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Old 17-01-2014, 06:30   #226
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re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

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Originally Posted by sigmasailor View Post
Thick walled pipe of the same weight is stronger than solid bar. Most of the load will occur in the outer fibers of a shaft. The farther away these are from the neutral line (the center) the stronger the pipe gets. Compare this with oversized tubes on bicycles. Strength increases by at least the square (close to cubed) of the diameter. I know of similar sized cats with 70 mm rudder shafts.
All you say is true. However, 1.5" tube is weaker than 1.5" solid stock. Your point is that when they weigh the same, the tube is stronger. By that time, the tube is also 2-3 times larger diameter!

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Old 17-01-2014, 06:33   #227
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re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

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Old 17-01-2014, 06:39   #228
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re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

That's my point exactly! Strength can best be found in diamater. The material in the middle of a bar gives very little resistance against bending since it is so close to the neutral line and can be put to better use at the outside diameter of a pipe.
If I could choose I would prefer a 3 inch pipe above 1.5 inch bar stock (at the same weight) anytime. I realise there are more variables like rudder thickness.
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Old 17-01-2014, 06:44   #229
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re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

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I had suggested the possibility of a rogue wave driving the boat back so that the rudders were not only damaged, but bent at an acute angle making it impossible to steer the boat. This now seems to be the case, if one accepts the word of the captain (and I do). Yes, Yeloya is correct that running the starboard engine would only push the boat further to port - rather obvious and hardly a mistake that a captain with the experience of Captain Schmitt would make and not realize over several days. Surely it is far more likely that he misspoke.

One can scoff at the notion of a rogue wave, but they exist and in greater numbers than had previously been thought. Remember, in 2004 European Space Agency satellite images were used by scientists for three weeks to study the phenomenon and in that short period they were able to pick up 10 rogues that were 82 feet or higher! Remember, a rogue is defined as being AT LEAST 2 time the significant wave height (rather than just the mean). The scientists were also able to confirm that they occur on every ocean on the planet.

Certainly, to drive a boat backwards that has forward momentum and 18,000 lbs displacement would take a very large and powerful wave. Would other rudders have survived this event? Possibly, but unless someone has evidence that the rudder stock on most cats of this size are substantially stronger, I would be hesitant to call it a design or construction flaw.

Is it surprising that the rig would have survived this event? Not unless the boat did a backwards pitchpole - something which has happened to boats encountering rogue waves in the past, but which blessedly did not occur here.

The captain indicates that the diesels were functioning after the event - but again, with the boat only able to go in circles, they were of no more use than the sails. After a few days at the mercy of the waves in a disabled boat in a very cold North Atlantic, what were they to do with a forcast for worsening conditions? Wait until they were at imminent risk and rescue might be impossible? IMO that would have been irresponsible.

Brad
It is the damn spin that gets to me. I would believe in a rogue wave if they were not also trying to sell me on the boat traveling 8kts at the time when they were suddenly stopped dead and "violently" thrown backwards. AND, they "never felt like they were in imminent danger". Maybe I'm a wimp, but I would have browned my pants and suffered whiplash if our boat encountered a wave rogue enough to stop it dead from 8kts and throw it violently backwards.

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Old 17-01-2014, 06:45   #230
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re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

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Old 17-01-2014, 06:46   #231
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re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

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Originally Posted by sigmasailor View Post
That's my point exactly! Strength can best be found in diamater. The material in the middle of a bar gives very little resistance against bending since it is so close to the neutral line and can be put to better use at the outside diameter of a pipe.
If I could choose I would prefer a 3 inch pipe above 1.5 inch bar stock (at the same weight) anytime. I realise there are more variables like rudder thickness.
OK, we agree! Now, do you think 1.5" tube is appropriate as rudder stock on a 42' 20,000lb boat? If so, do you think it is also "massive", like Tarjan does?

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Old 17-01-2014, 06:48   #232
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re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

After days of watching the thread I finally have to pipe in... (bos'n if you please....)

Obviously Tarjan and Aero have HUNDREDS OF THOUSANDS OF HOURS... designing, building, and commissioning highly successful yachts.... I wish them and everybody else nothing but complete success in furthering the industry which we all love....

BUT as been previously ponted out.... (especially by Mark=colemj)

"It should be noted that the rudders of the boat were built of massive 1.5 inch solid stainless round tube welded to a closed framework of 2″ wide by 1/4″ thick stainless bars with (2) vertical and (3) horizontal members. Unfortunately no rudder is designed to suddenly lurch into reverse and have 10 Tons of torque applied to them."

My NON-MASSIVE 22 footer has 1-1/2" tube rudderstock... My 34k displacement boat, 3" solid stock....

I'm no naval architect.... but I AM a mechanical engineer.... I do understand bending moments and MOI (moment of inertia) of roundy thingys very well....

IMHO..... ridiculously undersized


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Old 17-01-2014, 07:02   #233
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re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

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Originally Posted by colemj View Post
OK, we agree! Now, do you think 1.5" tube is appropriate as rudder stock on a 42' 20,000lb boat? If so, do you think it is also "massive", like Tarjan does?

Mark
I think massive (Dutch 'massief' stands for solid) would mean solid and it probably is. I think it is not massive in relation to the weight and size of this cat. As I said earlier (did I?) I have seen similar sized boats with 3 inch (70 mm) stocks. I would say there is room for improvement. I also say that nothing is completely bullet proof.

I used to own a 33ft Sigma 33 OOD; have looked it up; the rudder stock on that boat (9000 pounds) was close to 2 inch (45 mm). Rule 6.2: http://homepage.eircom.net/~bowringd...gn%20Rules.doc
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Old 17-01-2014, 07:14   #234
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re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

Thanks to those with experience in terms of rudder stock - so it is beginning to sound as if those on the Alpha 42 may have been undersized (albeit the individual rudders on a cat are smaller than those on monohull).

Brad
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Old 17-01-2014, 07:35   #235
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re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

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Originally Posted by Southern Star View Post
Thanks to those with experience in terms of rudder stock - so it is beginning to sound as if those on the Alpha 42 may have been undersized (albeit the individual rudders on a cat are smaller than those on monohull).

Brad
This is the caveat about not being a naval architect!

Could I make a rudder from scratch that would point the pointy end the direction I wanted to point?

You Bet!

Could I design one with optimal balance for the hull form, sail plan, keel wash, and acceptable helm effort on the first go???

Uh... Maybe on design revision #23 or so....
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Old 17-01-2014, 08:01   #236
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re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

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Ridiculously undersized indeed. This is what happens when you are so concerned about weight that you build everything undersized. No margin of error for safety. It's the ocean, everything should be built oversized instead.



Five guys to install a teeny tiny rudder like that? How many are on the inside? No wonder the damn thing costs so much! If I was the foreman in this yard, these guys would meet the ogre! This is a two man job, one out, one in. New Yorkers. What a terrible place to build a boat...
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Old 17-01-2014, 08:14   #237
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pirate re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

I'm sorry... I do not buy the rogue wave from the description given and the visual of the boat..
I've been dumped on by a wave in that general area in a H37c in '04...
I was below at the time and hove to..
The jib was ripped and a forward bulkhead was punched out with the pressure on the hull and deck.. freaked me out enough to turn and run back to NC and leave the crossing till the following year.
Typically I've found 'rogue waves' (double the standard) not to be rolling waves in order with the sea.. they tend to rear up in isolation and then fall forward and collapse on themselves through their own weight.. (but then maybe these are not 'rogue waves'.. )..
What surprises me more is the fact the boat is traveling into sea's at 8 knots on autopilot (50kts & 15-20ft)... why was no one at the helm steering manually.. 2hr watches are not unmanageable.. hell.. even one hour watches would allow 2-3hrs sleep for the off watch with 4 on board..
If someone was at the helm going from AP to manual is a 5sec exercise... or.. more likely.. was the watch keeper in the saloon in the warm where suddenly response becomes a matter of minutes..
30sec's 'Oh ****'.. then standing up and getting to the door and opening it in a bouncing boat.. then get around to the helm and hitting the OFF switch... Buga... to late....
If that had been a monster rogue the topsides would not be so pristine nor the rig intact.
They were crossing what I refer to as the N wall where the cold Labrador and warm Stream meet.. this does throw up anomalies in sea patterns...
I'm inclined more towards an earlier report of cross waves that caused the incident..
**** Happens...
I cannot comment on the attempts to repair/jury rig the system... reports seem guess work more than visual and no way could someone go over to do any proper assessment in a sea and survive.
Oh.. 'SS'.. these are my opinions and not meant as a critique of the crew.. merely thoughts that run through my head as I read the posts and comments... so put the axe back down..
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Old 17-01-2014, 08:29   #238
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re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

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Ridiculously undersized indeed. This is what happens when you are so concerned about weight that you build everything undersized. No margin of error for safety. It's the ocean, everything should be built oversized instead.



Five guys to install a teeny tiny rudder like that? How many are on the inside? No wonder the damn thing costs so much! If I was the foreman in this yard, these guys would meet the ogre! This is a two man job, one out, one in. New Yorkers. What a terrible place to build a boat...
Standard FS (factor of safety) in design is 1.5 to 2.... lemme run calculations on 1-1/2" SS tube and rod....

Looks like there is room for 2 guys to guide the shaft inside the hull, probably two more at the top bearing with parts... and one deck super...

So my guess is 10 guys total....
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Old 17-01-2014, 08:36   #239
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It looks nearly identical to this FP rudder and stock. This rudder got damaged while the boat was towed off some rocks. The stock was not bent.
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Old 17-01-2014, 08:50   #240
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re: Alpha 42 "Be Good Too" rescue 300 miles off Cape Henry Merged

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It looks nearly identical to this FP rudder and stock. This rudder got damaged while the boat was towed off some rocks. The stock was not bent.
Gawwwwd... You guys are right.... Multi blades are tiny!!!

Those are standard building bricks holding it up right????
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