Twin keels or bilge keels..?

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kilkerr1

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What's the difference between bilge keels and twin keels?

tome mentioned, during my <A target="_blank" HREF=http://www.ybw.com/cgi-bin/forums/showflat.pl?Cat=&Board=ym&Number=480459&page=0&view=collapsed&sb=5&o=93&part=all>question about the Kingfisher 30</A>, that the designer of the boat, RAG Nierop, said: ‘We make twin-keelers, not bilge keelers. The boats are designed as twin-keel boats...'

Definitions please!



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I have read in some books that Bilge Keels are what some would call Bilge Plates & are added to stabilise a shallow fin keel when drying out. Maurice Griffiths Eventides were good examples of this layout.

What most people call Bilge Keels ie. two keels only & no centre keel are in fact Twin Keels.

Hope that helps.

Martin

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Twin keels are supposed to be narrower and more hydronamic ..... supposed to perform better and not degrade sailing performance so much ..... oh yeh ?

Bilge Keels are generally longer in length and designed more for standing the boat than real sailing efficiency !

But nowadays the difference has eroded away and its a very grey area between them - I for one would never call a Kingfisher a Twin Keeler, but Hunter - that is the UK version - yes.


<hr width=100% size=1>Nigel ...
<A target="_blank" HREF=http://www.qqbaltic.com/index.html>http://www.qqbaltic.com/index.html</A> For all those disbelievers ! /forums/images/icons/cool.gif
 
On a commercial ship your explanation is spot on ..... as there are steel plates welded at angle to the hull at turn of bilge ...... but these are for stability not sitting on .....
Many new builds in fact don't bother with them now.

On yachts bilge plates are plates, keels are keels. and Bilge keels do not necessarily mean there is a central keel - my Snapdragon was a triple keeler ....


<hr width=100% size=1>Nigel ...
<A target="_blank" HREF=http://www.qqbaltic.com/index.html>http://www.qqbaltic.com/index.html</A> For all those disbelievers ! /forums/images/icons/cool.gif
 
Dunno exactly, I also found this interesting and JJ never replied.

I get the impression that Mr Nierop (being an aircraft engineer) used fuselage theory when building his boats. All the pics I've seen of his keels reinforce this view. There's no doubt he 'over-built' with massive lay-ups, perhaps thinking of crash landings (joke).

My interpretation of his remark ‘We make twin-keelers, not bilge keelers' is that he worked out the loading using wing theory. This is probably very smart and I'd love to sail one of these hard-mouthed boats, if only to better understand the mind of Mr RAG Nierop.

Puzzled as you are!

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Hardmouthed?

The tendancy to gripe to windward as the yacht heels and needing excessive helm to bear away.

There are FAR worse early production bilge-keelers than Kingfishers in this respect, believe me! The K30 acquired this reputation from Chay Blythe, who attempted (and failed) a circumnavigation in one with no previous sailing experience, and who at the time had no standard of comparison and simply didn't understand the limitations of this keel arrangement and why, unlike the long-keeled short handed ocean cruisers of the day, it wouldn't hold course in big seas. But the yacht looked after him well enough for him to go on to better things.

Personally though I like the K30 much less than the K20 and K26. I met 'Rags' Nierop twice. Whether that helps understand his mind is a mute point - not an easy man, but then he was a pioneer.



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Re: Hardmouthed?

I see, I see. Thanks for that, v. clear explanation. Interesting to hear about Chay Blythe's experiences too. Have been trying to track down a copy of his book 'An Innocent Abroad', which details some of his Kingfisher exploits, but so far haven't found it.

Cheers for your answers all!

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Re: here ya go?

<A target="_blank" HREF=http://www.amazon.co.uk/exec/obidos/ASIN/024550480X/qid=1078847758/sr=1-7/ref=sr_1_10_7/202-2890910-8997436> chay blyth innocent abroad</A>

<hr width=100% size=1>Beer. Source of and answer to all life's problems.
 
The two terms have got a bit muddled up, to be honest, and are commonly used synonimously.

The term bilge keeler arose from the plates attached to the bilges to balance a shallow fin keeler as has already been mentioned.

The term then evolved with yacht design to refer to any boat with two keels side by side.

Some designers and builders who felt their keel designs were a cut above the original concept in terms of performance didn't like their boats being associated with them in name and so coined the phrase 'twin keel'. Nierop was one, David Thomas another

If you wanted to differentiate between the two I would suggest bilge keels for the outer two of a triple keeler and twin keels for the rest. Common usage, though doesn't reflect this. To differentiate between twin keels and bilge keels on the basis of performance would be very difficult, even envidious.

In the meantime I am afraid I will continue to use the two terms indiscriminately to refer to any yacht with more than one keel side by side.

<hr width=100% size=1>JJ
 
Re: here ya go?

Aythengew, Mr Sailbad. Now how is it that I was unable to find it, being both a literary lass and wise in The Ways of The Web?

40 squid though, blimey. Is it bound in Iroko?

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'twin keels' means my bilge keels are better than yours.

hunter have gone one better and refer to theirs as 'twin fins'

it's only a way of trying to beat the bad image created by early examples of the type.

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Surely, James, your "bilge-keel" boat would be referred to as a Triple-keeler.
Therefore the term bilge keel has to be redundant in your parlance.

However may I further confuse the issue:-

To me twin keels are generic - any boat with two keels can be called a twin keeler, whereas to me a bilge keeler has a dihedral of about 15 degrees on the keels and keels mounted at or near the list centroid.

It would be interesting to obtain opinions from say Colin Mudie, Bill Dixon and Tony Castro (as 3 extremely varied naval architects) to find out what they understand by the two terms.

As an aside, it's interesting to not how popular bilge (my definition) keels are becoming amongst avant-garde French designers.
Now what about Open 60s with that long tilting keel and their twin daggerboards...?



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