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Old 10-06-2005, 14:41   #16
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I have to agree with Wheels.
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Old 11-06-2005, 05:53   #17
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Please, gentlemen, let's have something approaching a sense of humor here.

I have no desire to begin an argument. I just found the thread fun to read.

Anyone can hit a target with a shotgun. The initial poster received a "Ready, Fire!, Aim" approach to his question. And after the smoke settled, he finds that returning gear to his vessel that brings her down near her drawn waterline (something he would have done anyway, and which involved absolutely no alteration on his part) was the solution.

I just can't keep from smiling at that. Surely, you can appreciate the irony, too.

I didn't didn't offer any advice because I simply had nothing helpful to say, so I kept my mouth shut. I don't know why focus should be shifted onto me: I wasn't at the scene of the crime.

Respectfully,
CJ

Oh, and I'm not sure what you mean by "windage aloft."
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Old 11-06-2005, 12:13   #18
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Mate, if I were nailing you to the wall for a firing squad, I wouldn't have put the "wink" caption in my reply. The one thing I like about this site, is it doesn't have the rude crap that puts people of posting and replying like some sites do.
One important aspect that you have highlighted and I have highlighted in my tongue in check reply about Sergions diagonsing via Email, is that one small detail left out of an initial posting question, can make a lot of difference to the end answer.
Ummm, "windage aloft", maybe I haven't used the correct term here. Correct me if I am wrong. I was inferring to things up in the rig that catch wind and add weight. Things like radar scanner, Arials, rigging ladders, Baggy wrinkles, yadda yadda.
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Old 11-06-2005, 21:16   #19
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Alan, if you're inviting me to post in a gentlemanly manner without fear of being slapped down, thank-you, but I've already assumed that freedom.

I must have completely missed the veiled humor in your response to me, because just reading the words left an acerbic aftertaste that violates the point of your follow-up about not posting "rude crap that puts people of [sic] posting," which would be hypocritical, or at the very least, irrational. The only possibility, I see now, is sly humor. The smiley: I must remember to look at the smiley.

At first, your claim of posting tongue-in-cheek confused me. I sometimes miss subtle humor, but after I pulled apart the mixed metaphor (nailing someone to a wall before the firing squad does its business presents an absurd mental picture, indeed) I chuckled a bit; then you really got me laughing when you say "the answer to the actuall [sic] problem was given in the threads[sic]]." Now I see you weren't being defensive at all: you are winking as you suggest the needle we were looking for really is in that huge haystack of a response, somewhere." And I really got rolling when you suggest the reason the haystack was piled up was because the original poster did not provide enough information, not because responders didn't take the time to ask enough questions before firing off their acquired knowledge, so how could it possibly be their fault? I realize now that your'e not justifying yourself; you're actually poking fun at yourself by using self-deprecating humor. Good one.

It's subtle stuff, all right, and I admit it took a couple reads for me to see it in the light of your true intent (I'm kinda slow on the uptake), but it's definitely there. The humor is coming though much more clearly now, and I think I'm warming up to your style. Thank's for setting me straight. I'm sure we won't misunderstand each other in the future.

Oh:

BTW, windage and weight aloft are two different concepts. Is it possible that you are blending the two?

In your discussion about rigging, you claim mass above the center of gravity is good because it will increase inertia, and therefore resist being pushed off of the center of balance. I've always understood mass (weight) aloft, beyond the necessary minimum for structural integrity, is always a liability, as it increases heeling arc and at some point requires more ballast to keep the barnacles wet. Am I reading you wrong?

Regards,
CJ
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Old 12-06-2005, 02:45   #20
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Kiwi's and Ausies have very "interesting" humour. It tends to go over the top of many other nationalies And if you could hear me say that, you would see even that had a cerain sense of humour. But seriuosely, I think it is because both Kiwi's and Ausies come live in a hard land. So we have to joke about life and ourselves, or we would all end up like a bunch of Pom's
Back to the original thread. Actually the subject is a very complex one. It even revolves around the ultimate goal a designer tries to achieve. Stability, thus good handling.
The two points, Windage and weight aloft, are kinda related, yet two different aspects. Anything and everything that is above the water line, will catch wind and thus be a resisitance to the wind. The higher above the water line the objects are, the more affect the objects have on making the boat move away from the wind. The hull will always want to roll at a fulcrum point. Maybe there is a more accurate nautical term for this point, but I am approaching this from a physics point of view. So even something as small as a wip antennae at the top of the mast will have a small bearing of resistance wich is transmited as effort down the mast and is then translated as a force applied to the centre of effort. The boat rolls till the Weight of the keel swings out far enough from that centre, to negate the applied force at the opposite end way up that mast. Of course, the mast, the rigging, anything at all above that water line, has some affect on the force applied to that centre point. Leaving out the shape of the hull at this point, the boat will roll, till the weight fromt he water line down to the bottom of the keel, matches the force applied from the water line up. OK, inertia comes into play as well. It takes effort to start a mass moving, but once the mass moves, it takes energy to stop it from moving. So all that weight above the water line, will tend to make the boat roll slightly more than the wind force made it move. When the wind force stops, the boat rolls back the otherway, and all that mass wants to keep on going and takes the hull over to the opposite side. A pendulum effect keeps this going, till water resistance absorbs all that energy.
Now lets take a look at the boat in question. First of all, yes you are right. No one could answer exactly, because all the facts were not presented. Sometimes maybe, all the facts can never be presented. In this case, the original poster may not have thought that the hull/waterline level would have an affect, so never considered that aspect, till presented with some replies that made a light come on in the thinking department.
So lets look at that part. Why did water line have an affect. Well it's all about hull shape, namely, it's beam at the water line and the shape of it below the water line. Narrow deep V hulls are going to roll more than squat wider hulls. This is because as the hull rolls, a lot of displacment is suddenly presented thus giving resistance to the roll. If a hull sits high because of little weight, then a lot of the hull that would normally give that boyancy is sitting out of the water. Thus less affect of presenting displacment and thus floatation to the hull in the event of a roll.
Now without knowing any of the details and facts, many many differing scenarios could and indeed were presented. None were wrong as a possible, it was just that one was right for this situation.
You were bang on with the Physician comment. The thing is, a Physician would never make a diagnosis via an email. It would be kinda like, Hey doc, I keep walking around in circles. The Docs reply maybe, hmmm, I suspect you have a blance problem. The patient then replies, well it seemed to have all started when I nailed my foot to the floor, but I am not sure if that could be it. The Doc replies, Nail the other foot to the floor and see if that stops you going around in circles.
Yep, that is meant to be deeper than it sounds.
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Old 12-06-2005, 12:29   #21
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STABILITY

We’re undertaking a discussion of a very complex subject, which would be an excellent topic for JeffH to speak to.

FWIW:

Wheels said: “...The hull will always want to roll at a fulcrum point. Maybe there is a more accurate nautical term for this point...”
I believe you’re referring to “Vertical Centre of Gravity” (CG or VCG).

Stability is found on two major axis, the longitudinal axis and the transverse axis. In most cases transverse stability is the major consideration, although for some large catamarans, longitudinal stability is also of major importance. Transverse stability looks at how much a boat heels, while longitudinal stability takes into account the resistance a boat has to flipping stern over bow or bow over stern.

A boat's Transverse Stability is contingent on the relationship between two key factors. One is the Vertical Center of Gravity (VCG), through which gravity exerts a downward force equal to the weight of the boat, rig, and contents.
The other is the Lateral Center of Buoyancy (LCB), the midpoint of the underwater volume of the boat, whose upward thrust counteracts the effect of the VCG.

LCG and LCB both fall on a line that passes through the exact center of the transverse section of the ship's hull, and points vertically downwards. This line is called the Transverse Metacenter (GMt).

In most cases, the center of buoyancy is below the center of gravity. LCG and LCB are expressed in terms of height above the ship's keel. To calculate the metacentric height LCB is subtracted from LCG to give the metacentric height (GM).

Ships have two metacentric heights, one being the transverse metacentric height (GMt) calculated using the transverse cross-section of the ship and the other the longitudinal metacentric height (GMl) using the longitudinal cross section of the ship. (GMt) controls the recovery of a ship from listing, (GMl) covers recovery of a ship from pitching.

A large GM gives a large righting arm. This means a ship will snap back from a roll quickly, but will also roll easily. This gives a violent motion. In contrast a low GM gives a small righting arm, which means the ship will roll slowly but return even more slowly.

When a boat is at rest, the center of gravity is positioned directly above the center of buoyancy. When the boat is forced by wind or waves to heel, and the shape of the immersed section of the hull changes, the CB shifts to one side, no longer acting in the same vertical plane as the CG. The transverse horizontal distance between the CG and CB is known as the righting arm (GZ), which provides an upward-acting torque called the righting moment (RM). The RM is calculated by multiplying the GZ by the boat's displacement. The more distance between the CG and CB, the longer the righting arm and the stronger the righting moment.

A few stability references:

”Is your boat stable? - by Ted Brewer
Top designer Ted Brewer explains stability and how it affects safety and speed
from Good Old Boat magazine: Volume 3, Number 2, March/April 2000
http://www.boatus.com/goodoldboat/stability.htm

”Ted Brewer Presents A Primer on Yacht Design”
The Numbers (More Than You Ever Wanted To Know!)
http://www.tedbrewer.com/yachtdesign.html

”Monohull Ballasted Boat Stability” - Royal Yachting Association
Stability Explained is an extract from the RYA Magazine explaining stability assessment in general form monohull ballasted sailing boats with particular relevance to the RCD and ISO 12217 (STIX).
http://www.rya.org.uk/images/uploade...lity_Intro.pdf

“ESTIMATING STABILITY” ~ by John Holtrop
http://www.johnsboatstuff.com/Articles/estimati.htm
”DYNAMIC STABILITY” ~ by John Holtrop
http://www.johnsboatstuff.com/Articles/dynamic.htm

”RORC Stability and Safety Screening Indices – SSSN and STIX
http://rorcrating.com/stix/stix.htm

”Naval Architecture on the Web”
http://web.nps.navy.mil/~me/tsse/NavArchWeb/1/toc.htm
including:
”Transverse Stability”
http://web.nps.navy.mil/~me/tsse/Nav...troduction.htm

Regards,
Gord May
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Old 12-06-2005, 21:06   #22
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I wonder what Southernman is doing right now?

Thanks, Gord, you're being your usual helpful self. I have high regard for Halpern, but once he's brought in, I know we're distinctly in the world of theory.

Alan, we must have different senses of humor. I may have missed yours, and I see you certainly missed mine.
____

One can become so lost among the trees of physics that one loses sight of the forest. Southernman needed a practical solution, not a chapter out of Newton's third folio. The thread quickly lost sight of him and his immediate need.

Notice how he hasn't posted for a good while? He doesn't really care much about all this: he's quite happy now that his gear is stowed and his cofffee mug doesn't make a sudden lemming-esque bolt for the edge of the table anymore.

The student has left the room. But the lecture continues.

Regards,
CJ

If I'm pointing out to you that windage and weight aloft are two distinct concepts, after you blur them, you might just make the acknowledgment, and thank me for the clarification. It would have saved many words.
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Old 21-06-2005, 11:31   #23
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actually still here laughing

Well I've got to say this post makes amusing reading. I've just been too busy to post and I've actually been doing my own research into hull design and stability etc. It would seem that a lot of your theory is in line with the various books I have read on hull design in the last few weeks. I'm going to fix that next year once and for all and buy a catamaran. That way I don't have to worry about having a lump of lead under me!

I've confirmed that our yacht sails well and is very safe - windage aloft has been reduced as much as possible and their is no extra weight above the water line.

As a fellow kiwi I've got to agree with Alan in that a lot of people outside NZ and Australia would not understand our humour. Not meaning to pick on our American mates but I work for an American company and quite frankly the Americans I work with every day in New York don't get our humour at all and the same goes for me - sometimes I don't see their humour.

Well providing the weather is good we are off to Fiji within days so wish us good luck sailing! At least I'll be out there doing it and not having to rely on the forum!!!

See ya everyone - heres to 20 knots and following seas!
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Old 21-06-2005, 11:57   #24
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Good luck on your cruise to Fiji, and remember that “Good luck is often with the man who doesn't include it in his plans.” (?). ~ it seems this may apply to you.
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Old 18-07-2005, 10:22   #25
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in the islands

Just thought i'd let everyone know we arrived in Tonga today and have internet for the 1st time in ages. We had a great trip to Tonga and have had some great weather here cruising for the last weeks.
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Old 18-07-2005, 21:08   #26
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Hey great to hear you arrived mate. Start an new thread and write down somne points of your adventure, I certainly want to hear. So how did she sail??
So did you miss all the blow's?? There has been a few rescues while you were out there. One is still missing. A tri from out of Nelson on her way to Raratonga I think. An Orion has been searching, but so far nothing. She has not been heard from for 5 weeks now.
You may also like to know, it's cold and wet all over at home. Flooding up on the Coramandel and far north.
Oh and, Na, stay away from Multihulls;-)
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Old 21-07-2005, 09:40   #27
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Hi there Wheels

running out of internet time so I'll start a new thread next time.

We had a good sail up and avoided most problems. Heard about the Tri and I have sat at the Anchor Bar and Grill and seen her sitting there a few times in Nelson. I heard they sailed it from Darwin to Nelson. To me it looked on the light side for serious offshore work - hope they are ok and found soon. Got to say that an automatic EPIRB would have been nice to have for them.

Well having completed my first offshore with my own boat got to say that it was stressful but good fun. I was especially happy that the NZ Cat 1 is so strict and that we had more than the required equpment for our own and our yachts safety. We only had one drama - the alternator died and the starter need a bit of blunt instrument action. We have an Air X and good solar so no probs for the batteries. In fact we had an excess of power and the Air X spent most of the time off. We faired better than the yacht that had a gear box stuck in reverse and had to motor a few hundrew NM in reverse to Fiji this year. They had no wind so that was their only option!!

Experienced max wind of 46 knots and estimated wave height of 6M so not too bad. Once 175nm North of NZ no problems.

My brother just got a ticket in Rai Valley from Helens Police Dept and warms they are doing a sting in the area so keep your speed down!

Keep warm.
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Old 21-07-2005, 09:59   #28
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Cool fun. I envy you.
Yep, Police had the Booze Bus out just down the road tonight.
Tomorrow I am taking a bunch of kids I work with out for a short 2hr trip. It's just out the channel and back. Basicaly to allow the slime to wash off the hull and give the engine a good work out. That's about as close to Fiji as I am gona get at the mo.
Have a cool one on me
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