Rudder Failures

[Polux]

Originally Posted by Dockhead

Like equating stability with seaworthiness, equating IRC ratings with speed for a cruising boat is an arm-chair fallacy.

Generically the main difference between a smaller boat and a bigger boat is stability. It is not the only thing that is important regarding stability but the thing that generically makes bigger boats being more seaworthy than smaller ones, all other things being equal. That was your point anyway.

Originally Posted by Dockhead

RC ratings are heavily driven by SA/D. But SA/D is only key to speed in light wind.
Saying that this boat is faster than that one because it has more SA/D is a bit like saying this car is faster than that one because it has a higher gear.

For what you say I assume that you don't know the main factors that count for the IRC rating, or any other rating.

Sure, sail area counts but sail area without stability serves for nothing and that's why the main factor is boat stability (stiffness) that on the IRC has to be measured effectively with the boat on the water. The proportion ratio between the stability and the weight of the boat is the main factor in what regards ratio. That is what corresponds to a powerfull engine. The ratios are the sails you use, but as you say, without engine( stability) you can use the sails you want that you are not going to be fast.

That's why you can find 37 feet performance cruisers with a rating hugely bigger than on the Moody 54, even if carrying less sail: Big engine

Originally Posted by Dockhead

Speed in a cruising boat - which will not have multiple sail changes on board, and will not be fully crewed - is determined mostly by waterline length, D/L, underbody form, sail condition...Saying that this boat is faster than that one because it has more SA/D is a bit like saying this car is faster than that one because it has a higher gear.

IRC ratings are heavily driven by SA/D. But SA/D is only key to speed in light wind. A boat with less SA/D will be faster once there's enough wind to be powered up. So without sail changes on board and crew to do them, a boat with high SA/D is at a disadvantage in winds beyond optimum strength for that sail plan.

IRC ratings also understate the advantage of size, since they assume racing condition without cruising gear on board.

Thus my boat has a similar rating to a Salona 45. In winds light enough for the Salona to use its much greater SA/D, and with both boats empty and stripped for racing, maybe they will have similar performance. But in cruising trim and in real life, my boat is one to two knots faster on every point of sail. In lighter wind, not so much. But when the wind pipes up to 20+, the Salona will be left far behind. This is not armchair speculation based on numbers, but real life experience with both boats.

Saying that this boat is faster than that one because it has more SA/D is a bit like saying this car is faster than that one because it has a higher gear. It might be true under some circumstances -- on a long downhill run, maybe. But in fact boats with high SA/D are just in a different "gear"; the optimum wind range is shifted downward, so that they have more power in light wind but have to be reefed earlier. So whether that makes the boat faster or not depends.

In the Med, I guess, or in Florida, a SA/D of 20 or more could be a good thing. Although I spent a few summers in the Aegean with the Meltemi blowing, and you wouldn't want that kind of sail plan there. Up here, it's way too much. If you're a cruiser with no changes of working sails, you'll be sailing around reefed all the time and being passed by boats with sail plans more suitable to the conditions.

Came on, there are a lot of performance cruisers that are designed to be solo or short crew raced. With modern furling sails and code sails you don't need a crew to be fast. And what is the problem with having a lot of sail if you can reef them? Sure with lots of wind I use only a 3thr reefed main and a slightly reefed jib (+30) and even so go over 10k downwind. More wind I will take out the main. More I will reef more the jib. With over stablished 40 I will mount a storm sail on a different stay. What is the problem to sail in bad weather (and have lots of power and control) with a small amount of sail?

Regarding the effective racing performance of those boats on races that imply a lot of upwind racing I have the results of all those heavy boats and the lighter performance cruisers, some sailed duo but you would not like the results. The performance and mass production cruisers generally sailed better to their ratings (that are higher) and therefore come better on the compensated results.

[neilpride]

You can see in this picture from a C&C 40 the underwater profile, they are not really well suited to pound upwind, they slice throug the waves very nice but beyond 6 ft waves they start to pound ..

[Polux]

Originally Posted by Dockhead

You beat me to it. Stability does not equal seaworthiness! Stability is in fact a quite small part of the picture of seaworthiness.

Much bigger parts of that picture are size and mass. Mass works against speed. That is why if you want a fast, seaworthy vessel, it has to be bigger.
....

Mass is one of the ways of getting stability, the other the size of the Arm.
For getting Righting moment on a boat you will multiply the weight for the arm at that point of heel.
You can increase stability increasing the GZ (size of the arm) or increasing weight. The final result in what regards stability will be the same.

Weight is not good on any sailboat, stability is always good but you can't have stability without some weight.

[Dockhead]

Originally Posted by Polux

Mass is one of the ways of getting stability, the other the size of the Arm.
For getting Righting moment on a boat you will multiply the weight for the arm at that point of heel.
You can increase stability increasing the GZ (size of the arm) or increasing weight. The final result in what regards stability will be the same.

Weight is not good on any sailboat, stability is always good but you can't have stability without some weight.

There are so many things wrong with this, I hardly know where to start.

First of all "stability", in the nautical sense, only concerns the ability of the vessel to right herself. This is a very small part of the picture of seaworthiness, and hardly relevant, since sailboats with ballasted keels have huge stability compared to ships. Stability is rarely a problem with modern sailboats, short of something like a MacGregor 25.

Also, larger boats do not indeed necessarily have more stability than smaller ones. Stability -- as opposed to seaworthiness -- comes from the distribution of mass (and buoyancy), not the quantum of mass. If you took a Laser, and hung a 100 kg bulb at the end of a 5m keel under it, you would have the most stable sailboat ever made, but not indeed the most seaworthy -- I trust that is a sufficiently clear illustration of the difference.

Seaworthiness is a much broader concept, which could be boiled down, I guess, to the ability of a vessel to remain under control -- resistance to broaching, right buoyancy to avoiding pooping, motion comfort, polar moment of inertia, and many other things. Here, unlike the case with stability, size and mass count, and older design, heavy built boats which are not fast to sail are generally better than newer higher performance boats, at least if you compare like size for like size. With some exceptions -- for example, old style double-enders don't have enough buoyancy in the stern to be very resistant to pooping. A light boat with little wetted surface will be less comfortable and more subject to being tossed around and broached than a heavy boat with more wetted surface -- for the same reasons the heavy boat is slow, it is good in really heavy weather.

That's why if you want a fast boat (and I do!), you have to either sacrifice some degree of seaworthiness, or you have to go bigger. Which, as I mentioned before, cheap production boats actually do, as the big volume makers are selling 40 -- 45 foot boats to the same people at the same price (if you factor out inflation) as were buying 32 to 37 foot boats a couple of decades ago -- which is right and good.

A Bene 45 will be tons faster than a Contessa 32, and should not be much if any worse in terms of seaworthiness.

And stability has nothing to do with any of it. Stability's close cousin, however, is stiffness, and that of course is a very good thing, as it allows more canvas to be carried in higher wind speeds. That's why the bulb keel is a totally superior way to arrange ballast with no downside.

Another question, however, is the aspect ratio of the keel. The higher the aspect ratio, the greater the hydrodynamic efficiency -- the keel is another wing. But the higher the aspect ratio, the more delicate, because of the lever arm. That's why few cruisers can accept the racing keels shown in Polux's photos, although they are undoubtedly more efficient, and undoubtedly will make you go faster upwind. So good cruising boats which are intelligently designed to go fast but without creating anything too fragile below the waterline don't go whole hog with the racing keel. The compromise is to make the bulb keel a bit longer and a bit more massive.

I can tell you that I was awfully glad to have one of these "compromised" keels this summer when I hit an uncharted rock in Finland, in a spot where I should have had 6 meters of water, according to the up-to-the-minute updated charts I was using. I hit it so hard that my boat came up out of the water so far that my bow thruster was out of the water.

If I had been in a boat with one of the keels in Polux's photos, or for example in the Salona 45 which I loved and sailed two summers in the Adriatic, the keel would be broken off for sure, and I'd have been in a heap of trouble. But my boat's keel comprises 8 tons of solid lead-antimony, bolted into the hull with huge bolts into the massive Kevlar-reinforced keel stub. When I hauled the boat in Cowes a month later, I found a flat spot on the front of the bulb the size of a one pound coin, and no stress whatsoever at the hull-keel joint -- the antifouling paint wasn't even cracked.

Yes, my boat would be a bit faster with a high aspect racing keel, but here is one of several compromises worth making for a cruiser.

[neilpride]

What about comfort ratio Doc, what kind of comfort ratio have the Moody?

[Dockhead]

Originally Posted by neilpride

What about comfort ratio Doc, what kind of comfort ratio have the Moody?

33.21 -- not so good!

That's because my boat is light for her size despite the very strong build. D/L of my boat is under 200 -- into cruiser/racer territory.

But Motion Comfort Ratio is only valid between boats of the same size -- so naturally the real comfort will be much greater than with smaller boats with the same Motion Comfort Ratio.

Heavy boats are much better where motion comfort is concerned, and this is an element of seaworthiness.

[Polux]

Originally Posted by Dockhead

There are so many things wrong with this, I hardly know where to start.

First of all "stability", in the nautical sense, only concerns the ability of the vessel to right herself.

This is a very small part of the picture of seaworthiness, and hardly relevant, since sailboats with ballasted keels have huge stability compared to ships.
Also, larger boats do not indeed necessarily have more stability than smaller ones. Stability -- as opposed to seaworthiness -- comes from the distribution of mass (and buoyancy), not the quantum of mass. If you took a Laser, and hung a 100 kg bulb at the end of a 5m keel under it, you would have the most stable sailboat ever made, but not indeed the most seaworthy -- I trust that is a sufficiently clear illustration of the difference.

?????

The total stability of a ship or a sailboat is represented by the total area under the positive Righting moment curve. The Right moment curve is obtained by multiplying the mass of the vessel by the GZ arm. The GZ arm is the horizontal distance between the center of gravity and the center of buoyancy when the boat heels. Its is 0 when the boat is vertical and positive till the AVS and negative after that being 0 again with the boat 180º inverted.


How Gz Curves Reveal the Truth about A Sailboat's Stability


"The GZ Curve or Curve of Statical Stability:The area under the curve up to any given angle, multiplied by the displacement, represents the energy needed to heel the ship to that angle. It is referred to as the ship’s dynamical stability and is a measure of the ability of the ship to absorb the energy imparted by waves and gusting winds".
The GZ Curve or Curve of Statical Stability

"If you took a Laser, and hung a 100 kg bulb at the end of a 5m keel under it, you would have the most stable sailboat ever made" you will have a big GZ curve put since the mass of the vessel is very small the overall stability will not be big (the total area under the RM curve) and a ship will by its dimensions not only have a bigger arm as it will weight hugely more. With an adequate CG its overall stability would be bigger than not only the small lazer but of any yacht. The total stability of a boat is the energy needed to capsize it (the area under the positive part of the RM curve.

"The region of positive stability is the region in which the boat will try to right herself. The integral of the righting moment curve (i.e. the area of the green region) is an indicator of how much energy is needed to capsize her."
Understanding monohull sailboat stability curves | M.B. Marsh Marine Design

[Polux]

Maybe this less technical and very good comparison between the advantages and disadvantages of two cruisers of the same size (50ft) one heavy and other light help the ones interested in understanding the differences:

"Light displacement versus Heavy displacement sailing yachts is an old and passionate debate in the monohull offshore cruising world (Luckily this debate is long gone when it comes to multihulls).
First of all, let me tell you what I mean by “Light displacement“, or “Heavy displacement” hulls, yachts or designs, and what exactly will be compared in this post:
In both cases, I assume boats are properly built, and especially the composite parts....Now, to give you a precise idea of what I call, in this light vs heavy displacement article, “light” and what I call “heavy”:

A typical heavy displacement 50 ft monohull offshore cruiser weights 18 to 21 tons,A typical light displacement 50 ft monohull offshore cruiser, with the same level of equipment, weights 12 to 15 tons thanks to carbon/epoxy composite and T-shaped keels.
Today’s offshore racing sailing yachts are “ultra Light” displacement yachts. For instance, the extreme IMOCA’s 60 footers , that run the Vendee Globe, weight under 8 tons. For more than 2 decades now, offshore sailors are debating “light vs heavy” and strangely the dominant argument of the heavy displacement enthusiasts is Safety.

I say “strangely” because the obvious and main reason to go for heavy displacement hulls today is because of the bigger inside space that can be offered and the big amount (and weight) of equipment that can be put on-board (generator, washing machine, air conditioning, water maker, etc.)....ight displacement yachts, when properly built by skilled and carrying craftsmen and properly equipped, are now as safe as heavy displacement sailing yachts, can be almost as comfortable and carry an impressive equipment inventory…and they are much faster....This being said, it’s also important to notice that whatever your choice is, none of those philosophies can, alone, make a great offshore sailing yacht. There are great boats, properly conceived and manufactured in both categories. ...

Safety at sea
Though they have usually a keel ratio around 40%, which is high, the center of gravity is usually higher on any heavy displacement yachts than on good light to medium displacement sailing yacht. This is due to the slightly deeper T-Shaped, , keels of the light to medium displacement. When it comes to safety, know that the lower the center of gravity of the boat is, the better. The center of gravity is very important when the boat is brought to extreme angles (above 90°) as the lower the center of gravity is, the more chances you’ll have not to capsize (we’re talking about really extreme conditions here, that can be avoided with a serious weather analysis). It means a well designed and properly built light displacement sailing yacht will perform better and be as safe in hard conditions....

In tough downwind conditions, when the boat is running with the waves, heavy displacement sailing yachts will be caught-up by waves more easily, due to their reduced speed potential. That will affect the steering reactivity, which is not good in hard conditions (note that the term “hard conditions” is relative. A professional offshore sailor will be just fine in 8 to 9 Beaufort, whereas some people will define “hard conditions” as a wind above 6 Beaufort, probably 5 when sailing upwind).

Speed is also a safety issue. When faced with the imminent arrival of hard conditions, speed allows you to get away as fast as possible or reach a shelter. Speed and sensations: This is the tipping point. A light displacement sailing yacht is a much better performer than a heavy displacement one, both in terms of speed and sensations...

Light displacement monohulls can sail to descent speed in light winds, where heavy displacement monohulls will have to use the engine propulsion. It means you need to embark and burn much more Gasoil and will be sailing less often. I think this is a very important point pleading for light displacements. Generally, many things on a heavy displacement must get heavier to get the same level of resistance or reliability as the light displacement yachts. A heavier anchor, a heavier mast, heavier rudders, heavier keel to balance the heavy structure and equipment, and so on. This is a vicious circle....

Heavy displacement hulls generally offer more living space at comparable length. To get the same level of equipment and space on a modern light displacement hull, the solution is to go for compact and clever accessories. Their draft is also generally lower (60 cm in our example), meaning you can go closer to the beach....

Heavy displacement sailing yachts are generally slower and less comfortable downwind. But in return, they can provide an improved comfort at helm station. The reduction of the boat’s windage is not a real concern on heavy displacement yachts, and a lot of them offer central cockpits with hard tops structures. The aesthetic is not really modern, but the result is a dryer helmsman in agitated condition. Basically, if getting a little wet in tough conditions is a central concern to you, a heavy displacement is what you need. I really consider this as a comfort issue, not a safety issue. A light displacement sailing yacht’s cockpit is as safe as the cockpit of a central cockpit, but definitively exposes the skipper more to water projections and wind. I find those conditions thrilling and rely on a modern, very comfortable and light full weather Gore Tex® gears, but others are OK to trade the thrill for a dry place under heavy conditions...

Light displacement sailing yachts tend to roll less downwind...

Light displacement sailing yachts above 50 feet can now benefit from a lot of equipment without having to embark tons of fuel and dozens of heavy batteries. Modern batteries offers 2 to 5 times more disposable energy than traditional lead batteries and their lifecycle is 2 to 3 times longer. And wait for it: They are lighter, at comparable capacity. With integrated hydro generators, light displacement yachts are now rewarded with an easy and durable energy source while sailing and the fact that they sail faster allow them to reach an incredible autonomy at sea....

Most of the heavy displacement sailing yachts brands keep using the same materials as 20 years ago (Fiberglass, Polyester resin and plywood).

In the meantime, materials like carbon and epoxy have made their proof on hundreds of sailing yachts’ laminate, they are now totally reliable and allow innovative builders to produce much faster, safer and durable yachts. I really think that a “state of the art” modern light displacement sailing yacht is the best fit for offshore sailing, even though the appearance of a good old heavy displacement keeps on reassuring some sailors.

I think a lot of brands are very conservative both in design and construction because they are used to it, and because a lot of customers are also used to those good old materials and design. They assume their qualities are better, since they are used for years on good quality yachts, and they assume they will naturally last longer. Well, that’s kind of wrong ! A properly built epoxy hull will automatically last longer and with better performances than a Polyester hull or deck, plus you don’t have to fear any osmosis any more."

Read more at Light vs Heavy Displacement monohulls in 14 facts

No, it was not me that wrote that even If I could As you can see he subscribes what I have been saiyng here.

The Writter(s) are the ones that built this beauty:

https://www.youtube.com/watch?v=iF5q71urO4w

[smackdaddy]

Originally Posted by Polux

Okay - now THAT'S porn.

Of course, instead you could have a fine classic bluewater yacht:

http://www.youtube.com/watch?v=mo8rcrOH5N8

Notice the rudder problems at about 10:00...if you can stay awake.

[neilpride]

Haa i though you write that!! but where the cropp is the Carbon fiber and all the wonderful stuff this dude is talking about in the low spectrum of the production boats list??

Another Marketing BS brochure, since the guy mention Polyester and Fiberglass and plywood like something from the prehistoric era but when in fact they are the regular material used in production boats , or Bavarias are made with carbón fiber? cmon, you can do it better...

[neilpride]

Now this part is really funy...


Light displacement monohulls can sail to descent speed in light winds, where heavy displacement monohulls will have to use the enginepropulsion. It means you need to embark and burn much more Gasoil and will be sailing less often. I think this is a very important point pleading for light displacements. Generally, many things on a heavy displacement must get heavier to get the same level of resistance or reliability as the light displacement yachts. A heavier anchor, a heavier mast, heavier rudders, heavier keel to balance the heavy structure and equipment, and so on. This is a vicious circle....

So a norseman 447 with a 35 kg rocna is using a heavy anchor? what about a oceanis 50? with a 15 kg rocna is enough based in what, in light construction?

A heavier mast???¿????? define heavy, mast sections Wall thicknes are not define by the boat displacement, compresión loads , torsional loads and a complex calculation based in the lenght of the spar and safety limits are used, to long to explain in this topic, i see the same Selden spar fitted in light boats and médium displacement boats, unless you want to use carbón , haha i think this dude still believe Steel masts are used today. he he...

Heavy equipment? again dont make me laugh!!

[Polux]

Originally Posted by neilpride

Now this part is really funy...

... i see the same Selden spar fitted in light boats and médium displacement boats, ...

If you see the same spar on a medium displacement boat and on a light performance boat that means the medium displacement boat is not built strong enough: A spar on a medium displacement boat has to be stronger. The boat is much heavier and will need a lot more sail to have a reasonable speed therefore the forces on the mast and structure will be considerably bigger.

[Polux]

Originally Posted by neilpride

Haa i though you write that!! but where the cropp is the Carbon fiber and all the wonderful stuff this dude is talking about in the low spectrum of the production boats list??

Another Marketing BS brochure, since the guy mention Polyester and Fiberglass and plywood like something from the prehistoric era but when in fact they are the regular material used in production boats , or Bavarias are made with carbón fiber? cmon, you can do it better...

Some mass production boat builders offer epoxy versions and many use the refereed infusion techniques. Almost all use some form of cored hulls, even if in what regards Beneteau and jeanneau they use to stiffen the hulls an integral intern molded hull.

We were talking about expensive medium weight boats, like Moody were on their day or Oyster so it is fair that we talk about expensive performance boats.

Oysters are expensive but don't use carbon hull and have luxurious interiors. Aureus use carbon hulls and have not so luxurious interiors.

Oysters are top medium small production weight cruisers, many top small production performance cruisers use carbon hulls. That's a difference as it was pointed out by the builders of Aureus.

[neilpride]

Originally Posted by Polux

If you see the same spar on a medium displacement boat and on a light performance boat that means the medium displacement boat is not built strong enough: A spar on a medium displacement boat has to be stronger. The boat is much heavier and will need a lot more sail to have a reasonable speed therefore the forces on the mast and structure will be considerably bigger.

Not really, depend of multitude of factors, height, number of spreaders, if is a keel or deck stepped mast, deck stepped mast need a thicker Wall section, sail área etc,,,,materials used, how long the unsuported áreas, etc,,, its really complex for spar makers , to claim that heavy boats need heavy weight mast is simple wrong, since heavy weight boats can sport carbón masts to, also depend if the boat is designed for inshore daysailing or for offshore sailing, mast scantlings vary from design to design ,,
To me dont make much sense to install a inmast furling spar in a perfomance hull and we see this day by day, putting weight aloft increase pitch and roll moment and weight a lot, so dont make sense to me, believe me, a Zspar in mast furling fitted in a small Bavaria can weight the same or more than in a bigger boat, so what this guy is claiming is unfair and incomplete..

But wait, this is another spot where some builders are saving pennys, masts and rigging, with the implication of some mast makers, market own always......

[neilpride]

Originally Posted by Polux

Some mass production boat builders offer epoxy versions and many use the refereed infusion techniques. Almost all use some form of cored hulls, even if in what regards Beneteau and jeanneau they use to stiffen the hulls an integral intern molded hull.

We were talking about expensive medium weight boats, like Moody were on their day or Oyster so it is fair that we talk about expensive performance boats.

Oysters are expensive but don't use carbon hull and have luxurious interiors. Aureus use carbon hulls and have not so luxurious interiors.

Oysters are top medium small production weight cruisers, many top small production performance cruisers use carbon hulls. That's a difference as it was pointed out by the builders of Aureus.

I never see a Aureus in this side of the pond, sure some builders build carbón hulls, fact is that the vast majory of mass production boats are still using Fg and Poly , vinilester and epoxy hulls are more and more used to, but to be honest you need to pay the Price, beneteaus and jeaneaus are solid FG below the waterline ..a big Oyster made in Carbon can cost twice or triple than Fg....