compressed natural gas engine

Discussion in 'Propulsion' started by engnr09, Jan 16, 2011.

  1. engnr09
    Joined: Jan 2011
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    Location: michigan

    engnr09 New Member

    I am taking on the task of restoring a 38' wooden cruiser. I was thinking fuel and wondered if high pressure cng would be better than gasoline with its benefit of being able to fuel the engines and other systems, water heat, heat, electrical generation, ect. is cng lighter? can I carry a greater quantity? I found little available on the net regarding cng marine engines.
  2. CatBuilder

    CatBuilder Previous Member

    The main issue with this is:

    Where will you fill her up when the tank empties? Which marinas have CNG or LPG/Propane filling stations at the fuel dock? Try to find some and you'll have your answer.

    I really longed for this as well because I wanted to use an RV/Caravan style refrigerator and freezer, propane water heater and then figured I could run propane generators and engines. There was nowhere to fill the propane bottle up, though, so I let the idea slide in favor of the accepted ways.

    Take a quick read of this link regarding the energy densities of gasoline(petrol) vs. all the bottled gasses:

    As you see, CNG isn't even good in comparison to LPG, which isn't good in energy density compared to gasoline and diesel. Looks like CNG is one of the worst ways to store energy when it comes to volume or weight.
  3. engnr09
    Joined: Jan 2011
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    engnr09 New Member

    What is the 'modern' way to power a boat and its systems? Is gasoline for the drives/generator and propane for the stove, fridge and hot water tank the way to go? I was hoping to have an old wooden boat with modern systems. I found a 38' Pembroke for my starting point. Many questions for the Shipwrights here to follow........
  4. CatBuilder

    CatBuilder Previous Member

    Well, you have a lot of freedom there.

    Depending on your engine on this power boat, you will likely build your systems around it. Is it a diesel you will run all the time, or will the boat mostly be at a dock?

    Systems design needs to take into account your primary source of propulsion and your intended use of the boat. There is not one accepted way.

    For instance: I've lived off the grid for many years using just solar panels to run refrigeration, lighting, anchor drag alarm, computers, phones, etc. I used propane for the stove because it takes an incredible amount of energy to produce the amount of heat it takes to cook food. You could produce that energy by running a diesel engine or generator, but in my case, I was at anchor all the time and didn't frequently run the engines. (sailboat) So for my use (anchored out and living on the boat) and my engine use (none), solar and propane were the best way to go with a gasoline outboard for the dinghy.

    Your situation will probably vary quite a bit from mine. You have that power plant that runs the boat. How often will you run it? When will you use the boat? How will you use the boat? Some power boats that plan on running often and using engines and generators a lot will run everything off 110VAC, even the stove. Fishing boats are a prime example. They're out running around all day dragging nets or hauling up traps, so they have plenty of excess power and/or gensets making 110VAC, so they can run everything from that excess power.

    You're an engineer, I imagine from the screen name?

    This one's all about conservation of energy. You figure out where the energy in the boat will come from (based on how you plan to use the boat) and then take advantage of that energy first. Next, you supplement it with additional power sources like solar, wind, gasoline or diesel generators, etc...

    I can walk you through the process here if you'd like. Just let me know how you will use the boat. You have to actually look at the wattage ratings of everything you plan to do on the boat, then see where you will get that power from the most cost effective way.

    PS: To answer your last post, the modern way is often diesel for the drives and generator, propane for the stove, fridge runs on 12VDC (or 110AC with holding plate) from the engine, hot water can be made with a heat exchanger to the engine's coolant system and run on 110VAC when engine is not running. That's fairly common, but your individual use of the boat may warrant different types of systems.
  5. cthippo
    Joined: Sep 2010
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    cthippo Senior Member

    For what it's worth, one advantage of CNG vs LPG is that it's lighter than air, so you don't have to worry about vapor accumulation in the hull. The idea of gasoline in a boat scares the hell out of me.
  6. CatBuilder

    CatBuilder Previous Member

    Gasoline on a cruising boat is unavoidable. You need it to run the outboard for your tender. It's something that needs to be managed properly, is all. Don't fear it.
  7. Submarine Tom

    Submarine Tom Previous Member

    I concur. A boat (vessel) is a confined space (or at least has many of them) and must be treated as such.

    I've had both gasoline and propane on my boat for years. It must be managed appropriately. However, if you do fear it, then I wouldn't recommend you use it.

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    FAST FRED Senior Member

    If you are interested I have a Series 50 Detroit that was built for Natural gas in a bus.

    Its about 250 hp , and in the diesel version usually runs 1,000,000 miles with ease.

    IN every respect it is a Diesel series 50 , but has spark plugs and coils where the fuel injectors would be, and a large EFI should run it fine.

    I think the bellhousing is Series 1 so a used Twin Disc could be installed.$ 1500 for engine.

    A modern 8 cubic ft propane fridge uses under a 20lb bottle every 30 - 40 days , we simply carry a refill down the dock.

  9. cthippo
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    cthippo Senior Member

    To me it falls under the category of avoidable hazards, or at least one that sould be minimized as much as possible. The fewer things that can go catastrophically wrong, the better IMHO.

    I'm less concerned about propane due to it's lower molecular weight and resulting faster diffusion.
  10. Boston

    Boston Previous Member

    I'm going to stick my neck onto the proverbial chopping block and suggest that the basic tender can be electric charged off the on-board systems. Or at least that what I have planned, my fuel source will be used motor oil running a standard diesel engine. Has superior energy density to diesel fuel and costs a whole lot less. My concern is that ye merry ole coast guard will frown on my creative thinking. Course there's nothing to stop me from running diesel while they do there thing and then run whatever I want through it once I have a sticker on my windshield. Filling up is somewhat of an issue but since the system is completely interchangeable in a pinch I can always use dino.

    CNG is going to take up a bunch of space and raise a few eyebrows among the coast guard. Not sure what they will say about it but I'm sure it will be an interesting conversation.
  11. cthippo
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    cthippo Senior Member

    I'm not so sure about that, Boston. CNG powered vehicles have been around a long time and it is a widely understood concept whereas WMO and WVO, while not really new, have only recently become mainstream. You know those Schwanz trucks that deliver frozen food? They're powered by either LPG or CNG (I can't remember which). In Australia most cars have tanks for both LPG and gasoline (or petrol as they call it), and use the fuels interchangeably at the flick of a switch. LPG is cheaper, but doesn't provide as much power, so they switch to petrol for going up the hill. I've looked into LPG for outboards but it doesn't look like there is any consensus on how best to do it.

    Battery power for a short range outboard is becoming more viable all the time with the increases in battery capacity and motor efficiency. Hydrogen fuel cells are probably the right answer for this application, but they too are not ready for prime time.
  12. Boston

    Boston Previous Member

    ya I had an engine out of an old Kodiak truck once that ran on propane. Thing is probably still running today. I used it in one of the ranch trucks and it worked fine. I guess I just wanted to do something different when tinkering around. The reason I mention WMO is that its got such a good energy density. Kinda important when your having to dedicate premium space to fuel storage. My take on electric power for the tender might be a bit biased but given that a tender is by definition only being used for short hops it seems the perfect solution to carrying alternate fuels. Hydrogen technology is a boondoggle IMHO. An excuse to kill the electric car with technology so complex and expensive it will never seriously be a contender. Long story that one so I'll suggest we not dig to deeply into that one here, there's a thread around here somewhere on Hydrogen fuel cells.

    I really like the idea that so many are exploring alternative fuels. Oil is up around $100 a barrel again and its not likely to be coming back down any time soon.

    I'm negotiating on a 300 series mercedes diesel now to convert as well to WMO cause I expect fuel prices to be about $4 a gallon by next spring, maybe summer, but there going up and there not likely to come back down this time.
  13. cthippo
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    cthippo Senior Member

  14. hcaz095
    Joined: Dec 2010
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    hcaz095 New Member

    Spark ignite detroit

    Fast Fred, Is the Engine Still available?

    I'm interested on many levels about this engine...



  15. tom kane
    Joined: Nov 2003
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    tom kane Senior Member


    All volatile fuels for boats can be made safe if you design the systems to eliminate the dangers but apparently boat designers do not know how to do that and still rely on patch up modifications approved by Regulatory bodies not in touch with good design practice.
    And perhaps reluctant to diverge from traditional boat building.
    Take a look at newer Liquid Gas Injection systems that inject the gas in a liquid form just like injecting petrol and gas efficiency and advantages spiral.
    And you have other options too.
    Last edited: Aug 16, 2016
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