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South Coast Sailboats

6 hp to 25 hp motor upgrade

Well what can I say? This was the single biggest upgrade I have made to the boat so far. In order to pull this upgrade off, several different things had to come together at the same time (rebuild the cotpit, replace the cotpit floor, remove the old transom, enlarge the tunnel, and rebuild the new transom, install a new floor). Ten years after creating the motor tunnel for the six hp motor, I later had to cut out the front of the tunnel to lengthen an additional 6 to 8" in order to accept the larger 25 hp motor. I combined several tasks into one to make this happen. While I was rebuilding the tunnel, I had to replace the transom that had worn out from ten years of use (it was getting old and the wood had split. I would not be able to use this for the new motor). The new transom also formed the front of the extended tunnel for the motor to drop into. Additionally, when I designed this new setup, I tied it in to the wood used to create the new cotpit. This all came together very well, but was a big project that required some advanced carpentry and fiberglass work.

Gutting the old cotpit

Rotted cotpit floor removed - I simply cut out the old floor back to the point where it was flush with the sidewalls. I did not remove any of the deck forward of the flip up cotpit floor, but I did cut out the back to where the new transom would be installed. At the same time I also cut out and removed all of the structural plywood under the cotpit seats (this was all completely rotted out).
Removed the existing transom that was installed when the original tunnel was installed. The wood was shot, although I can honestly tell you that this put up a really good fight. All the hardware that was used to bolt it in was rusted through and had to be cut out, one bolt at a time.
Cut out the front of the existing tunnel to allow for expansion.
Cut out more floor and hull to allow for the bigger motor

New cotpit laid out and installed

Structural ribs were cut and glassed to the inner hull
The upper part of the vertical side wells were slotted and installed to receive
the lower vertical pieces that formed the sidewalls of the foot well
The new sides of the cotpit foot well were laid out cut and installed.
Two steps leading up to the hatchway were installed (removable so that you could get to the bilge pump and float switch) from the upper side of the inner hull to the base of the hatchway.
The new transom and front wall of the tunnel were installed.
Additional sidepieces installed in the tunnel to close up the openings
Tunnel sides were then glassed in to make it water tight
New removable floor grate was installed.
New transom was then adapted to accept the 25 hp motor to accept 6 or 25 hp motor
Cotpit overhaul also included cedar decking panels built and dropped in over the seating, and heavily padded vinyl cushioned seat backs were installed against the cotpit walls

Click on a picture to see a larger picture

Just a note on the performance issue.

I haven't had too much experience with the 25hp motor yet because of motor problems I was experiencing when I first set this up. The motor had been under water, which involved several trips to the shop to get it fixed. I finally got that straightened out by the very end of the season (of the big rebuild), so of course I had to take the kickback out for a test drive. What a ride. If my SC22 didn't have a very large keel trunk under the boat (the entire keel is mounted under the boat. there is not one bit of the original keel trunk in the cabin.) I feel that this boat would definitely plane. But under existing conditions with the keel trunk under the boat here is the deal.
This thing really jams, and I love it.

I used to use a 6 hp Johnson (tunnel mounted in the back of the cotpit), I will only use the old motor to get into local lakes that have a 9.9 hp limit. With the 25 hp motor and the keel trunk below, the boat cannot plane, but it plows thought the water like no other sailboat I have ever been on. A conservative estimate on speed might be 8-10 knots (maybe more!), with out a doubt in my mind, we are definitely exceeding the design hull speed. Like I said, this thing really jams! The bow rides very high and the stern rides pretty deep. The boat creates a good size bow wave and creates an overly large stern wake, probably because the tail rides so deep. Believe me it is a piss. The stability is actually much better than I had expected. I feel this has a lot to do with the oversized rudder (previously mentioned). I use a tiller tamer for my own convenience when sailing and when under power. I can just set the tiller, and cover 300-500 yards with out any correction. Note that is not under full power. At 2/3rds throttle everything is very smooth. My best estimate of speed at this level of power is 2 to 3 times the full speed of my previous motor. When you go to full throttle, she really honkers down and that is when she wants to pull off to one side or another. Even thought she want to veer off under full power, this is still very controllable

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