robbarnes1965 wrote:Climbing is easier than lowering the mast
Wow, we must have evolved from different kinds of monkeys. Lowering the mast is a two-minute operation on my boat and climbing it would be a comedy of errors. I do leave the gin pole attached all the time though. Looks a little ghetto, but since I trailer there's no point in over-complicating things.
My other sport is rock climbing. That said, I'd rather lower the mast than climb it on the Mac. If it looked more stable I could easily get up faster than lowering the thing. Darn rind dings are always a struggle...
Ken..I think your 180 pounds at 30 feet is 5400 ftlbs torque.......splash!
You would be right, if the boat was laid over sideways so that I was horizontally 30' from the center of gravity. If the boat was floating normally, I would be 30' up, but less than 4' horizontally from center of gravity. 180x4=720 or less. If I stayed exactly over the CoG, there would be no tipping force.
Ken..I think your 180 pounds at 30 feet is 5400 ftlbs torque.......splash!
You would be right, if the boat was laid over sideways so that I was horizontally 30' from the center of gravity. If the boat was floating normally, I would be 30' up, but less than 4' horizontally from center of gravity. 180x4=720 or less. If I stayed exactly over the CoG, there would be no tipping force.
I got you..you were trying to calculate the actual tipping torque from someone at top of the mast vs my calculation of the holding torque once tipped over.
Rodger pulled the Mac.M over with a full ballast at 130 lbs. in a boat slip in flat waters.
That said , no way should anyone climb the mast even in a bosun chair in any condition.
Any boat wave or balance with any wind would have serious effect.
One of those things (don't try this at home, we are professionals)
Dave
Catigale wrote:I got you..you were trying to calculate the actual tipping torque from someone at top of the mast vs my calculation of the holding torque once tipped over.
Dang, a camara would come in handy if you were at the spot at right time.Sometimes those camaras get the shot, and worth a thousand words.
I will say this, when the tough gets going I am all hands on deck and camara's are not included.
Dave
RussMT wrote:This guy was out in deep (100') open water. I was waiting for some wake boarder to blast by him (oooooh look a sailboat, let's go rock him).
I kept telling the Admiral, "Why doesn't he just lower the mast? We're going to see a Mac fall over."
Pretty stupid thing to do, climb up a Mac mast.
180 lb of weight force on a vertical mast is zero lb-ft of tipping moment, regardless of how high over the water you are. Tilt the boat so you're a foot to one side or the other, and it's 180 lb-ft. 2 ft is 360 lb-ft. The restoring moment (from ballast and boat weight, and center of pressure of water on hull) also starts as zero when the mast is vertical, and increases as the boat tips. Eventually, you get to where the tipping moment (including the mast and rigging) is greater than the restoring moment, and it's all down hill from there. If the boat is big enough that you can't hold it on its side with your body weight on the mast, then it'll never go all the way over, but that's not the case on the Macs. The question is, for a given body weight and height up the mast, where exactly is the tipping point? Add some wind, some water movement, some unbalance to start with (mine lists to port a bit since the table and some other things are not in there), and I wouldn't think it would take much to get it going.
A ballasted but otherwise empty Mac requires 130 lbs. to hold it down at the mast tip according to the factory. This is a 31' mast + about 3' of hull to the center of buoyancy, so we'll call it 34'. So the torque required to hold it down is 34 feet x 135 lbs. or 4420 ft.lbs., which agrees almost precisely with the expected weight of a ballasted Mac.
Presuming that you need at least 4' of mast to hold on to, the center of gravity of that person will be at about the 32' height above the center of buoyancy. So we'll say that we have a 32' long lever arm when horizontal, and at that length, the hold-down weight would be 4420/32=138 lbs.
At a 45 degree angle the mast of 32 feet forms the hypotenuse of a right triangle where the lever arm is one of the opposite legs, so the length of the lever arm is 22.6 feet and the hold down weight is 4420/22.6=196 lbs.
Going from my fully ballasted weight of 260 lbs., the lever arm length would be 4420/260=17 feet. The tipping point angle is sin-1(17/32) or 32 degrees. Beyond 32 degrees of heel, I would pull the boat down.
Find your own heel angle with this formula: sin-1(138/Y) where Y is your weight. 138 is 4420/32.
So it would seem that pulling down the boat by climbing the mast is definitely possible, but unlikely for most people actually able to get up the mast in the first place.
Irrespective, it wouldn't be comfortable, and anything else at all going on on deck would contribute to heeling. You are also likely to get a re-enforcing wave period that sets you up like a metronome and adds energy to the heel angle each time the boat swings, taking you beyond the tipping lever arm length.
Back in the days before I had anti-fouling paint I use to haul and then clean & wax my hull every 6 weeks or so during season. One day I was at the boat and I could see the green stuff starting to recover the hull bottom and rather than do an earlier than usual full clean & wax I thought I could just pull the boat over by the jib halyard and wipe it off in between full clean jobs. Since my neighbour was gone for the week I had both fingers and the whole slip space to work in so I took advantage of it. From the pictures and video it looked pretty straight forward and easy enough to do so I moved the boat, readied all the lines and set about to simply pull the mast over and cleat it off on the dock then walk over the other side and wipe the botttom off on the top exposed half then pull the boat over the other way and do the other side. Yup that's what I'll do I thought. So I grab hold of that jib halyard and proceeded to yank that sucker over. Do youi think I actually pulled it over??? No way, I pulled with all my 220# of weight and all my strength and I believe I got about 30 degrees of heel at the most before letting go and trying again. I was quite surprised at how difficult it was considering how easy Roger made it look and started to wonder if perhaps his demo was done using empty ballast. Matter of fact I am not entirely sure if my ballast was empty or full as this goes back a few years and I don't quite remember but I would think that there was a good chance I might have tried it on an empty ballast to make it easier, who knows today, my memory fails me but not so much that I don't remember the attempt. Anyway suffice to say I failed at my attempt to clean the bottom in this fashion and left it green for a couple more weeks then hauled and cleaned. But lesson learned, it is not really possible to pull these boats over as easy as Roger makes it look and I do not recall any part of the video that actually shows him pulling it over, it merely shows him letting go of it while it promptly rights itself. I think they used a come-along or some 10:1 pully block system to get it broached on it's side like in the pictures. You should all try pulling that halyard as hard as you can to get a feel for just how much force is really required to get these boats over on their sides then you would have a better understanding of forces required.
Pulling down from the halyard would be extremely difficult by hand. As shown above, at 32 degrees of heel you need 260 pounds of force, which by definition a 220 lb. person could not provide.
neat topic , tipping , climbin, monkeys & torque i was thinkin of swimmin around my with a brush for a quick scrub, but ya'll got me gears goin! id like to c this "tippin boat video" can anyone point me in the rite direction?
by showing it a video of a white 
under sail - they just roll over and die in embarrasment.....
i was thinkin of swimmin around my