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  #351  
Old 05-21-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

I noticed the differences, but I am a cruising sailor and an extra knot under certain/optimum conditions is insignificant to me. "Racing boat technology" just is not of any use to me.

It has been mentioned that the new hulls are theoretically "faster", how there is less friction, wetted surface different entry angle, etc.....but you have yet to explain how a boat is "faster" than a boat that is sailing at 1/4kt under it's theoretical hull speed.

Last edited by wolfenzee; 05-21-2013 at 11:26 PM.
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  #352  
Old 05-22-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Wolf:
It's time for us to part company. I have no interest in humoring you any longer. I have no interest in trying to explain anything to you any longer.

Your comment, ""Racing boat technology" just is not of any use to me" pretty much says it all. Look at your sails. At one point in time your rags would have been considered "racing sails". They are dacron I assume. Or are you clinging to Egyptian Cotton? You are just not interested in anything new. You seem to have no desire at all to learn anything new.

Have fun sailing this summer. I know you love your boat and I applaud you for that.

Tsai chien woada tai bun pungyo. (Mandarin)
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  #353  
Old 05-22-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Bob,

Are you saying one can still buy dacron sails?!?!?!?! really?!?!?!? hmmmmmmmmm........Y?!?!?!

Marty
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  #354  
Old 05-22-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Quote:
Originally Posted by wolfenzee View Post
I noticed the differences, but I am a cruising sailor and an extra knot under certain/optimum conditions is insignificant to me. "Racing boat technology" just is not of any use to me.

It has been mentioned that the new hulls are theoretically "faster", how there is less friction, wetted surface different entry angle, etc.....but you have yet to explain how a boat is "faster" than a boat that is sailing at 1/4kt under it's theoretical hull speed.
Wolf,

I explained this in more detail in several posts above, but as a broad generality, the reason that the term, "theoretical hull speed" includes the word "theoretical" is that boats of certain designs can and do routinely break that that theoretical speed limit. The seaworthiness, speed, and motion comfort advances in this design do not rely on "Racing boat technology", even if they do rely on the kind of information that has been learned from the scientific research that was funded by race boats.

If you look at the boat designed with my tastes in mind, it starts with a theortical hull speed that is roughly 1 1/2 knots faster than the Capt Cicero. It has a lot more sail area, the stability to carry that sail area, and a little less wetted surface, so it should be able to achieve that hull speed in much lighter winds than the Capt Cicero. It is a semi-displacement hull form, so in a breeze, it should be able to easily sustain speeds that are perhaps 3-4 or more knots faster than the Capt Cicero.

The design for my taste should be able to get by without headsail changes in winds from nearly no wind up to winds into the high 20 knot range, and still out perform the Capt. Cicero in all conditions, making the newer design much easier to handle in changeable conditions. It should be more forgiving as well.

The taste for boats like these not about marketing, or being sold a bill of goods. The reason that a boat like the one designed for my tastes would be is appealing is that since boats are built by the pound, and its cost would be about the same price as your boat. Since it requires fewer sails, its operating costs may be less. And yet in all ways, its capabilities as a coastal or ocean cruising boat are far greater.

All that said, all that counts for any of us is that we like our own boats. And since you love your boat, that is all that counts for you. As much as I enjoy seeing boats like yours and enjoyed redrawing the lines as a history lesson, yours is not a boat that I would ever be happy owning. But that really does not matter either.

Jeff
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  #355  
Old 05-22-2013
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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
There are a couple of issues which I would like to touch on in more detail that may prove useful at this point. The first that I would like to start with the issue that Brent Swain raised in Post #312. In that post Brent said, “The so called "Modernized" version, with wide, flat aft lines and super lean bows, is the kind of hull which goes down by the bow, and the stern lifts up, when she heels, the centre of buoyancy moving well aft as she heels. This is the kind of hull shape which gets extremely hard to control downwind, a boat with zero directional stability.” Brent and I have had this conversation on other occasions on other forums around the internet, but for those coming in late this is something which you see people say but which is not necessarily true.

While it can be true that a poorly designed boat can and will change trim with heel angle, it does not have to be true, and it is not true for most well designed modern boats. I know that this may seem counter intuitive on a boat with a pinpoint for a bow and with a stern so wide that if asked to, ‘Haul ass’, would need to make at least two trips.

To understand why these ‘triangular’ boats do not change fore and aft trim with heel, I will give this example. Visualize a sailboat that was the shape of a cone, that floats with the point of the cone being the bow and located at or above the surface of the water and flat end as a transom, with a keel and rudder mounted.

You can visualize that as that cone rotates around its axis, in effect heeling, the cone would simply spin around its center axis without changing trim. The reason the boat of that shape does not change trim is that the shape of the boat is such that the fore and aft distribution of the buoyancy does not change as the boat heels, and assuming that the contents of the boat do not shift fore and aft with heel angle, the center of gravity remains the same as well. No matter how blunt a cone you can visualize, (effectively no matter how big the transom is) that cone would not change trim with heel angle.

Of course boats are not cone shaped. But the same principle applies if the boat is to remain in trim at a range of heel angles. What happens as a boat heels is that some of the bottom comes out of the water, and some of the topsides becomes immersed. Simplified by ignoring dynamic forces acting to change trim, the key to maintaining the desired trim is to make sure that the distribution of buoyancy does not move fore and aft with heel angle. This means that at each point along the boat, that the distribution of the volume contained within the submerged topsides and portion of the bottom still in the water needs to remain in proportion to the static upright buoyancy.

Before computers, this could be wildly difficult to calculate, but modern computers will comparatively easily calculate trim angle with heel, allowing the designer to tweak the topsides and bottom shape to allow the boat to maintain the desired trim over the range of heel angles at which the boat will typically be sailed.


There are secondary issues involved with big transom boats and maintaining control with heel. When you heel a boat with a fine boat and broad stern, the whole windward side of the boat, rotates upward (rolls up). This also raises the vertical center of gravity. For comparison, traditional narrow boats, typically rotated without rising and in some cases, actually ‘rolled down’ so that the vertical center of gravity actually moved downwards.

As the stern rolls up, to one degree or another, the centerline of the stern of the boat is being lifted out of water. I think this is probably the reason that many people are under the impression that the boat is changing trim with heel.

With a conventional centerline rudder, as the center of the transom rises, the rudder is being withdrawn from the water, moving closer to the surface or even out of the water. This allows the rudder to aerate, which means that the low pressure side of this partially extracted rudder blade is sucking air down the blade of the rudder. That air mixes with the water flow and makes the flow less effective as a steering medium, and therefore makes steering harder and in the worse case, impossible so that the boat wipes out.

This phenomena is the main reason that designers have begun using twin rudders on these broad transom boats. By offsetting the pair of rudders from the centerline at least one rudder does not extract from the water and remains fully effective. And once you commit to dual rudders there are a range of tactics that designers can employ to take fullest advantage of having two rudders instead of one, such as canting the rudder vertically so that the rudder is close to vertical at the normal heel angle that the boat is designed to sail at max speed. The rudders may also be oriented so their leading edges are slightly toed in when vertical, but which puts them on axis with the centerline of the immersed hull when heeled. That needs to be designed very carefully since there is some trade off in increased drag when sailing flat.

These boats have the possibility of tracking reasonably well if the shape of the immersed area is narrow enough and generate counter-rotational forces symmetrical with the heeled rotational of the rig. It is claimed (I have not sailed one) that these boats in effect behave like a skinny boat, which will track simply on the polar resistance of the long narrow hull form in water. Looking at video of these boats sailing in waves, that appears to be the case in that when heeled, there appears to be very small movements of the helm to keep these boats on course.

Jeff
As the cone heels, the hydrodynamic centreline changes , so it points in a different direction, rounding the boat up. I have changed a boat from abysmal lack of directional stability to excellent tracking by filling out the bow by 3 inches and fining down the quarters by an equal amount. The improvement was amazing. Harrison Butler had similar results with some of his designs.
A friend had Bob design him the Reliance 37 based on his asymetric waterlines. He was very disappointed by the total lack of directional stability, and went back to the more balanced Spencer designs.
A freind racing on a Beneteau said he couldn't leave the helm for a second withour the boat broaching, even in moderate conditions. Mine gives me enough time to go to the rail and take a leak, then walk back ,before it wanders noticably off course.
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  #356  
Old 05-22-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

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Originally Posted by bobperry View Post
JonB:
I am working hard right here on Port Susan trying to create my own alternative universe.

Hot rod Alberg 35:
I hate to kill a fairy tale but here goes.
If you removed the rudder from the A35 and moved it aft on a skeg you would probably be moving the rudder about 3' considering how long the chord of the A35 keel is as designed. The rudder would be tucked up under the counter so it would have to be a deep rudder. Now add a skeg and the net result will be a gain in wetted surface. So light air speed will suffer. The only possible benefit of moving the rudder would be to possibly improve helm feel, steering and most certainly handling under power. There is nothing about simply moving the rudder aft and adding a skeg that would improve the speed of an A35.
A well raked rudder, especially a huge one, acts as more of a brake or drogue than a vertical rudder.
What sails fastest, is fastest!
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  #357  
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Re: Bob Perry's take on Wolfenzee's dream boat

still you see these designs crossing oceans on autopilot tracking like a train n a good bit of wind and sea. would think even with a hydrogenerator they would be working hard and going through a lot of juice. Have no personal experience of those boats but have been on wide stern double rudder boats that seem to tract just fine.
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  #358  
Old 05-22-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

This thread was spin off from a thread that asked about motion in modern hulls. I used my older designed hull with a comfortable motion that did not sacrifice performance as a point of reference.
Everything in life is a compromise to some degree or another, it's just alot more obvious with boats. That said at one end of the spectrum you have high tech finely tuned racing machines they are fast, but when the weather gets dicey can be a real workout and be bone jarring and/or squirrely ride.....on the other hand there are boat that incredibly comfortable in just about anything nature can throw at it but from the performance end are sea slugs (please note these are extremes to make a point). Every time you try and "fix" one of the problems you detract from what makes that boat what it is.....the "perfect boat" is a boat that satisfies the owners priorities. Example, my boat is a displacement hull, to get an 1 1/2kt out of it by making it a semi-displacement hull, you would destroy the pleasant motion, something that is more important top me.
As far the autopilot on my boat, someone put a wind vane on once, then found out it didn't need it, a lashed tiller works fine.

Last edited by wolfenzee; 05-22-2013 at 09:00 PM.
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  #359  
Old 05-22-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

I am a cruising sailor, for my application Dacron is still considered to be the best materiel for sails. As far as the new materials used for racing sails, by the time I could afford them those materials would be obsolete. The new high tech sail materials would not prove their worth (or anything near it) on my boat anyway.
I try to keep my fantasies from being too fantastic, which is why I can kick back in the hammock on my 30' cutter rather than standing on the dock lusting after a 70' schooner.
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Old 05-22-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Yes I use Dacron sails, I am a cruisng sailor, not a racing sailor. I would not gain from the the new sail materials anyway, as I do not have an unlimited income for my boat the money would be better spent somewhere else (besides by the time I could afford such sails, those materiel would be "obsolete" anyway).
My boat is my home that I live on with a modest income....not like a "rich man's toy" that a racing boat would be.
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