Back to the Future

Discussion in 'Boat Design' started by Ad Hoc, Nov 3, 2020.

  1. Ad Hoc
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    Ad Hoc Naval Architect

    Nice to see the Jetfoil back. First brand new Jetfoil enters service, details HERE:

    [​IMG]
     
  2. bajansailor
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    bajansailor Marine Surveyor

    Brilliant!

    Some history about the Boeing Jetfoil here -
    Boeing: Historical Snapshot: Jetfoil/Hydrofoil https://www.boeing.com/history/products/jetfoil-hydrofoil.page

    One of the early Boeing versions was High Point -
    USS High Point - Wikipedia https://en.wikipedia.org/wiki/USS_High_Point

    And some info about the current version built by KHI -
    How does the Jetfoil fly on the water surface?|JETFOIL Mini-Encyclopedia|KHI JPS CO.,LTD. http://www.khi.co.jp/corp/kjps/english/emini/emini1.html

    The Royal Navy in Britain bought one from Boeing in 1980, but it sounds like they were not too happy with her, as they only kept her in service for a couple of years. Wiki reports that she is now a working as a high speed ferry between Hong Kong and Macau.
    HMS Speedy (P296) - Wikipedia https://en.wikipedia.org/wiki/HMS_Speedy_(P296)
     
  3. Ad Hoc
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    Ad Hoc Naval Architect

    Only time will tell whether is a market place for these amazing vessels.
    They do come with a hefty price tag though, so don't expect an avalanche of orders soon..
     
  4. bajansailor
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    bajansailor Marine Surveyor

    Re the hefty price tag, I wonder how much more expensive might a Jetfoil be in comparison to a fast cat or a SWATH that can carry the same number of passengers?
    The Jetfoil will have an advantage in being much faster, but how would it compare in gallons per passenger mile (or what would be the way of comparing different ferries?) against fast cats and SWATHS?
    In rougher conditions (I am thinking typical tradewind conditions here in the Caribbean, with the wind speed around 20 knots) in open ocean, would the Jetfoil have a better or worse motion for passengers when compared to a fast cat or a SWATH?
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    For a cat roughly 6-7 times more
    For a Swath roughly 5-6 time more.

    The price of a Swath and Cat, carrying same number of passengers, will be "similar". The cat being about 15% cheaper.

    These values are often a closely guarded secret..never sure why though.
    Once foil born it should be much less, but don't forget, the jet foil uses GTs, these are always thirsty beats! ..and the faster you go.. = more fuel.

    In Hs = circa 3.0m...the jet foil will be the better of the 3. But the Swath also able to run in Hs=3.0m and will be a very very close second.
    She wont be going as fast though.
    The cat, being the worst of the 3, and most likely limited to circa Hs=2.0m. ..but the motions may not be so pleasant... the ISO seasickness values (as a unit of measure) will be much higher in the cat.
     
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  6. bajansailor
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    bajansailor Marine Surveyor

    Thanks for the above - that is all very interesting.

    The bottom line seems to be that the best 'all round' ferry would generally be a SWATH, if comparing it with a fast cat and a Jetfoil.
    Yet SWATHs are still relatively rare - is this mainly because of latent prejudice against them?
    Or more because they are relatively more complex to operate perhaps (I am thinking re the drive trains down into the hulls, and accessibility)?
     
  7. Ad Hoc
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    Ad Hoc Naval Architect

    Best for what??...and that's the question.
    If the sea conditions are relatively benign, a Catamaran wins hands down. As you can design the ferry to have a high LD ratio, making it much more efficient ergo = less power = lower fuel consumption values.

    Yes and no!
    Where a catamaran is on a route with exposed sea states, many catamarans these days are fitted with motion control systems to help reduce the motions.
    The design of the cat and size of the cat dictates the overall success... in that sense. Also, size matters!

    Swaths are rare for many reasons, but the main one being very few companies/people in the world have the full knowledge to design one successfully.
    Some companies have copied others,... but do not understand the how's and why's...they think copying is sufficient on its own and to call it theirs, by say moving an engine etc.

    But the principal reason, is draft.
    Many of these fast ferries enter harbours/ports with low tidal values and require vessels with a shallow draft. Swaths have much deeper drafts, and this tends to put many prospective clients off a Swath.

    Thus it is more operational and "perception" than anything "technical" in that sense.
     
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  8. bajansailor
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    bajansailor Marine Surveyor

    Thanks for these answers!

    I am still thinking, longingly and wistfully, about an inter-island ferry service in the Windward Islands in the Caribbean - these are essentially the islands between Grenada and Martinique, while also connecting with Barbados which is 100 miles to the east of the chain of islands.

    A pal of mine had great ambitions about 5 or 6 years ago re setting up a high speed cat ferry service between these islands, using two old Fjellstrand cats - he assured everybody that these two cats would be on their way down here soon, he had it all sorted, but then it all seemed to fizzle out.
    One of them is Kommandoren, a Flying Cat 40m, which is now 30 years old -
    https://www.marinetraffic.com/en/ai...04355/mmsi:356/imo:8913239/vessel:KOMMANDOREN

    The other one is / was Aurora which is also 30 years old -
    https://www.marinetraffic.com/en/ai...mmsi:247066100/imo:8911360/vessel:SNAV_AURORA

    We have very calm conditions for quite a lot of the time for about 4 or 5 months during the summer, but during the winter the tradewinds can typically blow at 20 knots for weeks at a time.
    None of the harbours in the Windward Islands or Barbados have draft limitations that would affect a SWATH, hence in view of what Ad Hoc mentions above, I am thinking that a SWATH might be a 'better' ferry generally than a fast cat - although I appreciate that the motion control systems for these cats are so much better nowadays.

    Another reason for wanting to have a ferry service is that LIAT (one of the principal airlines in the region) went bankrupt as a result of the Corona epidemic and is now under Administration - https://www.liat.com/
    And although various governments are making noises about resurrecting the airline, nothing seems to be happening.
    I often used to travel on LIAT re survey assignments in the other islands - but it hurts when you might have to pay US$400 for a return fare to an island 100 miles away.

    The other main airline is Caribbean Airlines - Caribbean Airlines | Book flights, cheap tickets & low fares https://www.caribbean-airlines.com/#/ and they would usually charge similar fares.
     
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  9. Ad Hoc
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    Ad Hoc Naval Architect

    We had a very positive enquiry for a similar route in the Caribbean around 12-13 years ago now, not unlike you have noted. I can't recall the exact islands off hand right now.

    Indeed, initially a typical high speed fast ferry (catamaran) does appear the obvious solution. But when it blows, and if the seas are pretty bad for any period of time, then a Swath tends to start to win the day.
    As much less downtime - even compared to a motion controlled catamaran - occurs with a Swath.

    If the speeds required are not silly numbers like 40knots...then a Swath is an ideal platform for such a route.
    We designed one carrying 400 pax that ran between two islands in the mid-Atlantic...served every well for some 15years. Had space allocated for cargo too.
     
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  10. portacruise
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    portacruise Senior Member

    The bigger they (HF) are, the harder they fall, or not? Maybe not as big an issue for one of the other two designs?

    Hydrofoil collision safety https://www.boatdesign.net/threads/hydrofoil-collision-safety.64648/

    But the KHI jetfoil 929 link @#2 ( thanks Bajan!) above indicates at least some partial Solutions to collisions with relatively small objects like logs compared to the much smaller foil boats in my link. And KHI foils can be retracted to be flush with hull position for shallow Waters- see FAQ.

    Wonder if the jetfoil hull with retracted foils can be run in moderately rough water at slower speeds using a motion control system and how the ride and speed compares to an equivalent cat at the same speed and with motion control?
     
    Last edited: Nov 7, 2020
  11. jehardiman
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    jehardiman Senior Member

    The real problem with SWATHs is the draft... There are many more applications for cats due to draft limitations in harbors. Both have the same load capability realistically, but a cat can be faster if draft is limited.
     
  12. BMcF
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    BMcF Senior Member

    They can only operate at very low speed with foils retracted...and there is no motion control with the foils retracted.
     
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  13. portacruise
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    portacruise Senior Member

    Thanks, @ 12. Motion control would seem to work better with the generally more stable cat configuration compared to a mono. But a foil collision might be severe enough to flip a cat, which is not likely to happen for a mono, if they both remain intact?
     
  14. BMcF
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    BMcF Senior Member

    Actually...the opposite is true. The less initial and static stability any craft has, and the less inherent damping, the more effective a good motion control solution will be. That is why SWATHs, low-waterplane cats, and hydrofoils have the the lowest motions underway, actively stabilized, than any other craft.
    No cat has ever been "flipped" by a foil collision. Foil-supported and foil stabilized mono hulls and cats have indeed had appendage collisions of varying degrees...but the vessels remained upright and intact.
     
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  15. portacruise
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    portacruise Senior Member

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