Thistle Class Rudder

[10Hydro]

While I've read many post on this forum for quite some time I am a new to posting. I have built molds and I am familiar with many lay-up techniques including vacuum bagging and resin infusion. My molded parts have typically been in 1/2s and bonded/taped together. My question is how is the best way to mold and lay-up a thin foil shaped rudder for a Thistle Class? I can mold each 1/2 separately but am unsure of how to lay-up. With it being so thin from 3/4"to 7/8" it seems too thin to lay-up in halfs and bond together. However, I'm not sure how to lay-up with matched molds without having any voids inside. I really want to mold both faces as opposed to overlaying over a core, but am open to suggestions. Thanks for your input.

[alan white]

Just a suggestion. Such a thin rudder will be difficult to mold unless you make it from (heavy) solid glass/polyester (or somewhat fragile if you attempt to core it).
Why not make it from a few layers of thin plywood sheathed in glass/epoxy?

Alan

[rwatson]

Unless you have the moulds already made, building and fairing a rudder like alan suggests is going to be less work.

I would tend to go for some light but strong wood rather than plywood myself (the local wood shop can advise) , because shaping plywood with its multiple laminations is a bit of a bugger.

You can even pre-cut vertical sections to shape and laminate them for extra strength and efficiency. Cover with epoxy and cloth for strength.

If you do a good enough job, it can be a plug for a master mould if you want to do others.

I see the rules dont specify rudder size, weight etc, so using the wood technique you could build a few shapes for experimenting - perhaps have a few for different racing conditions.

[Phil Locker]

Thistle rules are in fact fairly restrictive on the rudder. They have to be within tolerances for both planform and thickness. And they also have a minimum weight to meet.

We CNC our thistle cores from strip laminated Douglas Fir, and have a proven fast shape. Why not just contact us to mill a core for you, then you take it from there with 'glassing and fairing?

Cheers
Phil

[rwatson]

Thats interesting Phil - I couldnt see any reference to the rudder in the class specs I found on the internet.

Do you have a better link?

Your CNC suggestion is the go - viva la computadora

[Phil Locker]

No link, sorry. I've just got a really bad scan of the appropriate page of the "Official Thistle Class Rules" that you have to look squinty-eyed at to make out the numbers. (given by the customer that first ordered one from me).