Pencil vs Rudder

[finding41]

I decided to take the rudder off my 26D and redesign the foil and glass it. It was made by the PO out of what looks like a pine 2x12. I noticed the rudder had a soft spot and started poking with a pencil that I was using to draw out a new foil shape on paper. The pencil went in aprox 7/8" in the bad spot. So I kept poking. Seems to go about 3/4 up and all the way down. Not as deep, only about 1/8 to 1/4". It's done!
So I am going to make a new one. I've got a few questions though.
Why was the original rudder foil shape so different than the dagger board shape? I have read that the best foil shape is 12 but am wondering what the foil is for the dagger board. It looks like attention was paid to the dagger board shape but not the rudder.
What is the recommended wood type? ( My plan is to wrap it with fiberglass for strength. Is this necessary as it will be stored on the trailer outside when not being sailed?)
I plan to copy the over all shape except for the foil shape. For the foil I'm going to use the plans from:
http://www.mothboat.com/Building/foils.html
Am I aimed in the right direction with these plans?

 

[MrBill_FLL]

AFAIK, the original is a wood frame, and glass skin. looks like your is similar.
I've only seen solid wood rudders built.

sounds like you want to do a frame and skin again? yes?

 

[finding41]

Yea. That's what I was thinking. Do it once, right. I will be keeping the boat outside in the winter too. I have noticed this winter that its pretty damp in side the cabin so I think the best bet is to let it hang on the transom. I have a bunch of waterproofing to do...
Is the dagger board hollow fiberglass? Could I make a hollow fiberglass rudder or would it be too light? I could make molds off the old one...

 

[MrBill_FLL]

The stock (non foil is hollow) most people with solid wood rudders need to add some lead weight to get them to sink.

not sure which wood I'd use... (white oak?) but I would seal it w/ epoxy

metal (alum) would be better, but the stock one lasted a long time...

maybe someone that's done it will chime in..

 

[finding41]

Aluminum. Hmm you have got me thinking.
Two tubes. One, leading edge a bit smaller than the larger 30% back. 1/8 sheet welded between them and out the back to the desired chord length.
Like this...

 

[MrBill_FLL]

or pop rivits and a fiberglass skiin? (since I don't have a welder for AL)

keep use updated!

 

[Mac]

Here is what I made for my M 25. Good luck! http://forums.macgregor.sailboatowners.com/showthread.php?p=742845#post742845

 

[finding41]

Thanks Jerry. I'm heading to the metal yard on Friday to get some prices for aluminum. I have been doing a bit of research and think that I can get the proper foil shape with a bent single sheet. On Sat. I'm meeting an old colleague I used to teach (sculpture) with to go over design and fabrication ideas. He has a tig welder so he is the man for welding it up.
I'm going to make it the same size as the old modified one that came on the boat when I got it. It lifts up nice and high.
I will look at reducing the flex in the castle while I'm at it. There is a chunk of wood stuck in it now. It probably helps but there is still allot of flex there.

 

[Right On!]

Hey Finding,
I posted all the steps of my new rudder build. Used a oak/foam core, shaped it to a a NACA 0012 foil with a template i made. check it. maybe you could at least get a few ideas from the post!

http://forums.macgregor.sailboatowners.com/showthread.php?t=126954&highlight=rudder

youll have to scroll down a bit untill you get to beggining of the build steps...i

 

[finding41]

Thanks Right on. I had seen your rudder build. I think that's ware I first came across the 0012 foil #. Thanks. I am really thinking of using aluminum. I went over it on Sat. with my buddy. It shouldn't be that hard to do. (rollers) It will cost bit more than I want but will out live the boat. The PO built the one I'm replacing 5 years ago! It was painted.
I could build one like yours (I'm a contractor) but by the time everything is considered it will end up costing about 2/3 of the aluminum one.
How does yours stay down? I know you tie it down like the rest of them but is it extra buoyant because of the foam?
Why not build it out of just foam and fiberglass? Maybe throw in some carbon fiber strips for side sheer strength... ( I know fiberglass resin eats foam but that can be avoided.) Has any one tried this? It can be easily cut or milled by C&C machine.

 

[MrBill_FLL]

epoxy doesn't eat foam...

aluminum should stand up to the prop better too!

 

[mate88]

Repace rudder + keel

The std Mac keel/rudder on my '95 26S were poorly profiled and 'cheap'. I designed a new shape for both and went to local HVAC sheet metal fabricator. Using 26ga galv sheet, he bent each blank (2 X FINISHED WIDTH) down c/l of length to about 60 degrees (inside). For the spar, I used 1-1/2" sq. steel tube about 1/3 chord of the foill, bringing the trailing edges together. You end up with a smooth,balanced shape. I added 1" blue foam ribs 12" on center down the length and finished by filling the bottom section with concrete. I've built 3 pairs of these, the last seems to be the best so I'll stop there! I enjoy the tinkering too much - but next is powered rise/fall for keel. Forgot to add - To ease fitting/removal of keel I added 10ga st. steel brackets for the pivot mount. 4 bolts out and you are now holding the @#*% thing on your belly!

 

[Right On!]

I use a uphaul/downhaul system that you can see in the pics towards the end.
Also West Systems epoxy does not eat foam...the stuff you get at the "Home Depot" stores will however

 

[finding41]

I was making a 5' fiberglass pear. Yes pear. I almost died when we put the first sheet of fiberglass on and it started melting the foam we used for the core. The foam was the blue hard stuff about 3" thick. The epoxy was the cheapest we could find. Probably Canadian Tire auto stuff. From that experience I figured foam and epoxy don't mix.
Our solution was to wrap the foam pear with 6 mill poly then we went at it again. Wish had a picture of that pear.

 

[MrBill_FLL]

I used west system, and it didn't eat Styrofoam, or closed cell.

next time around I'm going to try MAS....

OK, I'll bite,

Why would you want a 5' pear?

 

[finding41]

The pear was for some catering company, (I think it was called the Flying Pear) that wanted it to hang on there building. It was actually 3/4 of a pear. One wedge was out of it so we could fit on the corner of the building.

 

[Fred Villiard]

Epoxy doesn't eat foam, polyester does.

Fred

 

[finding41]

Updates to the rudder build. Well my buddy can't get to my rudder so I am working with the old one. It sat in his shop for 2 mo. and never dried out completely! So I took it to my shop and sanded it down with the belt sander to get an approximate 0018 foil shape. 0012 is out of the question as I'm limiting myself to what is on hand. (I expect to only need it this year.)
After sanding I let it hang in my wood shop with a fan on it to dry out for a week. Next was a finish sanding and coat of fiberglass cloth on both sides. Then sand again with the orbital sander to smooth things out and re-coat with resin and foam roller. This coat was with the rudder hanging in the shed.
That should do it for my fiber glassing on it. I'll give it a quick light sand with a sanding sponge and then prime and paint.
1st pic, Old rot repair on bottom of rudder.
2nd pic, rudder after 1st coat of fiberglass

 

[Chris & Lenore]

Just another solution (while we are talking about the various ways to build a rudder) - make friends with an R/C modeler who has a foam cutter.

Foam core, strips of narrow carbon fibre cloth full span at max cord followed by several layers of unidirectional fiberglass cloth.
Easy to get the exact airfoil that you want and stronger than anything you can imagine.
We use this for glider wings that take close to 1000 lbs force differential between root and tip on a 100+ mph winch launch.
Most of the highest performance race boats use this composite construction on their foils.

If you can find someone with a foam cutter to make the core, the rest is not very difficult - just don't put any structure internally except at the head so it doesn't crush. The strength is from the skin and integral CF "spars" which are just layers of cloth in the build up. There are many articles on the web detailing this type of construction for boat rudders.

In terms of airfoil, I am happy with the Ida rudder I'm now using - but it is the exact airfoil of the rudder that came with my 93 Mac 26. Same planform (except for rounded bottom) and pivot location as well.

Chris

 

[finding41]

Thanks Chris. I think I can find someone at the collage that can C&C some foam for me. I think I might try that instead of the aluminum one I was planning. I might do the dagger board before the rudder just because it might be a good idea to have an extra one around.
I sanded and primed and painted the rudder today. It looks pretty good for a fast job. I'm planing to put it on tomorrow.
I went down to the yacht club today and chatted with a few other members. I found out the guys that moor can't get out until the 4th of May. Something about the mooring field needing adjustment. I might put my boat in this week because I am using a dock. It was set up on Tuesday.
1st Pic, sanded glassed rudder. 2nd Pic, primed and painted rudder.