Rudder/Stern Thruster

Questions have been raised on what might be done to improve the handling characteristics of a Pilgrim.

 

Pilgrim rudders have sometimes been characterized as being undersized or generally inefficient.  It would also be nice to have a little more control of the stern to help spin the boat in place in tight quarters.

 

In reality we have managed to walk the Pilgrim around a stationary buoy, turning to starboard (the more difficult direction), keeping the buoy about 10 feet off our beam through judicious use of the bow thruster, throttle and shifter.  Admittedly this was done in a no wind/current condition and we were pretty hard on the gearbox and thruster so we wouldn’t want to do this on a regular basis.

We decided to gather some hard data so if we made some changes we could quantify the results.  The first order of business was to track the turning of the boat at slow speed in both directions.

 

Turning to starboard shows the boat needs about 150 feet to turn around, probably more as the stern is swinging outside the location of the GPS antenna which is mounted over the pilot house.

P1060688

A turn to port can be done in less than a circle of 90 feet in diameter.

P1060693

I know of at least two Pilgrims that have stern thrusters as shown in the pictures below.  Having spent most of my life with sailboats this arrangement doesn’t sit well with me.  It not just the drag thing, it just looks like it wants to snag something.

 

Initially we proposed the following; a Schilling rudder coupled with a stern thruster, although you might just be able to lop off the top of the Pilgrim rudder that is in the way of the thruster.  I don’t think the top of the rudder is doing much as it is out of the direct prop wash.

After studying they situation I was beginning to believe the thruster was out of the picture.  LIBERTY floats such that the static waterline is located just a few inches behind the rudder post.  This would position the thruster too high up and it would probably cavitate badly.

 

 

 

Giving this concept some more consideration (six months to dwell on it), maybe we could make it work.  We only need to get that thruster a few inches lower.  If the thruster was shimmed it is quite possible that this could be made to work assuming the reduction in area over the top of the prop is not an issue.  Maybe we could compensate by adding a few inches to the width of the rudder as shown below.

 

We sent this sketch into the Yacht Thruster people and they thought it was viable (I know, they want to sell me some hardware).  After some discussion we decided that the larger (Model 300s) would make more sense and that we would replace the two (pilot house and fly bridge) joy sticks for the Vetus bow thruster with Vetus controls that would operate both the bow and stern thruster with a boat shaped double control.  In addition a quasi-custom extension tube would be required to accommodate the shim.  They also suggested a 12v to 24v battery charger as this is a 24v system (two 12v batteries in series).  The ticket for this is just shy of $8k, for hardware alone, not including the batteries and breaker.  I did not find that excessive all things considered.

 

 

The Schilling rudder still holds some promise.  In our case the advantage in doing something about the rudder would be twofold.  The first advantage might be a decrease in the turning radius of the boat.  The second advantage would be that we could remove the prop without removing the rudder.  We carry a spare prop, compliments of the last owner.  Looking at our specific arrangement, it is difficult to see how you could get the four bladed prop off the end of the shaft without pulling the rudder.  In fact, the previous owner told me that the only way they could change props (which he did twice) was to drop the rudder.  The bottom of the rudder sits in a large casting which needs to be unbolted from the keel in order to do this.

 

We envision a rudder designed such that the fish tail portion will be able to be unbolted from the top and bottom plates and slid aft similar to what is depicted in the image below.  The green pins represent the rudder shaft, the bottom pin being the pivot in the casting.

 

 

 

 

Seeing how we are now sitting the hard for the winter, the rudder is not coming off this year (can’t ask to be picked up again) which is probably a good thing seeing how we have quite a few other projects in the queue.  It is still food for thought.

 

Months later and we are still thinking…

How about leaving the rudder alone (who cares how poorly it performs when docking if you have a thruster) and build a mini-skeg to get the Yacht Thruster down to a respectable depth below the water line?

scan0005

Bill Linscott (Sunshine, #16 ) liked the idea well enough that he had one installed in the spring of 2013.  We were in the Seattle area in June so we stopped in to sea-trial it. 

 

While Bill didn’t follow the “plan” exactly, we were impressed enough with it to order one.  Our installation should look more like the sketch with the thruster parallel to the water line and tucked up a little closer to the rudder.

Making/Mounting the Pod and Thruster:  A somewhat long winded document detailing our progress

 

 

Return to Prior Web Page