Spira International website quote.
The Sitka may be shortened or lengthened from 25-1/2' (7.7M) to 30' (9.1M) in 1-1/2' (457MM) increments. The plans also show an option for a vee entry to the bow, but these Pacific dories ride quite well in rough water with their upturned bows.The fact that I will need four stroke power plant,limits my options.Four stroke outboards are rare on the used market here and expensive.Then there is the cost of a gauge package and controls.That can easily add $800 to $1000 to the install, considering the length of steering control hydraulic hoses or cables I would need.So I contacted Jeff Spira about using a stern drive,or inboard outboard(I/O) if you prefer.He has approved the use of a stern drive and will make the needed changes to the plans when someone buys the plans.
With everything sorted out and a power plant type has been chosen,I can get on with deciding on which stern drive I want to use.I know that the stern drive will come from a used boat,probably one I buy for a parts donor.I know I need 120 recommended horsepower.I will also have to compensate for the additional weight from the added length,longer cabin,contents of longer cabin,and stern drive.Checking the horsepower chart,the Coast Guard recommended horsepower is 342.That isssss noooooot happening!This is a cruising boat,not race boat.I want some economy.I will mostly be on inland lakes for the first few years before I do the Great Loop Cruise.On lakes,I won't be dealing with fast currents or rough water.I really don't plan to run the boat on plane.It would be nice to have the option.Technically speaking,I could use 120 horsepower.I think I want a little more.
Looking around and asking the right questions,I have decided to go with a carbureted 135 horsepower four cylinder 3.0 liter Chevrolet engine with Alpha I Mercruiser sterndrive.I might get lucky and find a cheap donor boat with a fuel injected 3.0L.The reasons I have chosen this set up over others is numerous.The main one being parts availability.These were produced from the 1970's to present day.They are still being made.There are literally hundreds of thousands of these across the US,Canada,and Mexico,maybe millions.Most parts sellers either have the parts on hand, or can get them fairly quickly,usually overnight without additional charges.These set ups being as simple as they are,most anyone can work on them with basic mechanical skills and knowledge.
While I am cruising to local lakes and enjoying my new boat,I will be designing a new engine install using the 3.0L stern drive set up.The engine will be based on a retuned 1.9 liter turbocharged Volkswagen TDI diesel.Please don't confuse DEtuned with REtuned.Before anyone jumps on the Pathfinder VW diesel and starts bashing them,the only people that had issues with those set ups are the ones that don't understand how to properly run a marinized diesel.99% of all failures were directly related to operator error.CDK's forum post is where I got the idea for this set up.His twins are sweet.
Marine Conversions: Car Engine Conversions for Boats.
Now,where to start.The best place is with the adaption of the diesel engine to the stern drive.I plan to keep the heavy manual transmission flywheel.The weight will help the engine keep spinning and reduce fuel consumption a fraction of a gallon.Depending on the year of the stern drive,all I will have to do is machine the flywheel to accept the engine to stern drive coupler.Next issue will be lining up the engine to keep the engine's crankshaft center line centered with the center of the stern drive's input shaft center line.It's not a difficult process,just tedious.I will use adjustable motor mounts and an engine plate front and rear to mount the engine.Going with the mounting plates will allow me to mount the engine semi solidly at all four corners.The starter will mount to the rear plate in a position that allows access.The starter will be swapped out for an ignition protected unit.
I will use a completely enclosed and self contained cooling system like an automobile.Bowman and Lancing Marine both offer products to marinize a 1.9L TDI VW diesel.I plan to weld up my own using stainless steel tubing.The factory turbo is water cooled but the exhaust side will need a turbo jacket to help contain some of the excess heat.Most of the heat will be absorbed through the water cooled exhaust manifold.The exhaust will run dry.It will be expelled through the stern drive and out of the prop like the original set up.A water cooled oil cooler will help the longevity of the turbo and engine.In place of the cars radiator,there will be a liquid to liquid heat exchanger.Raw water will pass through a heat exchanger that circulates hot engine coolant through it.Then the raw water will exit the heat exchanger after it's cooled down the coolant.Think of it like this,it's a small radiator, that is sealed inside a box, with water circulating through it.The water box circulates the water around the radiator, to cool off the coolant that circulates through the engine.It's way more simple than it seems.Doing it this way, will allow me to remove the impeller in the lower unit and plug all of the water ports on the exterior of the stern drive.I could leave everything in place and route the water coming out of the stern drive over board.
Know Your Boat's Diesel Engine
The next issue will be the engine itself.Most people that have done this type of install,run the engine as it came from the car.I think I would like to go one step further and have custom ground camshafts to fit the type of use the engine will get.Along with that,I will upgrade the turbo and injectors.The injection pump is electronically controlled.This makes the engine difficult to use in a boat.I will have a custom built and tuned mTDI injection pump that will basically make a one wire engine.The one wire will be to shut off the engine.I will also have a bypass to allow me to run and shut down the engine with no electrical power on the boat.Think of it as a limp home mode.
An air intake for a boat has to be designed in a way that allows enough fresh air into the engine but keeps water out.There are many ways to do it.Mine will basically be two air dams inside a box.The air flows over the first one and under the second one.Then, onto the engine through an intake mounted high on the back side of the box.It's a little hard to visualize but I am no good at drawing with a computer.A lot of marine engines don't run air filters. I will be running a secondary air box with a filter.
Going with a diesel cuts down on the risk of fire.It does not eliminated it.Diesel fumes are not as flammable as gasoline fumes.Ignition protection isn't as critical with a diesel,but that doesn't mean you should use standard automotive electrical parts.I have already stated that I will use an ignition protected marine starter.That goes double for the alternator.As long as the engine is running the alternator could be sparking inside which can ignite any fumes around.I will be running an externally regulated Balmar 150 amp alternator package.
Marine Diesel Engines: Maintenance and Repair Manual