Catalina 25 Swing Keel Position Indicator System


This section describes a home made, but well tested, Catalina 25 swing keel position indicator.  This mechanism allows one to see at a glance the relative position of the swing keel.

(Insert photos and sketches of mechanism here.)

Theory of Operation 

Swing keel position is indicated by the height of a bead on a vertical line along the mast compression post.  The lower end of the line is connected to the swing keel ahead of the pivot.  The other end of the line is routed by turning blocks to inside the forward dinette seat where it is tensioned by a shock cord.

Fabrication Steps

Keel Modifications:
While the keel was removed from the boat, a groove similar to a V-pulley was added to the front of the head of the keel in an arc extending from a point tangent to a vertical line with the keel fully raised, to a point tangent to a vertical line with the keel fully lowered.  (Got all that?)  The groove was molded from reinforced epoxy resin.

At the lower end of the groove, an eye-bolt was installed in a hole tapped in the iron keel perpendicular to the pivot pin in the centerline plane of the keel.  A 1/2" stainless steel eye-bolt was used in the prototype, but an eye-bolt as small as 1/4" should work OK.

Hull Modifications:
A vertical "to-hull" style penetration was added to the front face of the head of the swing keel trunk.  This consisted of a 1" diameter piece of naval bronze pipe, threaded on the upper end, and cut at an angle on the lower end to match the shape of the keel trunk.  More specifically, the centerline of this vertical pipe is tangent to the V-groove added to the front of the keel.  The threaded top of the pipe ends just below the level of the dinette seat platform. 

The lower end of the pipe is very thoroughly fiberglassed into the front of the keel trunk using many layers of cloth and epoxy resin.  This pipe-to-keel trunk junction is below the water line.  If it ever fails, the boat sinks.  Got that?  This is a tricky step.  If you aren't 100% certain that you can pull this part off, based on proven past experience, then stop and get help. 

Attached to the threaded end of the pipe is a 1"x1/2" female bronze reducer bushing which extends upward through a hole in the seat platform just aft of the mast compression post.  Atop that reducer bushing is a 1/2" to 1/2" bonze hose barb.  Extending up from the hose barb is a section of reinforced 1/2" hose about 2' long with double hose clamps.

Turning Block Types & Locations:
There is a cheek block attached near the top of the mast compression post just below the deck. 

There is a 1/2" to 3/4" diameter hole in the top surface of the dinette seat platform just to port of the mast compression post.  Directly below that hole is a thru-deck turning block which deflects the vertical line horizontally to port. 

Just below the level of the dinette seat platform, as far outboard as practical, is another cheek block, its axle pointing fore and aft.  Its inboard mounting screw is actually a screw-eye. 

There is one more cheek block, its axle pointing fore and aft, a couple of inches below the level of the dinette seat platform, as far inboard as practical.

Line Routing:
A 1/4" Dacron double braid line is attached to the eye-bolt in the front of the keel.  This line is routed along the V-groove and up through the "to-hull" pipe and hose, and over the cheek block near the deck.  The position indicator bead is on the 1/4" line between that cheek block and the hole in the top of the seat platform.  After passing through the platform and around the thru-deck block, the 1/4" line is joined end-to-end with a stout shock cord.  This junction needs to be short and precisely located.  The shock cord is stretched around the two cheek blocks inside the seat, and is terminated at the screw-eye.

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