Did the 10” Box centered 10.8" behind the centre of buoyancy work out okay?
Attached were my original calculations showing the 10.9" behind CG (Center of Gravity) shown in GREEN. The CG is easier to measure than the Center of Buoyancy (CB) and ends up more relevant to balancing the teeter totter. The CG is just the balance point of the final board layup (no foil). I have added in YELLOW the distance to the Leading Edge of the Mast, which also corresponds to the center of the front Bolts on the Axis System.
After 99 sessions I am currently most comfortable running 5.3" behind the CG (Compare to YELLOW), which means I should have installed my tracks 1/2" further forward. This primarily with Axis Silly Short Advanced+ Fuse, 1401 and 40 skinny tail (but also have flown with 1201 and 1121). The 10" tracks, installed for light weight, give slightly more than 2" of travel and I am not quite all the way forward. So I am happy for now on the Advanced+ and Advanced (-40 mm) fuselages.
In simple form here is a picture of the bottom of the board.
Note: I now mark the CG on the bottom of all my boards and using a silver paint pen to note the distance from CG to the side of the base plate. A thin strip of clear packaging tape helps preserve the ink.
5.3" back from CG to Leading Edge of Mast / First Set of Bolts.
Be done with this Puh-hoooyeee of measuring the distance from the tail. There is no objective way to do that with boards ranging from 7’ to 10’. I have a pro-level rider in the neighborhood and we have standardized on this metric. He is running 5.5" behind CG with his Advanced+ fuselages.
The mass balance point of the board is not really the same as the center of buoyancy. It certainly is the easiest thing to find once you have a completed board. I would think the mass center is a bit behind the buoyancy center because of the track weight. But good enough for what we’re trying to do.
Thanks Beasho, that’s actually amazing. That’s got to be the most detailed response to a question I’ve ever received; much appreciated!
Jondrums point made me think I could measure the CG of the blank with the foil boxes resting on top, which would give a slightly more accurate measurement (except for the weight of the carbon reinforcement etc).
Beasho, my Insta is @espitaka if you’re keen to check out some of my board builds. I’ll use that same stringer/foil track system as it’s bombproof, but I think you’ll shudder at the weight of the stringers
