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
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
the lower vertical pieces that formed the sidewalls of the foot
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
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
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