Hang on - why is 13 the minimum number? If that's the most to date, does that not suggest that is what we need to exercise?
Exercises aren't done for fun, they are done for a purpose. What is the purpose of the exercise? A Sqn of helicopters (which 13 is) can lift a Bn of light infantry; what more is needed then?
You are very worried about the H in LHD, but do remember a couple of things.
1. I'd suggest in their entire RAN career, neither HMAS Kanimbla nor HMAS Manoora saw 13 helicopters across their decks ever. The ability to operate 13 helicopters from one ship is such a leap forward.
2. That ignores the additional aspect of undercover storage. Having 4x MRH-90 on HMAS Canberra is much superior to having 4x MRH-90 on HMAS Kanimbla as the maintenance can be done, and the helos stored, in shelter. Automatically everything about your helo's improve, as their exposure to the elements is reduced.
3. Along with that, these aren't USN ships. We have elected not to pursue deck storage as much as possible (see 2). So we can afford to operate smaller numbers of helos than max and still have little impact on long-term fleet avaliability.
4. As
@Todjaeger points out:
every helo on board takes the space of some trucks. Again, what is the point of the exercise? Your Bn of light infantry still need wheels for logistics and the like - if you take 24x - 30x helicopters, not only are you deck parking (see 3), you are also taking space on the light vehicle deck. Loading the LHDs is a never ending jigsaw puzzle
5. Deck quals are expensive to keep up all the time. And they need to be done regularly. Putting heaps of helos on LHDs all the time will lead to a situation where all 16 Bde does is practise deck quals. Which may be appropriate for a major amphibious operation or exercise, but 16X's responsibilities extend beyond that. There simply isn't enough AAvn helos to maintain large ship detachments. Should there be? I don't think so, I think there are better things to spend money on than more helos.
Overall, the amphib capability is where it needs to be. Can HMAS Canberra deploy tomorrow with 24 helo? Yup (allowing for loading and frantic deck quals). But could she sail around with a Sqn of Tiger, a Sqn (+) of MRH-90 and a Tp (+) of CH-47? Absolutely. If there was a mission that needed that, 16X and the RAN could. Do we need to though? No. not at the moment.