Composite rudder shafts

Wheel, tiller and autopilots
44c
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Location: Hervey Bay, Qld

Composite rudder shafts

Post by 44c » Sat May 12, 2007 7:11 pm

I think in the Perry situation Madaz was referring to, some of the bending of the ss shaft had actually occurred INSIDE the tube. It could not be moved either to port, starboard up or down. Which would mean the rudder tube would need to be cut out of the boat.



In such a case, if mechanical steering was employed, both rudders would be jammed, even if only one shaft were bent. Hydraulic steering could still work provided there was a bypass valve available on each ram.



I'm hoping I will have all the bases covered - the rudders are mounted on cassettes that can kick-up in an impact - but they will only work if the boat is moving forward. The rudder shafts are glass, so they cant bend, (but can break), and I will have hydraulic steering with bypass valves fitted.

northerncat
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Composite rudder shafts

Post by northerncat » Sat May 12, 2007 7:56 pm

thats fully weird, i have seen a rudder shaft stainless steel that bent when a 37ft overweight cat smacked into something but that bent at the point where it exited the hull( a testament to the strength of the hull) and they were able to drop it down 50mm

sean

madaz
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Composite rudder shafts

Post by madaz » Sat May 12, 2007 10:33 pm

I would of thought they would bend at the exit also, I am not sure though. Mr Perry said they had an absolute bastard of a job getting them out though so i could only assume the bend was a little longer, of course mini keels would hopefully do a god job of protection so maybe we should just all be careful going backwards?

I am making two rudders to install plus one spare, I ordered 3 shafts so I might as well make up a spare while i am at it..

malallo

Composite rudder shafts

Post by malallo » Mon May 14, 2007 8:46 pm

I have made a spare but seeing how heavy it is probably leave it at home.

puremajek
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Composite rudder shafts

Post by puremajek » Tue May 15, 2007 3:55 am

I too find it strange that the pole bent in the middle (in fact it’s the first time I have heard this occur) and feel for the person concerned, because it would be a nightmare to repair. I do like the idea of kick-up rudders though.
if mechanical steering was employed, both rudders would be jammed, even if only one shaft were bent.
The steering we have is all mechanical and extremely easy to disengage by removing a spilt pin and its associated pin, that simple and just as quick. This allows for either a single rudder disengagement, or both rudder disengagement if the 'link bar' or other components fail for whatever reason. The rudders can then be operated manually or together with the emergency tiller handle eliminating the need for hydraulics totally.



44C, will yours kick up right up out the water when the yacht is moored? Just thinking that it would be one less thing to antifoul, although I suppose antifouling inside the ‘cassette’ will prove a little tricky too.
James
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44c
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Composite rudder shafts

Post by 44c » Tue May 15, 2007 4:25 am

From second - hand info, the perry rudder shaft didn't bend in the middle, but at the end, where you would expect it to, but the bend carried up into the tube just enough to jam it hard.



I will most likely antifoul my rudders. Doing the cassettes and inside the cassette slots will be simple enough too.

CC40

Composite rudder shafts

Post by CC40 » Wed Jan 21, 2009 2:51 am

Madaz



Quick question I have been onto Excell re the Rudder tubes. What did you do regarding installing the tangs for the rudder or did your design not require them?

Also to the other guys who are using the Excell Stanchions have you drilled holes for the wires if so does it weaken the tube? Seems to me it would.

Jim
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Composite rudder shafts

Post by Jim » Wed Jan 21, 2009 5:34 am

On the bent rudder shaft thing, my mate with the Lightwave bent one of his shafts on the reef a couple of months ago. It still turned, but was very tight. He put the boat on the hard, as the bottom needed doing anyway, and we put a spectra rope sling around the bow going back towards the rudder and pulled it straight with a come-along. It was a s/steel hollow shaft, which I suppose puts it in front of the composite shafts on that point as composite or carbon doesn't bend, just breaks. The advantage of that (composite) is it doesn't rip the back of the boat out, and more often than not the boat just carries on with one rudder with very little or no damage to the hull.

Plusses and minuses again.

Jim.

madaz
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Composite rudder shafts

Post by madaz » Wed Jan 21, 2009 7:40 am

I have been busy ready my Boat owners mechanical and electrical manual (Nigel Calder) which James recommended. Out standing book, i highly recommend it also. it covers a huge range of things with outstanding detail and clarity.



One of them being rudder stocks.



I would be dubious about how long the rudder blade might last if it has been bent at the shaft from a collision, then force applied to re straighten it, that must put an awful lot of strain at the top of the blade where the shaft enters. I have no idea of there construction, but that kind of force could easily create a small crack/leak for water to enter. :shock:

Jim
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Composite rudder shafts

Post by Jim » Wed Jan 21, 2009 11:05 am

Most rudders I have had anything to do with from snail slow sailing cats like mine to 120MPH ski race boats have the rudder shaft approx. 2/3rds of the way down into the blade, so there is a lot of strength there. Also if a shaft is bent like the one I described above, that is it still turns but is tight, the actual amount of bend is very slight and spread over the length of the shaft, usually starting at the bottom bearing/bush. To straighten a bend like that is no problem at all and there is almost zero weakening of the shaft. Don't forget I am talking about a shaft over a meter long and with a bend of about 10mm in the middle. You wouldn't believe some of the things I have straightened over the years and a whole lot more critical than a rudder shaft on a boat that will never see 20knots. However if it is bent below the bottom bush, and the rest of the shaft is straight ie, turns freely, that is a whole new ball game and if the bend is not too extreme then you are probably better off leaving it bent, (we aren't talking about Americas Cup boats here) because to straighten it will weaken the shaft at a critical area.

Jim.

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