Long - Skinny Power Boats

Discussion in 'Boat Design' started by SAQuestor, Sep 24, 2004.

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  1. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    so your requirements need to be 'drawn' up...otherwise it is a list...just a wish list. You need the list, your SOR, to be made into a concept that some basics can be established...so you need to draw up the layout, does it fit, do u need a longer hull..do u need a catamaran..do u need a tri...too many what if's...you can only draw up what u want....you ahve to start somewhere....you're at the point where if you don't....it'll just remain a dream in words rather than reality.
  2. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    "...I think Ive made some good decisions go find myself a competent NA and let him do a cost analysis.."

    A shipyard will give you cost.

    A competent NA will just scrutinise your work and then tell you if it will work, not pay lips service to your wants. If you're serious, you need to get the basics with a NA now, not later.
  3. Boston

    Boston Previous Member

    Ill know what I want when I figure out what works best
    and Ill be a whole lot happier figuring it out by consensus in a group setting than going on one mans opinion
    no shipyard brother
    if its anything like home building
    most of those guys look like they just got out of prison and I wouldn't trust em to build an outhouse
    no thanks I am fully capable of building it with my own crew under the supervision of the NA

    thing I always hated about clients I was designing a house for was that they were generally clueless about how things go together and they tended to want mutually exclusive design concepts
    Victorian porch elements on a post modern house for instance or a multi story house that had 9' ceilings and looked like a single story from the outside or that you couldnt see from a mile away

    my deal with designing the boat is to strugle out the various components and get an idea as to what I want
    basically if yacht design is going to be a no right answer science
    then some of these decisions will be made by consensus of opinion in a place like this were the opinions are generally informed ones
    not sure if you have been over to the climate thread yet
    now that is one seriously misguided group of people

    point is that each design element has made itself self evident the more I got into it
    this one will as well
    box keels are supposed to be pretty dam efficient
    tri hulls are supposed to be pretty dam efficient
    one will be better in the open sea than the other
    one will get better millage
    bla bla bla
    so I thought Ild start with the millage
    whats the deal

    two boats of the same length and weight
    one a box keel
    one a tri hull
    given the same power plant
    who wins for fuel efficiency at the same speed
    whats the speed
    Ild like to see say 15 kts
  4. Guest625101138

    Guest625101138 Previous Member

    You have to iterate with this. You need to set out the requirements such as cruising speed, range, accommodation, amenities, tankage etc.

    Taking 19t as the upper limit the lowest drag 18m hull form gets quite unrealistic. It has a draft of 1.9m and beam of 720mm. The power on the hull has now gone up to 64kW.

    If the draft was constrained the power will go up again.

    The important thing is to set out the things you want from the boat and go from there. The problem with this concept is that you are starting from scratch so there are no readily available examples that you can take data from.

    Rick W

    Attached Files:

  5. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    "...my deal with designing the boat is to strugle out the various components and get an idea as to what I want.."

    Well, you have a basic SOR. But you need to progress from this, otherwise you be like "..clueless about how things go together and they tended to want mutually exclusive design concepts.."

    Because design is just one big compromise. Until you decide what is important, and list them in order of merit, ahve them drawn up on a general arrangement that satisfies your basic concept of what you want, you shall be clueless too, to why the reply is as it is. You're going around in circles.

    Hence, draw it up yourself, or get someone to do it for you, but you MUST get it drawn up before talking any details and making any radical changes/decisions based upon, what...er...um...another idea that's unproven for your boat!

    I cannot give any more advise, until you get your boat drawn up....it is meaningless to do so...
  6. Boston

    Boston Previous Member

    ya that hull doesnt look like its going to work at all
    there is a solution in there somewhere just got to find it

    speed should be 15 knt
    range should be 2000 miles
    fuel load is 7 tons to make that 2000 miles
    4 people in two dbl berths
    4 people need to to 7.5 days food and water so call it 1500~2000 lb of supplies
    that makes about 8 tons of cargo including fuel
    so there is about 26000 lbs of boat involved
    assuming 42000 ttl

    lets just stick to the basic comparison to hull efficiencies for the moment and Ill see how its incorporates once it is determined what is best under what conditions

    what happens if you make that hull wider
    say enough to get the draft up to about 1 meter
    then reduce the primary hull to only carry say 75% of the ttl disp

    think Ild want the primary hull in the trimaran configuration to hold say 75% of the weight
    so that 42000 becomes 31500 and the two outer amas hold about 5350 lbs each
    in a 60' vessel thats still going to be a pretty long skinny hull
    each one is long and skinny in itself so although Im paying in surface friction Im saving in pressure of depth
  7. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    "...lets just stick to the basic comparison to hull efficiencies for the moment..."

    well, you can discuss with Mr.Numbers and get hull forms that displace 5t when your fuel requirements is 7t...or you can forget efficiencies fro now and focus on what is required first.

    As I said before, amaterur designers, non-naval architects and those that tap away into programs on their PC will talk about efficiency until the cows come home..why.??..because they have never designed a real boat before and have no frame of reference other than a series of numbers.

    It is your choice if you wish to continue discussing numbers, that is your prerogative. But I gave you credit from your post about building for others etc that you understood this concept. Perhaps i'm mistaken....my bad!
  8. Boston

    Boston Previous Member

    I got the concept
    had I been designing a house for the first time I would have gone through the same basic process
    learn a few things
    then go talk to someone
    Im still learning a few things draw up some sketches
    which I have
    thing is its time to get a hull under these numbers and as you yourself said
    this is an inexact science
    what the sciences do when they have an inexact conclusion is derive a percentage of confidence from a consensus
    thats what Im after on this hull issue
    some folks will explain what hull they like and why what they do best and where
    so on and on
    those are the folks Im looking for
    I think you underestimate Rick
    he doesnt just seem like a pencil pusher to me as he's got more screwy designs he's worked through to floating than a lot of folks in here
    thing is being as how this is an inexact science a conglomeration of opinions is going to paint a better picture than just one
    should I go bother 10 designers into some kind of design contest
    or should I just join a design group and learn a few things before Im ready to rock and roll
    this is a great way to interview possible NA's for the task
    got some great folks hiding behind this computer screen
    one of em just might end up making a few bucks off me who knows
    I got lots of time before im ready to move back to the coast and start building

    thanks though
    I appreciate the help
    that hull resistance formula will come in handy

    comparing basic hull configurations
    say long skinny hulls
    is what this thread is all about though isnt it
    seems like an excellent educational tool that might just allow me to make a better decision in the end
    so I do appreciate the help
  9. Guest625101138

    Guest625101138 Previous Member

    Once you start getting up in weight there is advantage spreading the load across more hulls for a length constrained vessel. This is something that Matt Marsh arrived at when he developed the faux-tri concept for his needs. Although his ended up as a conventional trimaran.

    If you reduce the power requirement then the fuel load comes down accordingly.

    It is useful to set up a spreadsheet that sets out your requirements. This way you can link dependencies. Displacement is an important requirement to narrow down. Some things will not change through the iterative process as they are set and independent of other factors. Others will. A hull that is easily driven will have lower forces on the propulsion system so mountings get lighter. The engine will be lighter. You will need less fuel.

    At some point you need a complete list of all the items in the boat to build an estimate. Right now their weight is the data required.

    Rick W
  10. Boston

    Boston Previous Member

    the original numbers are all for that old elco
    so my thinking is that by optimizing the hull the fuel load and weight can only come down compared to a hundred year old design
  11. yipster
    Joined: Oct 2002
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    Location: netherlands

    yipster designer

    i'm trying to attend a session and this tread was on top, anyone "in" here
    Nigel Irens http://www.proboat.com/ June 10, 1 pm US EDT and Live: Designing Fuel-Efficient Powerboats
    i keep gettin "your allready registerd for this" but cant get in
    so what am i doing wrong how to get in later up to 90 day's after..
    anyway, here the masters filosofie on LDL http://www.nigelirens.com/
  12. Guest625101138

    Guest625101138 Previous Member

    Do you intend to build the boat yourself?

    Is unsheathed wood your material of choice?

    Are you wedded to the steam propulsion?

    If these are criteria for the boat then they need to be included in the design requirements.

    Rick W
  13. Guest625101138

    Guest625101138 Previous Member

    The first link just loops. I have no idea why some sites do this.

    The nigelirons link has some nice concepts. The little clip at the beginning of one of the LDL designs looks good.

    I like the way the LDL vessels slice through the water. I have recollections of beamier boats slamming into even moderate seas no more than 1 to 2m high. Absolutely bone jarring. I expect the same conditions in these fast LDL hulls would be less severe.

    Rick W
  14. Boston

    Boston Previous Member

    most definitely
    I just won a contract to do a black lacquer front entry on one of the old Victorians down town. I had to talk em out of a black lacquer hand rail around the deck and they are talking about doing the deck in black walnut although my vote is for baked poplar, its cheaper and better in this application. Ill be hand turning the rail components and the spindles in the same material. I think Im capable of building just about anything and have from highrises to antique English conservatories, my skills are not the issue its the vagaries of yacht construction that will require I hire a decent yard manager/NA to oversea each aspect of the build and double check my work similar to the inspection process Im used to as a builder. I have no intention of winging it nor do I plan on ignoring the advice of folks who do this for a living. I will also not be pressured to begin or throw my hat in with anyone until I am comfortable that I clearly understand the entire process and why each decision is what it is, which is pretty much why I joined this site.

    I have no decisions set in stone and believe that this process needs to be an organic one that is allowed to grow the more I learn

    steam propulsion is a strong contender but not the only one Im considering
    so far its main draw backs are the mass of the fuel and the blazing fire in the bottom of what amounts to my life raft
    course each fuel type has its draw backs

    I am glued to the idea that I will not start anything untill I have all the funds fully available, no bank, cash on hand
    which means I earn it off my trade account ( I had a stellar day by the way )

    Im all about low embodied energy
    wood meets that need
    if another material can be shown to be as easily reparable as readily acquired and as comparably cheep then I will consider it

    I plan on using natural glues wherever possible and only encapsulating the last layer of the double diagonal planking in epoxy under paint and copper bottom
    Im however pretty well set on it not exceeding 60' length 4.5' draft and 14'beam although a little smaller is ok
    I prefer to remain flexible throughout the process in order to incorporate the best of all worlds

  15. Guest625101138

    Guest625101138 Previous Member

    Your strategy is sound apart from the day trading aspect. You might get lucky and actually be one of the few that make money.

    I started with pedal boats to learn about efficient hull design and propulsion at a scale that is fun to use. After I sold my last yacht I began building model boats but i did not find them highly rewarding. Playing with pedal boats has taken me in unanticipated directions. Not a lot of new stuff but ideas and knowledge that are not widely known.

    Rick W
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