Is is safe to go aloft while on stands?
- Thread starter kmart
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Claptrap - Sorry
Okay - here goes!
If the boat is sufficiently well propped up to withstand a gale or two without blowing over and also to cope with at least one person standing on deck at its widest point, then nobody can develop anything near as much sideways force if they are up the mast and thus on the boat's centreline.
The thought that the leverage a 200lb man 60 feet up could exert bears no relationship to the actual vertical downwards force of said individual. The lateral (sideways) forces are minimal.
Even if he wanted to he wouldn't be able to develop anywhere near enough lateral force to tip the boat over.
Of course boatyards do not like having people up masts - private individuals that is. It's bad for trade and they don't like the paperwork that results from an accident.
Curiously you hit the deck just as hard whether the boat is afloat or ashore.
Okay - like always - it boils down to whether you understand the principles and are willing to take the risks. The only difference between afloat and ashore is your confidence in the shoring up or its cradle.
Shores and props are known to work loose but a proper cradle or proper jackstands that can handle a person or two on the gunwhale should pose no problems.
It's all in the mind!
I speak as a 200 lb one who had a snap shackle open one day whilst at the masthead and in my bosun's chair - and with a bucket full of heavy tools hanging below. The boat was afloat at the time.
I did a first class imitation of a Koala bear.
Okay - here goes!
If the boat is sufficiently well propped up to withstand a gale or two without blowing over and also to cope with at least one person standing on deck at its widest point, then nobody can develop anything near as much sideways force if they are up the mast and thus on the boat's centreline.
The thought that the leverage a 200lb man 60 feet up could exert bears no relationship to the actual vertical downwards force of said individual. The lateral (sideways) forces are minimal.
Even if he wanted to he wouldn't be able to develop anywhere near enough lateral force to tip the boat over.
Of course boatyards do not like having people up masts - private individuals that is. It's bad for trade and they don't like the paperwork that results from an accident.
Curiously you hit the deck just as hard whether the boat is afloat or ashore.
Okay - like always - it boils down to whether you understand the principles and are willing to take the risks. The only difference between afloat and ashore is your confidence in the shoring up or its cradle.
Shores and props are known to work loose but a proper cradle or proper jackstands that can handle a person or two on the gunwhale should pose no problems.
It's all in the mind!
I speak as a 200 lb one who had a snap shackle open one day whilst at the masthead and in my bosun's chair - and with a bucket full of heavy tools hanging below. The boat was afloat at the time.
I did a first class imitation of a Koala bear.
No, it's gravity that gets stronger every day. Or could it be...oh no... it's both!
I apologize, but I dont believe you have a very good understanding of the forces at work in a lever/fulcrum.
Most boat yards point the boats into the most prevaling wind so the likelihood is that the strongest winds will likely always face the bows. Even so, a broadside wind will put very little force on the bare mast until winds become exceedingly high. For the sake of conversation, a 100 mph wind has a force of 30 pounds per square foot on a round structure. A 6 foot section of 4 inch diameter mast would only have 60 pounds of lateral force against it in a 100 mph wind. And they do blow over, dont they? Well, the wind effects the entire mast, not just the top. But while the overall wind load is nearly 500 pounds at that speed, the leverage arm is getting shorter as we come down the mast.
Now lets put our man at the top. If, for example, the top is 60 feet above the ground with jackstands supporting the boat, what we have is a class three lever. If the tops of the jacks are at 3 feet, this gives a multiplier of 20:1 (60/3=20). While the 200 pound man at the top only adds 200 pounds of downforce, he has the potential to put 4000 pounds (200 x 20) of lateral force (torque) against the top of the jackstand, and even more if he were to make some accidental move that made him heave into it or away from it. The man could actually generate more load than a 100 mph wind!
If you moved very slowly, and stayed fully centered over the boat, you could get away with it. But considering the jack pad is usually resting against the hull on a piece of carpet..... I guess the question to ask is if you were up there at the top, and very still, would you want me to tie a rope to the top of the jackstand and apply 4000 pounds of pull to try and pull it out?
I think its a very, very bad idea to attempt climbing it in the yard.
A man walking the deck has only a very small percentage of arm/lever effect (torque) compared to a man at the top of the mast. There is no comparison. Even standing out at the farthest side he may only add about double his weight.
going aloft
I owned a pearson 10M for about 15 years Nice boat> and went aloft frequently in a bosuns chair while the boat was in the water. If things breeze up or get hairy in the water the boat just moves around. On the hard you would be putting strain on whats holding the boat. I WOULDNT GO UP ON THE HARD. See if the yard has a crane that can swing U up or wait for spring
I owned a pearson 10M for about 15 years Nice boat> and went aloft frequently in a bosuns chair while the boat was in the water. If things breeze up or get hairy in the water the boat just moves around. On the hard you would be putting strain on whats holding the boat. I WOULDNT GO UP ON THE HARD. See if the yard has a crane that can swing U up or wait for spring
Quick approximation:
Torque = r * F * sin@
Assume a 200 lb guy is at the top of a 60ft mast so his center of mass is 1ft away from the mast.
tan@=1/60
@ = 1deg.
T= 60ft * 200lbs * sin (1deg) = 210 ft lbs
How much torque is this?
Assume you are 5 ft tall and standing on the deck and pushing horizontally on the mast. (okay, you cant really be standing on the deck and push the boat over, but lets just assume you are pushing horizontally on the mast from that height (and yes it is a few feet over the fulcrum... we're are approximating here.)
How much horizontal force would I have to use to get the same torque?
5 ft * X lbs * sin (90deg) = 210ft lbs
5X = 210
X = 42 lbs
So, a guy whose center of mass is 1 foot away from the mast at the top, exerts as much torque as you would pushing with 42 lbs of force horizontally on the mast at about five feet above the deck.
I doubt the boat's going over.
(and before I get corrected, yes, lbs is not a unit of force per se, but you can get an idea of the amount of force that would need to be applied to the side of the mast to get the same torque)
ETA: here's a better comparison:
200 lb guy, standing on the deck at the toerail of the boat, 5 feet away from the mast.
Torque = 5ft * 200lbs * sin(90deg) = 1000ft lbs.
That's 5 times the torque than the guy at the top of the mast!!!
ETA2: Keep in mind newtons 3rd law (action/reaction and all that....) so that its not like the guy at the top of the mast will be able to accidently "kick" the mast away, or kick himself away from the mast increasing the torque.
ETA3: Now if the mast was HORIZONTAL and the guy was standing the top of the mast, you'd have 60ft * 200lbs * sin (90deg) = 12,000ft lbs. The angle between the lever arm and the direction of force makes all the difference.
Torque = r * F * sin@
Assume a 200 lb guy is at the top of a 60ft mast so his center of mass is 1ft away from the mast.
tan@=1/60
@ = 1deg.
T= 60ft * 200lbs * sin (1deg) = 210 ft lbs
How much torque is this?
Assume you are 5 ft tall and standing on the deck and pushing horizontally on the mast. (okay, you cant really be standing on the deck and push the boat over, but lets just assume you are pushing horizontally on the mast from that height (and yes it is a few feet over the fulcrum... we're are approximating here.)
How much horizontal force would I have to use to get the same torque?
5 ft * X lbs * sin (90deg) = 210ft lbs
5X = 210
X = 42 lbs
So, a guy whose center of mass is 1 foot away from the mast at the top, exerts as much torque as you would pushing with 42 lbs of force horizontally on the mast at about five feet above the deck.
I doubt the boat's going over.
(and before I get corrected, yes, lbs is not a unit of force per se, but you can get an idea of the amount of force that would need to be applied to the side of the mast to get the same torque)
ETA: here's a better comparison:
200 lb guy, standing on the deck at the toerail of the boat, 5 feet away from the mast.
Torque = 5ft * 200lbs * sin(90deg) = 1000ft lbs.
That's 5 times the torque than the guy at the top of the mast!!!
ETA2: Keep in mind newtons 3rd law (action/reaction and all that....) so that its not like the guy at the top of the mast will be able to accidently "kick" the mast away, or kick himself away from the mast increasing the torque.
ETA3: Now if the mast was HORIZONTAL and the guy was standing the top of the mast, you'd have 60ft * 200lbs * sin (90deg) = 12,000ft lbs. The angle between the lever arm and the direction of force makes all the difference.
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Wow. I've never even seen a photo like that one, but that looks like a million dollar mistake. Those boats look like they may have been set on cradles, so I imagine that it was very high winds or a hurricane that caused that domino tip over? I had a pro rigger go up my mast last year to replace my Windex, & it was on the hard. My boat was really well blocked up, but there are always risks in everything. My rigger actually preferred that the boat wasn't rocking around, as this is greatly accentuated when aloft & on the water. Also, don't fool yourself that anyone would be likely to even hit the water if they fall from the mast. Any boat with a good beam on it, you are much more likely to hit the deck first. Or if your in a slip then get killed hitting the dock or a piling. Ouch. Either way its better left to the pros. Although my guy actually used my bosun's chair, because it was brand new & had no wear or tear. I hate going aloft & will gladly pay others to do it.
One more thing I've thought of....
The "fulcrum" on which the boat would rotate about is NOT in the center of the boat as I had assumed above. It's the jackstand on EACH side of the boat. Assume the guy was on the starboard side of the mast. He would have to have to be out FURTHER than the actual starboard jackstands to induce a torque to rotate the hull around the top of the stand!
The "fulcrum" on which the boat would rotate about is NOT in the center of the boat as I had assumed above. It's the jackstand on EACH side of the boat. Assume the guy was on the starboard side of the mast. He would have to have to be out FURTHER than the actual starboard jackstands to induce a torque to rotate the hull around the top of the stand!
Weinie and Donalex,
The problem with your models is that they assume that the object on the mast is static and exerting only downward forces. I agree that you should be able to hoist a 200 lb statue to the top of the mast on a track without a problem. The problem happens when you send up a real person, trying to do work, reaching for tools and broken parts, fighting wind resistance, keeping their balance, and all other manner of moving about. At a 60 foot lever arm, even a small movement of a percentage of a person's body weight will exert a tremendous torque. A human head weighs over 10 pounds, so just moving your head (not torso, arms, tools, etc.) is like moving a 200 pound weight at deck level, except much easier to do dangerously quickly.
The problem with your models is that they assume that the object on the mast is static and exerting only downward forces. I agree that you should be able to hoist a 200 lb statue to the top of the mast on a track without a problem. The problem happens when you send up a real person, trying to do work, reaching for tools and broken parts, fighting wind resistance, keeping their balance, and all other manner of moving about. At a 60 foot lever arm, even a small movement of a percentage of a person's body weight will exert a tremendous torque. A human head weighs over 10 pounds, so just moving your head (not torso, arms, tools, etc.) is like moving a 200 pound weight at deck level, except much easier to do dangerously quickly.
No.. Newton's third law. If you are pushing your head out, your body is exerting an equal and opposite force on the mast. The net torque on the mast is zero.
That 60ft lever arm only really comes into play when it is PERPENDICULAR to the force like if you were to stand on the end of a yardarm on an old square rigger. Here, the perpendicular component of the force is very small and almost all of the force is directed downward PARALLEL to the lever arm.
ETA: Look here's a good sailing analogy. When a sailor is hiked out, the force of gravity is pulling his body down towards the water. Even though the sailor may be six feet tall, it does no good if he is standing straight up or standing on his head. But when he hikes out perpendicular to the force of gravity (i.e. parallel to the surface of the water), he maximizes his "leverage".
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I dont believe it is. I believe its a 3rd class lever making the fulcrum the keel, the top is the force (man at the top), and the jack stand is the load. That keel is not coming off the ground, and its not likely to skid until the hull contacts the ground, if at all. I believe the jack would simply push away allowing the boat to fall over.
Of interest is that even using your lower calculations, the man can easily produce lateral loads at the top of the mast that exceed the loads generated by a 100 mph wind.
In any case I just cant see how on earth its worth the risk. My life is worth more than any boat, and certainly more than whatever is on top of it. That jack slips and the boats going over, and the man at the top, 60 feet up, is going to have a very short period of time to contemplate his death.
Im not interested in the math, but I wonder what kind of velocity the man would reach at the top of the mast as the boat went over. Or, if the mans on a rope at the mast head, and the boat rolls over and slams into the next boat, will he twirl around the mast a bunch times like a tether ball before the mast breaks loose?
Your trying to say he cant shake the mast or put any lateral loads into it. I bet I could shake the crap out of that thing, same as I can at the top of a ladder. I can even make a ladder "hop". Not saying anyone would be stupid enough to screw around like that at the top of a mast on a boat on the hard, but any lateral motion is going to be amplified at the other end.
Actually, you're right. Just like hiking out above. If you move the center of mass laterally inward or outward you will decrease or increase the torque respectively.
Why not just wait and climb it after the boats back in the water and stop all this nonsense.
No one can say it will happen, and no one can say it wont. There are way to many factors involved. The only thing anyone can say as a fact, is if you jiggle something loose and its starts to go, your dead.
No one can say it will happen, and no one can say it wont. There are way to many factors involved. The only thing anyone can say as a fact, is if you jiggle something loose and its starts to go, your dead.
Weinie,
Sorry, no, Newton's 3rd law is exactly why there is a lateral force on the mast (torque). The law says that if you exert a force on your hand to accelerate it to the right, then there will be an equal and opposite force exerted on your body. Presumably, you're going to be holding yourself to the mast, preventing your body from accelerating in response to the opposing force. By holding yourself in place relative to the boat, you're making yourself and the boat one object, so the opposing force acting on you is also acting on the boat.
This is why the racing rules prevent "ooching" - quick accelerations of the body whose opposing force could "ooch" the boat forward if timed properly. (See ISAF rule 42.2c)
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