One of the more fun projects I'm doing this winter is replacing the rudder. I may actually build two, a copy of the OD shape and a second that is more balanced with at least 2" in front of the pivot point. I have a couple of questions: First for anyone that has the wider balanced rudder, what is the best new width? I see an old post on Sailing Anarchy where it was suggested to add 60 mm (2.36") and that seems like a reasonable amount. Second, I have lots of nice quartersawn oak around the shop and it would be easy to use it for the core. Since it has substantial structural strength itself compared to the old balsa core I could reduce the section thickness of the covering glass, or I could go get some spruce which would be a dramatically lighter core and then just use the same glass section thickness as the old rudder. My planned fabrication process requires the use of solid wood rather than balsa or other core materials.
No matter what I do the new rudders will be dramatically stronger than when they were new, since I will be using cloth rather than all the chop strand used in the original rudder. The glass section thickness covering on my old rudder is about 1/4" albeit with a substantial reduction in that actual section thickness now with the thousands of serious blisters all over it (and it didn't fail in some pretty hard use by the PO). A curious side note here, the blistering on the rudder in terms of the density of the blisters is probably 10 times greater than what I was faced with on the hull. I assume these rudders used the same polyester resin that was used on the hull, for sure the same chop strand mat, why would the rudder be so much worse for osmosis?
Once I sort out a couple of these issues I will build these rudder(s) and I will show how I went about it.
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This project is now well underway. Started with buying 3 large slabs of plain sawn white oak, 37.5 board feet for about $270 worth here in the NW, I may have as much as 10 bf. leftover after ripping these down. While the boards were plain sawn when you rip them and turn them 90° they become quarter sawn or rift, which is exactly what you want for this large lamination. These slabs were 8/4 (about 2" thick") and I surfaced them slightly bringing them to 1-7/8". Then I ripped them to several different widths depending on where they were going in the lamination. I could have easily ripped them all to 2-1/2", but I am cheap and I hate turning lots of good wood into sawdust. The tradeoff for ripping to different dimensions is messing with these different thicknesses in the glue up, since they have to be centered relative to the next piece. So I am doing this in four steps, gluing similar sized bits together first and then joining the combined sections.
I chose white oak because of its strength and the ease of milling it. I see some builders are concerned with rot, but using epoxy and barrier coats and a couple of extra construction steps I think I can mitigate that problem well. I do think it would be possible to use a less dense core material and rely more on the glass skin for strength, but I just decided to overbuild this thing.
There are lots of good videos and information out there on doing these rudders and centerboards and I have decided to go a hybrid route with a jig that will let me slide the router up and down the length of the slab and then fix the jig into place and carefully work the nose of the rudder.
In my wood shop I had already made a setup to mill large wood slabs that I can use part of for this project. It consists of two 2/4's that I have milled to be straight and true. They have a provision to allow me to clamp these rails to my work table and then using a bridge with the router mounted to it, I slowly move the bridge assembly back and forth over the slab and flatten it. So for this project I will use those same rails and smaller bridge that has the NACA0012 foil shape offset from the final shape by 40mm.
I started this project with some info from Duckworks that has a form you can fill out to create NACA foil shapes to your dimensions. But when I worked out my basic dimensions and printed it the offset line did not extend nearly as far as I wanted it to at the trailing edge. So I asked a friend with engineering experience to see if he could improve the plot and he did. Then the next trick was to get the print from my printer to match the actual dimensions I was going for and that took some messing around (that is why I included two slightly different spreadsheets). An actual plotter would be the way to go if you had access to one. In any case I got a print that matched the 18-1/2" width I wanted. Then using another highly sophisticated method of laying some carbon paper over some hardboard I traced the shapes, cut them on the band saw and faired them with a sander.
Next step was to cut these offset rails and I did that by using double sided tape and cutting the first pair of rails together and fairing them to match the template. I used some leftover plexiglass from my companion way to make a large oversized router base to ride on these rails. I purchased some aluminum right angle channel and made the two guides to attach to these offset rails and then added some flat aluminum to make the entire frame rigid. In one of those happy mistakes I built this fixture 24" wide since the aluminum I purchased was 4' and I needed two rails. Then when I sat the big new router base on the fixture I realized that when you slid the router to one side it would drop off the support rail. So I just made another wood offset rail and added it to the fixture. Now I can easily slide the router base over the fixture side to side or fix it in place and slide the entire fixture and router up and down the rudder blank.
So that is where this project is today. The blank has one more thin piece for the trailing edge to be added tomorrow. Then I can layout the overall shape and position of the hardware and the hole for the tiller. I am doing video on this project so there is much more to come. While I am a more advanced woodworker I really think this project can be managed by most garage type woodworkers once they know the steps.
Here are some images from today's progress. I have added some round head screws to the router base to insure that it does not rock on the offset rails and a pair of extra holes on each side of the base so that when I get to the nose section I can hopefully keep the whole thing stable. My plan for the bigger flat sections is to use a very large 2" diameter bit and take relatively light cuts on each pass. This has worked well on the tables I make. The advantage to the large bit is that it runs much cooler and so stays sharp far longer than a small diameter bit. The downside in this application is that if the router rocks on the rails the edges of the bit will dig in. The large diameter will also be hogging out material from the area on the next pass too.
I also made a minor change to my plan and decided to add one more thick piece on the front side of the blank. Doing this moves the entire foil profile forward and gives me more machining stock on the rear side. It also meant that an area that was rough stock that was going to get milled off now needs to get filled in.
I also used my very elaborate computer overlay system where I actually lay the old rudder over the blank to triple check I have laid out the various key features correctly. In the upper section the rudder is not completely milled to the foil shape in the area between the straps and I do want to maintain the basic appearance of the rudder above the waterline. If I do this right you will never know this is a balanced rudder because the added 2-1/2" of material is all below the waterline.
Tomorrow I will trim the blank square, add my centering and elevation arms and start making a lot of sawdust. I intend to weigh this blank before I mill it, but I may have to call in a crane to get it off my bench. I suspect that the blank will lose 2/3rds of it weight in the milling step. Then it likely will gain a 3rd of that weight back when I glass it up.
Made headway today, sorted out several key details on my tooling setup. Removed the leveling bolts and just went to blocks and wedges to position the blank. That allows the sliding fixture to move past the ends of the blank. Then the next giant leap was positioning the blank such that the centerline of the foil was even with the top of my rails. To do this and get the sliding fixture to actually ride on the rails I had to hog off a bunch of waste on the blank with a power planer and also create more clearance on the bottom side of the offset rails of the jig. Then it all started to work correctly.
Here is an image from the end of today's work:
You can see the foil shape is starting to get well developed. I think I will be finishing the leading edge with a hand plane. Trying to work with the router so far over on its side is very problematic and seems unnecessary.
This blank before I started working on it weighed in at 94 lbs. The old soggy J30 rudder weighed in at 75 lbs. The sawdust in my shop is currently ankle deep and I will be dumping the shop vac first thing tomorrow before I can even start the next round of cleanup. I am really curious what this wood core is going to weigh when it has reached its final shape.
The NACA0012 foil is taking shape nicely. I'm not rushing this project and this is a slow process. I want it to have the correct shape and dimensions and that is still another day away. I have been using my power planer more than I ever have for any other project that I have done before. It is the right tool to hog a lot of material away, but it is not in the least bit precise. The router sled is accurate, but slow. I have decided that working the nose section with a hand plane and the belt sander is a good solution to getting that part of the profile sorted. Once the router bit is within about 2-1/2" of the nose the whole setup gets dicey.
Currently the width of the entire blank is now 19-1/2" and the target is 18-1/2", so that little bit of profile line you see in this image still needs to be milled away.`
Once I hit the target width I will start marking the blank up for the cuts to remove 2-1/2" to match the top part of the standard rudder and then mill the relief for the the gudgeon straps.
The basic shaping is done. Current weight of this white oak core is 69 lbs., which is better than I expected. Hard to guess what the fiberglass will add, but I will be very happy if this much larger rudder blade comes in below 80 lbs. The original rudder is a saturated 75 lbs. Next step is sorting out the area under the brackets followed by drilling and then isolating the holes for the brackets and tiller. I have started coating the very bottom of the rudder with epoxy and will take several steps to armor and seal this area. On the old rudder the bottom leading edge corner showed signs of impact and crushing and was likely the main source of water ingress. This was likely always a weak point in the glass layup because of all the corners and when it was hit it gave way. Beside the oak core being far harder than the balsa core I plan to add a couple of layers of Kevlar felt along the bottom of this rudder. This stuff is crazy strong and resists abrasion extremely well and will be the outermost layer in the laminate.
When I was working with the straps and positioning them, one thing I noticed is that there will only be about 1-1/2" of projection in front of the pivot point. The standard rudder leading edge is well back from the actual pivot point. So part of the 3" of added width is used just getting to the pivot point. In my research before building thing thing all I found were owners adding the ~ 3" amount. I would be curious to know the effects of a more modest add of the 1-1/2" would be. My goal has been to make this helm be easily manageable by my wife, so once we get on the water this summer I will advise her report.
One of the minor surprises on this project is that the original and this new NACA0012 shape are modestly different for the given chord width. One thing this difference does is make the straps that attach to the rudder happen at a slightly different part of the chord, essentially further aft. So while max section thickness is the same between the two rudders the section thickness where the straps end is less than in the original. So I have had to build up some section thickness and maintain parallel surfaces. This has taken a bit of sorting, but I think I have it now. I also have to compensate for the planned thickness of the glass, so a bit more head scratching and hopefully I will get it right.
I am planning to use one layer of 29 oz. biaxial and two layers 10 oz. cloth, not counting areas that I have already glassed over like the bottom edge and the entire top of the rudder. I think this is way more than needed for strength considering the oak core, but probably adequate for moisture intrusion. I am planning to vacuum bag this thing and that will be a first for me, so hopefully I won't end up running out of the shop screaming.
One problem I could use some help with is figuring out a method to drill the holes for these straps once I get to that point. These straps are not perfectly square to the world in the first place and trying to drill perfectly through to opposite side to hit the opposing hole accurately is going to be tricky. One idea I have is to drill a 3/16ths hole all the way through to see the first shot lines up ok, then advance to larger diameters and more or less mill the holes as needed to get a final result. If someone has a better idea I would love to hear it.
I have been doing video for this rudder build as well and once I have a minute to get through editing I will post that. This will be a multi part video that shows the details as I sorted them out, and a bunch of sorting I have done.
You are on the right track with your drilling approach. Drill smaller pilot holes to get your right angle alignment fixed. Once that is set, get some SS or glass tubing that the bolts can pass through and drill holes so you may insert the tubing in the rudder and epoxy the tubing place. That will isolate the rudder from water intrusion on the mounting hardware. You can grind the surface smooth once the epoxy cures and gelcoat over the ends.
I wanted to show what my 'regular' router bridge setup looks like. This is something I use often when milling large waney edge wood slabs. The bridge is much larger than needed for the rudder project, but its main purpose is to allow me to mill slabs that are nearly 4' wide.
I used it on the rudder to mill the area under the straps so they would be parallel.
I am trying to decide now if it would be better to drill the oversized holes for the straps now, or wait until the rudder is covered in glass. I can make a case for doing it either way. My plan to isolate these strap holes from the oak is to drill 3/4" diameter holes and follow the West method for isolating fasteners. One advantage to a solid hardwood core is that the core itself can help with loads, whereas the balsa core relies 100% on the glass at all the bearing points. On my old rudder where this was most evident was the hole for the tiller. It had been seriously wallowed out and was another source of water intrusion to the core.
The final holes for the straps will have to wait until the rudder is essentially done and I can position the rudder on the boat with everything pinned up. Without some kind of specialized fixture there are just too many variables to risk bolting this up before I can confirm the fit up.
One thing I wanted to share from this project that would have utility in a bunch of situations is using peel ply over areas of thick filler. I had been trying to fair these added blocks with a putty knife and couldn't get the sticky 404 filler to shape very well. I had some peel ply laying around and simply put it over the area I was trying to fair and the slick nylon let the putty knife easily shape the filler, I could even use my fingers to press and shape the filler. Then just pulled it off after it had cured.