[PSUBS-MAILIST] home-built strobe location beacon

[Jon Wallace <jonw@psubs.org>]

Someone made the mistake of not supervising me this weekend, and so I 
decided to build a prototype Strobe Surface Location Beacon for use on 
small submersibles.

This project came about after the latest version of ABS rules were 
released which requires a surface location device be installed on all 
submersibles.  Since strobe lights typically have high intensity output 
they seem like a good choice to aide in surface detection of a vessel as 
long as some way can be achieved to make them not only watertight, but 
also resist the water pressure obtainable by a typical personal 
submersible.   I began to ponder what existing products could be 
modified for use on PSUBS and shared some email with Vance Bradley on 
various options.   My first thought was to use an aircraft beacon which 
are easily obtainable from various markets.   However, I couldn't find 
an aircraft beacon that was manufactured in a small enough format to 
transfer well to underwater applications.   Most are either rather bulky 
or specifically packaged to the physical requirements of a particular 
aircraft.   Additionally, the lenses for most aircraft beacons are 
irregularly shaped for aerodynamic purposes or to fit the shape of a 
particular aircraft.  Also, no specifications exist for those lenses 
which makes it impossible to project (without field testing) how much 
external pressure a particular lens would be able to resist.

I turned my attention to strobes used for emergency vehicles.   Light 
bars and roof beacons are typically too large for a submersible 
application and again, the resistence of their lenses to external 
pressure is a complete unknown.   However, strobes designed to fit 
within the headlight and tailights of vehicles (hide-a-way) did hold 
some promise and so I began to concentrate my efforts on these units.  I 
have found as a general rule that most products associated with 
emergency vehicles are inherently expensive.   This proved true with 
hide-a-way strobes as well since most of them are sold by emergency 
equipment suppliers or automobile safety shops.   I did a lot of web 
research in an attempt to locate the brightest strobe for the least 
amount of money.   Most of the strobes I came across advertised an 
output of 25-40 watts and cost $100.00 or more.

I finally came across www.autodirectsave.com who were advertising a 
12VDC strobe kit with an output of 100watts for only $49.99, plus 
shipping of a bit more than $14.  So for $64 and some change, I 
purchased the kit which consists of two strobe lights and a 
multifunction control box.  I attached the kit to my car battery and was 
somewhat disappointed with the light output.  While bright enough to be 
highly visible in daylight, it still doesn't look like 100 watts to my 
untrained eye.  I noticed that the packaging box had lots of information 
about the multi-function capability of the control box, but not a word 
about light output.  I contacted AutoDirectSave and told them I was 
disappointed in the light output and that since the manufacturer made no 
claim about light output on the packaging that somebody somewhere must 
have over emphasized the 100 watt output.  Their response was "everyone 
says these are the brightest ones".  Ok, whatever.  They offered to take 
the unit back, but since I paid $14 to ship it to me, and would require 
another $14 to ship it back, I decided that rather than losing half my 
money I'd just keep it.  In any event, they are certainly bright enough 
to spot easily in daylight.  I was just hoping for something incredibly, 
dastardly, blindingly, bright...all for $50.  Of course, it later dawned 
on me that I had viewed the strobes through my sunglasses, but please 
don't repeat that to anyone.

As I was researching some suppliers of acrylic tubing, I came across a 
company Harvel who manufactures clear PVC.  This seemed like a 
reasonable option to follow since the pipe properties are identical to 
regular PVC, just clear instead of colored.  Well...almost.  It turns 
out that clear PVC is not really clear, but has a bluish tint to it.  A 
very light tint, but still, not clear.  It did however turn out to be 
clear enough for this purpose.  I was hoping it would be "clear" in the 
strictest sense of the word since any pigmentation would reduce the 
light output.  I was able to find a local supplier and picked up a 10 
foot section of clear PVC pipe and two clear PVC caps.  The PVC pipe was 
$2.50 per foot which wasn't TOO bad, but the caps were $7 each which is 
outrageous.  I'm going to call the manufacturers rep this week to find 
out if the plumbing supplier had the wrong price attached to the PVC 
caps.  Given that white PVC caps are about 50 cents each, I find it hard 
to believe the clear is that much more expensive.  In any event, this is 
a prototype (and I'm unsupervised) so I just bit my lip and payed it.

I ended up using eight inches of pipe for the prototype which translates 
to about $1.75 when the cost of the 10 foot length is pro-rated.  A 
couple of other regular PVC fittings account for another dollar or two, 
so the entire prototype (pro-rated) ended up being about $83.00.  I 
created a photo journal on the website to document how I fabricated the 
unit, and the prototype is for sale to anyone who wants to install it on 
their sub.  I did this for proof of concept and am satisfied with the 
results, with the exception of the price for the 1 inch PVC caps.

While acrylic tubing is an alternative option for the housing, PVC is 
just easy to get and easy to work with.  According to Sched 40 
specifications, one inch pipe (which is what I used) can survive up to 
900 psi of external pressure which makes it applicable to almost every 
small recreational sub we might encounter.  I offer this project as a 
solution for sub owners to install a low-cost strobe location device on 
their vessel in compliance with ABS standards, and also as an incentive 
for others as a starting point in hopes they can achieve a better and/or 
lower cost "cookbook" solution.

The project photos are on the web site.
Go to http://www.psubs.org
Select "PSUBS Community" from the top menu.
Select "Projects & Photos"
Select "Jon Wallace" from the left menu
Select "Strobe Light Project" from the right page

Or just go to:
http://www.psubs.org/projects/1234567801/strobelightproject/





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