Safety and making the boat unsinkable?

Today, all production boats are designed to comply with safety and industry standards (ABYC, USCG, ISO etc.). Some of the best plans for amateurs (bateau.com) are also designed in compliance with those standards.
This is not the case of the free plans. While it is perfectly legal to build those boats as an amateur, you must take some points in account.

Most of those boats are not self bailing or unsinkable. Their cockpits drain in the bilges.
This can be corrected by redesigning the cockpit and raise the sole above the waterline.
You can also make the boat unsinkable using USCG approved buoyancy foam.
This foam is available as a liquid that you pour in some hull compartments were it expands and fill the volume. It looks like the spray foam sold in home improvement stores but there is a major difference. Marine buoyancy foam is a closed cell foam. Unlike foam used in home construction, it does not absorb water. It is also impervious to gas and diesel.
It is sold as a two part liquid in two gallon kits. One gallon of part A, one gallon of part B.
Two gallons produce about 8 cubic feet of foam and 8 cubic feet equals about 480 lbs of buoyancy.

In the case of outboard powered boats, the transoms are designed for smaller HP engines than what is common today: check your engine for size, bolting pattern and clamp width.
The old transoms do not have splash wells (motorwells). This is considered unsafe by the USCG but you can add a motorwell bulkhead.
Further down,we show a link to a USCG pamphlet that shows the industry standards for outboard well dimensions. Here is a link to a web page that describes how to build a strong and safe transom with a splash well and a motor well bulkhead.