Making a Composite Rudder Part One: Shaping the Foam Blank
April 2023
This footage starts mid-Atlantic. We’re three days without a port rudder, still four or five days out from land, watching the rudder angle readout and trying to keep it between two and five degrees in normal conditions. The breeze is light so we’ve got the big masthead asymmetric up, main down to reduce the tendency to oscillate on top of the waves, and Paikea is moving. The faster she goes, the more grip the remaining rudder has. So speed is our friend.
That context matters. Because everything that came next — the scavenger hunt in Antigua, the sourcing run across two islands, the build at anchor in Martinique — came directly from those days of watching a single number on a screen and knowing that the situation needed a permanent fix, not a patch.
Why We Built Rather Than Bought
We’d already ruled out finding a secondhand rudder. The wrecks we’d heard about in Antigua had been cleared by the authorities before we got there. Even if we’d found something, retrofitting a mismatched blade to Paikea’s stocks would have been nearly as much work as building from scratch — and we’d have ended up with someone else’s design on our boat instead of the right one.
Buying new wasn’t the answer either. Off-the-shelf rudders are expensive, they’re not designed for Paikea, and they’re not designed by Shayne. We’d spent four years collecting performance data across every rudder configuration Paikea had carried. We knew what worked and what didn’t. Building our own was the only option that made sense.
The carbon stocks came from C-Tech in New Zealand — Shayne designed the specification, C-Tech built them and shipped them to Antigua, where Janes Yacht Services received the package on our behalf. The cost of two carbon stocks delivered to the Caribbean was comparable to having equivalent stainless stocks made locally in the Windward Islands. Better material, better design, similar price. The foam came from Wind in Martinique. We had epoxy and enough fibreglass on board to get started.
The Foam Blank: How It Goes Together
The blade starts as foam — structural foam, glued up in sections and shaped by hand to a set of templates Shayne had made for his foil profile.
A few things worth understanding about why this works:
Structural foam takes load in shear — it’s rigid enough to hold its form and transfer loads through the blade — but it’s not a directional material. That means you can cut it, glue it back together in sections, and the bond lines don’t create structural weaknesses. The glue joint does become a hard point for shaping, but not a weak point for strength. So building the blank in three pieces, gluing them up, and then shaping the whole thing as one unit is a completely valid approach — and in the conditions we were working in, at anchor with no bench and no yard infrastructure, it’s the practical one.
The adhesive for bonding foam to foam is a cabosil aerosil mix — no structural fibres needed because the bond is foam-to-foam and the loads don’t require it. If Shayne had been bonding to a higher-strength substrate he’d have added cotton microfibre or milled fibre for additional strength. Here, the mix wants to be just thick enough to fill the gap and bond cleanly without creating an unnecessarily hard region that makes the subsequent shaping difficult.
Fitting the Stock
The carbon stock runs through the centre of the blade. Getting the hole right is the critical part — it needs to be the correct diameter, perfectly straight through the blank, and positioned accurately so the finished blade sits where it needs to relative to the hull.
The drilling operation didn’t go entirely to plan. Shayne got the first part of it done cleanly and then had to switch to a jigsaw operation to complete the run — at which point the goal becomes making a round hole of the right size from what is now an irregular cut. That’s a normal part of working without a machine shop. You adapt.
The stock itself is worth looking at closely. The wall thickness is not uniform — it’s tapered, thicker at the bearing location where the loads are highest, thinner elsewhere. That’s intentional design, not a manufacturing quirk. The tolerances are tight. There’s not a lot of margin.
One detail Shayne changed from his original intent during the build: the sectional shape of the blade. He’d started with one profile and ended up with a different one by the time the blank was done. Not a mistake — the design evolved during the build as he worked with the material. He’s happy with where it landed.
The Bearing Recess and the Hull Seal
Once the blank is on the stock, the next step before bonding is cutting the recess for the bearing in the head of the blade. This is what allows the top of the blade to sit as close as possible to the hull.
We’ve talked about the hull seal in detail elsewhere in this series — the short version is that a gap between the top of the rudder blade and the hull allows high pressure to spill over to the low pressure side, which kills lift across the upper section of the blade and moves the centre of effort in the wrong direction. Closing that gap with a proper seal keeps the full span working. It also places more load on the stock — which is exactly why the carbon stocks matter and why the wall thickness profile is designed the way it is.
Torque Transfer
The last structural detail before the blank goes together is the torque transfer tab — a small carbon laminate that runs from the stock and bonds into the blade skins. Its job is to transfer the turning moment from the stock into the blade without relying solely on the bond between the foam and the stock. Torque transfer, not load transfer — the distinction matters. The blade takes bending and shear loads through the laminate. The turning input from the tiller comes through the stock and needs a mechanical path into the skins. The carbon tab provides it.
Where This Ends
By the end of Part One, the blank is shaped, the stock is fitted, the bearing recess is cut, and the blank is bonded to the stock and ready to laminate. Part Two covers the glasswork — laying up the skins, vacuum bagging, and getting the blade to a point where it can go on the boat.
The full story of Paikea’s rudders — every version, every decision, and the design we’re working toward — is on our free cornerstone page: Paikea’s Rudders: The Full Story
For the detailed engineering behind the foil design, the ventilation analysis, and the build documentation that doesn’t belong in a public video, that’s in the Youngbarnacles members hub.