Not much to be gained by "formulating" your own cleaners...
'Cuz most marine cleaning products are environmentally friendly...many household cleaning products that you're likely to use to create your own are not.
Don't be fooled by a "biodegradable" label...it does NOT mean the same thing as "environmentally friendly! "Biodegradable" simply means that the ingredients will eventually break down...it doesn't mean that it won't kill you meanwhile. Formaldehyde is just one example of a lethal biodegradable ingredient. What's worse, only 70% of the ingredients in any product labeled "biodegradable" have to be capable of biodegrading at all...the remaining 30% can be toxic.
If you want to know whether any product is environmentally friendly or not, read the first aid warnings. If they say something like "harmful or fatal if swallowed, may cause blindness, if ingested call poison control immediately," that product isn't friendly to people, pets OR the environment. But if they only say something like like, "keep out of the reach of children, flush eyes with clean water, wash hands after handling, call physician if symptoms develop," it's not likely to do much harm to anything.