Special Ferrocement Deck Screws?

[Colorado Dreamer]

I have a ferro boat that is new to me and I am about to attach some deck hardware to the boat.

It occurred to me that there might be some sort of special screw I am supposed to be using or something. I asked around, and no one had ever heard of anything like that, but I could tell they were not ferro owners.

I have tried to search the internet with no luck, and so now I turn to you all for assistance.

HAve you ever heard of such things? If not, what do you use?

I am attaching a block to mount a winch on.

Repeat after me:

THRU_BOLTS AND BACKING PLATES!!!!!!

NO SCREWS!

Especially with ferrocement you HAVE to spread out the load. Drill holes and have a substantial metal backing plate of a size at least as big as the block above and bolt all the way thru the deck and the backing plate.

If what I said doesn't make any sense, you need local professional help with the installation.

[Boracay]

I'll second the comment about using backing plates.

I'd even go further and suggest using oversize washers over and mastic under deck hardware and backing plate.

I'd prefer galvanised bolts (if 1/4" or larger is to be used) and well painted (galvanised even better) steel backing plates, but others may have other opinions. If smaller bolts are being used I'd go with stainless.

Ferro cement will not take kindly to any tension load.

An additional thought occurs to me: Why aren't you bolting the winch through the block? It makes very little sense to bolt a block to the deck, then screw a winch to the block. You really should be through bolting the winch, right through the bock and deck with the backing plate, etc.

Boracay has a good point about the mastic, you don't want to crush the cement by point loading, you might be better with mastic on both the top and underside of the deck to be sure you aren't crumbling things.

What size winch are we talking about? What kind of loads are we dealing with? If it's a primary sheet winch, loads are high and you really need to do this RIGHT.

[stuartcnz]

Good suggestions so far. I would however go for plywood backing plates. They can be very big and they will have even less point loading than metal backing plates, make sure you use oversize washers though. And use a sealing compound to help ensure that there are no leaks.

[Boracay]

I can see merit in using thick plywood for backing.
I would suggest fitting closely, drilling holes, saturating with thinned epoxy resin, then fitting as discussed.

[Colorado Dreamer]

Thank you EVERYONE for your comments. I was a bit distracted when I wrote my original post and was thinking of two different situations that somehow got formed into one in my mind and then ended up neglecting the original question I had in the first place.

Rest assured, I have ALWAYS intended to use backing plates (and have) on every thru deck hardware piece.

What I was meaning to ask and did not do a very good job of was should the screws, bolts, or whatever be made of any special metal since they might come into contact with the inner frame or mesh on which the boat is formed up on? Could using the wrong metal cause some sort of reaction over time that would cause problems?

And also, I used brass screws to reattach a small teak piece to the deck. I also used an epoxy glue under the board....it seems to be holding nicely. I think that is where the "screws" came from as I had just finished doing it. Was brass the right choice? I thought they looked nice. But the more I think about the metal on metal issues, I am not sure.

[emeraldsea]

Brass will be fine, and you can get away with galvanized, but the only bolts or screws I would use on any boat for any application is stainless steel. I would seal the bolts with epoxy from both sides, and you won't have to worry about the metal on metal issue.

[stuartcnz]

I wouldn't use brass personally, because of the zinc content in it. Having said that I wouldn't be in a hurry to remove the brass screws if they are not being used in a structural roll, but would would replace them with bronze if you like that colour, or stainless steel ones, if they are coming into contact with another ferrous metal at such time as seems necessary.

[Colorado Dreamer]

Thanks for all the advice guys. I appreciate it.

[Alan Wheeler]

There are three components to an electolytic action between dissimilar metal. There are the two metals and the third component is the electrolyte being salt water. Keep the water out and you can have the two dissimilar metals touching with no issue. So if the bolt is sealed, then brass or SST against Ally or steel or whatever is fine.
Having said that, in general Brass against steel is fine. SST against Aluminium is not good. Bras against Ally is OK'ish. I imagine the winch is coated with something that woudl isolate the bolts anyway. So SST bolts woudl be best choice. There is no issue with the SST against steel as long as the water is kept out. Steel rusting will contaminate SST and also cause it to rust. But you do not get a galvanic reaction of any consequece between the two. I would presonally not use Brass bolts due to that fact they are not as strong. Galv bolts work OK, but eventually the galv erodes away and will need replaceing. I have may glav bolts on my boat I need to look at swapping out because all the exposed heads are corroding.