Scott: Hi!
Itchen Wrote:
Here’s a question for any engineering experts on
the list (“Rod of Iduna”?). I wonder how big a
difference in pitching moment would result from a
shift of those three batteries from the lazarette
to just aft of the galley bulkhead, or better,
under the companionway ladder? Plus getting the
anchor off the bowsprit and it and the chain
snugged down in the head? When racing, a couple of
seconds per mile makes all the difference, and
surely worth the effort, but cruising?
I’m no engineering expert, just another BCC owner.
Six years back, to commemorate Zygote’s 5th launch day, I researched some of the questions you ask. And put the answers in Zygote’s Stowage & Ship’s Stores handbook (I’ve forgotten if I uploaded the Stowage handbook to this Forum. I remember that John Cole preserved some of Zygote’s handbooks in the BCC Maintenance Tips sub-forum and suspect they are still there).
I formulated a few principles for stowing, the first of which is:
"Rule 1: Keep the ends of the boat (bow, stern and masthead) light.
The formula by which pitching moment of inertia is calculated is:
Pitching moment of inertia = mass x (distance from CG)2
Moving a mass equal to just 1% of the displacement of the boat (ie 60 kg) from midships to the bow or the stern would increase the total resistance due to heave and pitch by about 1600%. This is especially important when beating to windward."
Zygote has the Sam L Morse Co. bookshelf to starboard. I mention that because Zygote’s Centre of Gravity (CG) is in the vertical plane about 14-17 cm aft of the central divider of the bookshelf (it’s not possible to be more precise, because the exact location of the CG changes with fuel, water, stores, and bodies etc).
In short, all you need do is measure the distance from the CG plane to where your batteries, anchor etc are stowed, square that distance, and multiply the result by the mass of the battery, anchor etc to calculate the contribution of that item to your pitching moment of inertia.
Doesn’t matter whether you measure distance in the foot size of a now-dead English king, cubits, or decimal fractions of a metre. You soon see that squaring a distance makes a big difference.
Cheers
Bil