Swing Keels -- Pros? Cons?

[justwaiting]

Originally Posted by Dockhead

But neither of those would be any good for uncharted rocky waters. You need one which will swing back harmlessly if you hit something with it.

A couple of questions come to mind with what you have said so far ..

From my limited knowledge ... you have the options of either the swing keel being "weighted" and forming a significant part in the ballasting of the boat or an unweighted swing keel.

In the first case it would take more force for the keel to swing back on impact. In the second case while the keel would swing back more easily the boat would need more ballast mass to compensate for the lack of depth effect of leverage.

From what I understand you already have increased weight and raised the centre of gravity by (sensibly) requiring a protected helm position or full pilot house. I guess that this is in part offset by considerations about a dingy garage rather than having davits.

In relation to this you also need to consider the material that the swing keel will be constructed from. Assuming that you go with an Aluminium construction (in part from its qualities as well as the relative cost effectiveness in constructing a customised or semi customised boat) then having an unweighted swing keel would almost mandate an aluminium swing keel. A couple of things that you may wish to consider would be the use of encapsulate lead ingots as ballast (cost not withstanding) or possibly a stub keel with a smaller swing keel attached to the base of the stub keel.

I hope that makes some sense, lol

[belizesailor]

Originally Posted by justwaiting

...

From my limited knowledge ... you have the options of either the swing keel being "weighted" and forming a significant part in the ballasting of the boat or an unweighted swing keel.

In the first case it would take more force for the keel to swing back on impact. In the second case while the keel would swing back more easily the boat would need more ballast mass to compensate for the lack of depth effect of leverage.

...

The terminology is not used entirely consistently I think, but I would condiser an "unweighted swing keel" to be a "center board".

[Dockhead]

Originally Posted by justwaiting

A couple of questions come to mind with what you have said so far ..

From my limited knowledge ... you have the options of either the swing keel being "weighted" and forming a significant part in the ballasting of the boat or an unweighted swing keel.

In the first case it would take more force for the keel to swing back on impact. In the second case while the keel would swing back more easily the boat would need more ballast mass to compensate for the lack of depth effect of leverage.

From what I understand you already have increased weight and raised the centre of gravity by (sensibly) requiring a protected helm position or full pilot house. I guess that this is in part offset by considerations about a dingy garage rather than having davits.

In relation to this you also need to consider the material that the swing keel will be constructed from. Assuming that you go with an Aluminium construction (in part from its qualities as well as the relative cost effectiveness in constructing a customised or semi customised boat) then having an unweighted swing keel would almost mandate an aluminium swing keel. A couple of things that you may wish to consider would be the use of encapsulate lead ingots as ballast (cost not withstanding) or possibly a stub keel with a smaller swing keel attached to the base of the stub keel.

I hope that makes some sense, lol

Yes, I think it made sense, thanks.

This has now gotten beyond my meager understanding of the issues, so I probably don't have much of anything sensible to say about it.


I do know, however, that for power, you want the ballast as low as possible. That's why bulb keels are so good. If you can't put a bulb on a swing keel, then you can at least put the ballast (lead, or maybe tungsten) in the very bottom of the keel.

The greater draft possible with a swing keel improves the effect of the ballast -- you get more righting moment from the same mass of ballast. So compromising with the shape -- no bulb -- probably doesn't make any difference. Especially if you use something super-dense like tungsten, which is almost twice as dense as lead. Tungsten is also very hard, so maybe you just bolt a tungsten tip onto the bottom of the keel.

I don't know why having a lot of ballast in the bottom of it, would reduce the benefit of a swing keel in case of a hard grounding. The main thing is that instead of stressing the keel-hull joint, the keel will swing and allow the boat to continue moving forward. Of course more weight in the keel means the impact will be greater, so more damage to the keel itself, but if you save the boat, I don't really think I mind so much.


The issue of hard grounding is actually really important for anyone thinking about sailing in rocky uncharted waters, and I do.


I guess it would be quite an engineering challenge to make the swinging and lifting mechanisms for a three meter long swing keel (to make four meters of draft) with a few tons of tungsten in the bottom of it. For "quite an engineering challenge" read "$$$$$".

Part of the specification would be that the whole structure would have to be designed to exclude any chance of breaching the hull, from any kind of impact to the keel from any direction. It would be quite a complex design task I guess.


A stub keel would certainly simplify the design and make it easier to make very strong. This might be a worthwhile compromise.

Maybe it's also worth having some ballast in a stub keel to ensure that the boat still has a bit of stability in case of losing the swing keel. This would be harmful to performance, but a great benefit to safety.

[Polux]

Originally Posted by Dockhead

Thinking about my possible, hypothetical, new boat, which I would make for heavy duty, high latitude, long distance cruising.

I spent a fascinating day at the KM Yachts factory in Makkum, Holland, on my way back from the Baltic, in August, kindly arranged by CF's Noelex and SWL, and this yard is presently at the top of my list for my hypothetical new build.

Most of the boats they make -- and many of them are for the kind of duty I have in mind -- have swing keels.

I wonder if this is worth considering?

I've been living with 2.5 meters of draft, and other than in the Ijsselmeer, it has not really been a big problem.

But the next boat will be a little bigger (60' to 65'), and once we start to talk about 3 meters or even more, then this starts to be a different question.

And in any case -- any fixed keel is a compromise. A moveable one could be much deeper when down.

So despite the added complexity, which is very undesirable, I started to think that this might not be a bad idea. There are a few advantages that I can see:

1. Uncompromised deeper draft when down

2. Obviously, much less draft for shallow water.

3. Dry out.

4. Much easier to put the boat on the hard; much easier to get on and off the boat when on the hard.

5. Grounding is far less scary.

But disadvantages:

1. Complexity; cost; potential for failure.

2. No bulb; probably not ideally balanced and probably not hydrodynamically ideal either.



Am I missing anything? Views? Experience?

You are missing the "new" swing keels, the ones that have all the ballast mostly down on the keel and a kind of a soft bulb. Now aluminium voyage boats started to use them and I am sure it will be a strong trend in the future. KM is building or has built the first one of this type, I mean the first for that shipyard.

Regarding the others that are typical on Dutch boats, they imply much heavier boats since most ballast is on the boat and that is a big disadvantage. A performance disadvantage that you did not have mentioned (we are talking about several Tons of diference in weight on a 50ft boat)

Regarding the advantages you did not mention an important one for voyage boat: the possibility of taking shelter from nasty weather much near the coast on an anchorage or even using anchorages with excellent shelter that are not possible with a keel boat. That is a big advantage.

As you said the drawback is cost, maintenance and not so much potential of failure because they can have a manual override. One that is very slow and painful to work with.

These keels were first developed by Finot (many decades ago) and as they have been used by more and more boats they have been perfected and work very well now. I sailed on one boat with that kind of keel, a very sportive and fast one and it looked like I was sailing a boat with a deep fixed keel.

Some testing was made between a Sun Odyssey 349 with a deep torpedo keel option and other with the even deeper Swing keel of this type. They performed much alike and if there was some performance advantage was on the Swing Keel (posted about it on my blog at the time).

Off course that does not mean that the swing keel is more effective than a torpedo keel of the same depth, just that with a deeper swing keel (that is possible because it swings for allowing entering shallow waters) the swing keel can have an advantage in performance.

Another disadvantage is an increased difficulty in maneuvering the boat on the port with the keel up. Sometimes it is best to have the keel partially down for having more grip when turning sharply the boat. I saw it done, I mean putting the keel a bit down to maneuver better.

[justwaiting]

The ability of ice to dump house size boulders in random and unexpected places can lead to many WTF moments. I spent a few years in the Shetland so I have experience some of those joys - but that was not with a 3 or 4 meter fin.

One of the possible advantages with a swing keel in the areas you like to sail (freeze) in is that it may give you the ability to use haul out facilities designed for fishing boats.

[Dockhead]

Originally Posted by Polux

You are missing the "new" swing keels, the ones that have all the ballast mostly down on the keel and a kind of a soft bulb. Now aluminium voyage boats started to use them and I am sure it will be a strong trend in the future. KM is building or has built the first one of this type, I mean the first for that shipyard.

Regarding the others that are typical on Dutch boats, they imply much heavier boats since most ballast is on the boat and that is a big disadvantage. A performance disadvantage that you did not have mentioned (we are talking about several Tons of diference in weight on a 50ft boat)

Regarding the advantages you did not mention an important one for voyage boat: the possibility of taking shelter from nasty weather much near the coast on an anchorage or even using anchorages with excellent shelter that are not possible with a keel boat. That is a big advantage.

As you said the drawback is cost, maintenance and not so much potential of failure because they can have a manual override. One that is very slow and painful to work with.

These keels were first developed by Finot (many decades ago) and as they have been used by more and more boats they have been perfected and work very well now. I sailed on one boat with that kind of keel, a very sportive and fast one and it looked like I was sailing a boat with a deep fixed keel.

Some testing was made between a Sun Odyssey 349 with a deep torpedo keel option and other with the even deeper Swing keel of this type. They performed much alike and if there was some performance advantage was on the Swing Keel (posted about it on my blog at the time).

Off course that does not mean that the swing keel is more effective than a torpedo keel of the same depth, just that with a deeper swing keel (that is possible because it swings for allowing entering shallow waters) the swing keel can have an advantage in performance.

Another disadvantage is an increased difficulty in maneuvering the boat on the port with the keel up. Sometimes it is best to have the keel partially down for having more grip when turning sharply the boat. I saw it done, I mean putting the keel a bit down to maneuver better.

OK, thanks for this, but all this information is pretty clear.

With your photographic memory for boat design brochures, maybe you could post some photos of examples?

I'm not worried about maneuvering at all. Between thrusters and leaving the keel partially down, I can't imagine there will be a problem.

The key thing is DEPTH. A deeper keel makes more effective use of ballast (assuming that you've got the ballast in the bottom of the keel), and at the same time, is hydrodynamically more effective. One ton of ballast four meters down, is as effective as two tons of ballast, two meters down, and the weight saved adds to performance or you can make the boat stiffer and more powerful for a given amount of ballast.

The more I think about this, the more I like it, but I would like to see examples of this design feature being used this way -- come on, Polux!

[Hoosiersailor]

Is there not a concern of what happens with a swing keel in the event of a knock down or capsize? Upright it works great but get it further over than sideways and how do you keep all that weight from slamming through the boat? The only swing keel boat I ever had was a Catalina 22 which I used to sail pretty hard. I never had an issue but I used to always wonder what would happen if the boat got away from me.

[SV DestinyAscen]

Originally Posted by Hoosiersailor

Is there not a concern of what happens with a swing keel in the event of a knock down or capsize? Upright it works great but get it further over than sideways and how do you keep all that weight from slamming through the boat? The only swing keel boat I ever had was a Catalina 22 which I used to sail pretty hard. I never had an issue but I used to always wonder what would happen if the boat got away from me.

Can't speak for all designs but he ones I've seen are in tension when deployed?

[Polux]

Originally Posted by Dockhead

OK, thanks for this, but all this information is pretty clear.

With your photographic memory for boat design brochures, maybe you could post some photos of examples?

I'm not worried about maneuvering at all. Between thrusters and leaving the keel partially down, I can't imagine there will be a problem.

The key thing is DEPTH. A deeper keel makes more effective use of ballast (assuming that you've got the ballast in the bottom of the keel), and at the same time, is hydrodynamically more effective. One ton of ballast four meters down, is as effective as two tons of ballast, two meters down, and the weight saved adds to performance or you can make the boat stiffer and more powerful for a given amount of ballast.

The more I think about this, the more I like it, but I would like to see examples of this design feature being used this way -- come on, Polux!

It is not about "photographic memory for boat design brochures" it is about to know about the latest evolution in what regards boat design.

I have covered extensively the subject of this type of keels (from some years now) on my blog, talking about many boats that use them and the new aluminium voyage boats that use them. I cannot post (by the forum rules) links to those posts but you can look for them.

There are a post about the new KM boat with the new Swing keel, about Allures and Garcia and also about the Comet explorer the JPK 45 or the RM among others. Lots of fast voyage boats using that concept now. The NA that use more that type of keel are Finot/Conq and Marc Lombard.

[Polux]

Originally Posted by Hoosiersailor

Is there not a concern of what happens with a swing keel in the event of a knock down or capsize? Upright it works great but get it further over than sideways and how do you keep all that weight from slamming through the boat? The only swing keel boat I ever had was a Catalina 22 which I used to sail pretty hard. I never had an issue but I used to always wonder what would happen if the boat got away from me.

No, those keels are blocked when they are down. They don't move. They have been used for many years on very sportive boats that are normally pushed harder in sailing than slower voyage boats.

One of the first fast voyage boat to use them was the Pogo. They use it on all their models including the 50fter.

https://www.youtube.com/watch?v=6Z58M6gBXJw

[Hoosiersailor]

Originally Posted by Polux

No, those keels are blocked when they are down. They don't move. They have been used for many years on very sportive boats that are normally pushed harder in sailing than slower voyage boats.

One of the first fast voyage boat to use them was the Pogo. They use it on all their models including the 50fter.

That sounds reasonable. The little Catalina had a screw type "friction" lock. I wouldn't guess that it was going to hold that cast iron keel upside down. It did make a good "depth gauge" though.

[LeeV]

I'm sure it's included or understood in a couple of the replies, but the three reasons I would never have another swing keel include:

1. the organisms, decaying matter, etc...that find their way into every possible crevice.
2. the rust and other issues associated with the lifting gear (not to mention that it's a PIA!)
3. The cost of having it removed/installed, OR the work involved in staging the boat so that you can drop the keel to work on it or its hardware.

IMHO

[Dockhead]

Originally Posted by justwaiting

The ability of ice to dump house size boulders in random and unexpected places can lead to many WTF moments. I spent a few years in the Shetland so I have experience some of those joys - but that was not with a 3 or 4 meter fin.

One of the possible advantages with a swing keel in the areas you like to sail (freeze) in is that it may give you the ability to use haul out facilities designed for fishing boats.

Yup

[Dockhead]

Originally Posted by Polux

It is not about "photographic memory for boat design brochures" . . . .

Where's your sense of humor, Polux? Just teasing.

[roverhi]

Originally Posted by LeeV

I'm sure it's included or understood in a couple of the replies, but the three reasons I would never have another swing keel include:

1. the organisms, decaying matter, etc...that find their way into every possible crevice.
2. the rust and other issues associated with the lifting gear (not to mention that it's a PIA!)
3. The cost of having it removed/installed, OR the work involved in staging the boat so that you can drop the keel to work on it or its hardware.

IMHO

First, if it's unbalasted, other than to get it to deploy, and swings it's a CENTERBOARD. If it's ballasted enough to increase righting moment when heeled, it's a swing keel. If it's ballasted and drops down vertically, it's a drop keel. If it's unbalasted and drops down vertically, it's a dagger board. The Ovni's, etc are keel/center board boats. Hobie 33's are drop keels. The Catalina 22's are swing keels. Mostly multi hulls or very small dinghys use a dagger board.

1. Have had a couple of keel/center board boats and they've been pretty much trouble free. Did have issues on one with electrolysis of the lifting cable and had to change it annually. Dyneema line has banished any possibility of that on current boat though had no issues with wire pennant. Yes you can get stuff forced up in the center board well jamming the board on grounding. A little work with a screw driver banished the offending rock in a flash. Maintenance, other than changing the cable, has been Nada in the 10 years I've owned the boat. As far as I can tell, the center board and all it's related gear remains completely as built nearly 50 years ago and is still a virgin as far as repairs needed. Don't know where rust would be issue on a properly designed system as there will be nothing to rust.
2. Blocking the boat to drop the center board for bottom paint or R&R'ing is not a lot more involved than a fin keel boat with equal draft. All the maintenance on the board I've had to do, changing the pennant, has been done while the boat hangs in the travel lift slings waiting to launch the following morning. At 35' the boat is not huge and the center board light enough that I can push it around if it ever needed to be removed. A larger boat might have more costs should the board and it's systems ever need maintenance simply because of scale.
3. Marine organisms growing in the trunk hasn't been an issue. It's dark in there so the interior of the well remains pretty much organism free. Any hard growth on the edges of the trunk or the board itself get knocked off lowering and raising the board.

A center board has the possibility of breaking it off with a side load on a grounding. There are those out there that use the board as a depth sounder but think they are asking for major repair/replacement costs. Despite my ability to 'find' the bottom numerous times, this has never happened to me. On grounding, the board has simply retracted and only one time been jammed up by a rock.

Worst thing about a shallow draft boat is a problem serious 4x4'ers have a saying for. Four wheel drive lets you get stuck in in more out of the way places. Same goes for thin water boats as you can get much closer to shore when you get hung up. Have experience as I've been able to inspect the bottom with the boat high and dry at low tide more than once.