Swing Keels -- Pros? Cons?

[double u]

fwiw @uranium keels:
"The 22.25m ketch Pen Duick VI was built in 1973 to an André Mauric design. She entered the 1973-74 Whitbread Round the World Race, but endured mast breakage on two occasions. Tabarly also entered Pen Duick VI in the 1976 Plymouth to Newport Singlehanded Transatlantic Race, which he won, although the boat was designed for a crew of twelve and competitors endured five consecutive ocean storms. Pen Duick VI later competed against the carbonfiber-masted Heath's Condor in the 1977-78 Whitbread Round the World Race (see Volvo Ocean Race) as an unofficial entrant, due to its own exotic material - depleted uranium ballasted keel."
here:
https://en.wikipedia.org/wiki/Pen_Duick

[Polux]

Some more about modern swing keels with all ballast on the keel.

Those keels work through a single hydraulic mechanism that makes them rotate on a pivoting point. The mechanism is pretty simple and the basis were worked out by Finot back in the 70's used first on the 1978 first 22 and after that on almost all smaller first.



Except the case with Malango they are not designed to beach the boat, at least the same way the center-boarders are. On the Allures 45.9, the new boat from Allures (aluminum voyage boats) and the first one that has an option for a for a centerboard or one of those swing keels they say that the center-boarder is the boat to be beached and that the swing keel is the performance option to swallow draft.

That does not mean that the swing keel cannot be beached to do some work on the boat (you would have to talk with them to know for sure) but probably it can, like the new RM that has also a swing keel option besides the option of a normal deep torpedo keel and a twin keel. On a boat test from a main French magazine they have done that and I am quite sure they would not do that without the explicit consent of the boat builder. As you can see the boat stays quite heeled. Not a problem to work (even an advantage ) but not suitable to stay inside the boat.



I have the feeling that if there is enough interest they will work out a solution to have the boat horizontal, maybe beefing up two rudders to take the boat weight on the back. It does not seam difficult to design to me.

As most now there is already a mass production builder offering this keel, Jeanneau on the 349. I wrote extensively on my blog about that and about a sailing comparison made by the biggest European sailing magazine between the swing keel version and the deep keel version, both boats in the water at the same time. The results were surprising.

[Littlechay]

Just found this thread and saw my name mentioned earlier... However my experience on the Pelagics is far from what Dockhead wants as they are far from performance boats. The original boat sails well, not the second.

Having all of the ballast in a retracting keel makes things quite complex from a design point of view and moving that amount of metal in boat over 15m adds a lot of danger, structure (keel support and mounts for winches and hydraulics etc.) and weight whilst removing a couple of cabins worth of interior volume. There is great big hole in the deck giving you plenty of opportunities to drop stuff down the slot.

It has to be locked into place at sea and most of the existing designs mean that it has to be locked fully down so there is no opportunity to play with tuning.

Hitting, or rather grounding on, something with the keel locked is bad thing to do.

The advantage of a fully retractable keel are only in the ability to take the ground without the need for supports.

My preference especially for Dockhead's design brief may be to go for centreboard that swings into a keel stub.

I have seen a couple of nice designs that employ a fixed shoal draft keel with dagger boards that allow you to tune performance. These were in the 60' range so appropriate to this case. The dagger boards disappear into the interior furniture, are light and easy to operate, can act as legs when grounding etc. I think this would be my number one choice provided that the fixed draft can be kept at or below 2m.

As others have mentioned the rudder has to be retractable to match the keel's draft. That is usually achieved by having the top part of the rudder mounted to a skeg with the blade pivoting to a raised position behind that. Driving and maneuvering with the rudder up is virtually impossible. I would go for a design that can raise vertically but also kick out if you hit something. Not sure that anybody has done that yet but to my mind that would be the ideal. Raise it vertically to keep the steering light for maneuvering under power.

My thoughts so far... I'm not following this thread.

[Polux]

Originally Posted by Littlechay

..
Having all of the ballast in a retracting keel makes things quite complex from a design point of view and moving that amount of metal in boat over 15m adds a lot of danger, structure (keel support and mounts for winches and hydraulics etc.) and weight whilst removing a couple of cabins worth of interior volume. There is great big hole in the deck giving you plenty of opportunities to drop stuff down the slot.
...

The rest is debatable but even if a lifting keel occupies some space, much less than the one of a cabin (two cabins, you must be kidding), a swing keel is almost all out of the boat and the required space is minimum.

This is the interior of a 53ft boat with a swing keel with all the ballast on the keel. You can see the space that the keel hydraulics occupy, that is used as a small galley auxiliary table. You can see more about the boat, a very fast cruising yacht on the last post of my blog (24k on the maiden voyage).

Regarding danger to the structure on boats over 15 meters it is good to remember that a good part if not most of the new cruising super yacht (Maxi), mostly built in carbon, have lifting keels. They are high performance light cruising boats and even so have no problems with their keels. Technology and the design of swing and lifting keels evolved a lot on the last two decades.

[Littlechay]

Originally Posted by Polux

The rest is debatable but even if a lifting keel occupies some space, much less than the one of a cabin (two cabins, you must be kidding), a swing keel is almost all out of the boat and the required space is minimum.

I am talking about a lifting ballasted keel, not centre board or dagger board. Most designs on high latitude boats swing, very few lift vertically.

Edit: Just looked at the vessel in your blog post... Interesting but not a high latitude boat in any way. The keel doesn't fully retract. Good compromise to get rid of that kelp/line catching bulb though.

not kidding at all. On a big boat if the keel lifts all the way inside (swings all the way inside) it comes right up through the centre of the boat. It completely occupies the space where a central corridor would be forcing the need for a corridor or at least a walk space down each side of the keel well.

On Pelagic Australis for example the keel well occupies more or less 1m of width and about 5m of length. Add a corridor each side of that and you have at least two cabins of lost space.

In the above case the keel weights well over 11 Tonnes. There is further space occupied but the lifting mechanism, and the structure to take the loads. Remember you might have to be lifting this thing while it is bouncing up and down (if you are aground in a swell) and the loads really are enormous.

[JJ77]

Here is the interior keel case on a van de Stadt 84,it has a lead bulb of 16
tonnes which can be lifted to reduce draft from 4 to 2 meters









The white structure is the mast support,a lift keel definitely
consumes some space.

[Polux]

Originally Posted by Littlechay

I am talking about a lifting ballasted keel, not centre board or dagger board. Most designs on high latitude boats swing, very few lift vertically.
..

That it is not a dagger board or centerboard but a swing keel with all the ballast on the keel, an option regarding lifting keels with very similar performance.

Of course, it is not a boat designed for high latitude sailing but high latitude aluminium sailing boats are starting to use the same keels and the point there is not for what that particular 53fter is designed for but the space the hydraulics of a swing keel mechanism occupy on a boat. Not very different whatever the type of the boat.

Regarding modern lifting keels they don't occupy that much space and if the boat is well designed can be situated between the saloon and the cabin. not a problem at all for boats over 47 feet or so and even used on smaller boats without taking too much space. I don't have the time know. Later I will post some examples.

[Littlechay]

Originally Posted by Polux

That it is not a dagger board or centerboard but a swing keel with all the ballast on the keel, an option regarding lifting keels with very similar performance.

Regarding modern lifting keels they don't occupy that much space and if the boat is well designed can be situated between the saloon and the cabin. not a problem at all for boats over 47 feet or so and even used on smaller boats without taking too much space. I don't have the time know. Later I will post some examples.

I know the example you posted swings and is ballasted.

I agree that some of the high modern high latitude designs are using that type of design but as most don't go into high latitudes or if they do they don't go off the beaten track they don't have to be as strong or as fail-safe as the old school. They are yet unproven in terms of what kind of punishment they can take in a grounding.

Of course there is really no need to put a swing keel in a high latitude boat. Arguably a swing keel is more use when exploring the tropics. If you want a swing keel for an expedition boat it must enable the boat to sit upright when it dries so that it allows you to perform maintenance; that's a big plus for an expedition boat.

For a boat under 50' I just wouldn't bother with the added complexity and compromises. Over that length I would consider something that doesn't compromise the performance too much but I think I'd go with removable/replaceable dagger boards and keep the keel fixed.

[Polux]

Here you have the version of the Atlantic 51 with the lifting keel. As you can see it does not occupy so much space. It is a Dutch aluminum boat designed for high latitude sailing without loss of sailing capacity.

[stevewrye]

Originally Posted by Littlechay

I know the example you posted swings and is ballasted.

I agree that some of the high modern high latitude designs are using that type of design but as most don't go into high latitudes or if they do they don't go off the beaten track they don't have to be as strong or as fail-safe as the old school. They are yet unproven in terms of what kind of punishment they can take in a grounding.

Of course there is really no need to put a swing keel in a high latitude boat. Arguably a swing keel is more use when exploring the tropics. If you want a swing keel for an expedition boat it must enable the boat to sit upright when it dries so that it allows you to perform maintenance; that's a big plus for an expedition boat.

For a boat under 50' I just wouldn't bother with the added complexity and compromises. Over that length I would consider something that doesn't compromise the performance too much but I think I'd go with removable/replaceable dagger boards and keep the keel fixed.

I agree with Littlechay that a centerboard boat is not needed in high lats. A Mcurdy Rhodes aluminum design will do just fine. One thing though it makes it nice to have board up when running before a major storm which happens far more often than we would like at high lats. The centerboard option is for places with huge tides,(English Channel) and where there is a whole lot of coral. The Bahamas are made for centerboard boats as are the San Blas Islands of Panama. I know we used the centerboard option to our fullest advantage along the East coast of the USA this year. When there were weather reports of late afternoon squalls up to 50 knots we could find amazing places to pull into that traditional keel boats could not. Safe and sound at anchor in a shallow but well protected cove and we could actually enjoy watching amazing acts of nature go right on by. Big squalls happened often this year and we were glad we had the Boreal.

As far as working on a centerboard boat while beached, we found it not a good idea in the USA because there is always some big home with its owners watching and I would assume that they are not too keen on us scrubbing our buttside in front of their house. But hey in a Brazilian or Borneo tidal river the curious locals might even walk out and help.

[UNCIVILIZED]

On lifting keels, as shown already, their keel cases needn’t take up much space down below. And you can have very large boats which when their keels are up, draw less water than many multihulls. Beluga, a Lavranos design, for example, draws 3’ with her keel up & her rudders in place, yet she’s almost 50’ long. Lavranos // Marine Design

He’s also drawn many other large cruising & racing boats which prove wrong the assumptions that cruising boats need to be heavy in order to be tough, that they need to be made of metal to achieve same, or that deep draft is a requirement for boats over 50’ in length. As there are quite a number of large boats on his website alone which draw 2m, or far less. Much as is the case with many of the Dashew’s designs.
Nor is he unique in this regard. Whole issues of periodicals routinely are published detailing a multiplicity of such custom vessels.


One other point about the space lost to keel cases is that in boats of the size in question, having such a boat be open across her full width isn’t necessarily the wisest plan. Since, realistically, in any kind of seaway, one needs structure to brace against. Both when moving around belowdecks, as well as when sitting or reclining. The idea of having huge open spaces inside of a boat is a very recent development, & one which flies in the face of good seamanship, & seaworthy designs.

For as I said in another thread on boat buying, “when you become enamored with a (so called) modern boat’s large, open spaces, & her furniture which resembles that in a house. Have your mate push you across said expanses as forcefully as possible, onto those square cornered furnishings. It helps to weed out the poorly designed boats rather quickly”.


Another firm/NA who’s done a lot of work in these types of custom boats, & others, is Van Gorkom Yacht Design. Attached below is a link to one of their boats of 20m+ in length, but with a lifting keel. She draws 2.1m. They’ve also done a lot of work on water ballast, keel engineering, & other custom bits.
The Korora 68 - Van Gorkom Yacht Design
Appendage Refits - Van Gorkom Yacht Design
Why Keels Fall Off - Van Gorkom Yacht Design
Water Ballast....Race Boat Applications - Van Gorkom Yacht Design
Laminate Analysis...Upgrading with Reduced Risk - Van Gorkom Yacht Design


Also it’s relatively easy to design a crash box for lifting keels that will absorb the energy of an impact which is sufficient to stop her from 12 – 15kts, without holing her. This is also true of fixed keels on composite boats. Much as is the case with S/V Rocket Science, as I stated earlier.
Below is an out take of her design description, the link to which is also provided. BTW, she’s a 20yr old design, & her design wasn’t, nor is it, anywhere near the limits of yacht design or construction. So that a lot more is possible in terms of trick features if you have the $. Technical Details | The new Adventures of s/v Rocket Science

“To add to stability and maintain a low center of gravity a bulb was placed
on the bottom of the keel. The bulb is approximately 6500 lbs. and is all
lead. The keel strut weighs approximately 1400 lbs. and also has an
additional 700 lbs. lead poured into the bottom of the keel. The total
weight of the keel is 8600 lbs. The keel strut is welded out of mild steel
and is galvanized and then coated in epoxy. The keel is mounted in an
aluminum Crash Box that is bolted into a carbon fiber grid. The keel Crash
Box protrudes approximately 18 ” into the boat and the aluminum structure
takes the side loads. The keel is held in place by three pins and is
designed to pivot like a centerboard in the case of a grounding in order
to absorb the loading. The aft lower pin is the pivot pin, the upper front
pin is the “Fuse” pin and is designed to deform or break in a catastrophic
grounding that exceeds 12 knots and allows the keel to pivot and the lower
pin is bushed in a UHMW race that absorbs and controls the aft rotation of
the keel strut. In this condition the keel has pivoted approximately 20
degrees but the boat can be sailed or motored in this condition and is
structurally sound. The pins can be removed and the keel re-bushed and
reinstalled. Also this set up will allow for a modular keel such that a
person could easily fit the boat with a keel strut to allow for a 6 foot
draft. Also a person who wanted to motor the canals of Europe could easily
remove the bulb and strut and carry the strut in the dinghy garage or ship
it to a yard on the Med or Baltic bolt the bulb back in place on a very
short dummy strut and have a very safe boat to motor with less than three
feet of draft”.

[Littlechay]

Originally Posted by UNCIVILIZED

One other point about the space lost to keel cases is that in boats of the size in question, having such a boat be open across her full width isn’t necessarily the wisest plan. Since, realistically, in any kind of seaway, one needs structure to brace against. Both when moving around belowdecks, as well as when sitting or reclining. The idea of having huge open spaces inside of a boat is a very recent development, & one which flies in the face of good seamanship, & seaworthy designs.

I definitely wasn't supporting large open spaces. I have seen first hand the damage that can be inflicted on people flying across large spaces... lost count of the amount of broken ribs that I have seen because of that. In fact I designed removable dividers for one boat that fit into a ball socket in the floor and clamp to handrails on the deckhead to stop people from taking fliers.

However if the keel is to retract right up through the deck it does generally split the forward end of the saloon right where you might want to put a corridor to the cabins forward. If that case is long you'll need a corridor either side or have asymmetric cabins, no bad thing. It might also mean two watertight doors instead of one if you are putting compartments in.

Just a comment on bulbs .. for a high latitude boat (or even a temperate water boat is some parts) you don't want a bulb that projects forward of the keel as it will catch kelp right when you don't want it to; ditto pot lines.

[Ingersol]

BENETEAU 323 SWING KEEL. 2006

Have owned it for 4 years with no issues what so ever - great in the shallow waters around Tampa - sail well with it up or down - 31" up as in picture approx. 7' when fully down. Would highly recommend if you sail in the skinny area!

[roverhi]

If you are talking arctic sailing, a retractable keel or center board is a good thing to have. Get caught in the ice and have to winter over, a shallow draft boat cam pop up on top of the ice and survive where a deep keel boat will get stuck in the ice and possibly crushed.

[Littlechay]

Originally Posted by roverhi

If you are talking arctic sailing, a retractable keel or center board is a good thing to have. Get caught in the ice and have to winter over, a shallow draft boat cam pop up on top of the ice and survive where a deep keel boat will get stuck in the ice and possibly crushed.

Nah.. that is very debatable. Depends on a lot more than that. The hull form is what decides if the boat pops or not, the keel will follow. You would usually choose a fairly shallow area and be tied in so a retractable keel helps with site choice.