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Working on another rudder
http://www.hobie.com/au/en/forums/viewtopic.php?f=14&t=3039		 Page 1 of 1
Author:  JaimeZX [ Tue Feb 14, 2006 5:34 pm ]
Post subject:  Working on another rudder
Some of you may recall the first rudder my friend and I built in the spring of 2004.

Ref: http://www.JaimeZX.com/Boating/Hobie -> part 3

Of course the problem is that the boat is now unbalanced with one plastic and one fiberglass rudder.

So we are starting work on rudder #2. We have the foam cut and sanded to shape and the oak cut out. Not working on it tonight so he can spend time with his wife. You know. Image

Tomorrow or Thursday (or Friday) we'll start the layup on the first side. Two changes in version 2:
* No lead in the tip. The previous rudder was built before I figured out that the rudders lock down.
* Finer weave "deck glass" as the outermost layer to make smoothing easier.

I will report back with results as they come in. :)
Author:  yoh [ Fri Feb 17, 2006 9:11 am ]
Post subject: 
My attempt of making my own blades was inspired by your initial posting, reached the foam core stage and ended when I was able to get a set of original composite blades or some EPO's (not sure what they are). Some day I might finish them.
Glad to hear the lead is gone. But why the oak? I understand that you use the oak in an area where you are concerned that the rudder casting might compress the foam core to a point where the outer composite shell would fail. What I do not like about the oak idea is the weight, the tendency of the material to rot, and the risk that the blade would fail right below the area where the wood ends.
I am suggesting not using a solid piece of wood in the head of the rudder blade. Instead I would recommend laminating more or thicker cloth layers in the upper 8 to 10 inches. A stringer might be an idea if you would run it from top to (at least almost) bottom.
Just an idea...
Patrick
Author:  JaimeZX [ Sat Mar 11, 2006 9:52 pm ]
Post subject: 
yoh wrote:
Glad to hear the lead is gone. But why the oak? I understand that you use the oak in an area where you are concerned that the rudder casting might compress the foam core to a point where the outer composite shell would fail. What I do not like about the oak idea is the weight, the tendency of the material to rot, and the risk that the blade would fail right below the area where the wood ends.

Hey, sorry for the delay in responding! Actually the necessity of the oak is questionable. We could probably have just gotten away with using foam and injecting thickened epoxy into the areas where the bolts mount, but everything is a learning experience. The oak should never rot becuase it's totally encased in waterproof epoxy, but I concede the possibility the epoxy might crack. Still, I think the time necessary for the oak to rot away would far exceed the lifespan of the boat. I also don't think the blade would necessarily fail where the oak ends because the vast majority of the strength is in the glass fibers. The oak isn't doing much.

Quote:
I am suggesting not using a solid piece of wood in the head of the rudder blade. Instead I would recommend laminating more or thicker cloth layers in the upper 8 to 10 inches. A stringer might be an idea if you would run it from top to (at least almost) bottom.

I see what you're saying, but like I mentioned above, the oak is really just providing a rigid structure for attachment to the rudder casting, not for longitudinal rudder strength nor for resistance to twisting - what our plastic rudders really need so they don't snap off. Make sense?

Here are the first set of pictures:

Here's the foam and oak for the second rudder. You'll note the oak is smaller, and it probably could go away altogether.
Image

Me & Steve laying up the first side. I think this is either layer two (bid) or three (uni.) The green color comes from the epoxy hardener, which is sort of emerald-colored.
Image

Here's the layup for the first side, completed.
Image


Below you can see 3 of the 6 layers of glass used. The order (inside to outside) was Uni, Bid, Uni, Bid, Uni, Deck. (Wick's Aircraft Supply has several types of fiberglass - the last layer (deck glass) is thinner and finer. This should result in much less work when "finishing" the rudder and making it glass-smooth.)
Image

Some time in the next few days I'll trim off the excess glass and prepare for laying up the other side (which will probably be next weekend.) I'd like to finish this project before I go on vacation in 3 weeks. :)
Author:  JaimeZX [ Sun Mar 12, 2006 10:22 pm ]
Post subject: 
Okay, sooner than I expected to get around to it, we layed up the glass on the other side of the rudder.


The first thing we had to do was obviously remove the excess glass from yesterday's layup and make sure it was trimmed back far enough that it wouldn't keep today's layup from laying flat against the edges. The epoxy was mostly cured but still green enough that with judicious use of a heat gun we could cut through with an X-acto knife.
Image

Then I took the rudder into the other room and cut out the glass. I then organized it outside-to-in in this pile so that the next piece we needed was always on top:
Image


In this picture you can see we're measuring out the epoxy. The particular brand is not a 50-50 mixture, so Steve built this balance. Hardner is the green stuff on the left, the resin is clear. The random bolt is for tareing (sp?) the balance.
You can also see behind that the rudder. If you'll look closely you can see that we gouged out the outer (approx) 1cm of foam. I'll explain why in a minute.
Image


As with the previous rudder, we removed the outer 1cm of foam (slightly more at the tip) and filled that gap with flox (epoxy thickened with powdered cotton.) The result is a much larger area of chemical bonding around the edges of the rudder than would be possible if the glass were merely epoxied to some expanded polystyrene. (Instead of maybe 1mm around the edge for the sides to bond where the glass touches, you have a centimeter or more in areas.)
Image


We also mixed epoxy with microbaloons to fill the voids in the foam. We did this on both sides actually. We would've had to wet out the foam in any case, and epoxy thickened with micro weighs less than the same unit volume of just epoxy. The tensile strength might be slightly less but it still far exceeds that of the underlying foam so no loss in strength is anticipated.
Behind, Steve waits to apply the first layer of unidirectional fiberglass.
Image


The final picture for to day is of the completed second-side layup. Now that the work-week is beginning, I don't know when is the next time I'll be able to get back over there and start finishing it, but so far I'm extremely pleased. The various bits of wood & weights are to hold down the edges of the glass cloth to keep it taut - easily removed after it cures for 2-3 hours.

Image


Yesterday and today's layups both took about 75 minutes. On the previous rudder we built in 2004 the layups took more like 2½ hours. We aren't sure how to account for this discrepancy, but we're not complaining, either. :)

I'll keep y'all posted. ;)

Jim

Edit for spelling error
Author:  Captain Dave [ Mon Mar 13, 2006 11:18 am ]
Post subject: 
Jaime,

Once again - nice work. Well documented too.

Dave
Author:  xanderwess [ Mon Mar 13, 2006 2:26 pm ]
Post subject: 
I'll take 2. Can you drill them for a 16? Also, where do I send my $75? :D
Author:  JaimeZX [ Mon Mar 13, 2006 4:24 pm ]
Post subject: 
;) Don't get ahead of yourself.
Author:  JaimeZX [ Thu Mar 16, 2006 10:42 pm ]
Post subject: 
Okay, took a couple days to get back to it.

Once again Steve went out a few hours after we finished the layup the other day and knife-trimmed the excess glass. This evening when I arrived, the rudder looked like this:

Image

After sanding the seams smooth I mixed up some micro and both filled in any obvious depressions and also squeegeed it into the weave. Tomorrow I expect to do a bit of sanding to this side and mix up more micro to fill the other side. This process will probably be repeated 2-3 times until the rudder is super smooth and ready for paint.

As I left it this evening:
Image
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