# Need to make new rudder



## bobmcgov (Jul 19, 2007)

Our SJ21's kick-up rudder is trashed. Really not worth saving. (Lovely 3/4" twist down its length, too.) It's a mahogany blade about 40" long by 12" wide, thus:










So how should I construct the new one? This thing (as is) weighs a ton, so I'd like to do it the lightest way practical. I gots any amount of tools and some fiberglassing experience.

1) solid wood, probably mahogany, with spar or poly varnish. That's what it is now. And if it was good enuf for grandpa, by God it's good enuf for me.

2) wood core with glass mat and 2-part epoxy. In which case I'd probably consider painting the wood core before layup, or the final product, or adding pigment to the epoxy. Just because I like a pretty, white foil.

3) foam core with glass mat and 2-part. Should be nice & light. If so, what kind of foam to use, & how best to affix the pivot bushing?

4) carbon fiber. Never used it before. Over wood, foam, or air its own self?


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## Faster (Sep 13, 2005)

Choice 1) obviously good enough if you can find suitable stock to make it from.

2) Possible but may not end up lighter, but just paint the thing afterwards once it's all been faired.

3) Usually done with a two part mold and the halves sandwiched together... could shape a piece of rigid foam and glass it over, then fair and paint as above. You have to be sure it ends up strong enough for the forces applied and for the attachments too.

4) Pretty serious overkill for a SJ21 (but might be fun)


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## Giulietta (Nov 14, 2006)

Just make one out of wood.

You can make it in 2 or 3 tones of wood. Like his.

And to help the boat go fast, after varnis, sand it down with very very fine sand paper to remove the shining, that causes friction.










Don't bother with applying glass over it...its better looking and lighter in wood.

For foam, you need a lot of sandpapapr aftewrards, a vaccum system etc. etc.

CF, your rudder will cost over $800, and you need an oven.

Wood, simple good and beautifull.


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## Classic30 (Aug 29, 2007)

I had to fix ours up not long ago... This is how I did it:

1. Take 5 or so strips of oregon (glued & clamped) - enough to make a plank about 12" wide by 3/4-1" thick.
2. Plane to shape roughly by hand, then use 40-grit sandpaper to smooth and final shaping.
3. One coat of epoxy with one thickness of glass mat laid up whilst still wet.
4. Final coat of epoxy over the mat when dry.
5. Sand out any imperfections, prime and paint.

Using a soft wood makes it easy to shape the blade, whilst epoxy coating gives it strength - true, you don't *need *to glass it, but if the wood is a bit thin in places it helps. You could use straight glass or carbon fibre, but you'd have to mould it somehow and, unless you're after really light weight, if you're only making one rudder that doens't make much sense to me.

You could use a polystyrene foam sheet, cut it to size, sand it and glass it, but making the pivot hole strong enough might be an issue and later reshaping is impossible (foam isn't as forgiving as wood).

Good luck with your project.


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## danjarch (Jun 18, 2007)

I just made one for a friend. Got a piece of mahagany and cut it to shape. Planed it with my handheld power planer then a coat of epoxy and glass. One coat of epoxy and two coats of varnish. Epoxy has to be painted or varnished to protect it from UV rays. I wouldn't have epoxied it at all, but I couldn't get 5/4 and I needed to add an 3/16th of an inch to the blade.


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## timebandit (Sep 18, 2002)

http://www.idasailor.com/catalog/product_info.php?cPath=70&products_id=654
Hard to beat this rudder.


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## bobmcgov (Jul 19, 2007)

Terrific advice. Thanks & keep it coming! Given the condition of our lakes, we WILL be grounding on rocks occasionally. The trouble with wood rudders or centerboards is that when the bottom does get nicked (whether varnish or glass-coated), it exposes endgrain to the hungry waters. Once water wicks up into the wood, you are truly hosed, as the wood will swell and shrink and hydrostatic force will begin kicking off the hardshell.

So let's say I use cedar or mahogany for the main blade, then inlay an aluminum or brass or stainless strip down the leading edge, &/or add a metal prosthetic tip the last 2" of the foil. Inlays faired into the shape. I can do this easily: 8-foot beltsander laughs at such tasks, mwahahhaha. Worth doing?

Guessing a max-thickness to major chord ratio of about 10% -- or should I go fatter? Which is more important in the drag vs lift compromise, chord length or foil thickness? I.e., if I wanted more steering response, should I go fatter, or wider? This boat is slow upwind but flies on reaches and runs.

ETA: Holy Cow, Timebandit! *faints* Dat's a bootiful thing. Hmmmm. I have access to any sort of industrial plastics, too. Hadn't even considered HDPE or PVC. Guess we should add that to the quiver. Urf. Anyone got six bills they can lend me?
(FWIW, I'm not concerned with class rules as I won't be racing one-design, so anything goes.)


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## Classic30 (Aug 29, 2007)

bobmcgov said:


> Terrific advice. Thanks & keep it coming! Given the condition of our lakes, we WILL be grounding on rocks occasionally. The trouble with wood rudders or centerboards is that when the bottom does get nicked (whether varnish or glass-coated), it exposes endgrain to the hungry waters. Once water wicks up into the wood, you are truly hosed, as the wood will swell and shrink and hydrostatic force will begin kicking off the hardshell.
> 
> So let's say I use cedar or mahogany for the main blade, then inlay an aluminum or brass or stainless strip down the leading edge, &/or add a metal prosthetic tip the last 2" of the foil. Inlays faired into the shape. I can do this easily: 8-foot beltsander laughs at such tasks, mwahahhaha. Worth doing?


You probably don't need to do the entire bottom of the blade, but it's definitely worth doing.

I neglected to say that when fixing ours (it was suffering from the effects of the PO's tendency to hit rocks with the rudder blade), I hacked a piece of walnut from an off-cut in our firewood stack and shaped it in a wedge to fit the bottom-front corner of the blade - served the same purpose, but could be sanded to fit (just!  ).


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## TSOJOURNER (Dec 16, 1999)

So how should I construct the new one? This thing (as is) weighs a ton, so I'd like to do it the lightest way practical. I gots any amount of tools and some fiberglassing experience.



> 1) solid wood, probably mahogany, with spar or poly varnish. That's what it is now. And if it was good enuf for grandpa, by God it's good enuf for me.


Personally I'd choose this option.



> 2) wood core with glass mat and 2-part epoxy. In which case I'd probably consider painting the wood core before layup, or the final product, or adding pigment to the epoxy. Just because I like a pretty, white foil.


Wood and fibreglass have different expansion rates. Eventually - not sure how long it will take, it will separate. If you should happen to ding your rudder and the water gets under the outer resin layer, it's going to start to decompose. Also - it's harder to get this fair and congruent than you would think. The rudder is a fairly important piece, and your boat is "performance oriented" so I'd avoid anything that had the potential to disturb flow.



> 3) foam core with glass mat and 2-part. Should be nice & light. If so, what kind of foam to use, & how best to affix the pivot bushing?


You need a stainless armature in order for this to be durable. If there isn't one in the rudder already it could cost you a few hundred dollars to have one made. Also, it's difficult to get both sides of a rudder exactly the same unless you are using a mould. Both sides the same is more important than you might think.



> 4) carbon fiber. Never used it before. Over wood, foam, or air its own self?


Again - hard to mould and there have been more than a few documented cases of carbon fibre things failing at inopportune times. It seems that they are finding out you need specialised epoxies to establish great bonds. You need a stainless armature in order for this to be durable. You may well end up spending a pile of money for something that doesn't work as well as a nicely shaped wooden piece.


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## Valiente (Jun 16, 2006)

I usually resist throwing money at a problem, but I must say that plastic rudder is a nice piece of gear. I think the beauty of it is that you could pretty well make a spare blade from plastic or wood/epoxy _before you even install the new assembly_, and then if it gets damaged or just cruddy, you've got a replacement ready.


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## bobmcgov (Jul 19, 2007)

Hartley18 said:


> ...it was suffering from the effects of the PO's tendency to hit rocks with the rudder blade....


Looking at this sad lump of wood, I fear the PO was hitting the rudder blade with rocks. Or an axe. Or a locomotive. First thing when I saw the boat: "Well, that rudder has to go." (Not his fault -- we have more rocks than water these days.)

I can get a piece of HDPE locally to fit this for under $20. May be worth a try. It's not the stiffest material around & it's a bit heavy, but it is fairly easy to shape (tool speeds low so you don't melt it) and, since it's uniform in composition, dings don't expose any core material. It rough-sands well but is hard to bring to a high gloss. But as Giu notes, a slightly rough surface is faster than a glossy one (sharkskin and all that).

Square trailing edge is better than a sharp one, isn't it? Recall reading that.


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## Classic30 (Aug 29, 2007)

bobmcgov said:


> Looking at this sad lump of wood, I fear the PO was hitting the rudder blade with rocks. Or an axe. Or a locomotive. First thing when I saw the boat: "Well, that rudder has to go." (Not his fault -- we have more rocks than water these days.)
> 
> I can get a piece of HDPE locally to fit this for under $20. May be worth a try. It's not the stiffest material around & it's a bit heavy, but it is fairly easy to shape (tool speeds low so you don't melt it) and, since it's uniform in composition, dings don't expose any core material. It rough-sands well but is hard to bring to a high gloss. But as Giu notes, a slightly rough surface is faster than a glossy one (sharkskin and all that).


He's correct to a point - it depends on your idea of "rough surface". You don't have to see your face in it, but the foils I've seen on smaller boats are typically varnish and certainly smooth, because on a small rudder, a rough surface might be 500 grit... 



bobmcgov said:


> Square trailing edge is better than a sharp one, isn't it? Recall reading that.


Yep, that's true. For a rudder of the size of yours, the trailing edge should be about 1mm wide.


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## sailingdog (Mar 19, 2006)

I'd go with a foam-core rudder if you want it to be light weight. It'll be far lighter and stronger than a wooden rudder if properly built.


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## soulesailor (Nov 18, 2007)

For a protective strip on the leading edge you could resin in a cord of dynel. I've had excellent success with this on the edges of my wooden kayak paddles and under my butt in my glass kayaks. Dynel comes in cloth sheets and cords that look like rope. When it takes an impact it doesn't crush or crack but rather dissipates the energy by chipping away. My friend put a line of it of the leading edge of his centerboard and has taken a bunch of hits and it is still going strong.


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## deniseO30 (Nov 27, 2006)

Rather then toss out the old one why not cut it into some long 6" wide or wider boards? Then find somebody with a band saw to resaw them? (cut on edge) Then you can laminate them onto plywood with epoxy. I may be wrong but aren't kick up rudders supposed to have some weight?


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## chucklesR (Sep 17, 2007)

bobmcgov said:


> I can get a piece of HDPE locally to fit this for under $20. May be worth a try. It's not the stiffest material around QUOTE]
> 
> Stiff you need, it's a rudder not a signal flag flapping in the wind. Heavy is good to a point - it needs to sink in and bite with authority and not bob around back there when the boat gets moving - if it's too light you'll wind up having to cleat it down and then it won't kick up.
> 
> Go with the original plan, heavy wood, epoxy and varnish or paint (if you use marine ply) and a belt sander/power planer to shape it. I'd do a cardboard cut out of the current one to get the chord (shape) right. Brass strips are easy to cut and stick on the leading edge, look attractive etc. - but then you'd not need to make another one next winter and just be bored until you find something else to do...


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## bobmcgov (Jul 19, 2007)

deniseO30 said:


> Rather then toss out the old one why not cut it into some long 6" wide or wider boards? Then find somebody with a band saw to resaw them? (cut on edge) Then you can laminate them onto plywood with epoxy. I may be wrong but aren't kick up rudders supposed to have some weight?


a) cuz it's trashed beyond redemption.
b) cuz I'm a professional woodworker with a fully-equipped shop.
c) cuz I gets wicked discounts on lumber (see above).

Could make a new blade from rough stock to finished foil in two hours labor. A bit of friction at the axle will keep the rudder put, or I can arrange a simple hold-down.

Much of the weight in the old beast is in the rudderhead-tiller assembly:two 1/4"t slabs of aluminum sandwiching a solid mahogany or ash core. That's 22 lbs, and the rudder's another 12. Seems excessive for a 1500 lb boat. The SJ21 is said to dislike weight aft, makes it squirrely. Idasailor seems to think lighter is okay:










This is the current rudderhead:










What you might call "different design philosophies." I'd be happy splitting the difference. Make new head assembly too? S'okay, Chuckles -- we got long winters.


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## Classic30 (Aug 29, 2007)

bobmcgov said:


> .... Make new head assembly too? S'okay, Chuckles -- we got long winters.


Well.. - since you asked - your *tiller* looks okay! 

We look forward to seeing a photo of your new rudder - in a month or two.


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## timebandit (Sep 18, 2002)

Bob
The good things about my new rudder are that it got rid of a lot of weather helm. nevers needs paint and nothing seems to stick to it. It also is longer so the boat does not round up as ez. Their rudders are not just a duplicate of the original but an inproved one. The shape itself seems to cut through the water without any sound or bubbles. 
You can prolly get the shape out of an aviation book. 
I believe the material was chosen because it almost sinks in water. 
Rick


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## Giulietta (Nov 14, 2006)

AHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH

OHHHH My!!!! Jaysus, Mary, and Joseph, the Saints and Our Lady Of Fatima!!!!!!!! (All together at least 4 times)........

Bob, we need to talk.....Jesus...I spilled my water all over the floor.
That's your rudder???


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## Classic30 (Aug 29, 2007)

Giulietta said:


> AHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH
> 
> OHHHH My!!!! Jaysus, Mary, and Joseph, the Saints and Our Lady Of Fatima!!!!!!!! (All together at least 4 times)........
> 
> ...


Bob, I know that you meant well and were only asking for some help but you really should have cleaned the rudder up or set it up with a nice view of the ocean in the background or something before taking that photo. 

Now, look what you've done!! Giu will take *weeks* to recover from the shock of all this! A shocking photo of boat parts is worse than porn to him. 

Poor Giu ... don't worry. Bob will fix it all up and make it better soon.


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## bobmcgov (Jul 19, 2007)

Technically, Giu, that's my rudder head assembly. The rudder blade was in post one. Photoshop them together in yer head, and it's even more nauseating. Hey -- I just bought the boat Friday!

And made it better already. Here's a half-scale maquette of the replacement I'll be building. Fully functional, so if anyone is sailing a San Juan 10.5, call me. Imagine the masonite is 1/4" aluminum, possibly with a few lightening holes; the blade is 1" HDPE; and the main column (pintles not shown) is 1"x2" square channel (aluminum? stainless?):










And in up position:










The raising handle is tentative, but it would allow positive up & down and with addition of a bungee strap, it would be secure yet give way in a grounding. Also be real easy to know which position your rudder was in. Heh -- total time on the model was 25 minutes, half of which went to that bloody handle.

Wotcha think?


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## Classic30 (Aug 29, 2007)

That's exactly the same setup as on our boat!  ...using wood instead of aluminium (aluminium with lightening holes is probably better - our rudder head weighs a tonne!).









Our raising handle is aluminium rod held in place on the rudder by a couple of strips of stainless, a bolt and some springs to centre it. The T-handle is a block of timber with the rod embedded in it.

Edit: Actually, there are some drawings at the back of http://home.vicnet.net.au/~hart1821/pdf/HARTTS21Meas07-02-07.pdf that might help put numbers against your model.


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## bobmcgov (Jul 19, 2007)

Thanks, Cameron. Enjoyed the rudder pics -- the top of my blade prototype looks exactly like yours. And the pull-up handle, which I thought was clever and original. Design convergence is a wonderful thing. Does the handle work okay for you? I want something I can yank up to clear weeds, then positively push down while under way; hence the rigid device.


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## CharlieCobra (May 23, 2006)

I've got an Idasailor rudder on the V-21. Ya can't beat it with a stick.


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## Classic30 (Aug 29, 2007)

bobmcgov said:


> Thanks, Cameron. Enjoyed the rudder pics -- the top of my blade prototype looks exactly like yours. And the pull-up handle, which I thought was clever and original. Design convergence is a wonderful thing. Does the handle work okay for you? I want something I can yank up to clear weeds, then positively push down while under way; hence the rigid device.


The handle works fine! - although I did fit a wooden hold-down block on the top of the rudder head (the white thing on top of the white thing.. sorry!  ) because the original blade shape meant the rudder would work it's way partly up during a blow. The back of the rudder blade has a long groove in it to hold the rod straight when the rudder is down.

I've changed the blade shape now (more effort forward) so that's not a problem now - just as well, 'cause we hit botttom with the rudder blade coming back into Rye from our South Channel Fort cruise and the hold-down went overside. 

Having the pivot bolt low and forward does mean that you have to reach down a ways to tighten the blade. AFAIK, that's why many people prefer daggerboard rudders.

Glad to be of help.


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## jheldatksuedu (Jul 4, 2006)

*heavy might be a good thing*

Being a kickup rudder, it might weigh a ton to hold it down, lighter might float and not be a good thing. Think about this before spending money and building a lighter one. You might end up adding a bunch of lead after the fact to a lighter one to get it work correctly. If you modify it after the fact to add a hold down to a lighter one, then depending on the mods it might no longer be a kick up rudder and once more you might end up with a damaged one instead of one that just kicks up when it hits something or you beach the boat. Also it could become one more thing to remember to do when you do beach and people are probably watching. Just at that instant when you want to make it look like so much fun and how you are so in control of the boat, instead of a mad house trying to do 6 things at once in three different places.


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## Classic30 (Aug 29, 2007)

jheldatksuedu said:


> Being a kickup rudder, it might weigh a ton to hold it down, lighter might float and not be a good thing. Think about this before spending money and building a lighter one. You might end up adding a bunch of lead after the fact to a lighter one to get it work correctly. If you modify it after the fact to add a hold down to a lighter one, then depending on the mods it might no longer be a kick up rudder and once more you might end up with a damaged one instead of one that just kicks up when it hits something or you beach the boat. Also it could become one more thing to remember to do when you do beach and people are probably watching. Just at that instant when you want to make it look like so much fun and how you are so in control of the boat, instead of a mad house trying to do 6 things at once in three different places.


The last thing a small boat needs is a heavy rudder because that could upset the fore/aft trim to the point where the boat becomes unmanagable on any course other than downwind, so adding lead is a no-no. If all you do is cruise, make the blade out of steel plate, but you'd better fit bigger pintles and don't ask your friends to help rig the rudder - you'll never see them again! 

My rudder (and Bob's design) uses a hold-down rod which, personally, I think works better, but the more common (read easier-to-make) arrangement is a length of stretch line or shock-cord from the front upper side of the blade to a cleat on the tiller.

You most definintely need a kick-up rudder on a trailer-sailer. At our last outing to South Channel Fort, one of the guys with a dagger-board rudder hit the sand bottom quite hard when coming back in and snapped the rudder. It hit too, but only lost my hold-down - the rudder was fine.


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## TSOJOURNER (Dec 16, 1999)

*Ida Sailor Worked for me*

I'll agree with Bob "TimeBandit"

I have a PY26, a bit bigger boat that had what I thought of as a massive rudder. It was made of fiberglass with a foam core and lasted 30 years before shearing off at the lower pintle. Wind was pretty good.

I looked at all the options I could find for making my own, but my wife finally convinced me I didn't have the time. IdaSailor took my order and even called me to say they could improve the design while reducing the size. I trusted them and it turned out great! It was used this summer, but not allot because I don't have enough time to get all the other work done. Sigh!


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## timebandit (Sep 18, 2002)

Idasailor also makes a plastic hold down bolt that snaps cleanly so that you can just push out the old broken part with the the nw bolt and you are on your way.
You may have to stand on yur head to do it though, but it does keep the rudder in the proper position.


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## bobmcgov (Jul 19, 2007)

Thanks for all the helpful replies; your advice is much appreciated. For the nonce, I've made a wannabe Idasailor rudder assembly out of UHMW polyethylene. Reused the old cheekplates. Tiller mounting needs to wait until I can hang this on the transom and determine clearances.

Weight is 14 lbs less than the old beast, even tho the poly is denser than mahogany. Total cost: $80 in materials and maybe six hours of my time. I crave the Idasailor, but $500 savings will buy us new sails.










And in kick-up mode (lifting handle to follow -- I'll be cross-doweling it for strength.)










End view. The shape is based on NACA4 calculations for low-speed airfoils: eleven stations plus three more in the first inch, to get the leading edge correct. Maximum loft occurs at inch three of eleven.










Now we need to find a cheap anodizing shop. That's not something I care to try at home.... I've left the bottom of the blade squared off. Chopping it at an angle (per prototype) looks nice, but does it really give you anything except drag?


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## Classic30 (Aug 29, 2007)

Bob, you've done a fantastic job. I wish you was closer and could re-hash my piece of rubbish!... 



bobmcgov said:


> Now we need to find a cheap anodizing shop. That's not something I care to try at home.... I've left the bottom of the blade squared off. Chopping it at an angle (per prototype) looks nice, but does it really give you anything except drag?


From what I've read, the lower 20% or so of the blade doesn't do very much, so leaving it squared off would be my suggestion - at least until you have tried your new rudder out a couple of times.

Well done!


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## sailingdog (Mar 19, 2006)

That's what you get for living on the bottom of the earth... 


Hartley18 said:


> Bob, you've done a fantastic job. I wish you was closer and could re-hash my piece of rubbish!...


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## Classic30 (Aug 29, 2007)

sailingdog said:


> That's what you get for living on the bottom of the earth...


What I *meant*, SD, was that his rudder looks like a work of art compared to mine.  If UHMW Polyethylene can withstand the forces on a rudder without snapping in half during the first blow, I needs to get me some!

Bottom of the earth? Last time I looked, we were on top! 

Hey, 500 posts already!!..


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## bobmcgov (Jul 19, 2007)

Thanks for the compliments, Cameron. One of the lovely features of polyethylene is its resilience -- this is basically the same material as those ubiquitous 5-gallon buckets. You can smoosh em, stomp em, run over em with a car -- they're famously hard to break. I think a bushing at the axle bolt may be in order, to prevent ovalizing of the pivot hole. The blade does show a bit of beam deflection -- maybe 1" over its length before it really firms up. Hoping that won't affect handling too much. Shouldn't -- airplane wings flex like crazy. As long as it don't vibrate....


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## TSOJOURNER (Dec 16, 1999)

Nice job on your rudder. What's cross doweling?


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## bobmcgov (Jul 19, 2007)

These are cross dowels.










Is veddy strong way of attaching hardware. The lifting handle on the rudder will be pulling straight out at full hoist; a cross dowel should prevent the fastener from ripping out of the rudder blade. Good in materials like particle board that hold screws poorly; also nifty for knock-down applications or blind bolts (eg stair handrails or bed rails).


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## Classic30 (Aug 29, 2007)

bobmcgov said:


> ....
> The blade does show a bit of beam deflection -- maybe 1" over its length before it really firms up. Hoping that won't affect handling too much. Shouldn't -- airplane wings flex like crazy. As long as it don't vibrate....


Bob, that could be *really* interesting - I look forward to hearing of your adventures in a blow! Rudders have to put up with heaps more than an airplane wing does. 

I'm no eggs-pert on this, but did do ****e-loads of reading before modifying my rudder and I've read that it's really important that the rudder blade stay straight. There's a phenomenon called "dynamic stalling" that happens when you head down the back of a big wave and haul on the tiller to stop the boat broaching. Apparently this puts quite a bit of sideways load on the rudder because the rudder is then at a pretty severe angle to the flow and this can cause a flexing rudder to snap off due to the speed at which it can "snap" from being angled one way to angled the other.

You might like to get a short length of scrap rudder material and see what sort of weight has to be applied at one end for it to snap. Hopefully it's quite a lot..


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## bobmcgov (Jul 19, 2007)

Tensile strength of UHMW is ~7000 lbs per square inch; better than mahogany, close to oak. (Tho not as good as spruce!) Torsional rigidity is not great -- ie, it'll deform a looong way before it breaks, thus little chance of catastrophic failure. I could imagine twist screwing up the attack angle & causing stalling. So can over-enthusiastic tiller work on any rudder, however stiff. We'll have to see how it sails, I guess. May get bored & build a wood/glass blade for comparison. Only six more months of winter!


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## Freesail99 (Feb 13, 2006)

On the east coast we have a tree called a Locust. Farmers, myself included use this tree for fence post and anywhere you need great strength. It will not rot in the ground left untreated for over 30 years. You can't even drive a nail into it, it is so hard. Closest wood I ever found that acts like metal.


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## bobmcgov (Jul 19, 2007)

You have *two* trees called locust. Robinia pseudoacacia (black locust) and Gleditsia tricanthos (honey locust). Both wonderful trees. Black locust is the second hardest US timber species, after shagbark hickory. It's rot-resistance is legendary, as you note -- often used for direct burial. Also terrific firewood! Honey locust is also very hard, though less weatherproof than Robinia. Both are ghastly heavy & difficult to work.

Both woods are very brittle: never park your car under a locust tree! I'd worry about its lack of resilience in a rudder blade. It wouldn't flex, for sure. But it just might snap suddenly. While Sitka spruce, which is pretty limber, absorbs tremendous energy by deflecting. That's why it's the wood of choice for airplane wings and Jacobs wind turbine blades. Mahogany is a nice compromise: stiffer than most softwoods, but not as brittle as some harder woods like maple or teak. Also good strength-to-weight and natural waterproofing.

I've planted some Black locust and a variant, Bristly locust, on my land. Both are legumous, related to the pea plant (as is Caragana); they fix nitrogen in bacterially sterile soil like mine. So far my locust have suffered wind and snow breakage and aren't making it. Brittle wood. Good choice for handrails or brightwork, tho!

For a rudder blade, best choice might be a relatively limber wood that's laminated up. Glue lines add rigidity w/out weight or brittleness. Still face the vexing issue of that feathered trailing edge. Going to be prone to rollover failure or splitting, or may flex in a following sea as Hartley warns. Sucks when your rudder jibes on you.


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## Freesail99 (Feb 13, 2006)

Yes locust makes great firewood. But I do believe that the wood isn't brittle once it has been dried. The honey locust I believe is the one with thorns on the branches.


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## bakerha51 (Nov 22, 2007)

Bob - great work on your rudder. I am working on a glass over foam version but may switch after seeing yours. So why the switch from HDPE to UHMW polyethylene? Did you decide to anodize or go stainless? One more - how did you decide on the foil shape? Thanks in advance and good luck with your project!


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## bobmcgov (Jul 19, 2007)

Bakerha51: I went with UHMW cuz my plastics vendor didn't have a piece of HDPE that size. No other reason, tho it is a bit stronger. Flexed several pieces of each, didn't notice any difference in beam deflection. Both bend a bit.

Cut down the 1/4" aluminum cheek plates from the old rudderhead, using a sawzall, then a router on low speed with spiral bit. The pintles are recessed into the cheekplates and seized there by 1/4" binding posts. Main rudder post is a chunk of 1x2 aluminum tubing. I'd like to anodize it later, just to prevent filth from oxides. Plus it would look cool purple!

The formula used for the foil is based on old equations for low-speed wings, called NACA4. (Never let an English major handle Finite Element Analysis! ) Plugged it into a spreadsheet, then laid it out on quadrille ruled graph paper (10 squares per inch), glued that to masonite, & used it to check the profile. The router with a straight bit and fence made multiple passes to 'stair-step' the blade close to finished shape; hand planes got it closer (works good, but clogs the plane's throat); then finished up with belt and orbital sanders. 50-100 grit belts, then ROS to 400. My father sez I should iron it, restore the shiny surface.

Formula and discussion of foils here. Yields _y_ that is the elevation from center line (chord) at a given _x_ (distance along the chord from leading edge.) I wonder if many boat makers don't intentionally keep their blades fatter-than-optimal far back, accepting more drag to stiffen the thing and avoid an easily-damaged feather edge at the back?


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## bakerha51 (Nov 22, 2007)

Bob: Thanks for the info - will really help on my project. I had decided on the NACA12 foil but will do some reading first. Are you going to paint the finished version? I had read that the UHMW was not UV stabilized but I don't know enough about it yet. Thanks again - happy holidays! 
-- Catalina 25 - Nightwind -


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## FortAwesomeIII (Jul 15, 2007)

I have been the route of trying to fabricate my own rudder for a Macgregor 25...I would've saved a TON of money if I would have just bought the Idasailor rudder that I ended up purchasing that worked a whole lot better. This is not an ad for Idasailor(well it kind of is), but I would definitely talk to Joel there. The customer service is unparallelled as is the quality.


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## bakerha51 (Nov 22, 2007)

John - interested in what made your homemade rudder so expensive? I am yet to really start my own. I have cut the foam I'm planning to glass but reconsidering the plastic after seeing this thread. Bob's head design is very simple, effective and inexpensive so I'm interested in your experience.
--Catalina 25 - Nightwind -


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