Spade rudder build with limited equipment

Hello All,

I purchased a 1972 Ancom 23 last summer for next to nothing from a motivated seller. He had definitely neglected the boat for the couple of years he was sailing. When I purchased the boat it had a spade rudder fabricated out of sheet aluminum, nicely welded then bolted to a narrowed stainless shaft.



I was out about 4 days with the boat and each time the rudder would vibrate at any speed over a few knots. I assumed it was just a bad design as it was clearly not original. I moored the boat one night after single handing it and came back the next day to install some new bits. I give the tiller a push to find it was very loose. Thinking that the tiller hinge has sheared its pin I pulled up on the whole assembly. Much to my joy the rudder shaft came with the tiller and I found she had snapped off her rudder at the first bolt hole. Clearly not the best design.



So I decided to build my own. I am no expert by any standard and I didn't want to invest in vacuum bagging equipment. Here's how it went.

I researched some common rudder designs and sketched out what i wanted to scale on a piece of graph paper. Using this I calculated the size of stainless steel rod i needed to have welded. A local fabricator took care of this for me.



While the skeleton was being welded, I purchased some off cuts of Core Cell from www.noahsmarine.com. This was 1" thick. Basing my design around the NACA 0012 foil shape I determined the over all thickness over 1.5". I printed out the foil shape for different lengths down the rudder. By this I mean I printed one for 14" (widest point), 13", etc, down to 10" then 8" and 6". I traced these onto some 1/16" plastic sheeting and cut them out. I would use these for two purposes. One, to determine where on the rudder the thickness would be 1" thick (so I wouldn't add extra material there). Second to use as a guide when shaping the foam.

NACA 0012 foil shape

Knowing my stainless rod was 1" think, I traced out the rudder shape on two chucks of structural foam, one for the front and one the back. I used the foil templates to determine where on the steel rods i would have to taper down to keep the shape. This took way to long with an angle grinder and a ton of cut off discs. Once this was done, I used a 1" spade drill and cored out the location for these rods in the rear foam. I was fairly happy with this result after a little tweaking to deal with some slight off angles. The steel was roughed up, cleaned with acetone and West System epoxy with Colloidal Silica was used to attach them together and fill the voids.




After this had cured, I determined where the rudder was only 1" thick and marked the location. First I laid strips of wetted fiberglass around the steel webbing to reinforce and fill the void. This was followed by a sheet to cover and help distribute the forces from the webbing over the next layer of foam. I epoxied 1/2" strips in the area thicker than 1". I then proceeded to shape the rudder with an angle grinder with a course sanding disc attached. All the time, I was constantly checking the shape with my foil template negatives (seen the background).



Once happy with one side, I turned the rudder over and repeated the same process on the other. I filled and shaped the voids with a Colloidal Silica thickened Epoxy, and quickly rough sanded it when I was done.



Fiberglass time. I laid a sheet over the leading edge of the rudder, allowing it to cover both sides. I used 4 sheets in total, each covering both sides. I trimmed around the trailing edge leaving about an inch of over hang. I split the fiberglass on the lower curvature on the leading edge and removed any excess fabric over an inch. I with i had cut up a bit further as I found it hard to fold this excess in. Using the slow curing hardener, I carefully wetted out each sheet of fiberglass, leaving the other half on the opposite side. Once the side was complete, I started on the other side. The excess on the top and lower leading edge curvature was laid left and right, over lapping in these area making it 8 layers thick.



I just ran out of epoxy and it started to kick as I finished the final touches. I clamped strips of smooth 1/8 thick plastic on the trailing edge to keep it straight while curing.



I sanded off any imperfections and covered the rudder with epoxy and fairing filler. Sanded again, followed by a gel coat applied by a friend with a gel coat gun.




I cured the gel coat with some work lamps and made a new bushing with an old cutting board and a hole saw.



After installing the rudder, my steering performance has improved greatly. The vibration is gone, the stall speed reduced and stall angle has increased. The added 10-15% surface ahead of the rudder shaft and lightened the tiller without loosing too much feel.

Improvements: I was on a limited budget but I wish I have purchased one or two more layers of fiberglass and resin. Also, I thought about reinforcing the leading edge with kevlar (more off cut were available from Noah's Marine). This past summer the St. Lawrence was quite low. I smacked into a few good rocks but there was only minor damage to the rudder.



Overall I'm very happy with the result. Overall cost, approx $300 CDN.

 

yeah iv used the naca 0012 a few times not only on Yachts but also on 36 foot power boats and its a really good foil shape 15% FOR THE LEADING EDGE is cool be careful not to over do it or it can take control!!. when you let the wheel go it should want to pull back straight ahead . if it doesnt move then you have a problem need to knock some of the leading edge off more towards the lower end of the blade than the upper !!

 

nice work. A few comments, you should make the top edge square and the gap between the top of the rudder blade and the hull as small as possible.

Also, if you need more feel or it to come back to center faster, rather than shaving off the LE as tunnels suggested, it would easier to just add some more length at the trailing edge. The LE is the most important shape on the profile and you want to maintain as much accuracy as you can at the LE.

 

Dosent make that much differance the gap at the top !! Its all just old wives tales . if you get the blade straight ,true and fair as possible and spend some time on it , it all pays off at the end of the day!
My boss had a small 26 foot boat and the tiller was two man in a blow ! so took it out and made a complete new blade with foil and a leading edge past the line of the pivots !!
After the differant woods were laminated together i spent 4 days days plaining and sanding to get it right then 6 coats of polyurethan .
The first time out he could not believe it was the same boat was one handed and relaxing no strain and pulling hard till the tiller handle had a bend in it and even his 12 year old could use the tiller and steer the boat .
Was a stern hung rudder so was really easy to fit the blade into the stainless fittings and bolt up tight and directly replaced the original just made differantly .

 

Tunnels you know this isn't true and testing has shown this repeatedly. The hull acts as an end plate, if the gap is tight, preventing pressure bleed off.

 

And how many times do you see a boat hard on the wind with its nose buried in the water and the top of the rudder completely out of the water .

Its as bad as that post about sanding centre boards and rudders !! at the end of the day its the sailor that makes the differance and if he got a little more puff than the others !!.

 

I'm not sure what design this is, but the rudder is well "tucked", so likely will remain fully immersed. It's true most sailors wouldn't notice the difference, but this isn't a comment about filling the effectiveness of the rudder/hull gap, but a testament to the skills of the average sailor. Placed side by side with another, similar equipped boat, the tight gap version will so the advantage clearly.

 

Thanks for the input everyone. The rudder is well tucked and stays under unless she's really knocked down.

Unfortunately I wasn't able to pull the boat out while mocking up the new shape. I determined the angle between the hull and rudder shaft tube as best i could with a piece of paper, folding it to match. Mostly by luck, I was able to get the top edge square and within a centimeter gap of the hull.

I'm quite happy with the balance of the new design. Just enough feel while light enough to still be able to handle with the edge of my foot (while single handing).

 

Well done, that is all I can say.