. Talk is cheap, and so is paper.

Anecdotally: Right now we're drafting an entirely new emergency preparedness plan for my town, since we're line of sight from a nuclear plant and this fact greatly concerns a vocal minority of the townsfolk. We interviewed people for the Coordinator position - all but one had every Federal, State, OSHA, FEMA, and other qualification, and one lacked Incident Management, confined space operations, and a couple of other qualifications... That one came to the interview process having assessed the town, assembled a preliminary outline, expressed areas of concern, and brought thoughtful considerations for resolution complete with documentation to back up his thoughts. Turns out he was also the only one who had written these plans before, and had a record of success not slips of paper from taking tests. Two of the "Qualified" folks with a stack of "qualifications" as high as your waist couldn't articulate simple practical thoughts.

Now a question answered with a question... you believe physics about gravity, why not about centrifugal force being fictional?

We've strayed far from the topic.

Wow, this thread has gotten complicated. What in the world relation does a vessel on the ocean, which is not in any way secured to its base, have to do with a pendulum or a metronome which can't flip off because they are secured. Any vessel can turn turtle. Period. Once they've turned turtle very few can right themselves. That's due to a myriad of reasons, most notably its shape and weight distribution. Some boats can turn easier than others. The short answer is don't take a 36' carver out in more than 7' unless you are very good and very lucky, in fact don't take it out in more than a rough 4' unless you're a glutton for punishment.

Ward vs. the search engine! Congratulations, you know how to search key words, but even a basic understanding of a reaction force would allow the layman to recognize that the fictitious force was brought up. Not the force a body contained exerts against the centripetal force containing it from the moving frame of reference.

The rock on a string tied to a post example... the rock exerts a "reactive centrifugal force" which the string "feels" but the post does not... Now considering Newton's third law (all forces occur in equal but oppositely directed pairs) where's the reactive centrifugal force at the post?

The fact of the matter is, "reactive centrifugal force" is a term hotly debated to describe the kinematic phenomenon of the object in motion tending to put the force of its inertia in a seeming outward direction (it's actually tangential vectors to the arc, perpendicular to the string rather than in the same line as the string) in order to make a cleaner term than "counterpart force to satisfy newton's third law." It's not a settled matter, though, since centripetal force is kinematics and so-called "reactive centrifugal force" is dynamics. They're really distinct things, as centripetal force is not actually a force "pulling" to the center that can be offset by a so-called centrifugal force "pushing" to the outside.

(Centripetal means inward, toward the center not from the center. Centrifugal means to outward, away from the center)


So Ward, in trying to "one-up" or prove me wrong, actually points to the fictitious force as observed from the rotational frame of reference as his defense. "Failure" might be his next Wikipedia search term.

A pendulum or a metronome have mechanical forces holding them in place, but with sufficient outside force those mechanical forces can be overcome. Buoyancy is the corresponding term to that mechanical force keeping the boat upright, and sufficient outside force can overcome that as well. It's all relative.

OP - No. 1854: Rocking Boats explains it quite simply.

So for a layman, I now have some understanding on your statement regarding centrifugal force, but, you said it was, quote “fictional” which clearly it is not. Perhaps if you had said something like: in the circumstance the OP refers to, centrifugal force does not apply, it is the metacentric height that is the deciding factor, assuming I have understood your post.
As for Marmot, I think a dry sense of humour can be misunderstood by many people or even those just having a bad day. Anyway, he is capable of defending himself I am sure.
YF would be **** boring if we all agreed or if it were colonised by amateurs with little to contribute other than their own egos. Niether you or M are amateurs.
Thanks for the effort to post such an in depth response. And I look forward to the responses of others as qualified.
FWIW,
Send a PM to someone you have such animosity toward rather than a public post, it would probably serve you better.
Had your initial post given as much thought to the question, then the response, which was “Please elaborate” would not have occurred.

I have no input on Carvers, but a decent SF (without 7 people on the tuna tower) will take more punishment than you can.

I have been out on a 28, 36, and 45 and the boats have come back up from a big/steep wave when I hought we were going to see if the life raft self inflation mechanism would work (you know the dodad that realeases it when the boat goes under).

I was just asking for elaboration on how a link to a USCG how-to pamphlet stirred such outrage and a borderline hysterical rant about centrifugal force and papers(?) of all things.