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Twin Keels, Bilge Keels, Bi-quilles


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#1 frede

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Posted 17 October 2013 - 11:48 PM

Twin Keels came up in the Old Ideas thread and I found the discussion interesting, particularly as I've owned a modern high-aspect ratio twin keel boat (RM 1050) and have sailed others.  I find them a great solution to a problem: sailing in tidal areas, like Brittany in France and shallow draft, though the high aspect keels aren't necessarily that shallow.  I thought I would post some of the comparative polars Marc Lombard's office has done between single keel and twin keel versions of the same boat (RM 1060).  Remember that the single keel has 30cm more draft than the twin keel, so that is skewing the results.  My sense is that a single keel of the same draft would be still possibly a little a faster upwind in light air but that it would be very close.  In any event, I think the question is largely moot since most people who choose twin keels are choosing them over centerboard/internal ballast boats (dériveurs intégraux) and twin keels are in my opinion much better performing up wind than centerboard boats.  Anyway I thought these numbers might be interesting to some.  These are percentages measuring the gain of the single keel boat v. the twin keel one upwind and downwind across the wind range from 4 to 25knts, increasing by 2knts in each column.

 

Frede

 

 

 

VMG près 7% 6% 6% 5% 5% 4% 4% 4% 4%                     VMG portant 3% 2% 2% 1% 1% 1% 0% 1% 1%

 

 

        



#2 Trov„o

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Posted 22 October 2013 - 11:52 AM

Catamarans are another solution for tidal areas.

#3 spin echo

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Posted 28 October 2013 - 08:44 PM

Mr Frede, ive been interested in RM yachts for a while, how do  you like  your boat, build quality, sailing performance, etc.  Love the twin keels, wouldnt need a diver anymore to clean the bottom.



#4 frede

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Posted 30 October 2013 - 04:27 AM

Mr Frede, ive been interested in RM yachts for a while, how do  you like  your boat, build quality, sailing performance, etc.  Love the twin keels, wouldnt need a diver anymore to clean the bottom.

I loved my RM 1050, which I sold a couple of years back.  My boat was built under the previous owners of the yard, and it was very sturdy if more rustic on the inside than the current models.  When RM started the letters stood for resolutely minimalist; today, the boats are more plush, but as far as I've seen they are still very well built by current production boat standards.  As I wrote above, I like twin keels for sailing in tidal areas.  One traditional issue with RMs is a heavy helm, which most people tend to attribute to the size (very deep) and location (quite far forward) of the rudder.  The depth and location of the rudder are in some part due to the need to beach without propping up the hull: The rudder has to be as deep as the keel and the forward placement is, as I understand it, to prevent rudder ventilation at high heel angles with a single rudder and wide transom.  The somewhat heavy helm never bothered me, but it does some people.  I have the complete polars package for the RM 1060, which I'd be happy to send to you if you PM me.

 

Best,

 

Frederique 



#5 wombat6025

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Posted 30 October 2013 - 08:58 PM

A decent lifting keel boat is also a good solution - bilge keelers do tend to be slower upwind and when you do touch bottom there's a tendency for the boat to spin around the grounded keel and wedge both firmly in the mud - with a lifting keel you just raise it a few inches and you're sailing again...

My father a ran a 32' lifting keel boat from the same drying mooring he'd had 17' and 21' bilge keelers - the 32 could get in and out on lower states of tide.



#6 Tom Ray

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Posted 30 October 2013 - 11:52 PM

Ran across this on Facebook.


multicolored-sailboat.jpg

#7 Ishmael

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Posted 31 October 2013 - 12:02 AM

Ran across this on Facebook.


multicolored-sailboat.jpg

 

Yes, that just showed up on another thread. Dylan's all over it. It's a Westerly Something.



#8 Tom Ray

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Posted 31 October 2013 - 11:33 AM

That's good, I mainly brought it over for Dylan to see.

 

It's in the Florida 120 group if anyone's interested.






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