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Old 11-06-2019, 07:53   #121
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pirate Re: How many cats have flipped ?

I tend to look at it akin to a m'bike.. much of the steering is done by lean.. to little and you go into the opposite lane, to much and you lose your back wheel.

Sails depend on the slot for acceleration, to my mind when the balance is right the force generated from wind across the jib being squeezed between the slot between it and the main not only creates drive but also lift on the back of the main when just right.. veer away slightly and its lost and the force creates more heel.. same with too close where you lose heel as the main begins to becomes a buffer.
Re cruising cats upwind.. its not drag thats the problem, its the air dam between the hulls that builds up that drops the speed and increases leeway..
But hey.. I am just a simple guy who could just be talking outa my ass..
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Old 11-06-2019, 07:59   #122
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Re: How many cats have flipped ?

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Re cruising cats upwind.. its not drag thats the problem, its the air dam between the hulls that builds up that drops the speed and increases leeway..
Isn't that a form of drag?
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Old 11-06-2019, 08:26   #123
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pirate Re: How many cats have flipped ?

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Isn't that a form of drag?
Depends how one views it.. sit up on my bike I create an air dam, duck down and its gone..
Cats cant duck, just block..
Simple mind says drag = behind..
Air dam starts midships and builds forwards.
This is what happens when you talk to an idiot..
I stoopid..
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Old 11-06-2019, 08:29   #124
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Re: How many cats have flipped ?

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...

Sails depend on the slot for acceleration, to my mind when the balance is right the force generated from wind across the jib being squeezed between the slot between it and the main not only creates drive but also lift on the back of the main when just right.. veer away slightly and its lost and the force creates more heel.. same with too close where you lose heel as the main begins to becomes a buffer.
...

If “sails depend on the slot for acceleration” you might ask yourself why is it that development classes with a maximum sail area evolve to one sail – not a main and a jib. If the “slot” mattered A cats and Moths would give up some mainsail area in order to have a jib – they don’t.
You might consider perusing Frank Bethwaite’s High Performance Sailing. I think you would find his research and exhibits on sails and sail trim informative. I understand some newer/alternative books have come out since but I don’t have their titles memorized.
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Old 11-06-2019, 08:54   #125
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pirate Re: How many cats have flipped ?

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If “sails depend on the slot for acceleration” you might ask yourself why is it that development classes with a maximum sail area evolve to one sail – not a main and a jib. If the “slot” mattered A cats and Moths would give up some mainsail area in order to have a jib – they don’t.
You might consider perusing Frank Bethwaite’s High Performance Sailing. I think you would find his research and exhibits on sails and sail trim informative. I understand some newer/alternative books have come out since but I don’t have their titles memorized.
Single sails are nothing new.. see Opti's out there every day and single masted junks sail N to Greenland..
I am talking about the average Bermudan rig favoured by the mainstream sailor.. not Lazers etc.
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Old 11-06-2019, 13:14   #126
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Re: How many cats have flipped ?

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If “sails depend on the slot for acceleration” you might ask yourself why is it that development classes with a maximum sail area evolve to one sail – not a main and a jib.

SNIP
I know you ain't going to break the rules, because there ain't any.

Except for development classes which do have rules and following them means better performance from a single sail; but the boat would have even better performance if there was a foresail which created a slot.
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Old 11-06-2019, 13:37   #127
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Re: How many cats have flipped ?

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I motored all the way from Northern Greenland to Iceland last summer -- four days and nights -- in a dead calm between two howling weather systems. It was somewhat boring and you do get tired of listening to the engine, but compared to bobbing around and waiting to get smashed by that deep low rolling in from Newfoundland? No thanks!

I'm not a bit ashamed of "putting the hammer down", when I feel like it! It's great to have the option of sailing or motoring, according to what you're dealing with.
If you're happy enjoying the arctic by burning so much of the fuel that destroys it I guess that's for you. But pretty odd to read you moralizing about responsibility on the Rebel Heart thread for the risk they placed only themselves in when you're so blase about your own role in a global safety risk.
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Old 11-06-2019, 13:49   #128
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Re: How many cats have flipped ?

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If you're happy enjoying the arctic by burning so much of the fuel that destroys it I guess that's for you. But pretty odd to read you moralizing about responsibility on the Rebel Heart thread for the risk they placed only themselves in when you're so blase about your own role in a global safety risk.

Woah, how did we get from good seamanship, to saving the planet? Those are not the same subjects.


You can't really get to the high Arctic without burning diesel fuel. As I said, the best weather windows are dead calms and often you get them between storms, and without what we think of as a sailing wind. And anyway, in calm weather motoring at a moderate speed, we burn less than 1/2 a liter per mile, so from Iceland to Iceland including weeks of heating and power generation, we used only half a tonne of fuel, so less than you spend air conditioning your house in the summer or driving your car around. I don't have a car anymore and ride a bike to work. I'm a vegetarian, which saves more CO2 than boat and car use combined. So pardon me if I feel not even the slightest twinge of guilt for motoring in the Arctic! Mind your own carbon footprint and keep your nose out of other people's, please.
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Old 11-06-2019, 14:47   #129
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Re: How many cats have flipped ?

You're right, it is off topic in this thread. I should have said it in the thread where you are judging other peoples' safety decisions, which left me thinking you wouldn't mind candid feedback.
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Old 11-06-2019, 16:04   #130
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Re: How many cats have flipped ?

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I tend to look at it akin to a m'bike.. much of the steering is done by lean.. to little and you go into the opposite lane, to much and you lose your back wheel.

Sails depend on the slot for acceleration, to my mind when the balance is right the force generated from wind across the jib being squeezed between the slot between it and the main not only creates drive but also lift on the back of the main when just right.. veer away slightly and its lost and the force creates more heel.. same with too close where you lose heel as the main begins to becomes a buffer.
Re cruising cats upwind.. its not drag thats the problem, its the air dam between the hulls that builds up that drops the speed and increases leeway..
But hey.. I am just a simple guy who could just be talking outa my ass..

Boatman, you’re playing with us, yes? You’re confusing or at least combining two different things - hull form and sailplan.

Regarding your bike, heeling helps a monohull to turn to windward and decreasing heel helps it turn to leeward. Catamarans don’t heel, so don’t use hull form to help turn. So what? Nothing to do with sailplan efficiency. Arguable whether it has anything to do with sailing well upwind - certainly a catamaran has better tracking in a straight line, but has a greater radius of turn (except of course under slow speed when using motors to turn within on length).

Your understanding of the slot and the interaction of the two sails is incorrect as you’ve described. Refer to just about any advanced sail trim book if you’re truly not sure. The slowing air on the windward side of the jib increases the pressure on the leeward side of the overlapped main - this decreases the lift generated by the main. Jibs are helpful used in front of a main as they lift the apparent wind relative to when the main is alone and the combined efficiency of the two smaller sails is higher than just one larger sail.

Regarding heel, if you talk just about sail efficiency, heel is a negative factor. Don’t conflate a hull form feeling (performing?) better when heeled than when level with the efficiency of the sail plan. Any monohull will have an optimum angle of heel, with the understanding that increasing heel decreases the efficiency of the sailplan.

We use sheets and traveller and other controls to manage the angles of the sails to the wind. Optimising that for any given wind angle doesn’t have anything to do with heel, other than heel indicating too much power (and too little as it decreases), and allows us to have efficient sails at any angle to the wind.

Your ‘air dam’ between the hulls - that is aerodynamic drag. Same as for the hull sides, cabin, bimini, mast, rig, etc. - all contribute to the aerodynamic drag for any given boat. Including monohulls too. For a given size a monohull will have less drag than a comparable multihull. But a performance cruising multihull can be more easily driven than a comparable monohull, making up for the increased drag at lower wind speeds. At very high wind speeds total drag determines how long a boat can sail to windward - a boat with less drag can continue to sail on small sails for longer than a boat with more drag. This could favour some monohulls.
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Old 11-06-2019, 17:41   #131
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pirate Re: How many cats have flipped ?

I think your confusing what I am saying with my bike example.. which was an attempt to explain what I meant by achieving the right balance.. but hey ho.
If the wind passing the front of the jib increases pressure on the back off the main how is this not providing lift when the sails are trimmed correctly, bear off the wind 15 degrees or so and the heel increases if the sails are not adjusted to compensate as the pressure starts to move to the face of the main.
Turn 15 degrees into the wind and after the initial heel the boat begins to come up as the pressure increases and what you call drag comes into play slowing the boat speed.
Not talking about cats other than the effect of wind funneling between the hulls and underbody and creating resistance as pressure builds.. your drag.
But as I have said many times in the past, I am a seaman not a sailor.. I also try never to fall over the fence..
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Old 11-06-2019, 17:58   #132
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Re: How many cats have flipped ?

Isn't the heeling moment at it's greatest when you're hard on the wind? (But not luffing)
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Old 11-06-2019, 18:07   #133
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pirate Re: How many cats have flipped ?

Have not got a clue, I'm a gentleman..
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Old 12-06-2019, 00:12   #134
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Re: How many cats have flipped ?

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You're right, it is off topic in this thread. I should have said it in the thread where you are judging other peoples' safety decisions, which left me thinking you wouldn't mind candid feedback.

It would have been off topic there too.


And in general, like I said, mind your own carbon footprint, as we all should. Do you use your diesel engine? Do you eat meat? Do you drive a car to work? Do you use air conditioning? Do you fly in planes? This is a fundamentally idiotic conversation which leads nowhere.
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Old 12-06-2019, 02:31   #135
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Re: How many cats have flipped ?

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It would have been off topic there too.


And in general, like I said, mind your own carbon footprint, as we all should. Do you use your diesel engine? Do you eat meat? Do you drive a car to work? Do you use air conditioning? Do you fly in planes? This is a fundamentally idiotic conversation which leads nowhere.
Settle down, chief. It's a bit steep saying it's idiotic to question large emissions unless you have read none of the science.

My footprint will be fair game online any time I start promoting massive unnecessary discretionary emissions as a positive model of responsible behavior.

We will see much of the cruising grounds most loved by members of this forum damaged or destroyed in our or our childrens' lifetime. You wish to get warm fuzzies by talking about your arctic cruising while presenting a model of heavy engine use. This is bad role modelling and should be called out just like you call out Rebel Heart. It's many times an individual's available annual footprint in one short trip, and it's unnecessary. If you don't want to have the irresponsibility of your boat use scrutinized like you have done with Rebel Heart, change your behavior or stop modelling it.

People on this forum criticize use of TBT or dumping of black/grey water in the wrong places. This is a bigger problem. Is the reason you don't like it commented on that you don't understand the peril or just that you don't want to change?
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