Mast Compression Post Failure

[ChrisB]

During the Florida 120 this year, I experienced a failure of the mast compression post. On day one of the event, I noticed that there was much more slack in the leeward shroud than there should have been. We noticed a small crack in the cuddy floor on the starboard side of the mast step casting. The next day the crack had grown and the rig was getting even more slack and we returned to the launch point and retrieved the boat. I double checked the turnbuckles and they have not moved so the slack in the forestay and shrouds is a result of the mast step casting moving downward toward the keelson. At the same time, the floor of the cuddy is cracking and flexing upward. Pictures of the crack are in my gallery. Has anyone experienced a failure like this? Any suggestions as to how to repair it?

Chris Behnke
1980 DS II

[jeadstx]

Saw the post of a boat with mast failure on the FL120, didn't know it was your boat. Have you taken any pictures (thru the inspection ports) of the part of the mast support under the cuddy floor?

John

[ChrisB]

That was us. I noticed after day one that the standing rigging was loose. At the end of day two, we noticed the crack on the starboard side of the mast step casting. We took some pictures from inside the bilge but they didn't reveal much. Since we had to pass by the launch ramp on the way to day three's destination, I checked the crack before we got to the launch ramp and it had spread to the port side of the casting. We decided to pull out a day early before something broke badly.

I plan to take some tonight with additional lighting placed inside that will hopefully reveal more detail. Will post tomorrow.

[jdoorly]

Hi Chris, I repaired my compression post last year. My screws through the mast step were not holding so I bit the bullet and jig sawed the floor around the mast step to gain access. I found that just below the floor there was a square of plywood which was now totally rotten (built 1973). There was a 2 inch dia(?) PVC tube countersunk and glued to the ply and vertically mounted. The lower end of the tube was stuck into a short piece of 3inch dia PVC tube, telescope style, and glued. The lower PVC tube was glued to the keelson. The ply and 2" tube dissassembled fairly easily. I made a 1"h x 3"w x 12"l hardwood block to replace the bad ply and provide a good grip for screws, and used a 2" hole saw to partially countersink (1/2") the PVC tube. I used thickened epoxy to glue both ends of the 2" tube.

To fix the hole in the floor I glued some shelves on the underside of the floor lip where I had cut the floor and then glued the piece of floor I had cut away to the shelves so that the floor was returned to normal. If you try to use an adjacent inspection port you may have trouble with assembly since both the top and bottom components overlap the middle 2" tube and which will require being able to raise the floor temporarily by 1/2" or so.

[ChrisB]

jdoorly,

Thanks. It helps a bunch to have the wisdom of a pair of eyes that has seen the problem so I know what I'm getting into. A couple of followup questions. How big (approximately) was the piece of the floor you cut out to gain access to the bilge? Are there any stringers I should avoid cutting through? You said the 2" PVC was slipped inside the 3" PVC and glued so I assume you did not take that joint apart but rather built the wood block to fit the 2" pipe and then glued the wood onto the pipe, then re-assembled the floor and glued and screwed the floor to the wood block. Is that a correct assumption?

Thanks again.

Chris Behnke

[jeadstx]

Attached is a picture of my compression post below the cuddy cabin floor. Might give an idea of what you are dealing with. I've added two 6" inspection ports in my cuddy cabin floor to get better access under there.

John

[TIM WEBB]

You beat me to it John!

Chris, this is the best pic I was able to get of the post on The Red Witch. Still kinda hard to see what's going on at the top, but at least you can see where the stringers are. You can also locate their position by knocking on the cuddy sole, like trying to find a stud behind drywall ... ;-P

<clicky pic>

[ChrisB]

Thanks for the pics guys. I was not able to get my daughter's camera to flash last night so all I got was a bunch of very dark images! These pics help me understand what I'm dealing with. Based on: 1) the slack in the standing rigging, and 2) the cracks surrounding the mast step casting, I believe that I have a rotted piece of plywood on the underside of the cuddy floor. The missing plywood is not distributing the compression load of the mast and resulting in the cracking in the floor around the perimeter of the mast step casting.

Replace the wood, epoxy the cuddy floor back in place, and I'm back on the water.

[TIM WEBB]

So, the question remaining is what shape and size hole to cut - Jay?

[Alan]

Chris,

Until Jay chimes in, here's a photo from his gallery:



Looks like he took out the whole floor, including the stringer aft of the mast.

Tim,

Thanks for the photo - your compression post looks exactly like mine. I was thinking about posting a not-so-great one I took, but yours is really clear. In fact, I'll probably look at your photo while I'm planning my under-floor operations, rather than lying face down in the cockpit while peering into the inspection ports with a hand mirror and flashlight, slicing my forearms up on the port threads, and swatting at bugs just as my cell phone rings.

[ChrisB]

Looks like he took out the whole floor, including the stringer aft of the mast.

That cut is a bit more drastic than I want to make!

[jdoorly]

Hi Chris, sorry I'm tardy but my homework ate my dog.

I'll have to update that pic of my DS's interior: The battery box is gone and that area is now an enclosed footwell. The batteries are now enclosed athwart the CB trunk.

I cut a 12 inch radius around the mast but you can get by with a smaller square. What you need to do is remove the plywood and the fiberglass that encases it. I was able to grind the roughly fiberglassed plywood from the finished gelcoated floor piece and re-use it in reassembly. I didn't use fiberglass cloth on my replacement wood, just covered it with laminating epoxy, then glued the floor piece to it (and to the 'lip shelves') with thickened epoxy and screws.

After the fact- I probably should have used STARBOARD (plastic wood replacement) because moisture is going to find its way down those screws and rot any kind of wood!