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  #321  
Old 05-17-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Ski:
Yep. I don't know exactly how Monk arrived at 34' by I read that when I was a kid and it stuck with me. Might even be true.
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  #322  
Old 05-18-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Quote:
Originally Posted by PCP View Post
You mean boats like these?


We can see how difficult is to sail them and how little directional stability they have

Regards

Paulo
That video is an advertisement.The conditions were perfect to film them, very very mild.They might be great boats.To me they are butt ugly but thats just me.Id rather have the float plane.Last time I cruised in Maine I saw lots of new Sabres, Hunter and Benetoes.Most of them were under power.I rarely saw one sailing.Even in great conditions.They had every concievable electronic doo dads and acres of cloth covering the cockpits.All they really need are fish fightings chairs and beer holders.High performance is a very relative thing, a 40 year Newick Val will still sail circles around most mono's out there.It will be cold and wet as hell but at 20+ knots no time to think about it.
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  #323  
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Re: Bob Perry's take on Wolfenzee's dream boat

Quote:
Originally Posted by jak3b View Post
That video is an advertisement.The conditions were perfect to film them, very very mild.They might be great boats.To me they are butt ugly but thats just me.Id rather have the float plane.Last time I cruised in Maine I saw lots of new Sabres, Hunter and Benetoes.Most of them were under power.I rarely saw one sailing.Even in great conditions.They had every concievable electronic doo dads and acres of cloth covering the cockpits.All they really need are fish fightings chairs and beer holders.High performance is a very relative thing, a 40 year Newick Val will still sail circles around most mono's out there.It will be cold and wet as hell but at 20+ knots no time to think about it.
No, the film is not an advertisement but a test sail by Yachting World Magazine and regarding the weather they got the weather and wind they got on the booked test sail days. The tester is a very known one, a very competent and hugely experienced guy. I am surprised you don't know Toby Hodges.

This is a promotional video by Benetau: can't you see the difference?



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Paulo
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Last edited by PCP; 05-18-2013 at 09:02 AM.
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Re: Bob Perry's take on Wolfenzee's dream boat

"This is a promotional video by Benetau: can't you see the difference?."
Nice Babe.The music is excruciating, whoa!.Yachting Worlds music was much nicer.Sade Adu could have done it.Would have been nice to see her in it from her 'smooth operator' days.She could have been cranking on the winches, setting the point zero,climbing the mast or landing a tuna on that swimmimg platform thingy.I cant believe I dont know Toby either.
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Re: Bob Perry's take on Wolfenzee's dream boat

Bob,

maybe my perfect boat will have to go back to around 36-37' loa and a dwl of 35-36' from 39-40'/37-39'...........hmmmmmmm........wonder how the spouse will like that? NOT!!!!!!

Not sure a phrf on wolf boat would be in the low 200 range. I would swag at least locally in themid 240-260 range. Unless it is that much quicker than I think. as a lot of current design fin keelers with simaler size specs other than wt, are in the 190-220 range. Mine included in the faster end of that relm. Altho on the east coast, my boat is rated some 20 secs a mile faster. Then again, I've heard a rumour that phrf-nw takes the US ave and derates by 10% slower............this is across the board so it makes a more even race due to conditions here......how true, not sure.

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

Quote:
Originally Posted by jak3b View Post
...I cant believe I dont know Toby either.
For some years now Yachting World magazine has the movies of their test sails online. Most of them are performed by Toby Hodges. There are about a hundred of them on line...nice movies too.

http://www.youtube.com/user/yachting...ag_id=&sort=dd

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

Marty:
I agree with you. I was thinking around 235 so an initial "punitive" provisionsl rating of 225would see a reasonable place to start.
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Re: Bob Perry's take on Wolfenzee's dream boat

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
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  #329  
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Re: Bob Perry's take on Wolfenzee's dream boat

Jeff- are there any disadvantages to the wide stern double rudder vessels. I thought that given the designs we ( wife/self) looked at it seemed usable space ( carrying and accommodations) was somewhat comprised aft of the companionway. Also thought higher risk of picking up lobsterpot lines and seine nets. Also thought boat would be more sensitive to weight ( supplies, spare anchor, etc.) placed near the stern. Finally though broad reaching the part of the now aerated stern would be slapped by the wave train. Issues of rudder feel and reliability seem to have been solved by having direct linkage to wheels.
?Your thoughts. Note you designed a single rudder boat as your "ideal boat". ?Why.
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Re: Bob Perry's take on Wolfenzee's dream boat

Two of my most "radical" designs ICON 63' and MERIDIAN 70' both with very fine bows and wide sterns, single rudders, are both boats with very good directional stability. They drive like they are on rails. Of course with their big rigs, ICON's SA/D is over 27.00, you can put up a huge chute, push the boat to the limit and eventually wipe out if you try hard enough and it's blowing enough. But in cruise mode with a small chute they are both very benign and forgiving boats to sail. I've never seen a boat that would not round up if you pushed it hard enough. Of course some cruising boats have such short rigs that it's hard to ever push them that hard and in most cases the cruising crew is not going to fly a chute when its blowing 30 knots.

Again I don't buy into silly generalizations about boat shapes and performance. Too many variables.
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