Sloppy rudder

[Pete1177]

Here's another Supernova 'reliability' issue I discovered on my boat recently (at the Bowmoor Open). The rudder hole is wearing badly and looks bad - the hole is enlarged through wear and in poor shape so that the rudder has considerable play at the pivot. The hole is between 10.5mm and 13mm diameter (not exactly round). Since the pivot bolt is 8mm this does give a sloppy rudder. The consequence is that the rudder rake is a bit 'indeterminate' which can't do much for the feel of the boat (weather and lee helm). I did check the alignment of the rudder with a straight edge aligned to the stock edge and the leading edge of the rudder blade is aligned about 12mm forward of the straight edge at the rudder tip (for a bit of forward rake). Of course with the sloppiness caused by the larger hole, this won't always be true on the water.

Here are some pictures:

Pivot hole

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The second picture shows the dimensions of the hole centre - for reference (in mm)

Hole centre dimensions

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I have 2 solutions:

1. Fill the hole and re-drill with an 8mm drill - easy, but not a long term solution as it will wear again over time, or

2. Ream out the hole to a nice cylindrical shape and bush it out with a nylon bush with a hole for the pivot bolt. This would make it relatively friction-free too for uphauling and downhauling. I would need to source a nylon spacer with 25mm length and a 8.3mm hole. Although nylon spacers can be purchased, they are made to order and the minimum quantity is 175 parts - not economical for me.

So I am inclined to get a bush made with 3D printed technology. I can design this quickly, and will design in some keyway slots to stop the bush rotating. I'll order a few in case anyone else wants to do this modification. Let me know if you have this problem also.

Pete
Class Secretary
SN1177

[Pete1177]

I now have a design for a rudder bearing in Nylon 12 (grey) manufactured with 3D printing MJF (Multi Jetting Fusion) technology. I plan to ream out my rudder to 25mm at the pivot point then insert the bearing, giving an advantage of lower friction, less wear, and a more stable rudder feel (hopefully).

Here is the CAD model. The diameter is 25mm with a 25mm length (which is the width of the rudder at the stock). The hole diameter is 8mm to accommodate the 7.8mm pin. I have designed the bearing with two anti-rotation keyways which will help secure (with the possible addition of some epoxy).

Proposed design

Rudder Bush 011.JPG (19.14 KiB) Viewed 32976 times

The cost is £13 per unit as I have only ordered 3 pieces. Delivery in 2 weeks.

Watch this space!

Pete
SN1177

[Pete1177]

I now have the manufactured bearing in Nylon 12. On first inspection the 8mm hole is a bit tight for the 7.8mm bolt, but it is usual in 3D printing for holes to come out slightly undersized. It can be easily drilled out for a tolerance fit. The finish is cast grey as specified - although this isn't important as it is hidden by the stock anyway. The bearing diameter is 24.80mm and I intend to use a Forstner drill bit at 25mm. Hopefully it will be a good fit.

Time to drill out my rudder and fix in position.

Rudder pivot bearing

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Photos to follow when I have done it.

Pete
SN1177

[Pete1177]

Drilling out the rudder pivot wasn't too bad, being gelcoat over epoxy over a foam core. The Forstner bit made light work of it. The old hole was filled with Milliput epoxy putty which was left to set overnight, even though it will set hard in 3-4 hours at room temperature. The only critical bits were getting the hole centre in exactly the right position (this is where taking the measurements before helped), drilling out a small (2.5mm pilot hole), and making sure the drill was kept exactly perpendicular to the rudder plane. I managed to do it by hand using a cordless drill, but ideally you would use a bench drill with the rudder clamped appropriately.

Starting point with Forstner drill bit and Bush. Showing the old hole filled and the pilot hole drilled

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The keyway slots were easy to create using a hand file. I designed the slot widths at 4mm, which is the thickness of my hand file. The difficulty here is getting the keyways 180 degrees opposite, and also creating them exactly perpendicular. I think a redesign would just have one anti-rotation keyway to make it a lot easier, if doing it by hand. I am also wondering if the keyways are really needed as the bush is epoxied in anyway and can't go anywhere.

Drilling (halfway) before drilling from the other side

IMG_12651.JPG (27.17 KiB) Viewed 32925 times

The final stage was to epoxy in the bush (rapid set Araldite) and fill the surface with gelcoat, then sand flush with wet and dry. I wasn't too worried about the surface finish as it's hidden behind the rudder stock, but for a first attempt it's OK.

When assembled, the rudder works perfectly. No play at all. Problem solved

Completed job

IMG_12721.JPG (9.72 KiB) Viewed 32925 times

I added a rubber buffer to the stock made out of a scrap piece of Resitrix, which I have spare. This is an EPDM membrane used in flat roofing, 2.5mm thick, self adhesive. Also great for wrapping around the boom end as a protector against hitting the deck.

Pete
SN1177

[Pete1177]

Quick update - club sailing on Sunday in a fair breeze. The boat is faster upwind and more stable/predictable. Got a first place in one of the races out of 16 mixed handicap boats, which is better than I've had for a long time.

Pete
SN1177

[Pete1177]

I have decided to improve the rudder bearing and created a CAD file for a V2 bush for delivery of parts in 4 days. I have removed the 180 degree opposite keyways to make an easier retrofit to the rudder. It just needs a 25mm hole drilled to insert the bearing - now a cylindrical bush 25mm diameter, 25mm thickness with a slightly larger 8.2mm diameter hole. I have also changed the material to 'ASA' - Acrylonitrile Styrene Acrylate - a thermoplastic developed as an alternative to acrylonitrile butadiene styrene (ABS). This is better than nylon as it won't absorb water.

ASA has high outdoor weatherability; it retains gloss, colour, and mechanical properties in outdoor exposure. It has good chemical and heat resistance, high gloss, and is tough and rigid. It is used in applications requiring weatherability, e.g. outside parts of vehicles and outdoor furniture.

The bushes can be glued in if necessary with epoxy or cyanoacrylate to prevent rotation. I have ordered the parts in white - 5 of them. If anyone wants to do this mod then please let me know. The parts are £10 each including P&P - this is cost price in low quantities.

If anyone wants to see this modification, I will be at the Inlands 7th and 8th September.

Pete
SN1177

[Pete1177]

The ASA bushes arrived today taking only 3 days from ordering on Saturday. The parts are much smoother than the v1 nylon parts, and don't have keyways to make installation a lot easier. The diameter is nominally 24.75mm so should be a good sliding fit with a hole made with a 25mm Forstner drill bit. I designed the hole at 8.2mm diameter, so there should be no need for further drilling to take the 8mm pivot bolt.

Rudder bush V2 in white ASA

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The old nylon bush was a lot harder to drill out than the original epoxy rudder. Before any drilling, I marked the position of the rudder stock with a Sharpie pen. This is so that I could mark the exact centre of the hole on both sides of the rudder after the hole had been filled, using the stock as a template. I used quick drying Ronseal 2 part wood filler to fill the pivot hole - which sets off hard in about 15 minutes. You could use any rapid set filler as it's going to be drilled out anyway.

Marked out rudder

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I drilled out the exact centre with a 2mm drill bit for a pilot hole, taking great care to keep the drill perpendicular to the rudder. It's best to drill from each side. Then the 25mm Forstner bit was used to drill from each side. I then filled the old keyways with rapid set epoxy (Araldite), then when semi hard polished off any excess epoxy with acetone, after about 5 minutes. One trick I used was to epoxy the bush into the rudder, then assembled the rudder in the stock quite tight while the epoxy was setting. This ensured exact alignment. When the epoxy had stiffened up enough so that the bush couldn't move, it was disassembled for cleanup of any excess epoxy from both around the bush and the stock (with acetone).

Finally, I added gelcoat around the bush to disguise the old keyway slots, then cleaned up with wet and dry paper. Here is the finished bush which, being very hard, should last a long time.

ASA bush inserted into the rudder

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With a new epoxy rudder blade at £400, I do feel that the pivots should be bushed as standard as it's not sufficient just to drill a hole in the relatively soft cored blade and expect any longevity. Bushes would cost about 5 pounds at 50 off quantity - perhaps Hartleys should consider this as a standard fitting. I would be interested if anyone else discovers they have a very worn pivot hole.

I have 4 spare bushes left. Let me know if you want one to do this upgrade.

Pete
SN1177

[Tony1246]

Hi Pete.
I'll have one of the bushes please. I may take the opportunity to redrill the hole in a position that allows the rudder to drop down to vertical or just forward.
See you at the Inlands.

[Pete1177]

I've had the bush installed for 5 years now and there's no observable degradation of the bush. Hole diameter is 8.2mm (which is the original designed value but 3D printed creates slightly undersized holes, so original hole diameter was 8.0mm). 0.2mm wear after 5 years is pretty impressive.

Old rudders with a hole drilled in the rudder without a bush could easily be 12 or 15mm diameter as you are reliant on gelcoat + foam core holding up. Once the hole starts to open up, I think the wear gets worse more or less exponentially with time.

Pete
SN1177