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Old 18-01-2014, 22:51   #436
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Reinforcing Existing Rudder Shafts

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Originally Posted by neilpride View Post
I dont see the point, the nautitech rudder post is build to acomodate 2 bushings , made in plastic if i remember well for that shaft dimensions, 2 inch shaft?? doesnt matter , in case of collision is going to bend anyway, and we talk about to build 2 new rudders, rebuild the rudder posts, no sense... could be maybe good idea to make the bottom half of the rudder sacrificial, in case of collision , bang! the bottom is gone but you have the top ... the gap between the top of the rudder and the bottom hull is just mm , any small bend and is stuck!!!
I believe his rudder shafts could be reinforced with bigger diameter oversize 'sleeves' added to the exposed shafts of the existing rudders, ...then change out the bushings to accommodate the new larger dia shafts.

Even the existing quadrants might be modified and retained.

You would be reinforcing the 'fulcrum' of the highest bending load,...where the shaft penetrates the bottom of the hull.

I surely would NOT make any portion of the rudders 'sacrifical'
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Old 18-01-2014, 23:05   #437
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Re: Reinforcing Existing Rudder Shafts

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Originally Posted by beiland View Post
I believe his rudder shafts could be reinforced with bigger diameter oversize 'sleeves' added to the exposed shafts of the existing rudders, ...then change out the bushings to accommodate the new larger dia shafts.

Even the existing quadrants might be modified and retained.

You would be reinforcing the 'fulcrum' of the highest bending load,...where the shaft penetrates the bottom of the hull.

I surely would NOT make any portion of the rudders 'sacrifical'
If you read the account , one rudder failed internally , in that the armature broke off. The other was severely bent.

I'm not sure there a lot could be done. The rudders must have taken a severe thrust to fail like that

Dave
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Old 18-01-2014, 23:10   #438
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Re: Reinforcing Existing Rudder Shafts

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Originally Posted by goboatingnow View Post
If you read the account , one rudder failed internally , in that the armature broke off. The other was severely bent.

I'm not sure there a lot could be done. The rudders must have taken a severe thrust to fail like that

Dave


Severe thrust? When I was a kid, I had a bicycle made with 1 1/2" tube that I broke from jumping too high. I think I was 12....


Face it, this rig is a joke. Not even in the ballpark. Hope there aren't too many others like this out there, but who knows given the modern craze for lightness.
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Old 18-01-2014, 23:14   #439
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Re: Reinforcing Existing Rudder Shafts

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Originally Posted by goboatingnow View Post
If you read the account , one rudder failed internally , in that the armature broke off. The other was severely bent.

I'm not sure there a lot could be done. The rudders must have taken a severe thrust to fail like that

Dave
I was NOT suggesting this fix for the Alpha Cat, but rather the 40 Nautitech Cat mentioned above

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Originally Posted by chris in SG View Post
My Nautitech 40 rudders are probably a similar size and spec. The rudder stocks are 1 1/2" SS tube and the quadrant is attached by through bolt. The emergency tiller fits inside the tube and keys onto the through-bolt.

Perhaps this is also under spec'd but it's probably typical of European standards for production cats.
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Old 18-01-2014, 23:15   #440
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Re: Reinforcing Existing Rudder Shafts

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I was NOT suggesting this fix for the Alpha Cat, but rather the 40 Nautitech Cat mentioned above
Opps sorry , my bad
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Old 19-01-2014, 01:00   #441
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re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

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Not sure I understand your point here in relation to the thread. The boat had no power, so power tools would have been useless. Also, I don't see how an angle grinder and abrasive disk would have helped them in any way even if they did have power.

Mark
The fiberglass area holding the rudder could have been cut away (from inside the boat) and the rudder freed from its stuck position, which prevents the boat from going in circles so it can get somewhere to be fixed. In fact, I've cut things away by just drilling holes all around and then whacking with a hammer. Fiberglass is tough for impacts, but is no match to abrasion.

Some are more prepared, like this guy, with battery powered tools.
Maybe spring a few hundred extra to save the half-million boat.
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Old 19-01-2014, 02:01   #442
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Re: Alfa 42 "Be Good Too" rescue 300 miles off Cape Henry

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The shaft dont bend inside of the rudder post not even in the bushing or bearing , it bend in the only weak point between the rudder top and the entrance to the bushing, steering jam most cases because the rudder get stuck in the hull...
I take it from this, you've never actually seen a rudder....

There is no gap between the top of the rudder and the entrance to the bushing.
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Old 19-01-2014, 02:18   #443
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re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

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Originally Posted by donradcliffe View Post
Note to all rudder stock designers--I seem to remember from grade school that the strength of tubing in bending is proportional to the second moment of inertia, or

(Do^4-Di^4).

That would say that for wall thickness proportional to diameter, a 3" rudder shaft is 16 times as strong as a 1.5" shaft. Even maintaining the same wall thickness, the 3" shaft is about 10 times as strong.
Close, somewherer in the calculation you need to devide by the diameter, leaving a cubed relation between strength and diameter. Going from 1.5 to 3 inch would increase strenght 8 fold. Choosing the material correctly also has a proportional effect, 316 has a 0.2% yield of 200 N per mm2; duplex steel or aluminium alloys can reach double of that figure. This would make our stock 16 times stronger.
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Old 19-01-2014, 02:27   #444
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Re: Alfa 42 "Be Good Too" rescue 300 miles off Cape Henry

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Originally Posted by 44'cruisingcat View Post
I take it from this, you've never actually seen a rudder....

There is no gap between the top of the rudder and the entrance to the bushing.
There is some bare steel between the rudder and the bearing, my guess it would bend right there. This will probably deform the material inside the bearing making it hard ( not impossible) to remove.
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Old 19-01-2014, 03:02   #445
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re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

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...... I'm just the phylactic.
Needed a dictionary for this one

phylactic: serving to protect
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Old 19-01-2014, 03:11   #446
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re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

Well at least they are all home and safe.

Pete
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Old 19-01-2014, 04:20   #447
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re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

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Originally Posted by nimblemotors View Post
The fiberglass area holding the rudder could have been cut away (from inside the boat) and the rudder freed from its stuck position, which prevents the boat from going in circles so it can get somewhere to be fixed. In fact, I've cut things away by just drilling holes all around and then whacking with a hammer. Fiberglass is tough for impacts, but is no match to abrasion.

Some are more prepared, like this guy, with battery powered tools.
Maybe spring a few hundred extra to save the half-million boat.
I thought that is what you meant . How you then steer her is another thing!........but all (lol!) yer need to do is get her in range of a tow. Won't be quick or convenient - but that not the same as not doable.

Of course I am presuming that the crew felt as "safe" aboard her as reported and that she had survived (apart from the rudders!) some serious weather so the next dollop not a great concern - rather than only a bit of unpleasant sea..........

but they all got home alive - and if folks onboard did not think they would be able to get selves out of the predicament then IMO makes sense to jump ship early on.....no extra points for leaving things to last minute.
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Old 19-01-2014, 06:15   #448
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re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

Greetings and welcome aboard the CF, chris in SG.
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Old 19-01-2014, 06:29   #449
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re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

I guess with all of our modern communications/navigation and wonderful weather reports it sure changes the game for sailors. Years ago you tried to only sail tough boats that had a pedigree because often you never knew what you might be facing on a passage and if you lost your rudder and couldn't get home....well you may have eventually died. These days we read about rudder failures like its sort of normal, part of the game so to speak. I guess when asked about blue water boats..well anything is a blue water boat these days and anybody is a blue water sailor, just get on the phone if your having trouble. Times have changed, I guess they are for the better.
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Old 19-01-2014, 07:27   #450
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re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

No Rudder Stops in the Alpha 42 rudder design was the cause of its demise.

Most all production Cats have rudder stops, so the rudder cannot go hard over and become a barn door. The rudders have too much surface area to be hard over and have a large hydrodynamic force against them.

Here are a few pictures of a FP Helia 44 with rudder stops allowing a 30 to 45 deg rudder dead stop.

Alpha 42 rudder post and arms in the bottom pictures with No Rudder Stops
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