There are several ways that an investor could approach the goal of maximising returns on a $1bn investment in sustainable shipping. Some potential options include:

1. Investing in companies that are already leaders in the field of sustainable shipping: These could be companies that have already demonstrated a commitment to reducing their carbon emissions, improving efficiency, and adopting other sustainable practices. Examples of such companies might include AP Moller-Maersk, CMA CGM and Hapag-Lloyd.

2. Investing in start-ups and emerging technologies that have the potential to revolutionise the shipping industry: This could include companies that are working on developing electric or hydrogen-powered ships, or new technologies for optimising fuel consumption and reducing emissions.

3. Investing in companies that provide products or services that support the transition to sustainable shipping: This could include companies that manufacture environmentally-friendly fuels, or those that provide logistics or supply chain management services to support the movement of cargoes in a more sustainable manner.

In terms of specific policies or regulations that could be implemented from 1 January 2023 to benefit shipping, one option could be to implement a global price on carbon emissions from ships. This would create an economic incentive for companies to reduce their emissions, and could help to drive the transition to more sustainable shipping practices.

Another option could be to establish mandatory targets for reducing emissions from the shipping industry, similar to the targets that have already been established in other sectors such as power generation and transportation.