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Thread: wood core rudder question

  1. #1
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    Default wood core rudder question

    I'm strongly considering making a new rudder for my S-2 7.9. Yes, that's a 'glass sailboat, but the rudder would be wood core. Approximate dimensions: overall height about 6' 6"... submerged foil section would be about 3 feet.... chord is 16 inches. I'd balance the rudder by about 15%.

    This is a transom-hung rudder. Basically it's about the same size as the J-30 / J-29 rudder.

    I want about a 15% foil. I want NACA 0015. instead of the more usual 0012 or 00125 because the current rudder is preposterously fat...almost 3 inches thick, and "thick is good" in terms of keeping flow attached even at large rudder angles. The S-2 7.9 has a very large mainsail and a relatively small foretriangle so when the wind pipes up, you're working the rudder a lot. I'll trade off some drag for some extended attached flow, in this case.

    I plan to buy some nice doug fir, ripping it into 2 -inch wide strips and epoxying them all back together to make a 7-foot long, 16 inch side, 2-inch thick plank.

    My question is about forming the foil. I was considering doing this:

    https://www.youtube.com/watch?v=55_TunTfXj4

    However, lots and lots of folks make a template out of something hard, like maybe aluminum or even melamine, tack it to the bottom of the board. Then they just work away with a power planer and belt sander, or even hand tools.

    Which would you suggest, and why? I want a pretty accurate foil.
    CLC Skerry = "Vingilothiel"

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    Default Re: wood core rudder question

    Will your rudder have a constant chord?The video shows a technique that is limited to parallel foils and if thats what you intend to make you may get the right result.Alternatively,you might want to seek out Mark Drela's system of cutting a number of planes tangential to the surface and then fairing the ridges that are left.

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    Default Re: wood core rudder question

    I would love to design a semi-elliptical rudder with a swept tip, but I suspect that such exoticness is beyond my abilities, so I'll settle for a straight foil/constant chord.

    I'll go look up Mark Drela's and his method, though. Thanks!
    CLC Skerry = "Vingilothiel"

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    Default Re: wood core rudder question

    What John said. The same logic as rounding a spar from 4 to 8 to 16 sides. It will do a tapered foil as easily as constant chord.
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: wood core rudder question

    I've done several constant-chord foils using a very similar technique... learned from Michael Storer.

    The version in the video is more elaborate than what I've done, but there's nothing wrong with it that I can see. See Storer for details of a simpler process.

    In terms of bits - I am not in love with his choice of a core-box bit. The first few I did with straight bits. That worked ok, but there was some tearout from the sharp corners. But at least the cuts were straight across the bottom, and you didn't have to make sure you touched nearly every millimeter with the apex of that rounded core-box bit. Subsequent foils have been done with a 'bowl' bit. Rounded corners, like a core-box... but a nice flat bottom section. Best of both worlds.

    Also - if you leave the middle 1/4 - 1/3 of the chord flat (not a true NACA profile)... you lose very little in performance, while making the fabrication process much simpler. For anyone wanting to understand the system, in a more elegant version - I'd recommend spending $20 or whatever OzRacer plans cost these days, and the building instruction manual will lay it all out for you.

    I've never experimented with Drela's system - but if I owned a CNC, and though I needed the small reduction in drag that tapered foils garner you, I might be tempted.
    David G
    Harbor Woodworks
    http://www.harborwoodworking.com/boat.html

    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

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    Default Re: wood core rudder question

    I did a straight foil daggerboard (NACA 0012) using douglas fir with what looks to be the same technique as the video you posted. I found a tutorial in duckworks magazine (http://www.duckworksmagazine.com/09/...oils/index.htm). There's a link to download a spreadsheet that calculates and prints out the foil shape and desired router offset based on the input NACA type. I used it to build the jig out of 3/4" MDF. I used a 1/2" straight bit with a flush bearing. It worked really well and I'm really happy with the results and it was surprisingly easy to do.


    Last edited by galleywench; 10-11-2017 at 08:10 PM. Reason: add photo

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    Default Re: wood core rudder question

    Good article.
    David G
    Harbor Woodworks
    http://www.harborwoodworking.com/boat.html

    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

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    Default Re: wood core rudder question

    [QUOTE=galleywench;5369272]I did a straight foil daggerboard (NACA 0012) using douglas fir with what looks to be the same technique as the video you posted. I found a tutorial in duckworks magazine (http://www.duckworksmagazine.com/09/...oils/index.htm). There's a link to download a spreadsheet that calculates and prints out the foil shape and desired router offset based on the input NACA type. I used it to build the jig out of 3/4" MDF. I used a 1/2" straight bit with a flush bearing. It worked really well and I'm really happy with the results and it was surprisingly easy to do.


    [/Q]
    Thats a darned good looking foil galleywench. You built the jib so it fit right over the actual board, and not on a support platform with side rails, it looks like.

    How long is your daggerboard? How long did it take to do the actual routing of the shape?
    CLC Skerry = "Vingilothiel"

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    Default Re: wood core rudder question

    Quote Originally Posted by Alan H View Post
    You built the jib so it fit right over the actual board, and not on a support platform with side rails, it looks like.

    How long is your daggerboard? How long did it take to do the actual routing of the shape?
    Right, I built the jig once I had the dimensions of the daggerboard blank that I had glued up. I simply ran the dimensions through the spreadsheet referenced in the article (chord, NACA profile, and router offset if I remember correctly and printed out the paper template generated. Super easy. Then I simply transferred the dimensions onto MDF and cut out 2 copies (for the 'rails') and screwed them together about 4 inches apart with some scrap wood (wide enough for the router base to ride on). Once finished, the jig used the daggerboard blank as the platform and it just slide along the length of the blank. On the router I used a dovetail guide that I have for a dovetail jig that serves as a stop when the router hits either jig 'rail'. Hope that makes sense, it's harder to explain than to actually execute.

    The daggerboard foil is 3'9" and took about 45 minutes per side with the router. I made several passes where I was removing more material near the edges so I wouldn't have any tear out. One thing to remember if you go this route (and the article I referenced mentions this) is to leave a bit of material on the top and bottom that you can cut off later. Otherwise, if you cut off all the material on the first side, once you flip the board over, you will no longer have a stable surface for the jig to ride on.

    Below is a picture of the printed template with 40mm offset (to account for the router bit). I'm sure if I were building a rocket or something that required extreme tolerance control, I would have printed the template on mylar or something more stable than regular printer paper, but I'm pretty pleased with the results. Hope this helps.



    Here is a shot after one side is partially completed. Note that I left the bottom section uncut, so that once the board is flipped, the jig will still ride on the blank properly.
    Last edited by galleywench; 10-11-2017 at 10:59 PM.

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    Default Re: wood core rudder question

    Alan,

    Apparently you don't intend to rate your 7.9 as a one design in races any more. In that case, you are free to build to any design you wish instead of the 7.9 Class design. I found the balance of the standard rudder allowed for low force on the tiller under just about all conditions, assuming sails are trimmed properly. The rudder was often very heavily loaded though and breakage at the weakest point at the waterline was often a problem. A fir core would be much stronger than the original foam for any design although a balanced rudder will always be weakest at the waterline and a constant chord foil would be even more heavily stressed at the waterline.

    Why would you not duplicate the standard rudder? While unforgiving of poor handling, the 7.9 Grand Slam is a great boat.
    Tom L

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    Default Re: wood core rudder question

    Quote Originally Posted by galleywench View Post
    I did a straight foil daggerboard (NACA 0012) using douglas fir with what looks to be the same technique as the video you posted. I found a tutorial in duckworks magazine (http://www.duckworksmagazine.com/09/...oils/index.htm). There's a link to download a spreadsheet that calculates and prints out the foil shape and desired router offset based on the input NACA type. I used it to build the jig out of 3/4" MDF. I used a 1/2" straight bit with a flush bearing. It worked really well and I'm really happy with the results and it was surprisingly easy to do.


    Nicely done. Shows the level of accuracy that can be achieved with this method.

    For future foils - and for those just embarking on such a chore - I'd suggest two small refinements. First - the grain orientation of the aft-most stave. I'd have used a stick with more of a 'flat' grain or 'rift' grain orientation. The 'vertical' grain that's there leaves a weaker short-grain orientation at the most fragile part of the foil. Second - I tend to make that stave, and the forward stave out of something denser/tougher, and less prone to splitting/splintering. Iroko, Ipe, Black Locust, Teak, etc. The aft one because of the fragility, and the forward one because it tends to take the worst beating.

    Of course, the grain orientation issue is much less critical (though NOT totally obviated) if you are glassing the whole shebang. Which I normally do.

    Oh, and for those wondering about routers - note that the machine used here is a Porter Cable 690... a mid-sized machine. Not a trim router. Not a top-heavy 3 hp beast.
    David G
    Harbor Woodworks
    http://www.harborwoodworking.com/boat.html

    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

  12. #12
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    Default Re: wood core rudder question

    Quote Originally Posted by David G View Post
    Nicely done. Shows the level of accuracy that can be achieved with this method.

    For future foils - and for those just embarking on such a chore - I'd suggest two small refinements. First - the grain orientation of the aft-most stave. I'd have used a stick with more of a 'flat' grain or 'rift' grain orientation. The 'vertical' grain that's there leaves a weaker short-grain orientation at the most fragile part of the foil. Second - I tend to make that stave, and the forward stave out of something denser/tougher, and less prone to splitting/splintering. Iroko, Ipe, Black Locust, Teak, etc. The aft one because of the fragility, and the forward one because it tends to take the worst beating.

    Of course, the grain orientation issue is much less critical (though NOT totally obviated) if you are glassing the whole shebang. Which I normally do.
    You are absolutely right on the grain orientation, that never occurred to me. I did attempt to have alternating grain patterns by gluing the pieces end for end, but now that I look at it, I kind of screwed that up as well. I did consider using a denser wood on the leading edge, but I am hoping that the layer of glass sheathing I added will help with that somewhat. When I destroy this one (my track record almost guarantees it), version 2 will incorporate these refinements.

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    Default Re: wood core rudder question

    Quote Originally Posted by Tom Lathrop View Post
    Alan,

    Apparently you don't intend to rate your 7.9 as a one design in races any more. In that case, you are free to build to any design you wish instead of the 7.9 Class design. I found the balance of the standard rudder allowed for low force on the tiller under just about all conditions, assuming sails are trimmed properly. The rudder was often very heavily loaded though and breakage at the weakest point at the waterline was often a problem. A fir core would be much stronger than the original foam for any design although a balanced rudder will always be weakest at the waterline and a constant chord foil would be even more heavily stressed at the waterline.

    Why would you not duplicate the standard rudder? While unforgiving of poor handling, the 7.9 Grand Slam is a great boat.
    I really like my 7.9. I've owned about 5, 20-30 foot keelboats and this one is truly the best fit for me. It's big enough to take offshore but small enough that I can muscle-around most everything with the exception of the mainsheet. I was going to dry-sail it, which makes the lifting daggerboard really attractive but some local development politics killed that idea for the medium-long-term. Now it's in the water at a local marina. Since that's the case, if I had my 'druthers, I wish I had one of the fixed-keel models. On the other hand, on the way back from a cruise-in last month, we brushed the bottom in about 4 feet of water and stopped, sailing on a light air afternoon. I simply cranked the board up 6 inches, turned the boat and we were on our way again. No fuss, no bother. Also the fixed keel model is a masthead rig, the standard 7.9 is fractional, and I like having a spinnaker that I can yank down by hand if I have to. My one and only complaint about the 7.9 is the steering. The rudder/tiller have NO directional stability. If you let go of the tiller for half a second to cleat off a sheet, POW the rudder is on the other side of the boat and you're rounding up. It doesn't matter how light the helm is, the tiller just takes off when you let go of it. I've mentioned this to guys who own 7.9's and 9.1's and they all say the same thing.

    ANYWAY...I plan to take this boat to faraway places...as in do a California-> Hawaii race in it. The guys who've done a Pacific Cup in one tried it once with the stock rudder, and busted it off about 400 miles out. They said "get a solid rudder". So that's what I'm doing. The rudder I'm planning on putting on it is not as overall enormous as the stock rudder, but it's big for a 26-footer. Basically, it's a J-30 rudder, so I'll be replacing the transom hardware with the J-30/J-29 hardware and glassing in some significicant transom reinforcements.

    On another note...

    I will probably 'glass on a layer of unidirectional carbon fiber over the wood, and then a layer of light carbon cloth and then some 8 oz cloth over that. I'm considering putting kevlar cloth on the leading edge instead of the linear carbon. Actually, I'll have my buddy Greg, who does this stuff all the time and is an expert at it, vacuum-bag all that. I think the end product will be rather robust.
    Last edited by Alan H; 10-12-2017 at 11:27 AM.
    CLC Skerry = "Vingilothiel"

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    Default Re: wood core rudder question

    It's the cutting of the foil, as accurately as I can, that's my concern. However, a couple people here have done the router-and-jig thing, so I think I'll try it.

    BTW, Waterline systems makes an unbalanced J-30/J-29 rudder for $1400 plus shipping. That's a good price but it's not a balanced rudder and the J-boat guys are constantly on about how the tiller is wrestling match when on a power reach.

    Rudder Craft makes a wood-core vinylester unbalanced rudder for about $2K. They also make a balanced one for $2,200
    Phils Foils wants about $1800 for a CNC-cut, wood core balanced J-30 rudder.

    I bet I can make this one for about half of that, including paying Greg for his time.
    CLC Skerry = "Vingilothiel"

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    Default Re: wood core rudder question

    Quote Originally Posted by Alan H View Post
    I really like my 7.9. I've owned about 5, 20-30 foot keelboats and this one is truly the best fit for me. It's big enough to take offshore but small enough that I can muscle-around most everything with the exception of the mainsheet. I was going to dry-sail it, which makes the lifting daggerboard really attractive but some local development politics killed that idea for the medium-long-term. Now it's in the water at a local marina. Since that's the case, if I had my 'druthers, I wish I had one of the fixed-keel models. On the other hand, on the way back from a cruise-in last month, we brushed the bottom in about 4 feet of water and stopped, sailing on a light air afternoon. I simply cranked the board up 6 inches, turned the boat and we were on our way again. No fuss, no bother. Also the fixed keel model is a masthead rig, the standard 7.9 is fractional, and I like having a spinnaker that I can yank down by hand if I have to. My one and only complaint about the 7.9 is the steering. The rudder/tiller have NO directional stability. If you let go of the tiller for half a second to cleat off a sheet, POW the rudder is on the other side of the boat and you're rounding up. It doesn't matter how light the helm is, the tiller just takes off when you let go of it. I've mentioned this to guys who own 7.9's and 9.1's and they all say the same thing.

    ANYWAY...I plan to take this boat to faraway places...as in do a California-> Hawaii race in it. The guys who've done a Pacific Cup in one tried it once with the stock rudder, and busted it off about 400 miles out. They said "get a solid rudder". So that's what I'm doing. The rudder I'm planning on putting on it is not as overall enormous as the stock rudder, but it's big for a 26-footer. Basically, it's a J-30 rudder, so I'll be replacing the transom hardware with the J-30/J-29 hardware and glassing in some significicant transom reinforcements.

    On another note...

    I will probably 'glass on a layer of unidirectional carbon fiber over the wood, and then a layer of light carbon cloth and then some 8 oz cloth over that. I'm considering putting kevlar cloth on the leading edge instead of the linear carbon. Actually, I'll have my buddy Greg, who does this stuff all the time and is an expert at it, vacuum-bag all that. I think the end product will be rather robust.
    I know carbon fiber is all the rage. But don't fall in love with 'hip'. It has its uses, and strengths, and weaknesses. I'd question whether this is the application for it. But if your buddy is knowledgeable... he'll be in the best position to advise you.
    David G
    Harbor Woodworks
    http://www.harborwoodworking.com/boat.html

    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

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    Default Re: wood core rudder question

    Nice looking board. Ive done foils like this with the table saw.
    Establish the centerlines on all six sides of the blank. Ideally, the blank is an inch or so wider than the finished board and as thick as the widest point of the foil.
    Trace the foil on either end of the board being sure to accurately center them in both directions. You should have a half inch or more of waste from the ends of the foil to the edges of the blank.
    Start at the fat or the skinny edge; lay the blank on the table and adjust the height of the blade to just kiss the line on the blank. Run the blank through the saw, flip it over and run it through again. Reset the fence, adjust the blade height and make another pair of cuts. Continue across the width of the board. The waste at the long edges and the widest point of the foil will ride on the saw table and stabilise the blank as you hog out the material. You can use a dado set to make wider cuts. Id keep it no wider than 1/4". Once youre rolling, the process is surprisingly quick and the opposing faces are mirror images of each other.
    When its all roughed out, smooth the faces with a plane and a longboard. There will be a lot of parallel lines the length of the board to guide you.

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    Default Re: wood core rudder question

    Quote Originally Posted by willin woodworks View Post
    Nice looking board. Ive done foils like this with the table saw.
    Establish the centerlines on all six sides of the blank. Ideally, the blank is an inch or so wider than the finished board and as thick as the widest point of the foil.
    Trace the foil on either end of the board being sure to accurately center them in both directions. You should have a half inch or more of waste from the ends of the foil to the edges of the blank.
    Start at the fat or the skinny edge; lay the blank on the table and adjust the height of the blade to just kiss the line on the blank. Run the blank through the saw, flip it over and run it through again. Reset the fence, adjust the blade height and make another pair of cuts. Continue across the width of the board. The waste at the long edges and the widest point of the foil will ride on the saw table and stabilise the blank as you hog out the material. You can use a dado set to make wider cuts. Id keep it no wider than 1/4". Once youre rolling, the process is surprisingly quick and the opposing faces are mirror images of each other.
    When its all roughed out, smooth the faces with a plane and a longboard. There will be a lot of parallel lines the length of the board to guide you.
    Many years ago I bought a Cal 20. It had a beautiful but very old and split mahogany rudder. One day that thing split, out on the Bay and I was unable to recover the split-off part. I couldn't afford a new class rudder and wasn't racing in the class anyway. I determined to make my own. I started with a 2 x 12...didn't cut it down into strips or even attempt for form the class rudder shape, but just left it in one piece. I did more or less what you recommend, only I did it with my little floor-mounted table saw. I made a straight blade with an approximately 12 inch chord.

    Basically I made two cuts to start shaping the leading edge, and then cranked the blade on the saw up as high as it would go, about 5 inches, and did two longitudinal cuts to shape the taper. Then I used a plane and sandpaper to make it all more or less foil-shaped and smooth.

    It wasn't NACA-anything, and it had slab sides, but it steered the boat just fine..
    Last edited by Alan H; 10-12-2017 at 02:33 PM.
    CLC Skerry = "Vingilothiel"

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    Default Re: wood core rudder question

    You people are amazing with your woodworky stuff. Nicely done.

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    Default Re: wood core rudder question

    Quote Originally Posted by Alan H View Post
    I really like my 7.9. I've owned about 5, 20-30 foot keelboats and this one is truly the best fit for me. It's big enough to take offshore but small enough that I can muscle-around most everything with the exception of the mainsheet. I was going to dry-sail it, which makes the lifting daggerboard really attractive but some local development politics killed that idea for the medium-long-term. Now it's in the water at a local marina. Since that's the case, if I had my 'druthers, I wish I had one of the fixed-keel models. On the other hand, on the way back from a cruise-in last month, we brushed the bottom in about 4 feet of water and stopped, sailing on a light air afternoon. I simply cranked the board up 6 inches, turned the boat and we were on our way again. No fuss, no bother. Also the fixed keel model is a masthead rig, the standard 7.9 is fractional, and I like having a spinnaker that I can yank down by hand if I have to. My one and only complaint about the 7.9 is the steering. The rudder/tiller have NO directional stability. If you let go of the tiller for half a second to cleat off a sheet, POW the rudder is on the other side of the boat and you're rounding up. It doesn't matter how light the helm is, the tiller just takes off when you let go of it. I've mentioned this to guys who own 7.9's and 9.1's and they all say the same thing.

    ANYWAY...I plan to take this boat to faraway places...as in do a California-> Hawaii race in it. The guys who've done a Pacific Cup in one tried it once with the stock rudder, and busted it off about 400 miles out. They said "get a solid rudder". So that's what I'm doing. The rudder I'm planning on putting on it is not as overall enormous as the stock rudder, but it's big for a 26-footer. Basically, it's a J-30 rudder, so I'll be replacing the transom hardware with the J-30/J-29 hardware and glassing in some significicant transom reinforcements.

    On another note...

    I will probably 'glass on a layer of unidirectional carbon fiber over the wood, and then a layer of light carbon cloth and then some 8 oz cloth over that. I'm considering putting kevlar cloth on the leading edge instead of the linear carbon. Actually, I'll have my buddy Greg, who does this stuff all the time and is an expert at it, vacuum-bag all that. I think the end product will be rather robust.
    Alan, I sheared the rudder of #107 off while blasting along at 8 to 9 kts just off Royal Shoal in Pamlico Sound. Worse part was the Coast Guard running behind me when the boat automatically did a 180 toward the CG Cutter with the crew pointing their automatic rifles at us. It all came out well on that score. After docking the boat at Ocracoke and going through the CG hoops, I brought the rudder home to repair it. Some grinding showed that it had at least one previous breakage That was evidently not done well enough.

    I ground out a tapering hollow and reinforced mainly with lots of non woven biaxial 1808 which I have found to be the strongest and stiffest glass I've used. I'd say it was then far stronger than original. I also doubt that adding carbon fiber will be of value to more than the pockets of the seller. A carbon fiber layup must be properly engineeed to contribute anything useful to your rudder. I reinforce all my foil leading edges with epoxy soaked Dacron or Nylon double sheath line before wrapping with glass cloth. This makes an impregnable nose that can withstand anything. We once hit an old engine block or other mass of unnatural hard stuff on our shallow creek bottom at about 5kts that stopped the 7.9 dead. As usual there was no damage at all.

    The fixed keel 7.9 has more sail area, is more stable, is faster and is easier to find and stay in the "groove" but lacks the features that make the DB version more popular for those who like to travel to regattas or sail and dock in very shallow water. A DB 7.9 Grand Slam has very little directional stability which contributes to its quick and sensitive maneuvering. The shallow hull with no keel offers almost zero side force unless the Daggerboard is at least part way down to provide a steering couple with the rudder. If you pull the daggerboard fully up, the boat simply cannot be steered. This makes it a great small racing boat but it must have some rudder input or it goes haywire. On a Transpac, someone or something must control the rudder at all times, which can be very tiring on a such a long run.

    Good luck and I wish you well on your venture.
    Last edited by Tom Lathrop; 10-12-2017 at 03:12 PM.
    Tom L

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    Default Re: wood core rudder question

    Quote Originally Posted by Alan H View Post
    Many years ago I bought a Cal 20. It had a beautiful but very old and split mahogany rudder. One day that thing split, out on the Bay and I was unable to recover the split-off part. I couldn't afford a new class rudder and wasn't racing in the class anyway. I determined to make my own. I started with a 2 x 12...didn't cut it down into strips or even attempt for form the class rudder shape, but just left it in one piece. I did more or less what you recommend, only I did it with my little floor-mounted table saw. I made a straight blade with an approximately 12 inch chord.

    Basically I made two cuts to start shaping the leading edge, and then cranked the blade on the saw up as high as it would go, about 5 inches, and did two longitudinal cuts to shape the taper. Then I used a plane and sandpaper to make it all more or less foil-shaped and smooth.

    It wasn't NACA-anything, and it had slab sides, but it steered the boat just fine..
    I think you may be misinterpreting what I did. All cuts were made with tbe blank on tbe table flat side down, cuts made the length of the blank parallel to the long edges. Blade was normal to the table.

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    Default Re: wood core rudder question

    Quote Originally Posted by Tom Lathrop View Post
    Alan, I sheared the rudder of #107 off while blasting along at 8 to 9 kts just off Royal Shoal in Pamlico Sound. Worse part was the Coast Guard running behind me when the boat automatically did a 180 toward the CG Cutter with the crew pointing their automatic rifles at us. It all came out well on that score. After docking the boat at Ocracoke and going through the CG hoops, I brought the rudder home to repair it. Some grinding showed that it had at least one previous breakage That was evidently not done well enough.

    I ground out a tapering hollow and reinforced mainly with lots of non woven biaxial 1808 which I have found to be the strongest and stiffest glass I've used. I'd say it was then far stronger than original. I also doubt that adding carbon fiber will be of value to more than the pockets of the seller. A carbon fiber layup must be properly engineeed to contribute anything useful to your rudder. I reinforce all my foil leading edges with epoxy soaked Dacron or Nylon double sheath line before wrapping with glass cloth. This makes an impregnable nose that can withstand anything. We once hit an old engine block or other mass of unnatural hard stuff on our shallow creek bottom at about 5kts that stopped the 7.9 dead. As usual there was no damage at all.

    The fixed keel 7.9 has more sail area, is more stable, is faster and is easier to find and stay in the "groove" but lacks the features that make the DB version more popular for those who like to travel to regattas or sail and dock in very shallow water. A DB 7.9 Grand Slam has very little directional stability which contributes to its quick and sensitive maneuvering. The shallow hull with no keel offers almost zero side force unless the Daggerboard is at least part way down to provide a steering couple with the rudder. If you pull the daggerboard fully up, the boat simply cannot be steered. This makes it a great small racing boat but it must have some rudder input or it goes haywire. On a Transpac, someone or something must control the rudder at all times, which can be very tiring on a such a long run.

    Good luck and I wish you well on your venture.
    Hmm. Maybe I should re-think my proposed large use of carbon. Hmmm.

    since I sail on San Francisco Bay and very seldom get down to the extreme South Bay where "shallow" is an issue, I really do wish I had the fixed keel version. Even better would be one of the four MORC- tricked-out boats (Little Feat and her sisters) because they don't have the cabin-eating daggerboard case. Even Better would be a Mariah, but I got's what I got and I like it. WHen it comes time to ship the boat back to California from "far-away" I will be glad that it sits on a low trailer.

    I completely agree on the steering/daggerboard issue. We pulled the board up halfway during the last two hours of a recent downwind race and the helmsman said it was squirrelly. Drop the board again, and all that just goes away.

    Regarding rudder input, I just purchased and am installing the newest, hottest tillerpilot system out there from Pelagic Autopilots. It gets its racing audition in two weeks. Before I cast off for the start line of the 2020 Singlehanded. TransPac, I will build, install and test one of these: http://www.windautopilot.de/docs/alkema/RHM-USD.pdf
    CLC Skerry = "Vingilothiel"

  22. #22
    Join Date
    Jul 2009
    Location
    California
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    961

    Default Re: wood core rudder question

    WillinWoodworks. Ah, now I understand. Basically you cut longitudinal grooves, and then planed/sanded down until the grooves disappeared.
    CLC Skerry = "Vingilothiel"

  23. #23
    Join Date
    Jan 2011
    Location
    Norwalk CT
    Posts
    668

    Default Re: wood core rudder question

    Bingo!

  24. #24
    Join Date
    Jul 2009
    Location
    Sunshine Coast, Queensland, Australia
    Posts
    1,033

    Default Re: wood core rudder question

    I used a similar method and used a concentric offset foil shape, plus a harder piece of laminate for the foil tail. It wasn't totally easy but worked well. I used a medium square bit and sanded for the finish.




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