JohnMB

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About JohnMB

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    Super Anarchist

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    Evanston
  • Interests
    Sailing

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  1. JohnMB

    What mods to accommodate lithium battery bank?

    I have never heard of watt hours either, just makes my head sore seeing watts being used for energy :), that's just plain wrong.
  2. JohnMB

    What mods to accommodate lithium battery bank?

    This is confusing, You said your battery can deliver 720Ah (note the h) earlier. POWER is instantaneous VI so if it coming out at 5A and 24V then you are getting 120W if its coming out at 120A then you are getting 2880W. You are getting 1780Wh (watt hours) whether you are at 5A (and 120W) or 120A (and 2880W). Rated capacity is in ampere hours (Ah) not in amperes. (A) W (Watts is an instantaneous measure of Power) (Energy/time), Wh is a measure of Energy,
  3. JohnMB

    What mods to accommodate lithium battery bank?

    Because of the phase shift between A and V (inductive loads)
  4. JohnMB

    What mods to accommodate lithium battery bank?

    That is all I was saying, either unit will cause some inaccuracy in determining the actual energy delivered by the battery depending on the discharge cycle. I have no idea which units are more useful, but noting that this aspect of the battery should not be ignored if proposing one vs the other. I suspect that using an energy unit is a more useful option.... but have nothing to back that up beyond my preference for using the 'right' unit :) What matters is how useful the units used are to the user, not which one is more intrinsically 'right'.
  5. JohnMB

    What mods to accommodate lithium battery bank?

    There is a slight twist with batteries in that unlike a fuel tank the battery itself is an energy sink, at high outputs it is a very significant energy sink. You need to account for this loss somewhere.
  6. JohnMB

    Rudders and roundup

    Actually just thinking about this again, this assumes that the boat is not making any leeway. If the boat is making leeway, then the keel is not aligned to the flow of water, and i would suspect that there is less drag if the rudder is aligned with the water flow rather than with the keel?
  7. JohnMB

    Rudders and roundup

    Yes two foils inline create less drag, but they also create less lift. Are there no circumstances where this lift is beneficial? I know some of the 12m AC boats had trim tabs on the back of the keel which increased drag but added lift on the keel.
  8. Weight is a force not a mass. In the US people give their weight in pounds, in Europe people give thier mass in kilograms. Remember you weight less on the moon.
  9. JohnMB

    Was the Ugotta Regatta just cancelled?

    Yes, Just had the official message. Hearts go out to LTYC, hope thier employee recovers and no one else get ill.
  10. JohnMB

    2020 Hook Race

    If I say someone is one of the best sailors I know, that to me means they are in the top 5% of sailors I know, not that they are in the top 5% of sailors worldwide. I know a lot of sailors, some are newbies, some are not very good sailors, some can sail very well on 3 person keelboats but have little to no experience on 40+ft offshore racers. Some of the best sailors I know have never won or placed at national events. The best sailors I know are not superstars, but they are competent amateur sailors, who I would trust in a variety of scary situations. Its possible that you are one of the best sailors I know (I'm not sure as I have only narrowed you identity down to one of 2 or maybe 3 people and it was 19 years ago that we would have sailed together)
  11. JohnMB

    Rig wiggle

    Isn't that the point? The OP is more likely to get irrational (responses) numbers if they use metric, this may disrupt the harmonics.
  12. JohnMB

    No problem

    I had a friend who named his laser
  13. Then you will probably have to keep digging to find the supporting documents, or pay someone who has already gone through this to show you where this stuff is documented. Asking for a quick answer on the internet sometimes yields results or at least a pointed in the right direction, but sometimes not. The website I linked refers to the international convention on load lines, I take it you have read that document? (I have not, it does not interest me, but if I was trying to figure this stuff out that would probably be where I looked next.)
  14. This stuff seems to come for regulatory documents. The terminology and complex definitions are simply ways to try and get agreed terms that fit 90% of the situations. Most of these things come with drawings that you can consult. For example https://www.dco.uscg.mil/LLLength/ This has little to do with first principles engineering, and a lot to do with compliance.
  15. JohnMB

    same old, same old - not quite!

    I'm not able to get a picture of this in my head. My gut reaction says that mark room doesn't include room to sail your proper course to the next mark, and that generally if you are owed room by a boat who tacked inside the zone they should also be keeping clear of you as the windward boat to your leeward. (I may have the wrong picture but I can't picture how they tacked in the zone, owe you room and have right of way.)