new rudder - advice / comments requested

[Dark and Stormy]

I'm planning to laminate some wood for a new rudder this weekend, and was hoping for a bit of advice.

My plan is to laminate multiple 2x4's into a large block, and then route it down to the 0012 foil shape using a sliding router jig. Finish / seal with epoxy.

1) Do you see any major problem using pine? I was expecting to simply get some 2x4's from home depot, and laminate them together for the initial layup. Should I be looking for a different type of wood.

2) Can / should wood glue be used for the initial lamination, or should epoxy be used?

3) I'm planning a 0012 foil with a 14" chord. Any obvious issues here?

4) What should the overall length of the rudder be for a venture 25? The rudder I have is in pretty bad shape, and I suspect it was itself a handmade piece... I don't know whether to expect that it is correct or not.

[RobertB]

I admire your willingness to make rudders yourself but I am very confident the rudders you are proposing will fairly quickly split. Why? I assume you are just going to do a long grain lamination. When installed, the pivot bolt will be a hard spot on the grain and the foil aft of that the lever (if you made from marine plywood, this would not happen because of the cross grain laminations). BUT - Easily Fixed.

Make the foil as you described as a core - make it at least 1/8 inch undersize to account for at least two layers of bi-directional fiberglass you will lay over it using either epoxy or polyester resin (my favorite is epoxy but polyester is cheap and easy to find at any auto supply shop). Sand the layup fair and recoat with resin to fill in the weave. Paint and done. The fiberglass will do two things: It will provide bending strength in every direction and it will provide impact strength to the edges.

As far as the other items you mentioned, the wood used in not as important as how dry it is. 2x4 pine/spruce is an acceptable lightweight wood but as bought from the hardware store probably has a pretty high moisture content. Better to buy the trim lumber (1x) that is kiln dried and handled a bit better than the framing lumber. Epoxy is good to glue, for your purposes a waterproof wood glue such as TightBond III (not I or II) will work fine. dimensions, I am not the one to ask - I have a

[Dark and Stormy]

Thank you, I didn't want to lead-off with that concern (poison the well), but I was worried about precisely the condition you describe.

I'll construct as you describe, wrapping the whole deal in fiberglass.

Being able to use TightBond III is awesome! I will be able to get started this weekend, as I won't have to wait for delivery of the Epoxy.

[RobertB]

I would also be tempted to beef up the pivot area - such as with a bronze thru bushing and a couple of metal discs or extra fiberglass laminations on the surface.

[Dark and Stormy]

I've been thinking about that... my goal was more to prevent water from infiltrating core rather than reinforcing. How does this sound:

Overdrilling the wood core
Fill this hole with epoxy
Drill the epoxy to set brass through bushing

Am I overthinking this?

[RobertB]

That would work, still would install bushing "wet" with some epoxy and make sure a couple of extra laminations of fiberglass in the pivot area since there the metal bracket is bearing on this surface.

[mastreb]

If you're going to glass over the entire thing, why use wood? Expanded polystyrene is much easer to carve and easy to glass over. In fact, you can buy 0012 NACA foils in polystyrene off the shelf perfectly molded.

[finding41]

I'm in the process of making a modified rudder. I can't post pictures here so I have the whale find rudder mod on the other macgregor site. link. http://forums.macgregor.sailboatowners. ... p?t=152934
There is also a bunch of info on this site in this thread. link. http://www.macgregorsailors.com/forum/v ... 10&t=21832
There is lots of great advice on both mac. sites. You may want to think out of the box as well and look at other places foils are used. (A foil is a foil.)
Wind energy, airplanes, gliders, etc... Some university's have there wind tunnel results posted on line too....
The guys that race the 1M sailboats are crazy competitive and can do wind tunnel testing quickly and easily.
Good luck!

I'm about to pop my rudder mold off tomorrow!
Have you a link to a place I can get ready cut foam foils? That would save a ton of time.

[Hamin' X]

I can't post pictures here...

What is your limitation on posting pics here?

~Rich

[Crikey]

Thanks for the link to the other article. I thought I'd explore (eventually) the tubercule/rudder idea with a slip on sleeve, to see how it works. That way I could equip just one and compare the difference, however from what I've read so far the thing seems to work as advertised.
The 'whale' daggerboard really got my attention!

[Crikey]

This subject got kicked around earlier: http://www.macgregorsailors.com/forum/v ... =8&t=21841
The 'cules' you have look much larger than the 'cules' they have: http://www.thedailysail.com/dinghy/12/6 ... les-rudder
With a real whale, I'm not sure how rigid they are - do they flex according to pressure?
R.

[mastreb]

Here's a site you can buy exactly what you want, CNC cut and cheap.

https://www.flyingfoam.com/content/quic ... ps-cores-0

Pick your foam (EPS or EPP), choose the foil shape N0012, match the length and cord of the existing rudders, and choose the taper style you want (taper actually matters very little on a rudder). You have to double the length because they're selling you two "wings" and you are specifying the wingspan, so keep that in mind.

I selected: Airfoil: N0012
Total Wing Span for 2 Panels: 72"
Chord Length: 12.0"
Taper Style: Straight LE
Taper amount: Tip 75% of Root
Leading Edge Size: 3/4"

And the cost for both wings was $26.

Also, if you cut water holes and heat the finished rudder to 110C, EPS foam should melt and form a thin layer on the inside, leaving a proper cavity for water to fill when submerged so it's neutral density rather than being buoyant. Just be sure you're using resin and glass that won't have any trouble being post-heated. EPP has a melt point of 170C, so I'd use EPS if you intend to melt the foam core out.

Matt

[mastreb]

This site: http://www.tinypic.com

Is a very simple way to upload pictures. No logon required, just choose your file, upload, and copy the BBS code they provide and paste it into your post.

Matt

[vizwhiz]

Mastreb, i really like that idea, and thanks for the links cuz I might undertake to do this too for another rudder... But I think our rudders have a wood or resin core at the top for stiffness and compressive strength, don't they? I can see using the foam core for the main length of rudder, but would want a stringer or two, some kind of stiffener, inside the length...don't you think? I don't think torsional flex would be good for a rudder...

[mastreb]

Mastreb, i really like that idea, and thanks for the links cuz I might undertake to do this too for another rudder... But I think our rudders have a wood or resin core at the top for stiffness and compressive strength, don't they? I can see using the foam core for the main length of rudder, but would want a stringer or two, some kind of stiffener, inside the length...don't you think? I don't think torsional flex would be good for a rudder...

I really don't know what kind of lateral forces the rudders are subject to, so this is just speculation on my part.

You could just build up more glass and resin than the factory does and get to whatever compressive strength is required. The top would need a solid structure to handle the rudder attachment bolts, but that could just be a resin and sand mixture poured in after the foam is melted out from the water holes.

Frankly it would be simplest to leave the foam core in place and just have rudders that float. With the pull-down line their buoyancy shouldn't matter.