Help with listing stability.

Discussion in 'Stability' started by bakeefe4, Aug 26, 2014.

  1. bakeefe4
    Joined: Aug 2014
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    Location: North Fort Myers Florida

    bakeefe4 Junior Member

    I just purchased a homemade boat that kind of looks like a tug. When I took it out on the first day it was a very calm day soft wind and smooth water. Also no water traffic to speak of. It handled like a dream. on the next day it was breezy and rough water, and a little water traffic with mild wakes. the boat listed hard even to a point that I thought it would or could roll.

    Here are the specs:
    Length 11'
    Beam 5'1"

    side walls:
    2'8" at the stern
    3'2" at the bow
    Mid point (Wheel house so to speak) 4'8"

    Draft 2.5"

    merc 6 horse 4 stroke

    NO ballist and NO deck except on the bow.
    the floor is in fact the bottom of the haul.

    My ideal is to build up the floor about 6" having a 1' hollow center like a v-hull boat for ballist. This should give me upto 250lb of ballist and about an extra 50lb in boat weight. I am thinking if I can get the draft closer to 10" it would handle better....

    can anyone help me with this. am I corrct in my thinking?
     

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  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    If you build a false Vee bottom it will provide a lot of extra floatation. It will also increase the lack of stability. The ballast should be more than the added floatation. The design appears to have several defects. One of them is being top heavy. If you start doing so many modifications, it will be cheaper to re-use the outboard and build a new hull.
     
  3. bakeefe4
    Joined: Aug 2014
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    Location: North Fort Myers Florida

    bakeefe4 Junior Member

    But would increasing the draft improve the stability, also if adding a false v bottom then I would have to cut the transom to lower the prop correct? that is why I was going with the ballast in the center of the flat bottom.
     
  4. bakeefe4
    Joined: Aug 2014
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    bakeefe4 Junior Member

    how much displacement could I get by adding 250 of water as the ballast and could I expect an increase in draft especialy when live weight is also added.
     
  5. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    The easiest way to describe what you have is:

    If you have a flat tray..say 300x600mm (or 1 x 2ft) and has a small amount of water in it. Try and carry the water without spilling it...not easy!!

    You have such little draft that any movement off centre whether from waves, or person(s), the buoyancy required to support that trim/list, is a very large %'age of the total. As such to accommodate the change, the hull trims/rolls to maintain its equilibrium. As shown below:

    box hull roll.jpg

    If you had more draft, to begin with, that would help matters since looking at hull above the "d" if this is small, you have not got much stability. More hull needs to be submerged to maintain the buoyancy. What that means is the buoyancy required to aid it to restore it back to up right when list/rolling is small. Since the restoring arm (a measure of its stability), to bring the hull back to up right, is a function of the displacement.
     
  6. bakeefe4
    Joined: Aug 2014
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    Location: North Fort Myers Florida

    bakeefe4 Junior Member

    ok then if I was to raise the floor 6" and leave a cavity in the center line 1' wide and 8' long that would get me aprox. 4 cubics of water at 62.5 lb per cubic that should sink the boat some and increase the draft the only problem i come up with is it going to be enough to get me to the draft needed. How much water ballast would I need to displace enough to reach the 10" draft i am looking for and will that help with the stability.
     
  7. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    It's a double edge sword.

    Since the stability is governed by the BM = I/V

    Where I = waterplane inertia...which in your acse is constant.
    Then V = volume.

    You initially have a high BM, because your volume by comparison is low, but as you increase the draft the volume increases which reduces your BM. There will come a point when the BM, linked to your KG may be worse. As shown below in a similar example:

    box stability.jpg

    So you really need someone to investigate this properly for you. To get the hull into a simple stability program and then someone to do an inclining experiment to determine your KG in the lightship condition. Once you have that info...it is a lot easier to advise. Since a simple "what if" can then be conducted within the stability program. Since, you may find that no matter what changes you make, the end result is the same, so a waste of money...but you won't know until you investigate it.
     
  8. Milehog
    Joined: Aug 2006
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    Milehog Clever Quip

    Is the structure up to the added stresses this would create?
    IMO you have a novelty suitable for mill pond conditions.
     
  9. bakeefe4
    Joined: Aug 2014
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    bakeefe4 Junior Member

    Well my Mai concern is that my kids get to enjoy it sadly that is why I bought it. I do thank you for your help. But it seam that what I might need to do it take it back to the same spot put about 300 lb of weights in it and check ck the draft then before I do anything else. At worse case they can use it on days that are sunny and nice. I still think the floor ideal is a good one at least for looks even I I don't do the water ballast... I just thought if I added water for the weight that would help and also allow me to pump it out so not to increase the trailer weight... I have noticed the errors in the design and have thought of building another one but with the improvements.... I do welcome any more suggestions. Thanks
     
  10. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    I'm not sure how you've "noticed errors in the design" considering the whole thing is an error, obviously by someone that hadn't a clue about the dynamics involved.

    The best suggestion anyone could offer is to use this as a garden planter, before your kids get hurt or worse in the thing. Simply put, it's a joke (to say the least), built with ridiculous materials and designed to capsize.

    For example, the rub rail is from a product we call "smurf" in the trades, mostly because of it's color. It's been banned for electrical use in Florida as it has nearly zip UV resistance and will literally turn to dust, in typical summer temperatures. I've replaced hundreds of feet of this stuff used in homes and after just a few years in someone's attic, it crumbles on touch. Just imagine what will happen if used as a rub rail in the Florida sun. Another example is the delaminating plywood, indicative of non-WBP grade material. If these are the choices of the builder, the rest of the boat has to be similar, so do yourself (and your kids) a big favor and park this puppy on the hard somewhere and buy a set of plans for a new, simple, stable and reasonable little putt putt, so you and your kids can have a safe day on the water.

    Something this size requires just a few sheets of plywood, some 1x2's, a little glue and paint. Get one from a real designer, not a freebie found on line from an unheard of nobody, that doesn't answer his phone, once the plans are delivered.

    Bluntly, I see so many things wrong with that thing, I'd considering burning it, just to prevent someone else from buying it and making the same assumptions you have. I'm sorry if I've just burst your bubble about this project, but it's a drowning waiting to happen IMO. You live in the same state I do and we hear all to often, about people getting hurt and drowned on boats built by respectable manufactures. This thing isn't even remotely close, so . . . it appears to be Wylee Coyote's latest acquisition from ACME products, to catch the RoadRunner . . . maybe just missing a few rocket motors?
     
  11. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Damn, I guess I killed this thread . . . sorry, was it the RoadRunner crack?
     
  12. SukiSolo
    Joined: Dec 2012
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    SukiSolo Senior Member

    Nah, the Roadrunner left with the 4 HP mercury as the only salvaged item.....;)
     
  13. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Well the battery, fuel tank, it's hose and bulb, the fire extinguisher and possibly that very stylish foam padded PVC ships wheel would be worth saving too. I still picture it with two ACME rockets duct taped to the top of it, with Wylee holding a match . . .
     
  14. bakeefe4
    Joined: Aug 2014
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    Location: North Fort Myers Florida

    bakeefe4 Junior Member

    I tried to be nice and let it all go but I guess this is no Shively at all on the web. Just to give a little info to your joke. I elderly man I k ow once had the dream of building a boat. He found out that he was terminal with just a short time to complete the things he had dreamed of. And this boat is what he built. And no not everything he did was correct and up to your standard but he was able to complete it before going on to a better place. The electrical outlaw conduit is in fact pool vac hole you ***** and the wheel is wooden... But atleast he tried to do something good with his life and accomplish a dream not try and make himself feel better and crush the attempts of others.I did not look to have hua dream insulted of completely change his vision only improve a little to improve the stability so I will gladly say thanks for spitting on the grave of a man I am proud to call a friend and for you showing that I fact there is no truly descent person that can just simply be a help with out belittling someone else to do nothing but make themselve feel bugging..... Wake up call we all come from the same place and we all go to the same place. Let's just pray you memory is not treated the same.... Good day to you sir....
     

  15. bakeefe4
    Joined: Aug 2014
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    Location: North Fort Myers Florida

    bakeefe4 Junior Member

    So again PAR you could learn a thing or two... Like I'd you have nothing nice to say then don't say anything at all.
     
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