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Old Apr 02, 2007, 11:23 PM
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Canting keel servo?

I was wondering if people thought this servo would be powerful enough to cant a keel on a 30'' model. If not, what about this one?

I don't know exact weights or lengths yet but I'm just wondering, as a general idea, will it be powerful enough?
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Old Apr 03, 2007, 12:31 AM
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...unless you have an idea of the weight of the keel and the distance you want it to swing, you cannot really know how powerful a servo you will require - though I would think that the S3305 would be adequate with 9kg's of torque...!

A cheaper alternative would be a TowerPro MG995.
They have coreless motors and are high speed, and have 13kg's of torque... almost as much as the large S3801 in your second link.
Also, the MG995 servos are the same physical size as a standard servo - as is the S3305.
I have a couple of MG995's, somewhere...

Welcome to RCGroups...

Keven.
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Old Apr 03, 2007, 12:45 AM
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Forgot to mention...

Look at eBay shops ( such as the one in my link ) for incredible prices on the TowerPro servos - which are just as good as Futaba or Hitec items...

http://stores.ebay.co.uk/Compass-Sto...dZ2QQpZ2QQtZkm

Keven.
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Old Apr 03, 2007, 07:56 AM
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Thanks for the welcome! I'm doin this for a school project but it's gonna end up as my toy, with costs offset and tools provided by my school...

OK, so since it's close and easy we can use a preliminary bulb weight of 2lbs. i.e. 1kg.

Also, a 15'' keel fin seems about right... I can do up to a 3'' lever arm inside the hull, but a 2'' one would be easier (The boat has 4'' of freeboard).

Oh, and I'd like the keel to can to about 50-55 degree's.

Another question, I know 99% of people are looking for servo's that go as fast as possible, but I'm looking for something quite a bit slower. I'm thinking I'd like between 1 and 3 seconds from extreme to extreme. Probably about 1 would be best. These servo's are all talking like fractions of a second in their speed.
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Old Apr 03, 2007, 06:14 PM
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Better option for the canter servo I think!

http://www.robotshop.ca/home/supplie...rvo-motor.html

It's an actual winch so it should work better, no?
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Old Apr 03, 2007, 07:22 PM
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Have you looked at any kind of linear actuator?

A.
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Old Apr 03, 2007, 07:42 PM
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.. In laymen's terms por favor? lol Sorry but for all my sailing experience, if I want something done, I physically pull on a line to do it. I've never dealt with this stuff.
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Old Apr 03, 2007, 09:02 PM
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Ahh, I found out what a linear actuator is, and from some of the people I've talked to with experience in R/C canters, a continuous loop systemof string going from the lever arm, to a pully on the side of the keel bulkhead, then around a winch a couple times, then another pulley and back to the lever arm. It keeps the weight of the servo on center, and requires lee structurally.
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Old Apr 12, 2007, 09:35 PM
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Explain, if you care to, why you are canting an underwater keel. Heeling automatically cants a keel, I don't know why you'd want more (or less). Canting up (towards the surface) would give you more righting action, at the expense of lateral resistance; you would right the boat, but skid off downwind. Canting down gives you better bite on the water, but you will heel more and spill air off your sails. If you want more lateral resistance while heeled, how about adding wings to the keel? If you want more righting moment, how about using movable ballast on deck?
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Old Apr 12, 2007, 09:51 PM
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I'm adding a foward rudder (canard) just in front of the keel. Look online for any of the full size boats with it. You cant it to windward to keep the boat flat and keep your sails efficient. It also allows you to use a much lighter keel bulb (or much more sail area... or a much narrower hull... or all kinds of faster options). I personally am going for a wider hull, heavier bulb, and a crap load of sail.
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Old Apr 13, 2007, 02:54 AM
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Ballywho I took your advice and read up on the canting keel (Wikipedia has a nice article: http://en.wikipedia.org/wiki/Canting_keel). The design has been patented, and boat owners are required to pay a licence fee (should not affect modelers, though, I would imagine).

The loss of lateral resistance that I mentioned as a negative is handled by adding separate, non-canting keels to the hull (called foils in one article). I learned that several ocean racers with canting keels have been lost when the keel failed (fell off, or jammed in one positon, leading to capsize at sea). So, in the ocean world, looks like the technology is not reliable yet. But for a model, achieving adequate strength should not be a problem, though jamming may be a factor; perhaps a piano type hinge would help.

I've never sailed my models in breezes steady enough to make movable ballast a desirable option (I'd need fast fingers to keep the ballast in the right place), but I've always thought the idea was a good one. An automatic system of ballast adjustment would be nice. Submariners have devices to keep their subs level, automatically adjusting dive planes. Perhaps you could incorporate one of those in your ballasting, to make canting automatic. Good luck with your boat!
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Old Apr 13, 2007, 12:09 PM
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The technology has been no less unreliable than other new ideas as of late. There were a few problems in the Volvo Ocean Race associated with underengineered rams and hydraulics. However, of the 7 boats, only 1 had a major failure. Also, there are quite a few maxi's out there with very reliable systems. For instance, Wired, Alpha Romeo, Wild Oats, Skandia, as well as a few series builds like the Cookson 50's all had canting keels and are going as fast as some multihulls reliably.

Only the CBTF technology has been patented, the twin canard system has not. I will be using CBTF (canting ballast twin foils) because of it's ease of use.

As to the fast fingers issue, you're not neccesarily going to be canting the ballast to the wind, but trimming the sails to keep the boat upright. A canting keel boat will never sail to it's potential in winds light enough that it's keel is at center. You put a big tall rig on them so they can power up early and will only have to depower later. This allows the boats to sail steadily in inconsistent breeze by powering and depowering the sails. The idea is to sail the boat with the keel canted slightly less than what is needed and dump in the puffs and trim in the lulls. It's really, really fast.

The hinge is the most difficult part, and I still haven't come up with an idea that I feel will be sufficient.
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Old Apr 13, 2007, 01:43 PM
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I am more than ever convinced that canting keelers are an aberant fad that will soon go the same way as the Herreshoff articulated catamaran and the Czar of Russia's circular yacht. This is not because I am getting ancient and they are innovative - rather becaue they are not innovative in any sensible or clearly thought out way.

They have made one design decision - go for moveable ballast - and then implemented it in about the most stupid way possible. Compared with a boat with a larger scale analogy of a trapeze, sliding seat or windsurfer rig, a canting keeler

1) Drives its ballast through a highly viscous medium (water) rather than a less visous one (air). Hence high form drag.
2) Barring incredible mechanical complexity (and weight) cannot retract all or most of its appendages downwind when their lift and stability enhancing characteristics are not needed. Hence high induced drag.
3) Compromises shape, angle, position of foils with consequent need for canards, etc. High induced drag.
4) Has a relatively limited range of stability enhancement and hence a poor power/weight ratio
5) Is almost certainly mechanically more complex and heavier - so again a poor power/weight ratio.

Really fast (for their size) moving ballast monohulls have had the option of canting keels for years. But when did you see one on a skiff or a widsurfer? Never. Really fast monohulls shift ballast sdeways above water in air.

My cynical mind does wonder whether the mechanical unreliability that is likely to be a long-term feature of these boats is entirely unwelcome to the sponsors of the races in which they take part.The odd death or rescue generates lots of column inches, as do the testosterone soaked young, high on the latst tehno-gimmick- which is what the whole thing was all about.

Hmmmmmmm


A
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Old Apr 13, 2007, 04:28 PM
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Originally Posted by Angus R
I am more than ever convinced that canting keelers are an aberant fad that will soon go the same way as the Herreshoff articulated catamaran and the Czar of Russia's circular yacht. This is not because I am getting ancient and they are innovative - rather becaue they are not innovative in any sensible or clearly thought out way.

They have made one design decision - go for moveable ballast - and then implemented it in about the most stupid way possible. Compared with a boat with a larger scale analogy of a trapeze, sliding seat or windsurfer rig, a canting keeler

1) Drives its ballast through a highly viscous medium (water) rather than a less visous one (air). Hence high form drag.
2) Barring incredible mechanical complexity (and weight) cannot retract all or most of its appendages downwind when their lift and stability enhancing characteristics are not needed. Hence high induced drag.
3) Compromises shape, angle, position of foils with consequent need for canards, etc. High induced drag.
4) Has a relatively limited range of stability enhancement and hence a poor power/weight ratio
5) Is almost certainly mechanically more complex and heavier - so again a poor power/weight ratio.

Really fast (for their size) moving ballast monohulls have had the option of canting keels for years. But when did you see one on a skiff or a widsurfer? Never. Really fast monohulls shift ballast sdeways above water in air.

My cynical mind does wonder whether the mechanical unreliability that is likely to be a long-term feature of these boats is entirely unwelcome to the sponsors of the races in which they take part.The odd death or rescue generates lots of column inches, as do the testosterone soaked young, high on the latst tehno-gimmick- which is what the whole thing was all about.

Hmmmmmmm


A
I absolutely could never agree less.

I will begin by adressing your 5 points:

High form drag, yes, but vastly less than the drag it would take to use water ballast or some other above the waterline contraption. Also, ballast just above the waterline will induce absolutely REDICULOUS amounts of spray and wave drag, not to mention the odd wave hitting it and stopping the boat.

"2) Barring incredible mechanical complexity (and weight) cannot retract all or most of its appendages downwind when their lift and stability enhancing characteristics are not needed. Hence high induced drag."

I see that most certainly you have never sailed the skiff or windsurfer that you talk about. The extra appendages are absolutly faster downwind on anyboat of even relativly high performance. Apparent wind boats rely on loaded foils 100% of the time. Some canting keel boats who can lift their foward rudder do so maybe 1' of a possible 10, but never all the way. Also, the VO70's with twin canards were hoisted by the primary winches... Human power. The leeward canard was always in the water, upwind or down.

"3) Compromises shape, angle, position of foils with consequent need for canards, etc. High induced drag."

Again, when or if you sail a true apparent wind sailboat, you will see that the high induced drag of more foils wis more than compensated for by the extra speed, and associated extra depth, especially downwind.

"4) Has a relatively limited range of stability enhancement and hence a poor power/weight ratio"

Completely backwards. A canting keel boat has a higher power/weight ratio than ANY other boat. Far and away higher. This is because you can put more sail on with the same sized bulb or a much lighter bulb with the same sail.

"5) Is almost certainly mechanically more complex and heavier - so again a poor power/weight ratio."

More mechanically complex, of course. Heavier, not a chance in hell. The weight saved in the bulb will make up for the hydraulics every single time. No question.

"My cynical mind does wonder whether the mechanical unreliability that is likely to be a long-term feature of these boats is entirely unwelcome to the sponsors of the races in which they take part.The odd death or rescue generates lots of column inches, as do the testosterone soaked young, high on the latst tehno-gimmick- which is what the whole thing was all about."

These systems have become exponetially more reliable with every new generation. Carbon fiber also had it's extrordinary failures, as did fiberglass before that. I'm sure there were plenty of people who saw those as passing fads.

"They have made one design decision - go for moveable ballast - and then implemented it in about the most stupid way possible. Compared with a boat with a larger scale analogy of a trapeze, sliding seat or windsurfer rig, a canting keeler"

There is one absolutely MAJOR difference. How many boats with trapeze's, windsurfer rigs, sliding seats, or the like have you seen cross the Atlantic? How long did it take? The boats with stability induced like that are all inshore bouy racing boats. Trust me, I sail a skiff, I've windsurfed, I've kiteboarded, if it goes fast by wind power, I've probably used it. None of those systems are compatable for longer passages (which I've also done).

"Really fast (for their size) moving ballast monohulls have had the option of canting keels for years. But when did you see one on a skiff or a widsurfer? Never. Really fast monohulls shift ballast sdeways above water in air."

Simply because keelboats are probably the least effiecient sailing vessels ever. Trust me, if the 18's had a keel rule, they would have had canters looonggggg ago.

Lots of people thought the internet was a passing fad too.
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Old Apr 13, 2007, 06:46 PM
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Guys in aussie have tried canting keels on smallish 6-8m sport boats without sucess so far. boats relying on crew weight have proved better so far.

Most agree that canting keels on boats less than 32 feet are not much chop.

I think canting keels are a viable option for large keelboats(above 32 feet)
less than that then human ballast is better.

Of course the large super maxis etc sprouting these "new" canting keels arn't real sailboats anyway..The keel cannot be canted unless the engine is running.Might as well just attach a prop to the engine instead of a canting keel.
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