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Old 25-06-2013, 22:47   #61
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Originally Posted by DefinitelyMe View Post

Seconded. For the sake of laziness you're sacrificing so much!

1) Sail shape. No battens. Sail has to be cut flatter so that it rolls.
Sail area designed for the vessel in mind , battens can damage sail
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2) Sail area. No roach due to no battens
Taken into account by design , often taller rig
[QUOTE ]
3) Safety. Beating up the English Channel in a force 8 gale, the roller-furling main gets stuck and i have to go aloft, cast off the clew and wrap the damned thing around the mast? Not cool!
[/QUOTE

Very unusual , vast majority of jams are with un furling , all are typically operator errors , by the way why was the clew at the tip of the mast !

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4) Safety again. All that weight aloft does atrocious things to your angle of vanishing stability - reduced by about 15 degrees! If you should ever have the misfortune to become inverted you've now got a huge, heavy keel keeping you there.
No so , modern vessels are designed ground up to be within the designed spec with an in-mast , yiu do more damage to the figures mounting a radar !

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Why oh why would you do something so horrible to your rig?! It's just criminal!
Cause its a versatile , easy to use , safe rig as 100,000s can testify

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Rant over. Don't have a ketch. Want one. SO much more versatile and forgiving.
Twice as many things to fail , I could argue that last comment of yours all day , Ketches evoke nostalgia , but I'd prefer not to drive a Austin A7 over a Corolla an day though , but the A7 surges looks " cute"


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Old 25-06-2013, 22:54   #62
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The angle of vanishing stability is the agle of heel at which a boat goes from having a positive righting moment to a negative righting moment. Picture a boat sitting upright. It takes very little force to induce a small amount of heel. However, as the boat heels further the force that is trying to right the boat increases and increases, let say to about 60 dgrees of heel. This is about average, and is a combination of the force of your keel (which is now sticking out at a 60-degree angle) and the buoyancy produced by the side of the boat that is in the water. Conversely, the weight of the mast (and any other part of the boat that is higher than the centre of buoyancy) is having the opposite effect - trying to heel the boat further.

Beyond about 60 degrees the force attempting to correct the heeling moment decreases, but it is still positive up to about 120-degrees for your average modern sailboat. That means that if you were to heel that boat over 120-degrees (so that the mast is sticking into the water) it would still right itself and pop back up once the force that put it there in the first place is removed. But what happens if you make the mast heavier? Well, that extra mass is going to increase the tendancy for the boat to invert. Imagine trying to hold a PVC pipe in your hand horizontally. Now try it with steel pipe. That pipe wants to go down and hang vertically from your hand, and it's just like that with your mast.

The attached picture is a good diagram that i found on sailtrain.co.uk. RM stands for 'righting moment'. Notice that beyond the angle of vanishing stability, the righting moment is actually acting to keep the boat inverted. Fortunately, the kinds of conditions that are likely to roll a boat sufficiently that it becomes inverted are also likely to provide enough force to roll the boat from an inverted position back past the angle of vanishing stability so that it rights itself once again.
This is rather a beginners guide to boat stability, you need to add in dynamic factors just as roll moments of inertia , since stability is dynamic and not static as AVS suggests. Weight aloft can be beneficial some times , there was a reason square riggers hauled chains aloft in storms !

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Old 26-06-2013, 00:04   #63
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Re: Why do I have a Mizzen?

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Cause its a versatile , easy to use , safe rig as 100,000s can testify
Hundreds of thousands with in-mast furling?

Cite, please.
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Old 26-06-2013, 11:30   #64
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Re: Why do I have a Mizzen?

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Originally Posted by goboatingnow View Post
This is rather a beginners guide to boat stability, you need to add in dynamic factors just as roll moments of inertia , since stability is dynamic and not static as AVS suggests. Weight aloft can be beneficial some times , there was a reason square riggers hauled chains aloft in storms !

Dave
What's your source regarding the chains hauled aloft on square-riggers? I can see how it would work to dampen roll, but i've sailed about 40,000 miles on square-riggers and i've never even heard of this tactic. In fact, owing to the weight of the yards, sails aloft and various other paraphenalia that one finds aloft on any square-rigger their roll period already tends to be overly long.

Regarding your facetious comment about the clew of the sail not being at the top of the mast, can i ask you to actually think about the situation? Cast off clew from the end of the boom and wrap the sail around the mast. Great, but the spreaders are in the way, so the head of the sail doesn't go around the mast. Someone has to go aloft to gasket it. That experience alone put me right off in-mast furling.

I'm sure many cruisers are very happy with their in-mast furling, i simply think it's a ludicrous idea myself. If you must go with in-something furling, why not in-boom furling? That way you can have battens, keep a good sail shape, keep the weight low and any jams don't cause big problems as you can still drop the sail.......... It means a heavier boom i suppose, which is more likely to injure someone when it hits them, but to be honest if you're going to get hit by any boom you're probably going to feel it fairly acutely! Am i forgetting something?
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Old 26-06-2013, 11:41   #65
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Re: Why do I have a Mizzen?

when they fail, it is nearly impossible to rid the boat of that sail. have a fun day.
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Old 26-06-2013, 11:57   #66
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Re: Why do I have a Mizzen?

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when they fail, it is nearly impossible to rid the boat of that sail. have a fun day.

On the contrary. You only need a spare halyard, bosuns chair, and sharp knife when the in mast furler jams.
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Old 26-06-2013, 12:06   #67
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Re: Why do I have a Mizzen?

Oh, and as you say, stability is indeed dynamic but the stability gained from your boat's movement through the water can be ignored (unless you're doing 35 knots in a high-performance boat) since a large breaking wave on the beam (the most likely scenario for a roll-over) will negate all righting moment from under-water foils since the movement of the water under the surface is perpendicular to the direction of the movement of the boat and the forces involved are way in excess of any positive righting moment generated by your foils. Roll moment of inertia is likewise a moot point, since any righting moment generated by it at the right time is governed largely by chance. Sure, you might be rolling the right way into one large wave and reduce it's rolling potential, but the next one might have you doing the opposite. Of course, i'm referring solely to righting moment where it is most important - in very adverse weather conditions. The rest of the time that weight aloft might be nice as it will dampen the roll (while increasing it's amplitude) and make for a more comfortable movement.

My apologies - i appear to be getting carried away and i've gone rather off topic as a result! I'm merely attempting to support my viewpoint..........

Ketches: lower centre of effort, shorter rig = less roll amplitude and higher AVS :-)
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Old 26-06-2013, 12:10   #68
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Re: Why do I have a Mizzen?

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On the contrary. You only need a spare halyard, bosuns chair, and sharp knife when the in mast furler jams.
Only if the sail is not already partially rolled, as was the case in my particular bad experience.
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Old 26-06-2013, 13:53   #69
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Only if the sail is not already partially rolled, as was the case in my particular bad experience.
That's what I meant! Cut all exposed sail from leach to foot along mast.

If it's not obvious I am not a fan of in mast furlers....
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Old 26-06-2013, 14:01   #70
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Re: Why do I have a Mizzen?

Ha ha ha ha ha! In that case i commend you for a most suitable solution!
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