tabernacle plate bending

[dpatrick]

I also ordered a replacement bottom plate for the tabernacle that was badly fatigued!

[Alan]

I just measured the distance from the aft edge of the mast stub to the aft edge of the transom - it's 10' 10". As nearly as I can tell, the mast stub is directly on top of the compression post.

[dpatrick]

This is where 10’ 10” lands in my boat. This is also where it was to begin with, so my compression post was just barely touching the mast step. What a pain!
What to do, what to do!

[Alan]

I'm glad we're having this conversation - I just discovered something new about my boat. The base of my mast stub isn't on top of the compression post at all, as I'd been thinking for 10 years. It's completely aft of it, just about where yours is. In this photo, you can just see the two long screws that secure the mast foot to the cuddy floor.

DSII compression post and mast base screws.jpg (111.69 KiB) Viewed 12033 times

What else is interesting is that the mast stub, when attached, is angled forward at the top. When I disconnected it from the cuddy floor and placed it in a vertical position, it moved to a point that's probably directly on top of the compression post. So, in other words, if my mast stub had been attached to the cuddy floor where it should be, I'd probably be a lot closer to 11 feet than 10' 10".

If you place your mast base on top of the compression post, how close is it to vertical?

[dpatrick]

If I move mine to 11’ its raked back a good ways. Mine is plum or vertical when it’s behind the compression post.
I’ve been studying the line drawings and it definitely shouldn’t be straight up vertical/plum. The line drawings show a decent rake backwards.
I’ve been discussing this with my brother who’s a professional rigger and he says I should probably move it forward a little.
Now the 11’ mark really applies to the DS1, which has the mast step on the keel. The DS2 has a cuddy floor and bulkhead in the way to get that exact measurement. So who knows what it should be for my boat. All of the real data is DS1 specific which does work for most everything but the mast step.
I’m going to move my step forward to maybe 10’11” , give it a little rake and see how it goes, Not sure if there’s enough room in my forestay and shrouds to do it!

[dpatrick]

I see there being many scenarios for this issue...
O’day didn’t place the comp. post in the right place? I think unlikely
They changed the cabin top and the hole didn’t line up where it should’ve ? maybe?
Someone did some work and didn’t put the mast step on the floor in the right place? very possible!
Mast height measurement throws me off as well, mine is 24’ 3”, oday says 24’9”(assuming ds1) so if I count the floor/ bilge area my mast would probably be at 24’9”

I’m going to measure the ds1 cabin top hole in my driveway and see if it matches my boat, kind of nice to have one here to measure!

[GreenLake]

Misplaced compression post support is not uncommon on DS2's. (There are war stories of masts crashing through the cuddy floor - you will find some of them in older posts here.)

If you have a tabernacle, actual mast rake is not really determined by the placement of the compression post, because the tabernacle is a hinge which could open a small amount to allow less mast rake. This is different from a continuous mast.

Finally, the position of the mast tip is solely determined by the shrouds/forestay combination. With a keel step mast, some of those positions result in mast pre-bend, but with a tabernacle, that would only work if it was jammed shut (and the front pin loaded on tension, not compression) - if not jammed shut, then the mast is free to rotate around the hinge as a whole.

So, things are a bit complex.

[dpatrick]

Right, I do realize the difference between the tabernacle and a solid keel stepped mast.
The hinge is obviously going to have some play. I do think the comp. post is not in the right spot. I’m just left with trying to engineer a way for the mast to actually have more than a sliver of support. So I am going to move the base forward possibly up to an inch and see... the only other proper solution is to relocate the comp. post, not thrilled about that option

[Alan]

How about installing a second compression post behind the first one?

Just in case you haven't already spotted it, there's something to watch out for if you do cut into the floor: There's a stringer running crosswise on the underside of the cuddy floor, not far behind the mast. It would be easy to cut it accidentally and weaken the floor.

[dpatrick]

I’m back!
After all the work I’ve done, my new bottom plate of the mast hinge is badly deformed again.
It is bent down towards the cabin top, just like the last one. My rig is tensioned pretty tight but I don’t believe it’s too high.
The boat sails great and I feel if I loosen the rig any it will be sloppy. Could it be the mast hinge is just a bad idea and too thin to take the load?

[GreenLake]

The tabernacle should not be supporting the main compression load. That load should be supported by the compression post. Where the tabernacle intervenes, the load needs to be transmitted by parts resting flat on top of each other with no give. Looks like in your case there's something off in the geometry and an unsupported piece of the tabernacle gets loaded (and therefore bends - probably just enough to let other parts make contact and take the load as designed).

My thinking would be that as long as you can still raise the mast, you might not need to do anything.

On your photo it looks like the tabernacle is wider than the compression post, which would mean that the overhang of bottom plate needs to hold the entire load - can't imagine that it's strong enough for that. (But, disclaimer, I don't have one of those in my mast, so I don't have practical experience).

[dpatrick]

I think you nailed it. It just can’t possibly take the load. I bought the boat with this installed already so maybe it isn’t even the right application for this hinge plate. Seems it would work good on a deck stepped system (as in bolted to the deck) but it sure doesn’t cut the mustard in this scenario. I may try and make a solid filler piece to insert in between the plates.
But like you said I may just keep sailing it the way it is.