erdb

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About erdb

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  1. erdb

    I'm making a rudder

    I figured I'd post pics of the finished rudder. Everything seems to work fine, boat sails great and so far nothing has broken. Have you finished your rudders Alan?
  2. erdb

    I'm making a rudder

    Here is another pic showing the whole cassette from below.
  3. erdb

    I'm making a rudder

    I decided to use fiberglass instead. I was originally planning to use carbon, as it seems a lot of people use that, but then though that glass is supposed to be more forgiving, flex is not a problem here, and I don't mind a couple of extra grams. I really don't know, I guess carbon would have been fine, too. I laminated the final layers and did the first rough clean-up of the edges. This is how the cassette looks like now: Here is a close look at the lower gudgeon: First I wrapped the SS rod with packing tape, then 2-3 wraps of 6oz glass cloth to make the tube. Once that cured, I removed the SS rod, and used my jig to position the tube accurately relative to the rudder blade. I made that inside "A" seen above by putting a glob of thickened epoxy with chopped glass between the tube and the cassette and covered it with a few layers of glass. Later I built up a few more layers of glass on that, then glued the cedar on for core, faired it and then laminated a bunch of layers of glass on the outside. For both the inside "A" and the outside layers, I mostly used glass uni with a few layers of 45deg biax mixed between them. The glass uni I had was 6oz, so it took a lot of layers and a lot of time. It would have been better to have fewer layers of heavier glass I guess. The thickness of that outside wrap is about 1/4". Hope it answers your question. The whole cassette is very sturdy, in fact it feels a little overkill, but that's fine. I want the rudder to stay on the boat. The only issue now is that the gap between the cassette and the blade is not as tight and uniform as I wanted. I'm planning to use the fuzzy side of a velcro tape for gasket, and now I'm thinking of ways to put some thickened epoxy or some gasket glue under the velcro tape to make the gap tighter. It should be tight, but at the same time, I may need to replace that velcro in the future, so I don't want to glue it on too permanently either.
  4. erdb

    I'm making a rudder

    Progress has been a little slow here, but finally the cassette is taking shape. 1st I made tubes by wrapping fiberglass around the SS rod I'm using for the pins, then glued these tubes to the cassette using my templates as guides and an arrow shaft making sure they're in the center-line and had the proper angle to the rudder blade. The laser-cut templates sat on the blade as I've shown it above. They had the proper NACA profile, I just had to make sure the blade was also faired properly... Wrapped a few layers of glass around the tubes, and filled the void between the cassette and the tubes with a mix of thickened epoxy and chopped glass. Then glued on pieces of cedar as core to increase the thickness of the lower and upper straps and shape the rudder head: The rod is only there to check alignment, it will be cut into shorter upper and lower pins. Now I'll wrap a scientifically guestimated number of glass uni and 45 deg biax layers around the cassette. Then, I'll clean up the edges and do some fairing to have a smooth surface. The tiller will be fixed, glued to the cassette, I just wanted to do it in two steps to have better access to the cassette while I laminate and and fair it. I'm using glass everywhere except at the trailing edge where I have a few layers of carbon uni running down inside and outside of a couple of layer of glass biax creating basically U channel-shaped sandwich to resist against torsion of the cassette. The part of the cassette covering the leading edge of the blade is made mostly of 45 deg biax glass. It already feels very sturdy, but I'm planning to build up around another 1/4" thickness of glass on the outside of the straps (mostly uni, with a few layers of 45 deg biax and maybe 1-2 layers of 0 - 90 in between). What do you guys think?
  5. erdb

    I'm making a rudder

    Oh, so you were just conducting tests using your toe.. I see.
  6. erdb

    I'm making a rudder

    Yes, that's my preferred method as well!
  7. erdb

    I'm making a rudder

    It's certainly a good and easy method, and if the wood is thick enough, the wood and the carbon will be strong enough to handle the loads. I think the glass is only there to seal the wood in this case. However, if the aspect ratio of the foil is high, and you don't really want to go higher than 12% on thickness, the wood core will not give enough strength and the skin will have to be much thicker to take the load.
  8. erdb

    I'm making a rudder

    That's a great source, thanks. I've been using "Principles of Yacht Design" as a source for load calculations, but when it comes to cassette rudders, there isn't really anything to use other than the various build blogs that usually lack explanation on how the layup schedule was designed. I think in most cases the design process is something like - let's put x layers of carbon, glass and kevlar on - that should do it! I try to use some numbers, but I'm a neuroscientist, not an engineer....
  9. erdb

    I'm making a rudder

    Thanks, the 1.5" width is the final minimum width, I may end up a little wider. I'm planning to cut 2" strips of glass from a wide roll then clean up the edges as needed. I don't really have to match the original gudgeons, but I figured unless everything is lined up perfectly (I'll try but there's a limit), increasing the width of the strips much further won't help, because it's unlikely that the forces will be spread equally among the fibers anyway. As for creating a core to increase the width of the strips, I'm thinking maybe I could use small pieces of end grain cut cedar and glue them on in a row with thickened epoxy then sand the outside smooth. It seems easier than trying to carve out a bigger piece to match the shape of the cassette. Also, this way the grain will be perpendicular to the laminate.
  10. erdb

    I'm making a rudder

    Thanks Zonker. So yes, this is interesting, most builds posted on the net use carbon uni for those horizontal strips, but I agree with you, it seems to make much more sense to build it from glass. The distances are short, so flex is not a problem, but fatigue from repeated stresses certainly is. Glass should be better for that unless I'm missing something. I already had that pdf, and while it's very helpful for the general building method, that's for a much lighter boat, and without knowing the exact dimensions of the cassette, just simply taking the layup schedule would be dangerous. This is how I'm trying to estimate the loads - tell me if you notice something seriously wrong with it. I can estimate the max sideways force on the pintles from max speed, max CL and dimensions of the blade, then use a simplified geometry like this (looking at the cassette from above): I'm only calculating with tension on one side. I guess compression from the other side would help as well, but decided to ignore that as a safety measure. Using 1.5" wide horizontal strips, a 3x safety factor (is that reasonable?) and 30 deg for the alpha, it seems I'll need a ~ 7mm-thick laminate (little less than 5/16") going around the pin. I have 6oz glass uni and 17 oz +/-45 biax, and according to vectorlam, I can make up the 7mm thickness with 18 layers of the uni and 3 layers of the biax. Does this seem believable? If I used carbon uni, I could get the same numbers with about half the thickness, but the weight difference is negligible for my boat. Instead of having those horizontal flanges, I plan to just bulk up the horizontal strips. I'm not sure what's the best way to do that, I could use wood as Alan suggested or just build up thickness with thickened epoxy. This would act as core within those strips so there would be layers of glass inside then the thickened epoxy ~3/8" thick, then more layers of glass on the outside like this:
  11. erdb

    I'm making a rudder

    Looks good. This pic shows really well why construction methods and laminate schedules vary so widely when you do a search on the net. That's a massive piece of wood! You must have some strong bones if it didn't break your toe. I hope it heals up quickly! In your case, it doesn't really matter what you use to laminate the rudder, because the wood itself is strong enough to carry all the loads. My rudder is probably half as thick and I only have wood core in the middle of the blade, so I needed lot more fiber to make it strong and stiff. It becomes a problem when people use a layup schedule from someone else's build on a completely different rudder. It would be nice if someone did a write-up or made a simple enough calculator to help home-builders with laminate schedules. I searched a lot for something like that, and there's basically nothing on the subject. The vectorlam software is a good start, but it's not that simple to use and how you use the output is not trivial either. I'm quite confident I made my blade strong enough, but the cassette is lot more complicated in terms of figuring out the loads and how many layers of what should be laminated. I'll probably just pile up as many layers as I can before it becomes an ugly piece of mess . This is how I wish it looked at the end: ...but it will probably end up being much bulkier with a lot of filler and fairing needed to look relatively decent.
  12. erdb

    I'm making a rudder

    I also made some progress. Rudder blade is done. The shape came out pretty close to the NACA profile except for the first inch along the leading edge. I had to do some fairing there. Here is the laser-cut template on the blade: Now it's time to build the cassette. Carbon or glass??? I'm going to use two of those templates above to set the location and angle of the gudgeons. I've made a skeleton of the cassette that was vacuum bagged onto the blade for proper fit. Here is how it should be positioned at the end: The plan to build the horizontal strips is something like this: Gray is the blade, light blue is filler, black is (many) layers of carbon or glass. White circle is the pin. So what would you use to laminate these strips? I have both carbon uni and glass uni, glass +/- 45 biax and some carbon twill. Weight doesn't really matter, I just want to make sure the rudder stays on the boat. Carbon is stronger, but glass is tougher, right?
  13. erdb

    I'm making a rudder

    Zonker may have been talking about how I'm planning to rake forward the rudder for balance. I toyed with your idea, too, but then decided to go with foiled shape blade all the way with a foil-shaped cassette, because I'd like to be able to pull up the rudder and maintain steering in shallow water with raised centerboard (around boat ramps or in shallow bays/rivers). However, I still haven't completely figured out how to secure the blade in the cassette. I'm afraid that if I make the cassette very tight, it will be hard to move the blade up and down. On the other hand, if I make it loose enough to move the blade easily, the blade may move a little under sail. Side-to-side a degree wouldn't be a huge issue, but if it tilts just a little bit aft, it would mess up the balance of the rudder. So I thought I could make an insert incorporated at the aft edge of the cassette that could be tightened by a knob/bolt, but your wedge idea is interesting as well. I'd just have to make the inside of the wedge foil-shaped to correspond with the aft edge of the rudder. Then push it down and lock in place somehow. Maybe I'm just overthinking it. For me, the KISS approach would be just to laminate the cassette around the blade and hope I can get the tightness, material and friction of the gaskets right. Also, a question about your rudders. If I understand correctly, you're planning to use one cassette for both rudders and the main rudder will have to be inserted from below since it's thicker than the cassette, whereas the E rudder can be lowered from the top, right? How are you planning to build the cassette? You'll have to make it stronger than your rudder to make sure you'll have an intact cassette to drop your E rudder in ;).
  14. erdb

    I'm making a rudder

    So are you building two rudders then? Will you make the emergency rudder a one-piece rudder as well with the same attachment points as your primary rudder or will you make it a cassette rudder? I'm almost done with fairing the rudder blade that and will soon start working on the cassette. I haven't made up my mind on what gasket to use between the cassette and the rudder and how to glue that in place. I'd be interested in how you're planning to do it if you're also planning to use a cassette for the emergency rudder.
  15. erdb

    I'm making a rudder

    Good luck... Are you using some kind of template to get the right foil shape? I'm also in the fairing phase, which is the part of every project I hate the most. Luckily, I don't have to do too much thanks to using the female template. I was hoping I could get a perfect shape without any fairing, but the leading edge of the blade somehow flattened out a bit either when I glued the two halves together or when the epoxy cured. Here is one of the halves with cedar stripes glued in and the polyurethane foam shaved down flat. The blade as of this morning. The two halves glued together and the pic rotated to show the approximate final position on the boat - angled forward to balance the forces. A little more fairing, then I'll have to start working on the cassette using the rudder blade as template.