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  #41  
Old 04-19-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Bob-
"If spent uranium not not illegal for racing keels "
Since Wolf isn't racing and this IS a blue-sky project...it might be interesting to see what a proper keel material would bring to the picture, after you got to the numbers stage. Now that we've confirmed iron bulbs aren't the way to go.
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Re: Bob Perry's take on Wolfenzee's dream boat

Quote:
Originally Posted by bobperry View Post
Jeff:
On draft:
Wolf sails in my backyard. He can live with 9' draft. I say we go 5'10" to start and se what that looks like. It will mean a shorter fin but that can be good so long as we keep the fin long enough to sit the boat on. We should be able to do a bulbless fin given that we will have the planform required to get the lead low on a deep sump. Like the Valiants.

Maybe we should keep in mind an adjustment to the L/B. He's pretty narrow now with a full bow. Maybe we should think about an L/B around 3.85. Do you know what his current L/B is?
I like going to a 5'10 draft. I think that should help a lot. The current L/B at the waterline is 3.56 and for what it is worth, it is 3.33 at the deck. I can certainly push the beam out to somewhere around 3.85 on the next round.

Jeff
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  #43  
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Re: Bob Perry's take on Wolfenzee's dream boat

Hello:
The other problem with spent uranium is that it is very expsive to buy and very expensive to cast into a keel shape. It is much harder to work with than lead. Besides I'm not sure in this "green" world I would like to have spent uranium on my "green" vessel.

While this is a pie in the sky project I'd like to keep the materials within the relm of reality.
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Re: Bob Perry's take on Wolfenzee's dream boat

The lines of my boat got me looking at fishing schooner lines, there was a very elegant looking vessel that was a knockabout (no bowsprit) the fishing schooner Helen B. Thomas (built 1901) is very simlar in design but predates the "meter boats"


"East Coast 12 meter" picture overlaying the knockabout schooner, the 12-meter has only a few tweaks.

Extreme overhang in for fishing boats was done to eliminate the bowsprit and make the boat easier to maneuver in harbor.

Last edited by wolfenzee; 04-19-2013 at 02:43 PM.
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Re: Bob Perry's take on Wolfenzee's dream boat

Wolf, although not very relevant to this conversation, you might want to look at the schooner George Steers......
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Re: Bob Perry's take on Wolfenzee's dream boat

Quote:
Originally Posted by Jeff_H View Post
Wolf, although not very relevant to this conversation, you might want to look at the schooner George Steers......
The schooner Alcyone is a 65' downsized Gloucester fishing schooner and lives right here, above and below the lines are very similar to mine, she is as fast as she is beautiful.

If I were to go with a schooner I would rigg it something like this (this is useing the above mentioned knockabout schooner hull)

That pic is the Resolute, which won the America's cup in 1920

Last edited by wolfenzee; 04-19-2013 at 03:16 PM.
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Re: Bob Perry's take on Wolfenzee's dream boat

Quote:
Originally Posted by bobperry View Post
The premise was that you could build a more efficien( better performance) keel with iron than you could with lead.

To retain the same VCG of the keel the iron keel would have to have a much bigger bulb and a lot more frontal area I also think the fin portion of the keel would have to be bigger so even more wetted surface and frontal area is added.

It does not make any sense and I don't give a rip who did the study.

Think of it this way. If an iron keel could provide "better performance? why does every serious racuing boat in the world use lead for ballast. If spent uranium not not illegal for racing keels they would use that like they did back in the earkly '70'. It's denser than lead.

Open you eyes, not another book, the answer is easy to see in any boatyard. The more dense material gives the designer more freedom of design. Bulbs are slow. They cut into the clear span on the fin and reduce apparent aspect ratio. They add wetted surface and frontal area. Bulbs work because the allow for a very low VCG. This is far easier to achive with the more dense material.
Bob,
For the third time I say that I agree with you, as certainly the authors of the study. It is evident that a keel with a bulb made of lead is more efficient than an all iron keel, assuming the same shape. That was never the point.

you say that :

"The premise was that you could build a more efficien( better performance) keel with iron than you could with lead."

but you are mistaken, they did never assumed that or wanted to verify that possibility. In fact the lead fin keel was only there for comparative purposes. They were studding basically different types of bulbed keels.

The fact that they had found that in some circumstances a torpedo iron keel could be more efficient than a fin lead keel was accidental and that is only valid to a fin lead keel versus an iron torpedo keel.

It is evident that if both keels had the same design, one in lead and other in Iron, whatever the design the lead keel would be more efficient (for the same RM) since it would have a lesser volume and a smaller drag.

what the study was aimed at was:

"The aim of this project is to evaluate four different keels and determine which one has best performance upwind. "

and about the keels and regarding the use of lead on the fin keel:

"The four keels should have the same righting moment in order to be comparable. This means that the static moment of the yacht which counteracts side forces from the sails should be the same. In the
redesign of the T-keel, this righting moment has to be kept constant. For an easy comparison between the keel designs the draft will be kept constant as well, and the fin size and shape will be identical between the bulb keels. ...

Keel 1 (Fin keel) was used only as a comparison for the other keels. It does have the same righting moment and maximum draft, but in order to fulfil this it had to be designed to be made of lead instead of cast iron as the other keels. This implies it will have a comparably smaller wetted surface, and consequently the drag forces will be smaller. The effects of these aspects were expected to occur in the results."

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

Regards

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

"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."

Paulo:
Those are your words, not mine. I disagree strongly with that statement. Plain and simple.

Please exlain to me how I am misinterpreting your initial statement. I'm not seeing it.
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Last edited by bobperry; 04-19-2013 at 03:54 PM.
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Re: Bob Perry's take on Wolfenzee's dream boat

bob-
I agree with you about spent uranium and suspect that tungsten is the green alternative. At something like $50/lb. it would be 50x more expensive than lead and only twice as dense but I suspect the foundry would be happier to work with it. And "twice" usually is enough to make a difference in things.

How much of design is black art and how much is available in software these days? i.e. can you just plug in a number for density, and have the software refigure the keel volume and various effects on VCG and all?
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Re: Bob Perry's take on Wolfenzee's dream boat

Hello:
There is software to do the drafting and the calculations for you but there is no software to make design decisions. You first must come up with a shape and then run the numbers. Some programs stream the changing numbers to you as you design. That is a big help. It takes a lot of "art" to determine how the keel performance will be balanced, i.e. upwind vs downwind requirements. Of course if you knew you would be sailing 95% of the time on a close reach in 20 knots of TWS the keel design could be more scientific. But it's hard to define the performance envelope of a true cruising boat.
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