Minimal offshore power proa

Discussion in 'Boat Design' started by BrendanfromNZ, Aug 11, 2020.

  1. BrendanfromNZ
    Joined: Apr 2020
    Posts: 42
    Likes: 5, Points: 8
    Location: New Zealand

    BrendanfromNZ Junior Member

    OK
    No more talk of sailboats or Catamarans.
    20200816_141614.jpg
    Back on the stabilized mono / outrigger :)
    • 12m W.L.
    • 5m beam
    • 1.2m W.L. beam (10:1)
    • 1.8m wet deck beam
    • 2.3m sheer beam
    • 3200 - 4000kg (need to confirm hull weight)
    • Ama 6m x 0.3m x 0.55m
    • 600 kg buoyancy in Ama
    • Yanmar 3JH40 40hp
    • 750L fuel
    • 300L water
    • Semi Immersed transom
    • Self draining deck
    • Sailboat style hatch for safety in survival conditions.
    • Netting on port side
    • Ama beams Stayed fwd aft & vertical
    • Roll up Clears to cabin sides
    • Collision bulkhead fwd
    • Fold up boarding platform
    Yes its tight fitting it all in, storage is definitely at a premium.

    But it might be the difference between getting it made

    And spending the next 20 winters in the tropics in a narrow boat, rather than sitting at home grumpy, saving and dreaming for that perfect boat.

    Thoughts?
     
    bajansailor likes this.
  2. Russell Brown
    Joined: Jul 2012
    Posts: 115
    Likes: 31, Points: 28, Legacy Rep: 25
    Location: washington state

    Russell Brown Senior Member

    The outrigger hull should be at least 3/4 as long as the main hull.
     
    jmolan likes this.
  3. clmanges
    Joined: Jul 2008
    Posts: 376
    Likes: 41, Points: 28, Legacy Rep: 32
    Location: Ohio

    clmanges Senior Member

    I'm wondering why the ama is so far aft. Just guessing, but it would seem logical to place it so that the ama's lengthwise center of buoyancy would be parallel to that of the main hull. I can't tell from the drawing if it is or not.
     
  4. BrendanfromNZ
    Joined: Apr 2020
    Posts: 42
    Likes: 5, Points: 8
    Location: New Zealand

    BrendanfromNZ Junior Member

    Yes good point, it needs to be a bit further forward,

    And longer as Russell noted.

    Trying to keep the Ama beams attachments in sensible positions on the main hull, external preferably.
     
  5. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,061
    Likes: 640, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    I'm interested to see an explication of the "uncomfortable motions" the learned member mentioned early on, re such a boat, without sail. It might look good on the smooth, but any tiring motions on ruffled water, will become a pain on a long excursion. What is the nature of these motions ?
     
  6. BrendanfromNZ
    Joined: Apr 2020
    Posts: 42
    Likes: 5, Points: 8
    Location: New Zealand

    BrendanfromNZ Junior Member

    Particularly with sensibly thin hulls and weighed down to 3500 - 4000kg mainly aluminum, fuel, beer and fishing lures
     
  7. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,061
    Likes: 640, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Well, one can imagine the motion is not a pendulum roll, it has to be assymmetrical, like the boat.
     
  8. tropostudio
    Joined: Dec 2014
    Posts: 5
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: St. Paul, MN, USA

    tropostudio Junior Member

    New to forums and little late to the game, but this is a great thread. Attached pics are from a 1996-97 design/build with a group of high school students for a solar/electric boat competition in the Midwest. We called it a proa at the time, but let's go with 'outrigger' ;)

    FWIW: 4mm tortured ply vaka @ 20' LOA. Ama was 3mm tortured ply, scaled down from vaka 2/3 in all dimensions yielded 30% vaka displacement . IIRC, vaka design displacement was ~ 550 lbs. Ama ~165 Lbs. We had one 65 lb Group 27 battery as 'ballast' in ama - other battery was in vaka. 8'-4" beam for trailering = ~2.4 L/B ratio. Kick-up rudder with wheel steering, drum, cables, and quadrant. Surplus ThermoKing series-wound DC motor and Minarik 60 Amp DC controller run as 24 VDC system. Max 1.9 HP at motor for short duration. No reverse, which sucked (we were on a tight budget). Handily won the MN state competition that year for top speed and endurance. I eventually sewed a Cordura tramp with aluminum tubes, which replaced the PV panels, and allowed for a passenger.

    After taking it on Lake Pepin in 2' chop, I recollect being a bit nervous. Not sure why, because in a s sea kayak I would have been fine. Expectedly, quartering waves were much more comfortable. Fine enetrey + no spray rails made it wet. The plexi 'windshield' helped. Having ability to adjust ballast ama would have helped. There was ample reserve displacement. I'd think having to screw around with altering that would be a abit of a PITA? I dunno - maybe not so much if your heading was consistent for a while. I recall the asymmetrical roll due to ama lifting and dropping.
     

    Attached Files:

  9. Russell Brown
    Joined: Jul 2012
    Posts: 115
    Likes: 31, Points: 28, Legacy Rep: 25
    Location: washington state

    Russell Brown Senior Member

    Had you built a tortured ply hull before? Sure looks like you know what you're doing. Very nice looking boat!
     
  10. tropostudio
    Joined: Dec 2014
    Posts: 5
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: St. Paul, MN, USA

    tropostudio Junior Member

    Russel Brown - First tortured ply boat. First design/build ever actually, but had experience with wood/epoxy construction for sculpture and worked alongside a a really good boatbuilder/teacher - Brad Buxton. HAd made a couple aircraft ply models based on Gougeon book. Gota lot of good tips off a Kurt Hughes Cylinder Mold video that made controlling the process easier. Main hull was still scary, 'cuz we were pushing for a pretty full bow and stern to gain a high CP. Definitely designed for the task at hand. I'd think it would need a flatter run and less rocker for more HP and speed.

    More apropo to OP, perhaps: With one battery in the float, one in main hull, and a pilot, the boat sat right on its lines. If the the outrigger/ama has sufficient displacement to carry water ballast, how simple do you think it is to add and remove ballast? Our float had plenty of reserve. It was probably good for 125% of total loaded displacement at deck level. I'd think the ability to easily adjust ballast ratio on a power outrigger based on wave height would be essential. But maybe not? The hulls could side-slip along the surface because you don't need boards?

    BrendanfromNZ - I like the last layout, and get the concern with beam placement re. intrusion on main hull. If the outrigger gets longer, could the front beam run under the aft end of the Master berth? Gives you a full-width bulkhead to tie into.
     
  11. gonzo
    Joined: Aug 2002
    Posts: 14,564
    Likes: 685, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Proas were designed for shunting. I see no advantage on making a tacking proa. It takes away all the advantages of the design, which are stability from moving ballast to the windward side, and less wetted surface when the ama flies.
     
  12. Russell Brown
    Joined: Jul 2012
    Posts: 115
    Likes: 31, Points: 28, Legacy Rep: 25
    Location: washington state

    Russell Brown Senior Member

    Actually, single outriggers have some advantages as sailboats and better advantages as a motorboat. For a single-engine motorboat where ultimate fuel efficiency and seakeeping are the goals, it could be the best. Long skinny displacement hulls work and the cleanest way to stabilize is with one outrigger.
     
  13. clmanges
    Joined: Jul 2008
    Posts: 376
    Likes: 41, Points: 28, Legacy Rep: 32
    Location: Ohio

    clmanges Senior Member

    In the event anyone thinks this is a good idea (I don't know), you could use an air bladder to push the ballast water out. This is typical in well-pump pressure tanks.
     
  14. gonzo
    Joined: Aug 2002
    Posts: 14,564
    Likes: 685, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    I think that flare is the cleanest way to create form stability. It is probable that a long skinny hull, in the trough between waves would get the ama submerged and turn out of control. I am not convinced of the advantages of an asymmetrical power boat.
     

  15. Russell Brown
    Joined: Jul 2012
    Posts: 115
    Likes: 31, Points: 28, Legacy Rep: 25
    Location: washington state

    Russell Brown Senior Member

    You need a ride on one...
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.