so why doesnt it work?

Discussion in 'Hybrid' started by jbehr, Sep 23, 2010.

  1. ACuttle
    Joined: Aug 2008
    Posts: 85
    Likes: 3, Points: 0, Legacy Rep: 40
    Location: UK

    ACuttle Marine Design Engineer

    The change seems odd but their own spec-sheet only gives the max speed as 14 knots, av. speed of 7.5. Perhaps there is something of a language barrier/quick blogging to blame.
     
  2. ACuttle
    Joined: Aug 2008
    Posts: 85
    Likes: 3, Points: 0, Legacy Rep: 40
    Location: UK

    ACuttle Marine Design Engineer

  3. pistnbroke
    Joined: Jan 2009
    Posts: 1,405
    Likes: 34, Points: 48, Legacy Rep: 404
    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    During a routine control dive for whatever reason I broke a tooth. We tried to repair the tooth on board but now decided with our expedition physician Patrick Schotteker to take care of the necessary medical procedure in more appropriate conditions before we cross the Atlantic. Therefore, I will leave the ship when we dock in Almeria and fly to Switzerland. Until my return to the ship Captain Patrick Marchesseau will take care of the blog.

    Well there you have it No dentists in spain ....
     
  4. apex1

    apex1 Guest

    No, that does not sound true! 25km/h would be a good result.

    Sounds much more likely. And I am sure we will not see the claimed 7kn average speed over the distance.

    Regards
    Richard
     
  5. pistnbroke
    Joined: Jan 2009
    Posts: 1,405
    Likes: 34, Points: 48, Legacy Rep: 404
    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    If you zoom in on the trace it seems to show them going out into the atlantic and comming back to Tangers

    That was friday ..looked again today Sun and its still in Tanger harbour ....they dont seem able to steer a steady course either .....
     
  6. apex1

    apex1 Guest

    Did I call it a failure?


    I did...........
     
  7. pistnbroke
    Joined: Jan 2009
    Posts: 1,405
    Likes: 34, Points: 48, Legacy Rep: 404
    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    Turned back for bad weather ....???
    half way to Canaries Now at 4 kts
     
  8. apex1

    apex1 Guest

    Let me dare to bet, they are crossing the pond with the ARC, to have a free rescue team nearby!
     
  9. Man Overboard
    Joined: Oct 2006
    Posts: 246
    Likes: 13, Points: 0, Legacy Rep: 129
    Location: Wisconsin

    Man Overboard Tom Fugate

    It could be due to this:
     
  10. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 494, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Any vessel that considers removing a rudder to improve the vessel's speed, is a grotesquely engineered machine. So, how many watts do they save with the rudder out? The sea weed stuck to the drive pods will make more drag.
     
  11. CDK
    Joined: Aug 2007
    Posts: 3,324
    Likes: 148, Points: 63, Legacy Rep: 1819
    Location: Adriatic sea

    CDK retired engineer

    Frankly I do not see the need for a rudder if there are 2 props that far apart. Only in case of prop/engine damage a rudder may be helpful to limp home.

    And if you are clearly underpowered, a rudder placed where the water velocity is highest will noticeably reduce performance.
     
  12. daiquiri
    Joined: May 2004
    Posts: 5,372
    Likes: 255, Points: 93, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    The problem in this case is in the hull form, imho. If you look at the pics in the previous pages, you'll see that hulls are very smooth and rounded towards transom, offering no lateral resistance. No false keels, skegs or chines to help directional stability, probably because they wanted to eliminate any possible source of resistance.

    It means that, with props that far apart, a minimum difference in thrust between the two props will translate in a steering moment. Same for a lateral wind action on the superstructure.
    It would require a very precise automatic control system to keep the two propulsors perfectly balanced and the course straight.

    That rudder is the only surface giving them some lateral resistance aft, and in fact they are unable to keep the course straight with it removed. Maybe they could try to use a mixed technique: put the rudder in the water only for short course-correcting actions and then pull it up, if the two props' thrust can be balanced with sufficient precision.

    Cheers
     
  13. CDK
    Joined: Aug 2007
    Posts: 3,324
    Likes: 148, Points: 63, Legacy Rep: 1819
    Location: Adriatic sea

    CDK retired engineer

    Daiquiri, these guys seem to have no budget limitations. It simply cannot be that they only have a rheostat to control the prop power, they probably have - or should have - a processor based power controller, so they can adjust the prop speed within a single rpm and waste no energy on course corrections due to wind or current.
    My electronics knowledge is a bit dated, yet I would gladly accept the challenge to make a controller for such an application with a reasonable amount of cigars as a reward.

    When I was still believing in jet propulsion I observed the behaviour of the nozzles from the 300+ seats catamarans here. They are kept straight during the whole trip, course corrections are made by slightly varying the engine rpm. Only near the quay they turn the nozzles to an extreme angle to pull the stern in the desired direction.
     
  14. oceandreams
    Joined: Nov 2010
    Posts: 26
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: denver

    oceandreams Junior Member

    Hey everyone my second posting here. Not to be disrespectful to those of you with much more marine experience but this 41' sailing catamaran was built from the factory with electric motors. It is even charter-able. According to the quotes in the article the captains who have sailed her thought you could just about do away with any sort of backup generator, just regeneration under sail. At one point they had to start turning things on to keep form overcharging the batteries.... and that was almost 7 years ago. And she doesn't have solar or windgeneration at all.

    http://www.catamarans.com/ElectricLagoon/multihulls_waypoint_article.asp

    This may not work for big commercial boats or powerboats, but sailing can be just about fuel free.
     

  15. ozflyer
    Joined: Dec 2010
    Posts: 12
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: North QLD Australia

    ozflyer Junior Member

    Hi guys, they were planning to average 6.5 kn around the globe. The "25 up to 30 knots" is most probably referring to the experienced wind speed. The skipper is French and his English may not be perfect. A bit like mine...
     
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.