Search for marine advice on the internet. There are also a few good books available by marine experts. I gained much from Rod Collins at marinehowto.com. He has some health problems now and could use a donation. But his instruction is still available at no cost.
There is also a facebook page by marine professionals, but I lost the link.
Here is a link to the 2008 version of the ABYC E-11 Electrical Standard that is freely available
Newer versions cost $$$ Here is a link to the USCG Boatbuilders Handbook which is a good partner to the E-11, it is free.