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Old 03-11-2023, 13:12   #46
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Re: Stable, yacht

This may be of some interest too, since this is CRUISERS Forum:

page 20 of "Sail Performance" by Marchaj, Chapter 5,

"Although the word 'cruising' means many different things to different people, we may all agree 'that cruising first of all means living'; it is a way of life rather than a sport. We may also agree that the most desirable quality in a cruising boat is seakindliness. In broad terms, this means that quality in a boat that enables her to receive the forces of a violent sea and render them kindly, giving them easy motion through the seaway."

He goes on to say that boats are subjected to accelerations in their motion at sea and that heavier boats will experience lower magnitude and frequency of accelerations as will boats with a lower ratio of area and volume of the hull above the waterline to that below.

(So boats with flatter, lighter hulls and with more freeboard and higher superstructures are, as a rule, more likely to be less seakindly and less seaworthy, though they may be faster and nicer at the boat show.)

The figure included from his book show the effects of rolling and acceleration when pitching and heaving on crew capability.
Really seems to argue for a multihull, doesn't it?
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Old 03-11-2023, 13:20   #47
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Re: Stable, yacht

Quote:
Originally Posted by Don C L View Post
Yeah, I agree, a heel angle of 30 (or more!) is a really overpowered boat. Time to reef was long before that. My boat is tender and if I go past 25 or 30 degrees, which is easy to do if the wind is up, I am not really sailing anymore; there is probably more leeway than headway. It will SEEM like you are sailing though!
And I'd echo what Happ said too, consider broad reaching and jibing more rather than sailing DDW too much. (My boat rolls downwind too)
OK, I'm getting the strong feedback that heel is almost 100% the skipper, and about 0% the boat. That any boat can be (and should be) sailed at a heel angle between 10 and 15 degrees.


Just to add a bit to the fray, I do reef. Early and often. We are down to a full main and 95% jib when the wind tops 10kts, 1st reef comes in at 12 kts, and by 15 kts I'm at the third reef and considering 95% jib alone. By 25 kts, the 95% jib by itself will give us 30 degrees of heel, maybe more. Above 25 kts, the boat is unsailable with winds forward of the beam, at least with my limited skills.


I have yet to experiment with reefing the 95% jib. It's something I've avoided because I assumed (without verifying) that the lead angle on a self tacking jib wouldn't do well with a reef. But as the season ended, I added a barber haul to allow better sail shape off the wind, and next season will experiment with reefing it.
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Old 03-11-2023, 14:13   #48
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Re: Stable, yacht

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Originally Posted by sailingharry View Post
Just to add a bit to the fray, I do reef. Early and often. We are down to a full main and 95% jib when the wind tops 10kts, 1st reef comes in at 12 kts, and by 15 kts I'm at the third reef and considering 95% jib alone. By 25 kts, the 95% jib by itself will give us 30 degrees of heel, maybe more. Above 25 kts, the boat is unsailable with winds forward of the beam, at least with my limited skills.
OK that does sound odd. I doubt your boat is really that tender, but I could be wrong, I have not seen a Saga.

edit: ok that is a tall rig. That 95% jib up is too much and too high I reckon. The center of the sail area has to be brought down a lot closer to the deck.
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Old 03-11-2023, 16:53   #49
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Re: Stable, yacht

Quote:
Originally Posted by Don C L View Post
That 95% jib up is too much and too high I reckon. The center of the sail area has to be brought down a lot closer to the deck.
Yeah, I agree.
While the term "Roller reefing" gets tossed around a lot, a better discription might be "Roller furling".
A 25+Kt. wind that's forward of the beam is not fun for the long term, and when you roll-up a 95% to, say a 60%, (just using a number, every boat is different,) the sail shape usually goes sideways.
It works, but an issue is that when you roll-up a jib the CE, (Center of Effort,) moves forward, (too far forward when the wind is forward of the beam).
That's a primary reason why many sloops are outfitted with a removable forestay that can sport a staysail.
Now we have a sail that sets well and being pretty flat has the shape that's desirable in strong winds.
It has not only a low CE but a CE that's not out at the bow.
You'd, (not you Don L,) have to talk to a sailmaker/rigger, but I'll bet you'll be surprised at how well your boat will do going to windward in a blow with a well reefed main that's balanced by a staysail.
Robert Perry is no slouch, he knows how to design a boat that will perform well in conditions that most of us would rather avoid.
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Old 03-11-2023, 18:14   #50
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Re: Stable, yacht

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Originally Posted by Bowdrie View Post
Robert Perry is no slouch, he knows how to design a boat that will perform well in conditions that most of us would rather avoid.
Ah I missed that it is a Perry design. Better call him up and complain. I bet that will go over well. But seriously, he'd be able to set things straight.
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Old 03-11-2023, 20:39   #51
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Re: Stable, yacht

Yes it does
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Old 03-11-2023, 22:52   #52
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Re: Stable, yacht

Quote:
Originally Posted by Adelie View Post
As I wrote, beam and weight generally scale with length so length is a proxy for the other two.
.
.
In real life beam, mass, and sail area scale up as a boat is lengthened and the tradeoffs become complex.
Which is true, but not the point. The point is that when the OP asks:
Quote:
Originally Posted by ARW View Post
The question does the length yacht improve stability...
The answer is YES. Length, even by itself, improves stability. If you add in the other stuff (beam, displacement, etc. also increasing), then stability improves a lot.


Quote:
You make a point of distinguishing form stability from gravimetric/ballast stability. Good catch I didn’t address it.
They aren't two types of stability. They are two different components that make up stability. You need both.


Quote:
Let’s take a rectangular box shape and put a mast and sails on it. A 10kt wind will cause it heel a certain amount.
Let’s double the length of the hull (and double the weight but beam and depth and center of mass stay the same), install another mast and sail same as the first (, adjust the location of both so they balance and don’t interfere with each other) and in the same 10kt wind it will heel the same amount as the first box. The overturning moment has doubled but so has stability.

Now take the two box-vessels above and put them beam on to the same wave. The larger one has twice the roll moment of inertia and when it is hit by the same wave it presents twice the area and is driven with twice the energy of the smaller box. They roll the same amount. Of course this is a dynamic event not a static one so stability doesn’t come into play.
I don't understand your point here. You've changed more than just length...


Quote:
The place length is important in stability is in pitch stability but that generally isn’t very important to people, when people think of stability it is generally roll stability.
Obviously, length plays a bigger part in trim/pitch. That's because the WP inertia about the transverse axis becomes C x L^3 x B. You'll note that beam also plays a "roll" (ha!) in pitch response, just much less so.



Quote:
I doubt that the Vertue or any other sailboat has an AVS of 170 or greater.
Agree. Who said otherwise?


Quote:
A ballasted tube might.
Let’s say there was a sailboat with 180* AVS.
Let’s say the boat is asymmetrically loaded. Then the boat will ride with a lateral trim. Heel should then be measured from actual testing waterline, not from design waterline.
I'm not sure that's how the nomenclature works w.r.t. measuring.

Regardless, consider the barge shape below, but we've added an asymmetric triangular superstructure as shown. The beam is 6 units (cubits?), the hull depth is 3 units and the SS height is 3 units. (All chosen to make the math simpler.) The displacement is such that the draft is 2 units. The CG is on CL; upright she floats with 0 heel. The longitudinal shape can be prismatic or whatever, it's just for demonstration, so 2d is fine.

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Now look at it when inverted (heeled 180 deg, assuming no downflooding). The "draft" will be 4 units (to get the same immersed total area).

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As you can see, the center of buoyancy is not underneath the CG; there is still a positive righting arm. The vessel could heel another 10-15 deg (I didn't do that math to figure it exactly) and would still roll back. Thus, this vessel has an AVS of ~190-195 deg.

It's certainly unusual, but maybe not impossible.
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Old 09-11-2023, 13:32   #53
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Re: Stable, yacht

Quote:
Originally Posted by ARW View Post
The question does the length yacht improve stability as many yachts that travel the world are less than 35 ft
As I am thinking of buying a Catalina 302
I disagree with the premise-< 35 feet.

We have been living aboard for 8 years while cruising the Caribbean. Most boats here are over 40 including the catamarans. We are 58. Our rally group of 80 is all larger boats. I raced a 37 foot Heritage for many years. Great boat but too small for extended cruising. One single handed sailed an old C&C about 34’. It was a crowded storage chest of tools and spares with accommodations inadequate for creature comfort.
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Old 09-11-2023, 23:04   #54
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Re: Stable, yacht

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Originally Posted by Nicholson58 View Post
I disagree with the premise-< 35 feet.

We have been living aboard for 8 years while cruising the Caribbean. Most boats here are over 40 including the catamarans. We are 58. Our rally group of 80 is all larger boats. I raced a 37 foot Heritage for many years. Great boat but too small for extended cruising. One single handed sailed an old C&C about 34’. It was a crowded storage chest of tools and spares with accommodations inadequate for creature comfort.
Well, I dunno 'bout that!

Ann and I cruised full time for 17 years in our previous boat, a retired IOR one ton class racer, and she was only 36 feet long. We logged a bit over 86,000 miles in her and never thought she was too small. We still encounter boats of that size and considerably smaller in our travels, even in remote anchorages.

That is not to say that we do not appreciate the space and comfort of the 46 foot boat we have lived aboard and cruised in the subsequent 20 years, far from it. And we have during all those years become a bit old and creaky and that tends to add to the appreciation of comfort. When younger and less affluent, folks find joy in smaller boats... because they do work and they can be afforded much more readily.

Perhaps if you got away from your rally group you too might encounter such happy folks in smaller cruising yachts!

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