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Old 07-04-2016, 08:09 AM   #1
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marine trader cracked deck beam

I have annihilated the rotten bulkhead that separated my lazarette storage area from my aft cabin. I also tore out an overhead section (see picture) next to the bulkhead that was in poor condition. In doing all this, I discovered another nasty little secret: a cracked deck beam. The cracks are located directly under the aft corners (port and starboard) of the structure that forms the sides and roof of my aft cabin. The designer/manufacturer botched the job of providing adequate structural support for all that weight. Over time, I think the weight of the aft cabin roof pushed down on the side decks until it eventually cracked the deck beam supporting the rear of the aft cabin structure. The deck beams are hollow 'U' shaped structures, made of fiberglass, and attached to the underside of the decks with fiberglass. I plan to install a pillar in both locations, with enough wood above and below the pillar to distribute the load a little (yet another item on my boat's to-do list).


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Old 07-04-2016, 09:03 AM   #2
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Hat channels made of 'chop' aren't nearly as good as one would wish. Wood posts would be fine, presuming you can accept their existence. Using glassed-in knees might be worth considering. Jacking the after end of the aft cabin structure back up to where it was intended and reinstalling the bulkhead properly would be best, I think.

Our lazarette bulkhead is rotted, delaminated and much-repaired. It does not appear to have adequate limber holes to allow water to flow forward to the bilge sump. It has not yet collapsed enough to cause damage elsewhere. A project!

I had similar hat channels made of glass cloth in a Flying Dutchman hull. I glassed over the cracks which were just forward of the relatively stiff bottom-cockpit floor. The whole boat was lightly constructed and the urethane foam core was turning to dust. Repairs enough to go sailing! (But not good enough the race the 'bananna boat'.)
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Old 07-04-2016, 11:51 AM   #3
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And I still have people tell me their MT is just as good a boat as my GB was.

Good luck with it. I'm sure all your hard work will pay off with a better boat in the end.
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Old 07-04-2016, 12:47 PM   #4
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Hey! I was walking the docks the other day and saw the cloud of fiberglass dust coming out of your boat! Not envious at all

I'm over at Cuttysark if you need a hand or just have someone drink beer and watch you work, ie. "helping"
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Old 07-04-2016, 01:05 PM   #5
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Hat channels made of 'chop' aren't nearly as good as one would wish. Wood posts would be fine, presuming you can accept their existence. Using glassed-in knees might be worth considering. Jacking the after end of the aft cabin structure back up to where it was intended and reinstalling the bulkhead properly would be best, I think
I had thoughts similar to yours. I even considered installing a little bulkhead, very similar to your "knees" idea. But, it would make a mess of my main cabin, so I think the "pillar" thing might be the least-bad idea.

I was thinking about a 4"x4" pillar made of "something", and then add a thin layer of teak over that. My question is the "something". Do you think I should laminate together a couple fir 2x4s, or maybe a 4x4 pressure treated post, or maybe something else entirely?
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Old 07-04-2016, 01:09 PM   #6
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Hey! I was walking the docks the other day and saw the cloud of fiberglass dust coming out of your boat!
I had to laugh when I read your post. A "cloud of fiberglass dust" pretty much described it perfectly. You would think I would know better at my age. Thanks for your offer to help. I'll give you a shout if I do.
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Old 07-04-2016, 01:13 PM   #7
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OUCHHHH! Best luck on speedy, lasting repair. Happy 4th!!
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Old 07-04-2016, 07:59 PM   #8
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SBG, I don't understand where the failure is. Do you have a plan view showing the layout? You said you'd chopped out a rotten bulkhead to discover the problem. Is not the cracking related to the rotted bulkhead?
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Old 07-04-2016, 08:48 PM   #9
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SBG, I don't understand where the failure is. Do you have a plan view showing the layout? You said you'd chopped out a rotten bulkhead to discover the problem. Is not the cracking related to the rotted bulkhead?
The rotted bulkhead divided the lazarette storage area from the aft cabin. It was not a load-bearing bulkhead (thank god). Hopefully, this sketch will give you a better idea how things are laid out in my boat. The purple outlines the rotten bulkhead I tore out (I will replace it very soon with fresh wood). The green lines represent where that bulkhead was secured with fiberglass tape to the hull. As you can see, the bulkhead did not have any structural connection to the structure forming the underside of the deck. Not only that, but the bulkhead doesn't even touch the bottom of the boat in the vicinity of the steering gear. When I removed the rotten bulkhead and some other rotten structure around it, it then exposed the cracked deck beam (or at least the aft face of the cracked deck beam). No way that rotten bulkhead was supporting the weight of the deck. Besides, that rotten bulkhead is about 20" aft of the deck beam (the deck beam is shown in red). The deck beam is directly under the aft face of the aft cabin structure.

For my pillar, do you think I should laminate a couple fir 2x4s together, or go with a 4x4 pressure treated post?

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Old 07-04-2016, 09:43 PM   #10
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Use good quality lumber, ideally air dried fir. House lumber (kiln dried) belongs in the house. I would not use. that pressure treated stuff. Whatever you use I would paint with a couple of coats of epoxy, especially soak the ends.
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Old 07-05-2016, 07:21 AM   #11
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So is the beam actually visable in the cabin or is it behind the headliner or paneling of some kind?
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Old 07-05-2016, 08:09 AM   #12
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On my boat under the side decks in the same spots are little square cabinets that add support.


If you do go with pillars, check the strengths of different kinds of wood. you may find that a true dimension 2x2 will support a heck-of-a lot of weight.


The pillar that supports the deck beam under my flybridge is only 2x2 and is turned down even further like a spindle on a chair for cosmetics.
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Old 07-05-2016, 08:33 AM   #13
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So is the beam actually visable in the cabin or is it behind the headliner or paneling of some kind?
In the vicinity of the crack, only the aft face of the beam is visible. The bottom and forward faces of the cracked beam is hidden my other structures. Once everything is put back together, the cracked portion of the beam will not be visible or accessible.
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Old 07-05-2016, 08:36 AM   #14
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Use good quality lumber, ideally air dried fir. House lumber (kiln dried) belongs in the house. I would not use. that pressure treated stuff. Whatever you use I would paint with a couple of coats of epoxy, especially soak the ends.
Got it. We have a reasonably good lumber store in town with stuff like teak and marine plywood. I'll see what they carry. Thanks for the feedback.
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Old 07-05-2016, 09:37 AM   #15
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In the vicinity of the crack, only the aft face of the beam is visible. The bottom and forward faces of the cracked beam is hidden my other structures. Once everything is put back together, the cracked portion of the beam will not be visible or accessible.
If the beam is straight with no camber to it you could use aluminum square tubing. The exposed portion could be wrapped in veneer, wrapped in vinyl that looks like wood or painted.
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Old 07-05-2016, 10:30 AM   #16
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What is inside the beam?
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Old 07-05-2016, 10:36 AM   #17
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What is inside the beam?
Nothing. The beam is hollow.
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Old 07-06-2016, 12:55 AM   #18
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from your pix, the beam looks like it was never continuous. It doesn't look like a crack, rather, it looks like one piece of it stops, then another piece continues on, with no connection between the 2.
Is this a molded deck? Or is it built up on beams?
If molded, as most FG Tiawan boats, there shouldn't be a beam in that location, as the deck structure should be strong without one. If not molded, there should not be a hollow, choppergun beam, rather, there should be a solid hunk of teak or mahogany in that location, as you will likely find holding up the floor in your saloon. That object might be something altogether different. Especially if there is no deflection of the deck or cabin roof in the area of the "crack"
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Old 07-06-2016, 12:59 AM   #19
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Yes Keith, that was my thinking too - wondering if a water line or electrical or something was located in there.
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Old 07-06-2016, 01:06 AM   #20
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Tom: Good to see you are following along. Are you getting out on your boat again?
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