Wet and unstable boat - what can we do?

Discussion in 'Powerboats' started by johnnythefish, Jan 23, 2021.

  1. johnnythefish
    Joined: May 2016
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    johnnythefish Junior Member

    This boat belongs to a friend of mine. It is ply on frame and I am not sure was built from any plans. I think the builder just sort of thumb sucked it as he went. Having said all that, the boat has sentimental value to my friend for various reasons.

    It is incredibly wet - even on a mirror calm surface you get wet - and it is also very unstable - particularly stationary - but also on the move.

    I think it might have quite a high center of gravity as it has a raised foredeck...
    But I am sure the hull shape plays a part too ....

    It is quite long and narrow...

    Does anyone have any suggestions how to improve things?

    [​IMG] [​IMG] [​IMG] [​IMG] [​IMG] [​IMG] [​IMG]
     
  2. cthippo
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    cthippo Senior Member

    Where are you getting wet from? Over the bow?
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    It is wet and unstable, what is the good news part ? It's actually a bit of a mystery to me why it would be either of those two, the bow looks as though it would not shed water upwards on flat water, and the boat is fairly flat bottom and what beam there is, is carried well forward, though it does appear to be a fairly narrow boat. Could be too much weight built into it high up, it could be trimming too flat (does trimming the engines out make it less wet ?) It does seem a likely candidate for one of these things, I don't know whether there is anything in your part of the world similar.
    Kapten Boat Collars - the best stability & performance-aid for small boats
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    I do think if you have some fairly hefty people standing up in that boat, at rest or underway, it is going to be a bit wobbly, if only because it is a narrow boat.
     
  5. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Your bow is too bluff.
    The angle of entrance should be much more narrow.
    It is shaped more like a displacement boat, in that sense.

    The chines, well, they are not really real chines either, look at this:
    upload_2021-1-24_8-25-33.png

    That is not promoting the flow to separate and be in a downward direction.
     
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  6. TANSL
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    TANSL Senior Member

    Since I don't think you want to change the shapes of your boat, the angle of entry, the shape of the "no" chine, solid ballast, as low as possible and towards the stern to help lift the bow, could be a solution. Move the console aft, if possible.
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    Anopheles is a species of mosquito, and this boat is a little "skeeter" of a thing, in boats that small more than one person standing up is a problem, but I don't know why it would be wet, on flat water, it has two outboards weighing the stern down, on a quite narrow waterline of around 4 feet, the bow should not be throwing water into the air, on flat water, unless he is talking about crossing wakes. It really is a candidate for one of those boat collars, but too far way to get hold of one.
     
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  8. Mr Efficiency
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    Mr Efficiency Senior Member

    Note the heel that is evident is the picture taken from behind, and to the left of the console, looking forward ! How heavy was our photographer ?
     
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  9. cthippo
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    cthippo Senior Member

    I'm also wondering if it might not benefit from some ballast down low. I would try a couple hundred pounds of sand bags and move them around to see if it helps any.
     
  10. fallguy
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    fallguy Senior Member

    Here's an idea, take a poorly designed hull and overhorse the hexk out of it, make it stern heavy and then load it real heavy with ballast. Really?

    Silliness.
     
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  11. KeithO
    Joined: Jul 2019
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    KeithO Senior Member

    I have never personally seen the strange "strake" feature carried up either side of the bow. It would seem that could cause some strange things to happen to the water flow which might make for some splashing... I would try removing the parts that go up to the bow and leave only the part that is on the underside of the hull and fair the entry points nicely.

    A second thing with such a narrow hull is that you may benefit a lot from adding the largest trim tabs you can find to the outboard sides of the transom and set it up that the trim tab is completely inline and flush with the end of the hull on either side. Then when at running speed you might tweak is slightly further down if needed to load them up a little. Not too much but it should stiffen up side to side movement a lot. In the center you could add foils to the outboards to reduce cavitation and potentially suppress splashing from the impact of the water on the outboard legs. Some boats can get water on the deck from that angle, one of my last aluminum boats suffered from that pretty bad. There might have been a slight mismatch in height between the outboard cavitation plate and the hull too but the transom was not very high so made raising up the outboard more problematic.

    bow.jpg
     
  12. kapnD
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    kapnD Senior Member

    “Long and narrow” begs for clarification, are there relevant numbers available?
    How about weight?
    Overweight boats can be very wet, even on a very well designed hull.
    The bow arrangement must create quite a battering ram effect at speed, and is likely responsible for a good deal of spray!
     
  13. johnnythefish
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    johnnythefish Junior Member

    Could you explain what is meant by the “bow being too bluff” ?

    Do you mean that strange “pad” that is carried all the way up the bow?

    I am pretty sure that could be removed if necessary.

    I see what you are saying about the chines - I was wondering whether it would be worth building out chine/ spray rails and obviously sharpening that break.

    Mr Efficiency - the boat is 23 foot long - so not tiny - I will measure the waterline length and width. It should carry those twins fine and doesn’t seem overloaded; but I do feel that front deck raises the center of gravity a lot.

    The water comes up and over from about 2/3 towards the bow, particularly in a turn.

    I can’t help but feel that perhaps that weight up high exaggerates that balance insane if so noticeable in a turn.

    Will try and get a video of it running and turning.


    Do you mean this sort of “keel pad” thing that goes up the bow? It’s a bit odd isn’t it?
     
    Last edited: Jan 24, 2021
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    A good way to test if the COG is a bit high, for the hull, run it along at about 5 knots (no squat) and put it into a sharp turn, if it leans outward noticeably. then it does suggest that COG is higher than desirable, should turn without too much lean, ideally. Then, with the boat cleanly on plane, put into a sharp turn again, if it banks heavily, then that supports the idea of a high COG.
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    The seemingly hefty timber inboard of the gunwales does arouse suspicions of weight high up.
     
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