Couldn't right my cat solo. Need advice

In all those diagrams, it shows the beams perpendicular to the water.

Are we discussing the difficulties associated with getting the boat past this point?

Last I checked when we were over, the beams were actually past 90 degrees to the water, since the tip of the mast was in the water.... Is this perpendicular point that which the greatest torque/force must be applied to continue the righting of the boat, since the sail/mast is out of the water (and applying the greatest resistance to your rotational effort)?

Anecdotal evidence in my own personal experience, getting the main clear of the water was the hardest part. Once the water was off the sail it seemed to go vertical much more easily.

And how would standing on the tip of the lower daggarboard change the force/torque diagram?

With or without (like I was just standing on the board) the righting line being applied?

Once again, this analysis is correct.

The position of the line has no bearing on the amount of righting moment applied to the system. Another way of looking at it- if you were able to make your body completely rigid and affix your feet to the bottom hull, there would be no need for the righting line (essentially make yourself a cantilever beam). You would have exactly the same amount of righting moment without the line.

Standing on the tip of the daggerboard makes the sailor taller, i.e., it move's your CG farther away from the bottom hull (the fulcrum) so it increases the righting moment of the system.

For example, if you're 6 feet tall & 200LBS, with your CG 4feet up from your feet, then leaning horizontally, you can produce a righting moment of 800 FT-LB. If you stand 2 feet out on the daggerboard, you can now produce 1200 FT-LB, so you increase righting moment by 50%.

sm

Because the whole thing is to be considered as a closed static system, it is theoretically not interesting where the x-axle is. In other words it makes no difference that the mast is beyond his perpendicular point.

But, but..... Ofcourse there is the matter of water in the mainsail. That's a breaking force ofcourse, so maybe you have to get rid of that water first (swimming to the top).
After that it should even be easier because the leaning from the masttop on the water will take some weight away.

You can easily demonstrate this to yourself the next time you'r fully rigged on the beach: attach a rope to a trapezewire and pull the cat over on its side.
Now it's lying with the rig down on the ground supporting on the masttop. Start hanging on your uphaulline and in case your weight is critical you will see that with the initial pull you lift the whole thing easy one or two feet from the ground. Then it will stop and you can pull what you want, but it won't go further then that.

(At the same time the non-believers of the static system can easily check their own theory of the lower attachment of the uphaulline.)

However the experience on the water which Jay describes differs a bit from the above described, but first let me say that he is right; his description is also mine and I think it is the common experience.

This phenomenon has to be explained by the force in the mainsail which is starting to catch wind. By the way if you haven't unsheeted the jib, it will definitly catch even earlier. (But this will lead also to headway after the righting of the cat.)

ronald

OK, a question for non-believers:
I have my righting pole, it is attached with two lines below the hulls, one forward and one aft. But I also use a line over the hulls that I hold with my hands. Would that be average between the two cases? Should I tension more with the hands?
<img src="<>/wink.gif" alt="wink" title="wink" height="15" width="15" />

Regarding the analysis only at right angle, I say nothing changes in the analysis as long as you are still standing on your feet, lets say 10° towards one side or the other. At some point after you succeeded to raise the mast above the horizontal, you come to a point where you are hanging from the rope rather than standing on the lower hull. When that happen, yes, it's better than the rope is over the hulls, but that's way after the critical point. Success is not conditionned by that situation. Maybe it doesn't even help, actually. As soon as you passed the equilibrium you want it to go slow so that it doesn't go the other way.

Not sure how many times it needs to be repeated, but apparently at least one more time... the angle of the line(s) has no bearing on whether or not the boat is righted. Over the hull, under the hull, using a righting pole, holding with your hands, holding with your harness, or holding with your teeth, it makes no difference. All that matters is the horizontal distance of your center of gravity from the fulcrum (which is the center of bouyancy of the lower hull). How you get your CG into position only effects the reactionary forces on your body (your comfort level), it does not effect the righting moment applied to the boat.

It is just like the teeter-totter we played on in elementary school- the rig is at one end, you're at the other end, and the hull is in the middle. Weight times horizontal distance.

sm

I'm with you amigo...

I guess I'm a semi-believer as I think there is still something missing. The following quote I think points us to where there is a problem in the assumptions.

Another way of looking at it- if you were able to make your body completely rigid and affix your feet to the bottom hull, there would be no need for the righting line (essentially make yourself a cantilever beam).

I agree with this statement. The problem is that in reality we can't rigidly affix our feet to the hull and thus our feet cannot apply leverage or righting force to the hull and the righting force must be transmitted through the line. While it may not make much difference whether the line is tied at the top beam or over the top hull, as you progressively lower the tie point it seems you will eventually reach a point where your inability to be a

fixed cantilever beam

will prevent righting of the boat. I don't know where that point is but if line position didn't matter everyone would tie off at the bottom beam where it is easier to reach? Since I can't fully grasp all the physics involved, I'm going to have to do some experiments with my cat in a calm lagoon this spring and see it for myself.

Higher line = lower tension. That makes a good reason to run the line above the hull. But it doesn't give more righting moment.

Rope Tension = W /(cos a)
Righting moment (*) = W * d

Where
a= angle of the rope against the vertical (0 = vertical, 90° = horizontal)
W is your weight
d = horizontal distance between your center of mass and the hull (or the axis on which the boat rotates while righting )

No

a

on the second formula.. that is all the point of the discussion. Of course if a = 90° or close you cannot right the boat. That's probably what makes people skeptical

(*) That is the righting moment that you produce, not the total righting moment. It has to overcome the opposite moment produced by the mast, etc.

OK - I can't help myself - time to throw my 2 pennies in.

Its been many years, but I remember the term

force couple

being used in applying torque to a system. There are several forces being applied to the boat. In addition to windage, wave forces, etc. there is the CG and the CB.

Regarding CB, assuming you have enough buoyancy in the mast not to go turtle, you end up in a stable position where the CG of the boat is nestled between the buoyancy forces of the mast and hull.

Regarding the CG, since we are on the boat, we are effectively part of it from a calculation standpoint. By using the righting line and leaning out we move our body mass such that the CG of the boat+person system moves outside the stable point between the two buoyancy forces. Once that happens you have a force couple (CB pushing up and CG pulling down) and the boat begins to rotate.

Again, the mass of our body is connected to the vessel both through the righting line and our feet so we are part of it. If we move the righting line far enough away from the CB we don't have to use our feet and as we dangle from it, the force on the rope is simply our weight. If we have a long enough (and strong enough) dagger or righting arm to stand on, we don't need a righting line, so rope force = zero. Key point is getting the CG of our body outward as far as possible so we move the CG of the boat+person system past the stability point between the hull+mast buoyancy.

By moving the rope attachment point down (toward the dolphin striker or below), the rope force on our hands goes up - presumably to infinity if the attachment point gets low enough. Moving the rope up or over the hull reduces the force, thus the intuitive feeling that there is better leverage. Neither of these make the boat right any faster due to strength limitation or other reason they allow you to get your body CG further outboard.

Somewhere along the line in this interminable but legitimate discussion, someone introduced the concept of

acceleration

by changing the direct of the line. I confess to not understanding the idea even a little.

Next thing you know, you'll be telling me an ice tray full of hot water will freeze faster than a cold one due to thermal acceleration.

Your position contradicts my personal findings in the field. Others disagree with you in theory.

Yes

Exactly.

All the boat/system

cares

about is location of CG relative to location of CB. How this is achieved is inconsequential- righting line over the hull, under the hull, stand on a dagger board, righting pole, nail your feet to the hull and stand out real straight. It doesn't matter. Moving your CG outboard is all that matters.

For those that still believe that the routing of the righting line has some effect on whether or not the boat is righted, take a look at every monohull dinghy in the world...they right their boats by standing on the dagger board using NO RIGHTING LINE. The key is simply to get your weight as far outboard as possible, how this is done makes no difference.

sm

Christ, I love this part.

But by the 20th century the phenomenon was only known as common folklore, until it was reintroduced to the scientific community in 1969 by Mpemba, a Tanzanian high school pupil.

Holy cow! It's on the internet! It must be true! <img src="<>/grin.gif" alt="grin" title="grin" height="15" width="15" />

by the way, that article offers no evidence that it exists, only possibilities (external to the water) as to why it might happen. There is no such thing as thermal acceleration. If the hotter water freezes faster it is a result of some other circumstances (hotter subject causing the freezer to increase cooling capacity, currents in the hot water, etc.). Added to which

hotter

here is a very unspecific clause...are we talking 33 degrees vs. 110 degrees or 33 vs. 33.1?.

I implore anyone here to try it and show me how you beat physics.

And how the hell did Aristotle get a freezer? His experience was likely more related more to radiant cooling on a cloudless night (why you can freeze water outside on a clear night even if the outdoor temperature doesn't get to freezing) or evaporative cooling.

If there is no such thing as thermal acceleration, why did you introduce it into the the discussion?

I introduced the word

acceleration

without modifier and freely admitting I did not understand the concept in response to post #256774.

What is your intent here?

should have kept reading...

I've debated this elsewhere and the general premise is that there is thermal

acceleration

. As such, the

reason

hot water would freeze faster than cold water (everything else being the same) is that the hot water cools at a faster rate (true because the initial temperature difference is larger) and that it maintains this cooling rate

momentum

so it freezes faster (not true). The problem is that there is no cooling

momentum

. When that water reaches the same temperature that the other one was at (previously), it is cooling at the same rate that the other one was when it was at that temperature. It won't cool faster because it had a higher cooling rate previously....all things being equal.

I've always understood it using hot, like almost boiling our boiling water, will freeze faster than cool water just because of evaporation making it cool more quickly.

I don't know, that was high school physics, and a quite a few empty bottles ago.

Does it really matter? Are we that bored?

if the water is evaporating, wouldn't there be less to cool?

Hasn't Jake already made a carbon-fiber resin infused test chamber for this experiment? Complete with wrap-around graphics?

When water turns from liquid to vapor, it cools. Same reason we sweat.

But...when you are cooler, you become more dense, thus weighing more, so you can right your cat, just as soon as you cool down enought to tip the CG past the CB, which is a BFD if you're not wearing your PFD, you could be DSQ'd.

+1

And if the water is warm you recover your normal density and that explains why sometimes the cat tips over to the other side..

Wait a minute. When I'm cool I don't get more dense.. I get smaller!

try it.

and...yes.

noooo, we sweat because all the alcohols in our system has to escape, and you can only pee so much

Yup, and at some point, it is the same temperature as the other water started at...so is it still cooling faster?