Jet Boat Hull Design

Discussion in 'Powerboats' started by Ziggy_Mustard, Jul 12, 2006.

  1. Ziggy_Mustard
    Joined: Jul 2006
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    Location: Vancouver, British Columbia

    Ziggy_Mustard New Member

    Gents, :eek:

    I'm a Mechanical Engineer and I'm new to this site. Couple of weeks ago I started designing a jet boat hull and I was wondering if someone could recommend one or two good marine engineering/powerboat design books?

    There are a lot of books out there, but I only want to purchase one of two good ones. Unfortunately may background is s in aerospace/automotive/machine design and I'm just getting into boat design.

    Thanks guys,
    Peter
     
  2. Tim B
    Joined: Jan 2003
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    Tim B Senior Member

    Renato Levi Wrote three books on the subject of designing Powerboats. They all concentrated on shaft-drives but should give you somewhere to start. As I remember, they are nigh impossible to get hold of (you may have to order directly if you can find the website) but they are well worth reading.

    Tim B.
     
  3. Tad
    Joined: Mar 2002
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    Tad Boat Designer

    Ziggy,

    Do you want Hydrodynamics or Structure?

    Sonny Levi's books are great history, and clearly illustrate what he did 30 years ago. But that's not what you need to actually design a decent boat using available science and constuction methods/materials.

    Best book currently available on powerboat hydrodynamics is Hydrodynamics of High-Speed Marine Vehicles, by Odd M. Faltinsen, ISBN 0-521-84568-8

    Best on design loading, composite construction, and form is Principles of Yacht Design, 2nd ed, by Larsson and Eliasson, ISBN 0-07-135393-3

    If you are working in Aluminum, go to ABS, Lloyd's, or ISO and get rules for construction of high-speed vessels.

    Jet boats are tricky, most major water-jet manufacturers have lots of data on what works, talk to the supplier.

    All the best, Tad
     
  4. Ziggy_Mustard
    Joined: Jul 2006
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    Ziggy_Mustard New Member

    Gents,

    Thank you for your recommendations - very helpful input!

    Tad, you mentioned that jet boats are tricky ... can you give me more information - what should I be careful with. I planning on using a Mercury Sport Jet and I'm doing the design (including flat form layout) on ProEngineer.

    Thanks guys,
    Ziggy
     
  5. Tad
    Joined: Mar 2002
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    Location: Flattop Islands

    Tad Boat Designer

    Zig,

    Relate 20+ years of experience with jet boats in one post??...Hey, that's why they pay me the big bucks! :D

    Okay, a short list.

    Watch your weight!!
    Minimize deadrise aft.
    Reduce chine beam as much as possible to minimize trim and hump drag.
    Run a series of drag calcs, isolate hump speed, adjust LCG to minimize drag in that area.
    Pay attention to planing surface area vs weight.
    Carefully map thrust vs drag, especially at hump speed.
    Keep the bottom clear forward of the intake, no lifting strakes in line.
    Be careful of the transition from vee to flat at the intake (pad)
    Watch your weight!!

    All the best, Tad
     
  6. Ziggy_Mustard
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    Ziggy_Mustard New Member

    Thanks Tad! I'll keep you guys posted as I work on the design and work out some of the details. The current plan is to start cutting material on the CNC by the end of the year.

    Cheers,
    Ziggy
     
  7. speedboats
    Joined: Jun 2006
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    Location: New Zealand

    speedboats Senior Member

    How big of a boat are you after. The merc sj175 does offer a reasonable amount of thrust, but the downside is that in their infinate wisdom, Mercury put the exhaust from the engine in the cavity between the hull and jet unit. While this doesn't effect performance, if you have an alloy boat it can get rather loud. Put some thought into sound deadening, like hull liner throughout the inside of the boat, use urethane to glue any items that may be stitched to absorb vibration, and use a ply floor (but NOT the marine treated stuff)

    A phenomenon known as porpoising can occur if you are not caqrefull of what you are doing on the bottom, particurly in the 6' infront of the transom. This area needs to be longitudinally flat. If you have a 'rocker' the boat will bounce around, or porpoise, if it has a hook it will bow steer badly, possibly causing the boat to spin in a turn. This is because there is nothing at the back of the boat causing drag.

    Make the delta pad on the bottom nice and long, no-one says that the boat needs a 'keel', where the bottom sheets meet to form the vee. I tend to think of those that do as 'old school', and perhaps we should scrap the shuttle and fly the appollo missions again.

    As previously stated, do not put any apendages infront of the intake. As in aerospace, the trailing edges create a vortex, much like the tips of a wing, only in water that usually means that air is bled off, if that air makes it to the intake the pump will cavitate causing loss of thrust. Look at not only straight line performance, but also where any vorticied will end up in a tight turn (if you terminate your strakes ahead of the intake), if the unit cavitates during a turn and you loose thruse, a real nice jet spin often occurs, sometimes at an inconvient moment!!!

    Look at other jet boat manufacturers and what they do, we spend many hours making sure we get it right so we can sell a safe and well performing product.

    Check us out at www.speedboats.co.nz We specialise in trailerable jet boats and commercial adventure jetboats both in New Zealand and the USA.
     

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  8. hmattos
    Joined: Jun 2004
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    Location: Devon UK

    hmattos Senior Member

    We have worked with Hamilton Jets on several jetboat designs - diesel powered for sportsboats and for rescue / police missions.
    I would thoroughly recommend a visit to their site www.hamjet.co.nz
    You can see some photos of our boats on our site www.explorermarine.co.uk
    As has been said the key is power to weight and planing area in both laden and light conditions. We use 15 or 2 degree vee angles at the transom and keep the strakes wide .

    Good luck

    Hugh Mattos
    www.explorermarine.co.uk
     
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