Sea Sled madness. It’s in my brain.

Discussion in 'Fiberglass and Composite Boat Building' started by DogCavalry, Nov 11, 2019.

  1. baeckmo
    Joined: Jun 2009
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    baeckmo Hydrodynamics

    The outboards we use in the salt water of the european side of the North Atlantic are only flushed once a year (at the very best...), and that is when we pick them up to "get them out of the winter ice". Remember most boats here stay in the wet for the whole boating season, even all year around, save for an antifouling job in the spring, before the worst growing period. With the easily available flushing connection on some of the newer engines, it would be a standard procedure to flush, but then you have to have fresh water right on your quayside. So, in practice only some of the trailer boats get their engines flushed.

    As to your earlier question about flushing and thermostats et c.: There are two system requirements to understand:
    • There must be a cooling flow to the exhaust jacket (and in an outboard mixing with the exhaust) at all conditions, even from a cold start.
    • Pumps must always have a through-flow. They can not operate with zero flow against a counterpressure, since all losses in the rotating unit will be transformed into heat that will kill the pump, sometimes in a matter of seconds.
    In a basic "classic" system the water from the pump is divided in two; one branch directed into the engine and one into a bypass. After the engine the two join again via a thermostat designed as a shunt valve. When engine is cold, water flows through the bypass directly to exhaust jacket and out (or to cooler/heat exchanger). As soon as the engine temperature reaches working setting, the thermostat shunt is opening the engine flow and restricting the bypass, simple and effective as long as the thermostat/shunt is in place. Take it away, and all flow takes the least resistance through the by-pass, and the engine is damaged from overheating.

    The E-tec is a two-stroke. The highest thermal load is seen in the block/cylinder sleeves around the exhaust ports. The cylinder heads are very robust and will tolerate quite some "thermal abuse". Ergo, the designer's focus for the cooling is directed to the block. For four-strokes, it is the reversed picture; there you have a set of valves opening and (supposedly) closing whithin a hot (500 degree C and above) exhaust flow, while the cylinders are symmetrical and reasonably easy to control. Of course these differences are reflected in the design of the cooling system.

    For your concerns about maintenance of your engines, start with the owner's manual, written by the engine manufacturer!
     
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  2. DogCavalry
    Joined: Sep 2019
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    Location: Vancouver bc

    DogCavalry Senior Member

    IMG_20221211_114822159.jpg
    Hole above thermostats for clearing trapped air.
     
  3. baeckmo
    Joined: Jun 2009
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    Location: Sweden

    baeckmo Hydrodynamics

    That seems to go straight down, not the 45 degrees shown in the service bulletin. With the lid in place, the thermostat bulb seems to stick into the inside of the lid; I can't imagine how the air is supposed to escape to that hole, unless there is a passage above the threads in the lid. As you have the pieces open, please check if there is a venting possible at all with the present arrangement.

    Edit: Seems that those thermostat covers/lids should have a set of vent holes just above the threads. But for other engine models there are lids that look similar, but without the vent holes, so check that they are there, and not blocked by anything.

    This housing design is really bad, typical "rookie job", and seems to have caused lots of low speed overheating problems.
     
    Last edited: Dec 12, 2022
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  4. DogCavalry
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    DogCavalry Senior Member

    I'll check for them.

    Checked the primary fuel filter/ water separator today. One single drop of water.
     
  5. DogCavalry
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    DogCavalry Senior Member

    IMG_20221222_141419859_HDR.jpg
    I fondly remember the days when it was painfully hot out.
     
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  6. DogCavalry
    Joined: Sep 2019
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    DogCavalry Senior Member

    IMG-20221231-WA0004.jpg
    Serenity at 15 knots. 4400 rpm, 13.5 gallons an hour, 51 liters an hour, 4° trim. Probably be faster without the barnacles and mussels covering her bottom. Engine was trimmed in as much as possible. Fuel consumption indicates the engine was making around 140hp. About 880 pound of stuff on board, as well as my big ol' self. Blew past Anne in her kayak, she didn't notice any wake. Here's a picture out the back, a moment after I cut power. IMG_20221231_153652112_HDR.jpg
     
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  7. DogCavalry
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    DogCavalry Senior Member

    Prop was turning for 60km/hr, but only moving at 27.75km/hr. Big slip
     
  8. baeckmo
    Joined: Jun 2009
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    Location: Sweden

    baeckmo Hydrodynamics

    Aha, some progress; the m/s Seaweed Express finally seen in a normal trim attitude..... How was the steering in this condition?
     
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  9. DogCavalry
    Joined: Sep 2019
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    DogCavalry Senior Member

    Since the prop was trembling on the edge of ventilation, the steering was tenuous. I could make very gentle corrections, but more than that would cause immediate power loss. I was very gratified by the timy wake though. A small fraction of the wake our 17', 70 hp commuter makes at that speed.

    I haven't cupped the prop yet. I have no replacement. I'll get a very cheap one online and hammer that.
     
  10. Barry
    Joined: Mar 2002
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    Barry Senior Member

    DC, some of the viewer might forget that you are living in Canada which uses Imperial Gallons

    So some confusion here

    13.5 Imperial gallons per hour = 61.37 lph
    13.5 US gallons per hour = 51.10 lph

    As Canadian pumps are in litres, I suspect that you took the 51 litres ( the volume that you purchased) and converted it back to 13.5 US gallons.
    So if the 51 litres is that actual benchmark

    51 lph = 11.2 imperial gallons per hour = 13.5 US gallons per hour

    Therefore (if I assume that the benchmark for the volume is 51 lph )
    Serenity, rough bottom, ventilating prop and all, is getting 15 nautical miles /11.2 Cgph = 1.34 nautical miles per imperial gallon


    Thread 2586, first picture illustrates the massive air entrainment into the tunnel which is no doubt the source of poor performance as the prop is handling a water and air combination. Already discussed in previous
    posts, but I believe that the previous pictures that you provided might not have been at 15 knots.
     
  11. DogCavalry
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    DogCavalry Senior Member

    Barry, you are correct. Previous pictures showing entrained air are generally at 7-9 km/hr. So more like 5 knots.

    The computer on the engine reports fuel consumption in US gallons, so I multiply by 3.785 to get liters. I could reset it to report in liters per hour.

    Yes, that's what I figured. That seems pretty miserable mileage to me. I hope for several times that when everything is working properly, but maybe my perspective is skewed. When comfortably cruising, I'm getting about 6 times that.
     
    Last edited: Jan 2, 2023
  12. baeckmo
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    baeckmo Hydrodynamics

    So, what is your total weight estimate for the 15 kn run then?
     
  13. DogCavalry
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    DogCavalry Senior Member

    My best guess is ~2400kg, or 5300#. There's about 750# of cement, tools etc. The big unknown is how much rainwater made it into ostensibly sealed compartments, and under the sole from leaking windows . I guessed 800#.
     
  14. DogCavalry
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    DogCavalry Senior Member

    IMG-20230119-WA0000.jpg
    Dawn
     
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  15. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Is the sheer supposed to be level on Serenity or is it pitched forward? Great pic.

    I think many of the times I've looked at it, I've been suffering from misperception about the sheer.
     
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