Mast Support Corroded

[jonathanhsm]

The bottom of my steel mast compression post is badly corroded. See pix. It had been sitting in bilge water for months/years, and while I had fixed the leak so the area is dry ages ago, I only papered over the rust with anti-rust paint etc.

Now during lockdown maintenance I have finally chipped away at the rust which inevitably came away in great slices.

There is still solid metal left although it is perforated in a couple of places. So without major or expensive surgery I am wondering how I can support the support.

Possible options :

Get it welded .. but it’s a tight space and surrounded by fibreglass and welding expensive ?

Build a small dam and surround the base with concrete…or resin

Fill the hollow post up through the perforation holes with maybe builders polyester resin for filling concrete or epoxy. Then glass around it.

Bolt wooden blocks sitting on bilge floor to each side of it – to take the strain.

Any combination of the above … or any other suggestions welcome.

The mast truss it is sitting on appears to be OK – I chipped a hole through the fibreglass and the metal is showing grey rather than brown !

I will have to cut away the woodwork/bulkhead from the rear of the post to get at the inevitable rust on the rearside.

As I say all suggestions welcome.

NB boat is a 30+ year old 27 foot fibreglass sloop with deck stepped mast sitting on metal support

 

[Catalina36]

No pics, but based on the description, how about remove it altogether and replace with a length of stainless box section?

 

[vyv_cox]

Difficult to tell without the photos but by far the best option is to remove the support and either have it welded up, not expensive if you can take it to a welder, or make another as Catalina 36 suggests. An interim might be to bolt steel plates/half tubes to the post (is it round or rectangular?)

I fear that most of your other suggestions are bodges. Having dealt a great deal with companies who repair equipment in offshore oil we worked on the principle that anything done should be mechanically sound and the resin/plastic/filler was a bonus.

 

[jonathanhsm]

Many thanks ...I did attach photos which for some reason didn't attach ( I think they were too bit) here I'm trying again... if possible I'd like to effect a repair without taking down the mast

Difficult to tell without the photos but by far the best option is to remove the support and either have it welded up, not expensive if you can take it to a welder, or make another as Catalina 36 suggests. An interim might be to bolt steel plates/half tubes to the post (is it round or rectangular?)

I fear that most of your other suggestions are bodges. Having dealt a great deal with companies who repair equipment in offshore oil we worked on the principle that anything done should be mechanically sound and the resin/plastic/filler was a bonus.

 

[rogerthebodger]

OK square tube.

I would remove and cut the bottom 300 mm off and plate it up with 6mm thick stainless plate unto about 500 mm so a 200mm overlay. weld the stainless plates to the mild steel. A 50 to 200 mm 8mm or 10 mm stainless plate on the bottom to spread the load.

My compression post is in fact an arch from 100mm 2mm thk square MS tube then galvanized after fabrication. The fit was such we had to hammer it in place with a sledge hammer. My boat is steel with steel cabin top

 

[vyv_cox]

Doesn't look too difficult to get out. The base seems to have been covered with something (concrete, resin plus filler?) to hold it in place. Careful attention with a hammer and chisel should free it, unbolt the top and remove. Weld up in the way Rogershaw suggests and all should be well.

 

[rogerthebodger]

Doesn't look too difficult to get out. The base seems to have been covered with something (concrete, resin plus filler?) to hold it in place. Careful attention with a hammer and chisel should free it, unbolt the top and remove. Weld up in the way Rogershaw suggests and all should be well.

Vyv I would start by cutting it with an angle grinder with a cutting disk and remove it in two pieces then clean up the bottom mounting

 

[vyv_cox]

Vyv I would start by cutting it with an angle grinder with a cutting disk and remove it in two pieces then clean up the bottom mounting

Roger, I agree that will do it but I am very reluctant to use any form of grinder in the boat as it makes so much mess. When I replaced my P-bracket I chipped away about 2 inches of GRP over an area nearly 1 ft square. Tedious but much easier to clean up.

 

[rogerthebodger]

Roger, I agree that will do it but I am very reluctant to use any form of grinder in the boat as it makes so much mess. When I replaced my P-bracket I chipped away about 2 inches of GRP over an area nearly 1 ft square. Tedious but much easier to clean up.

Vyv I was only think of using the angle grinder to cut the post in two pieces, the rest depends on what the mterial below the post is as you say it could be GRP or concrete.

Having cut the concrete wheelhouse of a ferro boat with a full size angle grinder with a diamond cutting blade I know how much dust can be generated.

Also having a steel boat and when cutting steel on deck know hen mess steel grinding can make which usts very quickly if left.

Oxalic acid soon fixes and rusty grinding.

 

[jonathanhsm]

OK many thanks – yes the base is covered in about 1 cm of rock hard resin… underneath that is a metal truss of some sort. Presumably the mast base will just lift off the truss once the resin is removed ? Or could it be welded on?

Also if I remove/cut out the mast support presumably I will have to take down the mast? which might be a bit tricky at the moment, especially as I’d quite like to go sailing this year!

Is there an interim solution where I could keep the bad post where it is (it’s rustproofed reasonably sturdy and has probably been like that for years) and reinforce it somehow.

I am thinking of two L shaped stainless steel plates either side of it … bolted through the mast support and screwed to the bilge sole… something like attached badly drawn diagram?

 

[peteK]

You could support the mast by slackening off the stays a touch and wedgeing a baulk of timber in next too the mast,the correct length,and then remove the support from the boat to replace or repair.

 

[Catalina36]

OK many thanks – yes the base is covered in about 1 cm of rock hard resin… underneath that is a metal truss of some sort. Presumably the mast base will just lift off the truss once the resin is removed ? Or could it be welded on?

Also if I remove/cut out the mast support presumably I will have to take down the mast? which might be a bit tricky at the moment, especially as I’d quite like to go sailing this year!

Is there an interim solution where I could keep the bad post where it is (it’s rustproofed reasonably sturdy and has probably been like that for years) and reinforce it somehow.

I am thinking of two L shaped stainless steel plates either side of it … bolted through the mast support and screwed to the bilge sole… something like attached badly drawn diagram?






View attachment 93978

The problem with that approach is that the bolts will be going through rusted steel which is so thin as to have holed in places. Sorry, but faced with what you have there I'd whip that out entirely and replace it. As PeteK says, slacken the rigging, put in a 4x2 timber prop (the mast on a 27 foot boat is not that heavy, I had one for 10 years), remove the rusted prop and instal a stainless one so you'll never again have to worry about it rusting on the inside. Really, you could have the bulk of the job done in a day with some preparation and pre-measurement.

 

[Spirit (of Glenans)]

The problem with that approach is that the bolts will be going through rusted steel which is so thin as to have holed in places. Sorry, but faced with what you have there I'd whip that out entirely and replace it. As PeteK says, slacken the rigging, put in a 4x2 timber prop (the mast on a 27 foot boat is not that heavy, I had one for 10 years), remove the rusted prop and instal a stainless one so you'll never again have to worry about it rusting on the inside. Really, you could have the bulk of the job done in a day with some preparation and pre-measurement.

Or hire/borrow an Acrojack. (Or two acro jacks with a baulk of timber top and bottom, to spread the load).
IMHO you need to get the corroded compression post out and have a stainless replacement fabricated.

 

[peteK]

As a matter of interest what boat is it?

 

[rogerthebodger]

As a matter of interest what boat is it?

And what are the dimensions of the current mast support.

 

[jonathanhsm]

I doubt you've heard of it... it is a Victorian 27 (not Victoria) designed by Holman and Pye and originally built by Wauquiez - it was known as a 'baby Elizabethan' and one selling point was that it could be loaded onto a train for Belgians and Frenchmen to take to the Med .... ! I'll dig out a pic.

Not on the boat at the moment but mast support is about 8 cm by 4cm ... ish

 

[jonathanhsm]

Pic attached ... painting topsides at the moment in stages between the showers ....

 

[peteK]

Looks a nice tidy boat.

 

[jonathanhsm]

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.

 

[peteK]

The cheap way of doing it is take it too a steel fabricator and get the bottom part replaced in mild steel or get a complete new one in stainless A2.Get prices for both then decide.