Swing Keels -- Pros? Cons?

[Djarraluda]

As a Pom, you will know of the Practical Boat Owner magazine. There was a very interesting article a couple of months ago where a chap (must have been an engineer, or a mathematician, can not recall now) designed a drop/swing keel that could be ballasted with a bulb. The complex (?) part of the movement was actually very simple and all above the waterline.
Copyright prevents me forwarding the article, but you can always get a copy direct.
He built a smallish cruiser to prove the design. Will look-out his name later, it is worth considering by the designer of your choice.

[Dockhead]

Originally Posted by Djarraluda

As a Pom, you will know of the Practical Boat Owner magazine. There was a very interesting article a couple of months ago where a chap (must have been an engineer, or a mathematician, can not recall now) designed a drop/swing keel that could be ballasted with a bulb. The complex (?) part of the movement was actually very simple and all above the waterline.
Copyright prevents me forwarding the article, but you can always get a copy direct.
He built a smallish cruiser to prove the design. Will look-out his name later, it is worth considering by the designer of your choice.

Not Pom, but Yank! Just an intruder in Pommieland.

I don't read PBO in paper and can't find the article you mention, but maybe you're talking about the Steynor Keel? Steynor Retracting Keel Company - Profile

[Djarraluda]

Originally Posted by Dockhead

Not Pom, but Yank! Just an intruder in Pommieland.

I don't read PBO in paper and can't find the article you mention, but maybe you're talking about the Steynor Keel? Steynor Retracting Keel Company - Profile

We can probably forgive the origins, after all, I am also an ex-pat but I am staying here, although as an Ex-Pom, I still read the mag.
Yes, that name sounds very familiar. It may be worth a discussion with your designer.
A while ago, I spoke with Graeme Radford here in Sydney and as far as he is concerned, Fixed keels, or drop keels with a case that runs full height in the saloon are the only way to go structurally. He was not interested in an engineering discussion re bracing a casing thad did not run full height. He may have a point on the flexing issue that is worthy of inclusion in your chats.

[Rohan]

Originally Posted by fallingeggs

Why not consider a lifting bulb keel? Seems like you could get one that also cants (awesome) or that telescopes so that it doesn't need a keel box inside the boat.

Probably because lifting keels are extremely rare. I have seen a couple on custom boats, but the only production boat I know of that uses them are the Seawards. And Seawards are really semi-custom boats.

No one has mentioned one downside to swing keels - weight. I could be wrong, but it looks like swing keel boats weigh significantly more, even more than shoal draft keel boats of the same size.

[Dockhead]

Originally Posted by Rohan

No one has mentioned one downside to swing keels - weight. I could be wrong, but it looks like swing keel boats weigh significantly more, even more than shoal draft keel boats of the same size.

If the ballast is in the swing keel, then the weight will be on the contrary less. Because the ballast is more effective, the deeper it is placed, so you need less of it.

What you say may be true in cases where all the ballast is in a stub keel, and the board is not ballasted, but I am not considering such an arrangement.

[Pete7]

If you are going for a custom build, how many of these swing/lift keels are you thinking of fitting? oh now that is a completely different train of thought You know my views on multiple keels.

What would happen if it fell off? is there sufficient ballast left to sail home either with a stub keel or flooding tanks?

If you have a swing keel what happens about the rudder? is this left exposed if the keel is raised more than say half way? Eek! Twin rudders perhaps?

Down wind you don't need so much keel down so raising it reduces the drag, feasible?

What's the plan for the propellor? rather exposed for sailing in ice and rocks, how about a jet drive?

Pete

[Dockhead]

Originally Posted by Pete7

If you are going for a custom build, how many of these swing/lift keels are you thinking of fitting? oh now that is a completely different train of thought You know my views on multiple keels.

What would happen if it fell off? is there sufficient ballast left to sail home either with a stub keel or flooding tanks?

If you have a swing keel what happens about the rudder? is this left exposed if the keel is raised more than say half way? Eek! Twin rudders perhaps?

Down wind you don't need so much keel down so raising it reduces the drag, feasible?

What's the plan for the propellor? rather exposed for sailing in ice and rocks, how about a jet drive?

Pete

Well, there are quite a number of different arrangements.

Here's how it's done on an Ovni:



This is how Southerly do it:



They are twins in the case of the Southerly.

Here is how it's done on the Allure:



And Boreal:



An article on all this on the Morgan Cloud site: https://www.morganscloud.com/2010/10...der-options-2/


Partially lifting the keel downwind will give a good performance boost; another argument for a lifting keel.

[UNCIVILIZED]

Originally Posted by Rohan

Probably because lifting keels are extremely rare. I have seen a couple on custom boats, but the only production boat I know of that uses them are the Seawards. And Seawards are really semi-custom boats.

No one has mentioned one downside to swing keels - weight. I could be wrong, but it looks like swing keel boats weigh significantly more, even more than shoal draft keel boats of the same size.

Originally Posted by Dockhead

If the ballast is in the swing keel, then the weight will be on the contrary less. Because the ballast is more effective, the deeper it is placed, so you need less of it.

What you say may be true in cases where all the ballast is in a stub keel, and the board is not ballasted, but I am not considering such an arrangement.

The comment about needing more ballast in swing keel boats is mostly correct. As with a boat with such a keel, the dead, unused space inside of the trunk cannot be filled with lead. So you need to add more ballast inside of the hull in order to compensate for this loss of Rm. Which, since the lead isn't placed as low as if it were in a (fixed) keel, you need to add more of it in order to make up for it's less than ideal location.

Going to a swing keel is more of a trade off than is a fixed, shoal draft keel. It's just hard to get around this. And in the real world it's easier to design a fixed keel which won't be damaged (much) by a grounding at moderate speeds, than it will be to assemble a swing keel with this in mind.

It's worth reading about the design of S/V Rocket Science's keel. As it was designed from the outset to survive a full speed collision with UFOs. And so are many lifting keels. The best of which are tied into the deck for more support, in addition to having "crash boxes".

On lifting keels, this one is discussed in the Dashew's Offshore Cruising Encyclopedia, though I can't recall whether or not she has a crash box for her keel. Though the 3' draft that it allows is a nice feature. http://www.lavranosyachtdesign.co.nz/py_beluga.htm
And while Icon isn't exactly a shoal draft boat, she too has a keel that retracts in order to reduce her draft (a little) http://www.iconsailing.com/boat/

[double u]

"Partially lifting the keel downwind will give a good performance boost; another argument for a lifting keel."

I'd be loath to do that: this would reduce stability, & in the event of a broach...
btw: the Ovni's isn't a "keel", it's a "centerblade" (no ballast!) - & that could be raised going downwind.

[IdoraKeeper]

The further north you go the further you are from services. Keep the deep draft. spend money on forward looking sonar. Keep a bigger dink for the longer run to shore. You dont see high maintenance stuff like that pn fish boats.

[double u]

...& what's gonna happen to the mechanism if one grounds in reverse or get shoved backwards by a sea when grounded?

[Dockhead]

Originally Posted by double u

"Partially lifting the keel downwind will give a good performance boost; another argument for a lifting keel."

I'd be loath to do that: this would reduce stability, & in the event of a broach...
btw: the Ovni's isn't a "keel", it's a "centerblade" (no ballast!) - & that could be raised going downwind.

You'd be well screwed in a broach, if it happened with your ballasted swing keel up!

Nevertheless, people do it. Common practice, for example, in Pogos.

I think the answer is this tactic is only for light weather. But that's also when this tactic is most needed.

Sent from my D6633 using Cruisers Sailing Forum mobile app

[leftbrainstuff]

The shards have some good feedback from their Southerly ownership

Sent from my SM-N900T using Cruisers Sailing Forum mobile app

[Polux]

Originally Posted by UNCIVILIZED

The comment about needing more ballast in swing keel boats is mostly correct. As with a boat with such a keel, the dead, unused space inside of the trunk cannot be filled with lead. So you need to add more ballast inside of the hull in order to compensate for this loss of Rm. Which, since the lead isn't placed as low as if it were in a (fixed) keel, you need to add more of it in order to make up for it's less than ideal location.

Going to a swing keel is more of a trade off than is a fixed, shoal draft keel. It's just hard to get around this. And in the real world it's easier to design a fixed keel which won't be damaged (much) by a grounding at moderate speeds, than it will be to assemble a swing keel with this in mind.

It's worth reading about the design of S/V Rocket Science's keel. As it was designed from the outset to survive a full speed collision with UFOs. And so are many lifting keels. The best of which are tied into the deck for more support, in addition to having "crash boxes".

On lifting keels, this one is discussed in the Dashew's Offshore Cruising Encyclopedia, though I can't recall whether or not she has a crash box for her keel. Though the 3' draft that it allows is a nice feature. Lavranos // Marine Design
And while Icon isn't exactly a shoal draft boat, she too has a keel that retracts in order to reduce her draft (a little) ICON Sailing

That is only true for boats with a swinging non ballasted centerboard not for the new Swing keels with all the ballast on the keel (see my previous post). On those, because they can have more draft than fixed torpedo keels (for cruising) in some cases the efficiency is even superior, in weight and performance.

It is a strong market trend. Last year in Dusseldorf I was discussing that with the project manager of Garcia, over the Garcia 52 and he told me they were going to propose it on their boats. I said to him that it made more sense to come first on the Allures series, also aluminum voyage brand (but faster) from the same company and here they are, not the Garcia yet but the Allures featuring an all ballast in a swing keel. A good move for a better boat I would say.

[Polux]

Originally Posted by Dockhead

You'd be well screwed in a broach, if it happened with your ballasted swing keel up!

Nevertheless, people do it. Common practice, for example, in Pogos.

I think the answer is this tactic is only for light weather. But that's also when this tactic is most needed.

Sent from my D6633 using Cruisers Sailing Forum mobile app

I never heard that sailors sailed Pogos with the keel up (and I know some) and that is certainly not recommended by the factory (I heard discussions about it) but regarding broaching let me tell you that a Pogo even with a keel up as an AVS of 100º while some older sailboats boats have an AVS very close to that and even modern OVNIS are not far from that.