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Aluminum or steel for safety critical part on vessel?

Trboatworks

Diamond
Joined
Oct 23, 2010
Location
Maryland- USA
This is on my plate-

Replace emergency tiller arm on a fifty footer.
So big boat and it sees ocean service so the gear has to work under high loads and tough conditions.

What is there is a simple 'T' fabricated from plain steel with a round post bottom which inserts into rudder head.

What is being specified is redoing in aluminum.

Hold on a sec and I will get photos posted but I have to come up with a robust way to use welded up aluminum for this part.

Old tiller:

A4B5F17F-2E63-4376-9E4E-C9AD22144DE6.jpg

Critical bit:

B3684C60-FBA8-4DAF-9326-0F161D0E2717.jpg


The solid at lower end is 1-7/8” diameter and the slot cutout is 1/2”.

I am not liking that solid out of alloy and I’m really not liking welding up the vertical to it and this is not mentioning the problem of welding up the T arms..

Tell them to jump I can’t make it strong enough out of alloy or…?
I suppose I could bring the solid up further and drop a tube over it and filet weld the bottom of tube to solid- that at least would keep working the tiller from loading the weld except in rotation.
 
This is on my plate-

Replace emergency tiller arm on a fifty footer.
So big boat and it sees ocean service so the gear has to work under high loads and tough conditions.

What is there is a simple 'T' fabricated from plain steel with a round post bottom which inserts into rudder head.

What is being specified is redoing in aluminum.

Hold on a sec and I will get photos posted but I have to come up with a robust way to use welded up aluminum for this part.

Old tiller:

View attachment 325922

Critical bit:

View attachment 325923

Well, welded aluminum is not as strong as the un-welded sections.
Welded aluminum suffers fatigue much sooner, cracks more frequently.
 
I can not see the photos on my mobile... welded Al is not the last material I trust in critical applications but pvc was not one of your suggestions. Steel is real. Stainless is pretty good at handling the ocean air also.
 
Convince them to leave the material as steel or stainless steel. This isn't a place for welded aluminum.

If they insist on spending money make it from Gr5 Ti. From solid...
 
Convince them to leave the material as steel or stainless steel. This isn't a place for welded aluminum.

If they insist on spending money make it from Gr5 Ti. From solid...


Yep- we are going to have a talk- this is a subcontract and the general is specifying the material- I don't know why but I don't think it is driven by client.
There was probably an offhand comment made- "Oh we can replace this with aluminum so it won't rust" and now they are rolling with that.

The boat got slammed by a breaking following sea and shattered the aluminum quadrant on the way over from Bermuda so they were on the emergency gear for half the passage.
They are headed back over as soon as everything is sorted.

This is a big boat and the emergency gear has to work- if they can't steer in rough enough conditions the boat could go beam to and be rolled with loss of life etc.
I am not happy taking it on in alloy.

I think an aluminum solid could shear at the slot and everything about a weldment out of alloy at the rudder head seems like a crap ideal.
 
This is a big boat and the emergency gear has to work- if they can't steer in rough enough conditions the boat could be rolled and loss of life etc.
I am not happy taking it on in alloy.

I've read enough of your posts to know you have a good sense of what works. Follow your gut. If you have to, refuse this part.
 
I've read enough of your posts to know you have a good sense of what works. Follow your gut. If you have to, refuse this part.

Oh I just get scared sometimes.

Really though I can't do fabrication work when someone else is setting parameters like this.
I wouldn't even think of trying to do this in aluminum but here I am- trying to build in enough strength to overcome the problems with alloy.

Stainless has its own problems- crevice corrosion could set in a trash the thing in the decades they sit in wet lockers till they are needed.
The smart play is probably what was done- STEEL and just keep it painted or greased or maybe send it out to be galvanized.
The damn thing will be strong enough when it's needed.
 
Well could go titanium maybe:D

Then there is the question what is that going on to?
2 D shaped holes or just a tab sticking up like a straight slot screwdriver blade.

Don’t weld the shaft socket part at all just turn down the smaller diameter part.

Aluminum has it’s own corrosion problems as you well know.

Helmsman K Cong is probably the weakest link there
 
Then there is the question what is that going on to?
2 D shaped holes or just a tab sticking up like a straight slot screwdriver blade.

The FRP rudder post is hollow for about 3" at top with a cross pin which holds the lock plate.
The tiller slides down into the hole in rudder post and has a milled slot to index on the cross pin.


Don’t weld the shaft socket part at all just turn down the smaller diameter part.

Ah- got it.
Good ideal
 
I don't believe alum would be strong enough. I would build it from stainless or steel.

Sent from my SM-G960U using Tapatalk
 
"The boat got slammed by a breaking following sea and shattered the aluminum quadrant on the way over from Bermuda so they were on the emergency gear for half the passage.
They are headed back over as soon as everything is sorted."

That and the condition of the emergency steering make me think this is a bit of a shit show. is she an old race boat? SS seems to be the best long term option me, could make it from heavy wall tube to keep the weight down a bit. doesn't seem to have any way of attaching ropes/tackle to it so is only hand operated and can't see so much force.
I have only spent a few hours on a boat under emergency steering, great fun. The emergency steering was a hand operated hyd pump down aft, it had a gyro repeater in front but the whole show was facing backwards. we did a couple of loops while the guys figured it out. brought home the importance of doing drills for real not while sitting at the dock. I was under the bridge console for most of it trying to find the issue. turned out to be a single cat5 cable that took it out..... on a fully redundant certified bridge system.....
The manifacture didn't believe me and flew out the "experts" to sort out the stupid engineer. we got a new redesigned console and i tested it to hell and back!
 
That and the condition of the emergency steering make me think this is a bit of a shit show. is she an old race boat? SS seems to be the best long term option me, could make it from heavy wall tube to keep the weight down a bit. doesn't seem to have any way of attaching ropes/tackle to it so is only hand operated and can't see so much force.

Yep.

The yard wants the new tiller to have bails so lines will be taken to the secondaries on the cabin top so if they ever use it the gear will see more than man force load.

"I have only spent a few hours on a boat under emergency steering, great fun."

Yep- back when I was less timid I took a clients boat across a busy river and into a busy harbor to dockside calling steering down to my sister who was on the emergency tiller down below.
As soon as I got it secured and lines good a yahoo on a big cabin cruiser hit the throttles and drove his bow right over the boat behind me on the seawall.
For you guys who don't know an inexperienced guy will grab those throttles and ram them forward when in a panic- like they think the brakes go on when you hit the stops...
I have seen lots of boats jump up and ride down docks and other boats.

Great fun indeed......

Yes- an old race boat.
 
Ah with the additional information aluminum probably isn’t up the task
No one has mentioned but you know the steel pin working on the aluminum slot.

Might point out that they could save more weight by just having skinner crew
 
Why even weld it? Can you not just machine an end of an aluminum rod? Turn down the rest of the shaft if needed. Not a huge deal for a one off.

In any case, I wouldn't trust a single weld like that. If it must be two pieces I would consider a pinned or bolted connection as well. My normal go to would be to thread the rod and end and then weld it after assembly but seeing that this appears to be used in torque that's obviously not a great idea.
 








 
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