Copernicus Rudder

BOAT REPAIRS & MODIFICATIONS

New Rudder for Copernicus

Here is another example in which SYDI has done a second project for the same boat. Copernicus, as you can see over in the Free-standing Masts/Copernicus article on this website, was changed from a stayed rig to a free-standing rig, a project that was quite successful. Next, owners Bryan and Carey Pollock wanted to change the rudder from the original behind-the-keel design to a new spade design.

Fig. 1. To begin the new rudder design for Copernicus, I started with my drawing of the rig design that I did some years ago.

Copernicus is an old CCA rule design with a full-length keel and attached rudder, as shown above. Bryan and Carey wanted more steering authority and performance, so they came to SYDI for a new spade rudder design with carbon fiber blade and stock. The boat had a retro-fitted hydraulic wheel steering system, and the new rudder was to go back to a tiller design. Originally, Bryan and Carey wanted to build the rudder themselves, but ultimately they chose Composite Solutions Inc. of Hingham, MA, to build the new rudder, complete with bearings, and Bryan and Carey did the installation work. What follows is the story of how we accomplished this new rudder design.

Fig. 2. In Copernicus' cockpit, the existing steering pedestal base is at the upper right in front of the box seat. Behind the seat is the existing rudder stock head with the old tiller attachment. The new rudder stock head is to come up through the aft seat, mid-lower-left, between the traveler and the seat front.

The existing rudder steered the boat OK, but there were control issues, particularly in gusty conditions, which left Bryan and Carey with a feeling of not-total control. Also, because of the inclined rudder stock, the more one pulled on the tiller, the harder is was to steer--turning a rudder with an inclined rudder always tries to pull the stern underwater. Moving the rudder aft and making the stock vertical so that there is no downward component would make steering easier and give it more authority, more efficiency.

The area of the rudder should be approximately the same as the existing rudder to guarantee enough steering power. An argument could be made the make the rudder smaller, but we decided to err on the side of caution--we did not want to make a rudder too small and then later have to buy a second larger one. We also knew that the new spade rudder had to have a shallower draft than the keel to keep it protected from grounding. Finally, the tip should be more rounded on the lower leading edge to minimize the tip vortex. So all these things governed the overall shape and size of the rudder planform area.

Fig. 3. Copernicus' new spade rudder profile. Note that the 1/4-chord line is just aft of the stock centerline at the root of the blade. The stock centerline is at the 18% chord position.

Of course, aerofoil section thickness is important, too, for low profile drag, but the rudder stock has to fit inside the blade and be strong and stiff enough. Starting with a 14% modified GA(W) aerofoil section, a couple of iterations around the design spiral checking for strength and stiffness led me to settle on a 20% thickness section. This is not unusual. The GA(W) sections have what is known as a "drag bucket", which is a region of pronounced low drag at zero to small angles of attack. Interestingly, as the aerofoil section gets wider, the drag bucket also gets wider at slightly higher angles of attack. Also, thin aerofoils will stall at lower angles of attack than thicker aerofoils, and rudders frequently operate at large angles of attack. So, I like thick aerofoil sections for these reasons, and the figure below shows Copernicus' new rudder section shape.

Fig. 4. Copernicus' 20% modified GA(W) aerofoil section shape and proportions.

Once these basics were done, I proceed with engineering the blade and stock carbon fiber laminates. I have to know what carbon fabrics, resin, and molding process are going to be used in order to assess the strength and stiffness of the finished parts through my laminate engineering. I typically check equally spaced and critical stations from the top of the stock to the tip of the blade in order to determine laminate thicknesses. Once I am satisfied with these numbers, I then have to convert the thicknesses to an actual laminate schedule that is compatible with the builder's molding and fabrication process. This whole work is done using a spreadsheet for engineering and hand calculations that end up in a graphic representation in an AutoCad drawing. The figure below is an excerpt showing the arrangement of the stock sections, their varying shape, position, and thickness, and the associated laminate schedule for the stock from the rudder construction drawing.

Fig. 5. The laminate schedule layout for Copernicus' carbon fiber and foam rudder stock which is glued inside the carbon fiber and foam rudder blade. The foam is 5-lb/cu.ft. (min.) Core-Cell foam.

Once the drawings were done, they were sent to a selection of builders, and the owners ultimately chose Composite Solutions of Hingham, MA. The Pollocks arranged the contract separately, and I remained in contact with Composite Solutions to work out additional construction details. Our original thought was to use neck and carrier bearings from Tides Marine in Florida, but Composite Solutions had used Danish Jeffa bearings successfully before. We deferred to their choice which has worked out well. The completed rudder was shipped to the Pollocks needing only the final primer and painting of anti-fouling paint to match Copernicus' bottom.

Fig. 6. Copernicus' new rudder as delivered, simply gorgeous! The stainless steel bearing sleeves were made from standard-size tubes, polished to a high sheen, and glued onto the stock. The top of the stock was to be finished by the Pollocks for the stainless steel rudder head and tiller that they had made separately.

Fig. 7. A dry fit of Copernicus' new rudder. Note the old rudder still in place to the right, and the Hydrovane self-steering rudder to the left. The boat's original rudder had to be cut out and the space it occupied filled in. See the next three photos.

Figs. 8, 9, & 10. (L) The rudder and upper bustle are removed; (M) The original keel trailing edge is filled in and faired; (R) And the new neck bearing tube is built and the rudder slipped into place for a dry fit.

Fig. 11. Copernicus' cockpit and rudder finished, repainted, and sailing. Note particularly the stainless steel rudder head and tiller, and the layered reinforcement on the cockpit aft seat to support the rudder weight and steering loads. The Pollocks took care of those details themselves.

The entire project was a great success. It is perhaps fitting that I quote Bryan Pollock in one of his emails reporting on Copernicus' performance:

From Bryan: Needless to say sailing qualities have of course improved. Things such as boat speed at all wind strengths, tacking on a dime are noticeably improved. At higher wind speeds and wave heights the boat is nowhere near that old feeling of being slightly out of control at nine or ten knots boat speed as it did before with the old contraption. Light air was a revelation. We completely baffled a Jeanneau 45 in the light stuff (2 to 5 knots) upwind. I have to admit even if I do say so myself that I can usually make good tactical choices in those conditions, so a lot of that particular trouncing may have been that as opposed to any qualities the boat may possess.

And:

Maneuvering in tight quarters under power as long as we are in forward is a real treat. What a notion, actually knowing by feel where the rudder angle is and what it is affecting instantaneously as opposed to the old time delay with the contraption we had before. Backing up is a whole other story, however. It is absolutely horrible. There is every indication that what ever direction the boat decides to take is entirely based on the whim of a lesser and obviously bitter pagan god, who, I might add, really should have better things to do. Tentative tests (remember all this testing under power involves expensive marinas and boats in the near vicinity) seem to suggest that keeping the main rudder straight and instead using the Hydrovane rudder to steer backwards is showing a bit more promise. I will have to rig a tiller extension on the Hydrovane to make more accurate experiments.

The finished glass thickness on the bottom bearing tube follows Jeffa rudder specs on glasswork. Perhaps a bit more in finished thickness, maybe five-eighths of an inch thick as opposed to one centimetre in the specs. My estimate for weight removed out of the aft end of the boat was originally about two hundred pounds, but that stern is really out there now so maybe three hundred pounds. All I know is that I spend an inordinate amount of time moving weight around looking for some way to shave weight out of the bow to get the boat back to its original trim. Looks like I'll have to revisit the idea of somehow moving the anchor chain locker one locker aft (about three feet). We also haven't done a purge of stuff on the boat for ten years so doing that might help. We used to be really good about purging junk and weight every year, I don't know why we stopped. At any rate we will be forced to do that by next spring as we will be heading to Central America next summer.

Fig. 12. Copernicus in her final dress.

The success of designing, building, and fitting Copernicus' new rudder was due to a number of things, but most importantly, I think, to Bryan and Carey's realistic expectation of budget ($4,000 for design, and just under $12,000 for the rudder itself, not to mention painting of the cockpit and bottom, yard bills, and the cost of their own labor). I also give just praise of the quality of workmanship to Composite Solutions Inc. They were not the cheapest builder by any means, but you get what you pay for. They have excellent building skills and working with them is a joy. You can reach them at their website here: Composite Solutions Inc..

If you have a similar project and would like SYDI to do the design work, I would be happy to hear from you, and you may use the Contact Us link below.