dimensions for kick up rudder

Discussion in 'Fiberglass and Composite Boat Building' started by seanseward, Dec 15, 2013.

  1. seanseward
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    seanseward Junior Member

    Making a kick-up rudder for my Neptune 16.

    After reasonable research I have decided:
    It will be 2x 3/4" marine plywood pieces glued together to make a 1 1/2" board, planed to foil shape, glassed, finished with epoxy filler and painted with gel-co or some marine paint. Cheeks will be 1/4 alluminum. gudgeons will be inset on inside of cheeks (similar to Laser Bahia system). I have foil dimensions from http://en.wikipedia.org/wiki/NACA_airfoil and http://web.utk.edu/~pdf/newport/newport/newport.htm. I will use current rudder for template.

    I need to reduce wood width to accommodate glass work and finish in order to fit within current pintles made for 1 1/2" rudder. What would normal glass work (layers) look like and what is skin thickness (http://www.fastcomposites.ca/site/marine/design-tips-fabrication-overview/helpful-calculations/) of this glass work?


    Questions:
    1. What is basic glass work layout for this job? How many layers, of what type of glass and what weight? I will use West Marine Epoxy.

    2. What is final "skin thickness" of this suggested glass layout?
     
  2. SukiSolo
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    SukiSolo Senior Member

    It is stronger to use laminated solid as a core rather than plywood. Lighter too.
    Quarter sawn Sitka Spruce, Western Red Cedar, Douglas Fir would all be OK even better if mixed. If you want a really strong one the D Fir would be incredible. The Cedar may be a little light but with a spruce centre, plenty strong enough.
    Glass weight, personally for ultra durable long term use about 280 -300 gsm woven (plain or Biax) or roving. If more racing you could go as light as 200gsm, but the Neptune is not really a racing craft. Put a good protective epoxy microballoon mix at bottom of leading edge wher the normal scuffing occurs, also a little along the bottom. This just gives it more protection.

    If it gets a hole ever gets through the glass, dry it out and repair. Do NOT leave, I have had to replace rudders where water has lifted the entire glass sheathing....they were high quality foils but the owners had ignored leading edge damage.

    Don't forget to fully coat the timber/ply so it is sealed prior to putting the glass on. Best to fair off the glass too and apply a clean coat to get a good sealed surface for paint/varnish
     
  3. PAR
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    PAR Yacht Designer/Builder

    Welcome to the forum.

    Agreed, plywood isn't the best choice on rudders (or other appendages), as it can fail from rolling sheer, within the veneers. Solid wood, strip planked (most common) or my personal favorite inert materials are the way to go.

    Strip planked rudder blades are covered in many places on line, with West System having a good PDF for their construction. I prefer inert materials, as they don't rust, swell, absorb water, usually are neutrally buoyant and can't rot. Foam or honeycomb core, all 'glass, all HDPE, etc. are the usual choices. You can also buy pre-CNC cut foil blanks or an HDPE blade CNC cut. These vary in cost, but you get precision formed foil sections.

    More important then foil sections is a symmetric blade, at least for your boat. The plan form (profile) is okay, though I'd radius the lower portion of the leading edge a lot more then yours currently has, say at least an 8" diameter circle.

    The section shown in the Newport sketch is pretty primitive. It sort of looks like a slab sided section, which is fine, though it looks a lot thicker then it needs to be. A 1.5" thick blade on your boat is a lot more then you need, especially if you want to improve it's efficiency a bit. A 1" blade would be all you need if strip planked and sheathed with a light cloth (4 - 8 ounce). I wouldn't bother with biax on a solid or stripped blade, but would use it on a cored rudder. If you do select a foil section, stick with the 4 digit 00 series as the best bank for the buck.

    1/4" aluminum cheeks sounds just fine, though use 6061 alloy (T-6) for strength and corrosion resistance.

    Lastly with a plywood, solid wood or strip planked blade, the 'glass sheathing is just for abrasion resistance, so a light cloth is all you need. I'd prefer Xynol or Dynel for this reason, which are far better then regular 'glass at abrasion. A cored blade will need the 'glass skins to be structural, so intelligently arranged biax with a finial finish cloth skin, is what you want. Also bond the pivot bolt hole with epoxy, so water can't get into the blade, regardless of wooden method you employ.
     
  4. seanseward
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    seanseward Junior Member

    Sukisolo,
    Yes, I saw a photo of a J30 rudder made from "sticks" and arranged to change direction of wood fiber/grain. I can find some nice 2x12 and rip it into 1 1/2" x 1 1/2" sticks, epoxy it together and shape that. I was hoping for the plywood lines to help with shaping the foil. The D Fir sounds cheaper and easier to find than marine plywood.

    Here is my layup plan: (previously improperly referred to as "layout") Please critique and suggest changes as needed.

    1) epoxy 1 1/2" x 1/1/2" d fir sticks and then shape foil

    2) before initial epoxy coats, cut/sand back wood (approx. 1/8") along lower leading edge and bottom

    3) two good coats of epoxy on wood...

    3) refill cut back lower edge with epoxy microballoon mix

    4) 2 layers of 280-300 gsm woven

    5) additional strips to close edges

    6) microballoon mix for fairing, then primer and gelcoat

    Is this a good plan? Am I missing a primary layer of matting? What is skin thickness if I follow this plan? General skin thickness rule?

    I remained preoccupied with "skin thickness" just because my pintles are set for 1 1/2" thick. What is general rule for skin thickness?
     
  5. seanseward
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    seanseward Junior Member

    Par,
    First, Thank you to all for your expertise!

    OK...light single layer of 4-8 ounce just to keep her dry.

    I will think more about wood core options.....I'm sure that the core will be wood.

    Thickness, I may take your 1" idea. It will simplify reusing 1 1/2" pintles with 2x 1/4" = 1/2" added aluminum width. I will not need to inset them on the inside of the cheeks but rather use them to hug the entire sandwich. I will counter set allen screws/bolts inside the aluminum cheek.

    My plan re-edited:
    1) epoxy 1" x 1" d fir sticks and then shape foil; still pondering 1" exterior plywood blade

    2) before initial epoxy coats, cut/sand back wood (approx. 1/8") along lower leading edge and bottom

    3) three good coats of epoxy on wood...as per Dave Gerr

    3) refill cut back lower edge with epoxy microballoon mix; (to strengthen possible rock kissing edge)

    4) single 4-8 ounce woven layer, just to keep her dry; maybe two layers for "ultra durable" long lasting

    5) additional strips to close edges

    6) microballoon mix for fairing, then primer and gelcoat

    Will follow plug concept for all drilled holes
     
  6. SukiSolo
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    SukiSolo Senior Member

    For me some of that is overkill, here's why.

    Step 1 is fine, make sure the grain is quartered and laminate any angle (in grain) to be opposite on next strip.
    Step 2. I prefer to keep the centreline markings as long as possible as reference for templates or profile guages so do that prior to removing any leading or bottom edge.
    Step 3. One coat is normally enough, two definitely makes sure. Dependent on absorbancy of substrate ie if it sinks in a lot you will need two coats. End grain of timber will need 2 coats. Step 3 (b) use epoxy and microfibre (my mistake earlier) but you can leave this until after glassing. Most beneficial at this stage on trailing edge if sharp.
    Step 4. One layer is plenty.
    Step 5. This is where you should build up microfibre mix on any edges required.
    Step 6. Personally it is unlikely you need to fair in much at all. Better to lightly sand and seal with final coat of epoxy clear. Then sand that and paint. Further fairing is more than possible on the first undercoat of paint especially if a high build type.

    The drawings for the foil section show a very inefficient foil shape. The side view you may wish to play with. Generally the strongest hinging rudders have moved the pivot point back to 'close the jaw' of the stock. This makes it much harder to wedge the jaw open when subjected to sailing with the blade near the up position where loads on the stock are high.

    With respect to PAR, very light timber cores, WR Cedar and Balsa do use the glass skin as a significant structural part of their strength. I'm with him on needing only around 28-30mm thickness on the blade, down to 25 if using the D Fir. Stiffness is by the cube so a few mm in thickness make a huge difference in strength ie stiffness down blade.

    Make the blade (leaving the top flat in side section) but pack the top with cheeks up to 38mm (1 1/2) if that is your stock width. Allow for glass thickness. Best to go slightly shy and get level with multiple glass coats ie 2 or 3on the cheeks to get perfect fit. Pivot hole should be say 25mm diam then filled with epoxy/microfibre. Then redrill so the epoxy is the bearing for say an 8 to 10mm pin.

    Fairly straightforward actually. You should be able to shape the blade entirely by hand with a No 4 Plane to very good accuracy in about one hour. Spend a little time getting your template/guage really good. You will also need a short fairing board to get perfect finish. A little bigger than a sanding block, I use a plaster float with 80 grit double sided onto it for this size of work.
     
  7. PAR
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    PAR Yacht Designer/Builder

    All epoxy formulators will recommend a solid 3 coats of epoxy, to insure sufficient film thickness to make the wood waterproof (especially end grain as Suki suggested). Two coats just isn't enough, especially after fairing.

    A structural skin over a low density wooden core "may" be necessary, but the usual choices of Douglas fir, SYP or the SPF stock from the big box stores is more then dense enough to tolerate the loads, imposed on the blade for this little puppy, so I wouldn't get too worried.

    The leading edge and the bottom of the blade should be reinforced. Epoxy soaked single braid, set in a shallow groove works well. Using a pulverized stone filler, with epoxy also works, though is hard to shape when cured. I try to avoid metal and plastic half ovals for this, as they're the wrong shape, but admittedly quite tough.

    I would shy away from a balsa or WRC core, just because you'll have to engineer a sufficient laminate to take the loads and your "goo factor" goes way up.

    For a boat like this, keeping it simple is the best route, so a stripped blade with abrasion protection gets my vote.
     
  8. SukiSolo
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    SukiSolo Senior Member

    PAR, I find an aluminium file very good for shaping microfibre or other 'hard' additives in epoxy. Not trying to 'suck eggs' etc but the Bahco ones and and ancient Trimatool double sided files I have are the best I have found so far for hand work and careful shaping. Unfortunately Sandvik no longer make that replacement blade. Pity it is way way better than any other surform on pretty much all FRP work. I won't wreck it on carbon though!. That is a different animal for blunting sharp steel....as my plane blades can testify...

    Very good on other plastics like acrylic sheet too. Gives more control than the mini power files and pretty quick once you are comfortable with it. Finish with sand paper covered template (female) form for consistent leading edge parabola.

    Often when coating the end grain, do it first, then go back at the end of coating and recoat just the end grain. That way it allows 'sinkage' to occur and you effectively get close to two coats in one - still needs that extra coat though.
     
  9. PAR
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    PAR Yacht Designer/Builder

    I've been using diamond blades on most 'glass and dense filler work for some time. They don't wear down very easily and with some practice can be quite precise.
     
  10. SukiSolo
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    SukiSolo Senior Member

    Well done PAR. I've been using diamond stones for blade sharpening since mid 90s' and some diamond files. They are a great help. Cheers.
     
  11. seanseward
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    seanseward Junior Member

    Thank you again to Sukisolo and Par for sharing your wealth of knowledge.

    Having read your responses, plan 3:

    1. 1"x1" d fir sticks epoxied together; this will be a 1" plank 12" x 41" for the entire board. I will not thicken up the top end but rather sandwich the 1" board between two 1/4" aluminimum cheeks to form a 1 1/2" sandwich. For this reason and because there is a desire to strengthen specific edges (narrow trailing edge, leading edge, bottom edge and top end to endure abrasion from swivel), I will overbuild the entire board with two layers of 4 or 5 oz. clothe. The suggested techniques to build up edges are too complicated for me to understand. I will not over soak the wood....redo only if porous. Thank you for hints on double dip technique for ends.
    2. form foil using good foil model (not images offered on referred web site) but rather proper foil shape; NACA foil website; techniques questions below.
    3. Yes, I set back the swivel point aft of centerline on the rudder to maximize hold down with forward line. I have used the laser bahia sample which put swivel about 2/3'rds aft of forward edge.

    questions:
    Techniques for shaping foil.

    Technique 1: I sit and imagine using a male shaped half foil template to run a router for/aft across the flat board to at least set some markings in the plank. I imagine I could do most by router, a strip at a time with fine tuning by planer and/or power sander. Is this doable and real or am I in a dream world?

    Technique 2: with technique 1 route marking ribs that can be depth references to meet using a power planer.

    Technique 3: use power planer and frequently measure with female template to eyeball what you need to be taken away to meet desired/templated shape. This seems harder and prone to error.

    If I use one or two epoxy coats for wood (depending on wood's need) and 2 layers of 5 oz. clothe, do I need to reduce 1" thickness to accommodate 1 1/2" wide pintles (include 1/2" of 2x 1/4" aluminum cheeks)? What is skin thickness of 2 layers of 5 oz. clothe done by an amateur?

    Does anyone have direct link to program that can offer me printable template for foil parabola? If required I can use graph paper and do the math.
     
  12. PAR
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    PAR Yacht Designer/Builder

    I will say it again, 3 coats of epoxy - period. You can't over soak the wood, but you can use not enough, which just makes the blade subject to moisture gain and rot. This isn't opinion or subject to debate and everyone that uses epoxy extensively will tell you the same thing, including all (not some), but all of the epoxy formulators. The wood isn't going to tell you "this is enough", it's a film thickness issue, not an absorption issue.

    Since your blade is 1x12 the logical section is a NACA 0012. It's easy to make using several methods. I use templates and a router to rough it in and fine tune by hand as part of the fairing/smoothing process. If the blade has parallel leading and trailing edges, you can make the templates full length, which saves some time. If the leading and trailing edges aren't parallel, you'll probably need to use chord templates and do it in sections, with changing templates. Making paper templates and using hand tools can work just as effectively too. Rough it in with a power plane, then fine tune by hand with a jack.

    The thickness difference between the cheeks could be simply handled with spacers, maybe HDPE, so abrasion doesn't exist. I do this, though typically with Teflon sheets, which serve the same purpose. Personally, I'd be inclined just to make the cheeks 1" on the inside with a few shots from a deadblow.

    Another approach would be to mill the blade from 1.5x1.5 strips, but carve the blade portion at 1" so you have the thickness you need between the cheeks, but a skinny blade for efficiency. On a boat like this, I'd be inclined to have an unsheathed board, maybe stained up nice and pretty. I'd still reinforce the leading edge, probably with thickened epoxy, but no sheathing. I'd use Teflon or HDPE sheets between the blade and rudderhead cheeks, but just a natural (encapsulated) board.

    A heavy sheathing will not hurt, except in weight. Reinforcing the leading edge and the tip is highly recommended, if you bump into things frequently. Placing the pivot in the forward portion of the rudderhead, has good and bad points to consider. I place pivots in the center of the rotational arc, because it provides more mechanical advantage over the blade then an offset forward pivot does. This configuration also places fairly uniform wracking loads on the cheeks, compared to an offset pivot. I find this especially important on high performance dinghies, where light weight is important, so smaller scantling are employed, but more so on blades with significant balance and those carrying a portion of the design's lateral area.

    Lastly, an "over center" downhaul, usually arranged on the rudderhead, often under the pintle metal work and a light, buoyant board, is the usual ticket, for this arrangement. The downhaul can be simply a bungee cord and the board will bounce over light bottom strikes and self immerse once past it, though once pulled up, so the attachment point is "past center", it hasn't the mechanical advantage to pull it back down. On bigger boats, I prefer to use a weighted board and an uphaul instead. The weighted board sinks and self immerses, when it hits something and the uphaul should be obvious.
     
  13. seanseward
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    seanseward Junior Member

    Wow!...no sheathing!? that means no glass ...right? I like the look! Stained fir with smooth finish.... the price is right!

    "I'd still reinforce the leading edge, probably with thickened epoxy, but no sheathing."

    Reinforce kissing edge....? How? If you pack some hard edge, I would think that you would displace wood rather than build UP and distort foil shape. Reinforce = displace core material with harder solid unit to spread load of strike...which means cutting out a bit of wood...right? You mentioned above a gorge, inset in leading edge...no, you said...

    "Epoxy soaked single braid, set in a shallow groove works well."

    In my own words, this means a shallow groove inset with carbon braid? something like that?

    OK, this is doable and much cheaper than I expected.

    Where I get lost is in your foil making techniques. For example, I quickly get lost with "you can make the templates full length, which saves some time".

    I need a picture or video to visually demonstrate what you are saying because I get lost with your experienced tongue. I need a simpler explanation sticking to a reasonable doable way without all the complex options. I have experience with apprentice carpentry and some experience working on boats but very limited.

    Here is a specific; you said, "I use templates and a router to rough it in and fine tune by hand as part of the fairing/smoothing process."
    Easy details to explain "roughing it out" would be great. Does my description above of a male template sitting on the flat board, square to center line, running router out from center line to either edge make sense?.. is this doable? Taking away about 1/2" per run and repeating until I get to transition to pivot head?

    Thank you for all your time and knowledge.
    Sean
     
  14. PAR
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    PAR Yacht Designer/Builder

    Yep, no glass, just encapsulated strips glued together (no sheathing) and a reinforced edge. To reinforce the edge, you can cut a flat and mound up thickened epoxy, or a shallow groove with a length of line (not carbon, but polyester works well) saturated and faired in. There are other techniques as well.

    A longitudinal template would be two sectional forms, one at each end of the foil blank, over which a trolly the router rides, can follow the forms. This is fast, but maybe not so much for the novice. The usual method for the beginner foil maker is to use chord wise templates or forms, again to check the progress or use as a router guide (I use a laminate trimmer).

    [​IMG]

    http://www.jamestowndistributors.co...em/Rudder_Blades_and_Centerboards_000_448.pdf

    The link is a West System text and you're interested in the first few pages really.

    http://messing-about.com/forums/topic/8476-core-sound-17-hull-357/

    This discussion has some more images that might be helpful too.
     

  15. SukiSolo
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    SukiSolo Senior Member

    Agree with PAR, you don't need the sheathing if you don't want it with D Fir. However I would go to at least 4, maybe 5 or 6 coats of epoxy. By the time it is sanded smooth and faired you will lose 1 or 1.5 coats. Not sure about staining the Fir, it looks pretty good, beautiful pinky heartwood. I did a GP14 rudder in this, with Sapele edges (unsheathed but microfibre bottom tip reinforcement) and it looked good. Done an Oppie one too..... BTW even sheathed you end up with this number of coats. The reference to one coat (or two) was perhaps misunderstood - it applies to needing to seal the timber prior to applying glass sheathing NOT the total number of coats required to seal the wood completely.

    That is the alternative too. You can help the edges (hardness and toughness) by putting a small strip of something really dense like Sapele as your last laminate. Equally if you have a 'flat' bottomed foil it is sometimes (depending on design a little) worth sealing the end grain by glueing a dense piece across the bottom. A bit trickier to plane but usually a light diagonal sweeping action will do it. I personally would not use Titebond as one contributor in the linked article says, use epoxy or Aerolite 306 for edge glueing the initial layup. Even some of the foils I built 25 years ago have not disintegrated so I have faith in these resins, even if the latter is a little unfashionable. Do not use Cascamite either - I have an Enterprise dinghy locally that I could part every hull joint in 20 minutes with a chisel because she was built with that....and a mid 90s' GP14...

    Couple of shots of a board made a while back. First shows quarter sawn laminate, second one getting towards final section shape with profile guage etc. Guage setting referenced to CAD plot. Note, because this is not a parallel sided foil, front and back the section is a bit harder to maintain. I've seen lots of foils with the assumption that the max thickness stays the same from the leading edge.... well only with parallel sided foils. That is what PAR is referring too. Hope that clears that up for you.
     

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