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  #131  
Old 04-25-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Quote:
Originally Posted by Brent Swain View Post
Paulo
I have no doubt that tank tests show this type of keel to sail well, but tank tests dont ask the question of how you get a fouled anchor rode off one when you are abeam to a strong wind and sea on a dark night. Numbers and math dont answer that question, and a lot more practical questions about actually using the boat..

Skinny keels fold over, regardless of what you put inside. Perhaps these boats are designed to the standard plastic boat standards, where they are simply expected to break up if they hit anything.
Brent you always seem to be worried about the things that can be engineered or designed around. Solving these issue does to take some additional care, but they are not all that hard to solve. If you are really worried about anchor rodes fouling the aft end of your bulb keel, but you want the sailing boostg that comes from a bulb, you simply run a cable from the very lower aft edge of the bulb to a spot on the hull well aft of the bulb to keel rodes out of there.

Engineering a skinny keel and its connection does require careful engineering, but the forces are well known, and it is a far easier engineering problem than designing something like a high rise building, which qualified professionals design routinely and which very rarely fail.

Quote:
Originally Posted by Brent Swain View Post
My first boat was a Pipe Dream designed by Francis Kinny and tank tested inthe Davidson lab in New York, the tank where all the US Americas cup boats were tested. She had a short keel with rudder attached. With zero sailing expereince, I looked at the rudder and thought " Maybe a rudder on a skeg six feet further aft would be better." Then I thought " Gee, I have no expereince so I beter do what the designer drew." Off the wind the boat was almost uncontrolable in strong winds,an absoluite abortion of a design screwup, so when I got to New Zealand, I replaced the rudder with a separate rudder six feet further aft on a skeg, just as I had originally thought, with zero experience.. The improvement was huge. That completely blew my confidence in the infalibility of world reknown "Experts."
Einstein said "Wisdom doesn't come from studying , Wisdom comes form showing up for life."
Your story about the 'Pipe Dream' is a good one. It shows how over time designers have learned to improve designs. Pipe Dream was optimized for a specific racing rule. Kinney had come into the profession when racing rules still restricted the use of separate rudders and so the design followed the 'traditional solution' of its day.

But around the time that 'Pipe dream' was being designed, designers began to experiment seriously with separating the rudder from the keel in one form or another. By the time that you owned your 'Pipe dream', it was pretty common knowledge that splitting the rudder from the trailing edge of the keel improved handling and lightened steering loads.

So what was radical in Kinney day, became a reasonably well accepted norm by the time you decided to modify your boat.

Even then designers were still learning how to design fin keel-spade rudder boats, and so these early fin keel boats had a mediocre reputation.

It hard to predict what radical idea will become the next norm. But your Angus Primrose story shows how an early experiment in boat design does not always tell the whole story. Angus Primrose's boat actually broached and pitch poled. He was known for designing boats which were lightly ballasted and which had a flaring bow with chine below the deck and a lot of buoyancy near the deck line. The version of the story that I read said that they punched that bow into to the back of a wave, and wiped out, getting rolled by the next wave. It was not about reducing beam, but about shaping his boats better.


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Originally Posted by Brent Swain View Post
Angus Primrose, while crossing the Atlantic in one of his very beamy designs was capsized, and was dismayed at how long she took to right herself. He later did some calculations and found that even a slight reduction in beam made a huge improvement in ultimate stability.
Again, boats staying capsized was never a problem, before excessive beam became the norm.
A beach ball with a high CG and a tiny ballast ratio has a very high ultimate stability. A wide raft with a very high ballast ratio and low CG will have a very poor ultimate stabilty. Thousands of pounds of buoyancy in a wheelhouse will be the equivalent of adding far more weight in the keel, in the inverted position, when it comes to ultimate stability. The more the midships section resembles a beach ball (Trunk cabin with high camber) the higher it's ultimate stability.
But like many radical experiments, even the beamy boat world is making progress in dealing with its inherent deficiencies. When you look at the cruising versions of these beamy boats, they often have a lot of freeboard and high deck structures, which serve to destabilize the boat in the inverted position.

If you look at this moment curve for a Malo 40, which is not terribly radical adaptation of the beamier hull forms, two things seems obvious, first it has a positive stability to 130 degrees, and second it has virtually no negative stability when inverted to 180 degrees. I have seen a plot of a much beamier and more radical design which had positive stability to a bit over 140 degrees and achieved maximum righting moment at around 110 degrees. What I did not like about that plot was the very steep drop in stability between 110 degrees and 140 degrees which could catch a skipper unawares.



Jeff
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  #132  
Old 04-25-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

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Originally Posted by Jeff_H View Post
....
If you look at this moment curve for a Malo 40, which is not terribly radical adaptation of the beamier hull forms, two things seems obvious, first it has a positive stability to 130 degrees, and second it has virtually no negative stability when inverted to 180 degrees. ...


Jeff
You mean a very small inverted stability?

Regards

Paulo
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Re: Bob Perry's take on Wolfenzee's dream boat

You guys and your graphs. Do you really understand how inadequate a 2D graph like that is compared to the dynamic forces of the sea. But if it amuses you then play on. I'm not sure this is the right environment for me.

Do you really think for a moment that when the wind and waves are capable of heeling you 130 degrees they really give a rip about another 5 degrees. Do you really imagine that a 2D stability study can compare with the forces that will pin the boat down and prevent it from righing itself. Show me a computer program that factors in the heeling moment, water sucking moment of storm trysail and storm jib in a rollover situation.
We live in a world where people think computers can provide ultimate answers.

Do me a favor, go back and determine how many designs from the S&S office had full stability studies done. Surpirse! Now do it for Phil Rhodes office. Surpise! All this preoccupation with numbers is a function of the computer age and the ability to use some bozos program to get some numbers.

I did a full stability study of the Valiant 40 about a year after production had begun. I did it because people wanted to know. Not because I was concerned. I was never concerned. I knew I had it right. I did a zero to 30 degree stanility study earlier because that where boats operate.

Silly people. Scared yet?
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  #134  
Old 04-26-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

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Originally Posted by bobperry View Post
...

Do me a favor, go back and determine how many designs from the S&S office had full stability studies done. Surpirse! Now do it for Phil Rhodes office. Surpise! All this preoccupation with numbers is a function of the computer age and the ability to use some bozos program to get some numbers.

...
Maybe that's why they are not major design cabinets anymore?

I don't know of any of today's major design cabinet that does not use computer generated stability curves as an instrument to access boat stability during design and more than that they all use Computer Fluid Analysis to study how the boat perform in several hull, keel and rudder configurations.

Bob, the past is the past and it is not only for Wolf's boat.

Regards

Paulo
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  #135  
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Re: Bob Perry's take on Wolfenzee's dream boat

Paulo:
I answered your post on the other thread.

Many thanks for the tip " the past is the past" I'll write that down.

Of course we all do stability studies now. All it takes is the push of a button. I usually do multiple stability studies for a new boat while I evaluate keel config and draft options. I think I have a pretty good handle on how th modern yacht design office works. That could be why I get requests from student from all over the world to come and do an intership here.

See the other thread.
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  #136  
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Re: Bob Perry's take on Wolfenzee's dream boat

Seriously, Bob -
"Show me a computer program that factors in the heeling moment, water sucking moment of storm trysail and storm jib in a rollover situation."

If you can't find software off the shelf that does that, I would bet that the computer/engineering department at any local university would be willing to let you pitch that to one of their programming classes as a challenge project. They LOVE to find a real world programming challenge to give a class, and say "OK, show us how smart you are, write a program that will accomplish this" and then grade the class by how well the different programs work.
If the program has any value and that can be turned into a small prize or put into some type of license afterwards, all the better, but they use real-world challenges all the time. It beats ll heck out of "write a program that predicts leap years".

Please don't mistake me for suggesting a computer can replace expert skills, I'm just saying that this type of modeling CAN be done on computer and it can be one more tool in the box. The folks at Industrial Light and Magic and the other graphics houses that do virtual reality rendering tend to be experts at modeling complex physics, but they're not so easy to get for free.
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Re: Bob Perry's take on Wolfenzee's dream boat

Bob,

On most levels I agree with you, meaning that for all the numbers, there are some very big breaking waves out there, and if one of those waves has your name on it, you are going to get rolled pretty much whatever you are sailing and no matter what the numbers say. And in sailing smaller boats in tough conditions, there is a combination of a downdraft, and seastate which can get a boat sliding on its topsides and once the mast hits the water, the next step is inversion.

But I also think that stability plots are helpful in understanding the bahaivor of a design when its is in the planning stages, and especially critical when exploring designs that press the limits of accepted practice as is the case with many of the newer distance racers and the newer crop of EU cruisers, which are based on the principles deriving from these distance racers.

In the absense of these plots, it seems like designers are running blind. And while these plots may not guarentee that no one will ever capsize again, and they hopefully provide a window that would prevent the kind of scary capsizes which happened with more frequency in earlier flat topped designs.

I think that the other thing that these studies provide is a kind of operating manual that gives the skipper some sense of where his limits are. If you sail a boat that the stability curve looks like a cliff when you get past max righting moment, you sure don't want to sail near the edge. But also as you note, there is a whole lot which can never be modeled without a very intensive program and even when the results of those studies are counter intuitive they are just one tool in getting understanding the way wind and water operate. Interestingly enough, one of the papers that I attended at SNAME dealt with the fact that they have been modeling the square topsail schooner the current 'Pride of Baltimore' for just that reason. They unexpectedly discovered that during a knock down, the lower edge of a square sail, becomes the leading edge of the sail and serves to generate a lot of force pulling the boat over. Who knew?

Respectfully,
Jeff
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Re: Bob Perry's take on Wolfenzee's dream boat

Jeff, seeing your mention of "modelled" makes me think there is a new tool for designers to consider: The 3D printer.

This would allow any designer who has 3D CAD renderings of a new design to literally print a model of it for tank testing or other purposes. There would still be some questions of making the model reflect actual balance, etc., but given how cheap the printers have become (way cheaper than laser printers and CAD plotters were in their infancy) this should be a valuable tool for the designer who wants to play some hunches.
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Re: Bob Perry's take on Wolfenzee's dream boat

Hello:
You are probably right but I',m not sure that project would be a priority at most universities. If it could be done then you would have to massage the program to make it work with existing hull modelling programs and that's another big step. The typical small yacht design office of today does not work in the hypothetical and just plain can;t aford to fund such programming. There is not a big market for programs like that. Maybe if we had people pop up from the gun'l and shoot machine guns at pirates we might find a bigger market.

Jeff:
I have so many stability plots for my new 60' ketch that I have lost count of them. I do this all the time and as I have said I use stability studies to evaluate keel configs and draft options. I am not blind to this stuff. I have been using computer stability studies for the past 35 years. I still have some that were printed out on that wide, greenish , striped paper with the holes running down each edge. It puzzles me that some of you respond like I am just beginning to figure this out.

I suggest a better breakfast.

Hello:
I do lots of 3D modelling these days. Here are some studies of the pilot house shape for the new 60' ketch that Pacific Seacraft is now building. I don't need to hold the model in my hand. I can hold it in my eye and rotate it to before long I can hold it in my brain.
Attached Thumbnails
Bob Perry's take on Wolfenzee's dream boat-catarijulyo28.jpg   Bob Perry's take on Wolfenzee's dream boat-catarijulyo29.jpg   Bob Perry's take on Wolfenzee's dream boat-catarijulyo32.jpg  
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Re: Bob Perry's take on Wolfenzee's dream boat

Bob, the type of purpose of the program would not matter. You are right, it would not be a priority at universities.

However, many of them do need challenge projects, or enjoy assigning them for extra credit, and the more oddball and unusual the project is, the more complex it is, the more atttractive it is, simply because it hasn't been done before and that makes it a better challenge.

Working with niche software that already does other things, might be enough of a problem to be a stopper. I think I can imagine just how small a market "yacht design software" must be, given how small the entire yachting market is.
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