Engine options

Discussion in 'Boat Design' started by infy, May 6, 2019.

  1. infy
    Joined: Jan 2019
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    Location: USA

    infy Junior Member

    This is a bit of a strange concept outright, I admit. But what are the challenges of adopting modern, efficient, and mass produced engines to as inboards for sailboats?

    Fuel supply.

    If these could be solved then old sailboats could be repowered for a fraction of the cost of rebuilds on 40 year old blocks. Parts are getting harder to come by. Manufacturers are dropping support. While mass produced engines are becoming very inexpensive, compact, and potentially better options.
  2. Ad Hoc
    Joined: Oct 2008
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    Location: Japan

    Ad Hoc Naval Architect

    Firstly, you should read Marine Conversions, by Nigel Warren.
    The book is dedicated to this very subject.
  3. infy
    Joined: Jan 2019
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    Location: USA

    infy Junior Member

    Awesome. Thanks for the suggestion.

    I typed that up just as I was boarding for a flight so I had some extra time to think about it.

    One main challenge I left out is the safety. You don't want fumes or spark. So marine starters, distributors, and alternators have fire suppression built in. In addition, fuel pumps are designed to prevent leaks on failure. None of these can be bypassed. So you would be adopting marine parts as substitutes and it would essentially wipe out any price advantage found elsewhere.

    So maybe just a pipe dream...
  4. Squidly-Diddly
    Joined: Sep 2007
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    Squidly-Diddly Senior Member

    Overheard some guy getting hassled over exhaust manifolds at the lake. Gotta have water jacketed.Lightning Water Jacketed Headers https://www.cpperformance.com/products/exhaust/lightning-headers.htm
    Brings back the time my 1974 Mustang II was dripping oil on the exhaust. One time it started a little fire, like a candle flame, so I just blew it out. Later, parked up on a hill, some lady tells me "Your car is ON FIRE!" and I see the smoke and tell her "it always does that". Later, at lunch I see the entire hood is scorched and musta been flames out the grill! I just keep thinking about what that old lady musta thought when I said "yeah, don't worry, it always does that".
    cracked_ribs and rwatson like this.

  5. Phil_B
    Joined: Mar 2019
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    Location: New Zealand

    Phil_B Junior Member

    I would be looking at the small diesel engines used in small European compact town cars. Economical, quite advanced designs and put they out plenty of horsepower for their size. A 1 litre engine will put out somewhere in the region of 60 to 70 BHP - though this is at maximum power but you will be likely running it at a much lower throttle opening.

    Two likely problems:-

    1) The engine will need a gearbox to reduce the RPM down to that needed by the propeller though an adaptor to take a marine gearbox would not be an insurmountable problem Or even have it powering a hydraulic pump and the hydraulics powering the final drive. A loss of efficiency, but means that the engine can be put anywhere in the hull and the hydraulic lines lead to where needed.

    2) Cooling. Raw water cooling will wreck the engine in short order so freshwater cooling with some sort of a heat exchanger will be needed.

    Use a "North Sea" exhaust - a transverse pipe that emerges on both sides of the hull just above the waterline. The exhaust from the engine joins the transverse pipe at the middle from above the pipe. No matter how the boat rolls, there is always one end above the water. It eliminates back siphoning as there is always one end of the pipe above the water to prevent any suction building up.
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