Cost analysis

Costing something like this is a bit of a black art, and I'm not convinced I've gotten sensible numbers out of this process.

I think that I've either overpriced this horribly at ~£150 or I have dramatically underestimated the manufacturing costs, I'm not sure which.

Speccing Electrical Components

Relaxing the packaging constraints has made it possible to reduce costs by using standard electrical components. The most significant of these are the motor and the batteries.

The benefits to using these standard components are measured in cost, both in manufacture and in the design phase. It also happens to reduce the number of calculations and ensure that a reliable, fully functioning product comes out the other end.

Both of these components have been sourced from an RC hobbyist website that lists extensive specifications for each component as well as the type of vehicle they would be used on. The information is there for you to make an educated choice as to which would best suit your application, ideal for this project.

Unfortunately it was not possible to calculate the speed of the motor and hence the prop specifications and power consumption without building and testing a fully working model - a process I simply did not have the time or budget to follow through with during this project.

Packaging Improvements

The radical redesign has allowed for much improved packaging within the Lifeline itself.

These images illustrate the difference:

The top image was the first design. It was entirely limited by the need to pack in as much line as possible. IT relied on miniaturised technology, super capacitors and custom built motors to function. It was not a good design.

The Mk2 version at the bottom is far superior. There is ample room for the torpedo, enough line to create a 50M radar cross section, as well as space to fit a conventionally sized PLB plus batteries for the LED signal light.

The design is far simpler and does not rely on integrating and optimising components to the very cutting edge of materials technology to function.

Switching to a RADAR Detection System

After some more thought on the idea of generating a large RADAR cross section rather than a visual target I have come to the conclusion that it is a no- brainer. The shift fixes the majority of the problems I had with he visual line and generally increase the overall workability of the concept.

Here are some key improvements:

- All S&R helicopters make use of radar, as do most fishing boats

- The radar cross section does not have to be as big, 50M diameter across would be more than enough.

- This radically decreases the amount of line that is needed to be fitted inside as well as  the length of time the torpedo has to travel for.

- RADAR allows the area to be found rapidly and from a great distance

- The search party can track the PLB as well as the radar signal  to home in on the MOB. They can then pinpoint them precisely using the built in signalling tools.

- Metallised line is incredibly simple to manufacture, just mix in a metallic filler compound to the plastic. The is no new technology to research, develop, and invest in.

This is the ideal discovery, it does fix a lot of the holes I was poking in the product and does it all very neatly too!

RADAR!

After a lot of abstractly thinking about searches over sea I got to thinking about how radar works. It turns out that radar is essentially radio waves emitted with a measured response that is a reflection.

Now, what else reflects EM waves? Faraday cages! You can see a Faraday cage in action on the door of your microwave, the mesh is tuned to the wavelength of radiation to prevent it passing through and harming you.

My reasoning is that, a spiral of metal should not be that far removed from a grid of metal. If a grid can interfere then so must a spiral, especially when the wavelengths used range from 1-10m.

Some inspired searching later I've managed to find a paper that studies the possibility of searching for an infinitesimal metal wire using radar which would suggest that it is entirely possible for a metallised line to create a radar cross section.(http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=1338286)

Torpedos

With the changes made to lifeline it is clear that the outer casing containing signalling lights, reflectors and transponder will have to stay with the MOB.

In this case it is simply a launcher tube for a torpedo.

This improves things dramatically from a standard components perspective as we can now place a motor, gearbox and battery from an RC boat inside a casing and ultrasonically weld it shut. This will allow us to meet IP67 rating at very low cost using quality components. The trade-off here is with cooling but it should be possible to use water cooling or completely ignore it as the motor will be running for such a short period.

Re-Think

As I said before, Lifelife currently makes no sense as a product.
The main problem just now is that sending all of your assets away on a string is a bit pointless.

It all needs to be considered from the usefulness to the person in the water. For example, the PLB will need a separate battery as before in order to stay functional even if the other battery is flat.

If the light is staying with the user but the line is still travelling then we need another separate battery from the LED lighting.

So in all we have 3 electrical  systems in one product. This should not be a problem, they should even be able to charge and be switched on my the same systems. The added complexity is worth the value added to the product. The system will look something like this on a high level visualisation:

My next big issue is that I don;t know who to rectify the line visibility problem. None of the solutions such as dyes and luminous coatings can't last long enough to be worthwhile and you are unlikely to see them in the day still anyway. It needs to be passive but non bulky....