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Old 04-07-2017, 23:11   #1
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Deck support beam have come lose

This winter I had my dufour 41 on the hard with the deck stepped mast still on. I loosened the rig a little after hauling. When I came out to the boat this spring I noticed vibrations from the mast inside the boat. Now I realised that the beam supporting the deck just aft the mast have come loose on one side. I have two questions:
1. Do you think the vibration in the rig is the root cause?
2. How should I repair the loosened beam?
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Old 04-07-2017, 23:13   #2
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Re: Deck support beam have come lose

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And a picture of the damage
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Old 04-07-2017, 23:43   #3
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Re: Deck support beam have come lose

Quote:
Originally Posted by Flod View Post
This winter I had my dufour 41 on the hard with the deck stepped mast still on. I loosened the rig a little after hauling. When I came out to the boat this spring I noticed vibrations from the mast inside the boat. Now I realised that the beam supporting the deck just aft the mast have come loose on one side. I have two questions:
1. Do you think the vibration in the rig is the root cause?
2. How should I repair the loosened beam?
1. No, the rig vibrating shouldn't cause any parts of a boat's primary structure to come loose. Such structures should be able to withstand HUGE forces without a second's thought. Think about the kind of loadings they get if you're out at sea when it's blowing 30kts, or even 50kts. There's LOTS of vibrations then, from the wind in the rigging, & on the spar itself. This along with gigantic loads due to punching through waves, along with those generated by the sails. And the static downforce on rigs can on some boats be more than twice her displacement... Before you hoist any sails.

Also this design appears poor in both design, & execution. Especially in that it appears that it was attached with less thought to how to do it properly, than your average mirror. Meaning with just a little adhesive between an undersized mounting pad & the overhead, with zero fasteners or tabbing.
So it's mounting strength was entirely dependent on that small surface area of glue underneath of the mounting pad at the beam's end.

2. I'd need to see lots more pics of how things fit together on this boat to even begin to offer up guesses. And get a sense of how the loads are designed to be carried.

You might talk to the builder, as well as finding an owner's group/forum, about this. As well as hiring a good shipwright to first inspect things, & then make recommendations. Possibly having him doing the fixes as well.
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Old 04-07-2017, 23:51   #4
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Re: Deck support beam have come lose

flod, my heart goes out to you, but UNCIVILIZED is right, on all counts. Fixing Plexus built boats is extraordinarily expensive, if they are to be made sound. Good luck with it, man, it is a huge disappointment.

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Old 05-07-2017, 00:30   #5
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Re: Deck support beam have come lose

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Thanks for your advise! I agree that the beam seems to poorly fastened with just some glue and silicon. I have a good shipyard (same place that it sits on the hard) that have helped me with other plastic jobs before. I'll consult them next winter. I think it should be ok to do normal family coastal cruising as is this season and have it fixed next winter. The mast is deck stepped but have a supporting pole under it to the keel.
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Old 05-07-2017, 00:32   #6
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Old 05-07-2017, 03:19   #7
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Re: Deck support beam have come lose

Would need a picture of the compression post to be sure, but to me that looks like some sort of cover, not a support beam.

If you left the rig untensioned over the winter and it experienced high winds, vibration could certainly have caused the cover to come loose, especially if combined with being only 'glued' on with silicone (as appears to be the case) and the hull distortion induced by being on land...

If you're unsure get some advice from someone who knows about these things in person, this isn't something you want to guess at.
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Old 05-07-2017, 04:11   #8
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Re: Deck support beam have come lose

From that last picture it looks like it separated enough to maybe get a finger behind and feel the part that came loose. If it's a hollow shell without heavy structure inside, then most likely it's just a decorative cap. That it was just lightly glued on makes it even more likely. The yard should be able to tell on close inspection, and the manufacturer owes you at least a phone consultation.
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Old 05-07-2017, 06:46   #9
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Re: Deck support beam have come lose

Hi yes It is "hollow" inside. Maybe it's just for decoration. I doubt dufour can give me a good answer on a 12 yo boat. I tried emailing them before on other subjects and have had no luck in getting answers.
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Old 05-07-2017, 06:47   #10
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Re: Deck support beam have come lose

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Old 05-07-2017, 07:45   #11
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Re: Deck support beam have come lose

I have seen a similar damage on another Dufour where the cabin structure stove in. There seems to be some design / execution challenge at Dufour that they refuse to address. Maybe wrong adhesive. Maybe wrong engineering.

Imho you are in for a proper fix. Lift the mast, remove the whole thing, re-fit with an adequate method, etc.

I would not go sailing like this, too much risk of a secondary failure.

Cheers,
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Old 05-07-2017, 07:52   #12
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Re: Deck support beam have come lose

Doesnt look structural to me. Dufour has a solid reputation. Show us a pic of the compression post and its relation to the damage.
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Old 05-07-2017, 08:00   #13
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Re: Deck support beam have come lose

@barnakiel what kind of damages would you be afraid of? The mast has its own support and the deck seems to be holding up just fine. We did a 40 distance passing over Skagerrack yesterday and I really couldn't notice anything. I will take it down and have the shipyard rebuild it but I was kind of hoping to do it after the season (which is kind of short up here in the north)
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Old 05-07-2017, 08:02   #14
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Re: Deck support beam have come lose

Got to agree with previous posts, this looks like a decorative cover piece only, the mast should be mounted over a compression post or over a main bulkhead, even if securely fastened this would not support the compression loads of a deck stepped rig,
If there is a compression post or for that matter a bulkhead check under the floor for any decompression in that area as some builders use wooden blocks encapsulated with GRP but still can go soft allowing the mast to compress this and load the head liner from the deck collar fitting
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Old 05-07-2017, 08:20   #15
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