DREDGE

I found a reliable way to get all research parts to complete this achievement, here is what i did:

!!!!(By this point i had unlocked the bait and explosives)!!!!

- Go to the merchant (any outside of Great Marrow)
- Buy explosives and the two baits she sells.
- Sleep until next day.
- Check if she sells research part. If not, sell back explosives and bait.
- Sleep until morning.
- Check if she sells research part. If not, buy explosives and bait. (By this point the research part should show)
- Sleep.

By now there should be one research part available to buy.
Just repeat the steps of buying, sleeping, selling back and sleeping until you see it.

I got her to reliably have a research part for sail following the steps above, and i bought the last 9 research parts i needed.

Hope it helps.

(It seems tied to either spending money or selling items)

You can earn the necessary research points through a couple of ways: side quests, returning dog tags to the solider in the swamp region, dredging, and buying them off the traveling merchant.

When it comes to the traveling merchant, I found that if you keep sleeping through the days while also checking her stock daily, she will restock it with a research point every few days or so. So once you finish doing all the side quests and returning the dog tags, that can be a quick way to go about it.