Keel nuts/studs - mild or high tensile..

[Martin_J]

I know in my Moody s38 the keel studs and nuts are not stainless.. I also know they are very rusty looking although the visible stud threads clean up very nicely.

Hoping it will be an easy job to replace nuts/washers and will draw a stud out if needed and then paint the new ones and cover with Denso tape.

Mild steel or High tensile steel though...
Is high tensile needed for nuts and studs or is it usual to use mild steel for both?
Is there a way to tell whether the existing Moody 1997 ones are mild or high tensile?
Is zinc plating usual? Current ones don't appear to be plated..

As examples, neither look to be that expensive..
M24 Mild steel studding (4.6), 3 metre length bright zinc plated. DIN 975
http://www.orbitalfasteners.co.uk/product_detail.php?id=4268

M24 High tensile studding (8.8) 3 metre de-embrittled bright zinc plated
http://www.orbitalfasteners.co.uk/product_detail.php?id=4270

M24 Mild Steel Full Nut Galvanised DIN 934
http://www.orbitalfasteners.co.uk/product_detail.php?id=8508

Thanks in advance... Will keep you updated with progress... and also say how easy it went!

 

[vyv_cox]

Proper high tensile bolts or studs will be very difficult to file or cut with a hacksaw. The 8.8 ones in your link have a Vickers hardness of about 250, which can be cut but the blade will tend to skid. Mild steel ones will be easy.

With a centre punch the 8.8 will mark, but not deeply. You could use something with known hardness, e.g. a bit of mild steel, as a comparison. That should indent quite well.

 

[Martin_J]

Thanks Vyv...
I could angle grind the 300cm studs to length if needed (well away from the boats). I was just worried about High Tensile perhaps being more brittle.. or just 'not right' or 'not required'.
Same with nuts - I didn't want to go 'high tensile' and then sbdy say that they are very strong but too brittle.

Sounds like the studs (from photos of other Moody studs) should be good anyway...

 

[vyv_cox]

8.8 is probably the lowest grade of bolt steels that could call itself high tensile. No problem at all with ductility. I can see no reason why it should not be used but best to stick with what was originally specified.

 

[DownWest]

The bright plating is electro-plate and pretty useless in sea water. Might as well use the plain steel rod, 8.8 sounds about right, but Vyv knows best.

 

[Martin_J]

Vyv..
It's been a long day and I wondered why you described the difference by using a center punch (when I've not even ordered any bits yet..)

A quick re-read and a fresh mind.. Yes - I'll centre punch a stud on the boat this evening and do the same to an 8.8 bolt that I have and also to a standard mild steel nut that I also have (for comparison).

Too simple - but thanks!

 

[Martin_J]

Mild steel it is!

Vyv
Thanks.. Back on board and 1 hammer, one center punch and one second later...

Bingo.. A light tap with a hammer and a 1mm indentation on top of stud and a 1mm indentation on a new mild steel nut.... They match!

Mild steel it is!

Just need to work out what to put around the studs under the new washers now..

 

[30boat]

Why not go for 316 Stainless?The large majority of modern boats use them to hold their cast iron keels in place.Can't see the point of mild steel when stainless works so well.

 

[electrosys]

Stainless is ok when either water flows freely around it (thus supplying oxygen), or when it's 100% sealed from moisture. Anywhere in-between is asking for trouble from crevice corrosion, especially around screw-threads.

 

[Tranona]

Stainless is ok when either water flows freely around it (thus supplying oxygen), or when it's 100% sealed from moisture. Anywhere in-between is asking for trouble from crevice corrosion, especially around screw-threads.

That was Moody's argument for using mild steel. However 316 is commonly used by other builders apparently without problems. Moodys also used mild steel for fuel tanks. Many owners have found to their cost that long term it was not a good idea.

 

[30boat]

Stainless is ok when either water flows freely around it (thus supplying oxygen), or when it's 100% sealed from moisture. Anywhere in-between is asking for trouble from crevice corrosion, especially around screw-threads.

Yes but experience has proved that it's a perfectly suitable material in this application.My 30 year old bolts for instance are as good as new.I know because I removed them.

 

[Martin_J]

Just back from real world chat on another boat... When I can work out a way of updating threads with links to Live Spaces photos rather than photobucket I will..

As Electrosys and Tranona have just mentioned.. Mild steel studs/nuts look really bad from above but once the surface rust is cleared they look good underneath. Perhaps best not disturbing the surface!

Previous thread I have just discovered with pictures.
http://www.ybw.com/forums/showthread.php?t=199027

Whilst in the water last night, two visible stud threads cleaned up in half an hour.... Bilges still dry 24 hours later.. Time to replace the washers/nuts and move on to the next two...

Photos to upload once Live Spaces links working...

PS - Thanks Vyv for suggestions earlier. Obvious once tried!

 

[Dipper]

I replaced all my keel studs about twelve years ago. My boat had been sitting unsold for over a year with water in the bilges and the nuts on the studs had rusted badly even though they were encapsulated in GRP. When the studs were extracted (made easier because the nuts were rusted onto them) the threads were as new. I replaced them by purchasing a length of non-galvanised 1" steel rod from an engineering firm and cutting lengths off to fit.

I asked the firm for the same grade steel as the original but I've never been able to confirm that - until now. Thanks to Vyv's centre punch technique I've punched an old stud and a piece of the replacement studding and the indentations are exactly the same. It looks like they were mild steel.