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Member Since 11 Nov 2009
Offline Last Active Today, 04:05 AM

Posts I've Made

In Topic: LOA vs LWL

19 February 2017 - 10:36 PM

^^^ All else being equal, the slower you go and the lower you point the drier the ride. A lot of "wet" boats that I've sailed become "dry" boats when they're slowed down and cracked off in cruising mode. "Corky" boats are just boats that never go fast. ;)

In Topic: 'The Tesla's of the sea are not far off'

15 February 2017 - 06:38 PM

For short trips all electric is nice: quiet, smooth running, zero emission, good low rpm maneuvering. I often day sail on a boat that uses a Torqueedo and, when it's working, it's very pleasant. However, the effective energy density of the best rechargeable batteries is about 1/50th that of diesel. A pure EV needs to find ~~much more displacement~~ and much more volume for its energy storage than a diesel all else being equal.


Diesel electric sounds good on paper and has its uses in commerce. However, It's not an obvious choice for yacht auxiliaries if priorities are weight, volume, cost, reliability, fuel efficiency or simplicity. 

In Topic: coincidence..., or am i being tracked?

11 February 2017 - 12:26 AM





any google app is going to track you... if you're not using a gps app at the moment, just turn location off..   every web  page you access, every app you have,  tracks you...there's no such thing as "free" 





My son kinda works in this space.  The saying around his office is there is no free lunch on the internet, if you're not paying you're what is being sold.


It's very likely that if you don't pay you're the product, but when you pay it's typical to have your info sold as well. How's about buying a fancy internet connected TV that can id most anything you play on it from ~any~ source and sells that info?



In Topic: Calculating change in waterline/draft due to added weight

08 February 2017 - 09:01 AM



The PPI calculation is essentially a 2D solution to a 3D problem as the only variable is 2D (waterplane area).  The rest of the terms can be reduced to a constant.

I'm still not entirely on board with that. The general form of the formula is: Cf * L * W * H * Y. Where Cf is a coefficient, L is LWL, B is BWL, H is the height of the prism (1/12 ft), and Y is the unit weight of seawater. Given H, we could combine Cf, H and Y into a constant K and get K*L*W or combine H and Y and get Cf * L * W * K but either way I think it's still 3D. To the extent that one twelfth of a foot is a very small number it's a 2D ish problem. If an inch isn't a very small number relative to the boat then the formula probably won't work correctly.

Sink (or PPI or kg/mm) is a derivative, thus it's accurate only for a very small change of weight (or draft). It is not calculated for one inch, lbs, mm or kg, which are just the units of this derivative.


So it is just water plane area multiplied by water density and possible unit conversion constant. It does not take into account the change of water plane area.


Yeah, that makes sense with the units.  But I don't like it.


If it's only accurate for a very small change of weight (or draft) then it isn't an answer to the OP's question. I'm not sure what use it would have.


The examples given calculate PPI as displacement for exactly one inch. Worked that way the answer is in pounds not lb/in. Oll korrect. And useful and 3D.


It's easy to describe the calculation as a percentage of a rectangular prism. All the numbers are exactly accounted for.


I think the rate of change is just assumed to be linear and an inch is assumed to be a small number. So it can be presented as a derivative but I think what's going on is that volume is being estimated at one inch and then some extrapolation is being used. No?

In Topic: Forecasting for gusts and what drives them

08 February 2017 - 01:05 AM

You mention that you're downloading your own GRIBs so you might have access to the Lifted Index or the CAPE. They kind of get at instability or at least potential instability. I think they're already built into gust prediction for most models but they might be worth a look anyway.