Hints and Tips



Mast Compression Post Issues

Some Jeanneau's have suffered from gradual failure of the compression post support pad where it is stepped onto the keel. This is typically is due to water penetration that over time has allowed the wooden pad that the factory used to rot and eventually collapse.


Indications that a boat may be suffering this problem, may include problems in keeping shroud rigging tension and possible leaks from forward windows in the area of the shrouds/masts. Cracks around the base plate or deformation of the deck around the mast step may also be noted. A good surveyor should be able to quickly determine if a boat is effected by this problem.

The good news is that it is relatively straightforward to effect a permanent repair, and indeed many boats produced in the 1990 -2000 era's may have already have been repaired.


The problems are documented on the Sun Rise, Sun Odyssey 43DS (early models) some of the Sun Odysseys such as the SO36.2 and SO45.2.


This article details repairs to the compression post support, but also refer to the associated articles, how to make deck step repairs as well as the one to avoid water penetration from the mast wiring fittings.


The images used below are drawn mostly from the Sun Odyssey 43DS which seem to have been particularly badly effected, but note the images are not all of the same boat - they should only be considered as a generic aid to assist identifying the problem and then selecting the most suitable repair method.


The cause of the problem


Jeanneau typically fit a substantive stainless steel tube, to transfer the mast and rigging compression loads to the hull above the keel. Below left is shown the 43DS and right the 39i.

Where this compression post is stepped onto the keel, on some boats Jeanneau produced, they used a wood insert block to transfer the load forces.


This is not unusual as many production builders often use wood blocks to spread loads where components are bolted to the fiberglass structure. Provided such wood remains dry, for example if it is fully encapsulated in resin/glass, then it can remain effective for very long periods. But problems will arise if the wood does not remain hermetically sealed, allowing moisture or even water to penetrate. For example compression posts are typically installed using coach bolt screws direct into the wood, which must remain sealed with a waterproof mastic.


In many yachts water in the bilges is very common, for example arising from condensate from refrigerators and air-conditioners. Whilst it is often not practical to have a totally dry bilge, it is important to keep them as dry and aired as possible and ensure that drainage limber holes are clear of debris and regularly mop out surplus water.


Repair options


The mast and rigging will first need to be removed. To remove the compression post it may be necessary to insert a large jack and post to support and marginally lift the deck to allow the compression post to be removed.


Jeanneau issued these repair instructions for the Sun Odyssey 43DS - PDF download


Jeanneau advises removing the wood and replacing it with chop strand and resin mix. But a number of boatyards have chosen to add additional reinforcement, such as fabricating an "I Beam" out of heavy G10* and also increasing the size of the base plate to better spread the compression posts loads. Additional laminate may also be added to hull ribs in this high load area.


*G10 is a solid fiberglass/epoxy material which is very dense and strong and has virtually nil water absorption properties. G10 Specifications


As with all GRP lamination, preparation is critical, so once all the original wood has been removed and the area fully cleaned, it should be left to thoroughly dry, possibly using a dehumidifier, before being prepared for the re-lamination.


The final choice of support material and resin type may vary from boat to boat, facilities and experience of the repairer and possible advise from a surveyor.


Some yards have also again used wood, on the proviso that it is a suitable hardwood capable that will not significantly compress and remains fully encapsulated to protect it from any water ingress.

Initial investigations

Below shows the final layer of fiberglass applied. The whole void is now filled solid, both the fore-aft stringers and the athwartships ones now form a continuous support.

Finally "Freeflow" a 43DS owner who has made this repair advises: "One tip I would add is to use the floorboard to know exactly where the post location was. I had it measured and marked, but was off a smidge and had to file a bit out of the floor board cutout hole to fit. Grrr."


The above information and images were originally detailed here on the Jeanneau Owners Forum