I’m not entirely sure I understand your first question, but the adjustable pitch refers to the sound of the engine. Crocodiles have become accustomed to the sound of the boat engines which makes it difficult for the crocodile team to get close to crocodiles, so they are wanting to reduce this noise to be able to get close. I hope this answers your question, but let me know if I have missed something!
For your second question, the depth of the water will vary – the crocodile team needs to navigate urban creeks, rivers and drains. The boat will also need to withstand other factors such as navigating and bumping into mangroves and being covered in mud when it gets stuck. If you take a look at the photo gallery and interactives, you can see the types of engine on the boat that they use currently, and I recommend taking a look at some of the main rivers in Yirrganydji Country to understand the varying depths that might be encountered.
I hope this helps, but please let me know if something is still unclear.