What moves you!

With a power boat, what moves you becomes very important as do the decisions about placement, mounting and a host of related topics like gear reduction for the transmission, prop and shaft analysis and material choice for their construction...

There is also a "Goldilocks" principle in play around size.  Yes size matters, but you don't want one too big because diesel engines don't like to just coast along and you don't want one too small or you may find yourself wishing for more and/or asking your engine to deliver more than it can.  So, you have to select one that's just the right size.  There are a couple of ways to do this.  The design includes HP and speed charts that give you a sense of how much you need to keep the boat moving at different speeds under calm (no wave/no wind/no current) conditions.  Then you need to add a magical number of horse power to acknowledge how it will really be on the open ocean and then, reality check it with the experiences of people who are out there cruising in ships similar to yours.

In the end, I selected a 135 HP IVECCO 6 cylinder diesel that is B-rated.  I was particularly fond of this model because it was one of the last naturally aspirated 6 cylinders out there AND its mechanically governed (vs electronically governed).  Having some tendencies toward being a luddite, I was averse to being out in the middle of it and having the engine error code E6 come up.  This is a simple and basic engine design very similar to a Cummins engine block with a good track record for reliability.  It should burn about 1.8 gallons of fuel per hour at a cruising speed of 6-8 knots depending on conditions.

Another interesting decision is when to put the engine on the boat.  Many builders say put the engine on first and then build the boat around it- which is what I did.  Many put it in later.  There are pros and cons to both approaches but I will tell you that even with blue sky it was a little tense getting the engine to sit just right on the flexible motor mounts.  I couldn't imagine trying to position 1200 lbs of steel through a little opening and then position it (the Goldilocks way) just right.   The engine bed is a hybrid of Doug Fir cut to the shaft angle (the prop shaft runs at a shallow angle through the keel) and welded steel flat bar so that the motor mounts could be through bolted.  At the suggestion of another builder I notched the wooden bed to tie into the underlying floor timbers which will help disperse the thrust across four floor timbers.  Engine Room frames and fuel tanks next!