No thermic layer: bottom or surface?
 

Where is it better to hide from ASW passive and active sonar when there is no layer present?

It depends on positive or negative gradient but mostly it doesn't matter in DW.
More important is combination SSP TYPE bottom limited with type of bottom because mud or sand decreases sensors effectiveness (sand only 25% mud 50%)

Positive gradient curves acoustic wave up and negative down

https://i.imgur.com/FfkabR9.png

(Diagrams above shows situation where source of pinging is close to surface)

But "bottom limited" is usually in shallow waters and differences are minimal

Too shallow depth will disturb your sonars - too close to surface waves noise
Too close to bottom is dangerous with higher speeds because turning could change your depth about 2-3 meters

It depends on the situation.

The first mission in either 688i or SC (??) had you depart from Groton and sail south to deep water while avoiding surface ships. The intro to that mission was sneaky, but it advised you stay close to the bottom (like 20 feet above) so you could arrive at the proper point on time.

So, it depends on your situation and what the bottom is like (pre-RA). It also depends on depth and your mission tasking. Besides layers, the bottom type could be rocky (smooth), sandy, or muddy. Check the mission description and briefing for clues on the bottom type or take a quick peek at the mission in the editor to find out what you're dealing with. :up: You can also use sea state to your advantage (pre-RA). Rough seas can make detection tougher but also carries the risk of broaching.
In both cases, what helps hide you can also make it tougher to track the enemy. So plan wisely.

Figure out who's trying to find you. If you have four contacts you're tracking, take the time to position yourself so you can identify them. If it turns out you're tracking two ASW platforms, a torpedo retriever, and a fishing boat- that gives you a lot of information to exploit.

Thanks for the information I always wondered why there is no way in the mission to find out about the bottom type as it is difference like back and white when muddy or sand is helping you why rocky hard bottoms make it even worse for your sub due to reflections. But editor is at least a workaround.

In order to translate the graphic to the SSP display of DW, am I correct that figure 2) is when sound is getting slower with bigger depth and figure 3 is when sound is getting quicker with bigger depth right?

What do you mean with pre-RA, are there drastic changes in RA about this concept?

FYI, bottom type only matters for the bottom limited SSP (number 3 in p7p8's figure). In game, all bottoms act as "rock" in surface duct or convergence zone layer types. So, bottom type should only be a concern in shallow areas, provided the map maker chose a sensible SSP. Also note that SSP examples 1 and 2 in that figure do not exist in Dangerous Waters, only SSP examples 3, 4, and 5 do.

When you look at the boxes to the left of the ray-tracing in that figure, they show velocity and depth. As you move left to right, velocity increases, and as you move up to down, depth increases. Therefore, for example 2, the speed of sound is decreasing with depth and in example 3, the speed of sound is increasing with depth. The speed of sound increases when the water temperature goes up and the speed of sound increases when the pressure goes up, and vice versa.

I made a video to visualize all of this because there's a lot going on with SSPs that I think a video makes it easier to understand, check it out if you want. :up:

https://www.youtube.com/watch?v=Euy8U763N4I

Quick tip about sound propagation gradients:

https://i.imgur.com/m5oxnf0h.jpg?1