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28-06-2008, 15:32
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#1
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Registered User
Join Date: Jun 2008
Location: Australia
Posts: 24
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Catamaran: Retractable Rudders
I am interested in different designs of retractable rudders, specifically for 10 to 12 metre cats. How does yours work?
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28-06-2008, 16:26
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#2
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Registered User
Join Date: Sep 2006
Posts: 9,398
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On my boat there is a conventional rudder set in a hinged cassette. http://www.cruisersforum.com/gallery...00&userid=3477
They can be held down by a wooden or fibreglass dowel, which will break on impact and release the rudder. The dowels can be removed to manually lift the rudders. They will still offer some steering ability when partially lifted (and allowed to float) too. I think it's one of the simpler retractable rudder set-ups to build.
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28-06-2008, 19:08
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#3
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Registered User
Join Date: Sep 2007
Location: St. Augustine, Florida
Boat: C&C 40
Posts: 193
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28-06-2008, 23:42
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#4
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Registered User
Join Date: Jun 2008
Location: Australia
Posts: 24
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Thanks for replying, I really appreciate the detailed photos from you both. idrhawk, that's one of the best looking set ups I have seen, is that system cable or hydrolic driven?
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29-06-2008, 04:41
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#5
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Marine Service Provider
Join Date: Dec 2006
Location: Brisbane Australia
Boat: Multihulls - cats and Tris
Posts: 4,859
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Col
there the GBE style Lift up blade arrangement, The kick up arrangement like 44 said and that is evidenced on a lot of peter kerr's boats, and there is a section on this topic in Chris Whites book, the cruising multihull.
On kite its a swing up arrangement, but there is no steerage once you pop the rudder, at that stage its use the steerable outboard. Wheresas the dagger board style rudders offer steerage but dont have the advantage of being able to pop up if they hit.
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29-06-2008, 14:01
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#6
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Registered User
Join Date: May 2008
Location: Vancouver, BC & Seattle, WA
Posts: 639
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Here is a photo of the Shuttleworth currently being built in Washington with a link to it's construction process. It's got a 'kick up' rudder design...
Shuttleworth 52 AeroRig Construction Pictures
__________________
I'm On point, On task, On message, and Off drugs. A Streetwise Smart Bomb, Out of rehab and In denial. Over the Top, On the edge, Under the Radar, and In Control. Behind the 8 ball, Ahead of the Curve and I've got a Love Child who sends me Hate mail. - (George Carlin)
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29-06-2008, 15:23
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#7
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Registered User
Join Date: Jan 2008
Location: Denmark
Boat: FP Tobago 35
Posts: 721
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A 47 ft >Shuttleworth was launched a couple of years ago in Capetown with this same lickup rudder set-up. Last year, he was fed up with all the problems and had the glassed in so they no longer can kick up.
Shuttlworth uses a transverse piece of foam/glass that breaks when overloaded, this apparently caused some inadvertent tripping of the rudder.
Ellen Macarthur had some kind of a rope "fuse" on the rudders of B&Q.
The Gunboats have a kickup system, but I know that some owners have changed this. I don't know the reason.
Unless your drives are retractable also, I would probably go for fixed rudders.
Regards
Alan
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29-06-2008, 16:54
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#8
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Registered User
Join Date: May 2008
Location: Vancouver, BC & Seattle, WA
Posts: 639
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Quote:
Originally Posted by Nordic cat
A 47 ft >Shuttleworth was launched a couple of years ago in Capetown with this same lickup rudder set-up. Last year, he was fed up with all the problems and had the glassed in so they no longer can kick up.
Shuttlworth uses a transverse piece of foam/glass that breaks when overloaded, this apparently caused some inadvertent tripping of the rudder.
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Wow! Am I understanding correctly? He uses cored glass on a point of articulation that receives the type of loads a rudder does? I can't even begin to guess as to why??? It would make absolutely no sense!
__________________
I'm On point, On task, On message, and Off drugs. A Streetwise Smart Bomb, Out of rehab and In denial. Over the Top, On the edge, Under the Radar, and In Control. Behind the 8 ball, Ahead of the Curve and I've got a Love Child who sends me Hate mail. - (George Carlin)
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30-06-2008, 03:04
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#9
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Registered User
Join Date: Jan 2008
Location: Denmark
Boat: FP Tobago 35
Posts: 721
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It is not as you think,
If you look from above, the hinged rudder stock can flip out backwards if something is hit.
Aft of the rudderstock there is a tranverse piece that gets broken. Even with the rudders up you still get some steering.
Looking at the photo above, you can see a space behind the 3rd step up, the tranverse piece could be mounted across the opening there.
I don't have a good picture of it, but all these lifting rudders add weight and complexity with limited advantages IMO.
Regards
Alan
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30-06-2008, 19:29
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#10
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Registered User
Join Date: Sep 2006
Posts: 9,398
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Quote:
Originally Posted by Nordic cat
I don't have a good picture of it, but all these lifting rudders add weight and complexity with limited advantages IMO.
Regards
Alan
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The system on my boat adds very little weight. Less then 10 kg total, (both hulls) certainly. In fact, probably no more than than 5. It's a very simple system.
The advantages - if I hit something at speed the rudder will kick up. The only damage will be a broken dowel, of which I will carry spares.
I can lift the rudders to beach the boat.
I can partially lift the rudders for maneouvering in very shallow water, but still use them for steering.
I can lift the rudders to clean them, and the underwater lights.
With sail drives some of these advantages would be lost though.
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07-12-2009, 14:12
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#11
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Registered User
Join Date: Sep 2009
Boat: Shuttleworth 31
Posts: 70
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Quote:
Originally Posted by 44'cruisingcat
The advantages - if I hit something at speed the rudder will kick up. The only damage will be a broken dowel, of which I will carry spares.
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Any chance you could post the dimensions of your dowel and it's location relative to the hingr of the rudder cassette? I'm building a Shuttleworth 31 and I'm considering modifying the kick-up 'fuse' mechanism to make it even simpler and more accessible. It's hard to calculate how strong the fuse should be though.
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07-12-2009, 16:26
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#12
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Registered User
Join Date: Aug 2008
Location: Slovenia not Slovakia; gulf of Triest
Boat: owned a 6m single hull sailing boat, a HIRONDELL 23 cat and chartered modern +8m ELAN boats
Posts: 79
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my Hirondelle had rudders like this http://www.2hulls.com/images/catamar...nixRudders.jpg
worked OK. in a storm i managed to broke the both at the same time
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Rosso di sera, bel tempo si spera. Rosso di mattina, mal tempo si avvicina
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07-12-2009, 22:50
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#13
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Registered User
Join Date: Nov 2007
Location: Cruising in the SUN! Now hauled out in Malta for the winter.
Boat: 37' Oldenziel cat
Posts: 461
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Here is a Norwegian-built cat with transom-hung rudders which looks like a neat installation:
__________________
Roger
Catamaran "Burnout"
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08-12-2009, 03:38
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#14
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Registered User
Join Date: Mar 2008
Posts: 92
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Quote:
Originally Posted by 44'cruisingcat
On my boat there is a conventional rudder set in a hinged cassette. http://www.cruisersforum.com/gallery...00&userid=3477
They can be held down by a wooden or fibreglass dowel, which will break on impact and release the rudder. The dowels can be removed to manually lift the rudders. They will still offer some steering ability when partially lifted (and allowed to float) too. I think it's one of the simpler retractable rudder set-ups to build.
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A very interesting thread. I do however wonder what happens when a rudder kicks up. Does one suddenly loose steering in both as the kicked up blades rotation is now confined by the hull appeture. This may be very dangerous in marginal conditions where large helm changes are required to hold a course . I would imagine that the fused link is designed and tested ( not just guessed at) to fail at a point where no damage occurs to the rudder (this must involve some pretty interesting maths and materials testing,hardly repeatable with selected pieces of whittled fence post jammed in a hole), hence the whole rudder mechanism is built reasonably lightly as it no longer needs to be able to cope with grounding loads. Where as, a non kick up balanced spade will be engineered to take grounding loads (One of the late Lock Crowthers catch cry's) ,Hence the non kick-up will be so much stronger for the same weight. ( no case etc required)
There were some pictures of an Oram cruising cat kick-up rudders doing the rounds a while back that had failed when accidentally side loaded and hence the kick-up couldn't function. Were these "dog on cats"? I'm not sure. I'm sure someone here will remember the boat and maybe even dig up the pics.
How much draft does one actually save with the rudders up? Most moderately sized round bilge cruises are going to draw 600 to 900 mills anyway.
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08-12-2009, 08:21
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#15
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Registered User
Join Date: Dec 2005
Location: Cat in New Zealand, trawler in Ventura
Boat: 46' custom cat "Rum Doxy", Roughwater 41"Abreojos"
Posts: 2,041
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I used a dagger and cassette system set in a rotating drum on my boat. Pros and cons are as stated above plus it eliminates the stainless shaft.
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