3D Printed Catamaran Rudder!

I need a project to keep me busy over the winter and so I invested in a 3D printer. I have an ambitious first project: a rudder. We damaged one of our rudders in Sardinia last year. At that time we were able to get a new one shipped from Nautitech in France. I kept the old rudder stock with the thought of rebuilding a spare one day. That day has arrived!

The rudder is quite large, the foil is about 1.1m long by 0.5m wide. The conventional way to build a rudder is to first build a mold and then use the mold to fabricate two clam shells that were then glued together around the stock. I found out that Nautitech rudders are built by Jefa in Denmark, they show their build process here. Of course with the Orca's taking out rudders in a daily basis here in Portugal this is a very appropriate project.

Others build rudders by shaping foam either manually or on a CNC, then skinning them in fibreglass. My plan is to 3D print the core and then skin that in fibreglass. The core provides no structural role; it is simply there to form a scaffold to provide the shape for skinning with fibreglass. In order to match conventional methods, I would also like to foam fill the shell. This will give it more structural integrity and also prevent damage due to water getting into the rudder and freezing. The foam will allow for expansion during freezing. My Method I created a little tool to capture the rudder outline from a accurate image of the rudder.

From this I created a 3D model of the rudder foil with a NACA aerofoil shape. I also created a 3D model of the rudder stock which was used to cut out a void in the rudder foil. The foil is then split in half and chopped up into printable sized pieces (320mm maximum). These can be printed and dry fitted around the stock. If all is well, they can be foam filled and then glued in place. Then they get a fibreglass skin and gelcoat.

This is half the foil showing the cutout for the stock.

I've printed out the first section and it fits perfectly around the stock. I am very impressed with the quality of the prints from my Bambu Labs H2D printer. I left some slots to allow the two halves to be secured to the tines.

My next step is going to be to foam fill this segment. I'm not yet sure if the 3D printed plastic will be able to stand up to the expansion temperatures and pressures of the foam. The alternative will be to foam fill the entire rudder from the top once it has been skinned. I took the first pieces to Slick Hulls Chandlery in Portimão to find the foam filler. Vasile was very helpful and showed me the foam they use, it is a high density epoxy expanding foam (quite different from regular construction foam). It is expensive and comes in large containers, but Vasile was interested in the project and volunteered to try it himself, testing the foam fill and how well the epoxied fibreglass will adhere to the plastic. This sample was printed with PETG-Carbon Fibre. This is the best choice for marine applications as ithe resin will adhere well to it and it has similar thermal expansion characteristics to fibreglass.