Shackles From the Deep by Michael h. Cottman is about discovering the path of a sunken slave ship and how throughout the story you can see that there is racism and discrimination is also happening to the African-Americans. You would also see some more detailed research about shackles and the story of Henrietta Marie. While Michael was on the trip to find out the story behind Henrietta Marie he met a lot of friends that helped him a lot in his further journey and what he did at the end.
I think that this book is very interesting and after you look through my notes below you would know more about the central ideas and the themes that I found.
The first central idea that I came up with was: Racism and Discrimination against black people and their history and you can see some of my ideas here.
As I read further in to the story I realized that there is a lot of places talking about rasicm and discrimination against black people but I saw another central idea: Tracing the path of The Henrietta Marie and answering some questions of the sunken slave ship.
Another place where I gathered all my ideas together is in lesson #9. So in this lesson we looked at Cause and Effect of things happening in this story which then connects into my central ideas.
When I was done doing all the pages above I think that I should add a bit more details and how they can all connect to each other so I pushed myself to make another page about the connections and racism. In this book Michael wanted to really show us the detailed ideas of slave trade from Africa so he added a lot of ideas to support the one main idea is tracing the path of a sunken slave ship and how racism is also occured in here. 
Thankyou for going through my post, The book Shackles From the Deep is a really good book so if you are interested please check it out.