chine too high?

Discussion in 'Boat Design' started by tugboat, Oct 6, 2013.

  1. tugboat

    tugboat Previous Member

    just want to know if a chine can be too high at the bow and what is the practical limit? could this as it is, work on a tugboat design?...see pics..
    steel hull 30 ft'er.
    note waterline

    thanks in advance...

    Doug
     

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  2. El_Guero

    El_Guero Previous Member

  3. tugboat

    tugboat Previous Member

    center of floatation and LCB = about 15 ft on this 30 ft boat- right where it should be isn't it? i.e. balance point is right at the center...but maybe your right...ill investigate further
     
  4. El_Guero

    El_Guero Previous Member

    Yes, 'your balance point' is in the middle, but so is all of your flotation. It will make your tug behave like a very narrow kayak instead of a tug.

    IMHO.
     
  5. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    I think it is the big vee you have in the bottom , rather than something flatter, that is what he refers to. Certainly the initial stability will be a touch less than what you might like.
     
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    It's hard to tell without a full body plan, but it appears you have a full, deep but moderately steep entry and considerably more bearing area aft. Again, without a full body plan, I'm just going by the profile, which I assume loses deadrise and flattens out aft of midship. If this is the case, she will not be as rolly as some might think. An old school approach would be much steeper V shaped entry, with more deadrise then you're showing midship and flatter sections aft.

    I'd tend to agree, that this isn't the shape you want for comfort in a seaway. Make the entry with much more U shape and have this transition, into nearly dead flat midship sections (stiff bilge turn), and lastly transition aft, to flattish V sections for power or a bit steeper (more deadrise) for efficiency.

    You don't want your "balance point" at 50% of the LWL. Generally, on a vessel like this you'll want a steeper chine forward, with more belly amidship, steeper buttocks and you'll likely need to drag some volume aft, to make her trim properly, which will drag the garboard plate out toward the rudder a bit, with significant twist.
     
  7. tugboat

    tugboat Previous Member

    in some ways that's a compliment- I wanted the tug to move easily since it is a steam design...it is only 10 ft beam...? isn't that like the old fantail launches?
     
  8. tugboat

    tugboat Previous Member

    how much would a "touch less" actually be? do means a lot? I can deal with a little bit more roll. Or I could decrease the deadrise on it and flatten the hull out a bit at the bottom but with the compromise of more pounding in a chop?
     
  9. tugboat

    tugboat Previous Member

    Thanks again Par-- you've always been helpful to me.
    seriously--im just thinking of giving up and throwing in the towel-
    I understood about half of what you said. I guess im just not cut out as a designer.

    but the paradox goes like this- I like a certain vessel off the shelf. but it always has something I hate. like the Fred Murphy- Id build that one- its "almost" perfect-and yes I do know there is no perfect- but it has a huge flaw in mho.
    it has flared sides. and thin plate which cannot be increased.
    1. no tug should ever have flared sides for true work.
    2. you cannot weld thin plate very well even though they state their "shrink" wrap method is so fair it needs no fillers and looks like a hull molded in frp.

    but I know welding- and 3mm plate will distort unless you can tig it...and that's just not an option.
    but the flared sides is what really kills me....

    so maybe after 5 years of seeking the right design in the right material -it may be over. my dream is/was a tugboat. its all I wanted.no other boat comes even close. most I find ugly. and wanted to have a good tugboat that could handle the great lakes...but Im checkmated here. I could build a flat bottomed rockered design as shown in my early posts- and even though the
    white paper by the designer suggests nothing to worry about- prefer a sharp entry ona tug- like the old time steam vessels. even though its not as effective for working. so Im left with a very very few options...
    Par - I may just disappear from here- and if I do- thanks for the help... time will tell...see how I feel. Ill do a little more research on it I guess. But im almost through...maybe some dreams just aren't meant to happen...
     
  10. El_Guero

    El_Guero Previous Member

    Tug,

    Get an NA to actually help you with the design process.

    Five years and steam? You are not doing this to make a profit, you want what you want.

    wayne
     
  11. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

  12. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Godzilla is "tug like" (toy like?) but not what I think he wants. It has some styling clues, but that's about it.

    Ultimately, you'll have to decide what you want. A working tug is a burdened beast and though it has the styling clues you desire, just not much good for anything else. They aren't especially good sea boats, though their mass does make them survivable in rough conditions (not comfortable, but tough enough to survive).

    If you want a working tug, there are lots of stock plans available. If you can accept the design decisions, made for the underwater sections, you can then modify the topsides to suit your aesthetic requirements. If you want a tug looking boat, you can look into an acceptable hull form, maybe one with some efficiency and modify the topsides to have a tug like look.

    I don't think you have a difficult set of decisions to make. A real tug, well a set of stock tug plans is in order. A cruiser that looks like a tug, maybe with some abilities to earn her keep, well this will be a semi or full up custom, but you could probably do much of this work yourself, though the underwater areas might need some professional help, in regard to moving the chine to a more acceptable location, while still retaining some level of efficiency.
     
  13. u4ea32
    Joined: Nov 2005
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    Location: Los Angeles

    u4ea32 Senior Member

    The problem is you have all that buoyancy so deep. When the boat heels a bit, that buoyancy is right where you do not want it -- to "windward" if it was a sailboat. Make the hull flatter near centerline, especially where you have beam (e.g., its ok to be deep in the forefoot, because its skinny there, so very little buoyancy).
     
  14. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    U4ea32, I'm not sure what you're trying to say, but the "buoyancy" on that hull isn't especially deep at all, especially compared to a real tug.
     

  15. tugboat

    tugboat Previous Member

    RWatson, funny you should mention that- I did try to redraw my vessel using an almost flat bottom- same as the Godzilla. using a slight vee. everything unrolled perfectly. I think it was the huge "v" in the hull that gave me issues. so it looks like the problem might be solved- it wont be a heavy see tug- but good for the GL's!...I like Devlins design but not wood.im a steel guy.

    thanks mate!
     
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