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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 08-19-2004
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Building a New Ruuder

I''ve built a new rudder for my boat a ’77 Newport 30’. Old one was indeed not working like I had assumed (Stock slipping in the rudder). The bracing on the stock inside the rudder had corroded and was sheared off. The rudder post turned about 60 degrees through the rudder before engaging and actually moving the rudder. After a bit of thought about what to do, I decided I’d try my hand at building my own. Quotes for new ones (with the same 27 year old design) ranged in the high $2K to mid $3K’s. Too much for my blood.

So, after a bit of research, I chose to design a new one and build from scratch. The foil shape I decided on is the NACA 0012 foil. It''s a narrow elliptical shape and has undergone thousands of hours of testing by the aero industry. Turns out that its the best foil shape for both lift and the absence of drag for air speeds in the range of MACH 1.0 to 1.2. Also turns out that the fluid dynamics of air speeds in that range are very similar if not identical to underwater fluid dynamics at 4-7 knots. Lucky for us sailors. Its the foil design going into almost all new production boats out there (Hunter, Catalina, Beneteau, etc.)


So, based on width and length of the rudder (20” x 51”) the midrange for a boat of my size, I was able to get the cross section measurements of the foil. Some website out there which I can’t seem to find now had a shareware program which kicked out the cross section numbers for a given set of measurements. A lot of RC airplane people fiddle with this as well as a number of aero engineering people, so its not too hard to get hold of the numbers.

I hand shaped a blank of cheap poly foam from home depot. I knew the depth I needed to cut into the blank from the numbers generated by the program. At each ½ inch (from leading edge to trailing edge) I ran a router down the length (top of rudder to bottom) of the foam at the desired depth. I then used a 12” rasp to cut the foam down to the grooves made from the router, this gave me the general shape to within a few 1/8’s of an inch. I cut a piece of ¼” plywood 24” long by 3” wide and cut a female pattern (reverse of the foam) to do the final detailed shaping of the foam “blank”. I hand sanded in front of my plywood pattern board to get the perfect shape. I then ran the entire foam blank with a board 18” long covered in 100 grit paper to get a final smooth surface and to take off another 1/8” to account for glass and fairing compound. The blank cost about $10. I figure I''m about 96-98% accurate to the designed foil shape which is good enough for me. This only took a few hours.

I then laid out 3 layers of 6oz fiberglass with 2-part West System epoxy in laminate layers (I left the top of the rudder open so I could later carve out the foam blank, leaving the fiberglass shell). Cost about $150 for all the supplies and another $30 for the various tools (squeegees, rollers, pots, pumps, etc.) and such. I bought everything from the US Composites website www.shopmaninc.com which is about half the price of West Marine or any other place around here. I spent about 1 hour a day on each layer and filleted the edges between each layer using the West additive 403 filleting compound for epoxy. After I completed the glassing I filleted the voids and any seams still showing. Another 3 days for about an hour each. Then into the fairing stage. A few coats of epoxy with the West System 410 fairing compound additive to really give the whole board a smooth finish 2 days for an hour each, very easy to sand down with a long board (3 inch wide and 18 inches long 1/2 “ thick) with 3M 100 grit sticky back paper (the best sandpaper in the world, it lasts forever without losing its bite, but very expensive up front. I bought a 45 yard roll a few years ago for about $45). I finished with a few coats of pure epoxy to really seal everything up, another hour.

My next step was to carve out the foam blank around which I built the rudder. It was very easy and took less than an hour. I used a 6'' piece of 3/8” rebar sharpened to a chisel edge. I was left with the finished fiberglass shell.

I was going to order a new Stainless Steel 316 post (the old one was actually bent and had lots of pitting). The post was 50” by 1-7/8” O.D. but the damn things cost about $100. Plus I''d have to get the cross tabs welded on and I''d still have a future issue of corrosion and failure. So I opted for going with 100% composites. I ordered a Carbon Fiber (and Epoxy) post, www.rolledcomposites.com out of MA (super pricing on any rolled composite) with the same O.D. as the stainless but with a wall thickness increase of about 100% (1/4"). This post will have its weaves and threads at 45, 90 and 180 degrees at various stages and have about 135% more torsional, compressive, and modulus strength as the old stainless measure, so I''m basically very comfortable with it. Post was $130. I just glassed the tabs onto the post for its entire length within the rudder to about 6 inches wide, it basically looks like a rudder without the fiberglass shell I’ve made, another hour.

I lined up the tabbed post inside the finished fiberglass shell at the proper angles from the old rudder (i.e. post is longitudinally straight and about 9 degrees off the vertical looking at the face of the rudder, the angle between the top of the rudder and the post is about 81 degrees). I also moved the post toward the trailing edge at a split of about 11% to 89% leading edge to trailing edge. In other words I left about 2.3” of the rudder forward of the center of the post and 17.7” aft of the center of the post. This was so I could get more balance but not enough to get lee helm, the old rudder was not at all balnced and could get very squirrely when the wind piped up or was gusting. I poured a two-part closed-cell expanding Urethane foam into the shell. (Remember I left the top open for this). This foam is what’s called 16 lb foam, i.e. it weighs 16 lbs per ft^3. It also has a buoyancy of about 50lbs per ft^3. It has a very high compression strength (in the neighborhood of 400-800 psi) in other words you can barley dent it with a swinging hammer, and it sticks like epoxy. Its a liquid during the mixing of the two parts and pours very easily. It begins to expand within about 30 seconds of mixing to about 4 times its liquid volume, fills any voids and then hardens like a rock. I believe its what’s used in all rudder manufacture today (or maybe they use 20lb foam, whatever). I needed about 1.0 ft^3 which cost about $48. Picked this up at US Composites as well, www.shopmaninc.com/foam.html this took another 2 days for about an hour each day.

I glassed over the top of the rudder where I inserted the post and poured in the foam (which has been left open all this time), faired it and completed the rudder with an epoxy barrier coat, primer, and bottom paint, another 3 hours over two days. All the paints and primers cost about another $75.

All said and done the whole project cost just less than $500 in materials and about 20 hours of labor over the period of a 2-3 weeks. The old rudder came out of the boat pretty easy (didn''t even need to dry dock the boat), just undid the tiller attachment and the quadrant from old post and the rudder basically slipped out. There is a fiberglass sleeve inside the hull that the rudder post slips into/out of and rides higher than the water line. The new rudder slid into place easily. I will eventually (this fall) install a lower bearing for the carbon post so as not to attract too much wear and tear (another $100 and some more fiberglass work when the time comes). So now I have a racing rudder with about ¾ ft^2 more surface area (turns on a dime now) but less fluid drag than my old rudder, has more lift, weighs about 20 lbs less (it actually still has quite a bit of positive buoyancy, I had to tie dive weights to it so I could get it into place), and is brand new. Plus I’ve learned an awful lot about how rewarding some projects on the boat can be.
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Old 08-24-2004
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Building a New Ruuder

Thanks for the detailed description of your process... hope we never have to do it! (We''ve had our own fun, trying to remove our 20 year old stainless machine screws on our aluminum quadrant.) There is a reason for sawzalls.
Please don''t forget to note your new rudder on next season''s PHRF application!
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Old 08-30-2004
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Building a New Ruuder

Thanks for a very easy-to-follow description. Your writing is very clear and just detailed enough.

One quick question. I''ve worked with two-part expanding closed-cell foam before. How did you calculate the starting volume so that you''d get just a bit more, instead of just a bit less, than you needed to fill up that cavity? <em>"…about 4 times its liquid volume"</em> sounds like a vague guidline.
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Old 08-31-2004
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Building a New Ruuder

I appreciate the feedback. I hope more people ask questions. This is probably far more detail than you need but, hey its fun and details are the key.

"...about 4 times its liquid volume" is vague. But its the only description from the supplier, US Composites. Turns out that the expanded volume depends on the ambient temperature as well as very much on the temperature of the two parts just before mixing. As a result they have to do the "...about..." thing since its different for everybody.

I initially calculated the volume I needed to fill the fiberglass shell by averaging the width, length, and height. I basically divided the shell into 1" wide rectangles and then averaged the depth and length every inch along its length. This gave me about 20 rectangles with their respective average depths and lengths. So, 1" times average depth times average length on each of the 20 gave me a very accurate volume. This is a very easy way to measure volumes of abstract shapes. Its actually the foundation of using calculus. The smaller you make your rectangles the more acurate your measure.

The volume was just under a cubic foot, good enough to place an order for the product. When I finished the shell I was going to fill it with water and measure its volume more accurately. But, as I was blissfully filling I realized that the shell was expanding out from the weight of the water. I would not get an accurate measure and I could damage the shell. So, how to measure an accurate volume? My 3 and 4 year old nephews are playing in the garage with me in a big box full of packing "peanut styrofoam". Well thank you nephews, I pour the packing peanuts into the shell, pour them into a box and measure the volume they fill in the box. The volume came to 1,662 cubic inches give or take, (.962 cubic feet).

It just so happens that the 16lb two part foam is sold in 1 ft^3 amounts. It basically comes in two 1 gallon containers. So, I was lucky I guess that the volume I needed happend to be about what was sold. (Although I think the very helpful and friendly people at US Composites might help out with different quanities than what''s listed, since its obvious from the product packaging that it came from bulk containers.)

Anyway, I was concerned that I might be right on the edge of "...enough". Furthermore, the two containers from US Composites were not of equal volume. "Part A" had about 1 pint less volume than "Part B". So I called them back to find out the deal.

They said that the mix should be by weight NOT volume, and that the weights were equal as I saw them (Part A is heavier). They also gave me some pointers to work with: to get the maximum expansion, warm the two parts in a water bath to a temperature in the mid 90s F. Mix small batches by weight so that the final volume of each batch is about 1.5 quarts. So after finishing the the entire process I''ve mixed 5-6 batches of the foam and allowed each pour to expand, harden, and cool. Remember that this foam, like epoxy, is exothermic, it gives off mucho heat and can damage epoxy laminated fiberglass. (i.e. if you mixed all of the two parts you''d have a huge expansion and this could get very hot, somewhere in the high 190''s.)

I was very satisfied with the outcome. The foam did exactly what it was suppossed to do, expanded into all the nooks and cranny''s and stuck like epoxy to everything inside the shell. After my 4th pour I was pretty good at estimating the last pour. My last pour expanded out of the top of the shell about 1" and was easy to shave off with a rasp before it hardened completely (about 5 minutes after pouring). I still have a couple of cups of the 2 parts left.

Hope this helps.
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Old 08-31-2004
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Building a New Ruuder

Sawsalls rock!!!

PHRF can suck my rudder post. No, honestly I love the idea behind PHRF, but the politics (poly = many, tics = blood sucking insects) and the subjective rating adjusments are too much. Why do you suppose it is that the boats of the current board members and president always seem to get rating adjustments in their favor...Hmmmm??

I race ALOT, but not on my boat, thats for cruising only.
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Old 08-31-2004
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Building a New Ruuder

Your rudder construction description has been interesting, thank you. One caution regarding the rudder post, first some background. I believe the Newport 33 was an extended Newport 30. The first two Newport 33''s that made the delivery trip to Alaska both lost their rudders crossing the Gulf of Alaska. Not in storms, just the normal 10'' or 12'' seas. I remember looking at them at the time, thinking the rudder post looked way too skinny. Newport responded by sleeving the regular post with another SS tube - only on the boats coming up here. Your 1-7/8" diameter tube sounds similar to the 33''s post. If you wander around a boatyard looking at rudder posts, suspect you''ll find 1-7/8" unusually slim.

In addition to diameter, there is material and stiffness to consider. Although carbon fiber is very stiff, a composite post will usually still flex more than one of stainless steel. Carbon is stronger than steel by weight, but a much heavier SS post can be stiffer than a light carbon one of equal diameter. On our new boat if you wanted the optional carbon post they mandated spherical bearings to accommodate the greater flex without binding.

I fully appreciate all the reasons to stay with the same diameter. For coastal cruising in good weather you are probably fine. If going off-shore or if you are at all cautious you might want to consider sleeving the interior of the post. Full length wouldn''t be necessary, only the area around the lower bearing. That''s where the 33 rudders broke, at the point of maximum bending moment.

Thanks for the thorough and informative discussion.

jon k

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Old 12-11-2004
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Building a New Ruuder

I have my rudder removed from my 81 Seafarer 30 this winter and you all talking about 1 1/2"+ rudder stalks , Seafarer used 1" stainless , which I know isnt a subsequent owner modification since I have seen too many exactly the same .......

Tim
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Old 12-12-2004
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Building a New Ruuder

We all have our ideas this was my idea and it worked very good. I found the shape I wanted a long tapered foil took the old stainless shaft cleaned it up and had it trued for twenty bucks at a machine shop. The next step was the local salvage yard and I found a piece of 3/16th plate four feet long and ten inches wide. The welding shop cut a slot in plate and welded it using the piece they cut out to make gussets and I had a stainless core to end all cores. I could have sailed the boat with what I had. then I took plywood and cut templates in the foil halfs shape and built a mould with two X 4 and the two parts were lined with formica and it was glued to the foil tenplates. Next it was coated with seperator and using triaxle cloth three layers were layed on, one coat of mat was the last layer On each half. Now the shaft was set into place and high dinsity foam two part stuff poured in and after it cured the top of the mold was glassed in and the mold seperated and removed and what we had was a smooth as a babys butt rudder which only required an hour to fair with glass tape and a a little more resin and another hour to primer and another to bottom paint. All this for $500. Beats $3000 any day.
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Old 12-13-2004
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Building a New Ruuder

Armchair,

Thanks for sharing the detailed info on the rudder rebuild. Very interesting!

2 questions;
1) as it looks like you had just 1 chance to get the rudder post lined up just right (with foam that dense I can’t imagine how you could re-do the work once the first pouring of the foam hardened) how did you hold the post and shell in place to eliminate any movement, and how did you make measurements to ensure they were lined up perfectly?

2) how did you keep the walls of the shell from losing their shape as the foam expanded - were the walls of the shell so thick that when the foam expanded it only expanded upward toward the opening without pushing hard enough to deform the foil shape?
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Old 10-16-2006
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Hi, it is now 2006. My stainless steel rudder post has some corrosion due to electrolysis due to DPO. It is missing about a knuckle to thumb tip of material. It was puddle welded prior to some blue water cruising and seemed to be ok. But I always worry about what is going on cause it still leaks and results in standing water.

So, I am considering having the post replaced. It is on a 46 foot sailboat, and skeg hung. Any ideas? Cut it out and replace? Replace with carbon fiber and a tube? What could be done to make it lighter?

On the list for 2006 winter.

Thanks.
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