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  #71  
Old 04-20-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Quote:
Originally Posted by Jeff_H View Post
...

So here is an update lines drawings:



And here is a fist look at the updated rig which is loosely modeled on a Folkboat rig, but with a taller foretriangle:

Nice drawings Jeff.

Looking at the lateral view I thought how well the boat would sit in beach like that, for cleaning repairing and doing antifouling. Of course, for that you need one more leg I am talking about a twin keel. With that draft and taking into consideration that it is a narrow boat that will sail with considerable heel, I think a twin bulbed keel would work better than a bulbed fin keel boat.

I have been following the French developments in what regards twin keels. Thy use them in performance cruising boats when they want to propose a version with a smaller draft. They are less efficient than a deeper keel providing the same RM but more efficient than a single keel with the same draft of the twin keel.

They arrived there after many years of development and as several brands propose the boats on the two versions they have been testing them in the water with boats side by side, boats equipped with the two types of keels: RM and JPK have made public the results and as I say, they are amazingly good in what regards twin keels. I would have expected a bigger difference due to drag but the results come very close, being of course slightly better on the deeper fin keel.

Regards

Paulo
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Last edited by PCP; 04-20-2013 at 02:01 PM.
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Re: Bob Perry's take on Wolfenzee's dream boat

Realize the small main and large genny was a distortion from racing ratings but don't understand why they have fallen out of favor. Seems convenient to pole out in light to moderate air downwind rather then dealing with dedicated downwind sails. Please teach us. Thanks.
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  #73  
Old 04-20-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Paulo:
Unless you can retract the keels twin keels have proven over and over to be very slow. There is a huge increase in wetted surface. I think there are places where a twin keel boat would be ideal so the boat can sit upright on the mud at low tide but for Puget Sound that is not very likey.

I would be interested in seeing the study that shows otherwise. I'd have to know exactly how they are defining "efficient". Can you provide a link to that study please? But if it is in French then I won't be able to read much of it.
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Re: Bob Perry's take on Wolfenzee's dream boat

Out:
It is pretty clear now that putting the big sail on the boom and keeping the fore truiangle small is the best and most efficient way to sail. It's an easier rig to handle and it's faster.

With a big fore triangle you need a vast inventory of jibs and genoas to cover the wind range. With a fractional type rig you can shape or reef you main to poower up or power down the sail plan while sailing with two jibs. The jibs are small so they are eqast to change and the big sail is on the boom where it's easier to control. Advances in sail fabrics have helped to make the fractional rig work. I owned a fractional rig boat for 15 years. I sailed with two jibs and in 15 years I never once reefed my main.

Not sure we can use "convenience" and "performance" in the same sentance. But if there is an Achilles heel to the frac rig it's that downwind they do need a dedicated off the woind sail. Poling out the small jib does not do much for performance. But with an asym or a Code Zero style sail you can sail quite nicely.

As you mentioned the old masthead big fore triangle rig was a product of the CCA and IOR rules where headsail area was "cheaper" than mainsail area.

I go into this in some detail in the two articles I did for GOB on the CCA and the IOR.
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Last edited by bobperry; 04-20-2013 at 02:16 PM.
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Old 04-20-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Firstly it wasn't a new Genny, local sailmaker actually refused to "measure and assess" it for me telling me "the only thing it's good for is covering a wood pile" (it's a nice light air sail, going to windward as a cutter rig I no weather helm and can get alot closer to the wind).
I usually don't sail at that heel,the whole exercise was a test of how the boat behaved under waaaay too much wind for the canvas up and it was easier/safer to put up lots of sail in only 20kt wind than less sail; in a lot more wind, I learned alot about the performance of my boat, center of effort/lateral resistance, weather helm with particular sail combinations, etc. As far as what you said earlier about how she would behave with out shortening sail under circumstance where you should have shortened sail anyway it's sort of a moot point. As a cutter rig shortening headsails is easier and safer(lower one small sail rather than lower a big sail then raise a smaller sail), The main I have has a deep second reef
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Re: Bob Perry's take on Wolfenzee's dream boat

Wolf:
Here we go again:
Your words were, "To try out my new 180% genny I sailed with it and unreefed main ."

Now you say, "Firstly it wasn't a new Genny,"
One statement cannot be correct. Or do I have reading comprehension problems?

The English language is very good at communicating accurately.
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  #77  
Old 04-20-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Quote:
Originally Posted by bobperry View Post
Out:
It is pretty clear now that putting the big sail on the boom and keeping the fore truiangle small is the best and most efficient way to sail. It's an easier rig to handle and it's faster.

With a big fore triangle you need a vast inventory of jibs and genoas to cover the wind range. With a fractional type rig you can shape or reef you main to poower up or power down the sail plan while sailing with two jibs. The jibs are small so they are eqast to change and the big sail is on the boom where it's easier to control. Advances in sail fabrics have helped to make the fractional rig work. I owned a fractional rig boat for 15 years. I sailed with two jibs and in 15 years I never once reefed my main.

Not sure we can use "convenience" and "performance" in the same sentance. But if there is an Achilles heel to the frac rig it's that downwind they do need a dedicated off the woind sail. Poling out the small jib does not do much for performance. But with an asym or a Code Zero style sail you can sail quite nicely.

As you mentioned the old masthead big fore triangle rig was a product of the CCA and IOR rules where headsail area was "cheaper" than mainsail area.

I go into this in some detail in the two articles I did for GOB on the CCA and the IOR.
My boom is 50% of the length of my boat, with the J measurement being 47% though headstay is 2/3 fractional, My sail inventory is "vast" only because I haven't decided what works and what doesn't
sails:
Yankee 17'luff (storm jib which doubles as small flying jib)
Yankee 25'luff (110% Genny on headstay or flying jib on topmast stay)
Yankee 35' luff(Flying jib on topmast stay w/headstay moved to parallel)
working jib 25' luff (flown on headstay)
working jib 35' luff (flown on topmast stay w/head stay moved parallel)
110% Genny 25'luff (flown on head stay)
180% Genny (roller furler flown w/head stay detached)

note: both working jibs are reefable, 35' is heavy triple stitched
110% Genny is a light air sail, is in bad shape and is redundant because of 25' Yankee (which has several uses).
Roller furler is the old type w/no head foil, just swivels at each end, any jib with no-hanks ans wire luff works and luff of <40' works, When lowered it coils up on the deck or the bunk under the deck hatch )

Main 37'luff/15'foot
Head stay 27'/ 2/3 up mast =24' off deck
Topmast stay 40' / 39' off deck
J=13' 47%
Alternate position of head stay = 8' ahead of mast

Sorry about that Genny was new to me, I'm a poor sailor, the idea of a brand new sail is too exotic for me, I did pay more for it than any sail I have ever aquired ($300 including roller furling gear and shipping) of the 4 sails I have added to my sail inventory since I got the boat the average price I paid was $100

Last edited by wolfenzee; 04-20-2013 at 03:15 PM.
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Re: Bob Perry's take on Wolfenzee's dream boat

Quote:
Originally Posted by bobperry View Post
Paulo:
Unless you can retract the keels twin keels have proven over and over to be very slow. There is a huge increase in wetted surface. I think there are places where a twin keel boat would be ideal so the boat can sit upright on the mud at low tide but for Puget Sound that is not very likey.

I would be interested in seeing the study that shows otherwise. I'd have to know exactly how they are defining "efficient". Can you provide a link to that study please? But if it is in French then I won't be able to read much of it.

No complete study published that I know off. I am talking about direct comparisons of the same model equipped with the two types of keels, namely the RM. The efficiency I am talking about has to do with the reason some builders of performance cruisers uses twin keels: they use a deep draft fin for absolute max performance and a twin keel as the way to maintain good upwind performance with a small loss of performance on a more reduced draft.

The one that started to work on that many years ago was Marc Lombard, one of the main French NA and he was designed many performance cruisers with twin keels but probably they are not the type of keels you are thinking about.

Here you have one of his designs with the two keels on the lateral view. The one higher and with the smaller bulb (since each one has one) is the Twin keel:



I read that comparison between the two versions of this boat, both on the water and the difference was really minimal: Some few tenths of a K.

Here you have a post that I posted on interesting boat thread about twin keels. In it two articles are cited.

Note that I am not saying that a deep draft bulbed keel is not more performant. It is. I am saying that the twin keels have several advantages in what regards a reduced draft and that in this case eventually would have some advantages. The post:


Quote:
Originally Posted by PCP View Post

Quote:
Originally Posted by robelz
Speaking about JPK: What about the 38FC with double keel: Will there be a big lack in speed oder stability?


No, the stability is almost for sure the same. They normally calculate the need in ballast to have an identical stability curve. The difference in speed is marginal and will only matter to competition.

If you look, somewhere in this thread is a comparative between a RM with a mono keel and another with a twin keel, made by RM yachts. The differences are small, some tenth's of a knot.

The boat will have a better mass distribution and without sails the boat will roll less, not to mention the advantage of a smaller draft and the possibility to beach the boat for repairs or anti-fouling.

There is a good reason why lots of French performance cruisers that are used mostly for cruising use twin keels. The advantages are many and if well designed the inconvenients are not significant, just a small loss in performance.

This is a good article about twin keels, a bit partial towards them, but a good one anyway:

And from France we have what I consider to be some of the most innovative and technologically advanced Twin Keel boats ever seen, although not particularly offering shoal draft capability.
The RM range of Twin keel sailing yachts... Marc Lombard, a prolific and talented designer with Open 50 and 60 ocean racing machines to his credit, has designed the most recent boats in this range....

On many large cruising yachts it is obvious that as soon as they heel, the wide body of the hull pivots the short fin keel into a position where it is presenting no lateral resistance to the water and thus the whole boat slips away to leeward.

Indeed it could be argued that Twin Keels are the obvious choice for the
modern voluminous hull shape providing excellent accommodation for todayís
sailor who still requires good pointing ability and straight tracking....


http://www.wrightonyachts.com/wp-con...ftwinkeels.pdf

Here another slightly partial article on Twin keels.

Bray Yacht Design and Research Ltd. - The Advantages of Twin Keels

Don't let they foll you: regarding performance the only thing better than a deep draft torpedo keel is a deep draft canting torpedo keel (even if they require foils).

But when draft becomes part of the question it is well possible that the same medium draft twin keel is more efficient than a medium draft monokeel and with smaller drafts, the advantage of the twin keel becomes bigger. At least is what the French think and they have a lot of experience on the subject.

For example, regarding the RM 10.60, the two keels proposed are monokeel with 1.95m and twinkeel with 1.65m. They say that the difference in performance between both keels is marginal, even if the monokeel has a better performance but if they used both keels with 1,65m I doubt very much the monokeel would be a match. That's their point and that's why they offer mostly and recommend twin-keels for cruising.

Performance cruisers like the JPK 38, RM or Bongo they made the boats with twin and mono keels and they will provide you with all the information regarding the advantages of both systems. All of those twin keels are high performance keels.

..
Regards

Paulo
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  #79  
Old 04-20-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Interesting design Paulo and certainly not your typical twin keel boat. I know Lombard's work and he is very good. Is the boat designed to sit on the twin keels?

I can see how two relatively high aspect ratio keels could be more effective that one low aspect ratio keel in the shoal draft config. I have really never given it much thought.

Wolf:
Do you have a sail pland drawing of your boat that you can post?
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Re: Bob Perry's take on Wolfenzee's dream boat

Quote:
Originally Posted by bobperry View Post
Interesting design Paulo and certainly not your typical twin keel boat. I know Lombard's work and he is very good. Is the boat designed to sit on the twin keels?

I can see how two relatively high aspect ratio keels could be more effective that one low aspect ratio keel in the shoal draft config. I have really never given it much thought.

Wolf:
Do you have a sail pland drawing of your boat that you can post?
With head stay attached to stem (2/3 fractional) though there is a tad more camber and rake to the mast


With headstay attached parrelell to topmast stay (actual sail plan would depend on the sails)


The sailplan on the Atkin web page had an 18' boom that cleared the companionway by <1' w/self tending jib...bad weather helm and there were issues with the self tending jib
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