Wrap them carefully in bubble wrap, then put them in an oversized box buried in lots of styrofoam peanuts. Even though I carefully did that recently, I had some minor damage that I couldn't believe how it could have happened.
I have a very large old balsa stick and sheet model of an old Waco cabin biplane that I couldn't find a box big enough to hold. The movers hired in a subcontractor to build a wooden crate for it that cost me about $125 but I couldn't bear to leave that 40 year old model behind. It survived with no damage.
So, for a masted ship model, that may be your best option. A good crater will build the crate and fasten the model down so it can't be bounced around inside. But it will cost ya, unfortunately.