Suitable Hullshape for 35m fast ferry in exposed seaway?

Discussion in 'Powerboats' started by BIGBOATBUILDER, Oct 16, 2007.

  1. BIGBOATBUILDER
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    BIGBOATBUILDER Junior Member

    Hi,

    I like to pick your brains regarding the best hullshape of a 35-40m fast ferry going about 35kn cruising speed.

    From a monohull perspective a planing hullshape.

    The tricky part starts here, as the seaarea is exposed to long ocean swell and the sea seems choppy between islands, something classic planing hulls do usually not excel very well in.
    To make matters worse, ride comfort seems to be of high importancy too.

    Any suggestions to a good compromise? Wavepiercing cat was my first thought, but my boss is not so fond of cats.
    Second thought bow T-foil stabilised planing monohull? Has anyone experience with these?

    Any other thoughts & experiences?

    Does anyone have a contact to a ferry operator working under similar conditions who might be willing to share some thoughts?

    Thanks for all input,

    regards,

    Charlie
     
  2. Time
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    Time Junior Member

  3. Jarrod
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    Jarrod Marine Designer

  4. Vega
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    Vega Senior Member

  5. RANCHI OTTO
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    RANCHI OTTO Naval Architect

    Fast Passenger vessel with excellent rough sea qualities...

    Length lwl = 56 m
    Speed = 35 knots
     

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  6. rwatson
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    rwatson Senior Member

    The japanese have similar sea states - went for an Incat ferry
    http://www.marinelog.com/DOCS/NEWSMMVII/2007aug00031.html

    I am not a designer or big boat builder, but I have travelled on these big wave piercers across Bass Strait, one of the roughest stretches of water in the world.

    The boats utimately got rejected by the Tasmanian government for the tourist trade because of their unpopularity - made everyone sea-sick.

    For what it was worth, I studied the phenomenom during the trip. On auto pilot, the steering was done by altering the thrust on the twin waterjets. This would cause the 'on power' hull to dip slightly as the course was corrected. The to and fro of the correction (say once every 2 minutes) produced a most horrible sensation to travellers even in calm conditions. It would have been much better to add trim tabs, if not full rudders, to stop this constant change of direction and pitching for passenger comfort.

    Good luck with the project - and for gods sake put some decent fully reclining seats, properly spaced so you dont get vomited on.
     
  7. BIGBOATBUILDER
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    BIGBOATBUILDER Junior Member

    Thanks to all of you! Especially Otto who even posted some lines.

    Ride comfort is the key. This is the reason why a 35m-37m cat seems not such a great option.

    People around me favour the option of a stabilised monohull over a multihull, even though I like multihulls generally.
    Primary reason is confined building space, limited beam (locks on delivery), and fast acceleration and deceleration in case of the multi.

    Otto's lines look interesting and surely work great, but the vessel has a quite different speed/length ratio, which puts it considerably closer to the semi-displacement range.
    So a more seaworthy semi displacement hull can be used, than for a smaller vessel with 35kn.

    Basically, what I mean is, that if I can gain more speed from the waterline length I can more easily:

    -Reduce the lifting surfaces in the bow by narrowing the bow
    -Thin down the bow sections by making them hollow as shown on Otto's lines.

    Both effects will allow the vessel to slice more elegantly through waves and reduce fast accelerations and decellerations which lead to seasickness.

    Still, my vessel should be max 37m long and go 35kn ;-(
    so I could do this "bow thinning" only in moderation.

    What is your opinion Otto, is this correct?

    Secondly I see the hollowed out running surface aft. Whats the train of thought behind it?

    Roll stabilisation?
    Trim angle reduction?

    Would be great to be allowed to pick your brains more, Otto.

    Anyone elses input is of course appreciated too!

    Regards, Charlie
     
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  8. RANCHI OTTO
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    RANCHI OTTO Naval Architect

    You right Charlie,

    the "bow thinning" always with moderation...

    I have designed the tunnels in the after part for the following reasons:

    * possibility to install larger propeller diameter
    * possibility to reduce the shaft inclination
    * increase the wake acceleration in the propeller area
    * reduce the dynamic trim angle
    * reduce the heeling angle
    * reduce the rolling at all speed range

    A central thin skeg was installed for lateral stability.

    Several tank tests were carried out at the Vienna Model Basin (resistance with and without appendages, selfpropulsion tests, painting tests to observe the wave path in the tunnels, etc.)

    The result for the propulsion efficiency was....."very good"...

    at full speed the ETAH (1-t/1-w) was 1.02..!

    I attached pics of the model (over 4 meter length), you can observe the model at full speed.

    The passenger ship was built in UK and the response in rough sea was very satisfactory...it was a good design.
     

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  9. RANCHI OTTO
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    RANCHI OTTO Naval Architect

    High Speed Craft for rough water missions:

    Length o.a. = 31 m abt.
    Speed = 45 knots
    Propulsion = submerged propellers
     

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  10. RANCHI OTTO
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    RANCHI OTTO Naval Architect

    Here you can observe the shape of the fore hull with an high chine in order to get smoothly trough waves..
     

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  11. BIGBOATBUILDER
    Joined: Sep 2007
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    BIGBOATBUILDER Junior Member

    Compromise...

    Hi Otto,

    the smaller version looks very good but also like a typical planing hull.
    Guess the passengers are strapped into bolster seats when running fast in seas. Guess thats not an option for a ferry.

    Hmmm.

    Guess I need to find a compromise between the two bow configurations.

    Maybe I can lean towards the bow configuration of the larger one if we use a computer controlled T-foil upfront to stabilise the ride and provide additional lift.

    Would you be willing to have a glance at the rough lines once they are done?
    As it will take a while to get to that stage, I'd appreciate if I can mail them to you.

    By the way, I saw a number of big (100m+) fast ferries with a vertical bow under the waterline. One of them is the NGV Liamone, equipped with a T-foil under the bow and this bow configuration. See the attached image.
    I'd think this bow is used on semi -displacement and fast displacement vessels. Therefore not the right thing for my boat but out of curiousity the question:

    Any thoughts what is achieved with this type of bow?

    -Constant LCG location at various load conditions?
    -Wave piercing?


    Regards & thanks again,

    Charlie
     

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  12. RANCHI OTTO
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    RANCHI OTTO Naval Architect

    This configuration has the advantage to modify the stem wave at high speed..
     

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  13. Squidly-Diddly
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    Squidly-Diddly Senior Member

    How about a WW2 German "E-Boat"?

    Fast displacement hull that works good in rough water. Not sure about 'ride comfort'.
     
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