Alberg 30 complete gut and restoration! Question of balancing the boat weight wise

Discussion in 'Sailboats' started by wesley Sherman, Dec 8, 2020.

  1. fallguy
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    fallguy Senior Member

    A sailboat is a different bird.

    A cruising boat can have less roll with weights off to the sides near dwl.

    But a sailboat heels and stuff, so I don't really consider a rolling issue at sail, but all the sailbot stuff is out of my wheelhouse. I am not your guy.
     
  2. wesley Sherman
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    wesley Sherman Junior Member

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  3. bajansailor
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    bajansailor Marine Surveyor

    Thanks for the link Wesley - that article does explain it all very well indeed.
     
  4. wesley Sherman
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    wesley Sherman Junior Member

    New question similar topic.

    If one has some random weight in the say chain locker in v berth 10' from CG of 250lbs. Then you Place let's say 250lbs 10' aft from CG in after cockpit locker, both approx the same distance and hight above the waterline. Let's just presume for discussion sake it is balanced, how will this affect performance? Would this cause the bow to settle into the waves so to speak and not hobby horse less or would it make it worse? Does the boat tend to settle more with equal weight opposite end of the CG? or would their force of the waves pushing up for and aft cause it to bounce more? I am also wondering if the weight in the aft locker was liquid weight howbeit baffled, and the forward weight was solid would make much difference.
    I'll add this in case it matters, the way I have my new plans laid out in my Alberg 30 most of my significant weight is in the cabin low. Except for the Engine and an equal weight of the water tank to counter the engine distance from the CG.


    I have read a lot of technical stuff on here from all the very knowledgeable members. I realize I am but a tiny fruit fly in the sea of intellect. However I read a lot on the internet but as I tell my wife ( there is a sea of nonsense out there) So I turn to you all.. so please forgive me and bear with me as I learn. I like to know things despite if it will affect my life or not. I appreciate your tolerance and appreciate the allowance of brain-draining your knowledge.
     
  5. bajansailor
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    bajansailor Marine Surveyor

    Re the 2 x 250 lbs, equally balanced longitudinally about the CG, it will have some effect - it will increase your longitudinal moment of inertia, so a bit more of your propulsive energy will be used up by by the ends moving up and down, rather than going forwards.
    But I really wouldn't worry about it too much.
    Just try to keep heavy weights out of the extreme ends of the boat, where possible.

    Bear in mind that you and your crew are also going to have an effect on the trim and stability of the boat (I think you mentioned that you are over 200 lbs?)
    If you are sailing along happily, with (say) 2 crew in the cockpit @ 200 lbs each, that is 400 lbs with a lever of perhaps 8' aft of the CG.
    However - on the positive side, if you both of you are sitting on the windward side, your weight is useful in helping to counter balance the force of the wind on the sails.
    And if you are on passage, and one person is asleep down below, then their weight will have a useful effect if they are sleeping in the windward bunk in the saloon, rather than the leeward.
     
  6. wesley Sherman
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    wesley Sherman Junior Member

    So even though equal weight higher up and the same distance will make the force of the up and down movement have more energy you're saying more force? So in uneducated terms, the bow and stern will sink with more force despite the balance placed? And the only wight 99% of the time will be me only. No one friends or family other than my son will be with me. Lol This is why I love this hobby.

    The weight I was trying to manage out is Water Tank and 2 210amp solar gell batteries.
    Not sure bilge is a good space even though I have it.. because I am gathering that even gel can off-gas.
    There I can always put 1 battery port starboard settees. I thought about bilge it could hold 3 batteries but I am reading that gel can off-gas however little.

    Sorry for the question for laymen's terms. I am 58, ex-farmer ag degree, 45 years ago, bad in math, small engine mechanic. My brain works along another line of logic lol;

    I saw a movie once that said "explain it to me as if i was educated in the penal system"
     
    Last edited: Dec 13, 2020
  7. bajansailor
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    bajansailor Marine Surveyor

    In a nutshell, the more weight that you have towards the ends / away from the centre of gravity, the more the boat will be inclined to 'hobby horse', ie pitch fore and aft.
    The energy to do this has to come from somewhere - and it comes out of the energy from the sails (or the engine) that is driving the boat forward.

    Think of a flywheel on (say) a traditional single cylinder diesel engine - it is massive, with a lot of the weight concentrated near the rim, rather than near the centre. This is to make it easier to start it by hand cranking.
    If the weight was concentrated around the centre, it would be much easier to turn by hand - but it will have much less inertia, in that as soon as you stop turning it, it will slow down quickly, and it probably won't have enough revs to start the engine.
    If you have weight out near the rim, it will be more work to build up speed of rotation initially by hand cranking, but once you have built up the speed (and perhaps flipped the decompression lever to 'on' from 'off'), the flywheel will keep spinning for a much longer time, which will help to start the engine.
    Weight in the ends of the boat is analogous (in a way) to weight in way of the rim of the flywheel.

    If you are sailing singlehanded, just you in the cockpit (say 200 lbs), then there is no point in adding 200 lbs of weight (eg stores or water) at an equal distance forward of the CG to compensate, unless you need these stores, and there is nowhere else lower or closer to the CG to stow them.
    You will only be increasing the longitudinal moment of inertia, which will slow you down a bit, especially so if you are beating to windward, and punching into the seas.
    Yes, you will be trimming down a bit at the stern (with some extra hull resistance probably), because you do not have that extra 200 lbs up forward to balance your weight, but your moment of inertia will be less, hence less energy going into pitching, or more energy going into forward boat speed.
     
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  8. wesley Sherman
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    wesley Sherman Junior Member

    Thank you Bajan geeze, got it .. thank you... I would like to borrow or rent a few of your brains for a day or two.. any rental rates? lol
     

  9. fallguy
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    fallguy Senior Member

    Place batteries to reduce wiring needs. I was going to place batteries forward on my boat for weight, but once I started considering the wiring; they got moved.
     
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