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mastreb wrote:Judy's math re: righting moment is essentially correct. .... At 90 degrees, there's zero force upon the sails (because they're horizontal) and the righting moment is maximum at 4375.

My math was more than essentially correct ! it was entirely correct-- as well as glaringly vague and incomplete.

Whaaaat on earth am I talking about

My math was intentionally incomplete so that I wouldn't have to go into more detail than I did. Here's more details, but I'm still not gonna go into full lecture mode.

1. Gravity acts on the center of gravity of a boat to pull it down. The center of gravity of the boat occupies a fixed position.
2. Water acts on the boat's center of bouyance to push it up. The position of the boats center of bouyancy moves around, depending upon what part of the hull is submerged.
3. When the boat is floating level and at equilibrium, the center of bouyancis is located directly below the center of gravity.
4. When the boat heels, the two centers become horizontally separated, creating a torque force (righting momemt) that tends to right the boat.
5. The maximum righting moment occurs when the COB and the COG reach maximum horizontal separation

A boat's righting moment reaches a maximum when the the horizontal level arm (usually notated as Gz) between the boat's center of gravity and the center of bouyancy is maximized. This condition typically occurs between 55 and 75 degrees of heel, depending on the hull shape.


When I googled looking for a good reference, I found this one:

http://www.sailboat-cruising.com/gz-curves.html

In the Promo Video they hold boat over at 90 degrees approx. to prove its self righting the salesman is stepping/standing on the mast head he steps off of it and the mac springs up proving its capability as the salesman explains the mock knock down he mentions it takes 125 pounds of force at the top of the mast to do this.

Judy said:

if the shackle got bent, it's probably not because it's too flimsey. It's probably because of the way it's aligned to the load. If it's aligned to take the load straight-on, it'll be fine. It's almost certainly getting loaded sideways rather than straight-on. In rigging parlance, we call that a "bad lead".

The halyard load on that shackle is, at most, a few hundred pounds. Any of the shackles you referenced will handle that load safely, if it's aligned straight-on.

Hope this help you to eliminate the problem, rather than use brute force to cover it up.

Judy,

I have no idea of what you are talking about. Most especially your comment about using "brute force to cover it up" I'm glad you do

Ray

Yes, Judy’s math is entirely correct.

Mastreb - your math, on the other hand, is in error because it assumes that the relationship between the righting moment and the degree of heel conforms to the simple trigonometric ratio (sine) you have used to describe it, which it does not.

So the maximum righting moment, as a simple trigonometric calculation using the sine function would tell us, does not, in fact, occur at, or even near to, 90 degrees.

Yes, you really do have to understand the physics and trigonometry of it when you decide whether or not to go up in a bosun’s chair, and the simple sine formula is not going to give a safe or reliable answer to that question!

Ormondude – I have stated this elsewhere before, but trying that demonstration for yourself carries the risk of breaking or damaging the mast for two reasons. The maximum righting moment happens, as Judy describes, at a heeling angle of less than the 90 degrees that the mast in the video is being held at, and; the mast is not designed to take such a sidewise point load at its apex.

In normal use, the forces on the mast are distributed along its length with the maximum applied closer to its centre, and less at its ends. As I recall (correct me if I’m wrong) the video says it takes that weight to hold it on the dock, and not that much weight (it would actually be more) to pull it down to that point. The simple purpose of the video clip is to visually demonstrate the self-righting capabilities of the boat. Each degree of heel of the boat will have its own unique righting moment, so while knowing the moment at 90 degrees is helpfull, it is just one small part of the bigger picture.

To experience this discrepancy first-hand, feel the change in force on an over-centre type suitcase latch. The force you need to apply gradually increases, and then decreases for a short distance right before it snaps closed.

Ray - I think Judy is just pointing out, and quite correctly so, that if the forces applied to the shackle are in a direction that the shackle was meant to take (ie. longitudinal) that it can withstand them without distortion.

But forces in a direction other than that (ie. lateral, or torsional) will damage it, and that simply using a heavier shackle, without determining the cause of the original damage or twisting, is simply camouflaging the issue with a band-aid solution. But, as Judy also points out, if it is in fact because it’s made from “junk metal”, then replace it.

Judy wrote ...

“The maximum load on any rigging on a boat is determined by the righting moment…”

Judy - Thank you for stating this – it was a point that was of significance during our thread on tensioning of the standing rigging and forestay, and bears repeating.

- Brian.

Hey Mastreb! I got an idea!

If you do make the trek to Ontario, I look forward to discussing things in person!

If the water is calm, and warm – I’ll climb to the top of the mast on your boat, and we’ll see first hand, once and for all, what happens!

(I weigh 140lbs).

Hope to see you -Brian.

Rob....

Wow - good for Sheri!

Looks like the next boat over would have been easier to climb.

So what's the reason you didn't scale the mast

- B.

I agree entirely I was simply giving a known reference to help fill in the variables and I am sure they had the demonstration boat prepared for the task. Oh I actually found my sail hardware - http://www.walmart.com/ip/Attwood-Unive ... 6/16927823 575 pound load capacity stainless and fast and easy - Cheap and affordable you guys owe me lol Treat yourself to one for $5.00 just think its stronger than the $25.00 west marine solution and easier nothing to lose.

seahouse wrote:Rob....

Wow - good for Sheri!

Looks like the next boat over would have been easier to climb.

So what's the reason you didn't scale the mast

- B.

I volunteered also but we all agreed it would be easier to lift/lower Sheri if there was a problem - that's the answer I'm sticking to

Ormonddude wrote:I agree entirely I was simply giving a known reference to help fill in the variables and I am sure they had the demonstration boat prepared for the task. Oh I actually found my sail hardware - http://www.walmart.com/ip/Attwood-Unive ... 6/16927823 575 pound load capacity stainless and fast and easy - Cheap and affordable you guys owe me lol Treat yourself to one for $5.00 just think its stronger than the $25.00 west marine solution and easier nothing to lose.

I would not use these - snap hooks have a realively low load rating since the load is thru one side vs the balanced load of a shackle thru both legs. Also, the snap hook you reference has some pretty sharp edges in the latching area that can easily snag lines and sail cloth.

I prefer the Ronstan snap hooks http://www.westmarine.com/webapp/wcs/st ... sNum=50047 800# for $14, 1400# for $17.

robbarnes1965 wrote:

seahouse wrote:Rob....

Wow - good for Sheri!

Looks like the next boat over would have been easier to climb.

So what's the reason you didn't scale the mast

- B.

I volunteered also but we all agreed it would be easier to lift/lower Sheri if there was a problem - that's the answer I'm sticking to

The truth be told while he is up their & should he say something MMM bad like what the Heck r u doing down their . She might just say I do not know ! walk away & say u tell me when u work ur way down from ur situation !!

John, as Sheri is also my dentist, I fear even worse retaliation often...

robbarnes1965 wrote:John, as Sheri is also my dentist, I fear even worse retaliation often...

Ah A dog with no teeth is all bark Eh !!! Oh the pain of it all !

J

seahouse wrote:Hey Mastreb! I got an idea!

If you do make the trek to Ontario, I look forward to discussing things in person!

If the water is calm, and warm – I’ll climb to the top of the mast on your boat, and we’ll see first hand, once and for all, what happens!

(I weigh 140lbs).

Hope to see you -Brian.

Well, this is embarrassing. I was mistakenly talking about negative righting moment, also referred to as heeling moment. It's the oppositional force to righting moment. Sorry Judy!

I would not use these - snap hooks have a realively low load rating since the load is thru one side vs the balanced load of a shackle thru both legs. Also, the snap hook you reference has some pretty sharp edges in the latching area that can easily snag lines and sail cloth.

I prefer the Ronstan snap hooks http://www.westmarine.com/webapp/wcs/st ... sNum=50047 800# for $14, 1400# for $17.

to each his own however they lock at the tip and are rated at 575lbs while yours says 800lbs in truth it has this this disclaimer - Economy shackles for use where you don't need them to swivel. Stainless models are 15-5PH. Bronze models are forged with stainless pins. NOTE: Functional load is the point at which snap shackles distort beyond usability but before they break. Use 50% of this value, at most, for working load.
So I use them I like them I save $ they are rated well above the original factory shackle and no PIN to drop (honestly I may buy a metal detector for all the lost hardware I have dropped and lost working on the boat) anyone know a good source for clevis pins? $3.00 for a inch of stainless steel with a hole in it is Insane! If i find a good connection I will share that too.
Did I mention my boat can do anything yours can do and only cost me $7000.00

Best supply for stainless steel clevis pins (and about all the other SS hardware I use) is my local Ace Hardware store. Prices better than Lowes and HD - much better than WM.