rs 800 centerboard

[ross_burkin]

...i'm sure we can put a sticky weekend together.  You are not alone making foils at present.

Yes please!

[john_hamilton]

1

[daryl_wilkinson]

On the whole foil thing.... Is there a class CNC mould for a T foil (horizontal foil?) I have a feeling I may need to make another one which is more standard as a base line.

[Phil Alderson]

I had CNC plugs milled for the lifting and rudder elements, it was finished off by Tom K and Dave Ching A mould has been taken and I think that Dave is close to making the first foil

[john_hamilton]

is this the type of mould you spray that high density quick hardening foam into (the type that builders use in some tight cavities but a stronger equivalent?)

[Tim Noyce]

On the whole foil thing.... Is there a class CNC mould for a T foil (horizontal foil?) I have a feeling I may need to make another one which is more standard as a base line.

Richard Taylor has a 3 piece female mould for the Daemon T-foil. We made a few foils from them and they have all survived. Very nice and easy to use, using the expanding foam you can make a foil in a day no problem as you can lay it all up and add the foam in one hit.

John, the expanding foam is a 2 part foam epoxy foam. You mix it up and then it starts to expand, before going hard. Quite cool stuff!

[daryl_wilkinson]

Cool.

[john_hamilton]

well iv just finished the carbon on the rudder and it has ended up as 120 cm long, with a 17cm chord tapering to 8cm at the bottom, weighs 1100g with some bits to cut off the trailing edge and fairing to be done (only a little though as i paid as much time as i could getting the core perfect) its got a layer of 200gsm carbon weave, then carbon uni up the trailing and leading edge, another layer of carbon weave at +/- 45, then a final layer of weave at +/-90. the core is high density foam. thanks everyone for the great advice i had. going to make a stock and t-foil for it in easter hols... probably a centreboard aswell.

[Phil Alderson]

Congrats, sounds good

[Banshee Ambulance]

First draft of my center board. Will start getting sticky after exams.

[john_hamilton]

isnt an elliptical one more effective?

[Ben Howett]

You want a broadly eliptical lift distribution but an eliptical planform doesnt guarantee that - and with a straighter leading edge the construction is a bunch easier if your draping fibres over it.

[Banshee Ambulance]

After some thought I have decided on a trapezoid foil with a 0.45 taper ratio. 0.5 is approximate for eliptical lift distribution and a little below that will reduce the moment. Also has the advantage of easier laminating with the straight leading edge.

[john_hamilton]

 John, the expanding foam is a 2 part foam epoxy foam. You mix it up and then it starts to expand, before going hard. Quite cool stuff!

is it heavy?

Also, how do you get that shiny finish on carbon?

[Sarah Kirk]

Phil says: thec weight of epoxy expanding foam is determined by a; the intended density of the foam formulation, b: the temperature that the foam is cured in.   You can mix foam that is intended to cure at 170kg/m^3 at 20 dgrees C and heat it further to reduce the density.

The shiny finish is due to applying additional coats of resin then lots of sanding.     A final coat of polyurethane resin or varnish and some polishing is required to make it look good.   

The easier way is to get the shape right by filling and fairing with a lower density filler (epoxy /glass bubbles) and sanding through to 400grit then paint with primer and 2 top coats.  very fine wet and dry and polish to finish.   You will never be able to stand on it though.

At present we would be best to put pro grip on the board to reduce our capsize time.   An extreme measure  though but puts things into perspective.