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Member Since 03 Jan 2012
Offline Last Active Jun 29 2015 07:43 AM

Posts I've Made

In Topic: Truk Odyssey and Truk Siren are schweckled-What to do?

03 April 2015 - 04:12 PM

I liked the Thorfinn as well.  We didn't like the food, and the hot water in our shower was hit or miss.  We were on the upper deck and apparently whenever someone showered in one of the lower deck cabins they got all of the hot water.  The boat isn't purpose built, so the dive deck isn't as deluxe as the other livaboard we were on, but it worked.  


The guides, and all of the rest of the staff were excellent.  I'd gladly go back.


The boat is old, and very seaworthy.  I'm not surprised that she's the one that survived the storm undamaged.

In Topic: Second thoughts about vacuum systems

26 March 2015 - 08:46 PM

I think you are onto it.  If the gland failure happened once already under water, then no additional air could get into the housing, thus not raise the pressure (decrease the vacuum) enough to trigger the alarm.  


But another interesting issue raised above by junior5  - once sealed, how is it possible for the pressure inside a rigid housing to significantly change at depth?  That would seem to violate the laws of physics. Not counting temperature effects of course.  


The only way the pressure can change is either a huge temperature change, not realistic, or something leaks into the housing to displace volume, and enough has to leak in to compress the air in the housing enough to make a big enough pressure change to trip the alarm.  In other words a fair bit of water.

In Topic: Second thoughts about vacuum systems

26 March 2015 - 08:17 PM

The forces on the housing are a function of the pressure difference between the inside and outside of the housing.  A vacuum of 10 psi at the surface is the same as going down 20' or so with a housing that has no vacuum inside.  So pulling a vacuum before diving is the same as diving a bit deeper.


Having said that, I can see that if you spring a leak at depth this could be a problem.  Lets say you evacuate the housing to 10 psi of vacuum (i.e. 4 psi absolute), and lets also guess that the alarm goes off if the vacuum drops to 9 psi (i.e. 5 psi absolute).  In order to do this you need to compress the air in the housing to 80% of it's original volume.  How do you do that?  By filling the rest of the volume with water.  I am guessing that the alarm deadband on these things is less than 1 psi, but you get the idea.  I don't know what the actual alarm setting of these systems is, but a small pressure change can amount to a fair amount of water in the housing when there is a leak underwater.


I think the real value of these systems is that you can find a leak before you go into the water.  If the leak starts once you're in the water I don't think they're likely to help much.


I still think they're great and my wife and I have them on both of our housings.

In Topic: Configuring a MacBook for Dive/Photography Travel

27 December 2014 - 11:25 AM

My wife has the 13" MBP with the 256 GB drive and I have the 15" with the 500 GB drive, both late 2012 machines.  They both work very well.  The 256 GB drive isn't big enough to store her whole catalog, so we set it up with a travel catalog and move everything over when we get home.  The smaller machine is a little slower than mine, but it works fine for travel using both Lightroom and Photoshop.

In Topic: Photographing Sea Lions

02 November 2014 - 10:53 AM

If you're getting motion blur I assume it is because most of the light on the subject is ambient, not strobe.  The strobe firing time is much less than 1/250th, so if all of the light was coming from the strobe you wouldn't get any blur.  This may not be practical, but if you can crank up your strobe power and lower your iso or aperture you should get a little less blur because more light will be coming from the strobe.  Of course this also means you'll have a very dark background, so it may not work in your situation.  You'll also need strobes powerful enough to overwhelm the ambient light.  


When I have shot sea lions this has worked because with our poor local viz the ambient light level was pretty low.