About 8 years ago my Johnson 9.9 two-stroke died. I wanted to replace it with a cleaner and four-stroke, but they were all way too big for the C27 transom mount so I had the Johnson re-built. Now it has died again and I still want a 4-stroke, but it must fit properly as intended by Catalina. I looked at the 10 HP 4-strokes and found that Honda and Tohatsu are still way too big. But the Yamaha 9.9 is smaller because it uses the same head as their 8HP. I measured carefully and decided the Yamaha 9.9 could/would fit, but the transom must be modified. I’ve seen some questionable C27 modifications and wanted my installation to be clean (no hatch or deck modifications). I was able to make the modifications and install the Yamaha 9.9 in my slip.
Using the back corner of the transom mount as reference, the pivot point on the Yamaha mounting bracket was in about the same location as my Johnson. But the lifting handle on the Yamaha is about 2 inches higher than my Johnson, and I only had 3/4 inch clearance through the hatch. To avoid modifying the deck or hatch, I decided to lower the transom mount 1 3/4 inches. I also had to widen the opening at the bottom by 1 1/2 inches (3/4 inches on each side). I used a hole saw and a reciprocating saw to do this. Rigid makes a nice one-handed reciprocating saw so you can use your other hand to vacuum up saw dust (marinas are fussy about pollution and you can get a ticket).
I first marked a horizontal line 1.75 inches below the existing transom (on the outside). Then I marked a vertical line coming down from the existing upper corner radius on both sides to intersect the horizontal line (0.75 inches outside the existing hole on each side). This marks the basic opening, but you will want to cut a nice radius for each corner. I used a hole saw to cut out the corners of the new transom (the radius just intersects with the vertical and horizontal lines). My hole saw would not go all the way through because the transom is too thick, but it still gave me a nice round corner to meet up with when cutting the sides with the reciprocating saw.
I cleaned up my cuts with an orbital sander and a file before filling and fairing with West epoxy. The C27 has a wooden stiffener in the fiberglass around the hole for the outboard. You have to cut this to make the hole larger. I called Catalina about this and they told me it was OK to cut it, but I should re-enforce the opening with fiberglass to keep it stiff. I’m not sure this was really necessary because I didn’t remove the stiffener completely. But just to be safe, I added fiberglass inside the bottom of the transom when I filled it with West epoxy. I wrapped the fiberglass cloth inside and down to make a hard corner on the inside of the transom, and up each side to connect with the wooden stiffener. After several layers of West epoxy and sanding, the transom was waterproof and stiff. I scrubbed the inside of the engine compartment and painted it with 2-part white epoxy paint. Then I painted the hole edges with blue LP paint to match my hull. It came out looking professional - you can’t tell that the transom was modified.
But if you want this to be really nice, you need an external control box to easily control the throttle when maneuvering. I purchased the Yamaha 703 control box with the 2013 Yamaha 9.9 LEB model – this is all electric with electric choke. It is very cool to just insert the key and start the outboard from inside your cockpit like an inboard. This motor does not even come with a pull start, but you can start it manually if you remove the cover. The real kick is how quiet this motor is. You cannot hear it when it is idling! When motoring around the harbor, the splash of the coolant from the pee-hole is about as loud as the motor! I love the Yamaha and I am very pleased with my transom modifications. Check out the pic’s. Good luck if you try this – measure carefully - it fits! Happy sailing!
Using the back corner of the transom mount as reference, the pivot point on the Yamaha mounting bracket was in about the same location as my Johnson. But the lifting handle on the Yamaha is about 2 inches higher than my Johnson, and I only had 3/4 inch clearance through the hatch. To avoid modifying the deck or hatch, I decided to lower the transom mount 1 3/4 inches. I also had to widen the opening at the bottom by 1 1/2 inches (3/4 inches on each side). I used a hole saw and a reciprocating saw to do this. Rigid makes a nice one-handed reciprocating saw so you can use your other hand to vacuum up saw dust (marinas are fussy about pollution and you can get a ticket).
I first marked a horizontal line 1.75 inches below the existing transom (on the outside). Then I marked a vertical line coming down from the existing upper corner radius on both sides to intersect the horizontal line (0.75 inches outside the existing hole on each side). This marks the basic opening, but you will want to cut a nice radius for each corner. I used a hole saw to cut out the corners of the new transom (the radius just intersects with the vertical and horizontal lines). My hole saw would not go all the way through because the transom is too thick, but it still gave me a nice round corner to meet up with when cutting the sides with the reciprocating saw.
I cleaned up my cuts with an orbital sander and a file before filling and fairing with West epoxy. The C27 has a wooden stiffener in the fiberglass around the hole for the outboard. You have to cut this to make the hole larger. I called Catalina about this and they told me it was OK to cut it, but I should re-enforce the opening with fiberglass to keep it stiff. I’m not sure this was really necessary because I didn’t remove the stiffener completely. But just to be safe, I added fiberglass inside the bottom of the transom when I filled it with West epoxy. I wrapped the fiberglass cloth inside and down to make a hard corner on the inside of the transom, and up each side to connect with the wooden stiffener. After several layers of West epoxy and sanding, the transom was waterproof and stiff. I scrubbed the inside of the engine compartment and painted it with 2-part white epoxy paint. Then I painted the hole edges with blue LP paint to match my hull. It came out looking professional - you can’t tell that the transom was modified.
But if you want this to be really nice, you need an external control box to easily control the throttle when maneuvering. I purchased the Yamaha 703 control box with the 2013 Yamaha 9.9 LEB model – this is all electric with electric choke. It is very cool to just insert the key and start the outboard from inside your cockpit like an inboard. This motor does not even come with a pull start, but you can start it manually if you remove the cover. The real kick is how quiet this motor is. You cannot hear it when it is idling! When motoring around the harbor, the splash of the coolant from the pee-hole is about as loud as the motor! I love the Yamaha and I am very pleased with my transom modifications. Check out the pic’s. Good luck if you try this – measure carefully - it fits! Happy sailing!
