Thwart repair

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Thwart repair

Postby cambo105 » Tue Aug 10, 2010 9:59 pm

Hi everyone, I recently purchased a DS1 and I am in the processes of making a handful of repairs. By far the biggest undertaking appears to be the thwarts. I noticed the thwarts were loose and seemed to have a lot of up and down play. After removing them I noticed the holes in the thwarts themselves had enlarged, and the screws were not holding well were they attach to seat.

I pulled out 2 screws per seat that looked like this:

Image

My question is, what are they anchoring to in the seat? Wood? Fiberglass? How can repair the mounts to ensure a proper fit?

Image

I have considered expoxying the thwarts to the seats, or some sort of bracket on the seat side. Is there a better way to repair the thwart mounts?

And finally, should that chip/hole in the second picture worry me? How would I best remedy that as well?
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Postby jpclowes » Wed Aug 11, 2010 7:43 am

Hi Cambo.
I replaced my thwarts a few years ago. I don't know for sure because I didn't take it apart, but I believe there is a wood backing inside the seat that anchors the screws. You might be OK just trying some larger screws in the same holes. I wouldn't worry too much about the chip in the seat. it should be repaired, but I don't think it is a major structural issue. you can probably fill it with some new fiberglass fairly easily.

Good Luck!
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Postby K.C. Walker » Wed Aug 11, 2010 9:23 am

Hi and welcome to the realm of Daysailers. If this is by far your biggest problem, you've got nothing to worry about. It sounds like you got a really nice boat.

My impression was that there is wood backing to that connection. With luck, it's just an enlarged hole and you could just move up one screw size. I would move to a sheet metal screw rather than use a wood screw, because they have deeper threads. I use the West System method of putting epoxy in the hole and waxing the threads of the screw to make this sort of attachment. If you use slightly thickened epoxy this method works for even the same size screw and is much stronger than depending on the wood alone. Also, it ensures that you have a good seal at this point for your flotation tank

The oversized hole through the thwart is not a problem as long as moisture can't get in there (to rot out the thwart). Again, I use the West System method of stealing the inside of the hole with epoxy.

I would not epoxy the thwart in place because at some point it will need to be disassembled. If you do want to bed it in place I would not use anything stronger than 3M 4200.

The thwart’s purpose is to resist side to side movement of the centerboard trunk. So, as long as the thwart is not jumping out of the pocket on the seat and is attached to the centerboard trunk it will be doing its job. Normally there is no vertical stress on the thwart so that should not be a problem. Of course, I have hiking straps attached to mine so I want to make sure there is no possibility of vertical movement.

It appears your chip is gelcoat only and is basically cosmetic.
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Postby ctenidae » Wed Aug 11, 2010 9:42 am

Mine has no wood on the inside of the seat, but the fiberglass there is pretty thick, so I just screwed right in, with latex caulk sealing the hole.

As for the chip, if you're not going to repair it fully, I'd at least sand it smooth adn put some sort of seal on it. You rub a bare thigh across that, you'll be picking fiberglass out for weeks.
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Postby GreenLake » Wed Aug 11, 2010 2:09 pm

To repair your chip, you have a few options. You could replace the gelcoat. Some places sell small quantities of gelcoat tinted to popular shades of off-white. If you can match yours, you could do a not-very visible repair. (Or you can get repair kits that include tints and match it yourself). Some gelcoat formulations require that you cover the gelcoat to keep oxygen away during the cure. Wax paper works fine for that.

An alternative would be to use a filler. 3M makes something calld "Marine High Strength Repair Filler". This stuff is great to have around for all sorts of repairs around your boat. Unlike regular fillers, it is reinforced by being mixed with short bits of fiberglass, hence the "high strength".

It's great material to repair chips in the leading edge of a center board, for example, because it's strong enough to not be chipped off right away. Or to fill a gouge you made in the keel when beaching your boat.

The only downside is, that it has a green color, so, if you care about looks you'd have to cover it.
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Postby MrPlywood » Wed Aug 11, 2010 2:16 pm

In case it wasn't mentioned, use stainless screws. If you end up installing inspection ports in the front of the seats, you might have enough access to use nuts and bolts to anchor the thwarts. I don't have thwarts so I'm not sure of the reach from the inspection port to the seat mount. I think that would be the way to go if you think you might attach hiking straps.
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Postby GreenLake » Wed Aug 11, 2010 3:27 pm

Yep, should be easy reach.

6" inspection porst in the front face of the seats are the way to go, just search for "flotation" in this forum to learn all about it.
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Postby ctenidae » Wed Aug 11, 2010 3:47 pm

Def easy to reach from inspection ports. I'd be concerned about using nuts, though, as the tool space is a bit limited, and I can envision a long bout of cursing trying to remove a couple of corroded on nuts.
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Postby cambo105 » Thu Aug 12, 2010 7:33 am

Thank you everyone for all the replies, it seems like these repairs shouldn't be too bad.

Greenlake, is the 3M filler you speak of similar to Marine-Tex putty? My boat has a little keel rash from beaching and I was thinking of possibly taking care of that with a little Marine-Tex. So maybe I could also use it to fill in the hole in the seat?

I think inspection ports might be a little ambitious for right now, but possibly a winter project.
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Postby GreenLake » Thu Aug 12, 2010 2:13 pm

The thing about the 3M product is that it has short strands of glass fiber mixed in, and it is polyester (vinyl) based - the latter means that applying gel-coat over it is not problematic.

The thing about Marine-Tex is that it is an epoxy based product, and it appears to not have glass mixed in. The advantage in your case is that your seats are white (close in color) and the chip repair is not heavily stressed. Epoxies tend to bond well, and are if anything, tougher than polyester.

For "keel rash" both might work. Except that gel-coat supposedly does not adhere as well to epoxy based products, so the marine tex (or some paint) may have to be the outer surface.

You can use glass with MarineTex (according to their suggestions, to allow it to fill larger gaps) the 3M product appears to the strong enough on its own to allow it to go unsupported for 1/4" - 1/2" at least that's what it seems to me after I used it to add a trailing edge to my centerboard.

Oh, and you definitely want to use a painter's "gas mask" when using any polyester based products....
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Re: Thwart repair

Postby jackal » Wed May 15, 2013 5:46 pm

Let me start out by apologizing if this is the wrong place to post this or if it's bad to post on an "older" thread. I was doing a search for "thwart" and this thread seemed the most relevant.

When I acquired by boat, my thwart screws were also very loose. After cutting the 6" inspection ports, I noticed the 7" or 8" long wooden blocks that had been "glassed" in inside the seats to "hold" the screws had broken loose. From what I can tell, it was just one layer of fabric holding each of them in. Since I've got about 1/2" of space between the end of the thwart and the seats on both sides, I figured this was why the wooden blocks had popped loose.

Back to the wooden blocks, they are kind of an "L" shape which fit exactly up against the inside of the seat where the screw holes are.

After examining the wooden blocks, it appears that when the thwart screws were installed, they went in between wooden block and the inside wall (laminate) of the seat tank. I've got thread marks on one side of the wooden blocks. I was expecting to see a perfect screw hole in each wooden block to hold a screw. It looked as if you had laid the screws against the wood and hit them with a hammer. An impression of half a screw.

Now, since the wooden blocks are out, when I look inside the seat, the screws are flat against the laminate on the inside (straight up and down). Now that it has come time to re-install the wooden blocks, do I try to re-align the thread impressions with the screws before I epoxy them in or start fresh and redrill the holes after I glass the wooden blocks in? I would install the blocks about 1" or so forward so the impressions wouldn't be there.

I probably need to post some pictures to really do this justice. I'll try and get some.

Thanks,
Matthew
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Re: Thwart repair

Postby GreenLake » Wed May 15, 2013 6:05 pm

As long as your question clearly continues a discussion in an existing thread, I think there's nothing against reopening an older one. If you start what is essentially a new topic, you may find your post forcibly evicted and put out into the street (forum) under its own header. :shock:

If I understand your description correctly, you would epoxy the backing wood where it belongs. Then you would drill some pilot holes. Then you would put a few drops of epoxy into the holes. Then you would wax your screws and screw them in. With this technique, you get the epoxy to help form harder threads in the wood, and with the wax you still get the screws to come out later.

Or you forget about the epoxy and in ten or fifteen years, you find the screws pulling out, and then you pour some down there to try to restore the holding power - your choice. 8)
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Re: Thwart repair

Postby K.C. Walker » Wed May 15, 2013 6:09 pm

Matthew,

Definitely start with fresh holes. I suspect that the reason the blocks popped off was because they were wedged away from the seat tank laminate by the screws. If the blocks you have are still solid, I don't think you would need to worry about relocating them, just relocate where the holes are. Using epoxy, as you plan, should work well. I would think it would be a good idea to use thin epoxy to wet both surfaces and then use thick epoxy to make sure you have a solid bond. You should be able to use the screws to hold the block in place, just wax them so they don't get bonded with the epoxy.
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Re: Thwart repair

Postby jackal » Wed May 15, 2013 8:03 pm

Using existing holes= Epoxy the wood back in exactly the same position as it was removed.

Starting with fresh holes= Simply move (slide) the wood toward the stern 1/2 to 1", epoxy in place, let cure, and drill new holes in the wood.

In both cases it would be best to fill the screw holes with epoxy and coat the screws with mold release.

Would simply bonding the wood in with thickened epoxy, after wetting all surfaces out with thin epoxy be enough? Our should I put a layer of fabric behind it for "insurance?"

thwartbacking1.JPG
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thwartbacking2.JPG
thwartbacking2.JPG (140.05 KiB) Viewed 5906 times
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Re: Thwart repair

Postby K.C. Walker » Wed May 15, 2013 8:41 pm

Okay, yes I would scoot it a half inch or an inch and drill fresh holes. I can't think of any reason to bother with putting cloth on. The thickened epoxy should fill up any spaces and give you a good bond.
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