Good point. I was assuming access via a hatch not removing decks!
Hopefully we have given enough info for the task to be completed. 😀

HI Dave,

he only reason I suggested putting test ballast on the deck initially was that putting it inside may require removing the deck in places. With the deck missing an inaccurate amount of ballast may be added to compensate. Just a thought.

I agree with the previous post regarding adding ballast but personally prefer to place the ballast inside the model as low as possible to bring to the waterline.
As to the amount you will have to add a little at a time. Could be the maker suggests a sailing weight so if you weigh your model the difference should be the amount of ballast required.
Depending on your chosen construction method and power sytem the final weight may be in excess of the makers so trial and error is really the best option.
Please let us know how you progress as it will help others when building their models 😀

It looks like a lovely model , pity the photo wasn't three times the size.

There's no way this can be determined by a forum post. Every model is different: Current waterline determined by materials used for construction and equipment on board.

The only way to do this is install battery's, fuel etc., and place the model in a tank filled with water. Then place small ballast blocks in various places on the deck to bring the model to the correct heel and waterline. Take the model from the water and glue or secure the ballast blocks in the hull in exactly the same internal position.

To make this accurate, for models running on liquid fuel, the tanks should be at the balancing point, not to far forward or aft. This will allow the model to rise out of the water correctly as the tanks are drained.