Yes, as propbeanie asked are all your gauges stuck at "noon" position ? If youre engines are at all stop, then definitely should not show them at 150 rpm. Its a bug, one I rarely see in TMO but it can happen, especially after loading a saved game. Typically happens when save was made near another unit or land, especially another submarine.
Hmm. Are you using the "Donation Narwhal Class" or the one included with TMO? I ran 14 patrols with the Donation Narwhal, testing the missions I made for it in upcoming version. She was was noisy and certainly could not get away with things could in a Gato etc. I honestly havent used the default Narwhal or Pseudo Narwhal as its called in TMO in a long time, but I recall its noisy as well. Honestly, have to use a lot of discretion in what and when try to approach and attack. For example, you run into DD's out to see , they are patrols...this means they are set to Elite skill level and are searching for submarines, not really something want to attack in a old noisy boat. I give them a wide berth typically even in a modern fleet boat unless have no other option or present such a favorable set up form outset, can't turn it down.
Night surface attacks on DD's, not a great idea either, esp in a slow diving boat like a Narwhal class. Larger, easier to spot, especially for a highly skilled DD. DD's are earlier non capital ships to get radar, a few of them get it somewhat early in 42(used historical records to assign dates) so then your boat is a even larger radar target.