Rudder Reinforcement After Rebuild

[rognvald]

Originally Posted by Nicholson58

I'm glad to help. Did you find my photos? I posted a mess on the forum. Member Galleries - Cruisers & Sailing Photo Gallery

Nicholson,
Excellent photos, especially the spirit figure that emerged after sanding. I'm still in the process of removing the aggressive barrier coat and will start cutting and grinding next week. Thanks for the reply.

[Nicholson58]

BTW - rognvald - the 635 resin does not blush so there is no need to worry about adhesion of successive build-ups. For Sanding & grinding, I use a 9" OD right angle buffer with a 40 grit carbide semi-rigid wheel. The wheels are standard at Home Depot. I used only one of these wheels on the entire bottom of my 58 foot boat to put on the new bottom. Very aggressive and durable. The grinderis shown in one of the photos along with the aluminum angle I used for leveling my lines. Note that if you work the angle like a concrete screed that black spots are left at high places. Makes it clear where to work. I wish you success.

[Jpserrie]

Originally Posted by Nicholson58

The drill & drain is a common quickie fix. The problem is that it deludes one into thinking the water has been removed. Urethane closed cell foam cast in place and faired is a standard construction. The foam is closed cell and repels water well for short exposures. If you look up the properties though you will note that it has a non-zero permeability. Over time it will become waterlogged just as a tree trunk will. Once water has made its way in, freeze/thaw will break the cells, opening the foam to more ingress. Add to this the mechanical flexing contributing to mechanical fracturing and the entire rudder will become a piece of florist's foam. Drilling a hole will let out a few pools of liquid from the most totally damaged foam but you only delay the inevitable.

The core in my own rudder was diminished to only about 30% of its original volume and the hollow interior was wads of fuzzy black mold. The skin was mushy de-laminated crud. I consider foam a poor filler for an object that is intended to be immersed 100% of the time. For this reason, I chose the 635 and ballooons. 3 gallons of 635 thin mixed with a drywall mixer and 10 to 12 gallons of balloons makes 15 gallons of syntactic foam. The 635 is very slow cure (days) so no heat build-up problems even in my 6" thick pour. The compressive strength is 3000 psi and the skin will bond 100% to the core so the resulting strength is massively greater than foam core. There was some question as to the density of the syntactic foam. It is very light. Based on my mix ratio, density is about 22 to 25 #/cubic ft. Definitely greater than new foam but way less than water-soaked foam.

One method of repair short of total re-build would be to open windows in the rudder suitable for digging out all of the foam. Clean and scrape thoroughly and solvent wash. Make sure it is baked dry (in the sun) and pour in the epoxy-balloons filler. Repair the windows - done. This assumes the skin is in good shape.

The recipe I noted will yield a mix that is nearly dry to the touch. Trust me - it will wet the contact area to the rudder's skin and give you a very strong bond. The dry mix is easy to handle since it won't stick to you with a casual touch.

What was your ambient temp when you mixed the filler? And how thick could you go before it generates to much heat?

Also, which type of balloons did you use? 3M glass bubbles or phenolic microballoons?

[UNCIVILIZED]

Originally Posted by Jpserrie

What was your ambient temp when you mixed the filler? And how thick could you go before it generates to much heat?

Also, which type of balloons did you use? 3M glass bubbles or phenolic microballoons?

Given the age of this thread you might want to PM him. That said, I asked him about how he rebuilt his rudder ages ago, & his reply's below, in blue.


"I have a series of photos on this site. I placed the rudder on the basement floor so that the upper most surface would be flat/level. Underneath, I had a layer of 1/8 inch crappy plywood paneling form Home Depot. Layered on top of that was a 7-mill polyethylene release film. The rudder stock and welded metal ribs defined the foil form. I had wrapped these metal bits with glass & epoxy to build up to the desired dimensions. I had kept intact the bottom and trailing edge hanging on by threads. I also had detailed dimensions from before I started. I used wood and blocks of foam rubber to lift and form the plywood to my foil. This defined the cavity to be filled.

Use US Composites 635 THIN resin. http://www.uscomposites.com/

http://www.uscomposites.com/epoxy.html 2:1 slow. Use pumps for small mixes or you will get it wrong. This stuff will give you several hours of work time. Cured to sand took 3 days. No heat at this temperature so thick pours are OK.

http://www.uscomposites.com/fillers.html Balloons

I mixed 3-gallon sets with a 4-gallon bucket of Micro-balloons in a large plastic bucket using a 1/2 inch drive drill on very low speed and a dry-wall paddle. Clamp the bucket between your feet & mix slowly or it will fly everywhere.

Pour this into your open mold. It will look like Kraft marshmallow crème. Be patient. It will slowly spread out and wet out all surfaced it contacts. It will find any crack you did not seal. It will start to cure at about 3 to 6 hours.

635 THIN has no amine blush so you can pour multiple layers if you need to fill in holes.

I used an aluminum 2x2 angle and a large right angle grinder to fair the surface. The grinder exposes balloons. Drag the angle over the surface to reveal the high spots as dark stains.

Once the filler is complete and fully faired, you can apply the skin. I could have don this myself as well but chose to hire our ship yard to vacuum bag it with my carbon fiber. Find all the glass and other materials you need at Us composites. Also find other cool resins and materials as well as some great tutorials.

The syntactic foam has a compressive strength of about 3000 psi. You will find it brittle though before the skin as applied. It is totally impervious to sustained immersion and has a density about like a marshmallow.

PHOTOS: Ours is 6 feet tall, 30 inches wide and 5 inches thick - a barn door.
http://www.cruisersforum.com/gallery...0&userid=49581 "