Cassette time!

 It was time to be brave and cut out the bottom of the boat.  A couple of posts ago, I set up a jig and drilled the rudder shaft holes through the bottom of the boat and the cockpit sole.  Now, we basically formed the basis of the rudder cassette and cut it out of the boat.  we did the starboard one only so far to insure it all worked.

This first picture shows the layout of the bottom of the cassette.  It is about an inch bigger fore and aft than the eventual rudder will be.  The width was just conveniently set to have the cassette large enough to work with. 

The rectangular shape was laid out and the four 1/2" holes were drilled  1/2" in from the corners.  The second picture is the same layout in the cockpit.  Except that the rectangle is 1/2" larger on all sides. 

The dowels line up the tops and bottom of the cassette and lock them into place.  The 1/2" wood size was chosen as it is readily available and is stiff enough to hold up. 

Our dowels are 36" long, so we just mixed up some 5 minute epoxy and glued them on place.  A little reaming is most likely needed to get them all to line up.  They need to fit tightly, however.

Once the glue sets, you can just zip off the extra length.


You can see that the four dowels converge.  This is because we are really making a wedge shaped cassette.  It will then self center and fit tighter.

 The hardest part is that first cut.  We used a cut off blade in a 4" angle grinder.  It smoked a bit but was easy to control.  The corners had to be finished off with the old time hand saw.

 This picture just shows the machine cuts made and ready for the corners.

I cut the top first, which I think now was backwards.  I had to support the cassette when I cut the bottom so it didn't fall on my face.

 Once done, we now had this large rectangular hole right through the boat!

 The dowel idea worked as well as I had hoped.  The result is a stiff framework from which we will build the actual cassette.  The plan is to install a flanged bushing in the bottom and then make an aluminum plate for the top that is larger that the cockpit section on the cassette to act as a flange. Another flanged bushing will be installed onto the aluminum plate.  Then a PVC tube will be glassed in between the bushings to provide the actual sealed area for the rudder shaft.

 After that, the outer cassette will be fabricated over the wood framework and glassed.  It will be finished and then the work on the well in the boat will begin.  This is to insure that the cassette will fit at all and fit tightly.

This technique could be used for a single centered rudder as well.  Chris Beckwith's circular bearing type "vara" rudder cassette is a bit different and he should be putting that up on his blog soon.

 This shot really shows how much it is wedge shaped.


I had a similar shaped cassette on my SR25 but is was not wedge shaped a somewhat awkward all metal framework. I am hoping that with careful fitting, the wedge idea really works as the alignment on the twin rudders is much more critical.

 The mock-up rudder installed with the shaft.  The actual rudders, it has been decided, will be carbon over foam and will be somewhat larger and longer than the one shown.

The vise grips are about the location of the clamp on aluminum arms that need to be fabricated.  They will be clamp on to allow for those adjustments that will be key to getting the twin rudders to perform properly.

To be honest, sometime I wonder why we do these things to ourselves.  The extra time to build these rudders may very well be equal to the time it would take to finish this boat with the standard rudders.

But they are kind of cool and this is the fun part of the i550 experience - coming up with new ideas and working out the ways to make those ideas work.

Next up is the port cassette and we should be building rudders next after that.