Monel keel bolts

[MikeJohns]

I'll answer this PM query here .

"I have a new boat under construction and am considering monel keel bolts but seem to remember reading somewhere that while the bolts should be Monel 500, the nuts should be Monel 400. I can't find that reference again and thought you might know something about this."

Doug

For fix and forget we would use Monel 400 for both the keel bolts/threaded rods and the nuts particularly if casting in the bolts.

The 500 grade is harder and higher tensile strength but is more prone to fatigue and similar to stainless steels is prone to corrosion fatigue when used in sea water environments.

If you specify 500 the bolts should be able to be withdrawn for inspection, and well sealed /packed. Then we would use the more ‘reliable’ and more noble 400 for the captive threaded receivers/nuts.

With its harder surface 500 is commonly used for machinery and shafting although there are plenty of 400 shafts around.

500's high tensile strength makes it atttractive but there is always a cost of reduced 'toughness' for increased tensile strength.


I hope that helps.
cheers

nicely put Mike
can I shove an oar in
look up duplex 2205 grade ss, highly resistant to salt water corrosion, and very high tensile, , used in prop and rudder shafting

[MikeJohns]

Originally Posted by lazeyjack

nicely put Mike
can I shove an oar in...........

Of course
That's why i put my reply up here, then everybody can either debate it or contribute or learn.

[Sea Jay]

Many thanks Mike. I was not aware that Monel 500 had those corrosion issues. I'll stick with the 400, as the required strength is easy enough to obtain with diameter. While we are on the subject of Monel, perhaps I can expand this inquiry a bit...

The specs for my keel call for a steel structure with poured lead ballast. (My hulll is GRP composite) There is a long thread regarding a similar construction using aluminium for the structure

http://boatdesign.net/forums/showthr...nium+keel+lead

Some of the issues discussed would not apply to steel, but still, it seems logical to me that it is likely that there could be some water intrusion between the interface of steel and lead. In addition I'll also have the maintaince issue of the external steel. I'm aware of the cost difference between steel and monel, but that aside, how do you think a monel structure would perform relative to steel or aluminum?

Best Regards,
Doug

[MikeJohns]

I am not sure of your keel design so I don't want to get specific here.

I don't think it is worth the expense of fabricating in expensive metals, you still have dissimilar metals no matter waht you use. Copper Nickle would be another consideration.

I don't think you will find steel high maintenance if it is well epoxied, Also melted lead actually wets bare steel and will stick to it if some flux is introduced and the surface is clean which it will not do to aluminium.

I have inspected/surveyed several mild steel keels (some huge ones too) attached to GRP hulls and never found much in the way of problems but you do need a pair of small anodes, mount them close to the keel root past halfway aft if it's a foil section.

[SeaJay]

OK. I've seen this steel keel detail a number of places so it must work, but after the thread about the aluminum/lead issue, I thought it best to check. Anyway, I'll save myself some money and stick with steel. Thanks.