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Old 28-08-2019, 19:10   #1
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Heavy sailboats are slower and

Question:


This is the way I understand it. The heavier the boat, the more stable and slower it is and the lighter the boat the quickler and less stable it is?


Correct?


Of course take into consideration of the draft and the shape of the hull. Seems like price and weight corresponse with each other.


Lee
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Old 28-08-2019, 19:13   #2
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Re: Heavy sailboats are slower and

Quote:
Originally Posted by agpilot88 View Post
Question:


This is the way I understand it. The heavier the boat, the more stable and slower it is and the lighter the boat the quickler and less stable it is?


Correct?


Of course take into consideration of the draft and the shape of the hull. Seems like price and weight corresponse with each other.


Lee
No, not correct.
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Old 28-08-2019, 19:28   #3
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Re: Heavy sailboats are slower and

I'd say that's basically right. But then it's a Hamburgler v Cookie Monster kind of thing. Get out there and sail them. Older boats tend heavier, and they go for cheaper.
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Old 28-08-2019, 19:48   #4
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Re: Heavy sailboats are slower and

Some well designed and equipped heavy boats can be faster in light and variable conditions as once they get going they tend to keep going for longer and can catch the next bit of breeze ahead while lighter boats tend to stop. Can be quite embarrassing to the lighter more modern boats.
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Old 28-08-2019, 19:50   #5
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Re: Heavy sailboats are slower and

Quote:
Originally Posted by agpilot88 View Post
Question:


This is the way I understand it. The heavier the boat, the more stable and slower it is and the lighter the boat the quickler and less stable it is?


Correct?


Of course take into consideration of the draft and the shape of the hull. Seems like price and weight corresponse with each other.


Lee
For displacement hulls, the primary factor for determining max speed (or hull speed) is the length of the waterline. Weight primarily influences how much power is required to achieve hull speed. Longer hulls with the same hull profile are almost always capable of higher speeds.

The VERY generalized formula for displacement monohulls is:
Hull speed in knots = Sqrt(Length of the waterline) * 1.34
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Old 28-08-2019, 20:49   #6
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Re: Heavy sailboats are slower and

Quickness and stability are not opposites.

In the first place, don't confuse "stability", as in the propensity to stay perfectly still, with "stiffness" or the resistance to heeling.

Because "stability" in the sense that it means it isn't so tippy, generally means faster, not slower.

Some heavier, older, boats are more tender (less stable?) then newer, stiffer, boats. And, they are slower. So, in that case, less stable is not quicker.

And some lighter, newer, boats are also stiffer (more stable?), meaning less likely to heel over in wind. And they are fast. So, in that case, more stable is not slower.

On the other hand, if you mean rock solid in big waves, then more stability means very little.

Think of an iceberg. It is very stable. Most of it is below the water. It won't move. If you are worried about a boat not being stable, or being too tippy. You need to do some sailing and find out what it is all about.

I wonder if you have been hearing something like, "This boat is heavier so it is more stable, it will have less motion, so if you are worried about how much it will move around in the ocean, this one is better, but of course it will be slower."

If that is what you are hearing, you are being sold.

Sorry.
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Old 28-08-2019, 21:39   #7
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Re: Heavy sailboats are slower and

We are 58 LOA, 47 LWL, 40 tons. 1984 Camper & Nicholson ketch. We made Hampton Va to Virgin Gorda three years ago (1500 mi) in 7.5 days. Big following wind, cutter and mizzen alone, 9.5 to 12 knots.

It’s all about the water line and sea state.
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Old 28-08-2019, 22:36   #8
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Re: Heavy sailboats are slower and

Quote:
Originally Posted by wingssail View Post
Quickness and stability are not opposites.

In the first place, don't confuse "stability", as in the propensity to stay perfectly still, with "stiffness" or the resistance to heeling.

Because "stability" in the sense that it means it isn't so tippy, generally means faster, not slower.

Some heavier, older, boats are more tender (less stable?) then newer, stiffer, boats. And, they are slower. So, in that case, less stable is not quicker.

And some lighter, newer, boats are also stiffer (more stable?), meaning less likely to heel over in wind. And they are fast. So, in that case, more stable is not slower.

On the other hand, if you mean rock solid in big waves, then more stability means very little.

Think of an iceberg. It is very stable. Most of it is below the water. It won't move. If you are worried about a boat not being stable, or being too tippy. You need to do some sailing and find out what it is all about. . . .

This is a good comment.


"Stability" is a word with many different meanings, which should not be confused. "Stability" is a technical term in naval architecture, first of all, and refers to "the ability of the vessel to return to the upright". This has nothing to do with whether the boat is heavier or lighter; it depends on the relationship between the center of buoyancy and the center of mass. A very light boat with a deep bulb keel will have more stability in the technical sense than any heavy boat.


The amount of sail a monohull can carry for a given wind force is a direct function of this kind of stability, so as WingSail said, this makes a boat faster.


Heavier boats for a given size are always slower, because more weight means more buoyancy required to float it, which means more hull volume below the waterline, which means more wetted surface. More wetted surface takes more power to move. If you maintain SA/D (sail area/displacement) at the same level as a boat gets heavier, you can have the necessary power, but this is hard to do as there are practical limits on how deep the keel can be be and where to get the righting moment to support all the extra sail area. In any case, heavy boats almost always are heavy because they have longer, if not full keels, and these provide less righting moment for a given amount of ballast, and more wetted surface per quantum of buoyancy, so these boats are simply slower.



Heavier boats for a given size may have a "more comfortable motion" -- I think this is what the OP was asking about, and we don't call this "stability". The inertia of the greater mass of a heavy boat dampens motion in a seaway. But at the expense of speed.


However, weight is not the only way to improve motion comfort, which increases not just by weight, but by size. And size makes a boat faster because of the possibility of a longer waterline. So if you want a boat with a comfortable motion which is also fast, you need to increase the waterline length. A larger, lighter boat can be as comfortable or more comfortable than a smaller, heavier boat while being much faster because of the combination of longer waterline and less displacement/length. This is one of the reasons why cruising boats have gotten larger over the last couple of decades.

Another important issue is form stability. Righting motion which comes from ballast, called "ballast stability", is not the only kind. A boat also resists heeling (and therefore can carry more sail) from the effect of the buoyancy of the hull. The wider the beam is, the greater this effect. A larger boat will have a wider beam and so a larger boat with the same weight as a smaller boat will be more powerful also because of this effect.


Quote:
Originally Posted by wingssail View Post
. . . .I wonder if you have been hearing something like, "This boat is heavier so it is more stable, it will have less motion, so if you are worried about how much it will move around in the ocean, this one is better, but of course it will be slower."

If that is what you are hearing, you are being sold.

Sorry.

Well, but other than misuse of the word "stability", the statement is correct. A heavier boat of the same waterline length will almost always have a better motion comfort (don't call this "stability"), and will almost always be slower.



The only way it would not be slower would be if it has a whole lot more sail area, than the lighter boat you are comparing it with. And such a boat can have a whole lot more sail area only if it has a correspondingly greater amount of righting motion. To get that, you would have to have a deeper and better keel. But heavier boats are heavy precisely because they have longer, that is, less efficient keels, with ballast distributed higher.



So if you would amend that statement slightly:


"This boat is heavier so it is more stable has better motion comfort, it will have less motion, so if you are worried about how much it will move around in the ocean, this one is better, but of course it will be slower."


Then it is absolutely correct, assuming the boats are of the same size.
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Old 29-08-2019, 01:40   #9
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Re: Heavy sailboats are slower and

You can see the stability in an anchorage. Watch a 5 tonne boat in as a rib goes past causing wake. Then watch a 25 tonne boat as one goes past.
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Old 29-08-2019, 02:12   #10
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pirate Re: Heavy sailboats are slower and

Depends on what you mean by slower..
A sprinter will always beat a marathon runner over his distance but once past that the advantage is lost.
The heavier boat can keep going strong when conditions worsen where the lightweight flat bottom will slam her guts out.
Downwind the surfing abilities will win out in all weathers but from the beam forward its another story.
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Old 29-08-2019, 02:16   #11
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Re: Heavy sailboats are slower and

You can use Carl’s Sail Calculator to look up sailboat dimensions, in a large database of boats, or enter your own boat's dimensions, and compare it to the others.
In addition, for any boat you can calculate a set of values that will help you measure how it will perform.
Carl's Sail Calculator v3.55Sail Calculator Pro v3.54 - 3200+ boats
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Old 29-08-2019, 05:44   #12
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Re: Heavy sailboats are slower and

It’s not unlike a woman - they come in various sizes. Do you want one built for speed or comfort?
Despite the protests, heavy boats do tend to be slow but we don’t buy them for speed.
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Old 29-08-2019, 06:24   #13
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Re: Heavy sailboats are slower and

Quote:
Originally Posted by agpilot88 View Post
Question:


This is the way I understand it. The heavier the boat, the more stable and slower it is and the lighter the boat the quickler and less stable it is?


Correct?


Of course take into consideration of the draft and the shape of the hull. Seems like price and weight corresponse with each other.


Lee

Unfortunately, you are wrong.


First, you must define what a light boat is.


If we assume that you define a light boat as one that has high sail to displacement ratio, then you still need to consider other essential factors as hull drag (related basically to hull shape and keel / rudder shapes.


Take one fact at a time: a boat with less drag from the hull and more sail will sail faster in light winds (simplified but close enough). It may also sail faster in strong wind but only if the hull will plane.


Stability is another thing. In dynamic conditions, a hull that planes is more stable than one that sails in displacement more. A displacement hull ('heavy' hull) is ultimately unstable going fast.


In static conditions, a boat with heavy rig (weight distributed out of the center) will be more stable - in the sense that it will require higher force input to tip it.


etc etc etc


Good sources everywhere. If you are anything technical, I suggest Marchaj's books or the Dashews to start with.


Cheers,
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Old 29-08-2019, 06:43   #14
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Re: Heavy sailboats are slower and

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Originally Posted by picklesandjesse View Post


Some well designed and equipped heavy boats can be faster in light and variable conditions as once they get going they tend to keep going for longer and can catch the next bit of breeze ahead while lighter boats tend to stop. (...)

Alas.



Some well designed and equipped heavy boats can be faster in light and variable winds UNFORTUNATELY not faster than equally well designed and equipped light boats!


It is actually in hull shape and foils (keel, rudder). Hulls with less drag (and same SA) will sail faster than hulls with more drag (this may account for some heavier, but hydrodynamicaly better, hulls being faster).


When two identical boats sail so that the heavier one wins, think of DRAG. Not weight.



Weight of the boat counts too. Brief explanation below.



Weight (displacement) holds you down when accelerating yet helps you go through the lulls (momentum). But you can only go thru lulls if you had managed to build speed, at which a heavy hull is worse than a light one (acceleration vs. weight).


So, all other factors equal, light hull is better in light winds. Light and with minimum drag wins.


Light hull is also faster in heavy winds, if it planes.



Empirically: take two identical boats (Lasers, e.g.) make one 500 pounds heavier (some sand bags). Let these two compete in the same area (close to each other to sail in the same puffs) and controlled by an algorithm. Result: the light Laser arrives first.


This is what is understood when we claim lighter is better (=faster) in light wind.


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Old 29-08-2019, 07:18   #15
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Re: Heavy sailboats are slower and

Let’s review - No one makes heavy race boats.
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