Won't bend or rust. What metal do I need?

[SVTatia]

What was there before and how old is the boat?
How long did the current one last?
Just replace it with the same and repeat the process more frequently as preventive maintenance.

Originally Posted by Markb250

I need to replace a 150 x 12 bolt that secures the hydraulic ram for the centreboard, to the centreboard case. Not permanently submerged but exposed to the sea. My understanding and experience is that 304 0r 316 SS is too ductile for this. The bending force is considerable.
What and where is the bolt that I seek?

[thunderhoof]

If your major concern is bending at the bolt I suggest you have a questionable design situation. Can the interface be enhanced to move the force on the bolt to tension or sheer? It would be good to have a drawing of the situation.

One possible solution is to enlarge the bolt hole so a larger diameter sleeve could be placed over the bolt. The sleeve, due to its larger diameter, should have a higher moment of inertia and thus tolerate stainless steel as a material.

[conchaway]

Kryptonite.

[Jim Cate]

Another candidate would be to use 2204 Duplex s/s. Bolts in this material are available or one could have a machine shop make one up if the required size was hard to source.

Jim

[sailingabe41ds]

Originally Posted by zstine

I used to build subs for the Navy. Standard exterior bolt material was Monel, if that wasn't strong enough we used K-Monel (K-500) and if that wasn't strong enough we used Titanium.


Titanium has come way down in price and when I needed a fork for my hydraulic ram I found one in Ti that was cheaper than any SS fork! below is the company I bought my TI fork from..

Allied Titanium - Affordable Titanium Now

Interesting about titanium, subs, and todays price and availability. The US has very little titanium and 5 of the 6 top titanium producing countries were our enemies during the Cold War. Solution.... the CIA created a company that would buy titanium from the Soviet Union which allowed us to build our subs.

Abe

[Steel sails]

In preference order
Highest strength balanced against sea water compatibility

MP35N
Ti 6Al-4V (grd 5)
Inconel 625
Monel K500
2507 super duplex

Cost would fall in line with this order too.
Depending on quantity you need I’m not sure you can buy the MP35N retail.
We sell it to the fastener companies for subsea blowout preventers and DOD uses. It’s prohibitively expensive.
For most non commercial uses the super duplex would be most cost effective And available .

Regards
Paul

[Cyrus Safdari]

Bronze under near water. Plenty strong enough but you can upsize. Galvanic reaction with steel minimal (turnbuckles are bronze threaded into steel) but you can always use bronze nuts and then even cover with fiberglass since bronze doesn't have same issues with crevice/pit corrosion characteristic of even 316l stainless once bedded and deprived of air

[GordMay]

This is an excellent basic tutorial on Bolted Joint Design , from FastenAl:
➥ https://www.fastenal.com/content/fed...t%20Design.pdf

FWIW: The Industrial Fastener Institute states that shear strength is approximately 60% of the minimum tensile strength.

[Pillroller]

If the bolt is correctly fitted in a bush so that there is very little play or gap between the faces, a 12mm SS will be more than up to the stress. The secret is properly close fitting so virtually no bending moments. I would also suggest the boat is Fibreglass and that is way weaker than SS. So bush the CB box and use a s SS bolt.

[CaptainRivet]

Originally Posted by Steel sails

In preference order
Highest strength balanced against sea water compatibility

MP35N
Ti 6Al-4V (grd 5)
Inconel 625
Monel K500
2507 super duplex

Cost would fall in line with this order too.
Depending on quantity you need I’m not sure you can buy the MP35N retail.
We sell it to the fastener companies for subsea blowout preventers and DOD uses. It’s prohibitively expensive.
For most non commercial uses the super duplex would be most cost effective And available .

Regards
Paul

Take grade 5 Titanum, i am using that for all high tensile strength with exposure to the elements on race and rally cars since 10years+
In race accidents always the surrounding material gave up, never a titanium grade 5. No corrosion issues too, works from alu to SS and normal steel, thats why i used them.
Easy to get in the sizes you need and reasonably priced now... Was outrageous 8-10years ago but was needed so paid the cost for it
M12 grade 5 is enough strength for a 1000hp V10 5.2l engine under all extreme loads you can withstand, so totally oversized for your needs...

[carstendenmark]

What is the reason for you to replace the bolt ? Perhaps a design flaw?
Not uncommon

Then you need to address the flaw first, and ask the maker or an engineer (or yourself) to make a good design.

From the new design, you can select the bolt to be used.
(Maybe it is not the same size as you have now.)

Step by step...

[col50]

Originally Posted by Markb250

I need to replace a 150 x 12 bolt that secures the hydraulic ram for the centreboard, to the centreboard case. Not permanently submerged but exposed to the sea. My understanding and experience is that 304 0r 316 SS is too ductile for this. The bending force is considerable.
What and where is the bolt that I seek?

Why do you need to replace the bolt?
What is the existing bolt made of?
Why not replace it with one made of the same material?
Is the existing bolt bending?

[pendragon]

If you have space on both sides of the hydraulic ram 'clevis' and the centerboard, you could fill these spaces with tight fitting bushes, machined to the exact diameter of the bolt and available width. This will alleviate the bending force in the bolt, hence the bolt will just experience sheer-force over it's 2 diameters.

[Icarus]

Originally Posted by Markb250

I need to replace a 150 x 12 bolt that secures the hydraulic ram for the centreboard, to the centreboard case. Not permanently submerged but exposed to the sea. My understanding and experience is that 304 0r 316 SS is too ductile for this. The bending force is considerable.
What and where is the bolt that I seek?

I would go for the strength
A high tensile grade 8.8 or higher.
Keep it greased and replace it every 5 years or so.

[Pauls]

The following is accurate. Not opinion.
1. As was posted earlier, bending strength is directly related to tensile strength. Fastener strength is always rated as tensile strength. That is your metric for comparing the strength of different fastener materials.
2. The common stainless fasteners are all 300 series (also rated as 18-8) stainless and they are weak, 60-70 KPSI.
3. There is a class of stainless steels called Duplex and Super Duplex. They have much higher corrosion resistance than 316. The most common Duplex alloy is 2205, which from memory is about 110-115 KPSI tensile, ie close to twice as strong as 316. Duplex and Super Duplex are superior in both strength and corrosion resistance.
4. Bolts can be found that are made from Duplex. One line is called Bumax 88. They are 110 KPSI.
5. As Jim Cate said, if you can't fine a bolt the length you need, a machine shop can take a piece of Duplex rod and cut threads on both ends, add nuts and you're good to go.