Building a replacement CB for an old DS1

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Building a replacement CB for an old DS1

Postby vermontsailor » Sun Aug 09, 2020 7:35 pm

Thanks Green Lake for the following suggestions, quoted below. I am posting in this section, hoping for any additional specific details on how to complete this CB replacement. I am comfortable shaping the blank and embedding the brass plate that engages with the pivot/handle. But I would love details on building the blank: wood and glue types and overall outline shape. I would have thought marine ply and fiberglass, but might that not be strong enough? Anyone out there built their own CB and can share that experience? All thoughts welcome.

And see image below of the CB I'm replacing.

Many thanks.


If you have moderate skills working with wood, making your own CB is definitely an option. Best way to do it is to glue several strips of wood with alternating grain and set on edge to make a plank in the desired thickness. Then look up one of the NACA foil sections and use a planer and/or belt sander to shape your blank so it has a nice hydrodynamic shape. Finally, some people cut a shallow groove at the thickest part and put down strips of fiberglass reinforcement, before wrapping the entire board in a thin layer of fiberglass cloth and epoxy. You'll also need to find a way to embed the brass plate that engages with the CB pivot. Use some fairing compound for a really smooth surface and sand down well, then paint. And done.
Attachments
CB, lever, well rig.jpg
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Re: Building a replacement CB for an old DS1

Postby tomodda » Sun Aug 09, 2020 10:18 pm

Good gawd, what is THAT? Well, definitely seen better days....

I haven't built a DS centerboard, but I've built two on other boats, and rudders (which are much the same). The centerboard drawing that you need is right in the DaySailer Assoc Bylaws:

https://forum.daysailer.org/pdf/dsbylaw3.pdf

Figures 6.1 and 6.2. Read up on the acceptable weight (20lbs, I think) and all the other whys and wherefores - Rules 6.1-6.3. You'll want to stay class legal, so you can race the boat and easier resale. For your build, Rule 6.2: "The centerboard shall be of built-up or molded fiber-glass and resin material or of wood covered with fiber-glass and resin" (emphasis mine). So you want to glue up a set of square strips, one on top of the other. The length of the strips go fore-and aft, 15" long, the width is just a bit narrower than your centerboard slot (measure it!). As GL says, alternate the grain of the strips for strength. Glue them up with thickened epoxy and then clamp them together with the appropriate long clamps. If you don't feel like building up a set of pipe clamps, then you'll need to build some sort of jig, no big deal. You'll wind up with a flat board, which you should then cut to the shape given in figures 6.1 and 6.2.

Now in theory you can leave it as a flat plate, but you'll have one hell of a slow and unmanueverable boat! You want to carve out at NACA profile - like an aircraft "fin". Do some internet research, but don't overthink it! A NACA 009 is probably just fine, in fact just having your max breadth 1/3 of the way back is fine. You WILL NOT be able to make a true NACA razor-think trailing edge, so just round it. There's even some hydrodynamic theories suggesting a square trailing edge! I'm not advocating a square edge or anything else, just saying that you should do some research and thinking, the rules give you some freedom. My personal favorite for this kind of carving is an angle grinder with a flap disk and then a small belt sander. Cut your NACA profile into a piece of plywood to use as a guide. If you have a drill press, you can drill yourself guide holes to appropriate depth. Otherwise, just scribble a pencil over any "high spots" then grind them off. Practice on some plywood!

Lastly, you'll want to cover your wood fin with fiberglass cloth and more resin (ideally epoxy). This is an art all to itself, probably the hardest part. Do some research, watch some videos, read on this forum, ask questions. Remember you'll have to subtract the thickness of your cloth and resin from the centerboard width. In other words, if your CB slot is 2 inches wide, you want a 1.75 inch wide CB, but the glass is .125 thick, so you want a 1.50inch board + .125x2 for the glass (made up numbers)!. You know the drill, measure twice, cut once. And don't forget that you want a smooth surface, so you need to fill in the grain of the cloth, put a bit of extra epoxy on top of that and then sand it back down....not easy! But we have several fiberglass experts on this board, so just ask (and do some test runs on scrap wood!). And it may be overkill, but I sanded my own fin all the way down to 3000-grit wet. Over that IS overkill though, there's only so much perfection you can get by hand. Wax it and call it a day - or don't wax... now we're getting into personal preferences and "art." Most of all, have fun! There's something very satisfying about building you own boat stuff - pride and accomplishment.

All the best!

Tom

P.S. Epoxy poisoning is real! During both layup and sanding, wear gloves, wear long sleeves, wear a mask, preferably something like the 3M 7500 series. The $40 I spent on my mask are the best boat-work investment I've ever made. Epoxy wont "kill" you immediately, the poisoning comes on as an allergic reaction over time - nasty hives and prickly skin, headaches, cold sweats. Avoid it by taking care of yourself. I don't mean to scare you off, just want to save you from having to work epoxy in a veritable bio-hazard suit like I must nowadays. Ounce of prevention, worth a pound of cure!
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Re: Building a replacement CB for an old DS1

Postby GreenLake » Mon Aug 10, 2020 4:06 am

Plywood is apparently not strong in shear. So, unless you build something where the skin is strong enough to take the load, which would be potentially heavy, it's best to use the laminated strip method. (Especially for a CB as opposed to a rudder - for the latter you can at least potentially catch if it degrades over time, the CB is out of sight and needs to be bullet proof).

If your strips are nice and flat without gaps, you could glue them with a waterproof wood glue. (Epoxy is not better for this: while it blocks water penetration it does not bond better to wood if it is allowed to get waterlogged). The gold standard for anything that might get fully waterlogged is Resorcinol, but as you are planning to seal your board, you might get away with merely waterproof glues - or epoxy.

If the latter: once you have built your board, take a saw and cut of the forward bottom edge at an angle --- and then glue it back on with epoxy: that creates a glue line right behind the part of the board most likely to strike something and prevents moisture wicking all the way up from any damage of the outer skin. Cheap insurance.

There are websites where you can find the NACA profiles 0009 would be the one where the thickness is 9% of the length - get the one that will fit your dimensions.

Now, after you've shaped the blank, sealed it in epoxy and sheathed it in fiberglass, you'll want to use a fairing compound to get the exact shape. (I'm partial to stuff that's premixed like SystemThree's QuickFair, because I only have to get the ration of the two components right and not also the ratio and type of filler.) If you've sanded down your blank in some place so far that you have to add a little thickness over a wider area, you can use a notched spreader to create a set of ridges that you can then sand back down to the desired level, after which you fill the "valleys" in a second pass.

Following that is usually a coat with neat epoxy and then paint. Wax is slow, whatever Tom tells you - there are physics/chemistry reasons for it, but sanding to 2000-3000 grit should reward you with about the best performing CB :) -- all this is about getting the hydrodynamics correct. Just as with the trailing edge, which should be left blunt at 1/8", but not at ninety degrees - a bit of an angle will allow the board to better shed vortices that otherwise might even set it thrumming.

All those are fine points and you'll probably want to dig up all the literature you can - but other than perfection, the process isn't all that hard and given what you are replacing almost anything will perform better.
~ green ~ lake ~ ~
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Re: Building a replacement CB for an old DS1

Postby tomodda » Tue Aug 11, 2020 12:34 pm

@vermontsailor:

My apologies, I was writing after a long day. Greenlake is right, you have to be careful with epoxy/wood joints due to water intrusion. Make sure your fiberglass sheathing is sound! I also realize that' I've actually built DAGGERBOARDS, not CB's. Same building method, but daggerboards I get to pull out of the water after every sail, as Greenlake pointed out CB's you never see. About Resorcinol, great stuff but your joints have to be perfect - unlike epoxy, it won't fill gaps. Shouldn't be a problem, these are just square strips, joining flat-to-flat, but ideally you'll want to use a tablesaw to cut them, and make sure it's true'd up properly - at the very least, make sure to square up your fence. A $10 digital caliper will help a lot here. And a nice finishing blade (more teeth, thinner kerf), Diablo makes nice ones for the price. Make yourself a good featherboard to keep the strips up against the fence, otherwise you'll get saw marks which will screw up your joint. Anyway, if you've done cabinet-grade work before, this is easy, otherwise read up, watch youtube, you'll figure it out. I also can see GL's point where building up your NACA profile with more resin may make more sense than carving down. The most important part is having a consistent profile.

So, two other corrections - About NACA profiles, I meant to write that anything in a range from 9%ish to 30%ish is fine, again that's a measure of your maximum chord (width of the CB). Also, I was just giving an example about the square trailing edge. In practice, you can't lay fiberglass over a 90-degree bend, so go with a curve, per GL's suggestion.

@GreenLake - I'm not going to rehash waxing again :) But, question - what if one uses graphite instead of wood flour/microballons/etc for filler to thicken the resin? At least for the outermost layers. Now, when you sand it down, you'll have a very smooth surface (at least once you get down to auto-grade grits). No wax or other magic lubes needed. Thoughts?

Best regards,

Tom
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Re: Building a replacement CB for an old DS1

Postby GreenLake » Tue Aug 11, 2020 3:02 pm

Tom: I wasn't disagreeing with you as much as trying to add some info. Well sealed and sheathed, epoxy may work well. Unlike wood glue or resorcinol, clamping pressure needs to be moderate, or you'll starve the joint.

Now, on the wax issue, the "debate" has been ongoing. However, the issue with wax is that it is hydrophobic. That interferes with the boundary layer. Or so claim people who have studied this. The other thing is that I think from 600 grit onward you are already smoother than you need from hydrodynamic principles. Again, because of a finite boundary layer that you will want so you get better attached flow.

Remember, it's not simply avoidance of drag, but also creation of lift that you want.

I wish I had remembered my sources for this, but I'll have to make do with my recollections on this for now.

About trailing edge. You want something that looks like L. You get that by making your two fiberglass skins meet in a ==< (where the CB is on the right) and (after cutting off excess ==) sanding the edge not fully "square" but at some slight angle so one side of your CB is a fraction longer than the other. That improves vortex shedding, or so the experts claim.

The thickness at the edge should be around 1/8", I believe.

Also, to clarify, I wasn't suggesting to build things up with "resin" if needed but with a fairing compound (yes, containing epoxy resin, but not simply pure resin, which is tough to sand). Ideally, once you have your skin over the blank, the difference to the true profile form is small, so you won't need much build-up. But even then, unless you are filling an existing "hollow", it's very difficult to add a layer of fairing compound with a flat spreader, so the notched spreader trick is worth knowing.
~ green ~ lake ~ ~
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Re: Building a replacement CB for an old DS1

Postby vermontsailor » Fri Aug 14, 2020 12:51 pm

Really appreciate the commentary and rich suggestions and guidance from you both. So great.

And I'm happy for all the safety info folks want to share too.

I'll likely be back with more questions once I have to time to begin buying materials and assembling.

Thanks again.
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Re: Building a replacement CB for an old DS1

Postby jboright » Sun Aug 16, 2020 3:02 pm

Hey @vermontsailer,

Thanks for sharing your experience!
I just bought a 1970 DS1 (my first one) and have taken her for a couple shake-down runs on Lake Champlain... one issue that came up is that the centerboard was difficult to lower. Closer inspection revealed that the centerboard handle is also bent in such a way that implies that I'm not the first to have trouble lowering it... it looks like the handle has been torqued on so hard that it has bent. So I need to inspect the centerboard mechanism (my suspicion is that the pivot pin is bent)... but my first question is how to go about inspecting it? I assume that I need to get the boat up on boat jacks to get underneath her and free the centerboard to work freely? rolling her over seems impractical and I'm not sure the centerboard mechanisms would work correctly while upside down anyway... How did you do it?
Thanks for any perspective you can lend... and apologies for the novice question.
Cheers
Jon (also-in-vermont :-))
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Re: Building a replacement CB for an old DS1

Postby GreenLake » Mon Aug 17, 2020 9:39 pm

Tipping the boat over sideways is far from "impractical".
  1. Launch your boat onto some grass (or carpet covered concrete)
  2. Raise the mast and use it as a lever (pulling on a halyard)
  3. Tip the boat (a small weight on the mast will prevent the boat from righting itself)

If you have a spot in your yard, it's easy. Or, if you just need to check for something, you can beach your boat:
1804
(However, you may not always have teams of helpers in coordinated attire :) - as John Alesch did at the Texas 200 when his CB wouldn't drop after a night on the beach)

I once tipped the boat on its side with the mast across a city street with a friend (for lack of other space, the boat was on the parking strip and the mast went clear across the street - just long enough to take the CB out / reinsert it, so, a minute or two). In that case, having a helper allowed one of us to act as a spotter. If you have two+ helpers, you can turn a boat upside down (onto some tires for cushioning) without using a mast.

Removing a DS1 CB handle and CB is a quick operation and then you can inspect things at your leisure - replacement handles can be ordered from DR Marine.
~ green ~ lake ~ ~
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Re: Building a replacement CB for an old DS1

Postby jboright » Tue Aug 18, 2020 10:23 am

Thanks GreenLake!
Hugely helpful perspective. I appreciate it!
I've got space in my back yard so I'll give launching it on the grass a shot... Any tricks to getting it on and off the trailer? I've never tried it on land before... and I'm a bit nervous about damaging the hull. Is the bow eye strong enough to withstand pulling the boat back onto the trailer from the ground? or do I need helpers to lift it? .. I'm sure the answers to these questions will become apparent once I start doing it...
Thanks again.

J
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Re: Building a replacement CB for an old DS1

Postby GreenLake » Tue Aug 18, 2020 7:28 pm

Much will be obvious if you use common sense.

If your trailer rides high and doesn't incline, you might want to launch onto some old tires.

You may want to disconnect it for the "retrieval" so it can incline to the angle where loading is easiest.

And yes, you may have to lift the bow onto the first roller. Bow "weighs" half as much as the boat, so lifting it a bit isn't that difficult. However, a nice long 2x4 makes a great lever (and you can block under the bow to "lock in" partial progress).

Use smarts (and or a helper) where you lack strength and all is well.
~ green ~ lake ~ ~
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Re: Building a replacement CB for an old DS1

Postby jboright » Sun Aug 23, 2020 2:28 pm

OK then... some developments!

Green lake, I took your advice. 'Launched' my boat onto my lawn and managed (with ropes, trees, and a come-along) to get it rolled enough to inspect the centerboard.

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What I found was that the board fits VERY snugly into the trunk... so snugly in fact that the CB handle has been bent by previous owners trying to get it down...

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Last edited by jboright on Sun Aug 23, 2020 2:34 pm, edited 1 time in total.
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Re: Building a replacement CB for an old DS1

Postby jboright » Sun Aug 23, 2020 2:33 pm

I took the CB out and found that a previous owner had attempted to reduce the thickness of the CB by grinding it down.

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... it looks like it was a pretty rough job but worked (ish) for a while.

I was thinking of continuing on in the same vein. Taking a belt sander to the CB until it fits easily into the trunk and then sealing it with a layer of epoxy...
Anyone see a reason why I shouldn't proceed this way? This will be my first foray into working with fiberglas and epoxy... so any advice will be appreciated.

Jon
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Re: Building a replacement CB for an old DS1

Postby GreenLake » Sun Aug 23, 2020 3:09 pm

To add a layer of fiberglass to seal a CB:

Get enough lightweight cloth (square weave) to cover the entire board in one piece (lightest weight you can get). If you get a bit more, you'll use it eventually, in my experience. Set the board up so it's supported on edge with the leading edge pointing up. Cover it in epoxy resin, and drape the cloth over it, so that it hangs down on either side. Use a spreader or roller to make sure the resin is pushed through the cloth, squeegee off the excess. On the bottom (trailing) edge there should be a bit of overhang where the cloth from both sides meet. If you are going to race your boat, you'll need to trim off enough of that overhang to stay within class-legal limits for the width. If not, feel free to let the two sides meet in a shallow V and after curing inject some thickened epoxy into any hollow part of the V. (If the two sides of the cloth don't want to come or stay together you may help the process with two battens clamping the two sides together some distance below the CB. Use a strip of packing tape on the face meeting the cloth and resin and they will come off afterwards).

You'll most likely find that you're getting some "print through" of the weave. Use a fairing compound (like QuickFair from SystemThree) to create a really smooth surface, then paint (epoxy doesn't like UV, and some part of the CB is going to get enough of that even when sitting on a trailer to eventually get yellow and brittle).

If you are new to fiberglass work, read up on it (e.g. the "Epoxy Book" from the SystemThree website). You'll need: lots of gloves, lots of stir sticks, quite a few small (!) graduated measuring cups, several little brushes and spreaders. Also vinegar to clean uncured epoxy (it neutralizes the hardener, so never get anything that touched vinegar onto your actual project).

Mix epoxy by volume, accurately and in small(!) batches, while stirring carefully and thoroughly, scraping both container walls/bottoms and stir stick repeatedly to avoid pockets of unmixed resin which later won't cure. I always retain the mixing container with a bit of the resin in it, so I can check whether it cures properly without disturbing the work. (Also, when you pop out the hardened plug from the measuring cup there should be no uncured remnants on the bottom: if you find -almost- none, you're unlikely to have issues with uncured epoxy on your work piece).

Carefully avoid skin exposure: the stuff is able to sensitize some people into an allergic reaction. Fumes don't smell nearly as bad as for polyester resin, but use a painter's mask (and a good dust mask etc. if sanding the stuff).

Dry fiberglass cloth will cause itching as tiny strands break loose and may act as tiny needles on your skin. Wearing gloves and good skin covering takes care of that.

There, you have the rundown.

Now, for the CB: as you grind away pay some attention as to what you are taking off the board. If it is just the gelcoat (off white), you're not affecting the strength of it. But if you deeply sand into any laminate (may look dark or clear) that's a different matter. And if you bottom out on some filler material (perhaps foam? wood? not sure what you would find) you might have to go deep enough to be able to rebuild the laminate to restore the strength of the board (several layers of fiberglass in that area, at least 5-7 of the lighter stuff or get some heaver stuff in form of a narrow tape, with 3-5 layers).
~ green ~ lake ~ ~
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Re: Building a replacement CB for an old DS1

Postby GreenLake » Sun Aug 23, 2020 3:11 pm

PS: check the CB opening whether someone at some point tried to narrow it. If the sides of the trunk are flush all the way to the edge, there's nothing you can do, but if there's a ridge that makes the opening narrower than the trunk itself that ought to be safe to grind away a bit.
~ green ~ lake ~ ~
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Re: Building a replacement CB for an old DS1

Postby jboright » Sun Aug 23, 2020 6:01 pm

Great. Thanks for the info...
I’m hoping that I’ll be able to take off enough thickness to make the CB workable without having to re-glass... I think that all I need is 1/16th of an inch. If I do end up needing to re-glass part (or all) of the CB how much thickness do I assume each layer of glass will add (both thick and thin stuff)?
I’ll check on the lip of the trunk to see if it is flush... I’m guessing that it is, but it’s certainly worth checking.
Any idea why a CB might be too thick? Does it mean there’s leakage someplace in the CB which is causing swelling? Is it possible that the trunk is shrinking for some reasons?
Is the core of the CB usually wood? Foam? It feels pretty dense...
Thanks again!
J
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