DaySailer.org Forum

Bad news. Dropped the cb and it is full of water. Sounds hollow with water sloshing around. Found a large crack.
Do not know whether to repair it or order a new one from drmarine

Is the centerboard meant to be hollow or has a wood core rotted away? It was filled with water when I dropped it.
There is a crack that can be repaired, but replacing a wood core would be a lot of work.

Whatever you do, do not buy a "stock" centerboard unless it is significantly cheaper than a CB with a correct foil section.

Suppliers don't always indicate whether the design is "stock" or whether it uses newer molds with good foil section, so ask.

If you choose a repair, you can use the occasion to "improve" the foil shape somewhat. Not as good as building your own or purchasing a well designed one, but definitely cheaper and (in the end result) better than purchasing a "stock" centerboard.

Is a repair feasible?

I would think so. Having water in the CB isn't necessarily a fatal flaw; there are many CB designs that are flooded on purpose (to reduce buoyancy). This does require a drain hole, though, otherwise you will get frost damage.

About the crack. If it is in the leading / trailing edge that would be expected the way the CB was put together from two halves. Adding a layer of laminate to wrap across the crack would probably be a sufficient fix.

If you can pardon a very crude drawing:


As you can see, across the leading edge, the stock profile needs to become blunter to approximate a reasonable foil shape. That gives lots of scope for adding not only filler but laminate. In an ideal foil, the maximum width would be at 1/3 of the chord (more or less) and that would mean that adding laminate in the entire forward half of the CB would not interfere with improving the hydrodynamics a bit.

For the trailing edge, there should be room to add around 1/2" and that can be done with 3M Marine High Strength Filler. It's polyester-based, but reinforced with chopped fibers. It's a "structural filler" that means it's strong enough for applications like this.

If your CB shows rust, then you have rebar, and water has gotten to it. Yes O'Day did use rebar on some DS. Any repair of that would be temporary, because the rebar will continue to rust and expand.
This picture shows the "stock" profile and where you can modify it with a bit of fairing compound.

I had a delaminating board on a '73 DSII. Those boards did fill with water, and O'Day had a tech sheet that actually showed where to drill holes to let the water out. But the board would not fit in the trunk any more, and I doubted my ability to fix it. I got a new board from D&R which was thinner and much heavier. If there was rebar in the old board, the rest of the material must have been really light. Stock D&R boards (at least in 2008) were not foil sections.

Building your own CB from scratch isn't a totally outlandish proposition either.

Opened crack with a dremel and starting sanding the vc17 off the cb. Discovered a second crack. Will fill with system three and tape over the crack.

Anyone ever thought about casting an aluminum CB? If someone has dimensions, I could estimate the volume and the weight. Assuming 100 cm x 20 cm x 2 cm. That's 40,000 cm^3 and 108 Kg. Heavier than I would have guessed, but that's just a solid plate with no taper in any direction.

It would be an interesting back-of-the-napkin exercise. I'm not sure the CB trunk would take the strain, mostly an issue while trailering. It's not purely exercise since I do some backyard metal casting, but what I've done is nothing on the scale of 108 Kg, more like 2 Kg.

That would turn the DS into a different boat, a swing-keel vessel with a ballast/displacement ratio of about 30%.
I think you are right -- you couldn't hang that much weight on the pivot bolt without substantial reinforcement. You would also need to engineer a more robust uphaul.

Another problem is that the ballast would not be as efficient as on a true keel boat, where the weight is located at the bottom of the keel to have maximum effect on righting moment. I think the Heavy Metal DS would be pretty slow overall, at least compared to a regular DS with an extra 100kg crew member hiking out.

My dream DS would have a standard-weight CB with a foil shape, foil-section rudder, and a carbon fiber mast. It wouldn't be race legal, but it would be fun to sail.

@KT: A tapered cast might come to 2/3 of your estimate, if you consider the area under this curve:


@Talbot: Foil section CB and foil section rudders are race legal. Carbon rig is not, but there have been classes that have upgraded mast sections over time, so if at some point in the future carbon masts ever become "cheap" and if a DSC (DS with carbon spar) truly sails more spirited, who knows.

But, alas, I think the hull shape of the DS, while nice, is just a generation or two behind, and might not allow you to get the full benefit of a carbon spar.