Cranky Badger wrote:
That's my thought, yet most aircraft use a starter/generator that turns the engine over and once it matches engine RPM begins to provide usable current. I'm using a trolling motor head as an example, perhaps a sealed alternator would have been a better analogy, though I'm not sure how you'd vent it. The F4U Corsair had and offset vertical stabilizer to counteract the prop wash over the rudder, so I guess a canted skeg might work as well. Even though it would have to be set for a particular speed, this would be simple on a sailboat.
It will work. Question is how much will you get back vs. how many knots will you give up in drag in exchange for that. All one has to do is take a computer fan with those led lights built in (removed from the computer of course), and hit it with compressed air in the right direction - those LEDs will light up as bright as if they had been powered by the motherboard. However keep in mind it only takes 20 milliamps to run an LED. You will get usable current to charge a battery, diode connected as i indicated. Question is how much - you need a fairly good amount of speed.
With a fixed pitch prop, a particular voltage would provide the necessary time component to calculate distance per revolution, i.e the time it take for the prop to travel through its pitch (1 revolution).
As it is, I'm thinking of basically a 'wet' wind turbine. Preventing the counter-rotation without increasing drag is the sticky wicket at the moment.
It will provide a voltage proportional to the rotational speed. This voltage needs to be integrated to get distance.
Remember first derivative of distance is speed (rate of change of distance with respect to time), second derivative is accelleration (rate of change of speed with respect to time), but I digress to Calculus 1 principles. To get speed from accelleration you need to integrate (first integral), to get distance from speed, integrate again (second integral).
From what I've read (never used one) they were compared with sextant sights to figure out SOG. Quite right though, current and leeward drift would throw it out to lunch, although (average) currents are pretty well documented.
You would need to take 3 sextant readings - the first two to get a running fix of the position of the second reading, and the next one to get a running fix of the position of the third reading from the second - this would give you two lat/long points and if you dragged one of these through water you would get a crude average reading of speed over those two lat/long coordinates.
However for a sextant reading keep in mind that the ground position (GP) that is the position directly under the sun for which no shadow is cast moves a mile every 4 seconds. To get an accurate reading from a sextant through either manual or calculated sight reduction you need something with time accuracy down to the second and a relatively stable time (i.e. low drift) over the course you plan to voyage. It is why when you are taking sextant readings you take your reading and then immediately observe the sweep second hand, and then write down the local time in hh:mm:ss in that order. If you don't then your sight reduction and your running fixes will suffer by potentially many nautical miles, which is worse if your running fix readings are too close together. I can't get into the details of why because it took me months to understand spherical trigonometry upon which sextant nav is based but basically if you are cutting a slice of pie and your two cuts are close to a right angle, the point at which they intersect is very easy to figure out and you can slightly change the position of the second cut without moving the apex of that triangle of any significance.
However as you narrow the angle of the two slices the certainty of the position of the apex can vary greatly (this is what happens when your running fixes are close together).
Bottom line, If I wanted to know my speed, sans electronic navigation, I would compute a running fix using my sailor's chronograph (i.e. high-accuracy quartz wristwatch
) and then when I got a running fix for the second position I would simply calculate my distance from the two coordinates, and the time it took me to get there which is an average.
If I'm that far away from land that I need to use a sextant as a backup to my GPS, then I'm really only concerned about 1) whether I am tracking to my destination and 2) my average daily speed which gives me an indication as to when I'll reach my destination.
until they reach saturation
S'cuse my dumb@ss, but what's saturation ?
It's when an electronic integrator (used to get distance from speed), no longer integrates because it's reached its maximum output. Your odometer on your car is a mechanical integrator. Another word for integrator is accumulator. They have a definite range before they're maxed out, rollover, etc. Once that is reached you are no longer integrating.
An inexpensive GPS unit
For nav, definitely but I'm thinking of a redundant, passive unit that will trickle charge a start battery, in the event that everything else has gone sideways in the middle of the Pacific. Apparently they make pretty good lures in bluewater though...
You could use it for that with the above caveats. I'm not sure I want something on the end of the line that is big enough to consider a trolling motor head "lunch"!!
As their ad says "let us give your girl some jewelry". Wow!
You know that means pics right ? I'm sure there's a few gaffers on here with sprits....
Pics will be forthcoming
Good to hear the SS is plugging along. Being a new design, I'll be interested to hear how she sails (I wasn't sure if your avatar was your own boat or not)
It's not my own boat but a representation from a very general sense of what she'll look like.
It will be replaced with the real girl when she's ready