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Old 03-09-2009, 18:59   #16
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A little help

This is a wonderful tutorial I ran across some years ago. Its for a Seidelmann 25...but the fundamentals might still be helpful to someone.

Seidelmann Rudder Build
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Old 03-09-2009, 20:10   #17
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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.
Hey, that sounds familiar! Oh yeah... I said it in post #12 above! Foss Foam is in Florida, and they were very helpful. Thanks, Chris
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Old 03-09-2009, 20:13   #18
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I cant really tell from the photos. Is the steel plate welded to the rudder shaft full length? 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....
The stainless rudder stock is stitch welded to plate. 6" welds every 1 1/2' or so. As for the foam, there are true closed cell foams out there...
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Old 03-09-2009, 21:43   #19
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The trick to keep the foam dry is not the type of foam: it's to keep the water away from the foam.

I have a rather convincing example: Boston Whalers have a PU foam core. It's makes them unsinkable and they last pretty well. A rudder with PU foam core would be very much alike, but with thicker fiberglass.

About 95% of the cells of PU foam are closed. So, if you submerge it in water for a long time, 5% of the cavity-volume will be filled with water. When you seal the foam (paint, epoxy) it's 100% waterproof.

cheers,
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Old 03-09-2009, 21:57   #20
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I have a rather convincing example: Boston Whalers have a PU foam core. It's makes them unsinkable and they last pretty well. A rudder with PU foam core would be very much alike, but with thicker fiberglass.
Now who the hell wants an unsinkable rudder? It would be sticking out of the water all the time...
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Old 03-09-2009, 23:18   #21
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Now who the hell wants an unsinkable rudder? It would be sticking out of the water all the time...
Man I hate it when that happens
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Old 03-09-2009, 23:34   #22
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Chris,

How about you stick some hydrafoils on them??!! ;-)

ciao!
Nick.
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Old 04-09-2009, 06:03   #23
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It could lift my rear end at speed!
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Old 04-09-2009, 06:29   #24
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Rudder weight and weather helm

I understand the weight of an un-balanced rudder can have an effect on perceived weather helm when heeled. The weight of a heavy rudder when heeled helps your steering effort to counteract weather helm. Your old rudder may have been heavy for a reason, if you make a new, lightweight, floating one you may find the feel of the helm significantly changed, and not in a good way.
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Old 04-09-2009, 06:41   #25
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Your old rudder may have been heavy for a reason, if you make a new, lightweight, floating one you may find the feel of the helm significantly changed, and not in a good way.
Understood, and a good point. Helm feel is low on this boat, as it has a hydraulic steering system. Way interesting though... as the boat heels, the weight of the rudder would "fall off" and help the helmsman counteract weather helm... I learn something new every day on this forum! Thanks, Oceansandmts!
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Old 04-09-2009, 09:07   #26
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I rebuilt mine from scratch. Made a solid laminate profile glued with epoxy to the rudder stock, glued foam stringers then laminated them with biax, then thru bolted the stringer flange to the rudder stock profile, glued foam panels between the stringers, faired the foam to the stringers, laminated continuous around the rudder. The thing about the foam is a pour quality foam is hard to carve and shape. Hope this is clear let me know if its not.



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Old 04-09-2009, 23:26   #27
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From the pictures it looks like you've got a good hand Stevens 47.

Chris one thing to consider using the spray foam from the can is what it means to be "fully cured".
If its in a confined space it will take several days before you would be safe to release what ever is constraining it like a mold or the like.
It likes air and moisture to cure...you may also find large air pockets or bubbles with in the foam.
The two part stuff is much, much better regarding both concerns.
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Old 05-09-2009, 01:38   #28
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James,

I have worked with the cans a lot, let's say I used several hundred cans. When you use the technique of introducing the foam at a low point, working up to higher holes when foam reaches that level, you don't get any voids. You can get some rather large bubbles so if structural support from the foam is important, using a rigid foam gives better results. But the spray cans produce a strong foam even with some larger bubbles. The only failures I have seen are cans with foam that doesn't expand. This is why each can should be tested before using it. I must say that it was one particular brand that had bad cans (the one sold in the US with red and green cans). I never had a problem in Holland, where the cans are also much bigger, like 3 times the content.

I brought this type of foam application up because I already discussed using expanding foam for supporting the mold. That doesn't mean I would do it that way ;-) I would use spray cans only to replace foam in a rudder without taking it apart (using acetone to dissolve to old foam). For building a new rudder, I would use Dow Styrofoam (the blue stuff) instead. I don't know what I have with foam, but I used that stuff a lot too ;-)

I have some tips for shaping it:
  • Use a Surform rasp. Attach it to a long enough piece of wood to use frame members as guides. You can get two types of blades for the rasp: a flat one and a round one. You probably want to use the flat one. The small one-handed version is more than enough.
  • When you are filling a cavity and the parts don't fit right because the foam is preventing that somewhere, use pins (the ones from needles & pins). Push them into the foam but leave the round head above the foam. Fit the parts together and it will become apparent where it needs more shaping.
  • Use spray expanding foam as the adhesive for both foam-to-rudder and foam-to-foam joints.
  • I like to under-cut the rigid foam and use expanding foam all around to seal it as this removes any voids in corners (the ones you can't see) and it is the perfect adhesive in this application.
  • You can use spray expanding foam to fill voids behind rigid foam using the same technique I described in an earlier post in this thread. This works very good but you must temporary clamp the rigid foam in place or it will be pushed out by the expanding foam. You must give it a way to escape or pressure will build up: use multiple holes for that.
  • And again: to keep it dry, make sure it is totally encapsulated with epoxy and/or fiberglass. So never use it around the shaft.
And I have another tip (used it in other applications but it's perfect for the rudder too): In my earlier post I described how to prepare the metal shaft before assembling the rudder. After you sand the epoxy into the metal and let it cure, sand and coat it with epoxy again. But instead of letting that cure, immediately wrap it with 2" wide fiberglass tape. Brush more epoxy on so completely saturate the glass (becomes transparent) but don't try to fill the weave. Do this an inch or so beyond the rudder blade position. After full cure, use water and a scotchbrite pad to scrub it clean from amine blush, do NOT sand it *damages the glass fibers). You now have a rough surface that bonds completely and very strong during assembly. Use high density filler around the shaft during assembly. Make sure to use enough where the shaft exits the rudder blade. After cure, you will have to remove the excess epoxy and tape on the shaft. First cut it around the shaft and next use that "sand-paper with woven backing that comes on rolls" or cut the belt for a belt sander open and use that.

cheers,
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Old 05-09-2009, 10:37   #29
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Nick
I always appreciate how thorough you posts are.
Thanks for taking the time.
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Old 05-09-2009, 16:54   #30
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Nick
I always appreciate how thorough you posts are.
Thanks for taking the time.
James, you are so right! Nick, James and Stevens...you guys make the forum what it is; GREAT! There are some seriously talented people here. Can you imagine getting us all together and forming a yacht manufacturing co.? We would kick serious butt!
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