river boat progress

Discussion in 'Boat Design' started by rfleet1066, Jan 19, 2013.

  1. rfleet1066
    Joined: Feb 2012
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    Location: New Kent, VA USA

    rfleet1066 rfleet1066

  2. rfleet1066
    Joined: Feb 2012
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    Location: New Kent, VA USA

    rfleet1066 rfleet1066

    IMG_0396 (1).JPG This is how we moved her down the hill from the assembly point into the water without scuffing the bottom paint.
     

    Attached Files:

    Angélique likes this.
  3. Angélique
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    Angélique aka Angel (only by name)

    Ryland, re post #61, maybe you want to redistribute some weight from fore to aft, so she becomes more level on the water, and congrats on this successful project. :cool:
     
  4. Angélique
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    Angélique aka Angel (only by name)

    [​IMG]

    I see Sebastian Marie looks to be floating level in post #58 (the above pic), so maybe in post #61 the long-tail is at a lower position, and so the upward component of the angled propulsion force looks to be pushing the stern up and the bow down there.

    If in the post #61 situation you lift the long-tail so far up that the prop just doesn't pick up air, then Sebastian Marie might be more efficient and floating more level under power.
     
    Last edited: May 19, 2019
  5. Angélique
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    Angélique aka Angel (only by name)

    To prevent the prop is ventilating air in a high position, you can mount an anti-ventilation plate above the prop, like on outboards...

    [​IMG]
    (image from wikipedia)
     
    Last edited: May 20, 2019
  6. rfleet1066
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    rfleet1066 rfleet1066

    Thank-you for your astute observation and the suggestion that you made. In #61 the vessel had just been launched and had only 100 gallons of fuel in the forward most tank with no fresh water on board. She has three fuel tanks totaling 900 gallons positioned along the center of her beam. All three tanks are fitted with transfer pumps in order to manage capacity and balance the load. There are four freshwater tanks totaling 300 gallons , two starboard and two on the port side, also fitted with transfer pumps for the same reason.
    The longtail has fixed raised and lowered positions. Air cylinders hold the assembly in both positions. This is a river vessel, so I built her expecting occasional large object floating hazards. A skeg under the prop is designed to allow it to contact an object, rise above, and pass it, then resume the lowered position. Also, at the helm, there is a red 'mushroom' button that the helmsman can push that will shut down the engine and raise the longtail should he observe a floating hazard ahead.

    The longtail is 20' in length with a down angle of 14 degrees. This matches the down angle of the transmission, allowing the engine to operate in a level position when underway.
    Your suggestion of an anti-ventilation plate may be quite a good one, and I thank you for that. If you send your shipping address, I shall not fail to reward you for that. Seriously, please do that.

    Presently, I have a four blade, 24" 12 pitch prop. I can only operate at 1800 engine RPM before it begins to cavitate or what I think to be cavitation. It may be ventilation, indeed. I have a 2400 RPM limit with a 2:1 reduction. Out of ignorance, I ordered a 24" 16 pitch five blade prop, hoping to load the engine another 25% or so.

    I was advised early on, that it would most likely take three tries before I get the prop correct. The new one has been shipped and we shall know the result in short order.

    Thank you so much for your kind attention and your time.

    Ryland Fleet

    New Kent, Virginia, USA
     
  7. Angélique
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    Angélique aka Angel (only by name)

    + 1 to that, it looks like an Old German Shepherd to me, below Ryland's dog to the right, from post #4...

    Old German Shepherd Dog.jpg
     
    Last edited: May 19, 2019
  8. Angélique
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    Angélique aka Angel (only by name)

    Sharing your builds and your thoughts gives me great pleasure to read, chatting about it and sharing views is what these forums are all about, if I post an idea that might help someone out then that's a bonus to me that gives me extra joy, so that's enough for me . . :)

    Here's an article published on Louisiana SportsmanIs it cavitation or ventilation ?

    These are two different problems, that mostly have different causes, which need different solutions, so to identify the kind of problem that occurs is an important first step to solve it.

    Good luck !
     
    Last edited: May 19, 2019
  9. Dejay
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    Dejay Senior Newbie

    Wow that is an awesome boat!
     
  10. Angélique
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    Angélique aka Angel (only by name)

    BTW, the "anti-ventilation plate" on outboards is often mistakenly called an "anti-cavitation plate", alas the latter naming is a common misnomer, and this gives the wrong idea of what the plate above the prop is actually for and what it does, the plate is against sucking and ventilating air by the prop when the prop in a high position, the plate has nothing to do with or against cavitation.
     
    Last edited: May 19, 2019
  11. Angélique
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    Angélique aka Angel (only by name)

    Cavitation isn't caused by any air, it's very temporarily boiling* water and its collapsing water vapor bubbles.

    * caused by too low water pressure on the prop's sucking side

    A good test to see if you're dealing with cavitation or ventilation might be to lower the long-tail to its max depth in deep water, and see if the problem then occurs when you give it full throttle, that is if for this test the long-tail can be lowered far enough to be sure the prop can't suck any air from above.

    The corresponding thing about ventilation and cavitation is that both are caused by hard (too hard in case of the latter) sucking of the prop, but each need a different solution to solve it, see the post #68 link for some options.
     
    Last edited: May 19, 2019
  12. Angélique
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    Angélique aka Angel (only by name)

    Usually the engine manufacturer specifies a max constant angle for the engine to be operated in, which is often different for angled forward and backwards.

    Engines placed at an angle are common in boats.

    [​IMG]

    Your current usual long-tail and prop shaft angle of ± 14° gives a bit performance and efficiency loss, which hard goes up above about 10° shaft angle, there isn't so much loss below ± 10° prop shaft angle, which is another reason to try to get the long-tail a bit less angled, which might be possible when mounting an an easy to DIY anti-ventilation plate above the prop, the plate should be angled contrary to the long-tail angle to become level to the water surface, with inboard engines and shaft drives usually the bottom of the hull is above the prop.

    Rice PropulsionTechnical NewslettersProp Shaft Angles

    ‘‘ Shaft Angle ~ Performance Loss: 3° ~ 0.14 % | 5° ~ 0.39 % | 10° ~ 1.52 % | 15° ~ 3.41 % ’’
     
    Last edited: May 20, 2019
  13. rfleet1066
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    rfleet1066 rfleet1066

    I'm not alarmed by a 3.4% loss at or about 14 degrees. I am concerned that the closer to the surface the prop operates, the chance for ventilation increases.

    Many of the design features of this vessel were born out of instinct and intuition rather than hard science. Indeed, I am not formally educated at all. High school in the early '70s was a waste of time considering the curriculum and the turmoil of the times. Real education did not begin until I joined a carnival and was assigned to maintain a roller coaster. From there I worked in the metal working industry and still do, commanding 200USD/Hr for my services. I learned early on that if I am the smartest person in the room, I am in the wrong room.
    Michelangelo did not paint the Sistine Chapel by number, he painted in strokes. Similarly I had no master plan for this vessel. I started with a napkin and a #2 pencil which I sharpened on the concrete. (NapCad) I have learned to keep a design fluid and let materials have a large voice.
    That may, in a lame fashion explain my choice to keep the engine level. That, and the fact that the assembly is perfectly balanced in the horizontal plane. That way, four 2" air cylinders easily raise and lower the tail and hold it in the selected position.

    I will construct an anti ventilation plate this week. It will have a variable angle, again, because the little voices in my head tell me to do so.

    Thank you again for your kind attention and your time with this matter. Clearly I am in the right room.

    Ryland Fleet
     
    Last edited: May 19, 2019
  14. Angélique
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    Angélique aka Angel (only by name)

    The fact that the drive system works and balances well, and the vessel itself floats level both in length and width, tells me all your shots are quite certain to reach the aim . . :)
     
    Last edited: May 21, 2019

  15. Angélique
    Joined: Feb 2009
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    Angélique aka Angel (only by name)

    Below some examples of an anti-ventilation plate on various long-tails...

    Amazon: Beavertail 23 HP Vanguard Long Tail Mud Motor

    [​IMG]

    eBay: Longtail outboard Elite mud - bisected - 2.2 m ~ 7¼' - for 5.5 to 7 HP (engine not included)

    [​IMG]

    [​IMG]

    The utility of the upward bend at the end of the anti-ventilation plate is beyond me, but posted here for the many adjustment options.



    Note the anti-ventilation plate is not well adjusted in the video, as shown when it's tilted above the water, this is also so in the last two above pics.

    The first shown one has the plate itself better designed in my opinion, but I wouldn't have the plate front end that much V shaped, I would rather have the full plate width from where it's mounted/welded to the long-tail, or only a very blunt V on the front of the plate, as the front and top side of the prop needs to be shielded from sucking air.

    About the setting, the plate needs to be horizontal and just above the prop, like on an outboard, later adjustment is only needed when the usual operating angle of the long-tail is changed, or when a prop of another diameter is mounted.

    Also the smooth rising skeg on the first one looks to me better designed to smoothly overcome obstacles.

    ( the pics are hot-linked and will disappear when the ads go off-line, so best save them if you want to keep them )

    Good luck !
     
    Last edited: May 22, 2019
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