Mast compression

[Kelpie]

Time has come to stop ignoring the mast compression on my 1978 Moody 39.
There was always a bit of a dip in the deck locally around the mast base, but following a rig tune up and Atlantic crossing it had become more pronounced.

I'm assuming that I need to remove the mast, cut open the deck, remove top layer of GRP, and remove the compressed material underneath. I'm assuming it will be ply.
Then reinstate using thickened epoxy and perhaps starboard. Replace top deck layer, and make good the cut lines with gelcoat filler.

Anything likely to catch me out?

 

[William_H]

I would perhaps suggest you just remove the mast and fill the depression with resin and glass. To make a small box that looks like it is intended to be that way. Whatever is compressing under the mast will probably not compress any more. So no need to get rid of it. How is that for a bodge? ol'will

 

[Fr J Hackett]

I assume you have a compression post beneath the mast. I would first investigate that and the pad either at its base or top. I suppose if the deck is cored then there will be solid ply underneath the mast heel fitting which could have compressed may even have suffered water ingress and softened but look at the easy area first.

 

[dansaskip]

Well worth checking that there is not a problem lower down - say at the foot of the compression post. I had a friend who had a dip as you describe in the deck (although not a moody) and the problem was eventually traced to faulty packing top and bottom of the compression post. Edited because Fr J Hackett just beat me to it as I was typing

 

[adamstjohn]

We had to do the same, cut open, remove ply that had become wet, glass in a piece of hardwood, fill, fair and paint, looks good and gives piece of mind. scary though cutting into the coachroof but needs must. good luck with it.

 

[B27]

Best to work out exactly what's going on while the mast is still in the boat with rig tension on.

Check the problem really is the mast foot pressing down into the deck, rather than the rest of the deck rising up due to the rig tension.

 

[Concerto]

I remember a Hustler 35 that had a problem with the mast pushing down and depressing the mast step, but it had only just been launched for the first time. We were racing from Harwich to Ostend, and we assisted after the race to sail with them to Breskins for it to be repaired. It was found that the mast post was resting on the top of the water tank in the keel stub. Ooops.

 

[thinwater]

Time has come to stop ignoring the mast compression on my 1978 Moody 39.
There was always a bit of a dip in the deck locally around the mast base, but following a rig tune up and Atlantic crossing it had become more pronounced.

I'm assuming that I need to remove the mast, cut open the deck, remove top layer of GRP, and remove the compressed material underneath. I'm assuming it will be ply.
Then reinstate using thickened epoxy and perhaps starboard. Replace top deck layer, and make good the cut lines with gelcoat filler.

Anything likely to catch me out?

NOT starboard. It will creep and it will not. useless for structural applications.

If you want something pre-made, buy pre-cast structural fiberglass sheet.

No, you do not just fill the cut lines. It will crack (A contractor for a PO did that to my boat--it cracked and I had to do the whole job over). They must be beveled 12:1 and layed up with fiberglass cloth strips to the original thickness.

The core will probably be wet for some area. You will need to remove all of the damaged core and dry it out. The area of surgery is probably ~ 4-8 square feet or so, not just under the mast.

 

[PetiteFleur]

Put your problem on the Moody Owners Association - are you a member? Lots of info and plenty of advice and cheap to join!

 

[penfold]

Put your problem on the Moody Owners Association - are you a member? Lots of info and plenty of advice and cheap to join!

Very likely to be a job other owners have tackled if it's a 'feature of the product'.

 

[bikedaft]

I remember a Hustler 35 that had a problem with the mast pushing down and depressing the mast step, but it had only just been launched for the first time. We were racing from Harwich to Ostend, and we assisted after the race to sail with them to Breskins for it to be repaired. It was found that the mast post was resting on the top of the water tank in the keel stub. Ooops.

Think OP's is deck stepped?

Hustler 35 is keel stepped - the mast foot is designed to be on top of the water tank - did that bit give way?

 

[Tranona]

From what I have seen there is no internal compression post as such because the lobby between the saloon and the forward cabins is central with a fore and aft bulkhead either side and half width bulkheads forward and aft of the mast step - essentially a box. The mast step is a raised plinth moulded into the deck and I would guess there is a wooden pad in that plinth. and some form of transverse beam glassed into the deck moulding.

First thing is to establish whether it is just the plinth that is depressed or the width of the coachroof and whether there is any sign of depression internally.

 

[Kelpie]

Thanks all.
There is a compression post, the passageway is offset to one side. I haven't ruled out some compression at the foot of the post but it does seem less likely, since the main bulkhead is also there with no sign of relative movement.
On deck, as Tranona says there is a little plinth built up and it's here that I'm seeing the deflection. It's pretty localised, rather than being a gradual bend in the whole coachroof.
I'll see what the Moody Owners' Association say, somebody is bound to have had this problem before.

 

[Zing]

I’ve got a hydraulic mast jack. If you are in the south East Med you can borrow it.

 

[Concerto]

Think OP's is deck stepped?

Hustler 35 is keel stepped - the mast foot is designed to be on top of the water tank - did that bit give way?

B27 in post #6 mentioned checking the base of the mast post. Naturally I commented about a failure internally with this Hustler 35 to back up his comment. The top of the watertank did not have any reinforcing to spread the load of the rig, causing all the rigging to go slack. Whether this was a design or builder fault I cannot comment.

 

[Supertramp]

I understand the concern, and your comment that it worsened after rig tune up and a long voyage. But it's lasted for 45 years!

I have slight deck compression (not mast step compression). Different boat, 35yrs old. My approach was to check the deck core by examining the removed mast wiring fittings and examining the underside of the deck where there is a steel plate at the mast step to confirm no water ingress. And now I am measuring the deflection of the flat mast step area (5mm) as part of my annual checks. It is not changing despite some stormy sailing. Interestingly, mine is a ketch and there is some deflection on the mizzen, again in the deck, despite much lower loads. The surveyor said this sort of compression is quite common and can be caused by damage/deterioration or simply a "manufacturing defect" that is unlikely to worsen or change. So my approach is to monitor rather than rip up otherwise sound deck.

Ask the Moody owners club but also check what you can for evidence of a deteriorating problem and monitor the deflection before doing surgery. Older grp boats may not be rigid like modern ones but they are solid.

 

[adamstjohn]

I have slight deck compression (not mast step compression). Different boat, 35yrs old. My approach was to check the deck core by examining the removed mast wiring fittings and examining the underside of the deck where there is a steel plate at the mast step to confirm no water ingress.

Good advice, thats probably the best way to find out if the core is soft.

 

[Kelpie]

Retuning to this question.
I've joined the MOA and after a few dead ends- everybody assumes that all boats are built just like their own- I've been in touch with another M39 owner. He rebuilt the plinth, using sheet grp.
There's clearly very localised deflection in that area so even if there are problems lower down, it needs done anyway. And I can't see any signs of movement anywhere else.

Now to get the mast off... great timing, being right at the start of the season here. SWMBO will not forgive me if this drags on...

 

[thinwater]

There is no reason for this o take a long time. I've done similar cabin-top rebuilds, and if organized, it's just a few days work. Two longish days taking it apart and cutting, and a day replacing the structure. The rest of the days are fairing, with only a few hours of work, the rest to be spent on other things, while each layer cures. Surely there are some other things that could be tended to. Some rigging to replace. The mast could probably use some love somewhere.

 

[38mess]

Sorry, wrong information