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  #41  
Old 01-30-2012
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In the case of your Morgan OI 33, if she does not appear to heel much it is as a result of whole bunch of reasons which have very little do with the type of keel that she has or the fact that she has a comparartively low-ballast to displacement ratio for a shoal draft boat.

In the case of the Morgan 33, these are very beamy boats, with small sail plans for their displacement. They also have a lot of freeboard so that the heel angle does not seem all that extreme since the rail remains high above the water at pretty large heel angles. In fairness though, designers like Charlie Morgan, Ted Hood, and Dieter Empachter were all able to model comparatively heavish displacement designs that are less drag than might otherwise be expected. Hood and Empachter, made up for the extra displacement with comparatively high ballast ratios and generous sail plans.....Morgan on the Out Island series, not so much.
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  #42  
Old 01-30-2012
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Thanks Jeff. I'm old, but I'm still learning more about sailing every day, thanks in a large part to the Sailnet.

Cheers,

Gary
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  #43  
Old 02-09-2012
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Not referring to centerboarders or swinging keels that are a particular case it is clear to me that the design of keels and the way they carry the ballast have suffered a technical big evolution on the last 40 years of the XX century, evolution made possible by new materials, new building techniques and computerized hydrodynamic analysis of hulls, keels and ruder and their behavior.

If it is true that a full keel has some advantages over a well designed fin keel it also true that the some of advantages that a fin keel brings makes its use more appropriated in almost all situations and the way the hull, keel and ruder design have evolved on the last 50 years are a proof of that.

Even in what concerns bluewater boats that is very evident. We can pick Halberg-Rassy, Najad, Malo or any other blue water cruising boat that is not made over a 30 or 40 year's old designs, but whose designs have been modified through the years to bring to the same initial program that lead to their design 50 years ago (blue water cruising), all the advantages and benefits that modern design and new materials and technologies permit.

Since Andrews have posted already a drawing of a Malo design from the 90's we can have a look at the Malo hull, Keel and ruder evolution through the last decades (the results with Halberg-Rassy or Najad would be similar):


From the 70's:





From the 80's:





From the 90's:







Already from this century:




Regards

Paulo
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Last edited by PCP; 02-09-2012 at 09:58 AM.
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  #44  
Old 02-09-2012
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Jeff - idle curiosity - you didn't mention twin keels. I remember seeing these in the UK, where in areas with a large tidal range and shallow water you could see many smaller boats standing up high and dry, sitting happily on their twin keels, at low tide. I read somewhere that these were becoming more popular in the US also. Any opinions? Seems to me like potential for a lot of drag; perhaps stiffer; clearly more stable at on the hard!!
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  #45  
Old 02-09-2012
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I think that there are a lot of very practical reasons why Bilge Keels (twin Keels) make sense, but none of them have much to do with sailing ability. Which is not to say, that it is not possible to design a very workable bilge keel design, which will offer reasonable performance, shallower draft and so on, but twin keels generally require taking a hit on performance as compared to the same hull and rig with a deeper draft fin keel. The reality is that by necessity, bilge keels with a shallower draft will have end up with some trade off of greater displacement (since more ballast is required to achieve the same vertical center of gravity), less stability, and/or more drag (more wetted surface and frontal area).

In theory you can try to optimize the configuration of the bilge keels to produce the best performance possible, but you can also do the same thing with a deeper fin keel, so it becomes something an arms race with the deeper fin wining in term of performance at any level of optimization.

Similarly, a deeper fin keel of equal stability and weight to a particular bilge keel design would also tend to have a better motion comfort since its deeper draft would generate a higher roll moment of inertia and better dampening.

But in a broad general sense, cruising boats are rarely optimized for out and out performance. Instead they are optimized for the practical requirements of their purpose, which means greater carrying capacity, simplicity, and robustness than would appropriate for a goal of simply going as fast as a boat possibly can. In that vein, bilge keels might be seen as simply another worthwhile compromise in performance for cruising practicality.

I don't know where you read that bilge keels are becoming more popular in the U.S. but I personally don't believe that bilge keel boats are becoming more popular around here. If anything I would suggest that they are a very hard sell here on the U.S. Atlantic Coast and so would probably take a bigger depreciation hit at resale time. That said, they may be a cult boat that holds their value since so few models are available on the market.

My own personal concern with bilge keels and the reason that I personally would not buy one for myself, is is similar to my concern with wing keels. In my experience when you accidentally run either aground, it is far harder to get free. An argument might be be made that a shallower draft boat is less likely to run aground as frequently, and that arguement may have merit for some people, but it does not work acceptably well for my own personal preferences.

Jeff
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Last edited by Jeff_H; 02-09-2012 at 03:57 PM.
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  #46  
Old 02-10-2012
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A cruising requirement for me is a skeg hung rudder, whatever you do, do that, my 2 cents.
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  #47  
Old 02-10-2012
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Quote:
Originally Posted by mdi View Post
A cruising requirement for me is a skeg hung rudder, whatever you do, do that, my 2 cents.
There are some cruising boats that in their low draft version have the ruder at almost the same draft as the keel. That looks dangerous to me and on those cases a skeg rudder seems to make semse to me.

But if a boat has the keel considerably deeper than the rudder, the chances of hitting with the rudder instead of the keel are not considerable and a more efficient spade rudder is the way to go :


Loose pounds, get better feel, reduce maintenance, improve lift, reduce drag and re-learn
the joy of driving your boat.


http://www.fastcomposites.ca/publica...padeRudder.pdf

Regards

Paulo
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  #48  
Old 02-10-2012
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Quote:
Originally Posted by PCP View Post

Already from this century:




Regards

Paulo
If it were financially possible I'd have that later model Malo (or Hallberg Rassey) in a flash and given the overall build quality of the beasts I have no doubt that the Malo spade would be stronger than many skeg hung rudders.

While I would never consider a deep fin/torpedo with leading edge exposed arrangement, improvements in underwater design allow us to have faster cruising boats that do not sacrifice their load carrying capacity. It may not seem much but that extra knot or two makes one hell of a difference on even a coastal passage and without doubt enhances the simple pleasure of the sailing.
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  #49  
Old 02-10-2012
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Hey all, OP just checking back in saying thanks for the responses. Some very good stuff in here and I appreciate it.
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  #50  
Old 02-14-2012
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Caveats: As people have already mentioned, the full/fin keel discussion is complicated by the fact that displacement and hull shape are often related to the designers fin choice. Also, the type of person who decides to go offshore cruising in a fin keel boat is probably a different person than the type of person who decides to go offshore cruising in a full keel boat.

We are on a fin keel, skeg hung rudder, reverse sloped transom sloop.

A few observations from cruising down the N American coast to Mexico:
- Cruisers motor a lot.
- Cruisers in fin keel boats motor less often.
- Although one hopes one's major passages are mostly downwind, we have done a fair amount of beating coastally, particularly if we are sailing on and off our anchor.
- There are a lot of offshore cruisers in fin keel boats.
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