Jeanneau Mast Compression post support collapsing

S

Splinter

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www.smallboatsurveys.com
Hello

The structure under mast compression post on my Jeanneau Sun Rise 35 has collapsed by about 10 mm. This has caused the coach roof to be concave around the mast step. Any advise on the right way to put this right would be welcome.
 
I recall a conversation with a Jeanneau owner some years back who had this happen to his boat. The problem then was water ingress that has rotted the crossgrain balsa core so that tightening the rig just pushed the mast heel further down on the compression post. I would suggest de-rigging as the first move and then have a poke around the deck step to see exactly what needs to be done.
 
They may well have used soft wood packing between mast compression post and deck.
To repair this correctly you are most likely going to have to remove the mast, to see if the compression is permanent. If so then coach roof under mast support will need cutting out and re-glassed and packing above mast post replaced with good hard wood.
 
The OP is talking about the structure under the mast compression post ie the bit between the post and the hull. Presumably its the packing that has given way a bit and its not an uncommon problem. The solution depends on the design of the individual boat but probably involves digging out the structure under the post and replacing it.
 
If the coach roof is now concave without having caused any cracking then you could remove the mast then jack up the coach roof from the inside using an extendable building prop. You can hire these at HSS hire shops I would only try and do this a few millimetres at a time over several days. You shouldn't push the prop through the hull as it will be very thick there but I would spread the load under the prop anyway. Once you get the coach roof back to where it came from I would dig out whatever was below the compression post and replace with new hardwood and glass all around it.

If the mast is still up and you want to save a bit of cash you could try it without mast removal. loosen the rigging slightly, jack up the roof a millimetre or so then loosen the rigging a few more mil then jack some and so on.

If this a stainless post with the saloon table built round it you will have a bit of extra work removing it to get the temp prop in

Thats how I would try it.
 
Last edited:
samwise said:
I recall a conversation with a Jeanneau owner some years back who had this happen to his boat. The problem then was water ingress that has rotted the crossgrain balsa core so that tightening the rig just pushed the mast heel further down on the compression post. I would suggest de-rigging as the first move and then have a poke around the deck step to see exactly what needs to be done.
Click to expand...

This is a very likely cause. Jeanneau used end grain balsa as a core between the deck surface and the inner surface. On some boats this includes the area under the mast step. It needs to be established whether the structure under the post really has collapsed or whether it is the balsa core. If the latter the deck will be depressed around the mast step, but internally it will still be OK because the compression post holds it up. If the structure below the post has failed then the inner lining of the deck structure will also be distorted downwards. The headlining needs to be removed to prove it one way or the other.

If the balsa core has rotted, then its a nasty job to repair, requiring the mast down and a section of deck cutting out to replace all the rotted balsa. I would suggest replacing the bit under the mast step with a solid GRP layup.
 
I don't think there's balsa wood under the mast step.I've fixed the same problem on a Jeanneau Rush for a friend and there was a plywood pad that had compressed.I cut the area open and replaced the plywood with stainless steel inserts of the correct thickness that were epoxy laminated in place.The Sun Rise is probably the same in that area.
 
Why do boat builders continue to put timber or ply into the bilges of boats knowing the risk of failre is common.

You will have to remove the useless lump of ply and replace it with a more suitable material, access will be the key to a good repair, trying to work between the compression post and the hull may well end up a second rate repair.

If you can slacken the rig and remove the post wile supporting the mast by other means then remove it.

Use epoxy resins and epoxy cloth (Not CSM) to ensure a good bond the existing hull material.

A stainless steel plate bedded on some epoxy and Micro fibres will ensure the load is evenly distributed and well bonded, glass over and paint with flow coat for a professional finish.

Good luck and fair winds. :)
 
If you read French,on the Hisse et ho website there is a thread concerning the Symphony compression post and how to repair it
 
Jeannea mast compression post

Hello to everyone who responded.

I seem to have both the problems mentioned in the replies. The packing under the compression post has collapsed by about 3/8" and the coach roof around the mast step is concave but the underside of this area is flat.

I have just started the repairs. The boat is out of the water, the head linings are out, the rig is supported (By halyards from four boats close by) the compression post is out (replaced with an Acro prop for now) and the GRP underneath it is being ground away. Once I get back to solid undamaged GRP I will build up the area under the compression post with a 316 stainless plate and reinforce the surrounding area with layers of GRP and put everything back together.

I think the problem under the compression post was caused by bilge water getting through small cracks in the GRP around the compression post base plate. I have found some rot under the plywood subframe just forward of the compression post. When I ground away the GRP from this subframe I found there was no filleting around the bottom of the frame ( I think this is called a root void) The compression post base plate probably had been glassed in in the same way as the subframe and small cracks in the GRP around it had let water in.

Needless to same there won't be any voids when I glass it back up.I will leave the repair of the coach roof until next winter, there are only so many hours in a day!
 
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