Daggerboards and rudders for AO14

[AlphaOmegaMan]

Ok, - yeah yeah, I know seasons already started, but new baby has delayed getting the other baby out of the carport. The other baby is a Alpha Omega 4.3 with the big (13.5 m2) cat rig.

My problem is this:

The previous owner was a recreational shallow lake sailer and has replaced the original boards with a lovely looking('glass over cedar and ash), but somewhat useless(for an AO) set of boards from a Paper Tiger - (hull depth at slots is much greater on the AO compared to a PT). Also - the rudders have been replaced by what looks like a set of shortened Hobie14 rudders (blunt, heavy and short).

The ensuing result is a cat that doesn't point very well, generally handles like crap, and is rather difficult to tack.

I have aquired LxW specs of the original boards and rudders but not profiles or shapes. I'm thinking NACA 00012 and 00010 profiles will be somewhere close, but not sure. Also, I have no idea what shapes would be best suited for each.

I can competently home-build in cedar and carbon(or kevlar/aramid) so construction is not a problem, but resources on the net in terms of modern fin shapes for cats are virtually non-existent.

Can anyone offer wisdom/plans/links/opinions or anything else that will help??? I aim to make them in the Chrissie break.

Many Thanks

btw: a lovely set of glass over cedar and ash dagger boards for a Paper Tiger will be on offer soon as new boards are completed!

[tonyquoll]

From my testing I reckon 10% thickness to width (NACA0010) is the most you'd ever need on a centreboard; as the angle of attack is low. Having them thicker helps prevent the board stalling at low speeds, but most of the time a thinner board would have less drag, with 5% (NACA0005) at the other extreme.

The trend with most cats has been in using high aspect boards, say 150mm wide x 15mm thick, maybe 500mm protruding through hull.

For shaping I'd print out the section on paper at exact size, then trace onto an ice-cream lid and cut out to make a template. Shape with small angle grinder fitted with sanding disks; it'll rip into it! Keep removing material, put the template over it, mark the high spots and turn 'em to dust. Start with 80grit, then 120, then maybe go to hand sanding with a large block, and go through the grades 120, 240, 400, 600 ,1200.

Let me know when you want to sell the PT boards; could be a good upgrade for 3038 "the Mystery Tiger"; tonyquoll@yahoo.com

[Darryl J Barrett]

rudders & C/Boards

From my testing I reckon 10% thickness to width (NACA0010) is the most you'd ever need on a centreboard; as the angle of attack is low. Having them thicker helps prevent the board stalling at low speeds, but most of the time a thinner board would have less drag, with 5% (NACA0005) at the other extreme.

The trend with most cats has been in using high aspect boards, say 150mm wide x 15mm thick, maybe 500mm protruding through hull.

For shaping I'd print out the section on paper at exact size, then trace onto an ice-cream lid and cut out to make a template. Shape with small angle grinder fitted with sanding disks; it'll rip into it! Keep removing material, put the template over it, mark the high spots and turn 'em to dust. Start with 80grit, then 120, then maybe go to hand sanding with a large block, and go through the grades 120, 240, 400, 600 ,1200.

Let me know when you want to sell the PT boards; could be a good upgrade for 3038 "the Mystery Tiger"; tonyquoll@yahoo.com

We still have all the moulds for all the Alpha Omega rudders and centreboards and can lay up new ones on order

If your interested give us a call on (08) 8326 0877

Darryl

[AlphaOmegaMan]

Hi Darryl, I understand you and your son designed and built these little rippers. How do the OEM boards compare with

"The trend with most cats has been in using high aspect boards, say 150mm wide x 15mm thick, maybe 500mm protruding through hull." as Tony has mentioned (i know he's a PT sailor, and a pretty active one at that). Originals were about 30.5cm - is any pointing ability lost with narrower boards?

[AlphaOmegaMan]

Tony - just thought of something - if i'm aiming for say a 15mm thick c/board, what sort of thickness should the 'core' be, and should it also be narrower to allow for leading edge layers and trailing edge thickness? I also have the option to build in balsa with kevlar and glass (or carbon) - any opinion?

[tonyquoll]

Darryl is offering moulds, so your best result may come from using carbon fibre, vinylester resin and foam core in those moulds. That would produce the strongest and lightest boards, with a proven shape. If this also means you dont need to modify your centreboard cases, then even better.

The cost of materials is huge, and the associated equipment (Vacuum bagging) also difficult to get and use. It may work out cheaper with a better end result to accept Darryl's offer.

The right shape more critical than the right dimensions. Maybe produce a test sample to see how thick your materials become.

I've been warned that using Balsa and other cores can warp, as the fibreglass (or other) coating heats and contracts when setting. This another reason why moulding is preferred.

A mate & I have just made rudders out of hardwood, which has the advantage of not requiring any fibreglass or coatings, was a freely available material and fairly quickly to work with. We'd rather be using carbon in moulds, but dont have the resources or expertise to do it - yet. Maybe next winter, ha, that's what we said last year.