Cast Iron Floors

[mulligan]

I am in the process of re-building a Robert Clark Mystery, I am unsure if I should replace all of the cast iron floors with 316 St.St or simply replace the three which are in less than perfect condition. I am concerned that there may be some chemical reaction between the different materials, has anyone got any suggestions.

Kind regards

 

[Guest]

Do you have a local foundry, you might find they can cast new ones using the old as patterns much cheaper than S/S replacements and she stays more origional.

Roly, Voya Con Dios, Glasson, Lancaster

 

[Mirelle]

Wrought iron floors

The floors in your Mystery class are not cast iron; they are wrought iron strap floors. (Well, they may be wrought iron; they may well be mild steel in fact!) Cast iron is too brittle for this job.

Your options are two:

1. replace in wrought iron or mild steel, galvanised.

2. replace all floors (no half measures possible) in cast bronze, using the originals as foundry patterns.

I can rabbit on about this as I have just been through this exercise with a boat of the same vintage. Is the keel lead or iron? If it is lead, think hard about replacing all the floors with bronze; you will of course need bronze keel bolts and bronze floor to frame bolts. And a deep pocket!

If the keel is cast iron, go with galvanised wrought iron or mild steel. Wrought iron is obtainable from a company called the Real Wrought Iron Co, who have a website, by the way.
In this event you need wrought iron keel bolts and galvanised steel floor to frame bolts.

When you get the bad floors out you may well find that the total number in need of attention is more than three. Look particularly hard at the floors in way of the mast step; they get the highest loads, and the floor(s) in way of the bilge sump. It is not unknown for a floor to look fine until it is sent off for re-galvanising and shot blasted at which point it falls apart - better at the galvanisers than in mid-Channel!

Wrought iron/ mild steel is fine; think how long they have already lasted! In fact they are almost certainly replacements from an earlier refit; you can expect them to do 30 years easily.

Stainless steel is not suitable in this location as it will rapidly develop crevice corrosion and fail. I do mean rapidly.

 

[mulligan]

Re: Wrought iron floors

Many thanks for your suggestions, Mystico is lying in Cyprus, I will try to find out if wrought Iron can be obtained in Cyprus, you suggest replacing all of the floors. I have chipped all of the surface corrosion of and they seem ok but I appreciate your comments. I don't know about Stainless, I work with St/St as part of my job and feel that if electropolished they would offer unsurpassed corrosion resistance. Anymore suggestions would be very much appreciated, two head and all that.

Cheers

 

[Plum]

Re: Wrought iron floors

lots of sound advice from Mirelle. I will just add a comment on stainless steel. You are right in that good electropolished SAE316 stainless steel will have avery long life, BUT, only while it is contact with oxygen. Because the stainless steel will be in contact with damp wood, mastic, putty, etc, there is a chance of oxygen starvation. Without the oxygen the oxide layer on stainless steel which prevents it from rusting, will break down and you will get rapid corrosion out of sight. There is also a risk of galvanic corrosion with stainess steel.

 

[mulligan]

Re: Wrought iron floors

I agree with what you say but if you passivate with a 20-25% nitric acid solution for 4-6 hours it will maintain the passive layor after electropolishing.

 

[Mirelle]

Re: Wrought iron floors

A strap floor lying in the bilge is in a very hostile environment for stainless. The visible face can maintain its oxide coating, no question, but the invisible face is in damp anaerobic conditions and the floor is highly stressed at the turn from keel to garboard. In my nonexpert opinion this is just asking for crevice corrosion, and since galvanised mild steel does the job perfectly well, and galvanised wrought iron even better, I would see no need to use stainless - if you use stainless, what keelbolts will you use?

One thing that I have been told time and again by professionals, and have gradually learned to accept, is "Replace it like it was; it has done all those years so you know that it works!"

 

[mulligan]

Re: Wrought iron floors

Many thanks for your good advice

Regards
Ross

 

[Mirelle]

Re: Wrought iron floors

Thinking further on wrought iron as a material, the Real Wrought Iron Company advise against galvanising it on their website (http:www.realwroughtironco.com) but I assume this advice is aimed at land use, where indeed it hardly seems to corrode. When we "did" Mirelle's floors, chainplates, etc. the yard (Robertsons) said that re-galvanising wrought iron is a rather uncertain game, and quite often galvanising will not take on old wrought iron, because of the salts that have got into it over the decades. We regalvanised some and put them back, and made new ones elsewhere.

My guess is that your three bad ones may need renewal but the others may be OK for a bit yet. One of ours had actually broken, which shows the load on them.

 

[mulligan]

Mirelle

You mentioned in a earlier posting that we ought to look at the floors either side of the mast step, my father who is overseeing the project tells me that the floors in this area a worse in this area than any other. I will take your advice and replace the floors in either wrought iron or mild steel galvanised, I will keep you informed. Many thanks

Regards

Ross