The benefits of using hero sailors for gunners are either a modest reduction in weight or a small increase in repair rate.

By comparison, using them for engine results in a notable increase in repair rate vs elites and super elites, at the cost of a slight amount of overheat time compared to super elites or the added benefit of a slight increase compared to regular elites.

My recommendation is to use them for engis.

For the record, my typical crew would be 1 scout, 7 engis, and 2 reps, with one replacing the front T-slot gunner. You don't really need the front T-slots for most purposes. If you want to keep all 4 gunners, 6 engis and 2 reps is doable if you have good ones with high vet count, 5/3 would be with less overvetted or lower base crew.

Thanks. Since I'm planning on using all super elite sailors. Might as well go with 7 engis and 2 reps.

How about for bb7. What should I add, 1 more engi or rep?

It depends on the crew. In my case, 2 reps puts me at max repair even with a BB6 crew, so having the extra as an engi is a no brainer. Getting max repair is definitely more useful than the extra overheat time though.

I went with a classic setup, 7/3/2

7 Engineers
3 Reps
1 Scout
2 Gun
1 BO (or 2)

MN AA is half decent but my main point I wanna say here is FRENCH is the fastest nation dude, use those engineers, get that extra speed. I am a strong believer in the 7/3 for almost all BB's except UK.

I have 9 engy and 4 guns, i reapair fast and overheat untill the end of the game