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  1. #1
    Join Date
    Sep 2017
    Location
    Taipei, Taiwan
    Posts
    292

    Default 2 persons vs. 8 persons aboard

    Good day , captains,
    My boat is Quicksilver 855 weekend with single 300 HP outboard.

    If I have 2 adults aboard, I can reach 31 knots, however, when there are 8 adults aboard, I can only reach 22 knots.

    If everything else be equal, is this normal?

  2. #2
    Join Date
    Sep 2016
    Location
    SoF
    Posts
    9,459

    Default Re: 2 persons vs. 8 persons aboard

    It’s normal! Weight is everything in a planing boat. But sometimes you can distribute your passengers better, for example if you make them sit up front that can help the boat get on plane and go faster.
    Make sure you have enough life jacket for everyone aboard.
    Neither a Leaver or Remainer be

  3. #3
    Join Date
    Sep 2017
    Location
    Taipei, Taiwan
    Posts
    292

    Default Re: 2 persons vs. 8 persons aboard

    Quote Originally Posted by Bouba View Post
    It’s normal! Weight is everything in a planing boat. But sometimes you can distribute your passengers better, for example if you make them sit up front that can help the boat get on plane and go faster.
    Make sure you have enough life jacket for everyone aboard.
    Thank you very much, Bouba, your explanation makes me feel better.

    4 of them sat in aft area, and the other 4 were in the wheelhouse.

    As regarding to the life jacket, no worry, I have 10 in my boat.

    Thank you very much.

  4. #4
    Join Date
    Nov 2001
    Location
    Medway
    Posts
    19,859

    Default Re: 2 persons vs. 8 persons aboard

    Personally would be very very careful indeed about taking that boat very far with 10 people on board....and.....yes have read the sales advertising fluff ?

    " Suited for 10 persons you can take it out to the sea,"....Hmm.

  5. #5
    Join Date
    Sep 2017
    Location
    Taipei, Taiwan
    Posts
    292

    Default Re: 2 persons vs. 8 persons aboard

    Quote Originally Posted by oldgit View Post
    Personally would be very very careful indeed about taking that boat very far with 10 people on board....and.....yes have read the sales advertising fluff ?

    " Suited for 10 persons you can take it out to the sea,"....Hmm.
    This is my first boat so I am still learing.

    In fact, I feel confused about some advertisements of bigger boats (and my boat).
    I mean, my boat is smaller but the manufacturer say 10 persons, but why some bigger boats can only
    have 6 or 8 persons?

    How do they determin the number of person to take?

    Despite the safety reason, I think it is more comfortable to have utmost 5 persons on my boat.

  6. #6
    Join Date
    Feb 2008
    Location
    Farndon
    Posts
    3,007

    Default Re: 2 persons vs. 8 persons aboard

    Quote Originally Posted by peterjaw View Post

    How do they determin the number of person to take?

    .
    I imagine the number of people or added weight is for the boat builder to decide. Some boat builders may be more optimistic than others.

  7. #7
    Join Date
    Apr 2011
    Location
    Boat- Western Med
    Posts
    5,187

    Default Re: 2 persons vs. 8 persons aboard

    Quote Originally Posted by peterjaw View Post
    Good day , captains,
    My boat is Quicksilver 855 weekend with single 300 HP outboard.

    If I have 2 adults aboard, I can reach 31 knots, however, when there are 8 adults aboard, I can only reach 22 knots.

    If everything else be equal, is this normal?
    The magnitude added kg,s say 450 for Ave 8 pax , against 150 kg for two pax depends on the % of added weight by pax and the Hp available to shove it with its lift inducing properties.
    If it can’t lift with its Hp much , ie just stays sunk or more sunken then the extra drag of its extra wetted area will kill its ultimate planing speed .

    So with abundance of power and a more lifting hull form you don’t really notice a great drop off of speed .

    That’s an awfully huge drop btw .
    So it’s underpowered and the hull form has ran out of lift tricks .

    If it got abundant power and a over generous lifting hull form then all that fully loaded does is dull acceleration a bit and yes a very slight almost imperceptible a knot or so of cruising speed for a given rpm .
    What it ( extra kg,s ) does do that is noticeable is improve wave crushing and soften the ride more and depending on exactly where the extra weight is change the trim .Trim change is adjusted out or should be with the tabs to get back at optimal AoA for speed / fuel efficiency/ range etc .
    This is the experience I have with my boat adding 3 tons +++ to 17 .

    Which in % is probably more than your net 300 / 400 kgs ( or what ever ) going from 2 to 8 pax ?

    So for me I would be suspicious of loosing so much speed and you are right to question “ is this normal “
    Last edited by Portofino; 19-08-19 at 07:59.

  8. #8
    Join Date
    Dec 2005
    Location
    Live London
    Posts
    3,746

    Default Re: 2 persons vs. 8 persons aboard

    Also bear in mind that people moving about the boat whilst underway in a small boat can have a dramatic change in its handling.

    I had a cranchi 33 ( so a few metres bigger ) and I had to ask people not to move or to tell me before hand as an abrupt weight shift could cause it to chine ride which was bordering on prettifying. I would hope your hull is better designed but people moving will make a big difference.

  9. #9
    Join Date
    Jun 2006
    Posts
    1,297

    Default Re: 2 persons vs. 8 persons aboard

    I have a smallish boat (7.7m long), but when loaded with full fuel (300litres),full water (70litres) and max people (7),its only marginally slower than it is with 1 person, low fuel, no water etc. Maybe its 2-3 knots slower.

    Yours soundslike a big loss in speed, it may be normal or it may not, might be worth checking with the manufacturer.

  10. #10
    Join Date
    Dec 2005
    Location
    Live London
    Posts
    3,746

    Default Re: 2 persons vs. 8 persons aboard

    Quote Originally Posted by julians View Post
    I have a smallish boat (7.7m long), but when loaded with full fuel (300litres),full water (70litres) and max people (7),its only marginally slower than it is with 1 person, low fuel, no water etc. Maybe its 2-3 knots slower.

    Yours soundslike a big loss in speed, it may be normal or it may not, might be worth checking with the manufacturer.
    Trim of load / engine ?

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