Thwart repair

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Seat and Thwart repair

Postby GreenLake » Wed May 15, 2013 9:34 pm

+1 on cloth not adding anything useful.

As for the epoxy; my goto epoxy is "GelMagic" from SystemThree in the cartridge with the self-mixing tip. That's a non-sagging formulation tweaked for gluing. The self-mixin tip makes it really convenient to mix as much as you need (and only losing what's inside the one tip) or you can squeeze out directly from the cartridge for smaller amounts and mix by hand.

The tip only needs to be replaced if any epoxy "kicks" inside it. Unless it's very hot that should not happen during a short break in the work, so you should be able to use the same tip for both port and starboard...

Despite this being "gelled" I've been informed that it wets out well enough to use it (in a pinch) to wet out some cloth or, as in this case, coat some wood. In other words, for a small project like this you don't have to mess with multiple types of epoxy.

West System's 6-10 comes in a cartridge as well, and it might be comparable - I don't know the details, nor have I contacted the manufacturer.
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Re: Thwart repair

Postby jackal » Thu May 16, 2013 11:37 am

Thanks everyone for all the helpful advice!!

I was just going to use the West System 105/209 I have on the shelf in the garage. 209 being the extra slow hardener since I'm in Texas.

Here's my anticipated order of operations:
1. Clean bonding surfaces with acetone (wax removal) and sand with 50-80 grit paper (so epoxy can "key" into the surface)
2. Epoxy blocks in place (wet out all contact surfaces first, then use thickened epoxy (with colloidal silica??);
3. Drill new holes with 1/4" to 3/8" bit (mostly for the wood's benefit here)
4. Tape drill holes from underneath;
5. Fill new holes with thin epoxy;
6. Removed tape to let thin epoxy run out. Re-tape holes
7. Thicken epoxy (colloidal silica??) and refill holes;
8. Coat screws with mold release and install.

Questions:
For #3, should the pilot holes be larger than the screw threads?
For #8, what's the best thing to use for the release? Wax (if so, what kind)? Non-stick cooking spray? At what stage in the curing process do I install the screws? Or does it matter with thickened epoxy?

Thanks Again!
Matthew
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Re: Thwart repair

Postby K.C. Walker » Thu May 16, 2013 12:06 pm

Matthew,

I think you'll be fine with the West System as you plan. I often thicken with sawdust, mainly because I have plenty of it. I don't think you need to get too fancy with the epoxy in the screw holes. I have had no problem with drilling a normal size pilot hole so that the screw catches threads in the wood as would be normal. That way you can just put epoxy on the screw before inserting and I use a toothpick or a Q-tip with epoxy to swab it in the whole before inserting the screw. Cooking spray should work fine for a mold release. I use paraffin wax.

What you are doing is not a high load situation. The main reason for using epoxy is to seal moisture out.
KC Walker, DS 1 #7002
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Re: Thwart repair

Postby GreenLake » Thu May 16, 2013 12:42 pm

I concur with K.C.
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Re: Thwart repair

Postby jackal » Sat May 18, 2013 7:26 pm

Well, I'm starting in on the project and I noticed my port thwart is 15 1/2 inches long, while starboard is 14 1/2 inches. Should this be a major concern?

I'm pretty sure these are the original mahogany thwarts.

Using my hand (at the top) to push and pull I can move the trunk about 1/4" both ways with the thwarts off. Do I need to strengthen the base of the trunk?

Thanks!
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Re: Thwart repair

Postby GreenLake » Sat May 18, 2013 8:26 pm

You could leave them - yours would not be the first boat to have issues with symmetry :D

You do not need to strengthen the base of the trunk. The thwarts are there to lock it in place - and at the top they have all the leverage they need.
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Re: Thwart repair

Postby seandwyer » Sat May 18, 2013 11:39 pm

Hey, Jackal,

+1 to Greenlake's assessment of symmetry. I just removed my thwarts to refinish them and noticed they, too, were different lengths, but not even a uniform inch such as yours. Mine were oddball sizes and didn't really even fill in the entire space between trunk and the slot in the bench. I epoxied blocks on to the ends to fill in the difference and the blocks also were different lengths from each other. I think when they made these boats they laid up the hull and then glassed in the trunk using the "eyeball" method of measurement, then, simply cut individual thwarts to length that would fill in whatever length they needed.

When I took mine off, I also had issues with the holes not really being sound enough to hold screws. The blocking was still in place, so I just slowly filled the holes in with epoxy over about three days or so. Each day the puddle I made on top of the hole would sink down and solidify. I just kept it up until they were filled, then drilled them out before reinstalling the thwarts. I think some guys might recommend you try to inject the hole with epoxy, then wax the screw threads and run them in while the epoxy is still soft. I didn't do that and everything seems to have worked out really well, but I just did this, too. Only time will tell.
Sean
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Re: Thwart repair

Postby K.C. Walker » Mon May 20, 2013 7:24 pm

My thwarts were also of unequal length by about an 5/8 of an inch. I think Sean might have the right idea with the eyeball method of centerboard trunk placement. Ideally your centerboard is in the same plane as your mast. Mine was not by a fair amount. My centerboard trunk was not even lined up with the keelson, let alone the mast. I was doing major surgery on the bilge area and my centerboard trunk had a fair number of cracks around it where it attached to the hull so I decided to straighten my trunk up. In doing so I distorted the hull a bit so ended up fixing that in faring. I had a lot of that to do anyway.

I guess what I'm saying, is be aware that you may distort your hull a bit by moving the centerboard trunk. It's probably not worth it. As has been pointed out, the boat does have a lot of asymmetries.
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Re: Thwart repair

Postby jackal » Thu May 23, 2013 11:25 am

Thanks for all the wonderful advice!!

I'm definitely going to keep the lengths of the thwarts the way they are. I don't want any unnecessary tension on the centerboard trunk/seat tanks when the boat is at rest (on the trailer).

-Matthew
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Re: Thwart repair

Postby Cliff » Sat Sep 29, 2018 2:01 am

Seat and Thwart 003.jpg
Seat and Thwart 003.jpg (27.18 KiB) Viewed 2433 times
I have an a DS with wood seats and thwarts. They were joined by a door hinge type bracket that does not seem to be something that would be original. I have removed the seats as they have become too springy and am replacing them with new boards. Attached are some pics of the seat & thwart.

My question is how did O'Day originally join them together? Also as the seats are too springy (fell they are about to fail) do some some owners put in intermediate post supports for the seats?

Seat and Thwart 003.jpg
Seat and Thwart 003.jpg (27.18 KiB) Viewed 2433 times


Seat and Thwart 002.jpg
Seat and Thwart 002.jpg (33.02 KiB) Viewed 2433 times
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Re: Thwart repair

Postby GreenLake » Sat Sep 29, 2018 3:43 pm

Few of us have a DS1 of that vintage and not many have even seen one. That said, we still might be able to give you some general suggestions. From the photo, I find it hare to picture who these boards were positioned in the boat. Is the configuration such that the thwarts go from CB to the side of the hull, and the seats extend aft of the thwarts only? That would be on contrast to the later design, where the fiberglass seat (tanks) extend forward of the thwarts and the latter only extend between the seat edge and CB.

If I understand your configuration correctly the sideways forces from the thwart go directly to a hull bracket. The connection to the seat (helps ?) support the seat (I assume there's some 'leg' below the seat to take most of the weight, but from what you show us here we don't know where it's positioned fore-and-aft.

The hole pattern you show in the picture (alternating) would match that of a hinge. There's no need to have that connection actually be able to flex, I think, so the hinge may have merely been a convenient way of doing a repair. I don't see why you couldn't replace it by a suitable wooden backing, like a piece of 3/4" plywood (nicely stained and coated in epoxy on all 6 sides and in any drilled hole - see earlier posts here about that).

You write that the seats are "springy". Is the wood affected by rot, or are they just undersized a bit (and / or possibly lacking the seat supports I was speculating about before). Unless there's rot, I don't think that wood becomes "springy" as result of age.

Do you find any indication, other than the hinge, that the entire set of seats/thwarts had ever been rebuilt before?
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Re: Thwart repair

Postby GreenLake » Sat Sep 29, 2018 3:58 pm

Ah, just found this picture in a neighboring thread (titled "#37"):
Image

Unlike your picture, here it seems that the thwart is a single piece (unless the mainsheet hides a split).

But it appears that there is no connection between seat and thwarts and that the seat supports are spaced so that the front end of the seat can sag. This makes it very likely that a PO tried to remedy the issue and found a hinge suitable for his purpose.

If the wood for your seat benches isn't actually damaged, but only undersized, I might consider gluing a strip of wood 3/4" x 2" under the inside edge (a bit recessed so it's not visible from across). I think you will find that this will nicely stiffen the seat (as the bending strength rapidly goes up with the thickness, the strip does not have to be all that wide). Same recommendation to seal with epoxy on all six sides after staining to match. (Water-based stains are preferred for use below epoxy).

If the seats are in reasonable shape other than being to flexible, this might be a cheaper/easier fix.
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Re: Thwart repair

Postby tomodda » Sun Sep 30, 2018 12:00 am

Guys.. Give me a chance for it not to be midnight and I'll post some pics. Yes, mine are original seats and they go straight across the top of the centreboard. The wood is rotted, so I building a new set. I just jammed the seats in place in the above photo so I could understand how they go, they're not actually attached and the trash bags of junk are holding them up. But There's a bracket underneath. Happy to share progress photos as I go along.

Tom
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Re: Thwart repair

Postby GreenLake » Sun Sep 30, 2018 2:45 am

@ tomodda: knew "borrowing" your picture would get your attention. Hope you guys can have a good exchange here.
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Re: Thwart repair

Postby tomodda » Sun Sep 30, 2018 10:09 pm

Hi Cliff!

As GL noted, I have DS1 Number 37 from 1957. Original seats, although rotted. I'll show you how mine is set up, but as far as I know - via Internet research - O'day and Marscot Plastics really didn't have a standard way of doing things in the early years. They popped one boat a day off the mold from 1957 thru 1960 and fitted it out according to the shop foreman's mood. Anyway, here's my seats and thwart taken out of the boat and fitted together upside-down on the driveway (mind the hurricane debris, I'm still cleaning up!):

IMG_20180929_131727 (1) copy.jpg
Seats from beneath
IMG_20180929_131727 (1) copy.jpg (164.91 KiB) Viewed 2411 times


As you can see, each seat has two c-shaped mahogany brackets underneath, they measure aprox 10" long x 8" high on the higher side (amidships), 6" high on the outboard side. I'm not going to reproduce these, I'll just do square legs, braced against the outboard side of the hull stringers (that bump in the bilges, assuming you have them on your early DS1). Here's a closer look at the plate that connects the seats to the thwart, it's just a 1/4" thick hunk of steel:

IMG_20180929_135038.jpg
Connection
IMG_20180929_135038.jpg (168.65 KiB) Viewed 2411 times


Lastly, the thwart goes straight over the centerboard, screwed to a set of original-manufacture L-brackets that were glassed to the centerboard trunk (with an additional sheet of cloth to spread the load):

IMG_20180930_102139 copy.jpg
Thwart Support
IMG_20180930_102139 copy.jpg (82.17 KiB) Viewed 2411 times


The outboard end of the thwarts are screwed to wooden cleats (long 1x1.5 piece of wood) which are, in turn, screwed to the outboard "wall" under the side-decks. These cleats support both the thwart and the seats - they go all the way aft and then there's a cleat on the back "wall" of the cockpit to hold up the aft end of the seats. Needless to say, these are quite important as they take most of the weight of the seats. So, some notes, for what they are worth:

-My original cleats are mahogany and were screwed in with wood screws with a bushing on each head, just like the first photo in this thread (except mine are bronze).

-My original cleats had rotted from the outboard side (against the wall) inwards, so I assume that water got trapped there over the years and caused the rot. The inboard sides (exposed) were fine. So, if you build new cleats, make sure to protect the outboard side. Now you're welcome to not believe me, but I brush antifreeze onto any wood that I want to preserve. Yeah, straight from Autozone or your local equivalent, get yourself a jug with the highest glycol percentage you can find. Where did I get this crazy idea?:

https://www.simplicityboats.com/chemorot.html

FWIW, I started doing this 5 years ago and no wood rot (I paint all surfaces as well).

-I'm replacing my cleats with 1" thick x 1.5" wide (true size not nominal) red oak from HD, it bends by hand to fit the curve of the side wall, and should hold out OK (with antifreeze and a coat of primer). However, I am not screwing it back into the side walls with the bronze woodscrews. I've closed all the screw holes from the original cleats using thicken epoxy and instead I'm using stainless steel drywall anchor screws. These are screws that come with a little plastic jacket that you tap into the hole and then the jacket "mushrooms" when you tighten the screw. This "mushroom anchor" winds up on the inside of the side tanks (against the fiberglass sidewall) and should prevent the screws from pulling out. Also, the nice plastic jacket should go some ways towards keeping water out of the side tanks - they don't have to be 100% airtight, there's foam blocks in there - but you want to keep the foam dry during ordinary use. Likewise, the jacket should spread the downward forces on the hole in the sidewall a bit better than just the woodscrew. I'll take pics if you are interested, otherwise just ask for expanding anchor drywall screws next time you go to the big-box store. I used #6 gauge screws, I figure they're enough, 10 to a side.

-In the original setup, the thwart is screwed to the cleats and L-bracket using a longer bronze wood-screw, the bronze bushing, and a bronze tube that fits around the screw. In other words, the screw threads never went into the wood on the thwart, instead there were slightly larger diameter holes in the thwart in which the bronze tubes were fitted. The screw goes through the tube and bites into the cleat or L-bracket, and there's the bushing at the top to hold it in place. The seats, on the other hand, are screwed into the cleats normally. My guess is that this tube setup is to allow the thwart to "play" a little as the hull and centerboard trunk flexes. Anyway, I plan to reuse the tubes... if it's good enough for George O'Day, it's good enough for me.. and I'll post pics once done.

OK, sorry for the exhaustive detail. Since our early boats don't have the molded in seats, the whole thwart/seat set-up gets deceptively complicated.

Just to make life more fun, I'm also planning a "wife-friendly cruising configuration" for the boat, in which I'll have additional removable thwarts covering the centerboard from the cuddy back to the mainsheet block, almost 4 feet. Why? So that my wife has a nice platform to sprawl out on - out of the bilges, amidships (keep weight off the stern!) and relatively out of my way. She can just scooch on over during tacks. She's a lead-mining keel-boater through-and-through and hates the dinghy tacking scramble/chinese fire-drill. On the other hand, she's done a lot more offshore passagemaking sailing than me and actually has an ICC cert, so I keep my mouth shut... and on the other, other hand, don't ask her to roll tack unless you want a winch handle upside the head! Anyway, see the John Welsford Navigator for what I have in mind, kind of a Bridge Deck:

https://1.bp.blogspot.com/-63hw7Sn-cRs/ ... %2Bsat.jpg

So, out for a picnic cruise with wife - drop in some extra thwarts and and a big floatable pillow, everyone is happy, the extra weight (of the thwarts not wife!) should keep boat more behaved as well. Out for "adventure" - take out the platform and rig the hiking straps :). This is an overwinter project, again will post pics. Also, I have to figure out what happens with the jib sheets in "cruising configuration"... decisions, decisions. But that's the fun of tinkering with our boats!

Tom
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