Mast Support Corroded

[Daverw]

I would get a price for fabrication, they will pay far less for the section than you and will put the plates on top and bottom. It also may look better in round tube and I would suspect that you don’t need as big, ours is 65mm tube, 10m boat

 

[Catalina36]

I know you’re all right just being lazy.– replacement/repair is the best option. I have done some digging and present mast post is set deep in concrete topped over with fibreglass.

I have tried chipping-drilling-cutting but its as hard as rock… and I don’t really want to take a concrete breaker to it – especially while afloat!

If I can support the mast with acrows/beams could I just cut the present mast post off flush with the concrete at the base, remove it, and clean up the sole with a grinder leaving some old embedded mast post behind. Then put new post in over old secured with more concrete/epoxy?

Maybe new post could have some sort of ss plate welded to the base..and the old mild steel top plate which is in good nick welded to the top ?

As suggested if I support the mast during all this with props/acrows obviously they can’t prop up the roof plate which is being removed (see pic). So I’m hoping propped up wooden blocks jammed either side of it laterally will suffice with rigging loosened?

And – if I replace the whole support I will need about two metres rectangular 8 cm X 4cm stainless steel box section. Anyone know a good supplier?

Which grade of stainless should I use … and what thickness should the plate be ?

Should I replace the whole post or just bottom section ?

Many thanks in advance … and sorry for the eternal questions – this is all a bit out of my comfort zone.

You're getting there, it's just a matter of getting your head round it. Don't disturb the concrete, just angle grind the post off flush with the top of it. Arrange a hoover pipe alongside the cut to collect most of the dust, though there won't be that much anyway, the bottom of the post is mostly rust. Once you've supported the mast either side, unbolt the flange at the top, remove the old post and slide the new one, which you've already had made from careful measurements (!), into place. It'll have a matching flange at the top which will just bolt in place and a new flange at the bottom with a couple of holes to allow it to be bolted into the concrete, solely to locate it - there'll be no lateral load on it there.

You're still being distracted by ideas of repairing the old post. Forget it, we're only talking about a 5 or 6 foot length of SS box section, it isn't expensive. and it'll be easier by far to replace the whole thing and bin the old one. Then you'll never have to touch it again. Good luck.

Where are you based if we're to recommend a supplier?

 

[vyv_cox]

You're getting there, it's just a matter of getting your head round it. Don't disturb the concrete, just angle grind the post off flush with the top of it. Arrange a hoover pipe alongside the cut to collect most of the dust, though there won't be that much anyway, the bottom of the post is mostly rust. Once you've supported the mast either side, unbolt the flange at the top, remove the old post and slide the new one, which you've already had made from careful measurements (!), into place. It'll have a matching flange at the top which will just bolt in place and a new flange at the bottom with a couple of holes to allow it to be bolted into the concrete, solely to locate it - there'll be no lateral load on it there.

You're still being distracted by ideas of repairing the old post. Forget it, we're only talking about a 5 or 6 foot length of SS box section, it isn't expensive. and it'll be easier by far to replace the whole thing and bin the old one. Then you'll never have to touch it again. Good luck.

Where are you based if we're to recommend a supplier?

Good advice, pretty much what I was going to suggest before I saw that it had already been said. You may be able to drill and tap into the existing plate for attachment of the new one, best to do this initially so that the new post can have the holes pre-drilled.

 

[rogerthebodger]

I agree cut the bottom off at the base and see what is imbedded in the concrete.

You could replace it with stainless or you could use mild steel and have it galvanized. Mine is galvanized.

If when cut off the existing the remaining post in the concrete is hollow you could make up the bottom of the new with a plate 6 or 8mm thick but also weld a spigot on the underside of the plate such that it will fit into the left over imbedded tube. This will locate the base and the top existing plate re-welded to the new tube.

 

[MikeCC]

I'd want to remove the whole thing before getting new one fabricated. You can be sure top plate holes are in exactly right position then. Put in an extra 4x2 if necessary. If foot of mast is reliant on plate being there for lateral position, you'll need to find a way to secure it on coachroof.
At the base, you may want to have tangs rather than a full flange so they can be bent in situ for any slope on concrete/resin area.
Until you cut it out, you won't know if the concrete/resin is inside the end of the section as well. All the better if you can locate new one in a recess though.
For angle grinding time, just tape dust sheet everywhere and take anything woven out of boat.

 

[jonathanhsm]

I think I’m getting all this and many thanks all. Vyv when you say drill and tap into existing plate do you mean the base of the old post? -assuming there’s a plate there. All I’ve found so far is concrete.

Presumably if I put up supports either side laterally of the top mast support plate I could remove the whole thing and take it to a fabricator who could copy it in stainless including the top plate with the wire and bolt holes which correspond with those through the mast step.

Catalina 36 - There is no shortage of marine fabricators around me .. I live in Lymington…. Although in the past I have found it cheaper to go to automotive welders in surrounding towns…!

Again all suggestions welcome

 

[peteK]

You could just buy the stainless off ebay plenty on there,cut it to size and just get it welded

 

[BabaYaga]

It seems that the compression post is on the forward side of the bulkhead. I foresee that there might be a problem getting a replacement post of the required length into place, especially with supporting plates welded on top and bottom. In other words, the post may have to be made a little bit too short, just in order to get it into position.
If so, this idea might be useful: I had a similar problem when repairing my wooden compression post, which had become a little soft due to rot at the base. I just had to cut off 40mm or so, which I replaced with some pieces of stainless steel plates, stacked up. To be able to adjust the total height of the post, I made some of the plates oversized, with threaded holes M16, to form a kind of 'jack' as seen in the photo below.
By inserting 'shims' made from thinner plate it is possible to adjust the height exactly right.

 

[vyv_cox]

I think I’m getting all this and many thanks all. Vyv when you say drill and tap into existing plate do you mean the base of the old post? -assuming there’s a plate there. All I’ve found so far is concrete.

Presumably if I put up supports either side laterally of the top mast support plate I could remove the whole thing and take it to a fabricator who could copy it in stainless including the top plate with the wire and bolt holes which correspond with those through the mast step.

Catalina 36 - There is no shortage of marine fabricators around me .. I live in Lymington…. Although in the past I have found it cheaper to go to automotive welders in surrounding towns…!

Again all suggestions welcome

I was assuming there to be a plate buried in the concrete. I had a GK29 like this, I dug the strut out and there was a plate on the bottom. You seem to be struggling to dig the concrete out so drilling it might be an easier option.

 

[jonathanhsm]

It seems that the compression post is on the forward side of the bulkhead. I foresee that there might be a problem getting a replacement post of the required length into place, especially with supporting plates welded on top and bottom. In other words, the post may have to be made a little bit too short, just in order to get it into position.
If so, this idea might be useful: I had a similar problem when repairing my wooden compression post, which had become a little soft due to rot at the base. I just had to cut off 40mm or so, which I replaced with some pieces of stainless steel plates, stacked up. To be able to adjust the total height of the post, I made some of the plates oversized, with threaded holes M16, to form a kind of 'jack' as seen in the photo below.
By inserting 'shims' made from thinner plate it is possible to adjust the height exactly right.

that looks a bit complex for me ! But I do share your concerns about getting new post in place and that it might have to come up short...but there's plenty of room for more epoxy/concrete mix under it if that sounds feasible ?

 

[BabaYaga]

a bit complex

Fully agree. I suppose it depends on how sensitive your coachroof/superstructure to some compression. Mine is wooden, so I was keen to be able to adjust precisely.