The sluicebox effect and the cockpit volume issue

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  • August 09, 2013 10:36 AM
    Reply # 1362025 on 1352017

    This is really off topic, but since you mentioned the exhaust outlet, I was reminded of something I thought about a while back. Would it be desirable to attach a removable length of pipe to the exhaust when running the engine at anchor (battery charging?) Even though diesels typically do not produce much CO, they do produce some and getting the exhaust farther away from the boat would seem desirable, even if by only a few feet.

  • August 11, 2013 6:55 PM
    Reply # 1363123 on 1352017
    Deleted user


    Like you, I am bothered by the exhaust issue. I'd prefer a dry exhaust like most commercial vessels use. The problem we face is that on a sailboat there is no good place for an exhaust. A mast would be the ideal place blowing it out of the top. With a wet exhaust the temperature of the gas is significantly cooled down, and indeed, one could use the mast with a suitable vent at the top be safe from seasickness inducing fumes. The wet exhaust injects water directly at the end of the manifold that connect to the exh. ports into a short length of steel pipe to have the water as it is mixing with the exh. gases turn into steam. The transition from liquid to steam absorbs the thermal energy through the expansion of the water into steam. (In the tropics, when it is blowing while sailing along, the water from the whitecaps have the same effect and winterclothes provide protection from the ice cold air.) The wet exhaust can be under the waterline and will with the pressure from the engine push the water up the exhaust loop. Btw. The water muffler is connected to the pipe from the water injection with a rubberhose, and then from the muffler also with a rubber hose, up with a loop over the waterline  then to a through hull up above the waterline. Some place a "flopper" cover ( my words) over the exhaust through hull. I do not know how effective this is, I have a Groco valve there. I had a valve lifter spring break on me in mid ocean once, and kept the exhaust closed from then on until in port where the engine was fixed(supposedly).

    After this lengthy explanation, I want to make clear that I am not a mechanic not is engine design my specialty. The issue as I see it is that the back pressure on the exhaust with each obstruction from the engine to the exit of the gases can be damaging to the valves and or reduce the output of hp. Making a special through hull to which you could snap a larger extension hose would be one solution.

    The question that concerns me, is a modification necessary? Are you using a lot of electricity?  I used a small Honda generator for running small power tools, a blender for making "screw drivers= Tang and Vodka), milkshakes and ice cream. Do not store the gas generator below decks, it took me a while to show the Coast Guard that the generator wasactually  totally empty as they tried to give me ticket.If you are a musician with an amplified system, the sound level of the generator is the same as the boat diesel.

     Are you in an area that is exceedingly dry hot at night? What about rigging up an evaporation type cooler (small water pump dribbling water through a screening type of sponge material and a fan blowing air through it producing cold air. I used to live in Oklahoma in the 60's and that was popular then.

    I would like to redesign the water muffler, so that the exhaust pipe can be above deck level and diverted to PVC pipes tied to the back stay or something else like an overboard hose that keeps the exhaust fumes from suffocating people below decks What about  a carbon  monoxide detector?. The water from the muffler can be collected.and drained elsewhere.

    Jay, can you place this off topic item into a new category topic like "Exhaust Fumes" or so?

    I think Frank brought this up and it is important to many of us.

    Thanks to Frank and Jay and Bud.

    Mike Z

    Last modified: August 11, 2013 7:35 PM | Deleted user
  • August 12, 2013 4:46 PM
    Reply # 1363795 on 1352017
    Deleted user

    If you pay close attention to your electrical system when outfitting you should rarely if ever need your engine to generate power when at anchorage.   We never run ours when anchored.  The small Honda generator is what cruisers are using for backup.  We would consider getting one if we were to cruise the pacific northwest, but so far we have never had a need for one in tropics or even in Calif. 

    A wet exhaust is quieter and controls the fumes better than  a dry exhaust. You can really tell when one of the few boats in the marina with a dry exhaust starts up.  I wouldn't concern myself with your exhaust, there are a lot more important things to concern yourself with when outfitting your boat.


    Last modified: August 12, 2013 4:49 PM | Deleted user
  • August 13, 2013 6:13 AM
    Reply # 1364110 on 1352017
    Anonymous member (Administrator)
    There isn't the feature of moving / splitting forum topics...  I could just copy paste the text into a new topic and then delete the existing -- I'll do this tonight.

  • August 14, 2013 6:00 AM
    Reply # 1364885 on 1352017
    Hopefully this will hit the forum before Jay does his cut and paste job. I guess I am in the minority of Westsailors in that I do not have any source of electrical generation other than my alternator. My boat spends most of its time at the pier plugged into shore power. When I do anchor out, I have typically run the engine for about an hour to top off the batteries before I turn in for the night. I think that Nigel Calder has written in one of his articles in Sail regarding electrical generation that for people like me the cheapest way to make electricity, aside from bringing it in batteries charged from shore power, is to use the engine and alternator. Gasoline generators are great and relatively inexpensive, but also the source of the majority of CO poisonings among boaters. As a matter of fact, I do have a CO detector on my boat, mostly because of the propane stove/oven and my (no longer used) Force 10 heater.

  • August 24, 2014 4:08 PM
    Reply # 3084757 on 1352017
    Deleted user

    Dear Frank,

    The issue of wet vs. dry exhaust is well dicussed and we all know that the steam mixed with engine exhaust is not as obnoxious as the dry product.

    I appreciated the use of a four stroke generator (the size of two shoe boxes side by side) enough to run a blender, a power tool or a projector to show slides or movies by using a sail as a screen. Mine is a 40 year old Honda EM400 and it still runs. The US Coast Guard does not like to see CO2 sources below, where you are it can be stored on deck with some protection against rain. But then again, if it works for you without - why bother. I assume your background seems to me stressfull enough.

    Fair winds and sufficient draft where ever you go,

    Mike Zorn (AKA deleted user).

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