Vintage aluminum Crestliner project

Discussion in 'Boatbuilding' started by Alumination, Oct 24, 2013.

  1. Alumination
    Joined: Oct 2013
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    Location: Knoxville, Tennessee

    Alumination Junior Member

    This is my first post, be gentle.

    I recently purchased a 14' Crestliner boat as a starting point to build a general purpose speedboat. I have big plans for major modifications so I decided it might be wise to develop an actual plan before cutting, riveting and welding.

    I had considered building a wooden replica of a vintage barrel back design but decided to try the aluminum route instead. I'd like to keep a vinage look above the water line but use the best design below. I'd like for it to do everything well but priorities are ride and handling in freshwater lakes and rivers, no 6 footers to deal with. I'd also like for it to be fast but not sacrifice much in the ride or handling department.

    I'm sure I have lots to learn and need to better layout my plans.
     
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  2. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    How will you decide on how to modify the hull? Have you tried the boat as it currently exists?
     
  3. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Welcome to the forum.

    Depending on the design's current arrangements, I think you'll find matching up the existing chine with a modified bottom shape very difficult to execute, as a retro fit.

    You can have a boat that rides like a '53 Buick, in protected waters, but isn't especially fast, nor maneuverable. On the other hand you can have a scary fast boat, that handles like crap and beats your dental fillings out. Think of it as a car, you can't have a Corvette that rides like a Caddy, nor a Caddy that'll handle and scoot like a Corvette and interestingly enough the same reasons it doesn't work in a car are true in a boat.

    I suggest you enjoy your boat, maybe some 1958 fins on it's flanks and have fun. If you want a refined design, you'll have to accept the compromises that come with it and likely approach it as a new build.

    Poat some photos and we'll see what you might be able to do.
     
  4. Alumination
    Joined: Oct 2013
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    Alumination Junior Member

    My general plan was to just copy a good hull design or use design aspects of hulls that work well. By good handling I meant something which is easy to drive and not a radical compromise to some other feat, top speed, fuel efficiency etc.

    I do like your comparison to a car so think BMW or modern Cadillac, Lexus etc., a compromise of good ride and good handling. I know a bit more about car and motorcycle suspension than hull theory.

    What constitutes a "new build" ? I can accept that a refined design may require some major re-working of various areas.

    Here is the Craigslist ad:
    [​IMG]
    [​IMG]
     
  5. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    That's a round bilge hull, meaning you'll have an exceedingly difficult time, retro fitting any "improvements" such as converting from the warped bottom that it is, to a monohedren (for example), which would be a better hull form at higher speeds in rough water.

    As she is, that design will do well with modest power and at speeds below 35 knots. For a boat of this length, that's fast enough. It you push it faster, she'll progressively display bad manners, eventually becoming dangerous to operate.

    What do you want this boat to do better? As designed she's efficient, fairly smooth riding in protected water, she's light and economical to operate. To go faster, you'll need an all new bottom, from rub rail down, maybe saving a few feet of bow, but everything else goes. She's too short o put a cabin on her and she'll be quite crowed with a center console, so . . . what do you want from this little tinny?
     
  6. Alumination
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    Alumination Junior Member

    I'd like to add a platform similar to what bass boats use and HydroStream was so famous(infamous) for. Whatever necessary for a good balance between speed, ride and handling. A bass boat would be a good example, the last few I've ridden in did all 3 well.

    As for use, just a speedboat for 2-3 passengers. No cabin, no center console.

    From what I have gathered here, length would need to be increased. This would also allow me to shape the rear more like a barrel back or some other vintage look.
     
  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The typical bass or flats boat is shaped wholly different then this tinny. I'm not sure what you mean by platform - a casting deck forward maybe? If so, this isn't a problem, attach a cleat around the perimeter and drop a hunk of plywood down on it.

    Maybe you need to look at the bottom of a bass/flats boat and take pictures, so you can compare them to your boat, which (again) is completely different).
     
  8. michael pierzga
    Joined: Dec 2008
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    Location: spain

    michael pierzga Senior Member

    Your little crestliner is a beautiful boat. I would clean her up, put a lightweight 10 hp on her and keep her as a classic ......then build a new boat purpose designed to fit your needs

    The detail in your crestliner that is hard to overcome is the shape of the transom and her round chines. A fast high power skiff will be hard chine with nearly square transom. When you go fast this aft part of the boat is the only thing in the water. It has to be correct


    Have a look at bateau.com http://www.bateau.com/studyplans/RB14_study.htm?prod=RB14
    Its a very simple boat with classic lines
     
  9. Alumination
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    Alumination Junior Member

    By platform I mean a flat area the boat will ride on when up to speed. I may be using the wrong terminology, I think "Pad" is a better term.

    Like this-
    [​IMG]

    So it rides with very little of the boat in the water for less drag, greater speed.[​IMG]

    I'll save the 4.0 Liter Toyota V8 and stern drive for a later discussion. :D
     
  10. michael pierzga
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    michael pierzga Senior Member

    Look at how the high speed boat rides a the aft section of the boat. The planing shoe

    You crestliner has the wrong shape
     
  11. PAR
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    PAR Yacht Designer/Builder

    The problem with pads is they're really difficult to shape well and they're only effective at specific speeds, just adding drag at all other speeds. Designing a pad takes a lot of high speed hydrodynamic understanding.
     
  12. Alumination
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    Alumination Junior Member

    Is there a thread or section where I can brush up on my vessel vocabulary? Like planing shoe for example.

    This is what I intend to change, the shape of the bottom of the hull, below the current waterline, almost like placing my boat on top of a wonderfully fast, agile, delightfully riding hull.

    Might you know of a website with a forum full of enthusiasts dedicated to the design of boats somewhere on the net? :D

    I read somewhere there is a fellow real good at this kinda thing, I think his name is Tunnels, maybe. ;)
     
  13. Alumination
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    Alumination Junior Member

    So, while I'm new and aggravating my new found friends, let me continue to blather on about the plethora of ideas I've conjured up over the years from the various designs I've been exposed to.

    Most recently has been watching how much better a Remote Control tunnel/cat hull performs. More stable at all speeds, less roll when turning, handles chop so much better and FAST! I understand there is a greater Aerodynamic element to tunnel/cat hulls than the traditional "V", the effective "wing/deck" area, managing lift, etc. However, not all tunnel/cat hulls I've seen are direct variations of the amazingly fast offshore racers, some have alot more above the deck area so no real top area to the "wing".

    Might anyone suggest some good reading here or elsewhere that I might use to better familiarize myself with the basic design and how the various aspects and measurements work together etc. ? I've seen the book Secrets to Tunnel Hull Design mentioned and would buy it if it truly has good information not only to explain how they function but also good guidelines on how to design and build something. I've purchased many a book over the years that has been highly recommended just to find it to be very vague and not as helpful as many would have led me to believe, especially with the vast information available on the internet.
     
  14. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    What you're asking is for a distillation of the hydrodynamics of planing hull design, which is well beyond what you can easy absorb here. For most of us it takes years of study, then we sneak up on high speed craft with progressive design expansion, built on previous experience.

    Simply put, what you're hoping to do is exceedingly difficult for a professional, so your prospects are less then desirable to say the least. This doesn't mean it can't be done, but does mean a professional aluminum builder would seek the help of a designer or NA, then would follow the plans carefully, knowing the risks of not doing so in high speed craft.

    This is why you're frustrated, as we've all danced around attempting to tell you, what you didn't want to hear. This happens frequently and I suppose in other fields as well, such as the aircraft industry. I can picture a fellow with a Cessna 152, thinking all he needs to do is move some new wings back, make a canard, install another engine and bingo he has a Rutan Long-EZ , but when told he just doesn't have a reasonable starting point both in the base ship and his aerodynamic/engineering skills, he gets pissed. This is the case with your boat. It'll be (again) exceedingly difficult to make this a high speed monohedren, tunnel hull, cat or cigarette, etc. type hull, without a huge investment in materials, time and of course the prerequisite hydro and engineering issues.

    This is an oxymoron. You should take a ride in a fast and agile boat. The first thing you'll notice is the ride quality and the real serious need for thick seat cushions and sprung seating. You can't have a Corvette that rides like a Caddy. You can have one or the other, possibly one that's sort of fast and comfortable or fairly comfortable and sort of fast, but not both. Having driven 100 MPH powerboats of my own design, I can assure you, ride comfort isn't something that was in the description of it's performance envelop. Pound your dental fillings out, blow your kidneys out, crush your knee cartilage, were much more accurate descriptions of her performance. I'm just grateful of the 4" high density foam in the seat. There's a reason you need to strap into these boats, with a functioning deadman.
     

  15. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    Alumination - Are you thinking of your proposed boat modifications as similar to an automotive hot rod project: start with a body from an old car, put a new frame and suspension under it, add an engine much more powerful than the original, etc?
     
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