by Tommy Yonley
Part 1: Prepare Boat for Overstern Rudder Assembly
1. Drill a vertical 5/16" hole roughly 1 to 1.5 inches from the tip of the stern. The hole needs to be deep enough such that it almost gets to the bottom of the surfski. Drill very slowly and periodically measure the depth frequently to ensure that you do not go through the hull (it is easy to do)! Check that the hole is the right size for a snug fit on a 5/16” bolt.
2. Odds are, the end of the boat is somewhat hollow, to the degree that the hole that you just drilled is not air tight. To check, put your mouth up to the hole and suck in some air. If the hole does not maintain suction, it is not air tight. If the hole is air tight (and the end of the boat is filled with epoxy), skip to step 5.
3. Get the inside of the boat dry such that moisture inside will not prevent the epoxy from bonding with boat. Use Xylene to clean out hole in stern. Use a hair dryer on the hole to ensure that it is dry.
4. Find a tree with branches such that it is easy to rest your boat vertically onto the tree with the bow pointing to the sky. Initially, set your boat at an angle such that the bow is up at a roughly a 35 degree angle—for a 21 ft boat, the tip of the bow should be ~12 ft. higher than the tip of the stern. Mix some 100% solids epoxy—the thinner the better. I used “Low V” from www.EpoxyProducts.com and would definitely recommend this resin. Pour mixed resin into the 5/16” hole. Fill up the tip of the stern with epoxy until the level of the epoxy is almost to the top of the hole. Place tape over the hole. Set the boat perfectly vertical onto the tree, strap the boat to the tree, and let the boat remain vertical until the epoxy has cured. To protect the boat from getting scratched by the tree, leave your boat cover on the boat (except for the extreme stern).
5. Take the boat out of the tree and re drill the hole from step 1 ensuring that the new hole provides a very snug fit on the 5/16” bolt. Check that hole is perfectly air tight per step
Note: If the hole is not air tight, you will need to re-apply epoxy and re-drill the hole. If there is even a tiny leak in this hole, you will regret it—trust me.
Part 2: Build the Rudder Assembly
1. Get a ~6" (maybe longer depending on your boat) stainless steel bolt, 5/16" diameter to use as a hinge. Cut off the head of the bolt, leaving the threaded end alone.
2. Get some aluminum angle. .125" thick, 6061-T6, 2"x2" available at onlinemetals.com
Cut two pieces of the aluminum angle to look like the pictures, they should be roughly 5” to 6” long. Depending on how far from the tip of the stern the pivot hole is, you may want to fine tune the length.
3. Get some spacer material that is slightly over 5/16" thick. I used “UHMW SHEET/PLATE - NATURAL (VIRGIN) 0.375" UHMW SHEET – NATURAL” from www.onlinemetals.com . You will need a piece of spacer material that is roughly 2.5"x2".
4. Clamp the 2”x2.5” piece of spacer material between the two pieces of angle and drill 4 holes near the corners and insert 10-24 stainless machine screws (<1 inch long). Tighten nylon locking nuts onto the bolts.
5. Drill a hole 5/16” hole vertically through the spacer. Insert the 5/16” bolt and ensure a fairly snug fit that still allows the bolt to easily rotate.
6. Cut a strip of 6061 aluminum plate ~1.5”x6” to attach to the bottom of the assembly. Drill a hole through the center and use the bolt to line it up. Use rivets or machine screws to attach the plate to the aluminum angle.
7. Cut the desired rudder shape from 6061 aluminum. I have been happy with the strength of my “general purpose flatwater” rudder which is .065” thick. However, if you expect extreme abuse, you might want to go for .08” thick.
8. Use a 1/4” machine screw (with nylon locking nut) to secure rudder to assembly. Obviously, drill the hole a bit larger to allow the rudder to rotate easily.
9. You will need 2” washers to space the rudder properly within the assembly—nylon washers are ideal, but you could also use aluminum, stainless, or perhaps Teflon or UHMW sheet. You have to be careful to get the spacing exactly right so that the rudder can easily rotate, but is still reasonably snug fitting.
10. Drill holes to attach rudder cables to the housing. For subtle steering, holes should be further toward the ends of the “wings”. For more aggressive steering (or less foot movement to get the same rudder action), the holes should be closer to the central hinge bolt. Having the holes somewhere around 2” from the hinge is likely a reasonable starting point. The plate on the bottom allows larger spacing of the ruder cable attachment.
11. Attach rudder cable to assembly. If you want to be able to switch back and forth from overstern to understern, Huki has special parts to accommodate this.
12. Test out rudder. It should be functional at this point with the rudder easily rotating on the hinge bolt.
13. Trim the hinge bolt such that it is the correct length assuming that there are ~1/4” worth of washers between the boat and the bottom of the assembly. There should be 1/2” worth of threads visible on top.
Part 3: Securing Hinge Bolt to Boat via Pin
1. Drill a small ~1/16” hole into the top of the stern at a ~45 degree angle to the deck such that the hole intersects the vertical 5/16” hinge hole a bit more than 1 inch below the top of the deck. The small hole should start a bit over an inch stern-ward from the edge of the hinge hole.
2. Insert hinge bolt into hinge bolt hole. Re drill 1/16” hole such that drill bit marks the hinge bolt.
3. Drill hole through the center of hinge bolt at 45 degree angle according to marking from previous step. It is possible to do this on the boat, but it is difficult—instead, take the bolt out of the boat and drill with bolt held securely in a vice. It is easier to start the hole in the bolt if you use a grinder to create a flat spot on the surface of the bolt. It is easier to drill through the bolt if you use some oil in the hole as you drill.
4. Once you have a hole through the bolt, put the bolt back into the boat and use drill bit to ensure that hole in boat and hole in drill are lined up. Then drill a bit more such that the 45 degree hole extends through the bolt and ~1/4” to 1/2” into the hardened resin on the other side. You need to re-check that these holes are air tight by taping over the 1/16” hole and testing the 5/16” hole for maintaining suction.
5. For the pin, use a piece of somewhat flexible solid metal wire. I used a piece of clothes line wire (strip off the green plastic coating), but this is not stainless and bends easily so it needs to be replaced every once in a while (depending on how often you swap out your rudders). Fully insert pin into the hole through the hinge bolt and to the other side in order to securely lock in the hinge bolt. Above the surface of the deck, bend the pin around the hinge bolt so that the pin can not fall out.
6. Place large nylon washer onto bolt such that the washer rests on top of the bent pin. Place rudder assembly onto hinge bolt on top of washer. Gently tighten nut onto bolt such that the rudder assembly freely rotates on the hinge bolt. If you over-tighten the nut, you can bend the pin inside the boat, making removal difficult. When the rudder assembly is tightened onto the bolt, the outside portion of the pin will be secure, between the washer and the deck.