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-   -   Does anyone recognise this weird keel? (http://www.sailnet.com/forums/general-discussion-sailing-related/12292-does-anyone-recognise-weird-keel.html)

Sasha_V 01-08-2006 11:37 AM

Does anyone recognise this weird keel?
 
This is a keel that we encountered when visiting a yacht club in Tasmania (Australia)...I have never seen anything quite like it and was wondering if anyone had any clue as to what it is and how it performs...and what it was built to try and do, that a regular keel cannot.

http://home.armourarchive.org/members/sasha/delta1.JPG

http://home.armourarchive.org/members/sasha/delta4.JPG

http://home.armourarchive.org/members/sasha/delta3.JPG

Just to show a few angles on the subject.

Sasha

Sailormon6 01-08-2006 03:23 PM

Does anyone recognise this weird keel?
 
I''ve never seen one before, but, as a guess, it might be an attempt to make the boat track as if it has a longer keel, without having the wetted surface that a longer keel would have.

SailorMitch 01-08-2006 05:43 PM

Does anyone recognise this weird keel?
 
It looks like a tandem keel (Etap currently uses them and others have in the past) with the addition of winglets. In total, it does look odd as hell, especially given the treatment at the hull attachment. Not very fair at all. It looks like someone read books on keel design and threw in all the options. What kind of boat is this on?

As for what it does a regular keel cannot -- shallow draft with lots of weight down low. But it sure looks like some extra drag in that design. Maybe the designer OD''d on Fosters and Vegemite. :)

Silmaril 01-09-2006 03:16 AM

Does anyone recognise this weird keel?
 
What a mess! I looks like someone decided to throw a whole bunch of design cliche''s all at once on to some poor unsuspecting hull!

When taken by themselves, each has merit, when incorporated into an overall deign.

The Tandem offers great tracking ability but is not usually associated with shallow draft. They are usually narrow chord/high aspect fins. The close proximity of these two, coupled with their thickness, would create a turbulence in the apeture between them that would most probably reduce the effectiveness of the trailing foil.

Wings were originally intended to give the keel an "End Plate" to help stop the downward flow off the keel. By sealing off the end of the keel with wings, a more efficient keel form could be devised, increasing all around performance compared to a traditional fin. As discovered by the American Cup team in ''83, you could not just bolt on a set of wings to reap the end plate benefit. It only worked when designed in as a system. The ones on this boat look like they are used to add a mass of lead low, to make up for the reduction in draft after loping of a few feet of keel lead.

The way it is joined to the hull shows that this was once a deep fin boat that someone wanted to go shoal draft with, while maintaining the same keel mass. Also hoping to make up for lost performance, the design cliche''s were thrown at it in what appears to be a drunken sailors nightmare.

I would imagine that this boat makes tremendous leeway, and tracks like a mouse in a maze. Probably why it is on the hard, but not being a naval archetect, it''s just my opinion.

Denr 01-09-2006 07:24 AM

Does anyone recognise this weird keel?
 
Yeah this is your standard "wingfincutaway" style keel, especially popular for those that want to go sideways as well as forward in shallow waters.

WHOOSH 01-10-2006 03:50 AM

Does anyone recognise this weird keel?
 
Sasha, you can read up on this keel development by visiting the Etap site, altho'' the keel you photographed is not an Etap as it has a broader wing than they use (as I recall, at least). There was a new brand intro''d at the London Boat Show in 2005 that featured a keel very much like this but I don''t think that brand will have circulated down to Tasmania so soon. No doubt, the keel design was applied to an earlier boat design which is what you are seeing...unless it''s an Etap.

It does raise a number of questions but it also provides some measurable performance improvements over a conventional keel. And of course, departures from anything conventional on a boat always invite lots of criticism (often in the absence of data, I might add). Perhaps it would look more ''normal'' if we viewed it in the geographic context in which it evolved: these designs come from a segment of N Europe where there is much shallow water and yet where the sailing can be spirited in winds off the North Sea. Etap (Belgium-built) is trying to appeal to a sailor who wants good performance out in the Frisian Is. or in the Dutch ''Schelde'' estuaries that have been dyked over, as well as in other waters like the Chesapeake Bay, W Florida and perhaps the Bahamas. This is just a different approach to try and minimize leeway, support ample sail area, and provide good stability, odd tho'' it might appear.

Jack

Silmaril 01-11-2006 09:15 AM

Does anyone recognise this weird keel?
 
OK, so I decided to do some digging on this. The basic design is credited to Warwick Collins.

Below is a quote from Robert Perry (IMHO one of the leading experts in sailing yach design)

"These tandem keels have been around for years and they do have some structural and pragmatic advantages but remember, there is no substitute for draft when it comes to performance. Of course, any boat with its keel imbedded in the mud is very slow. Curiously, the drawings show a deep rudder that goes with both keels and the rudder draws more than the shoal keel. I hope this is a drafting error."

Here are some other links that may shed some light on the subject:

http://www.heymanyachtdesign.com/in3a.html

http://www.sadlerandstarlight.co.uk/docs/sadler34.htm

http://forums.boatdesign.net/showthread.php?t=1058

Looks like this is an interesting subject. In addition, I found references to boats with this keel sailing at anchor. With the european prediliction to stranding a boat for bottom work, it was noted that with this keel, you need to have the boat hoisted to get to the large lower surface of the wing.

It seems that the common opinion is that the Warwick Collins keel is one of the better attempts at regaining the performance lost when one goes shoal draft.


waltward 01-11-2006 06:49 PM

Does anyone recognise this weird keel?
 


Sasha

I don''t think it is all that weird. I am not a hydraulic engineer and therefore do not know what effect the water flow would have with the two vertical keel members. If you fill it in it would not look much different from the short keel on a friends Catalina 34. Maybe there is something to be gained from the opening? Maybe it is as heavy as the designer wanted, to support the sail plan? It would be fun to see it in the water, maybe hang on to the tiller and see how she feels.To see how she really does, we could sail her against Denr''s Macgregor 26.

I think the design of that keel might be a lot safer than the swing keels the boys are sailing on the Volvo 70s down in the Southern Ocean right now.

Walt Ward

ftldiver 02-22-2006 08:15 PM

what about.........
 
that keel looks like it was made to sit on the bottom! when the tide goes out..

or is it just me?

what kinda tide ranges do you see over there?

sailnaway 02-23-2006 07:31 PM

What it does is the water passes over keel one #1 and as it does it flows to the oposite side of keel two #2 starboard to port port to starboard ect. The outcome is the boat is forced by water pressure to stay more upright and not have the healing moment it would have with a single keel. Jeff H a member here is a marine designer and could help with this subject a little more.


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