Rigging too tight - Mast compressed deck!

[Scorpius]

I've seen a number of older boats where the beam across the cabin, supporting the foot of the deck-stepped mast, and supported by either bulkheads on either side or posts, has rotted or otherwise failed over time, whether fiberglass-encased or not. Those cross-beams often have to be replaced. It is certainly doable DIY.

[dfelsent]

Originally Posted by dfelsent

When I raced semi seriously the backstay tension was up and down all the time. Upwind, downwind, light air or heavy air.
The tighter backstay tensions the forestay, flattening the jib. Even on my Sabre38II with a masthead rig the additional mast bend would flatten the main quite a bit too. Separate fore and aft lowers with a keel stepped mast helped make that happen.
One of my checklist items when leaving the boat way “backstay eased.”
Btw, on that boat I had sails and rig tune set up so the main and jib flatness and fullness played very well together. It was a dream going upwind.

By the way the head door would not close with the backstay on.
Boats move.

[SalingSue]

I thought that was the whole point of a compression post.

[Don C L]

[QUOTE=Marathon1150;3252681]

We rebuilt the step with triradial fibreglass cloth and epoxy resin, drilled multiple holes in the deck near the mast after jacking it up inside the boat (after removing the compression post) and injected the holes with very thin epoxy designed to saturate wood and restore its strength. Five years later all is good.
/QUOTE]

Previous owner of my boat tried that without much luck. Then he added ss straps bolted through the arch and straps. As you can see in photos, that just amounted to a springy hammock for the mast. I sailed it like that for a while when I first bought her and it was ok, it didn't collapse, but I'm sure it didn't do her upwind performance any good! You can see in the photo I removed the damaged plywood and the holes where he injected the resin can be seen. It may have worked for a while. The boat is almost 60 years old so its been through a few modifications.

[mikebikeboy]

[QUOTE=Don C L;3252946]

Originally Posted by Marathon1150

We rebuilt the step with triradial fibreglass cloth and epoxy resin, drilled multiple holes in the deck near the mast after jacking it up inside the boat (after removing the compression post) and injected the holes with very thin epoxy designed to saturate wood and restore its strength. Five years later all is good.
/QUOTE]

Previous owner of my boat tried that without much luck. Then he added ss straps bolted through the arch and straps. As you can see in photos, that just amounted to a springy hammock for the mast. I sailed it like that for a while when I first bought her and it was ok, it didn't collapse, but I'm sure it didn't do her upwind performance any good! You can see in the photo I removed the damaged plywood and the holes where he injected the resin can be seen. It may have worked for a while. The boat is almost 60 years old so its been through a few modifications.

Wow, would love to see a pic of what it looks like now!

That SS Strapping sure went buttery!

[S/V Illusion]

Originally Posted by mikebikeboy

This boat uses bulkheads as compression posts, there is no dedicated compression post, such as a metal pole.

!

Therein lies the real problem.

Compression posts are not optional.

[Don C L]

[QUOTE=mikebikeboy;3252962]

Originally Posted by Don C L

Wow, would love to see a pic of what it looks like now!

That SS Strapping sure went buttery!

Well, many boats don't have compression posts, but the strain must go down onto bulkheads. As I mentioned, the estimate for pressure was around 6000 lbs for my boat, and I don't have a wide beam. I suspect the CD27 is very close to that.

The ss straps are still fine, still got them, they just don't offer much support bolted the way they were.

I don't have a current shot of finished arch but here is one of it in process unfinished. I removed the section of rotten plywood arch. The head and locker on either sides there. I embedded 3 chevrons of 1/4" marine aluminum inside the laminated arch that I had to bolt to sandwich the bulkhead. I added the posts going down to sole framing. I should have consulted with engineers BEFORE building it, but as it turned out, it is stout enough. I would do it differently next time.

[mikebikeboy]

[QUOTE=Don C L;3252987]

Originally Posted by mikebikeboy

Well, many boats don't have compression posts, but the strain must go down onto bulkheads. As I mentioned, the estimate for pressure was around 6000 lbs for my boat, and I don't have a wide beam. I suspect the CD27 is very close to that.

The ss straps are still fine, still got them, they just don't offer much support bolted the way they were.

I don't have a current shot of finished arch but here is one of it in process unfinished. I removed the section of rotten plywood arch. The head and locker on either sides there. I embedded 3 chevrons of 1/4" marine aluminum inside the laminated arch that I had to bolt to sandwich the bulkhead. I added the posts going down to sole framing. I should have consulted with engineers BEFORE building it, but as it turned out, it is stout enough. I would do it differently next time.

Thanks for sharing!

Curious what you'd do differently now. What about using something like G10 instead of Plywood / Aluminum so it would be more monolithic

Although with all those fat bolts in there I'm sure it isn't going anywhere

[Don C L]

I'd think more in terms of fashioning a solid laminated arch with legs that go all the way down to the framing glued on the bulkheads to spread the load out as it was originally intended. The 2 and half inch wide aluminum on its side is strong inside the arch. I was considering that to be the basis of the strength, not the wood. And it did turn out about right, but the bolts introduce weak points, so the fewer bolts the better. And, each bolt presents a place for the whole structure to settle on. So even if it is only a tiny fraction of an inch, some of those bolts settling mean the arch will come down a small amount and stop. I think mine came down about a sixteenth to an eighth over the first year and now it's stayed the same. G10 is fine I'm sure. The arch is wide enough to span the whole mast shoe too (fore and aft) at 6 and a half inches. (The engineers on CF here really taught me a lot in the review of my design! Thanks again to all!)

[GrowleyMonster]

In most big yachting ports, you can't walk through tall grass around the harbor without tripping over somebody's old aluminum mast. Measure, saw it off a bit long, shoulder it and take it to your boat. Makes a dandy compression post. Make sure it is blocked in securely top and bottom so it can't shift. When I did this for a friend's boat I cut it apparently to fit, then hammered wedges from opposite sides between the top and the overhead. Eventually you might get a bit of electrolysis but it should work fine for 10 or 15 years.

[mikebikeboy]

I've gone back to the boat and made some observations.

#1 Bulkhead tabbing to hull looks great
#2 4 compression posts are in good shape / no rot
#3 upon closer inspection, appears this was an issue for previous owners as well

Here are some pictures I took and added notes. Any thoughts / tips greatly appreciated!

[mikebikeboy]

Another idea:

[thomm225]

Over tightening the rigging is sort of a common problem and can destroy or at least harm a boat.

There's a Tartan 3000 next to me with a couple chainplates pulled thru the deck.

I put prebend in my mast back when I first got the boat by cranking all stays the 450lbs and the front lowers to 550. Then a few weeks later I was like geez I may have bent my boat.

I didn't bend it, but I did see an old repair directly under the mast. My prebend is about the same as it was 7-8 years ago

Someone drilled a hole and put something in there like maybe epoxy while possibly having a beam in there holding that section in position.. The depression on my boat is at the mast on the exterior and there are a few stretch mark cracks I guess you could say that haven't changed and are almost filled with paint now since I've painted that area a couple times

My mast is still centered port and starboard so that repair from whenever the PO did to it has held.

[wingssail]

[QUOTE=Don C L;3252987]

Originally Posted by mikebikeboy

Well, many boats don't have compression posts, but the strain must go down onto bulkheads. As I mentioned, the estimate for pressure was around 6000 lbs for my boat, and I don't have a wide beam. I suspect the CD27 is very close to that.

The ss straps are still fine, still got them, they just don't offer much support bolted the way they were.

I don't have a current shot of finished arch but here is one of it in process unfinished. I removed the section of rotten plywood arch. The head and locker on either sides there. I embedded 3 chevrons of 1/4" marine aluminum inside the laminated arch that I had to bolt to sandwich the bulkhead. I added the posts going down to sole framing. I should have consulted with engineers BEFORE building it, but as it turned out, it is stout enough. I would do it differently next time.

Now THAT looks stout! (better than any deck strengthening I've heard discussed here)

[capt jgw]

Originally Posted by Chotu

No problem at all. This happened on my first boat.

Just loosen the mast until you can get the dent to pop back out. Then put a compression post inside, under the mast to keep the deck from deforming again. Tighten it back up as much as you like it and it’ll work just fine.

Not familiar with that model but often there's a narrow passage to the forward cabin under the mast. Putting a post there would block the passage. A post on either side supporting a beam under the mast would be better. It would be a head bumper but wouldn't block the passage. Many small boats are built that way.
At least you're not seeing a deflection in the outer skin and no deflection in the inner. That would mean deck core problems which would be much harder to fix.