Building a rudder

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Re: Building a rudder

Postby GreenLake » Mon Aug 16, 2021 2:24 pm

I recently had a mishap where the boat slipped off the trailer and was supported only by the rudder while being dragged a short distance. Because of the location of the rudder pivot, the transom never touched the ground, but I lost about 1/2-3/4" off the leading edge of the rudder. After drying out the exposed wood, I used penetrating epoxy (SystemThree S-1) to give a good seal and then used 3M High Strength Marine Repair Filler to build up the leading edge again. (It's fiber reinforced and works well for that purpose).

I located my original templates and made sure that the profile was as close as I could make it before painting.

Good as new. Gudgeons and pintles look fine.
~ green ~ lake ~ ~
GreenLake
 
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Re: Building a rudder

Postby GreenLake » Sun Jan 29, 2023 9:16 pm

More follow-up on how durable or not the rudder turns out to be in practice. (Pictures to come).

Latest data item: collision with a keelboat. They failed to duck me and hit the stern quarter of the DS. Other than some lighter spots on the rub-rail, no visible evidence of the collision --- except for the rudder.

The rudder didn't like the sudden sideways motion through the water, and the cheeks of the rudder head proved to be the sacrificial part. It wasn't a clean break. On the side towards the impact, the plywood for the cheeks failed and it delaminated, but there was enough there, or in the thin glass sheath to prevent the rudder head from separating.

The opposite side, away from the collision, broke cleanly in a pretty straight line. Wood and glass.

The rudder blade looks undamaged, and no damage to the pintles or gudgeons.

I'm not sure what to think. If allowing the rudder to break, allowed the stern to accelerate faster and thus take no damage, that would be a plus. On the other hand. if the rudder head can break before the gudgeons are bent, even a little, it might indicate that it broke a bit too easy.

Tentative plan is to switch all or part of the "cheeks" to fiberglass this round. But it won't be a controlled experiment, as I'm not planning on being rammed again. :shock:

(PS: looks like one of the POs also had a collision. There are faint weathered cracks on the deck on that side, but none on the opposite one.)
~ green ~ lake ~ ~
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Re: Building a rudder

Postby GreenLake » Wed Feb 01, 2023 9:46 pm

As promised:
P1100496-c2_1099.jpg
Rudder damage; click on image to view all
P1100496-c2_1099.jpg (54.27 KiB) Viewed 7552 times


This photo clearly shows how the boat was shoved from port side and the water kept the rudder in place. The other boat never touched the rudder itself. One of the two cheeks that hold the rudder blade simply tore clean across under tension. The other delaminated inside the plywood.

After taking it apart and looking at the wood, it appeared discolored, so it looks like water had gotten in at one point. Both the outside painted surface, as well as the inside were covered with a glass sheath. Except at the break itself, these surfaces are undamaged, unlike the interior of the plywood.

Because both rudder head and blade are undamaged, my plan will be to replace the cheeks (and beef them up a bit in the process). Anybody interested in using the information here to build their own rudder might want to take similar steps for a somewhat stronger design.

Note that the original design of the rudder did survive over a decade of use, something that hopefully means the repaired one will last even longer.

More details to follow.
~ green ~ lake ~ ~
GreenLake
 
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Re: Building a rudder

Postby GreenLake » Tue May 30, 2023 1:22 am

Here now the update after successful rudder repair.

As you can see above, the damage was limited to the two "cheeks" that attach to the rudder head and between which the rudder blade can pivot. That determined the strategy for repair.
  1. I started with removing almost all of the cheeks, and sanding the bottom half of the rudder head back to its original thickness.
  2. At the top of the cheeks there's that little "ramp" area, designed to give a more gradual transition in thickness. You can see that one side had split almost all the way to that location, while the other one broke much lower. I removed both to about the same level, but I left the ramp itself in place. Not least to have a fixed point for alignment.
  3. I took a piece of plywood, double the size of one of the cheeks and added several layers of fiberglass cloth (both light and heavy) as well as fiberglass mat (designed for use with epoxy resin). The original design had some fiberglass layers on both sides of the plywood, but think I more than doubled them, with an extra layer or two on the outside.
  4. Once that was done, I divided the board, and trimmed one edge for alignment with the ridge left over from the ramp.
  5. I then screwed both sections into the rudder head with deck screws, just to fixate them while trimming the rear and bottom, which form a somewhat complex curve. I found that a jigsaw barely works, and that the best result for rough shaping was achieved on a table saw (carbide blade and blocking the free ends of the checks to prevent them from bending while cutting.
  6. Final shaping with a belt sander. I decided to leave a bit more material than the 1" in my original design. The damage didn't show any weaknesses in that area, but I felt better adding about 1/4-1/2"....
  7. Locating the hole for the pivot was tricky. Originally, I had drilled blade and cheeks at the same time, which minimized issues of positioning. This time, I had to try to locate the hole based on a part that didn't really have too many straight sides (and even the nominally straight ones weren't really). However, I managed that to within about 1/8" of an inch. The rudder blade now overextends a bit beyond the vertical, consistent with the gap being too tall by a bit.
  8. The original design had a cutout where the bracket for the lower pintle is attached to the rudder head. That design was copied from the stock rudder, but proved to be a weak point (the fracture lines tended to end there). I decided to not do a cutout, but to only drill oversized holes that would allow the heads and nuts for the bolts to pass through and on one side, wide enough to fit a socket for tightening. The brackets for the pintles effectively go into a "slot". However, it did require sanding the underside of the cheeks, so there's now a "channel" where there used to be a full cutout. An electric file proved the tool of choice for that part.
  9. Even though some material was removed from the underside of the cheeks, the heavier laminate on the outside is almost fully undisturbed (except for the access holes for the bolts) and the brackets now go into a slit.
  10. After shaping an drilling, I unscrewed the checks, coated them with epoxy and reattached them again in the same place (with the heads of the temporary screws deeply countersunk).
  11. I also used some clamps.
  12. The full "ramps" where rebuilt with a wood flour/epoxy paste, and the same pasted used to bury the temporary screws. Any bare wood from sanding and drilling was epoxy coated.
  13. After sanding the wood flour paste, some areas could use cosmetic fairing, for which I used QuickFair.
  14. I also took care of some nicks in the trailing edge of the blade, using an epoxy repair paste (a MarineTex clone).
  15. To provide UV protection for the epoxy, I applied a coat of Pettit's EZ-Poxy.

I've sailed with this a couple of times and the repair appears fully successful. Not a full stress test, but I'm expecting this to work at least as well as the original design.
Pictures to come.
~ green ~ lake ~ ~
GreenLake
 
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Re: Building a rudder

Postby GreenLake » Sun Jan 07, 2024 4:59 am

As promised, pictures. If a bit late. As always, click on the image if you aren't shown the whole picture by default.

I've selected two that most clearly show the essence of the repair.

One shows the dry fitting. The cheeks are held in place by two screws that are countersunk and later covered with filler (wood dust and epoxy) and abandoned in place. They serve to fixate and also help in clamping when the cheeks are finally glued onto the main rudder head.

In the actual assembly there will be a large washer under the wing nut. The opposite side is just the typical carriage bolt head and doesn't get a washer.
P1100997-c1_1200.jpg
Dry fitting everything
P1100997-c1_1200.jpg (104.43 KiB) Viewed 5071 times


The other one shows the cheeks being sanded into final shape after rough cutting from the blanks. If you look carefully, you can see the beefed up outer layer of glass laminate (and the thinner, inner one). In order to strengthen the cheeks I opted to have the bracket for the lower pintle go into a slot between rudder head and the new cheeks, limiting the cut out to two holes that are large enough for the socket wrench for the through bolt. I was a bit concerned that I might accidentally fill that channel with epoxy, thus preventing the bracket to go in, but in the end, that part worked fine.

P1110001-c1_12000.jpg
Sanding the final shape
P1110001-c1_12000.jpg (111.82 KiB) Viewed 5071 times

Following this stage, not shown, I added another layer of cloth and a lot of filler to make a smooth transition between the part shown painted in white and the new cheeks. Both at the sides and the top. Ultimately followed by a layer of paint (Pettit EasyPoxy).

The restored rudder head does look a bit different because of the way I changed the attachment of the lower pintle, but it's held up fine for a season and without the small hairline stress cracks that I had become used to seeing at that location.
~ green ~ lake ~ ~
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Trailing Edge

Postby tomodda » Wed Jan 10, 2024 12:00 am

Greenlake:

Thank you for your detailed log of this rudder and cheek build! Question for you regarding the rudder itself - from previous posts of yours, I know you squared off the trailing edge of the rudder rather than feathering it to a point. Less eddies, at least according to the Duckworks article linked previously in this thread. The question is how much you rounded off the "corner" between the rudder face and the square end. Did you just sand it to remove sharp edge, or did you actually radius it (with a router and round-off bit)?

I ask because I took the rudder and centerboard off my dearly departed (i.e DEAD) #37 and am strongly considering reshaping them to NACA profiles (probably NACA0008) and using them on my "new to me" DS1, #169. That being said (writ), it's a long-term project, but I do wonder how I'd handle the back edge of both the CB and the rudder. Any insight would be appreciated.
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Re: Building a rudder

Postby GreenLake » Wed Jan 10, 2024 2:04 am

It's been a while and my most recent repair did not involve the blade itself. That said. Here's from memory:

Notionally, I let the profile come to a point as I build the foil. Then sand that back to where the two faces are a small distance apart. I don't hold the sander at 90 degrees, but at a slight angle; effectively the rudder isn't "squared off" as much as turned into a trapezoidal shape. The reason is that the asymmetry is said to have beneficial effect in shedding vortices.

The width of the profile at that point is something I probably eyeballed, but if you can find a suggested width, go for it.

From the point of view of creating the shape, the very thin end of the wedge (somewhere from 1/16" to 1/8") is hard to realize with plywood. So what I do is to replace the last 1-2" of the entire trailing edge with a solid bit made from high-strength marine filler (vinylester plus fibers). While mixing in the catalyst, I form a thin strip which I press against the truncated profile (remember, I cut off the last 1-2" -- and sealed the edge).

I use plastic sheet or waxed paper to help shape the filler into the same wedge shape that I just cut off, but I let it stand a bit proud. It cures fast, and I sand it flush. Next comes the cloth sheath over the entire rudder - I let the cover for the two sides meet. After fairing the two sides, the wedge should be again very thin, and is now made from either filler or cloth (exact composition depends on what needed sanding off. It's not critical)

That's when I finally "square" off the trailing edge. What is removed at this step is all relatively uniformly some form of fiber reinforced resin and not wood. The seal is maintained and the material is reinforced and can hold that edge (as long as you don't have a habit of backing your boat into obstacles).

Absolute last stage of the process is a layer of paint.

Because of the shallow angle, squaring off the end will remove about 1/4 to 1/2" of chord length. Better to plan for that.
~ green ~ lake ~ ~
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Re: Building a rudder

Postby tomodda » Wed Jan 10, 2024 6:48 pm

Thank you for the detailed explanation! Will keep it in mind for when I take on this reshaping task. Of course, at this point I'm just trying to mentally justify buying a hefty 2HP or above router to do the job. :D I have a door project in my immediate future (building a garage door), which is going to involve more mortise and tenon joints than I feel like cutting out with a chisel. So a router can be justified for that "bit of fun..." and then I can sneak it right from the Garage Door project to the CB project without the Minister of Finance (aka my wife) protesting too much.

At least that is the theory! Will let you know in a month or so, I'll either be happily building a NACA jig to do this proposed shaping job, or I'll be in the "Penalty Box." ;-)
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