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Old 02-09-2009, 18:53   #1
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Serious Rudder Repair...

Hi all! Just wanted your opinions about our next refit project...our rudder. I had noticed when we purchased the boat that the rudder had cracks in the skin and leading edge. This I attributed to water incursion and freezing. I figured I would split the rudder, carve out the foam, make skin repairs and glass the shell back together for re-foaming. WRONG! The rudder was SOLID. Basically a fiberglass skin filled with resin and some type of filler surrounding the mild steel reinforcing plate. This steel is welded to the 304 stainless pipe rudder stock. As you can see from the pics, I have cut away the leading edge of the rudder to expose the stock and steel plate at the welds. The stock pipe is bent and has crevice corrosion. This thing weighs a TON! I am now having second thoughts about repairing this rudder, and I'm considering using the old rudder as a plug to pull molds and start from scratch...What do you think?
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Old 02-09-2009, 19:26   #2
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Christian, I don't like the part about mild steel reinforcement and the corrosion on the rudder post. If you seal all this up, the problem will still be there and you probably won't be happy.

I would vote for fabricating a new rudder and using the old one for making a mold. Good luck.
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Old 02-09-2009, 19:45   #3
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See if you can contact the original manufacturer

Back when I ran Icefire aground on some rocks off the Maine coast (truly screwing up the rudder in the process), the boatyard I hired to fix her got in touch with Sabre. Sabre had all the old -28 plans sitting around, and they just made us a new rudder. Saved a lot of screwing around with slipshod repairs and whatnot. Now I'm not necessarily suggesting you have the boat builder make you a new rudder, but they may still have the plans available. If you ask nice, maybe they'll send you the specs so you can make it (or have someone else make it for you)....or maybe they'll make a new one for reasonable $. You never know.

Good luck!
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Old 02-09-2009, 19:48   #4
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I vote for start over with good quality materials and let this thing return to the earth -- sounds like it already has a pretty good start.

Really, Christian, no matter how hard you tried -- and I'm sure you'd try real hard -- would you ever truly feel comfortable with it, knowing what you know?

Not to mention, you'll free up a lot of weight there at the aft -- more beer!

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Old 02-09-2009, 20:46   #5
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I'm leaning toward completely new rudder. I have a replacement rudder stock, and I could simply cut off the old one and weld it on, but two things really bother me: the unknowns of the internal steel plate, and the weight of the damn rudder. It took four of us to move it, and none of us are small. If I created molds, had new internals welded up in stainless, and assembled the shells...foaming is my only real concern. I spoke with FossFoam about rudder construction, really nice people. They say that the foaming is the tricky part...

BTW, Challenger Yacht Corp. went belly up 25 years ago, so no help there. Thank you all for your take on this dilemma, Chris
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Old 02-09-2009, 21:31   #6
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I'm not a naval architect/engineer...

I'm not a Naval Architect/Engineer but it looks like you may be better off starting from scratch.

The shape in your photograph does not look at all flash, the area may not be what a more modern approach would consider, a redesign could give a lighter structure and modern materials may be able to save additional weight (reducing the strain on an old boat).

Do you know an experienced and qualified person who could advise you?
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Old 03-09-2009, 00:03   #7
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Is there a local boat builder that might be able to help you out? I do know of one in the Wilmington NC area that did a very nice job building us a new rudder (a deadhead on the Cape Fear River took ours out), but that's quite a ways from you. But, if you're interested, PM me and I'll give you the contact info.

You're right, though, doing the foam shaping was the tricky part. Being a cat, they took the dimensions from our surviving rudder and made a twin. Really can't tell them apart, down to an eighth of an inch.

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Old 03-09-2009, 00:06   #8
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Chris,

Is that back part solid too?

Anyway, I wouldn't worry about that tricky foaming stuff, they just want your money. You have an easy job because you are gonna save weight no matter what you do.

I see you have a bearing at the bottom of the rudder. That tells me you don't have to worry about the shape too much (you don't want to know why ;-)

So, I would not build a plug for it. I would glue the old bits back together, put plastic wrap over, next fiberglass cloth, wet out with epoxy (use epoxy) making the first half of the rudder (just one layer cloth), let cure, another layer of plastic wrap, duct tape around the edge so that the tape sticks up from the sides and pour (or spray) expanding foam to fill to top of tape; cure, more tape and repeat until foam is thick enough, like 2 inches or so. Now take it off the rudder, turn around, remove plastic wrap and start with the woven roving etc. to build it up.

The shaft: the part that's inside the rudder: Use one size heavier gauge stock and weld the frame on, rough it (frame plus shaft) up with abrasive disk on angle grinder to get shiny metal, brush epoxy on and immediately use 120 grit wet&dry sandpaper to "sand it into the metal". Let cure, sand a little and coat it another couple of times. Tell corrosion to "eat that" ;-) but don't forget to sand it again before assembling everything later.

The hours will go into the part where you finish the edges of the two halves that go together and the right angle/position of the shaft. Make the area around the shaft solid again, because you can expect water ingress around the shaft. Use a decent filler, not microlight. I think half medium density and half colloidal silica is great, peanut butter consistency.

Make the shell thick glass/epoxy and leave it empty when assembling. I would use epoxy + high density filler to ketchup consistency for assembling it. After cure, sand smooth.

Now the foam ;-) Put the rudder up like in same position as when installed and drill a row of 1/4" holes from bottom to top into the voids. You need a hole at the very bottom plus the very top and every 12" in between. If the void is wider than 12" you need a second row.

Now go to the supermarket and buy all the cans of expanding foam. Test every can before using it by spraying the tiniest amount in the lid to see if it expands. Put the spout in the lowest hole and keep spraying until it comes out the hole above. Tape the hole used for spraying. Work quick, do the other holes at the bottom, if any, before going one level up. You have to get there before the foam that came out cures. Work all the way up and let cure for two days. After that, re-drill the 1/4" holes with a drill bit one size up and fill with epoxy and colloidal silica filler (peanut butter again)

Back to the edges/seam. Put fiberglass tape + epoxy over the seam. You could do two layers, first 2" wide tape and second 4" wide. After that, use epoxy + ultralight fairing filler to "hide" the glass tape.

Now switch to the West System barrier coat thing and a layer of hard black Trinidad anti-fouling onto the last, still sticky, layer of epoxy. All the glass must be well under the level of epoxy.

You should save a ton of weight and have a much stronger rudder.

ciao!
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Old 03-09-2009, 00:23   #9
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I vote for building a new one...but I'd do it from the inside out....no need for making a mold.
I think I'd start with some thin (10 or 15mm) ridged foam board stock (airex or the like)...laminate the sheets together with fiberglass matt between the sheets...then cut the shape and fair accordingly...fab-up your shaft with its cheek plates...fix it to the foam rudder panel and wrap the whole thing with lots of glass....last bit is to fair it with filler.
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Old 03-09-2009, 06:39   #10
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Wow! Nick comes through with a really novel way of taking a mold, and ID and James go for shaping a male plug. Lots to think about. Both methods a great. I would love to try that foam mold process though...
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Old 03-09-2009, 06:52   #11
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Rudder fab

I have done this with the original mold for the rudder for my boat. Gel coat, cloth and resin wet layup on each half, bond the welded BRONZE stock and reinforcement into one side with thickened resin, more thickened resin around the edges and on the stock, pour in mixed two part foam for the voids and clamp together.

You need a heavy duty mold to do it this way to resist the force of the expanding foam, and need to calculate pretty closely the volume to fill.

To do a one-off I would make some patterns off the existing rudder and then duplicate the shape in closed-cell structural foam (Core Cell, Divinicell, etc) of proper strength by gluing it up then shaping with a power plane and sandpaper to the shape of the templates, then bond in the new stock (minimum 316 ss) and then fiberglass. It will be better than my rudder, as you can wrap the edges.
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Old 03-09-2009, 06:58   #12
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Quote:
Originally Posted by Oceansandmts View Post
then bond in the new stock (minimum 316 ss)
I thought 316 was important too, 'til I spoke with FossFoam. They use 304 ONLY, and have for the thousands of rudders they have built. Their rudders are on tons of production boats and they claim to never have had a return due to corrosion. My boat is 35 years old, and has a 304 stock, which has light crevice corrosion. I guess 30 years is pretty good for 304...
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Old 03-09-2009, 17:04   #13
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Expanding foam is amazing stuff and cruisers don't use it enough.

Just buy a can and spray it all empty on a piece of cardboard and see what happens. Let it cure and see how strong and light it is. Play with it and the ideas will come quickly ;-)

Also, this foam is one of the best adhesives I know. Take two small pieces of plywood and use the foam as an adhesive. You will have to cut it to separate it. I first discovered the qualities while renovating my house. It's normally used to close the gap between floor underlayment sheets and walls and there's just no better way. I think it'll last as long as the walls.

Chris: yes, you can drop a piece of plywood on top of the curing foam. This way, you only need as much foam as to make it level. If you want to make a durable mold, you can epoxy the foam later, or even put a layer of glass in.

The plastic wrap I mentioned: the thin sandwich wrap is okay but you can find bigger pieces a little thicker as drop cloths (the cheap ones) at the hardware store. The foil will basically come off cured epoxy but I always have some sandpaper ready if it needs some help.

If you do my mold technique and use spray cans you don't need a "tape wall" around the surface. After some practice, you don't need it with pour-foam either. Just watch how far it flows out before starting to set and you know where to stop spraying/pouring. The 2 component pouring foam: use disposable cups; fill a bunch with one component and another bunch with the other component all in the right ratio's so you can take two cups, empty them in your mixing cup, stir and pour and repeat.

Rudder stock: yes, bronze would be nice ;-) But as the old shaft was bent, you need to make it a little stronger (thicker wall).

ciao!
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Old 03-09-2009, 17:14   #14
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I cant really tell from the photos. Is the steel plate welded to the rudder shaft full length? is it badly corroded? if it's just got surface corrosion and stoutly welded...hmmm... steel may be better than stainless if water gets in there. Weight is not great, but I have had to scrape out and fill rudders that had been filled with foam. If a new rudder....I would never put expanding foam in a cruising boat rudder, it gets saturated with water. Epoxy and microballoons maybe... or fill it with non water absorbing foampieces to keep t he weight down and then fill it up....
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Old 03-09-2009, 18:28   #15
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Call Foss Foam in southern Calif. they build rudders for all kinds of boats may even have plans for your boat.
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