Any buoyancy mathematician's around ?

Discussion in 'Multihulls' started by Crashed, Aug 6, 2020.

  1. bajansailor
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    bajansailor Marine Surveyor

    Apart from the hydrofoils, is your boat essentially a sistership to Charlie Boy II?

    Can you post a photo or 2 please showing 'your' stern with the hydrofoils on the hulls?

    And I will second Bluebell's request as to where the waterlines are in the unloaded and loaded conditions, relative to the painted waterline shown.
     
  2. Crashed
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    Crashed Junior Member

    0000000000000000000000
     
    Last edited: Aug 9, 2020
  3. Crashed
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    Crashed Junior Member

    000000000000000000
     
    Last edited: Aug 9, 2020
  4. bajansailor
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    bajansailor Marine Surveyor

    Oh dear, I see what you mean re how she is trimming down by the stern, even when light.
    Do you have any tanks in the hulls aft of the engine rooms that you could possibly move further forward?

    Re the stern photo of Boy Connor, those 'hydrofoils' will give her a bit of lift while underway, but I doubt that they give any additional buoyancy - their weight is probably about the same (or more even) than the extra buoyancy gained by adding them.
     
  5. Crashed
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    Crashed Junior Member

    No tanks , couple of grp covered pound boards sectioning off the rear corners which are stupidly heavy since the wood got wet with age , 140kg together maybe as its not like you can't lift them and they will be replaced with aluminium . The engines are pretty much under that roof support , fuel tanks forward of them and nothing below deck astern of them but the prop shaft and steering gear .
     
  6. bajansailor
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    bajansailor Marine Surveyor

    Re the pound boards, could you perhaps replace them with foam cored fibreglass boards?
    Although even if you can save 100 kg at the aft end, it is not going to make a huge difference to the static trim of the vessel.

    How heavy is that 'basket' (for storing pot buoys?) on the transom?
    Would it be feasible to store this equipment on the roof behind the radar arch?
     
  7. Crashed
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    Crashed Junior Member

    "basket" we call catcatcher its mostly just an out of the way shelf to on which to throw damaged pots and the like to keep the working deck clear , the previous owner put that on and whilst its bigger than it needs to be its aluminium when everyone has one and most are stainless steel so lots of expense for little or no gain in messing with it i think .

    I'm happy with the squared off arch idea , new propellers designed specifically for my boat are on the way so they may help as well . It's a strange one because while say 2 ton on deck does sink it some it doesn't sink it much , indeed not enough to make it a worry if the boat didn't often muddle home through 40mph winds on the Irish sea .
     
  8. Ad Hoc
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    Ad Hoc Naval Architect

    If you are, for whatever reason, unable to add bouncy at the stern, why not remove buoyancy from up fwd?

    If you created a simple collision bulked just aft of you large bulbous bow. So the hull is sealed. Then perforate the bulbous bow with holes around 50mm in diameter. This removes the buoyancy, ergo prevents the excess aft trim, as the CoB is too far fwd... this moved the CoB aft... same effect.

    But having the bulbous bow perforated, it still contributes to damping in heave and pitch as the bow is filled with "heavy" water but not adding buoyancy.
     
  9. Rumars
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    Rumars Senior Member

  10. redreuben
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    redreuben redreuben

    Not doing the appropriate calculations created this problem why do you think avoiding doing the correct calculations will solve it ? TANSL asked you for the appropriate information and you have ignored him. Good luck with your guesswork.
     
  11. Crashed
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    Crashed Junior Member

    Interesting idea Ad Hoc i've never heard of a perforated bulbous bow but i have a front hydrofoil that keeps her good up front and prevents slamming almost entirely .

    Thanks for that Rumars , i understood the builder was the actual designer and so of course i have spoken to him but not Daniel at marinepsl .

    redreuben I apologize for not being an architect but some of us had to go to work long before we could legally leave school . As i explained to TANSYL the builder claimed he had no drawings for this boat to share and at the present time due to the coronavirus restrictions i can't even get to the boat to measure anything , so yes luck on a wing and a prayer is all i have so i signed up to this forum to share my amateur ideas with people i would hope are far more clued in about boat design than i ever will be .

    In fantasy where money is no obstacle i would love to chop her up add 8 inches above the waterline and glue it back together , trim would be no issue then .
     
  12. Rumars
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    Rumars Senior Member

    Assuming is dangerous business, I got the name of the designer right of the builders webpage. If the original designer is unwilling to do the work, your only option is hiring a NA to come out to the boat and lift her lines manually, then perform the necessary calculations.

    Just to straighten another of your assumptions, the EU and its bureaucrats have nothing to do with you not beeing able to lenghten the boat. All they ever said was that a boat under 10m could fish without keeping count of the quantity. Everything else is national regulation.
    Not even the London bureaucrats that created your current system forbid it, they just want you to hold a different licence if you do lengthen the boat.

    If you want to be mad at the current UK fishing licence system, you should curse the guys in London that set it up over time and the generation of fishermen who allowed and encouraged it. What you should not do is blame EU bureaucrats (wich by the way warned the UK about the consequences of their national regulations and advised against enacting such policies every time the UK did another stupid thing), especially when your boat is registered in a place that was never a member of the EU or the EEA.
     
  13. Crashed
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    Crashed Junior Member

    I really don't care about Hitler's plan B for world domination i'm just a bloke trying to make a living and i thank those who tried to help , however i don't have time for *******s who spent half their life in school while mommy paid the bills and were given a yacht for their birthday so if moderators would be kind enough to delete this thread i won't be posting another .

    Shame really because twice i phoned marinepsl this morning only to get an engaged tone before being convinced here i'd rather go without "expert" help
     
  14. fallguy
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    fallguy Senior Member

    I am just a builder. Been watching the thread as a lurker.

    The reason modifying hulls is done with great care is to prevent loss of life. If you overload the boat and she breaks in heavy seas; no good purpose was served. Please keep this detail in mind if you feel slighted. Lengthening the boat is the ideal for stern squatting.

    Deleting the thread is not fair to contributors.
     
    bajansailor likes this.

  15. Rumars
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    Rumars Senior Member

    Aren't we a thin skinned one.
    Anyway, after some educated individual determined the shape and placement of your buoyancy additions, in order to not have the boat out of commission for to long, have them CNC milled out of foam, preglassed and faired. Then all you need to do is haul the boat, grind the designated area clean, stick them on with thickened epoxy and some tape, some fairing, then paint. The whole operation can be done in one night, and the boat is back working the next day.
     
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