Thanks for the quick reply once again. I have had a look at your comments and gone back to amending the site.
I believe your plug in is what I require - I feel that I am almost there with it.
Right, I have created four categories (Parent categories) - Boat Size, Boat Style, Boat Price and Boat Location. I then created more categories, generating the hierarchy such as 10 feet, 20 feet, 30 feet which went below Boat Size and so on...
I then created a boat listing post (copying the same text and images from the previously created page), I checked the categories which related to the listing - location, size, cost and style.
Once that was sorted I created four category taxonomies using the plug in - Boat Size, Boat Style, Boat Price and Boat Location.
However, when I refreshed the site - the four taxonomies (drop down filters) I had created had all of the categories listed under each section, rather than the specific categories for the titles.
The search worked fine, I just assumed that as I created a hierarchy of categories with the parent ones having the same name as the taxonomy, the drop down options would have paired up some how. Basically I require the category hierarchy to match up top the search filters created - four main sections, with separate drop downs, not having all of the same options.
Is there any way of doing that, I assume there is, as that's how I originally had it looking using the custom meta option - even though that would not have worked. I have also seen that way of filtering options on other websites.
I look forward to your advice on the above.