help designing an inland huntin/fishing boat.

Discussion in 'Boat Design' started by bulletpruf40, Jul 24, 2012.

  1. bulletpruf40
    Joined: Jul 2012
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    Location: michigan

    bulletpruf40 Junior Member

    I've got Pro Drive X36 (which is roughly a 260 lb air cooled surface drive outboard mud motor, for those not familiar with it) on the back of a 15'x48" modified V 3° hull.
    My issue is, its slow to get on plane and with a light load, it tops out at 25 MPH. I know this motor is capable of 35 MPH. I want 45!
    I love the motor. I would do nothing to change it. My problem is the boat. Guys on other forums say "buy a new boat". That would be the easy way out. I am problem solver and always enjoy a challenge. I've been in the metal working field for over 15 years. Ive machined, fabricated, & welded various kinds of metals with alot of experience in the metal of choice for this build....aluminum. However possessing all these skills is only the beginning. I have no experience in marine engineering or hydrodynamics. Which is why I'm here.
    I've searched and read alot of topics before posting this. I've picked up a few tips but I know surface drives are a different kind of animal. Especially heavy ones that hang behind the transom.
    I'm looking for a little insight on hull design, length, & width. As well as placement of the livewell, fuel cell, batteries, passengers, etc. to achive the proper balance or center of gravity.
    I know a flat bottom is the way to go. Which is great in the marsh or bayou where the type of motor I'm running thrives, but I find myself busting whitecaps on 1000 acre lakes in November to breaking ice in January.
    What I'm looking to gain is faster top speed and a launch out the water from an idle position. I was thinking that a 17'x54" hull with a sport deck would help me obtain this. I like the modified V but rather that 3° at the transom I would make it flat. The thought of a stepped chine also crossed my mind though I'm not sure what could be gained. Less drag on plane while keeping bouyancy at rest? How would a tunnel perform? What is the purpose of the "ribs" (for lack of a better term) on the bottom of tthe hull and why are some boat manufacturers building flat bottom boats without them?
    I appreciate your taking the time to read and respond. Thanks
     
  2. bulletpruf40
    Joined: Jul 2012
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    Location: michigan

    bulletpruf40 Junior Member

  3. FMS
    Joined: Jul 2011
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    FMS Senior Member

    Designing an entire boat in words is a tough request. First you should post a drawing or some photos of your existing boat, itemize all weights and horsepower for a starting point.
     
  4. bulletpruf40
    Joined: Jul 2012
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    Location: michigan

    bulletpruf40 Junior Member

    I guess I'm not really looking for help designing the entire boat. Just looking for tips on a hull design and placement of the 3 heaviest things in the boat. The livewell, fuel cell, & batteries.
     
  5. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    WHen you say "mud motor", I presume that you are referring to the dragon tail type propulsion unit. Please verify.

    You told us the weight but not the horsepower. What is the claimed HP of the unit and what type of prop does it use? You want 45 MPH and that is achievable but maybe not so likely with a mud motor. You have to tell us a lot more than you have in order to get good and useful commentry.
     
  6. viking north
    Joined: Dec 2010
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    Location: Newfoundland & Nova Scotia

    viking north VINLAND

    Other than hiring a professional to help you design this machine, I would take a little fact finding trip down and chat with the Gator Hunting Boys in Louisiana. Seems to me one builder down there is very famous for this set up in aluminium.
     
  7. bulletpruf40
    Joined: Jul 2012
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    Location: michigan

    bulletpruf40 Junior Member

    I'm not sure what you're referring to with the term "dragon tail". Long tail maybe? No it isnt a long tail. With use of a Briggs & Stratton verticle shaft V-twin and a differential they're able to keep the prop about 24" or so from the transom vs. 50" like the long tail mud motors. The horsepower of the engine is 36. 45 MPH is not a realistic goal.....to my knowledge. 35mph would be a bit of a stretch but doable.
    I did contact a very well known builder in the south but he was of no help. He hasn't returned my emails. As a matter of fact I asked him to build the boat. Apparently he doesnt want to. So I guess I'm on my own......with the help from some experienced boat designers on this forum.
     
  8. BATAAN
    Joined: Apr 2010
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    BATAAN Senior Member

    Weston Farmer, a power boat designer for 60 years, put down a method of design review using cardboard and balsa flotation models in his book FROM MY OLD BOATSHOP that sounds like the answer to your questions about your projected design.
    Here are some screen grabs from that.
    You seem to have a pretty good idea of the hull shape you require, but need to further the design and especially the weight positioning.
    Using a floatation model for this process makes so much sense, as you can change the weight positions until you get good trim, all in a day or two of work and for less than $50, and it immediately shows up mistakes in motor, fuel or other significant weights.
    This is different from a dynamic or towing model, which is usually a larger scale, though not always in the past.
    For a thorough and very entertaining look at motor boat design, applicable to any boat, get the book.
    And please keep us posted on your, to most of us, interesting and uniquely specialized boat design and build.
     

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  9. HydroRocket
    Joined: Jul 2012
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    Location: Minnesota

    HydroRocket Junior Member

    Have you looked into building a semi-flat bottom? Being that you will be running a mud motor I'm thinking you'd like to be able to run logs and stuff but it sounds like you'd like a bit of the performance of a V hull. With the semi flat bottom (basically a V hull with the last half or 1/4th chopped flat) you'll get some of the log hopping stability yet get some of the V hull drag reduction.
    I googled and found this http://eastidaho.craigslist.org/bod/3140783673.html
     
  10. bulletpruf40
    Joined: Jul 2012
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    Location: michigan

    bulletpruf40 Junior Member

    I currently have a modified V with a 3° deadrise and it doesn't perform. It drafts too much and squats too much upon acceleration. I like the idea of keeping a V front with a flat bottom. I'm here trying figure out exactly how far forward to start the rise. Which will depend on the weight distribution and the waterline. I am picking up some good stuff in here. I really appreciate it. Keep it coming.
     
  11. bulletpruf40
    Joined: Jul 2012
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    Location: michigan

    bulletpruf40 Junior Member

    Isnt there a "rule of thumb" or a ratio to go by in designing a boat as far as weight is concerned? It seems like years ago I heard that 80% of the weight should be in the aft 60% of the boat. Is there any truth to that? Or are there too many variables to assume an equation like that?
     
  12. tamborjim
    Joined: Aug 2012
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    Location: Costa Rica

    tamborjim New Member

    Hey, Bataan, Peter, Jim Shaw here from old Sausalito days. Zack, the whaleboat, Cass, etc... Please write tamborjim@gmail.com
     
  13. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    the Pro Drive 36

    [​IMG]

    Take a garden tractor engine and marry it to a surface drive leg and you've got the picture.

    There are no simple rules or guidelines that will assist you Bulletpruf. The rules you might have read about, are purely generalities and nothing a designer would employ, other than for comparative purposes. The design process looks at countless, usually very conflicting variables and balances them out. Weights are the big issue and there's a lot more to it then just the "big three". Also your expectations might be a little unreasonable. If you have a boat that will hole shot nicely in shallow, smooth water, it will pound like a ****** outside a GM plant on pay day, in rough water. The difference between the squat on a 3 degree deadrise and a dead flat bottom will be negligible. In other words, a very modest 3 degree bottom and a flat bottom will both squat within a fraction of a degree (bow trim) of each other. It's a function of hydrodynamics and can't be avoided without a really excessive and obviously well executed, professionally done, custom design work. It would be very unlikely, you would be able to address all the "issues" associated with a design like this, though it would be possible for you to design a boat that doesn't, fairly easily.

    Simply put it would be nice if all you needed where a few tips on where things usually live on a boat, but you already know this: the engine is out back the pointy end on the front, etc. If you want a boat to balance and address the multiple concerns, desires and issues you've identified (and several you're probably unaware of), you'll need to hire a designer or start studying the process. If you're fairly good understanding math, you can self study into enough understanding, within a year. If engineering and basic algebra (high school level) aren't something you're comfortable with, then the process could be a wee bit longer.

    I don't think your needs are much different, than the needs that other designs have already addressed. So look around at Glen-L and Bateau.com for a design that saves you the heartache, of building a boat that doesn't do what you'd hope it might, because it's just as easy to build one of these, as it is to build one that is well suited to your needs.
     
  14. midnitmike
    Joined: Apr 2012
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    midnitmike Senior Member

    Encyclopedic knowledgedge and a true purveyor of wisdom. Why then will this be the image that stays with me the rest of the day? Thanks Par!

    MM
     

  15. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    If you want a shallow water hull form that gets up quickly, it'll be flat with a fairly bluff entry and proportionally wide in her butt. If you want a boat with good rough water abilities, then you desire a fairly fine entry, a reasonable amount of deadrise and less beam. She will not hole shot well, but it will "penetrate" much better and splay water to either side, as it bashes through the chop. I'm guessing my adjective selection here, hasn't helped your now seemingly disturbed dream patterns much, Mike . . .
     
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