Hull form for towed megayacht tender.

Discussion in 'Hydrodynamics and Aerodynamics' started by michael pierzga, Jan 5, 2013.

  1. michael pierzga
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    michael pierzga Senior Member

    Hull form for towed mega yacht tender.

    A friend asked me what would be the best hull form for a towed megayacht tender ?
    This would be an 8 to ten meter, outboard powered, fast tender, towed at 10 to 14 knots, all weather. ie Transatlantic..

    I suggested a classic hull with a fine bow entry, sharp vee forward , a flat run aft and a keel or bilge keels for directional stability when towed at 10 knots. Similar to the attached photo.

    Also...do catamaran hulls tow ?

    http://[​IMG]
     
  2. PAR
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    PAR Yacht Designer/Builder

    Not much of a mega yacht if you have tow a 30'er is it.
     
  3. Ad Hoc
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    Ad Hoc Naval Architect

    A tug!
     
  4. Landlubber
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    Landlubber Senior Member

    "towed at 10 to 14 knots, all weather. ie Transatlantic.."

    ...are you serious mate......
     
  5. tomas
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    tomas Senior Member

  6. michael pierzga
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    michael pierzga Senior Member

    Yup...Its the way things are done. All the Megayachts tow their megatenders transatlantic. AIS fitted, remote control lights, bilge, cameras on board, solar panels....


    Honest, swear to god, I aint making this up, its the truth.....so help me god

    So...in a tow tank, what sporty, sea worthy hull form would behave best, use least energy, at 10 knots tow


    The blue tender pictured would be typical tow

    http://[​IMG]
     
  7. keysdisease
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    keysdisease Senior Member

    Here in South Florida this is VERY common. Technically a Megayacht is anything 80' + so a 31-36ft tender is difficult to stow aboard smaller, and even larger "mega" yachts. There are Florida Builders like Jupiter and Intrepid (31' to 36') that actually target this market. There is also a specialized market served by niche manufacturers for towing harnesses and big reinforced bow eyes, remote sensors and controls, AIS for tenders, etc.

    If you take a look here http://marinetraffic.com/ais/ and look close at the Ft Lauderdale area you will find a great many "tender to M/Y Blank" in the immediate vicinity of their "mother ship." These are not 15ft inflatables.

    These boats make sense for the Bahamas and the Caribbean (and the Med, and So Pacific, and Down Under) where the offshore legs are short or a yacht has a "base of operations." This gives the yacht range with a "real" tender to do real bluewater fishing, hop to the next island for lunch with a handful of guests, or really haul a load of groceries and hardware. These tenders can also make a crossing like Bahamas-So Florida easily in good to moderate conditions which is a big plus.

    To answer the question, I don't like fine entries for towing because it may cause bow steering and wander. Cats do not tow well in my experience. Two of the most popular towed tenders here in So Florida are the 36 Intrepid and the 31 Jupiter, it's not just the hull form as it relates to towing, like all things "boat," its a compromise.

    I was responding at the same time Michael was posting. The M/Y Ohana's tender is a 2005 Jupiter 38

    Steve:cool:
     
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  8. michael pierzga
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    michael pierzga Senior Member

    Those are stepped hull and deep vee aft hull forms. These forms work great at 40 knots, but at tow speed they are really draggy , sit in their own hole and require more energy to tow.

    Im not a motorboat man. The operators of these mega beasts tell me that fuel burn, towing 10,000 miles a year ,is significant .
     
  9. michael pierzga
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    michael pierzga Senior Member

    Oh and the mothership terminology escapes me.

    All I know is that there are.... Super, Mega, Giga and Bigayachts. Im not sure of the CLASS size requirements.
     
  10. keysdisease
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    keysdisease Senior Member

    That may true (fuel burn) be for the globe trotting mega types but for the Island Hoppers around here and the Caribbean that's not the case. The passages are often 100 miles or less and often a portion of that is in protected or semi protected water. Ft Lauderdale to Abaco is about 100 miles with only half that open water. Often the tender will travel under her own power to the next port or anchorage because for short hops its easier than rigging the tow. 100 miles in a tender like we're talking about is like 4 hours transit time.

    If this didn't work for these yachts there would not be so many of them doing it.

    Mother ship: In this context the vessel to which the tender belongs. this would include everything from stand up paddle-board to the mandatory RIB to the 38 Intrepid.

    Steve :cool:


     
  11. Tad
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    Tad Boat Designer

    Well the ideal(lowest towing resistance) will be a hull designed to operate at 10 knots......problem is

    A) Those don't exist in the marketplace
    B) Mega yacht owner's/guests want their tender to run at 40-50 knots......

    A variable geometry stern would be the answer and a very interesting design project.....
     
  12. gonzo
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    gonzo Senior Member

    The problem with a hull like that is that it can overtake the tow vessel, particularly running. A tender should always have some drag so the tow line is somewhat taught. Tenders with little drag will hit the towing vessel when it slows down.
     
  13. michael pierzga
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    michael pierzga Senior Member

    I dont know much about a towed tenders behavior. When I see Megas towing tenders they have perhaps 100 meter of tow line.

    Fuel burn and tow tracking are evidently the big consideration.
     

  14. PAR
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    PAR Yacht Designer/Builder

    I would think something along the lines of a lifeboat hull, with fuller after sections and big, heavily crowned fore and aft decks, for the inevitable roll over. Lets see a 10:1 S/L power tender, that is well mannered and reasonably efficient at 2:1 S/L . . . Have one of your mega yacht owners give be a call. I'll pen one up right away. I think a fork lift rig, on the transom of the mega yacht, would be a better option.
     
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