After reading your blog its clear you have a heat problem which is common problem with most Seaeye Systems . Assuming your SDU is mounted in a 19 inch rack you should have no problems on installing some extra fans and keep them in place with tie wraps but without extra ventilation your see the over lay like the compass rose starting to break up and random characters appear as the cursor moves across the screen .
I think in all the Seaeye Systems I have worked on over the years if you were going to be in the water for hours we fitted extra fans or even installed a small free standing office type fan .
I think in all the Seaeye Systems I have worked on over the years if you were going to be in the water for hours we fitted extra fans or even installed a small free standing office type fan .