Winter Repairs Continue Into Spring...

[UCanoe_2]

...and on into the summer at the rate things are going. Boat repair time seems to be in short supply.

When I last posted, I had dropped the centerboard of my DS I and was sanding off the nasty, noxious anti-fouling paint applied by a PO. Then I used epoxy putty to fill the many chips and cracks in the board. A large piece of resin had split away to expose a steel reinforcing rod in the center of the board. I used a Dremel to grind off as much rust as possible, and then covered the "rebar" with epoxy putty.

A heavy snowstorm in early March left me with two days off work, but without electricity. Fortunately the shop has lots of natural light and some non-power tool work could be accomplished. I made a cardboard pattern for an insert to fit inside the square hole for the CB handle. Hopefully this will keep the handle shaft from abrading the inside of the square hole. Later I will make the insert from .025" copper.

I used a chalk line to establish centerlines on the leading and trailing edges of the board.


Then I leveled the board on the workbench and spiled a cross-section onto a sheet of poster board.

I laid out an improved cross-section on the poster board and used a thin wood batten to draw a fair curve. The new cross-section is not exactly a NACA foil, but it's close and will be a vast improvement over the stock centerboard.

I used the poster board pattern to make a template for building up the CB to its new improved cross-section. Think of the screed board a builder uses to level your concrete garage floor. (This works better on a flat concrete slab than it does trying to mold epoxy into a convex surface.)

Then I applied epoxy thickened with wood flour in an attempt to reconfigure the CB. I extended the trailing edge of the board to approximate a NACA foil shape, although as you can see from the photo there is still work to be done.

Here's where things went wrong! A combination of high ambient temperature (80* F), mixing too large a batch of epoxy, and perhaps adding too much thickener resulted in a mess when I epoxied the CB. The epoxy set up with a zillion tiny air bubbles trapped inside. They resembled the bubbles that form in pancake batter just before you flip the pancake.

So, guys, I'm seeking your advice on how to proceed. My thought at this point is to sand the whole mess, which I need to do anyhow, and open up as many bubbles as possible. Then I would apply unthickened epoxy to fill the exposed bubbles and continue building up and fairing the surface of the CB. Of course I will have to flip the board over and work on the opposite side to achieve a symmetrical cross-section. I'm planning to wrap the whole CB in a couple layers of glass cloth, so the risk of water intrusion or lost strength from the remaining unfilled air bubbles should be minimal.

What do you think of this plan? BTW, I don't recommend trying this repair method at home. Rather than trying to repair the old centerboard, building a whole new one would have saved time and money.

[GreenLake]

I would think of your epoxy "foam" simply as another sort of "filler".

It really isn't structural, and water shouldn't really be an issue if it's not the outer layer.

To continue from here, why not use some epoxy based fairing compound (SystemThree QuickFair or equivalent) to add a layer that clears all the bubbles. You can also use it to add even more "shape". I'd say up to about 1/8". Then you can add your single layer of glass cloth.

On the reverse, I would still start with a layer of epoxy but continue with fairing compound sooner (skip the "foam" stage ).

I did a similar project of adding some shape to my CB and I went through about 2 quarts of QuickFair. It should bond to recent epoxy (after removing the amine blush, if any) but if in doubt you could sand the epoxy to roughen it up. The QuickFair itself needs to be sanded after every layer. It sands very easily, but is still relatively strong.

I posted about my repair earlier, for example here.

[UCanoe_2]

Thanks, GreenLake. The Quick Fair is a good suggestion that I will file away for next time. I have a good stash of various fillers on hand already and need more straight epoxy for the rest of the project, so will continue to "roll my own" for the time being. I put down another coat yesterday and it looks much smoother. There may be hope for this centerboard to be pretty decent after all.

[GreenLake]

Rolling your own is fine, as is using what you have.

I can't advise you on the details of what to mix in, but it looks to me like your epoxy has too little filler. Even if you don't actually use a pre-mixed product like QuickFair, what you want (after the initial sealing coat, is something that is equally creamy (almost like soft ice cream or chocolate mousse). Yours looks like it might be more like a thick liquid (thick honey). In other words, you want something that's a filler, so it builds up bulk fast and can also be sanded easily. If you are worried about structural deficiencies, then you would have started with a few layers of some roving, cloth or whatever.

Anyway, that's the thought I had reading your adventures and looking at the photos, so I hope I haven't committed the usual misdiagnosis over the distance.

[UCanoe_2]

Yes, you are correct. My epoxy mix was about the consistency of honey, or maybe ketchup. I'll add more filler from now on. I have already applied glass cloth to the sides and tip of the board. The plan is to add a double layer of cloth over everything after I build up the thickness a little more (about another 1/8" total).

I have another idea, but it may not be so great. Instead of continuing to build thickness with epoxy, what about gluing on a thin layer of wood? So far I've been working on the port side of the CB but have not built up the starboard side at all. The starboard side of the CB is really flat and would be a good place to attach a piece of flat wood. But would there be a problem with having different materials added to the two sides, like maybe it would warp the CB and make it even more asymmetrical?

The epoxy I ordered online Sunday from Chesapeake Light Craft just arrived this evening -- pretty speedy service. Hopefully I'll find time for boat work this week in between the lawn mowing and other vegetation control.

[GreenLake]

About your idea with the wood. If you encapsulate it in epoxy, the wood would be "inert", that is it would not shrink and swell with moisture. That should cut down on any tendency for it to "warp" your CB by changing size on one side.

The other thing is that by adding cloth over everything, you have a layer that is capable of resisting a lot of tension - tension that would need to be applied if you'd want to bend your CB. Again, the way I see it, it would seem to resist any effects of asymmetry in the board's construction.

Assuming that this line of reasoning is correct, I'd class it as a low-risk proposition to add up to 1/8" of wood to make up volume. (If you were really worried you would take a router and cut a channel into your epoxy foam and put a strip of wood in there, but I think we agree that this appears to be overkill.)

Given all the other asymmetries in your boat it may even be impossible to notice if the CB really was not fully symmetric.

What you want to avoid is making the profile for the CB different on each side, but you have that cool jig that will help you make that even. I had a handheld template with less precise action and things seem to have come out OK.

[K.C. Walker]

I've been contemplating the idea of adding wood to the exterior of my centerboard to reshape it for a while now. Though I did a good job of faring the bottom of my boat a couple of years ago, by the time I got to doing the centerboard it was time to go sailing, so I just reshaped it to make it better than it was but not great. I thought that I would make a new one that was more accurate. It turns out that what I did was a noticeable improvement. So I may just refine the shape of the centerboard that I have at some point.

My plan for using wood to reshape the centerboard is to use clear "battens" or strips of wood. I was thinking probably I would use half-inch wide strips spaced more closely from the leading edge back to the 30% cord and more widely spaced towards the trailing edge. Using the foil template I could thickness my strips before epoxying them on. If there were lumps and bumps I would thickness my strip for the low spot and hand plane the strip at the high spots. After all the battens were epoxyed in place and fair, I'd fill between them with lightweight filler using a batten to spread filler. I would then use some lightweight fairing compound and a longboard to finish off the shape and then a couple of coats of glass.

+1 for what Green Lake said about encapsulating the wood with epoxy.

Resin is heavy so mixing it as light as possible with lightweight filler is a good idea. The heavier the boat the slower it goes.

[GreenLake]

K.C. I like your batten idea. Did you consider using paint stirrers? I think they make fine batten material.
To get different thickness, just double them for the thicker parts, or use the ones for 5gal buckets there and those for 1gal cans elsewhere.

Joke aside, encapsulated in thin strips, and used non-structurally, the type of wood would be less critical.

Why paint stirrers?

On my first set of (very baggy) sails the PO had fashioned his own battens from strips of wood he had sawed to shape (or found in a cutt-off bin). I replaced those by battens made from paint stirrers (I had to glue two of them to get the needed width). They were much easier on the batten pockets and worked amazingly well. (Given the sail's condition, they were, in fact, perfect).

[seandwyer]

And don't forget yard sticks and tongue depressors. I have used both as shims for different projects. Depressors are usually a nicer wood but you would need lots of them and they would mean more joints. Yard sticks are super flexible, so any curvature you would desire should be easily found by epoxy and clamping with some waxed paper between the clamp and stick. Either of these are pretty inexpensive. I bought 500 depressors for about 5 bucks at the pharmacy. Yard sticks are sometimes free at Home Depot, but never expensive.

[jdoorly]

So, what is the optimum (NACA or other) foil shape for the DS centerboard? Or do you just go for max width at 1/3 length, BTW what is max width, I don't see any spec in the handbook? What kind of leading edge radii is best? Can we assume the optimum trailing edge to be a 1/8" flat? Does adding width to the CB cause problems raising and lowering the CB, and/or more jamming? Can I find true happiness if I buy a bigger boat?

[GreenLake]

There are no class rules on the width - so it's whatever fits your CB trunk. I started with some NACA curves, but didn't do the bold move that K.C. suggested (adding strips) so I had a hard time getting enough bulk.

I did go to a half circle for the front that's approx 1/2" to 3/4" diameter and I did taper the rear to 1/8" (if it flutters, make it asymmetric there by filing one of the two edges slightly). And I tried to create an otherwise fair curve with the maximum where it would have been for the full profile (so about 1/3).

Like K.C. I found that a stock CB, especially if visibly used, can be improved upon quickly. I don't know whether re-doing this to "perfection" would buy me anything comparable, so the fact that I don't race the boat competitively is good - (so far the improvements were so noticeably that I didn't need a matching boat to verify them.)

For true happiness, get a smaller boat with bigger sails

[K.C. Walker]

For true happiness, get a smaller boat with bigger sails

+1 for bigger sails… I'm not so sure about the smaller boat, though.

[seandwyer]

You could try getting MORE boats. It's worth a shot and deserves investigation.

[K.C. Walker]

You could try getting MORE boats. It's worth a shot and deserves investigation.

I just got two more boats yesterday. I was definitely getting the, where are we going to store these, look from Diana. I was just helping out a friend that needed to clear some boats out of his barn, he has 21(make that 19). Yes, they are small boats, but still…

[UCanoe_2]

I found some nice clear "Phillipine mahogany," which I think is more properly called lauan, in my father-in-law's scrap pile, and ripped it into strips about 3/16" x 3/4". Last night, I epoxied the strips to the CB and then filled with epoxy thickened with wood flour. It came out pretty close to the proposed foil shape. There is a little more filling and sanding to do, and then we will be ready to cover the board with glass.