Hello brett62,
have a look at these results.
Same boat petrol V diesel on a similar weight boat to yours.
http://www.########.com/boats/boat_video.aspx?ID=1893
http://www.########.com/boats/boat_video.aspx?ID=1894
Have a look at this website, they have actually installed and tested a very similar setup.
http://www.australianboatmags.com.au/pub/index.php
I am glad that you have got over the $$$$ because from a financial position it make no sense at all for a recreational user. You will never recoup the startup costs and maintenance on a high-tech diesel will be heartbreaking.
If you don't believe me on that talk to a mechanic who services modern diesel cars.
I see that you are at Caboolture so finding a competent mechanic should be easy enough.
Diesel is safer from a fire, but if it ever does catch alight, stand well back.
I assume that you have an LP gas bottle on board, I would be more worried about that.
From the range figures above there would be no need to increase the capacity of the fuel tank.
To test for the extra 100kgs, have some crew members sit on the engine box for a while.
Make sure that the Yanmar is not made in China because I drive a work vehicle that has a Chinese diesel and it is hugely temperamental and no-one knows how to fix it.