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Old 01-16-2006, 10:55 AM   #1
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Default Twin keel sailboats

I've recently found myself intruiged by the advantages of twin keels. I'm not much of a performance freak, so the benefits in terms of planing aren't of great interest, but the draft reductions and ability to dry out on sand flats to work on the boat are intruiging.

There is amazingly little information out there on twin keel boats, though. How do they handle when it starts getting rough? Does the lack of a deep keel negatively effect their stability and capsize characteristics? Does a twin keel boat heave to effectively without as much lateral resistance as a deep keel?

Any pointers to information, or local Seattle twin keel boat owners who feel like chatting, are much appreciated!

Thanks,

--Derek
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Old 01-17-2006, 01:59 AM   #2
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Twin keels. Do you mean something like a monohull with "bilge keels"? Or are you talking about a catamaran?
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Old 01-17-2006, 02:07 AM   #3
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yes, a monohull with bilge keels is what I'm referring to.

Thanks,

--Derek
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Old 01-17-2006, 05:54 AM   #4
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I guess there is amazing little information out there on bilge keel yachts for the reason that there is an amazing few of them out there. The only ones I know of are of steel construction in the 'cruising yacht size' but I'm not in the habit of lifting a yachts skirt to look so maybe there is a few glass ones about.Without being complicated if the keel surface area of a twin bilge keeler is on par with that of a single keel then to my mind it should perform about the same. That's not complicating the thoughts about water being denser at 8' than it is at 4' but to keep it to a simple understanding.

That said, and bilge keelers being around for so long they haven't made an impact in numbers which makes me think that they have disadvantages that out weigh the only two advantages that they have; and you have mensioned those.... or that we have become a die hard single keel lover. Mmmm, a simple question asked has given us something to ponder about over coffee.[?]

Regards

Peter
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Old 01-31-2006, 06:04 PM   #5
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Hi guys was googling around twin keels updating self on recent designs when ran across this discussion. Cruised extensively for six years in a twin keeler some time ago. This was a Robert Tucker designed Mistress. Boat hove to comfortably in breeze to 40 knots or so and would lie a hull to in excess of 60 knots moving sideways at about 1 knot. Would never suggest this is comfortable though.

My current boat a minitransat 6.5m with foils for keel and rudder does neither of these things well however it was not designed for cruising. Am planning my next cruising boat which will almost certainly be twin keels again. Hope this is useful.
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Old 01-31-2006, 10:17 PM   #6
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Hi Guys,

Easy day at the office today - love these sites.

If you live in a non tidal area it is unlikely you'll see many as being able to take to the ground and sit upright is perhaps the only advantage of a bilge keeler - and its rare you'll do this elsewhere.

HOwever, if you live on a tidal coast and do not have berthing facilities behind dock gates - bilge keels, along with lifting or swing keels, are the way to go.

They don't - whatever others may think - go to windward as well as a single deeper keel.

Cheers

JOHN
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Old 02-01-2006, 04:35 PM   #7
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Hi,

I don't live in a tidal area and my sailing is confined mainly to the Baltic (at least for the moment) so I can see no advantage in bilge keeled boats in that area. In fact, there are astonishingly few of them but.....

get arround to the other side of Denmark, the North Sea side and conditions change greatly. From a tideless, brackinsh lake (the Baltic is really almost a lake; though a big one)one comes out into an area of tides, mud flats and sand banks. Not surprisingly bilge keelers have a much greater following arround the British Isles and the North Sea coasts of mainlan Europe.

Bilge keelers are immensly popular in this area. They are very practical as they can dry out (making cleaning the inderwater hull and anti-fouling a simpler job), cheaper half-tide moorings can be used and even when lifted out for the winter they need no cradle.

Many bilge keelers have performed well throughout the years. The British 'Kingfisher' is an example of a well built, sea-kindly, low cost bilge-keeler. Incidentally, the Kingfisher is rather unique in that she uses the bilge keels as fuel tanks - a bit like aircraft wings! Pick up a copy of Yachting Monthly or Practical Boat Owner and you will find stacks of them for sale. These mags also frequently include articles about bilge-keelers.

What's the down side. Well, bilge keelers don't point as well and tend to slam into waves more than a long keeled boat, but so does a fin keeler.

There is no doubt about it, if I saied frequently in a tidal area where I could creep up a little creek I would have a bilge keeler.

Cheers

Stephen

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Old 02-02-2006, 08:38 PM   #8
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Stephen's referral to YM and PBO is on the mark; many articles on both new designs with bilge keels and performance-oriented comparisons. As one example, they (both mags are owned by the same publisher) tested two new Sadler 29's side by side, one with bilge keels and one with the standard fin keel. The most interesting conclusion in their eyes was how well the twin keeler did relative to its deep fin sister (tho' the fin did perform a bit better to windward). Illustrating Stephen's comment about tidal waters invite sailors to favor bilge keels, one of the USA's main builders - Hunter - builds only with various conventional keels for the N American market but offers many of their smaller models with bilge keels from their UK manufacturing plant.

A good friend finished out a 29' bilge keeled sailboat and then cruised it for a while out of England's South Coast. What he had to say about the experience was a real eye-opener. While articles and cockpit discussions tend to focus on sailing performance differences, he found a bilge keel yacht impractical and even risky for some cruising grounds for a different reason. Basically, what he found was that many bottoms on which he wanted to take the ground at low tide were unfriendly or hostile to a small yacht - e.g. there may be large rocks unseen at mid-tide but which the yacht settles on as the tide runs out. Other bottoms may themselves be acceptable once the boat has fully grounded but the problem is that transition period when e.g. surge, wind-driven chop and/or wake causes the keels to bang off the bottom before she fully settles. This isn't a problem in some areas that are heavily tidal - e.g. the Dutch & German Frisian Is. or up some of England's East Coast rivers - because the tide is extremely high and so the transition period is short, and more importantly the bottom is mostly sand and forgiving. But for other areas (France's Atlantic coast, most of the UK and the Channel Is. all come to mind), this can be a problem.

Second, I notice that with few exceptions most bilge keelers are <10M LOA. I suspect one practical reason for this is that, in many sailing waters, tidal range can be <1-2M. Consequently, the advantage of drying out the hull is lessened because, when one starts with the insurance of some depth of water under the keel, the larger boat won't fully dry out.

There are some cruisers who swear by bilge keeled designs and love the fact they never pay for a haulout. They claim performance can be comparable. Other bilge keel boat owners complain of a range of performance and other problems, and move on to another hull form (such as my friend). However, it seems the overarching criterion should be how suitable the sailing/cruising grounds are for the bilge keel hull form.

Jack
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Old 02-08-2006, 06:09 AM   #9
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Hi again

Just to clarify the difference between twin and bilge keels. Twin keelers like the Robert Tucker "Mistress" have the ballast in the keels and when heeling are designed to have a ballasted keel vertical providing maximum lateral resistance with the other ballasted keel almost breaking the surface producing enormous downward force and stiffness. A bilge keeler like the Maurice Griffiths "Waterwitch" on the other hand has central ballast usually internal with two blates for sitting upright on the hard.

My experience is the twin keeler easily outperforms the bilge keeler and many long keel cruising boats to windward but will do as well as a fin keeler. I expect this is due to the additional wetted surface. Downwind they are incredibly comfortable refusing to develop a roll under any conditions unlike some single keelers.

If you are looking for a shoal draught boat and apprecite the benefits of being able to dry the boat out without slipping facilities I would suggest looking at a twin keeler rather than a bilge keeler.

Dave
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Old 02-08-2006, 07:06 AM   #10
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Oh right, how interesting! I was unaware of this distinction between twin keels and bilge keels. I had been using them interchangeably. Thanks! And thanks to everyone else in the thread for lots of informative responses...
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