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Old 30-09-2013, 03:52   #76
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Re: Questions About the Wider Beams on Newer Boats

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Originally Posted by El Pinguino View Post
So...... you agree with Mal that beamy boats can lose steerage due to the rudder coming out of the water?
OK....
I would agree loss of rudder control at high angles of heal is more of a problem with beamier boats, or probably more accurately boats with the beam carried a long way aft.

Beamier boats are happier sailed flatter and of course designers use deep rudders to try and negate the problem, but caught out over canvassed or by a sudden gust and loss of rudder control is more common in beamier boats.

A large part of the problem is the unbalanced underwater profile which creates greater weather helm as the boat is healed

These are of course generalisations and individual models will vary, but the fundamental laws of hydrodynamics are fixed.
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Old 30-09-2013, 04:19   #77
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Re: Questions About the Wider Beams on Newer Boats

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Note that inverted stability is very much determined by the cabin structure, modern yachts with significant top hamper actually exhibit better numbers then the hull AVS suggests ( from the incline tests etc) take for example the moody 45 DS which has no negative curve. ( ie it will never stay inverted ) yet its a typical beamy boat with the beam carried right aft ( and hence twin rudders )

Dave
Dave I agree with most of your post, but we do need recognise that beamier boats rely on more form stability and less on ballast (generally) to provide the righting moment. They will have a lower AVS. The high inverted stability of a wide beam makes the whole stability curve worse leading to a more stable upside down position. These are well known yacht design principals.

AVS angles have been getting progressively less over the years.

In many ways this trend has been negated by the increase in boat size. Larger boats are less likely to capsize and are therefore acceptable with a poorer stability curve.

Boats with a large superstructure (such as the Moody 45) will always have a higher AVS angle. A narrow beam boat will a high superstore will still have a better stability curve than its beamier cousin.

There is a price to paid with the vulnerability of the superstructure. Many people feel such features unless very careful designed and built, detract, rather than enhance the overall seaworthiness of a vessel, despite the always positive effect on AVS.

Wide beam boats with high super structures to counter an inherit poor stability curve is not a positive move in terms of blue water capability although such design features are great at anchor where a cruising boat will spend most of its time.
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Old 30-09-2013, 04:25   #78
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Dave I agree with most of your post, but we do need recognise that beamier boats rely on more form stability and less on ballast to provide the righting moment. They will have a lower AVS. The high inverted stability of a wide beam makes the whole stability curve worse leading to a more stable upside down position . AVS angles have been getting progressively less over the years.

In many ways this trend has been negated by the increase in boat size that are less likely to capsize and are therefore acceptable with a poorer stability curve.

Boats with a large superstructure (such as the Moody 45) will always have a higher AVS angle. A narrow beam boat will a high superstore will still have a better stability curve than its beamier cousin.

There is a price to paid with the vulnerability of the superstructure. Many people feel such features unless very careful designed and built, detract, rather than enhance the overall seaworthiness of a vessel, despite the always positive effect on AVS.

Wide beam boats with high super structures to counter an inherit poor stability curve is not a positive move in terms of blue water capability.
I wasn't commented on the " bluewater " issue. That's a whole other can of worms.

What I was making the point is that beam in itself isn't simply the while story. The fact is there is increasing deck structures in all yachts these says ( like oyster etc) and this is a factor in improving the ability to return from inverted.

Of course AVS is only a small factor in the survivability of yachts. ( see ovni )

Dave
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Old 30-09-2013, 04:37   #79
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Re: Questions About the Wider Beams on Newer Boats

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However! It took me years to learn to sail her correctly after a lifetime in older-fashioned "lead mines", with narrow transoms, deep forefeet, high ballast ratio, long keel, etc.

The main thing is -- and many people told me this, it just didn't sink in sufficiently -- you can't let them heel too much.
This is a common problem in discussion of "modern" boats. People blame the boat because they try to sail it the way they want to based on how they sailed older boats, instead of sailing the new boat the way it is suppose to be sailed.
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Old 30-09-2013, 04:46   #80
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Re: Questions About the Wider Beams on Newer Boats

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This is a common problem in discussion of "modern" boats. People blame the boat because they try to sail it the way they want to based on how they sailed older boats, instead of sailing the new boat the way it is suppose to be sailed.
Yep.

I sure regret not having listened enough when people told me this over and over again, over the last few years

Part of the problem for me is that my boat does not look like these post-modern wedge-shaped jobs. She does not look all that much different from my previous boat. So one stubbornly persists in sailing her the same way as one has always sailed , by pure instinct. But her underwater sections are different -- flatter everywhere, ballast ratio (just) below 40%, and SA/D ratio far less at about 200. It makes a huge difference.
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Old 30-09-2013, 04:59   #81
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Re: Questions About the Wider Beams on Newer Boats

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Originally Posted by goboatingnow View Post
What I was making the point is that beam in itself isn't simply the while story. The fact is there is increasing deck structures in all yachts these says ( like oyster etc) and this is a factor in improving the ability to return from inverted.

Of course AVS is only a small factor in the survivability of yachts. ( see ovni )

Dave
The OP asked about big beam not big bum.... I think we have wandered off track a bit.

Re increased deck structures... this will only improve the ability to return to the upright if the BGS that inverted you didn't demolish said structure and punch all the windows in.

Ovnis? Lots of them appearing in Patagonia these days.... and thats not an easy place to get to.

I accept that seriously big bum is bad but the argument in favour of , frinstance, canoe sterns is seriously flawed ... Oh they part the following seas... OK but I would prefer a bit of buoyancy aft to lift the stern out of the way of the following seas....
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Old 30-09-2013, 05:10   #82
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Re: Questions About the Wider Beams on Newer Boats

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The OP asked about big beam not big bum....
Here is a photo of the Beneteau Sense mentioned by the OP.

Almost a canoe stern
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Old 30-09-2013, 05:12   #83
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Quote:
Originally Posted by El Pinguino View Post

The OP asked about big beam not big bum.... I think we have wandered off track a bit.

Re increased deck structures... this will only improve the ability to return to the upright if the BGS that inverted you didn't demolish said structure and punch all the windows in.

Ovnis? Lots of them appearing in Patagonia these days.... and thats not an easy place to get to.

I accept that seriously big bum is bad but the argument in favour of , frinstance, canoe sterns is seriously flawed ... Oh they part the following seas... OK but I would prefer a bit of buoyancy aft to lift the stern out of the way of the following seas....

Yes Ovnis , beamy modern canoe body with beam carried aft , quite low AvS ( 100 degrees ) yet well regarded as a bluewater boat.

That's what I mean. It

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Old 30-09-2013, 05:26   #84
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Re: Questions About the Wider Beams on Newer Boats

Ovni's are certainly well regarded blue water boats. Their low AVS is due to their retractable non ballasted centreboard/keel (in most models) rather than the hull shape.

It is argued that the keel enables them to slide sideways in conditions where a capsize is likely. By sliding rather than tripping over their keel they can be safe with a much poorer stability curve. Their low AVS should not be extrapolated to justify the suitability of other boats with low AVS and a very different keel configuration.

It works for Ovni, I only know of one that has been rolled.
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Old 30-09-2013, 05:48   #85
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Re: Questions About the Wider Beams on Newer Boats

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Here is a photo of the Beneteau Sense mentioned by the OP.

Almost a canoe stern
I have obviously led a very sheltered existence.......
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