What is the Angle of Stability for our MGs?

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2BonC
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What is the Angle of Stability for our MGs?

Post by 2BonC » Mon Apr 16, 2012 9:49 am

Jose from Portugal has püblished this very interesting links:

http://www.videos.sailingcourse.com/flaking_wmv1.htm
http://www.sailingusa.info/points_of_sail.htm
http://www.sailingusa.info/weather_and_ ... he%20sails
http://www.sailingusa.info
herzlichen Dank/ thank you Jose

Visiting them brought me to the matter of vanishing stability with the formular there:
http://www.sailingusa.info/cal__avs.htm

Actually I´m not certain about what to fill in :? , especally the weight-points. Has someone done this? What are the values for our :macm: , :macx: or :mac19: ?

Rainer

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mastreb
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Re: What is the Angle of Stability for our MGs?

Post by mastreb » Mon Apr 16, 2012 1:29 pm

Its right around 110 for the Mac M when I calculated it.

It occurs to me that a very small float at the pinnacle of the Mast would absolutely prevent a sailboat from exceeding a 90 degree knockdown, presuming the mast wasn't broken. And since for most boats (including the Mac) that's lower than the angle of stability so the boat should right itself after a knockdown if such a float was in place.

By my math, a 1 cubic foot float (smaller than a beach ball) would have a righting force of over 2000 lbs. on a Mac M--certainly enough to prevent capsize even with significant overturning force. This would mitigate the primary danger on a Mac--forgetting to fill the ballast tank. It won't prevent knockdown, but it will prevent the boat from capsizing in the event of a knockdown, stopping the boat's rotation where it's still above water and much easier for occupants to hold to and potentially right.

Granted, nobody wants to sail around with a beachball lashed to the top of their mast, but a CO2 inflatable with the typical calcium carbonate trigger would do the job perfectly--it's like a life vest for your boat. Trivial to engineer in fact, and it would simply mount atop your mast like a small black container about the size of a soup tin. I doubt it would even be noticed. The water would have to inflow from the bottom in order to trigger it to prevent it from being triggered by rain, and frankly you'd have to put up with the fact that it might go off occasionally unintentionally when conditions are very moist, so it would be made for manual repacking and trigger replacement much the way current CO2 vests are.

Huh. Would you pay $300 for a device marketed as a "capsize preventer"?

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dtjoslyn
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Re: What is the Angle of Stability for our MGs?

Post by dtjoslyn » Mon Apr 16, 2012 2:51 pm

Would it be possible to get a similar effect if the mast were filled with a foam core?

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mastreb
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Re: What is the Angle of Stability for our MGs?

Post by mastreb » Mon Apr 16, 2012 2:56 pm

dtjoslyn wrote:Would it be possible to get a similar effect if the mast were filled with a foam core?
Less so. The mast is filled with a foam core, but it's displacement alone is not sufficient to prevent overturn, and the float is not entirely at the full length of the lever arm. Furthermore, the mast itself has considerable weight, so that moderates the effect. It definitely has some beneficial effect, but not nearly as much as a float at the top of the mast would.

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Re: What is the Angle of Stability for our MGs?

Post by Ixneigh » Mon Apr 16, 2012 4:48 pm

Will these boats actually turn completely upside down? I would think the batteries and engine would prevent complete inversion.
I put the 300 lbs of lead in the bottom mostly for added comfort while powering With empty tanks. Maybe that's what saved my butt when I forgot that I had emptied the ballast and put up the sails. She felt awfully tender for a moment.
I have sailed on very calm days with no water ballast. The boat is not markedly faster.

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Re: What is the Angle of Stability for our MGs?

Post by Hamin' X » Mon Apr 16, 2012 4:52 pm

Image

Hobie has been using these for years:
Image

Of course, you could roll your own:
Image

~Rich

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Re: What is the Angle of Stability for our MGs?

Post by Bra dor » Wed Apr 25, 2012 2:27 pm

Pool noodles stuffed down the mast works for me. Got that idea from this site.

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Divecoz
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Re: What is the Angle of Stability for our MGs?

Post by Divecoz » Wed Apr 25, 2012 3:06 pm

Well The wife's MG_B gets real unstable around 50 mph on tight turns :D I get real unstable after about 7 Manhattans :o

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cmagnus4
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Re: What is the Angle of Stability for our MGs?

Post by cmagnus4 » Thu Apr 26, 2012 12:08 am

Check this site for information on stability

http://www.rya.org.uk/newsevents/enewsl ... rboat.aspx

cmagnus

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Re: What is the Angle of Stability for our MGs?

Post by Mac26Mpaul » Thu Apr 26, 2012 3:26 am

So with ballast in, the boat should go over to 110 degrees before it turns turtle completely.
Without the water ballast, I guess the boat is essentially a powerboat and will go over around the same angle as other trailerboats. I think someone posted it somewhere before but what is that angle roughly?

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Ixneigh
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Re: What is the Angle of Stability for our MGs?

Post by Ixneigh » Thu Apr 26, 2012 5:39 am

My gut instinct is the M with full tanks is self righting even when inverted providing no damage and if the items below were fully secured. Not likely. But lets take an empty stock boat. The deck is so narrow I'd guess she'll come right back.
Add some weight and I'm sure she would.
This is academic. The conditions needed to fully invert this yacht will probably activate the failsafe (fragile rig) before that happens. with full ballast the video on the website shows it coming back up from 90 degrees.
Unless a giant squid attaches itself to the masthead at that exact moment I feel one is pretty safe without the masthead float.

Ixneigh

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Mac26Mpaul
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Re: What is the Angle of Stability for our MGs?

Post by Mac26Mpaul » Thu Apr 26, 2012 6:32 am

Yeah but the conditons in the video were very unlike the conditions in which one would suffer a knock down. Imagine being out there in say, 2 or 3 metre waves, and gusting to say 50 knots. You suffer a knock down and your mast crashes down into the side of a wave, several tonnes of water crashes down on your reefed sails pushing your mast down further under water.

What would happen then - would you go over completely, or if not, would your sails full of water, stop the mast from popping back up?

If you went right over, would you stay upside down, or since its obvoiusly going to be pretty rough, would the washing machine effect put you at an angle where perhaps, you might pop back up?

I have no idea, think I'll just stay out of those kind of conditions, or get my sails down quick if I somehow find myself in them........... :|

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Re: What is the Angle of Stability for our MGs?

Post by Phil M » Thu Apr 26, 2012 11:07 am

Giant squid? :D :D :D

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Re: What is the Angle of Stability for our MGs?

Post by Ixneigh » Thu Apr 26, 2012 2:47 pm

In 50 k of wind you will

Not

Have any sail up.

The boat will be heeling 30 or more degrees under bare pole. That rotating
mast may also act as a sail giving (perhaps unwanted) a couple knots headway.
Pandemonium will rein down below unless the boat has been prepared for these conditions.
Turn it upside down. Anything fall out? Then it's not prepared.
In such wind force expect to be knocked down flat in the water as waves explode on the exposed weather side of the hull.
Lying ahull, attempting to heave to in some fashion, or attempting to motor are all Bhaaaad ideas in those conditions in this boat. It *may* be able to be run off under a few square feet of jib, or even sailbags lashed to the pulpit, but then there are those rudders to worry about. Jordan series drogue anyone?
A sea anchor could work if you actually carry the line needed to deploy it.

I know these are academic discussions. We all know what the boats limits are.
I suppose experiencing massive screw ups while doing something insane like running from a hurricane could see you in these conditions.

Ixneigh

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Re: What is the Angle of Stability for our MGs?

Post by Mac26Mpaul » Thu Apr 26, 2012 4:20 pm

yes, I wouldnt be out there full stop in 50 knots (you'd be lucky to come back at all) but I said gusting to 50 knots. And so that could be an average wind speed of 25 knots or maybe 30. I'm talking similar conditions as Rogers video where he states 50 knots, and I believe he really means 25 or so (at the top of the 65s mast that is) and occasional gusts maybe hitting 50. Without my family aboard, I would probably give that a go and sailing along with reefed sail, I'd say you could easily get knocked down in a big gust..

Considering there are nearly 10 000 X and Ms out there, I'm actually a little surprised that we havn't had some stories of knock downs turn up on here.

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