Rule Of Thumb Formulas...

[hummingway]

Originally Posted by GordMay

According to Bowditch, the distance to the visible horizon in nautical miles can be calculated using the formula:

OK ... where's the rule of thumb for how high my eye is when I'm standing on the deck looking to the horizon

[GordMay]

Originally Posted by nautical62

I'd modify the hull speed equation to be the K value instead of 1.34 ...
... because I've seen many threads where people think the hull speed formula is wrong, but they are not using the proper K value for their hull.

See Chris Price’s interesting discussion about the Form Factor Constant (K, or C):
☞ Data - Marine Formulae #1

More good stuff from Chris Price:
☞ Sailboat Design Data

[s/v Jedi]

Originally Posted by Pete7

"A third of the watts of your solar panels is the output in amps for a 12 volt system in good coniditons"

I don't know if this is true or not, but could be a useful quick and ready reckoner.

Pete

I'm afraid it ain't true at all, wish it was ;-)

My 660W array gives me max. 50A at 12V so it's less than 1/10 of the watts.

cheers,
Nick.

[paradix]

Originally Posted by Pete7

"A third of the watts of your solar panels is the output in amps for a 12 volt system in good coniditons"

I don't know if this is true or not, but could be a useful quick and ready reckoner.

Pete

Should be 1/12th, right (rather than 1/3rd)? Since Watts = Volts x Amps by definition...

[chala]

Originally Posted by s/v Jedi

I'm afraid it ain't true at all, wish it was ;-)

My 660W array gives me max. 50A at 12V so it's less than 1/10 of the watts.

cheers,
Nick.

Nick 12V time 50A that 600W.
I told you it is all depending of some one thumb size.

[sandy daugherty]

The precise length of any line is exactly twice the distance from the middle to either end.

[s/v Jedi]

In reality: when I see 50A the voltage is at 13.5 or so... that would be 13.5 * 50 = 675W so either my panels are better than spec'd or my amp meter is off. I must admit that I never calibrated it. I am currently installing an Outback 60A MPPT controller that will report every little statistic I can imagine so we'll see ;-)

ciao!
Nick.

[joshea]

Nick, Can't believe your output would be that low. We get more than that with 170 watts. Tilting and a MPPT controller.


Jim
s\v Kismet

[chala]

Originally Posted by hummingway

OK ... where's the rule of thumb for how high my eye is when I'm standing on the deck looking to the horizon

Quiet simple.
Thumb = Pouce = 27.07mm, find how many thumbs between eye and sea, apply Gord formula and bingo another rule of thumb.

[Viking Sailor]

Think Amp-hours.

660/3 = 220ah,

170/3 = 57ah.

[s/v Jedi]

Originally Posted by joshea

Nick, Can't believe your output would be that low. We get more than that with 170 watts. Tilting and a MPPT controller.


Jim
s\v Kismet

I find it very curious that with 170W you get more than 675W. I think you found a source of free energy! ;-)

But my output is already more than the panel specifications so I guess with my MPPT controller and tilting I might get 1 kW?

cheers,
Nick.

[Pete7]

Originally Posted by Viking Sailor

Think Amp-hours.

660/3 = 220ah,

170/3 = 57ah.

Ah ha, so there was a rule, just got the units wrong.

Nick, can you confirm the rule, do you get 220 amp hours on a good day?

Talking of solar, I fitted our first 45w panel this morning, second hand bargin off e bay. Sadly it was so misty in Portsmouth Harbour this morning the commerical shiping even had their fog horns going with vis down to 400 yards. Wet T towel (it started off dry) over the panel so I didn't short anything whilst fitting the wiring. All connected up lights on the regulator looked good, just need some sunshine now to see how effective it is.


Pete

[s/v Jedi]

Originally Posted by Pete7

Ah ha, so there was a rule, just got the units wrong.

Nick, can you confirm the rule, do you get 220 amp hours on a good day?

Hi Pete,

Yes that rule sounds good. We will beat it on a good day in the tropics when we get 260-280Ah but that is exceptional.

cheers,
Nick.

[Pete7]

Nick hi,

Excellent, now then what to do with my free 15 amp hours each day

Pete

[roger.waite]

The 1 in 60 rule encourages people to steer accurately.

"After 60 miles, we are one mile off course for every degree off course."

So five degrees (or so) is another hour at sea!