Compression Post.

[VO5]

Several years ago I spotted a French built GRP sloop whose coachroof and decks were stove in.
On closer examination this boat did not have a compression post to support the mast.
The shrouds, forestay and backstay bottlescrews were tightened as far as they could be.
Has anyone else on this forum encountered similar ?

 

[Seajet]

VO5,

I can only guess the designer was trying a 'ring bulkhead' to take the mast loads; doesn't sound like it worked for that example !

 

[yoda]

Common problem on the Pioneer 9 where the ring bulkhead was reinforced to take the load but poor workmanship in fitting the mast step caused a weakness that eventually causes a failure. easy enough to repair, took less than a day.

yoda

 

[neil_s]

My own boat, when I first got her, used to feature a small pool around the mast step in rainy weather. I managed to conceal a substatial alloy girder above the headlining, but you still need to be careful with those bottle screws!

Neil

 

[Pavel]

That's a typical problem on the type I've got (Vivacity 650). When I raised the mast for the first time, I couldn't tighten the rigging enough, and then I noticed that the area around the tabernacle sagged down (with the mast off everything was fine).
Deck compression is commonly blamed on rigging over-tightening, which might be partially true, but I've also discovered that on mine, the beam (there's no compression post and quarter bulkheads have been alleged to carry a part of the load, but in reality the step lays only on a beam-like strengthening under it) was not a continuous piece, but rather at least three separate sections glassed in. The central one went down, and there you go.
Not impossible to fix - I've ended up opening up and filling in the gaps on the ends of the central section, and then gluing and bolting in a massive piece of iroko under it. Seems to hold to far. I've seen people doing other things, and the local marina guys have suggested something else altogether (parting with a grand and a half included).
The cost - about £100 in materials, maybe about three days work, mostly in foetal position in clouds of either plastic dust or chemical fumes. Not something I would do for fun, but this is better than the mast falling off.

 

[Lakesailor]

I've installed compression posts on two boats.
The first was a Valiant 18, which had a saggy coachroof and the second was a Foxcub Mk1.
That had a steel beam in the coachroof, but it wasn't that effective.
I notice the Mk2 (with a shorter mast) had a compression post as standard.

I am not a fan of tight standing rigging on small yachts. The loads are not much more than on dinghies (except the ballasted keel resists heeling forces).
The overtightened rigging merely drives the mast step down.