Homemade Foiled Rudder

[paydirt]

I was thinking about making a foiled rudder out of HDPE plastic sheets. do you think this is feasible? I know others have made them using foam. I thought I could fasten two pieces outside the rudder and shape it with a sander to make it foiled. I have never seen a foiled rudder in person but only in pictures so I am not sure exactly the dimensions. does anyone know the dimensions of the foiled rudder or would they be willing to share some photos?
Thanks

[tmw]

Mine was from a relatively soft wood, using a rough estimate of the foil shape, and sanded to shape.  it's not a perfect foil, but much better than the flat plate.  If you have access to thick enough HDPE sheets to make it work, and willing to sand enough to shape it, along with an approach to glue it in place, I'd say go for it.

[JTMeissner]

I don't think there's much difference using HDPE sheets versus some of the other methods, normal wood tools are supposed to work.  Foam is very easy to pare down.  The nose of my foil is made from a 2x2.

As far as shape goes, it depends on what profile you want the foil to follow, usually referenced in a variety of NACA (National Advisory Committee for Aeronautics) foils.  If you use the Excel spreadsheet foil calculator, you can set whether you want to use "fill" or "remove" from flat plates to get the profile desired (I used FoilStripV2.00 to create my foil, I think you'd be looking at using the Ply-Plane method in that software).

I think the latest version is at Duckworks: http://www.duckworksmagazine.com/07/howto/foilstrip/FoilStripV2.00.xls

Somebody had PM'd me recently about my foil build since the pictures were lost to Photobucket for a posting.  If I can find a place to host the project, I'll post the process I used.

-Justin

{I think I got a shrunken version small enough to post.}

[Duckie]

If you use hdpe, you can pare it down pdq with a hand plane.  I like working with poly because it is so easy to shape and doesn't wreck your tools.  When I make foiled rudders, I just put in an air foil shape that fits the size of the materials that I have to work with.  The idea here it to keep the flat sides of the rudder from turning into a brake too quickly.  Any foil shape will help with that.  You don't have to go nuts getting a perfect foil shape in order to feel a difference.  If you are cheap like I am, you can work with cheap plywood off cuts.  Bolt them to the aluminum center plate down the middle and whack the ply to shape.  If it isn't right, rip it off and go again.  If you go this route, glass the rudder to protect the plywood. 

Al

[Salty19]

I wouldn't mess with the HDPE for a few reasons.  First,it's a bear to shape with a plane and sander.  Second, it doesn't glue well except to itself and only with a special type of glue.    It's also pretty heavy and you want less, not more weight on the back of a CP16.

If I had to do the job I would follow along with the foiled rudder instructions from the member Greene (great guy by the way) in the DIY area (go back to the home page, then scroll to find the DIY section.

Essentially he took a piece of hardwood to make the leading edge---and it's important that you extend the front edge of the rudder during this project.

Then used pink foam insulation from the leading edge back to full in the material for the foil. Glued and shaped it into NACA0014 stype.  I would personally use NACA0012 style.  You want a 1 1/4" thickness at the maximum. I don't know what the best chord length is for a 16, but guessing you'll have the aft edge terminate right where the stock aft edge does.  So I am guessing the new chord length would be about 1.5" for the new leading edge + the existing rudder width.  I can draw you an outline of the NACA0012 shape if you are desperate, but if you google search a little bit you can find foil generators to play with. My template is a cut off piece of a NACA0012 foil for my CP19. 

Once shaped, he fiberglassed the rudder, filled, then painted it.   

Definitely wouldn't use softwood in the design---it's going to hit stuff underwater so why use wood that will get damaged more easily?

Check out Greene's post then get back to us with questions...

[paydirt]

Thanks. for some reason I cannot see any images on this forum. I will keep searching around to see what I can find. Some mention that it doesnt have to be perfect but I have read about people getting "vibrations" after building a foiled rudder. my reasoning for using HDPE was that if anything is off, it would be relatively easy to fix. also, it seems like that is what the ida sailer rudder is made out of. I know $300 seems steep for the rudder. I hopefully will get to this project soon

[Salty19]

Paydirt--the lack of viewing images is NOT you.  Many of us used photobucket to host pics and they changed their policy last year to disallow viewing pics people posted there unless the poster paid an outrageous membership fee.

I understand why you want to use HDPE.  There is no fiberglassing, painting or other finishing work.  Just shape, sand and go. I suppose if you really want to use it you certainly can.  You are right the ruddercraft blades are HDPE.   I'm thinking I would want to thru-bolt the two sides together through the rudder in 3-4 places as well as making sure the glue you're using is compatible with both surfaces (rudder alum blade and HDPE plates).

On the kickup/down assembly that ruddercraft offers, the blade is solid with no glue joints. I expect it will break someday once it ages enough and hits something hard, or is forced (such as the boat lifting up in waves then crashing down to a shoal).

The rounded leading edge is pretty important to the foil design. If you think you can shape and attach the HDPE material reliability--leading edge and the two sides, go for it!  Ruddercraft uses a programmed CNC machine to shape the foil--know that making this shape with HDPE will not be as easy to as shaping wood.   But once it's shaped you're done.

[Yamaha33410]

Thanks. for some reason I cannot see any images on this forum. I will keep searching around to see what I can find. Some mention that it doesnt have to be perfect but I have read about people getting "vibrations" after building a foiled rudder. my reasoning for using HDPE was that if anything is off, it would be relatively easy to fix. also, it seems like that is what the ida sailer rudder is made out of. I know $300 seems steep for the rudder. I hopefully will get to this project soon

I wonder how much of those vibrations are due to the foil design or just our boats in general, my stock 16 rudder will vibrate through the tiller slightly when my speeds get up there on a nice windy day... I do have some slight play in the mounting holes, that could also be a factor

[paydirt]

Salty 19 has some good points. HDPE is not cheap and any messup and Id be out $50. I am noticing a trend though. Compac 16 owners tend to be frugal. I am debating replacing the main sail or buying the ida rudder. I cant do both. so i may just use foam covered with fiberglass