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Go Back   SailNet Community > General Interest > General Discussion (sailing related) > How heavy is too heavy II ?
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Topic Review (Newest First)
09-21-2007 09:48 PM
denby Empresa, you are replying to a thread that is 2 and 1/2 years old and some if not all these members may not be around. I'ts not a good idea to revive old threads.

Dennis
09-21-2007 09:28 PM
empresa Well, for what it's worth, my Lady is 45 on deck, and displaces 34,600 pounds. She is sea-kindly through thirty foot chop, and for all that, She won the Americas' Sail tall ship race single handed. I personally do not believe there is a monohull (properly designed) that is too heavy. The heavier built, the better. Empresa is heavier than any production boat in her class ever built, and She can still beat boats more than twice her waterline. I am not saying I can beat a J, or a cat, but when it comes to 60 kts+ I know who will win.
03-13-2005 12:54 PM
PCP
How heavy is too heavy II ?

I have nothing against motorsailors (even if they are not for me) but 38 000lbs is a lot for a 41ft, even for a motorsailer. The Nauticat 44 (one of the best of its kind) weighs "only" 32 000lbs.
03-13-2005 05:51 AM
windship
How heavy is too heavy II ?

elhanly,
Actually, I started this thread and the original question was concerning boats that like my friend''s 41''er that displaces 38,000lbs(I was in error with the 33,000lb statement)has to weigh that much.
Why do people think that this kind of gross overweight is a good thing? Jeeze, you might as well have a motor sailor.

Dennis

Dennis
03-12-2005 12:52 PM
elhanley
How heavy is too heavy II ?

The original question asks us to evaluate "heaviness", not size, not hull shape, not what percentage is ballast, or how much sail area drives it. A "heavy" boat, to a designer, is one with a displacement/length ratio in the range of 300 to 350. 200 to 285 is "moderate", 140 to 175 "light", and <100 "ultra light".
Divide the displacement in long tons (2240#) by (0.01 x lwl) cubed. The 33,000# 41''er would have a D/L of about 310 - 320, depending on its lwl. That''s heavy.
03-09-2005 04:47 AM
PCP
How heavy is too heavy II ?

Jeff

I am discussing here only the importance of weight in ocean going boats.

On boats used only in coastal navigation I agree with you, for the same strength and stiffness, for me, the lighter the better and new materials and new technologies can make a light boat as strong as a heavy one, except perhaps in what regards collision. A coastal boat doesn''t need the same degree of safety stability, because if the weather goes really bad, you should not be at sea, and have plenty of time to make it to a port.

Of course, I don''t get seasick and I like the fun of going fast more than I care for comfort, otherwise I would disagree, because modern, light and fast boats rely a lot on form stability and have comparatively small ballasts (in many cases less than 30%) and heavier boats (ocean going ones) have a stability more dependent on ballast having a bigger %, some times approaching the 50%.

That means that the cruiser-racers tend to follow the movement of the wave (perpendicular to the wave hall) and the heavier ballasted cruisers tend to remain horizontal, regarding the wave hall. The implications of this are clear in motion comfort even if they don''t degrade (quite the opposite) the speed of the boat.

About the GZ (rightening arm) what you say is that a cruiser-racer has a better maximum GZ (and I agree, but also a bigger negative maximum GZ) and that a light cruiser racer, like the Swan 45, will have the same area (positive) or bigger, under the rightening moment curve. That area is the measure of the total amount of energy needed to capsize the boat; in other words, that it will require the same force to capsize both boats.

I think you are confusing things.

Let’s examine the stability data of the two boats and have a look at those curves:


Well, I agree that the area under the GZ (rightening arm) curve it is about the same for the two boats, marginally better for the Swan 45.
This is not normal, it only happens because the S45 has a very exceptional 150º AVS , when a typical cruiser-racer normally will have an AVS between 115 and 125. I have to say that the GZ curve of the S46 is also exceptional (and that almost makes things even), having an unusually good max. rightening arm (for a pure cruising boat) of 0.85 (S45 has 0.95).

what normally happens is that the extra area that is gained in the higher and more vertical initial part of the GZ curve of a cruiser racer is lost in the descending part of the GZ curve, that is more vertical in the first case and softer (going to a higher AVS) for an ocean cruiser, thus obtaining more area that way. In the end, for well designed boats, the area under the GZ tends to be similar.

Of course, as the areas under the Rightening Arm curve are similar, the areas under the rightening moment curve (that you obtain multiplying in each point the value of GZ by the meters of the water length and then by the displacement of the boat) are very different and a lot bigger on the Swan 46, because the boat has a much bigger displacement.

I could give you exact numbers but I just don''t have the time right now (I would have to import those curves to my computer), but, taking into account the marginally bigger GZ righting arm of the S45 I would say with reasonable accuracy that the positive area under the rightening moment curve of the Swan 46 is about 53% bigger than the positive area of the Swan 45.

That means that the energy necessary to capsize the Swan 46 is more than 50% bigger than the energy necessary to capsize the Swan 45.

If , in this case it is not very important, according to my personal safety standards (the energy necessary to capsize the S45 is already a lot) , the same reasoning applies to smaller boats, and there, the importance of mass as means of generating more stability, has a lot of importance. The boat will be smaller (as the force necessary to capsize it) but the waves and the sea will be the same.

I believe that Swans are some of the best boats around and not only in luxury, but in design. Those two, as Silmaril has pointed out, are just two excellent boats for different kinds of sailing.

And even if I would believe that the S46 has a much more comfortable sea motion (I do not have any doubt that the Swan designers know exactly what they are doing), I would prefer the S45. But that’s my personal taste (very fast, sporty and safe) , and that is right now, ask me 10 years from now and it is possible that I will prefer the S46 (reasonably fast, super comfortable and super safe).


Paulo
03-08-2005 09:13 AM
Jeff_H
How heavy is too heavy II ?

Paulo

You keep focusing on the weight aspect of the Righting Moment (RM) without looking at the generally negative changes in the righting arm (GZ) that is implicit with changes in weight. It is way too simplistic to assume that more weight is a good thing for stability.

Focusing simply on weight ignores that relationship between adding weight and the GZ of a boat. Generally speaking when you add weight to a boat the Vertical Center of Bouyancy (VCB) moves lower which reduces the RM of the boat by reducing the GZ. This can be mitigated a little but it comes at the price of a wider waterline beam which results in a quicker motion.

Also you do not seem to be focusing on the vertical location or typical sources of that additional weight. If the weight is added in a manner that maintains the same relationship between the Vertical center of Gravity (VCG) and the VCB so that the GZ remains constant, the ratio of ballast to displacement, as well as, the draft of the boat would need to increase. This would be the case because the vertical center of gravity would need to be lowered by the same amount that the vertical center of buoyancy was being lowered.

What generally happens in cruising boats is that the weight increases disproportinately to the increase in ballast and draft (in fact mosy cruising boats usually have less daft than higher performance boats.) And most of that weight increase occurs well above the VCB in heavier interior appointments, heavier deck hardware and heftier rigs to deal with the higher stresses that come from added weight, increased storage above the CB, larger engines and tankage and so on, all of which generally raise the VCG.

The Swan 46 to Swan 45 comparison is a good one. In the case of the Swan 45 (in contrast to the 46) all of the interior case work and components are very light, veneered cored material so as to reduce weight and the rig is proportioned to be comparatively light so as to reduce weight aloft. Deck hardware is proportioned to the lighter loads. Storage above the waterline is comparatively minimal. Freeboard is compartively low. All of the weight saved by these measures were placed in the bulb located very deeply at the bottom of the keel so in comparason the 45 has a much lower VCG and with its lighter weight a higher VCB. In other words you would expect the Swan 45 to have a similar or larger area under its righting curve. With its lower VCG and its better dampening relative to momentum, you would also expect it to have a more comfortable motion on five of the six degrees of motion, with heave being the exception.

When you look at the average cruising boat the VCG is generally at or slightly above the VCB in the static position. Small changes in the vertical height of either the VCG, or the VCB, or both can dramatically change the GZ so that owering the VCB even as little as several inches (50mm) can often result in a doubling or tripling of the GZ and consequently the RM. It is hard to get that kind of increase in the RM by increasing weight because of the attendant consequences to the VCB mentioned above.

The other side of this is the overturning moment, which also generallty decreases proportionate to weight so that the lighter boat will also have a significantly lower overturning moment than the heavier boat and therefore typically requires proportionately less RM.

One ofter point here, modern high performance boats have an amazingly comfortable motion compared to older performance boats of the IOR and CCA eras dispite being considerably lighter in weight. One of the advances of the early IMS was a careful study of motion. Early on in the IMS era it was determined that the kinds of motion that are uncomfortable for crew, is also really bad for performance. Quick or large amounts of motion tend to disrupt hydrodynamic and aerodynamic flows and so slow the boat and increase leeway. Designers quickly discovered that improved motion was an un-handicapped element within the rule that could add a lot to performance and so modeled boats to minimize both the amount of motion and the acceleration/ deacceleration during impact with waves, and during rotational motion. This has resulted in race boats that offer an amazingly comfortable motion as compared to earlier performance boats. There was nothing worse than slamming to windward in short chop in an IOR era boat despite their substanially greater weight.

(I need to finish my sandwich and get back to work.)

Respectfully,
Jeff
03-07-2005 05:30 AM
PCP
How heavy is too heavy II ?

Phil, you don''t know me and you are very wrong about what I like.

Going for the automotive example, I have a Toyota Mr2. It weights 2094lbs, with a motor with around 160 hp. It will have around 200, when I add a TTE turbo.

I have a special suspension set up with TTE springs (TTE are the ones that make the F1 Toyota), special konnies and the chassis is completely upgraded by a specialized German performance tuner.

I like it light and fast.

Weight in a sailboat only counts because it is a part of the stability equation.

For calculating the maximum rightening moment of a boat you have to multiply the max. GZ (rightening lever) by the meters of the waterlength, and then by the total displacement of the boat.

So, as you use to say, bigger is better, but in what concerns me, ideal size is around 40ft (maintenance, marina prices, handling the boat in tight marinas), and for this size, if you want a go anywhere boat, you have to make some compromises in weight, to have a good safety margin.

What is the weight of that compromise? The minimum to guarantee the safety stability for the use the boat is intended to, and of course that is also a personal choice, you can try to cross oceans in a Hobbie cat.

Paulo
03-07-2005 04:51 AM
PCP
How heavy is too heavy II ?

Silmaril, I believe older boats, even old racing boats, are normally "less radical" than most of modern boats and have a smoother sea movement.

They have a less flat hull and have more ballast, depending less on form stability.

I own a modern 36 footer ( length overall 37.4 ft) that is not even a racer, (only a fast cruiser) and it displaces only 10,361 lbs for a ballast of 2,954lbs. This displacement in a flat hull and 721 sq feet of sail makes a fast easy planning boat, but also (I believe) a less comfortable boat than yours in what regards sea motion.

Of course, this light displacement, which is what I want for the use that I give to the boat (costal, with some short ocean passages, like Madeira and Canary Islands), makes this boat not an ideal boat for Oceangoing, I mean go anywhere boat, even if it is U.E. classified as a class A boat (oceangoing).

You can have a 36ft much better suited for ocean travel, but it would be a lot heavier and a lot slower.

I am looking for the right type of boat to go anywhere as fast as possible, safely and with some comfort . I will only need it in 5 years or so, when I will have more time to travel.
I don''t want a slow boat, so I agree with you that the right size is between 40 and 45 (to handle the boat alone) and I don''t want a difficult boat to handle because I am not going younger and I want to sail and travel till an old age.

The balance will be between size, weight and price, knowing that a smaller boat will have to be proportionally heavier and a bigger boat will have a more costly maintenance, higher marina prices, and it will be a lot more difficult to handle in small marinas.
Everything considered (including price) I will look for a boat between 38 and 43 ft.

I know what I don''t want, but I still don''t know what will be the better choice.

I want a modern boat that makes full use of technology and design advances.
Lots of different choices out there.

The Vailant 42 is a great boat (and very expensive, too expensive to me anyway) but I think that there are other boats that offer the same qualities with a better price and performance.

Paulo
03-04-2005 06:01 PM
PhilMraz
How heavy is too heavy II ?

A descriptive form of shorthand that often helps is to apply automotive analogies to boat preferences. Vehicle identities are so well understood, in American culture at least, that it can facilitate boat comparisons.

Speaking of motion characteristics, for example, we all recognize the differences between a cushy Caddie and a tightly sprung Porche and the diverse individuals that drive them. Sailboats have similar differences, but for some reason we lump them all together when discussing their beneficial qualities, without acknowledging the fundamentally different personalities they possess. Who would ever compare a 911 to a Fleetwood? Yet many would prefer one over the other to cross the country aboard.

I have compared sport utility vehicles to motor homes before, by way of explaining different styles of cruising. An even further departure from the traditional concept may be found in an old TV show. How many recall and are willing to admit it, Route 66 and the adventures of Buz and Tod traveling the highway in their classic ’60 Corvette. It would have been far more practical to have taken a station wagon, but then how many would still remember. I admired their sporty traveling light aesthetic as they moved from town to burg achieving both chivalry and mischief, with an occasional race or chase thrown in. And I think that a sailboat can be made to do the same, especially with the technical improvements we have seen.

The world is a smaller and more developed place than ever before. We can only very rarely go beyond the reach of communications and the information safety that provides. Provisions can be replenished most everywhere and our sailboats can get there quicker and be used for broader purposes than ever before. I would not climb mountains with burdensome gear and I seek to tread equally as lightly across the sea. -Phil

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