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Old 04-30-2018, 09:39 AM   #1
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Drilling Into Stringers

As one big project begins to come to a close, another is on-deck waiting to take its place.

Our cockpit floor is sagging. There are two pics below of the hatch that leads into the engine room in the middle of the cockpit deck. One picture is with the hatch closed and where I am standing is where the sag is the most prominent... The other picture is of the open hatch (stern is up and bow is towards down). The big problem is that the hatch door is flat and the floor is not. It allows water into the engine room faster than the little corner drains can keep up with (nevermind the huge gap that lets it drop in directly without even getting to the drains) What you see in the second picture is the fresh water tank "hanging" in the middle between the boat's two main stringers. Those boxes are the batteries. What I am wanting to do is build an upside-down "U" bracket that bolts all the way through the two stringers, and comes up to support the floor back to level. It would have the added benefit of just making the floor generally more sturdy feeling. It is daunting to want to bolt right through them. Any tips?

I will come up with a 3D rendering I will share in the next week or so too if you are having trouble visualizing it.

Thanks!
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Old 04-30-2018, 10:09 AM   #2
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Yes, it can be done but you need to pay attention to some structural/coring principles:

Any hole through the stringer needs to be sealed with thin epoxy to prevent water entry into the balsa or wood core which is probably inside the stringers. Drill your hole a little bigger than what you need (and you only need a small bolt, all it does is locate the support) and wipe a film of epoxy inside the hole to seal it. Then run your bolt through.

You will be putting two new point loads on the stringers and you are weakening them a little with the bolt holes. So glass a couple of layers of heavy cloth around the hole and maybe 6" to either side of it to distribute the point load. I would build up about a 1/4" thickness of new glass. Try to get the new glass all the way to the bottom of the stringers as the bottom is under tension and will fail first if not strong enough.

David
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Old 04-30-2018, 10:37 AM   #3
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When you drill through the stringer, drill through the center not the top or bottom where most of the stress is located. Sealing the new holes is important as pointed out above.

Alternatively, if you want to avoid drilling the stringer, you could just rest the support structure on the bottom of the hull. Just make it wide enough to avoid creating any stress risers.
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Old 04-30-2018, 11:25 AM   #4
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Why not just come up straight off the stringers with 2 deck supports to any framing in the vicinity of the hatch? The upside down U you describe sounds unnecessarily complex.
Completely agree with sealing any holes with epoxy, and if the supports are vertical the fasteners can be very small because they won't be taking any load, just keeping the supports from shifting

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Old 04-30-2018, 11:36 AM   #5
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What's directly below your feet? Can you support it with a floor jack resting on the top of a stringer? I did something similar and designed the base as a 'saddle' to ride on the stringer without penetrating the stringer.



Here's a link to what I did on my Californian to support the sagging deck. Ironically, your and my boat were designed and built by the same guy, Jule Marshall, of Marshall Boats and Navigator Boats.

34 Californian Floor Jack Supports
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Old 04-30-2018, 11:45 AM   #6
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Why is the deck sagging in the first place? The most common cause is wet coring material which will continue to degrade and sag elsewhere. While it may be painful to take on the project, recoring the deck and reinforcing the perimeter of the hatch would be preferably in the long run. The supports from the stringers could serve as a quick fix for the season but ultimately they are probably a bandaid that will hamper access in the area.
If the core is dry and the deck was just under supported, than nevermind. Maybe some raging dance parties were held back there.
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Old 04-30-2018, 12:27 PM   #7
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Quote:
Originally Posted by Gdavid View Post
Why is the deck sagging in the first place? The most common cause is wet coring material which will continue to degrade and sag elsewhere. While it may be painful to take on the project, recoring the deck and reinforcing the perimeter of the hatch would be preferably in the long run. The supports from the stringers could serve as a quick fix for the season but ultimately they are probably a bandaid that will hamper access in the area.
If the core is dry and the deck was just under supported, than nevermind. Maybe some raging dance parties were held back there.
That's a good point. It may be a little wet in the core from a few snaps that were there until I took them out last month. I will check on that in the future. I will need to put two small access panels on the cockpit floor sooner or later to allow access to the top of the fuel tanks to pull out the level sensor for better tank cleaning. But... the floor isn't very well supported there. The floor is full beam width with no supports the below the entire cockpit. If I had to guess, it is an area about 15'x5'. Under the salon there is a great deal of framing. Under the cockpit are the 2x215g fuel tanks outboard and what you see in the picture.
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Old 04-30-2018, 12:39 PM   #8
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Quote:
Originally Posted by Keysdisease View Post
Why not just come up straight off the stringers with 2 deck supports to any framing in the vicinity of the hatch? The upside down U you describe sounds unnecessarily complex.
Completely agree with sealing any holes with epoxy, and if the supports are vertical the fasteners can be very small because they won't be taking any load, just keeping the supports from shifting

I might. Right now, the battery boxes are in the way. I would need to make a gap between them for something like that. Still, the sag "peaks" directly in the center of the hatch. So IDEALLY, I would like to get some support to the middle, thus the "U"-shape. Straight up from the stringers and straight across to connect them together. But I may try it your way first. Seems legit.
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Old 04-30-2018, 12:44 PM   #9
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Quote:
Originally Posted by FlyWright View Post
What's directly below your feet? Can you support it with a floor jack resting on the top of a stringer? I did something similar and designed the base as a 'saddle' to ride on the stringer without penetrating the stringer.



Here's a link to what I did on my Californian to support the sagging deck. Ironically, your and my boat were designed and built by the same guy, Jule Marshall, of Marshall Boats and Navigator Boats.

34 Californian Floor Jack Supports
Yea... Directly below my feet is the water tank and the crawlspace that goes forward to the engines. My reply to Keys above covers most of what I would say to you, but the picture will help a lot with the design of whatever solution I decide on using. If I decide to move the battery boxes, that would work well.

I will try to add some more pics when I get home to give y'all a clearer picture.
<img id="hzDownscaled" style="position: absolute; top: -10000px;"><img id="hzDownscaled" style="position: absolute; top: -10000px;">
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