Hmmm.
I use Microsoft Visio personally.
Just take an overhead layout plan of the boat and
work with Visio over the image.
You can do that easily with it.
Downside is that Visio costs
money, but perhaps you can use a trial version if they have that offered.
You can
google around for Visio add-ons as well. I found a couple boat specific stencils a while back.