Thread: Centreboard material

My 21 ft hartley has a galv cb and was on a mooring for a couple years with no probs. As to where in adelaide I can't help but a engineering place could cut it for you if given the dimensions
Pete

I know you Auzzies like you boiler plate boards, but they're full of issues. I've long ago given up on wood and metal appendages, just to avoid the problems associated with it. Use inert materials, such as 'glass or high modulus plastics. You can add a weight, which if placed low has added benefits over a boiler plate. Since it's inert, it can be well shaped and fit close to the case without fear it will swell from rust and jam inside it.

Translation anyone?

What is a boiler plate?

How do you make a centreboard out of plastic or glass?

Would it be the right weight? Would it be the right size/dimensions to fit in the case?

Would it be legal on a TS16 racing class dinghy?

Thanks for you replies BTW guys. Much appreciated.

A boiler plate centerboard is what we call a big hunk of steel plate, used in many boats as the centerboard. It works, but that's about all the good I have to say for them. The biggest problem is two fold; they rust and they don't place the weight very low in the the boat.

I recently had to split open a perfectly good centerboard case, in a late 60's production boat. It was a well built case, thick, strong and had a swollen up 'glass covered steel centerboard jammed inside it. The steel had rusted (there's a surprise), which swelled up, under the 'glass covering, which in turn pressed against the inside of the centerboard case, literally bulging the sides of this case. The case was a solid laminate of mat and roving, with an average thickness of 3/4" (19 mm) and was stoutly built, but I had to split it down the centerline, just to free the board. I did it this way so I could save the case, with a repair to the split, using epoxy, biax tape and lots of thickened goo. I replaced the centerboard with a 'glass and foam core board of exactly the same dimensions, though this time with a 290 pound (132 kilo) lead weight, mounted along the leading edge of the board. This placed the weight of the board at the very bottom of the boat with the board fully retracted, so her balance would be the same and had the added advantage of lowering her CG considerably when the board was lowered (the weight sinks well below the boat's belly).

This was a class racer and this type of repair was permitted, so long as the weight and the shape were the same. I suspect the Hartley folks would permit the same type of repair. In any case, this board can't rust, can't swell up, can't rot, etc. If the leading edge is damaged, you just have a damaged leading edge, not a potential source for rot or eventual rusting, etc. The only specialy thing I did was epoxy in a bronze bushing for the centerboard pivot pin. Everything else is just how it was externally.

How do you make one? Well there are several ways, but I use a mold, as I've found it's faster (not easier) over the years. I carefully shape a piece of foam to be the exact shape of the board. This is then covered in two layers of epoxy. Next I make a plaster mold of each side of this foam plug. The plaster female mold halves are heavy and easily broken, so I reinforce them with 1x2's (25x50 mm) strips of softwood. The inside of each female gets two coats of epoxy, then 3 coats of regular old automotive paste wax. With the molds ready I do a dry run with fabrics and a core, cutting and shaping until I have enough fabrics to insure it's going to be rigid. Lastly I arrange the weight.

The sequence goes something like: the one side is placed on a table and screwed down, then the whole insides of both halves are again coated with 2 layers of straight epoxy, which forms the outer coating. The fabrics go in next, working on just one side now, then the foam core, which is buttered up with epoxy, then the weight is lowered in and the remaining fabrics applied. Lastly I place the other side of the mold over this and screw it to the lower half. If I've done everything right (not a guarantee), there will be fabric and goo ooze out all around the edges. When it "gels" I trim off the excess and wait for it to kick (usually 24 hours or more). When I'm sure it's hard, I unscrew the top from the bottom half and pry open the molds, which often break, but this is the deal with plaster. A little clean up with a DA, maybe some leading edge reinforcement and a bushing or two for the pivot and lanyard and that's the ticket.

It sounds complex (okay, it might be a little), but once you've done it a couple of times, it's pretty easy. More importantly it's reliable. I tried using latex rubber for the molding process, but I had distortion issues, which is unacceptable after tossing a few hundred dollars of materials into the thing. I've also tried using polyester and epoxy as the mold halves, which work well, but dramatically increase the costs. Plaster is cheap and easy to work, though fragile, so I just try to be careful.

Lastly, I've made boards (rudders mostly) from HDPE and UHMWPE. These are high modulus plastics and completely inert and also neutral buoyant (doesn't float, but doesn't sink either). They are easy to machine, but you have to setup some sort of way to cut them into a foil shape. I use a template system for a router, which amounts to foil shaped ramps the router base rides on. This is really easy and fast, but these materials aren't cheap. They make perfect rudders because they need only a tiny weight to sink them. As a centerboard they are self lubricating materials, so jamming in a case isn't going to happen or sliding in a kickup rudderhead. They don't take fasteners well so through bolts are the only fastening options, but not a deal breaker in these applications. They don't promote sea life growth either, which is way cool too. If I could afford it, all appendages would be made from this stuff. In fact, I have a supply of cutting boards I get from the local discount store. It's HDPE and I use it for making all sorts of things, like linings for bee holes or fairleads, blocks sheaves, bushings, mast steps, handles, etc. Any place I need something that will rub against something else, bear weight or offer a sanitary grip. It also makes a nice cutting board for filleting fish.

Originally Posted by hereselmo1

Translation anyone?

Would it be the right weight? Would it be the right size/dimensions to fit in the case?

Would it be legal on a TS16 racing class dinghy?

I think the material wouldn't be the issue as long as you are in the weight range for the class but won't bet on it. Talk to the class secretary for info
Pete

I'll bet they want the size and shape to be class legal, but you can build it how ever you like.

It sounds complex (okay, it might be a little), but once you've done it a couple of times, it's pretty easy.

Did you read that Brett? When you've done it a couple of times it's easy...and if you are doing it a couple of times, I'll have a new centreboard too

As to the class rules, the measurement form states:

Centre board, mild or stainless steel (no ballast). Fairing allowed to a max of 38mm from any edge.

But, if you're not bothered by class rules then one of Par's boards sounds great.

No offense PAR but I think I might stick with Galv.

Is there anything I need to know in terms of painting Galv?

just for info Herselmo1 my cb is galv and has never seen paint....it was built about 79 and used in salt water and was on a mooring here in the gulf for a couple years or so and is still in good nick
Pete

I know it won't be seen but it would feel naked to leave it unpainted

mine (#1291) was even older than fxst's - also unpainted galv board.
Mixture of salt & fresh water use before I got it.
Kept on a trailer.
Board was in excellent condition.
Better than most of the rest of the boat...
Fairing the lead & trailing edges of a 3/6" steel plate only worth doing if you are after that fraction of a kmh of top-end sped which matters at club traing level.

cheers
AJ

Originally Posted by b.o.a.t.

mine (#1291) was even older than fxst's - also unpainted galv board.
Mixture of salt & fresh water use before I got it.
Kept on a trailer.
Board was in excellent condition.
Better than most of the rest of the boat...
Fairing the lead & trailing edges of a 3/6" steel plate only worth doing if you are after that fraction of a kmh of top-end sped which matters at club traing level.

cheers
AJ

3/6"???

I assume you meant 3/8th?

The plans say 3/8th or 5/16th from memory (there were definitely 2 options). Any ideas which is better (and why?)

ummm... yes.
An even integer between 0 and 10 anyway.

Best you ask the club racers or the association about the relative merits 3/8 vs 5/16.
Unless my maths is even worse than already displayed, the 3/8" board
would be 20% heavier than the 5/16", for a miniscule boost to stability.
And a 20% increase in effort required to lift it, both on & off the boat.
Also a little less likely to bend if it gets hit sideways by a submarine or you
drift onto a lee shore/rocks.
The hydrodynamics would be about the same.... pretty ordinary.

I can't remember where I saw it, but I remember reading that some club racers are not happy with the standard galv plate and put considerable effort in to improve it. Galv steel isn't the most frictionless surface, so as well as fairing the leading and trailing edges they also paint the board with two pack paint to make it slippery, and even pull it out between races to polish it.

Crazy if you ask me. If you're that interested in windward performance then you could row there for less effort.