DS3 tabernacle flexing

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DS3 tabernacle flexing

Postby SMichelsen » Fri Sep 28, 2018 12:37 pm

I have a new-to-me 1986 DS3. I have been stepping the mast singlehandedly, holding the mast up with a line from the mast to a bow cleat. I notice that the mast sways some while going through this process; the deck around the tabernacle shows a lot of cracking from flexing. Is this typical? How can I minimize this? Thanks!

tabernacle_2.jpg
tabernacle_2.jpg (115.06 KiB) Viewed 1615 times


tabernacle_1.jpg
tabernacle_1.jpg (89.84 KiB) Viewed 1615 times
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Re: DS3 tabernacle flexing

Postby GreenLake » Fri Sep 28, 2018 4:26 pm

Looking at your pictures, I am struck by how well the deck is fixed to the tabernacle bottom and how solid that connection appears. It is difficult for me to picture how raising the mast could bend that connection far enough to lead to these kinds of stress fractures in the gel coat.
(If you were to observe actual flexing of the deck when raising the mast, that would be a different story, of course)

However, when the boat slams into a wave or someone steps on the deck, the same rigid connection would create a 'hard spot' in the middle of the deck. I find it credible that in both of the latter scenarios the deck would flex everywhere else, but prevented from doing so by the compression post. That, in my view, could easily lead to the kind of stress fractures seen in your photo.

To alleviate that would require a wider backing plate below the deck or perhaps some stringers.

You may be able to reduce the swaying by pushing up the mast until its vertical and held by the shrouds (you do connect these before raising?) and then using the line from the bow only to act as a temporary forestay until you can get the real one connected. I read your description as pulling the mast up with that line instead.
~ green ~ lake ~ ~
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Re: DS3 tabernacle flexing

Postby SMichelsen » Sun Sep 30, 2018 9:00 am

Greenlake, sorry that my earlier post was not clear enough - I am in fact using the line from the bow as a temporary forestay AFTER I raise the mast. I raise it, tie it off, get out of the boat/trailer, connect the "real" forestay and remove the temporary one. And yes the shrouds are in place - In fact I never remove them.

I do try to rotate the mast up as "straight" as possible; however I suppose that there could be some side-to-side motion happening as it goes up. Also I notice that there might be some slack in the shrouds, as the mast may have some sway in it after it's up, and before I replace the temp line. I will attempt to capture this on video and post it in the next few days.

I may be "just the latest newbie" to discover this, but it occurs to me that the connection of the mast at the deck goes through more stress sitting on its trailer than while on the water. At least when the boat is floating, the whole thing moves together. On the trailer, the mast may sway but the boat is locked in place. Of course there's no way around this but to be as careful as possible when raising and lowering, I suppose. AND be sure the shrouds are tight.

As you suggested, I have been considering epoxying some support on the underside of the deck to stiffen it around the mast.

Of course, on top of my inexpert handling, being a 32 year old boat with multiple owners, there's no telling "where it's been" or what misadventures it may have had in the past.

Steve
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Re: DS3 tabernacle flexing

Postby GreenLake » Sun Sep 30, 2018 9:42 pm

Thanks for the further clarification. Looks like you are doing everything fine.

I think you underestimate the degree to which the distance deck/keel would move while the boat is on the water, were it not for the compression post. The support by the water is not fixed, any wave crest will preferentially support the part of the hull above it, opposite for a trough. Heeling produced asymmetric loads and so on. Also, don't forget any loads from people walking the deck. You may not do it, but I certainly walk on the deck a lot, and so may have any previous owners.

Note that the worst pattern of cracks is aft of the mast support. That does not tally with damage from some side-to-side motion in my view. It would however be explained handily by a heavy user stepping on the aft part of the deck.

You are correct that trailering also provides stress on the hull (and transmitted via the compression post) to the deck.

Considering the age of your boat and that you are not doing anything in raising the mast that a competent DS owner wouldn't do, I don't think you need to be afraid of sudden failure or noticeable deterioration in the near future. You could try filling the (bigger) cracks with white Marine Tex (an epoxy paste). This would prevent water from getting into the laminate, which, unless your boat is stored dry and frost free could lead to further damage. Epoxy is a bit less brittle than gel coat and bonds well to cured gel-coat and laminate. I think Marine Tex, due to its white filler, should be fine with UV exposure - usually epoxy turns yellow if not protected, but you might want to read up on it.

If you try to fill cracks, you need to first "open" them up by scraping so that they have a noticeable V shape.
~ green ~ lake ~ ~
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Re: DS3 tabernacle flexing

Postby SMichelsen » Tue Oct 02, 2018 3:20 pm

OK thanks much for the insight and suggestions. I will be trying out Marine Tex.

Best,
Steve
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Re: DS3 tabernacle flexing

Postby GreenLake » Tue Oct 02, 2018 4:18 pm

Won't make an invisible repair, because your typical "white" gelcoat is usually tinted to some shade of slightly off-white. So be sure to check that out before committing. But should seal well.
~ green ~ lake ~ ~
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Re: DS3 tabernacle flexing

Postby badgley » Wed Oct 10, 2018 5:09 pm

Yeah, I agree with GL here that you are probably putting much less stress when you raise the mast compared to almost anything else you are doing. In fact, I wouldn't be surprised if that would be more likely to bend the upper tabernacle plate before it did damage like that. I also agree that the pattern of cracks don't look like what I would expect if you were wrenching it side to side with the mast. It also looks like vertical stress to me where some kind of flex - either crew weight on the deck or the hull flexing upward during trailering or wave action - is basically trying to push the compression post plate up through the deck. For example, on mine it is not connected to the deck at all. The mast passes through an open collar in the cabin top and then the tabernacle plate is another couple inches above that. So the mast and deck are free to move independently. I don't know if what you have is common to DSIIIs or other versions, but yours is the first one I've seen connected like that.

Were the cracks there when you bought the boat? Or have you seen them develop? It's possible they are from some accident in the past and not caused by anything that you need to worry about now. For example, a heavy individual slipping and falling onto the cabin top could do that in a one time accident. My boat was blown off the trailer in a freak windstorm that was so strong that the boat flipped and landed on the cabin top, cracking it. The PO had to have it professionally repaired. As you say, you never know with old boats...
Brian Badgley
1982 DS II #10911 EGRETTA
Blacksburg, VA, USA
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