Catamaran Repower

Engine trouble

Yamaha 30HP on transom

After the sail, mostly motoring when the engine was working, down to Ensenada I decided that the old installation had to go. I don't know what the rational was behind the installation, but it was a near perfect example of how not to do it. I say near perfect because the engine didn't fall off, but it was trying hard.

The engine was way too large for the boat double the power required for hull speed, and consequently to way heavy. It was also the wrong type of engine, a go fast outboard with a fast gear ratio and to top it off an incorrectly sized prop. This contraption was mounted on the transom, which incidentally, wasn't designed to hold an engine of any size, but left the engine working hard at delaminating the transom.

I had the boat hauled out at Baja Naval, a flashy boatyard in Ensenada. They are not the cheapest but their quality of work is well known and their customer service was top notch. Weekly statements and photos of the work, they took the time to sit with me and figure out what we were going to do (besides drown the old engine). We planned the installation out, and they came up with a quote…. they aren't the cheapest.

Engine Installation

heavenly twins 27
Cockpit engine well

For details on the engine and propeller selection see Boat Repower example and the Boat speed calculator.

The heavenly twins 27 is an unusual design in that it is a center cockpit catamaran. Like any design decision it has its advantages and disadvantages. One advantage, for this installation anyway, is that there was an existing cockpit engine well. From the pic on the left you can see there was an engine in the well before someone hung 30 horses off the back. So the old girl is on to her third engine now.

catamaran nacelle
cockpit engine pod

You can see she has a nacelle running down the center of the bridge for strength and reducing slap, this provided a nice little pod to allow the outboard to be installed closer to the waterline.

outboard bearer installation
outboard installation cockpit

The center of the seat is cut out and the well is being made ready for the outboard.

A disturbingly large hole is cut out to put the outboard though. I had the choice here to simply glass her in but I couldn't bring myself to trust an outboard so I decided to allow it to be removable. The disadvantage is a rather large hole to let the waves in. I did however go out in reasonably rough weather and she was ok with it. A bit of splash in there but not to serious. I think at a later stage I'll put in a surge or splash guard of some sort to cover the hole. And a pulley system to allow me to pull the engine out of the water for sailing.

yamaha 9.9 high trust
boat gas tank installation

A box was built around the engine with boat the box and the boxes lid fitted with hinges to allow easy access for maintenance and quick access for general fiddling. At the top of the picture on the left you can see the fill cap for the tank. I fitted a fuel filter, not sure why, but it seemed like I needed one. The outboard hand fuel pump is quite accessible too.

In future I intend installing a water maker the pump, high pressure tubes, discharge etc. will be in the box… if I can fit it all in. There is also an additional outlet on the fuel filter for my generator, yet to be acquired.

A tank was also fitted under the seat a poly tank was fitted into the old tank rather than glassing the old tank. A bit more expensive but gives me a little piece of mind, knowing the tank effectively has double walls and is outside of the boat.

cockpit engine box
outboard propeller installation

On the left you can see the final results of the glass work. The box doesn't get in the way of the door, and is at a good level to double as a high chair or table.