RE: Building a boat from scratch
If you are new to rc/model boats, then building a boat from scratch is not the way to go, and certainly not with a 30CC chainsaw engine! - better to start with a kit. Find out where/when your local rc boat club meets, and go along to one of their meetings. Talk to the people present, have a look at the boats they are sailing. After a few visits, you'll have a better idea of what is available in the rc boat model world, and how to progress in the hobby.
Best of luck!
MITS