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  #21  
Old 04-18-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

It's not a matter of poor stability, boats of that time were designed to perform at a heel, doesn't take much to get my boat to 25or30degrees but takes alot to get to go beyond. Alot of modern day hulls are designed to sail flat or close to it.
The only reason I can figure that the alternate had a bulb on it was to be able to maintain the 5' draft anything else would require a deeper keel.
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Old 04-18-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

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Originally Posted by hellosailor View Post
Heeling stability was so poor that a change to a keel bulb instead of a foil was necessary? Or does a bulb somehow contribute to any other performance?
To have a lighter boat (less ballast needed for the same RM)

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Paulo
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Old 04-18-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Remember Bob's criteria: If Wolfenzee won the lottery.

Now, let's rethink that boat with a proper tungsten keel, none of this cheap lead crap. I have to ask, Bob, have you ever had a customer ask about a denser keel material for a better keel? Other than the spent-uranium-racers club?

Even at 20 degrees, having a keel with a foil shape that gains ground upwind ought to be an advantage. And it should have less drag than a bulb, at all times.

(Yes, I really am saving up old light bulb filaments. :-)
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Old 04-18-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

All boats are designed to sail flat. That's why we design them at a zero angle of heel. But they do heel and there is little we can do about it. But almost any boat, except in very, very light air will sail best if heel angle is kept to a minimum. The keel is more efficient that way and the sails are more efficient that way. But try as we might, the boat will heel.

People often ask me, 'What heel angle is my boat desigfned to sail at?" I always say zero degrees.

Bulbs per se are not fast. A clean tip to your fin is fast. But if a bulb can signifigantly lower the VCG then the bulb may contribute to boat speed in that it will help keep the boat more upright.
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Re: Bob Perry's take on Wolfenzee's dream boat

Quote:
Originally Posted by hellosailor View Post

Even at 20 degrees, having a keel with a foil shape that gains ground upwind ought to be an advantage. And it should have less drag than a bulb, at all times.

...
Not always. I have read a recent study aimed to evaluated the performance of several types of keels upwind and it turned out that an Iron bulbed keel had a better performance than a lead fin keel with the same draft, both keels providing the same righting moment. The study used lead for the fin and cast iron for the the bulbed keels but if they had used steel for the foil and lead for the bulb I think it is safe to assume that the difference in performance would be even more substantial since the bulbed keel would have a lot less drag.

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Old 04-18-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

PCP:
Iron weighs around 450 lbs. cu. ft while lead weights around 700 lbs cu. ft. So to have two keels of similar geometries and one of iron and one of lead is very hard to imagine.
I don;t buy the results of that study at all. I have nothing against iron keels my own boat for 15 years had an iron keel.
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Re: Bob Perry's take on Wolfenzee's dream boat

Quote:
Originally Posted by bobperry View Post
PCP:
Iron weighs around 450 lbs. cu. ft while lead weights around 700 lbs cu. ft. So to have two keels of similar geometries and one of iron and one of lead is very hard to imagine.
I don;t buy the results of that study at all. I have nothing against iron keels my own boat for 15 years had an iron keel.
Bob, maybe I did not make myself understood, the keels have not similar geometries. The objective was testing different keel shapes (all with the same RM and draft) regarding upwind performance. The bulbed ones were cast Iron, the fin one was made of lead and what I said was part of the conclusions.



The study is a serious one, it is a from the Department of Shipping and Marine Technology and Marine Hydrodynamics from the CHALMERS UNIVERSITY Of TECHNOLOGY (Sweden 2011), it is a Master of Science Thesis made on the sequence of a previous investigation and supervised by Prof Lars Larson, an authority in Hydrodynamics and with the participation of NA Stefan Qviberg, the long time designer of Arcona yachts, that was the one that come with the idea for the work.

The study:

http://publications.lib.chalmers.se/...ext/148387.pdf

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

Paulo:
Many thanks. Thst is a very interesting study and one that I would take very seriously.

But I would ask this:
What if they made a bulbed fin with lead and compared it to a bulbed fin with iron.
This seems a very conspicuous error in their study.

Seriously new,,,,,,If iron keels were more efficente we would see them okin more high performance boats. But the realitiy is we don't.

Reality has a way of sorting this out very quickly. I see it as all about lbs. per cu. ft.

If you want to join the ranks of "I see what I want to sse" then that is your choice. What I see is that every high performance boat built today uses a lead keel and at least a lead bulb.

Iron keels were all about saving money. It's a simple as that.
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Old 04-19-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

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Originally Posted by bobperry View Post
But I would ask this:
What if they made a bulbed fin with lead and compared it to a bulbed fin with iron.
The way I understood it from Paulo's description (haven't read the study yet) is that the different metals were used so that two keels could be made in different designs but have the same righting moment.. So that the designs themselves could be compared. If you compare fin vs bulb both in lead, the bulb would be better simply because it is has lower cg and greater RM- but by using iron for the bulb you could end up with the same RM as the lead fin, and compare just the shapes.
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Re: Bob Perry's take on Wolfenzee's dream boat

Quote:
Originally Posted by bobperry View Post
Paulo:
Many thanks. Thst is a very interesting study and one that I would take very seriously.

But I would ask this:
What if they made a bulbed fin with lead and compared it to a bulbed fin with iron.
This seems a very conspicuous error in their study.

Seriously new,,,,,,If iron keels were more efficente we would see them okin more high performance boats. But the realitiy is we don't.

Reality has a way of sorting this out very quickly. I see it as all about lbs. per cu. ft.

If you want to join the ranks of "I see what I want to sse" then that is your choice. What I see is that every high performance boat built today uses a lead keel and at least a lead bulb.

Iron keels were all about saving money. It's a simple as that.
Bob,
Yes, if you look at my previous post I have said that if they had compared the lead fin keel with a top bulbed keel with the foil in steel and the bulb in lead the results would have been much better in what regards the bulbed keel.

In fact in what regards top racing boats the preference seems to be for carbon or mechanical built steel foil (with a structure inside) and lead bulbs, being the massif steel (cut from a block) foil with a bulbed keel the less expensive option.

That test is interesting because it shows that it is possible to make an all iron cast bulbed keel ( a cheap one) with a better or equal performance than an all lead non bulbed fin (an expensive one).

That explains why European NAs, in what regards mass production mainstream cruisers are all opting for that kind of keels (iron), some even using the better performance type on cruising boats. Those builders make boats on a tight budget and that is an acceptable compromise in what regards price.

The difference between a steel/Lead keel and an all iron keel (on a 40ft boat) is over 10 000 USD so many brands don't even propose that as an option, with the exception of the ones that build performance boats.

Regards

Paulo
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Last edited by PCP; 04-19-2013 at 08:38 AM.
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