Angle of Vanishing Stability Grampian 30' 1974 - SailNet Community
 
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post #1 of 10 Old 09-03-2010 Thread Starter
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Angle of Vanishing Stability Grampian 30' 1974

Was in a little blow off the coast of South Carolina Georgetown a week and a half ago that got me to thinking that I need a backup main. It was dark and had some lighting to make it a little more dramatic. My yellow lab Leroy was with me as first mate.

I was about to go into the jetties but when I saw the lightning getting closer at about 10 pm I decided to spend the night out there. It maybe got up to 35 knot gusts and I was glad to be far from land. Though it tore my old tripple reefed mainsail a little it only lasted 30 minutes or so and the waves never got big.

All I had done was leave a few square feet of my "lightweight" roller jib showing and the main in three reefs. The main tripple reefed where I left it was just a little bigger than the rolled in jib. I tied off the tiller all of the way to make bow hard to starbord (hoping to slow the boat if necessary and rotated the ceiling mounted GPS behind the entry way before going below and dropping the hatchboards.

I like the idea of going below in any kind of storm but recently an old salt named Mike at the Cooper River Marina in Charleston told me that this might not work so well off of the coast of Venezuela where winds and waves can be.... different.

I read that for someone to leave the tiller in heavy weather they should have a high angle of Vanishing Stability. How about my boat? Mike said that it didn't work for him on his boat and the risk of being knocked down gets higher when someone is not there tending the heading.

I'd consider teaching the dog to steer, he can pull the jib sheets for me if his toys are attached, but I'm afraid he might be too scared and too uncomfortable to even chew on my tiller when outside during a real storm.

Last edited by akin_alan; 09-03-2010 at 07:34 PM.
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post #2 of 10 Old 09-03-2010
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Hi Alan,
You had an interesting time.

Hopefully, I havent misread your post, but;

I guess you were heaving to before the main tore. I think you need to keep a watch when heaved to, especially if on a lee shore - you can move up to a couple of knots.

If it was so bad that there is no plan B or T or whatever and you had plenty of searoom (also sure that there are no other like minded individuals around), then you can drop all sail, lash everything and the tiller and go below; find a secure place on the floor (padded) and lash yourself in and wait for the skies to get lighter. - This is when you find God again ....because there is nothing else you can do!

If it is this bad, then knockdowns are very likely and regular - I would not think of this near land or in 35kn. 35kn is what you can regularly get and is a good travelling breeze on passage if the seas are not a problem.

As for your main, I guess the fact it was gusting is what tore the old main. A steady breeze is obviously easier to set sail for than gusty conditions.

From my limited experience, a 'learning' experience is a positive thing and next time you are in those conditions or worse, well - you've been there before.

I guess you had a deep and meaningful discussion with Leroy - what was his slant on the situation? A bit ruff (sorry) Actually all he needs is opposable thumbs. He has the same brainpower as most of us sailors.

cheers mate


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Last edited by St Anna; 09-03-2010 at 08:58 PM. Reason: thinking of leroys addition to the conversation
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post #3 of 10 Old 09-03-2010
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You were on the right track to heave-to except,if I read your description right, you left out one important step. Once you have the right sail combination to be properly balanced when hove-to (you have to experiment to get this) you have to tack but without casting off the jibsheet. This means that the jib stays on the windward side trying to blow you away from the wind while the main is trying to push up into the wind. You adjust the tiller to get the balance exactly right. When you get it setup right it will be very comfy and much better than bare poles (all sail down)
Things to think of:
- decide which way you want to point after heaving-to (to give yourself more sea room or to take waves on the favorable side) and then start on the opposite tack before the maneuver
- you can't just go below and wait for morning or nicer weather; there may still be traffic out there so you can to keep watch from time-to-time - how often depends on visibility and potential traffic. For what is worth, if you heave-to on starboard you will right-of-way over other sail boats, but I would not trust that they will see you
- heaving to is not too hard on the sails since they should both be filled and not flogging
- you will not be stopped when hove-to but will be forereaching at 1 to 3 knots or so.

As to angle of vanishing stability, I think this is calculated empirically when boats are rated for racing with some of the fancier rating rules (IMS?). I suspect that a Grampian 30 has not been measured like this. If you go to the Sailcalc website you can see a number of measures for your boat and a couple of thousand others. One of these is capsize ratio which is a something similar to angle of vanishing stability (although it is not an angle). The capsize ratio for a G30 is 1.85 with a lower number being better and any value less than 2 being fairly good. The website is Sail Calculator Pro v3.53 - 2000+ boats

Back home on Lake Ontario after something over 36,000 nm circumnavigator. Not surprisingly there is a lot of stuff I want to get done on Ainia both cosmetically and functionally. Getting an early start so it will be ready to go for next summer (Lake Superior?).
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post #4 of 10 Old 09-03-2010
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Killarny I believe you to be spot-on with your analysis forgo one typo. It is my understanding that the higher number Capsize Ratio (Stability Ratio) is better with anything less then 2 being considered unsafe for offshore sailing. I referenced to my copy of 'Chapman: Piloting & Seamanship' and it seems to confirm this.
I will note that upon checking the book mentioned the values for CSV (capsize screening value) ARE recommended to be a value of no more than 2, in case you mistook the two.
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post #5 of 10 Old 09-04-2010
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Alan,

I think you would be lucky to find angle of Vanishing Stability details for a 1970's vintage boat. This website here gives a formula for estimating these calcs, which is probably the closest you will find.

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post #6 of 10 Old 09-04-2010
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Different measures of the same thing?

Quote:
Originally Posted by trisstan87 View Post
Killarny I believe you to be spot-on with your analysis forgo one typo. It is my understanding that the higher number Capsize Ratio (Stability Ratio) is better with anything less then 2 being considered unsafe for offshore sailing. I referenced to my copy of 'Chapman: Piloting & Seamanship' and it seems to confirm this.
I will note that upon checking the book mentioned the values for CSV (capsize screening value) ARE recommended to be a value of no more than 2, in case you mistook the two.
I suspect that we are talking about two measures, with similar names to add to the confusion, that indicate the same thing. I looked at the SailCalc site again and they say that less than 2 is what you want. I compared three boats: Grampian 30 is 1.85. Bristol 45.5 is 1.62, and Balboa 20 is 2.30.

Back home on Lake Ontario after something over 36,000 nm circumnavigator. Not surprisingly there is a lot of stuff I want to get done on Ainia both cosmetically and functionally. Getting an early start so it will be ready to go for next summer (Lake Superior?).
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I agree on the confusion. With your values I would say based on what I read you are talking about the CSV or capsize screen values which ARE supposed to be less than 2.
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post #8 of 10 Old 09-04-2010
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The SailCalc site has something called Capsize Ratio where the lower the number the better. Don't know if this is the same as CSV but I suspect not. I seem to remember that there is another ratio where numbers over 2 are better.

Back home on Lake Ontario after something over 36,000 nm circumnavigator. Not surprisingly there is a lot of stuff I want to get done on Ainia both cosmetically and functionally. Getting an early start so it will be ready to go for next summer (Lake Superior?).
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post #9 of 10 Old 09-07-2010 Thread Starter
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Sorry for taking so long to get back with you guys. I was working all the weekend. St. Anna my dog Leroy would rather be in the dinghy paddling around than anywhere well....... with exception of the dog park maybe. He does get a little seasick I think. His eyes get a little glassy and he lays flat on his side on the floor. When he was still a puppy we went out for a couple of days and the boat was heeled the whole time and rather rough. He just started peeing while still lying down. I felt for him because he had learned to hold it already. He is better now.

About heaving too. I don't think that I was "heaved too" per say. Isn't that where the main is pulling the boat one direction and the jib is pulling it the other? I'll go back to the store and read this concept a little more carefully. I think that I am leaving the boat stuck on a tack. The boat does not have enough forward momentum to come about fully. Instead it heads farther into the wind, stalls and then falls back off of the wind. After it falls off it starts gaining speed, 0.5 knots or so maybe, then heads back toward then wind before falling off again. It does it over and over and over when there is not much sail up and the tiller is tied. This is convenient I think. It keeps my boat heading facing the wind, for the most part and the boat stays relatively in the same place. The wind and waves are traveling in the same direction so the waves are never more than 30 degrees off of my bow. I have a 120% jib. That might make heaving too difficult? Maybe this is "heaving too" but my sailing lingo is weak. Maybe I am "in irons" instead. I thought that "in iron's" was the same thing as "heaving" too though. Anyway, whatever position that I put the boat in when the wind was a little to fast for my liking it seemed to hold pretty well.

With a 3800lb ballast my angle of vanishing stability has got to be pretty good but got to thinking. The cockpit on my grampian is quite large. The weeping holes are small by comparison. If waves fill it up the angle of vanishing stability might be rather different. Something like 8000 lbs of water if the cockpit filled. I might better figure out a way to drain that water. Drill some bigger hole or holes to let it drain.
P.S. I got a new dinghy today. The dog and I are enjoying it alot. We are about to go to the beach and row in the breakers some.
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Quote:
Originally Posted by akin_alan View Post
Sorry for taking so long to get back with you guys. I was working all the weekend. St. Anna my dog Leroy would rather be in the dinghy paddling around than anywhere well....... with exception of the dog park maybe. He does get a little seasick I think. His eyes get a little glassy and he lays flat on his side on the floor. When he was still a puppy we went out for a couple of days and the boat was heeled the whole time and rather rough. He just started peeing while still lying down. I felt for him because he had learned to hold it already. He is better now.


Alan, I can relate to this!!!


About heaving too. I don't think that I was "heaved too" per say. Isn't that where the main is pulling the boat one direction and the jib is pulling it the other? I'll go back to the store and read this concept a little more carefully. I think that I am leaving the boat stuck on a tack. The boat does not have enough forward momentum to come about fully. Instead it heads farther into the wind, stalls and then falls back off of the wind. After it falls off it starts gaining speed, 0.5 knots or so maybe, then heads back toward then wind before falling off again. It does it over and over and over when there is not much sail up and the tiller is tied. This is convenient I think. It keeps my boat heading facing the wind, for the most part and the boat stays relatively in the same place. The wind and waves are traveling in the same direction so the waves are never more than 30 degrees off of my bow. I have a 120% jib. That might make heaving too difficult? Maybe this is "heaving too" but my sailing lingo is weak. Maybe I am "in irons" instead. I thought that "in iron's" was the same thing as "heaving" too though. Anyway, whatever position that I put the boat in when the wind was a little to fast for my liking it seemed to hold pretty well.


All boats need different techniques to heave to - It sounds like you were. The effect is to roughly stay put with possibly a little speed to weather. It shouldnt really round back up - Maybe you could try pointing her more into the wind before lashing the tiller.

With a 3800lb ballast my angle of vanishing stability has got to be pretty good but got to thinking. The cockpit on my grampian is quite large. The weeping holes are small by comparison. If waves fill it up the angle of vanishing stability might be rather different. Something like 8000 lbs of water if the cockpit filled. I might better figure out a way to drain that water. YES, sounds smart Drill some bigger hole or holes to let it drain.
P.S. I got a new dinghy today. The dog and I are enjoying it alot. We are about to go to the beach and row in the breakers some.
Its great to see that you are enjoying the boat and the water. Keep posting your adventures and those of Leroy.


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