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  #561  
Old 06-07-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Quote:
Originally Posted by bobperry View Post
Brent:
Yes I see from your web site that your hulls are not all identical. I suppose if you were willing to add even more darts/chines you could do just about any shape you wanted. I just prefer the freedom of dictating my own shapes that often require compound curvature.

Your Genoa 55 looks very nice.

No. Jeff's rudder is better off without a skeg. This way it can have some balance area to it and that will reduce the loads on the AP. He doesn't need a skeg to mkake it strong. Maybe it's carbon.

" steel mast" Oh my.
There is no way you can get a spade rudder as strong without a skeg, as you can with one. A rudder behind a skeg has a much higher stall angle. Even a partial skeg with a balanced bottom is much stronger. Puts the bending load on the rudder blade, rather than on a shaft with very highly loaded bearings.
Some of the kelp beds I go thru further north would instantly ball up a rudder with no skeg.
A steel mast for a 36 costs around $1,000 material and labour included, ready to paint and step, with all fittings welded on. Whats your best quote for aluminium from a rigger? A steel mast lets you get cruising first then you can always change later, if you get a super deal and feel it worth the effort. Meanwhile you are underway, with drastically reduced expenses.
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  #562  
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Re: Bob Perry's take on Wolfenzee's dream boat

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Originally Posted by wolfenzee View Post
Not sure about pickling with salt, but what about penetrating epoxy....though a spar maker actually suggested resourcenol was a better adhesive to use than epoxy because it held up better to flexing.
As I pointed out earlier my mast is laminated (glued with resourcenol)and solid, the sheaves are actually cheek blocks on the outside of the mast (the one lower down is a loose block attached to a pad eye. The mast step is a square hole cut in the cabin sole sitting on top of a floor (with an opening on the side so if any water gets into the mast step it will drain into the bilge. Most sites of mast rot have been avoided where possible, my 40 year old mast is quite sound.
A freind used west system on a new wooden boat, with penetrating epoxy. It didn't penetrate anywhere near as much as advertised, and he had rot early on in its career.
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  #563  
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Re: Bob Perry's take on Wolfenzee's dream boat

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Originally Posted by Hartley18 View Post
Brent, as you'd know, as well as being a bit alkaline, salt attracts moisture and essentially stays permanently damp - not a problem in a wet bilge, but a big problem in the base of a vertical structure constantly exposed to the heat of the sun.

FWIW, I'm fairly sure salt would affect the adhesion of whatever glue you chose to use (chemically) a lot more than simply soaking the timber in a patent rot preventative and gluing up as normal.
Any moisture attracted by the salt would be salt water, continuing the pickling proccess.

Patent rot preservatives contain oil, which would prevent glue adhesion completely, unlike salt . When I was building my first boat in my early 20s, I asked my brother ,who worked in a chemical plant, if he knew of a preservative which doesnt contain oil, or anything which wont stop glue adhesion. . The solution may have been on my kitchen table. Being sure that salt would stop glue from sticking is not the same as having tried it. After all, everyone was once sure that the world was flat, and that the sun revolved around it. Had everyone relied on what was considered fairly sure, it would have kept us in the stone age. Some have not learned that lesson since.
Brining a bit of wood, then drying and gluing it, is not a huge undertaking, given the problems it could solve in the long run.
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Re: Bob Perry's take on Wolfenzee's dream boat

Borate is an anti-fungal used in treating wood, comes in a power which can be mixed into a solution or rods which can be inserted into the wood.

I found rot in one place on my boat, no problem as long it didn't spread, nothing structural. I removed all the rot and enough fresh wood to allow a block of wood to be fitted, saturated it with penetrating epoxy, filled the gaps with bedding compound, fitted the block and screwed and glued it....followed with a well bedded sheet of copper over the area to prevent further water incursion (something that the builder should have done in the first place.)

Aside from giving William Atkin the benifit of the doubt the Captain Cicero designed by William Atkin was a commision and I met someone with copies of the letter between the client and William Atkin....the photograph of the Captain Cicero attributed to Colin Archer not only had the same specs, but lots of small details also specific to William Atkins boat were present.

Last edited by wolfenzee; 06-07-2013 at 09:02 PM.
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  #565  
Old 06-08-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Quote:
Originally Posted by Brent Swain View Post
There is no way you can get a spade rudder as strong without a skeg, as you can with one. A rudder behind a skeg has a much higher stall angle. Even a partial skeg with a balanced bottom is much stronger. Puts the bending load on the rudder blade, rather than on a shaft with very highly loaded bearings.
Brent,

You really need to stop saying stuff like this. You are a professional yacht designer! When you write stuff like this you might give folks the idea that you don't understand basic engineering.

Take your statement "there is no way you can get a spade rudder as strong without a skeg."

Of course there is, it just takes better engineering. Both a skeg and a post hung rudder, and even the transom hung rudder in the 'my version' design are simple cantilevers. Each have a maximum embedment equal to the length between the hull and the deck to develop enough moment to resist the forces acting on them. And each develop a combinnation of lateral and longitudinal forces which relates to their physical shape, and what they encounter enroute. The forces that they have to resist are quantifiable and simply need to be engineered for.

Is it harder to engineer a rotating cantilever than a fixed one? Certainly! But does that mean there is no way to do it? No....in reality for any given skeg hung rudder design it is possible to analyze how much force that skeg and rudder can withstand, and then if so desired, engineer a rudder post, and bearings to withstand those identical forces. It's just not that hard if you understand basic engineering.

Similarly your statement that a rudder behind a skeg has a much higher stall angle, suggests that you stopped learning about yacht design at some point in the 1970's when that was still thought to be the case. Since then there is a much better understanding of how rudders in non-compressible fluids behave and designers can shape rudders such that a spade rudder does not have to be any more prone to stalling than a rudder behind a skeg. But beyond that, there is also an understanding that sailboat rudders don't usually stall in the same aerodynamic sense as this term is generally used.

What a sailboat rudder actually does at least most of the time that people think it stalled is develop so much low pressure that is sucks air down the blade, in doing so creates a fluid that is a mix of air bubbles and water, making the water a less effective media to generate lift and thereby reducing the ability of the rudder to create the needed turning force.

For this reason as rudders have gone to smaller area, and higher aspect plan forms, thereby generating greater negative forces, designers have pushed them further forwards under the hull, and away from the free surface.

A fairer criticism of the outboard rudder shown on the My Version design is that it would be more prone to sucking air since it is at the free surface. For that reason, I purposely drew a larger rudder than I would have had to if the rudder was.well beneath the hull, and took the penalty of greater drag in order to preserve some pragmatic solutions to other concerns explained in other posts of mine above. The greater area reduces the square unit pressure on the foil and therefore reduce the force needed to cause the water to aerate.

Respectfully,
Jeff
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  #566  
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Re: Bob Perry's take on Wolfenzee's dream boat

Word has it that the Genoa 55 is not Brent's dsign. Well, heavy sigh, that would explain why I like it.

Some one, tell me I'm wrong. I can see it's an alu boat but it popped up on Brent's link so I ass-ummed. Brent's web siteb is very lean on who the actual designer is. On the other hand it is very fat on copious quotes from other designers. What an interesting concept. Not sure why quotes from dead guys are particularily relevant regarding today's designs. But It's a cute attempt at something.
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Last edited by bobperry; 06-08-2013 at 12:39 AM.
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  #567  
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Re: Bob Perry's take on Wolfenzee's dream boat

Quote:
Originally Posted by Jeff_H View Post
Brent,

You really need to stop saying stuff like this. You are a professional yacht designer! When you write stuff like this you might give folks the idea that you don't understand basic engineering.

Take your statement "there is no way you can get a spade rudder as strong without a skeg."

Of course there is, it just takes better engineering. Both a skeg and a post hung rudder, and even the transom hung rudder in the 'my version' design are simple cantilevers. Each have a maximum embedment equal to the length between the hull and the deck to develop enough moment to resist the forces acting on them. And each develop a combinnation of lateral and longitudinal forces which relates to their physical shape, and what they encounter enroute. The forces that they have to resist are quantifiable and simply need to be engineered for.

Is it harder to engineer a rotating cantilever than a fixed one? Certainly! But does that mean there is no way to do it? No....in reality for any given skeg hung rudder design it is possible to analyze how much force that skeg and rudder can withstand, and then if so desired, engineer a rudder post, and bearings to withstand those identical forces. It's just not that hard if you understand basic engineering.

Similarly your statement that a rudder behind a skeg has a much higher stall angle, suggests that you stopped learning about yacht design at some point in the 1970's when that was still thought to be the case. Since then there is a much better understanding of how rudders in non-compressible fluids behave and designers can shape rudders such that a spade rudder does not have to be any more prone to stalling than a rudder behind a skeg. But beyond that, there is also an understanding that sailboat rudders don't usually stall in the same aerodynamic sense as this term is generally used.

What a sailboat rudder actually does at least most of the time that people think it stalled is develop so much low pressure that is sucks air down the blade, in doing so creates a fluid that is a mix of air bubbles and water, making the water a less effective media to generate lift and thereby reducing the ability of the rudder to create the needed turning force.

For this reason as rudders have gone to smaller area, and higher aspect plan forms, thereby generating greater negative forces, designers have pushed them further forwards under the hull, and away from the free surface.

A fairer criticism of the outboard rudder shown on the My Version design is that it would be more prone to sucking air since it is at the free surface. For that reason, I purposely drew a larger rudder than I would have had to if the rudder was.well beneath the hull, and took the penalty of greater drag in order to preserve some pragmatic solutions to other concerns explained in other posts of mine above. The greater area reduces the square unit pressure on the foil and therefore reduce the force needed to cause the water to aerate.

Respectfully,
Jeff
My rudders are hung on a 3/16th plate skeg, tied into several transverse webs and a half inch plate gusset on the front of the skeg. To build an unsupported rudder anywhere near as strong would make it massively heavy.
How do you make a shaft supported rudder strong enough to survive impacting rock at hull speed or survive a pounding on coral in a big sea, or pounding for 16 days on a baja lee shore in up to 12 ft surf, or pounding on a coral reef for 4 1/2 months ? Mine have .
Raking a transom hung rudder foreward means it is more inclined to draw water up it rather than suck air down it.
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Re: Bob Perry's take on Wolfenzee's dream boat

Brent: you live in a cave it seems. I can design a carbon fiber rudder that would rip the entire back end off a boat before it would break. They are monocoque and they can be as "massively strong" as you care to build them, strength vs weight is always a consideration. But even a "massively heavy" carbon rudder would be far lighter than one of your weldments. And,,,,ta dahhh,,,they don't rust. But I agree with you. There is a place for your approach. You have your home builder market and good for you. Home builders need a designer who has done all the "dirty work" of actually building a boat. You've got me there. I can't build anything. Your way is one way. There are many other ways. I take pride in seeing my designs built by skilled yacht builders. I have my own niche.

I love beautiful yachts.

But I'm not here to try and convince you, just to let other readers and posters know that you represent an extremely narrow and semi-educated perspective when it comes to engineering of yacht structures.

Here is a pic of WILD HORSES, welded alu hull, carbon deck and deck structures, carbon spade rudder and a family of proven offshore cruisers ready to take WILD HORSES offshore again. This boat is a very comfortable rocket, beautifully balanced and a joy to sail, a peach under power around the dock. I'm very proud of this one. Beautiful isn't it?

Just curious, glad all those rudders don't break off, but why do so many of your boats end up on the rocks?
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Re: Bob Perry's take on Wolfenzee's dream boat

"Here is a pic of WILD HORSES, welded alu hull, carbon deck and deck structures, carbon spade rudder and a family of proven offshore cruisers ready to take WILD HORSES offshore again. This boat is a very comfortable rocket, beautifully balanced and a joy to sail, a peach under power around the dock. I'm very proud of this one. Beautiful isn't it?"

Very Nice Bob. Just a curiosity, Why an aluminum hull?,Why not carbon or carbon composite?.
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Re: Bob Perry's take on Wolfenzee's dream boat

Jak:
We talked to various builders and one of them was Jim Betts down in Trckee, CA. His specialty was racing boats done in alu and his bid looked good
(that's another long and sad story) so we went with him. His build style preference was alu with a carbon deck so we knew that would work and we went with it. The boat is now over ten years old and there have been no issues with the build. Betts is a true artist with aluminum. He is a sculptor. The bowsprit was made from split mast extrsuions. If I could draw it, he could build it out of alu.
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