Minimal offshore power proa

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

  1. Bob Oram
    Joined: Jun 2009
    Posts: 20
    Likes: 8, Points: 3, Legacy Rep: 111
    Location: oz

    Bob Oram Junior Member

    Hello Russell,
    Found this thread after posting on the other one.
    Nice, simple explanations. Well done.
    I think this may be a way to incorporate some retro style into a very SIMPLE effecient long distance remote area cruiser, say around 12/14mts. A single 40hp 4 stroke should give 10/12kts @ 8/9 lph @ 3600rpm and 8kts at 5/6 lph @ 3200rpm.
    The nice thing about this configuration over the traditional bridgedeck cat is using the main hull for most accom etc thereby reducing cabin height (windage) down by a considerable amount, also improving motion.
    A watermaker and clever lithium setup will be essential to keep weight down amoung other demonstrable advantages.
    A light composite tender that can simply be dragged over the low hull side means no davits, reducing weight, work, windage etc.
    If using an extra long shaft 4stroke outboard as the tender motor, then at a pinch it could be used as a back up motor. There could also be small lowerable mast with a full cut reacher type headsail to help with economy and/or alternative propulsion(probably never be used given the reliabilty of 4stroke outboards).
    Hmmm will have to do some more thinking.
    Bob
     
  2. Bob Oram
    Joined: Jun 2009
    Posts: 20
    Likes: 8, Points: 3, Legacy Rep: 111
    Location: oz

    Bob Oram Junior Member

    Gonzo,
    Regarding 'flare' on a fast multi.
    Buoyancy at the forefoot works much quicker and quieter with little spray than a flared topside.
    No flare (and no tripping moment) on the big racing tris etc.
     
  3. BrendanfromNZ
    Joined: Apr 2020
    Posts: 49
    Likes: 6, Points: 8
    Location: New Zealand

    BrendanfromNZ Junior Member

    Thanks all, for your replies. its great to have such knowledgeable persons providing input.

    Outboards - I live in NZ home of $2.20 unleaded (and I guess the islands will be more) which really puts a damper on petrol power.
    Also concerned about keeping a transom mounted motor in the water in rough conditions, but I might be over thinking this, and it would be so easy to fit an outboard and go.

    Possibility of a tender outboard mount on the end of the Ama, for close quarter maneuvers i.e. fuel dock.
    Two person job but it wont be everyday with 750L fuel and 45hp

    I probably need to stress this is a coastal boat, with offshore capabilities, including speed to shorten passages (1000NM from NZ to the nearest Island)
    The difference between 7 knots and 10knots over 1000NM is nearly two days, from 6 down to 4, a big difference in a crappy stretch of water like this one.

    And 10 knots is a minimum speed to allow local fishing trips 30 - 50NM out over a couple of days without spending too long travelling.
    Not concerned about fuel usage at 7 knots when trolling, with a 10:1 ratio hull, its going to be economical no matter what

    Whatever the outcome - this project and plans will be assessed by a NA.

    I like the idea of low windage, and getting that living area down low, this is another reason keeping me from a cat.

    Probably better behaved on anchor than a 5m wide boxy wing deck cat, and with much less anchor load?

    What it boils down to is the pros and cons of a Single outrigger vs a Power Trimaran
    • Both single engine
    • Both similar Vaka beam and layout
    • Wave motion
    • Single bigger vs two smaller Ama's and mounting points
    • Haul out concerns
    Thoughts?
     
  4. tropostudio
    Joined: Dec 2014
    Posts: 44
    Likes: 4, Points: 8, Legacy Rep: 10
    Location: St. Paul, MN, USA

    tropostudio Junior Member

    Brendan -

    You mentioned early on in the thread re. building some Tennant hulls. Were they similar to this Bakewell-White power tri?
    https://autoinsiders.co.nz/autofair/sales-ad/21308/Blakewell-White-Power-Trimaran.

    I like the idea of a low DLR main hull with a long, low DLR outrigger for a power boat. Keep it all light and simple. Russell's contention that the outrigger should be 3/4-ish the length of the main hull makes sense to me. My 'seat-of=the pants' solar electric proa from '96 went that route. The small, aft-mounted amas sitting clear of the water in the Bakewell White tri, or even the as-built Kurt Hughes 38' tri-trawler seem like they'd allow for snap-roll in waves. Looks like the the latest version of the Hughes tri has longer amas, moved forward.

    Current sailing tri's are using longer amas, with LCB moved forward of the main hull, to mitigate pitch-poling. A single outrigger will always touch the water to an extant. Seems like with a power tri, you can hold course and have time to adjust ballast for wave conditions. A long, low DLR outrigger with that can pick up buoyancy forward when immersed, and sized to accommodate water ballast, seems reasonable. Otherwise stash some light cargo out there for lateral trim, or use the deck area for kayaks. The whole boat should be narrower than a cat, which makes it easier to pick with a Travelift. Slip access may still be a problem due to width - but , then you'd have shoal draft and a kayak, so maybe no problem?
     
  5. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,386
    Likes: 1,042, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    If you envisage long hops across the big blue, stability compromises are not acceptable, skinny boats with dinky outriggers frighten me, who wants an outrigger of the weather side, when the big one hits. I'd be looking elsewhere.
     
  6. BrendanfromNZ
    Joined: Apr 2020
    Posts: 49
    Likes: 6, Points: 8
    Location: New Zealand

    BrendanfromNZ Junior Member

    Yes the transoms were very similar except the Tennant had a straight keel right to the prop, with taper on the sides only
    Makes sense to me, surely there would be less squat aft at sensible speeds.

    Tennant displacement hull - Google Search https://www.google.com/search?q=Tennant+displacement+hull+&tbm=isch&ved=2ahUKEwij4cj21IbuAhV_IrcAHRiRDiYQ2-cCegQIABAA&oq=Tennant+displacement+hull+&gs_lcp=CgNpbWcQAzIECCMQJ1DB0gFYwdIBYIngAWgAcAB4AIABzQGIAc0BkgEDMi0xmAEAoAEBqgELZ3dzLXdpei1pbWfAAQE&sclient=img&ei=elb1X6O8LP_E3LUPmKK6sAI&bih=488&biw=909#imgrc=f0Z5sukSMcTfIM&imgdii=hMaVXbjaambCJM

    But then you have boats like Earthrace (Loomes I think) with the Ama's right at the back with a razor sharp wave piercing bow.
    I remember seeing an article about the 20ft test model they built, thinking that's never going to work....
    Blasting around the world at 30 knots.

    Perhaps we are all (even though I don't sail) thinking about Tri's and Outriggers Ama design through sailing tinted glasses?
     
  7. Bob Oram
    Joined: Jun 2009
    Posts: 20
    Likes: 8, Points: 3, Legacy Rep: 111
    Location: oz

    Bob Oram Junior Member

    Sorry All, nothing to do with this thread, but I'm just letting people know that there is some scammer that has started a website that has the address Boboramdesign.com.au. This is a scam and absolutely nothing to do with me, it has zero legitimacy.
    Most will know I have retired.
    Please advise others.
    With regards to all.
    Bob Oram
     
  8. bajansailor
    Joined: Oct 2007
    Posts: 3,595
    Likes: 1,560, Points: 113, Legacy Rep: 37
    Location: Barbados

    bajansailor Marine Surveyor

    Oh dear Bob - I have just had a quick look at the website and it appears to be very comprehensive and detailed, offering everything from boat designs to marine finance.
    Is it possible that another Bob Oram is genuinely doing this, or is somebody trying to trade off your good name?
    About - Bob Oram Design https://boboramdesign.com.au/about/

    Looking at the different sections now in more depth, a lot of it is quite hilarious (in a way) re the content, photos and what is on offer.
    They mention a contact phone number, but the number is blank..... and there is a form for contacting by email.

    Do you have any connection with any of the various boats mentioned, or none at all?
     
  9. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,386
    Likes: 1,042, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

  10. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,386
    Likes: 1,042, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    boboramdesign website is spoof-like, that is not a professionally written blurb
     
  11. Bob Oram
    Joined: Jun 2009
    Posts: 20
    Likes: 8, Points: 3, Legacy Rep: 111
    Location: oz

    Bob Oram Junior Member

    They mention designs of mine but no photos or drawings that I can see.
    Bob
     
  12. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,386
    Likes: 1,042, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    If you haven't already got a legal opinion about it, perhaps you should.
     
  13. Bob Oram
    Joined: Jun 2009
    Posts: 20
    Likes: 8, Points: 3, Legacy Rep: 111
    Location: oz

    Bob Oram Junior Member

    Hello Russell,
    Doing a few support jobs for existing builders.
    Was hoping Covid would be gone so I could slip over to the PNW for the summer but not to be it seems.
    Still going around in circles re next boat for myself.
    Played with various lengths in power cats from 6.5 mts to 9mts.
    To cruise up the QLD coast, across the gulf to N.T and W.A. waters requires fuel for 400/500 miles, as refueling is ver expensive and occasionally not available until the barge visits [especially in the west].
    I tried to avoid going too long [over 10mts] as I still wanted to bring the boat home when not in use.
    So this limits the beam to 2.9mts.
    A powered outrigger is still the easiest way to achieve this with a simple folding system for the outrigger.
    It is also the most econmical, comfortable [at sea] and requires the least power.
    Simple water ballast options improve ride comfort and stability issues and is easily and effortlessly controlled [filled with a simple valve, it takes no great skill to get water into a boat:)] and discharged using venturis or cheap bilge pumps]. I have used these systems on my personal boats over the last 25 years with great success and return.
    The issue is that you can get more functional accom into a 1400kg x 7.5mt x 2.9mt power cat than a 10mt Outrigger. Going to a longer Outrigger becomes a greater logistical excercise to build, finance,, maintain, berth etc.
    And so the wheel spins.
    Hope you are well.
    Bob
     

  14. fallguy
    Joined: Dec 2016
    Posts: 7,596
    Likes: 1,674, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    Isn't the beam distance a critical piece? Seems like a narrower boat would offer less stability, but where does more do less, if you will.

    The shunting concept is easy for island passages. It was never intended for more. But power erases the need for direction.

    But doesn't a single power outrigger experience different motions is the lee pod is or not to wind?
     
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.