Corrosion to Compression Post on LM 30

[baltics2]

I am looking into how best to address corrosion on the compression post at the base of the mast foot support on the LM 30 and am interested to hear from anyone else has travelled this road.

Is it possible to access the original drawings at LM?

Can anyone advise whether the compression post runs full height between the keel and the mast foot or is it just a short unit between the timber return on the bulkhead and the keel?

I am expecting the repair procedure will involve:

• de-rigging and unstepping the mast to unload the mast foot and bulkhead.
• creating access by cutting out a section of the heads compartment floor.
  

• cutting out the corroded compression post section or short unit as appropriate. 
• fabricating a replacement in stainless. 
• fitting the replacement and bonding to the keel and underfloor.
  
• replacing the cut-out to the heads floor; reinforcing as necessary and cosmetically making good.

Grateful for information and observations on the proposed repair procedure.

[Sula]

I have no direct knowledge, but can point you to the following thread from some years ago - lmowners.proboards.com/thread/70/mast-compression-post.  In that an LM30 owner suggests, in response to a query from an LM26 owner, he'd 'discovered a pretty rusted foot plate under the mast compression post'.  

However, though he did not report it in that thread, the owner of that LM26 subsequently found only wood, not metal, supporting the compression post, and repaired it with epoxy and a stainless steel plate.  This is what the same LM26 owner said in the course of a discussion on a different topic on the YBW Practical Boat Owner's Forum www.ybw.com/forums/archive/index.php/t-400807.html.

"The reason I lowered the mast was because the compression post was 'sinking'. It was sinking because the 'core' on which it was placed was actually solid mahogany which had rotted over many years of freshwater running down the inside of the mast.

Anyway, having dug out the **** I then replaced it all with a shoe box sized series of West Epoxy layers. The end result was very satisfying. I faired it, painted it and replaced the compression post and raised the mast.

The next day I discovered the **** was sinking again! Why? None of us here (some extremely better qualified than I) know. Perhaps it is air in the epoxy, exothermic heating (the amibient temp here was about 35 degrees), perhaps the last layer had insufficient hardener - we just don't know.  Anyway, the whole thing has to be re-done, and I have ordered a s/s plate to sit at the base."

". . . I am referring to the area beneath the grp cabin sole and the keel. This, substantial, area is to support the base of the compression post and the solution - back [when the LM26 was built] in 1983 - was to put a girt big hunk of hardwood in there. It worked - for a while, then rotted."

It is not clear from his post whether he used any filler or glass cloth in building up the epoxy layers.  I am no expert, but would think that one or other of these was essential.  

(I am also unclear how water running down the inside of his deck stepped mast found it's way to the support for the compression post below decks, but clearly water had got there from somewhere.)  

Do report back on how you get on with investigating and repairing it, as others may well face the issue at some time.

 

[oceandancer]

Hi baltics2,
I had he same problem on my LM27. the corrosion was due to fresh water dribbling down 2 cables from deck glands.These cables ran down inside the mast support column, exited just before the GRP and away across the top of the ballast to the switch panel. This,I think, was a standard factory installation. I re-routed these cables across the saloon deckhead in trunking which looks OK. I also installed a s/s plate below the mast support column which is resting on the ballast so it's not going anywhere.

Regards

Mick

[baltics2]

Sula, Oceandancer. This is very useful stuff, thank you.

For clarification Mick, am I reading you correctly:

- that the metal compression post runs full height inside the timber return on the bulkhead?
- that the metal post is drilled and moused with electrics, or do the cables run beside the metal post within the surrounding timbers?

If that is the case, then a different approach to the repair may be needed.

Regards

Alec

[oceandancer]

Hi baltics2,
I can only describe what I found on my boat which is of course much older and a different model. The compression post is not against the forward bulkhead on a LM27 but stands in the middle of the saloon. There is a timber pad at the top of the column on which the mast sits. This is encapsulated in GRP at deck level this aspect is prpbably similar in all models. Two cables from mast lights originally ran down my mast and exited near the base terminated in plugs. The plugs mated with deck mounted glands forward of the mast foot the cables from which were run within the deck sandwich back to the mast and (somehow!) through the support block down the mast support column, This was the source of my fresh water leaks and corrosion.

I can see that on the LM30 you cannot see the mast support column and that this looks to be against or forward of the forward bulkhead. You will have to search to see where your cable runs go within the boat. From pictures that I have seen the cables which are a probable source for fresh water leaks seem to run out of the mast on the starboard side to some sort of connector mounted on the deck and from there??...

Regards

Mick

[baltics2]

Thanks Mick

Even if the construction is a bit different, I'm sure there will be family resemblances and I suspect that the source of the water is likely to be the same on the LM 30.

That's given me some pointers to work with when I am next on the boat.

I have written to LM asking if they hold constructional details or whether they can point me in the direction of someone who does.

I will let you know what I find

Regards

Alec

[baltics2]

Apologies for taking so long to come back on this.

I got in contact with LM Energy in Denmark, but they had no-one with knowledge or technical details.

I gave the boat to Sterling Yacht Services at Port Bannatyne. They concluded that the mast support between the deck and the floor ws solid timber. This is supported between the floor and the top of the keel by a short galvanised steel fabrication.

They had to cut the floor support to gain working access to the mast footing, both next to the heads entrance and through the starboard side locker in the saloon.

Although the footing was ugly, they found that a lot of the corrosion was loose iron scrap - nuts, bolts and the like. I don't know if this is what makes up the encapsulated ballast. Investigation found the corrosion on the mast foot itself to be capable of being ground back to clean metal without significant reduction.

The repair involved levelling up the underfloor around the mast footing with glass and epoxy so that water does not pond around the mast footing and encapsulating the lower part of the post in fibreglass.

The underfloor was tidied with flowcoat. I am told this will provide a tell-tale on any future movement. The floor support was reinstated. After a short season of sailing in 2019, the area around the mast footing has always been dry and all seems sound.

I was very happy with this and other work done for me by Sterlings. It is a nice yard and they are helpful if you are doing work yourself. I plan to go back for a mast overhaul next year.

Alec

Attachments: