What is the difference between marine quality spray paint and outdoor spray spray paint?

The marine specific paints have plasticisers, UV protection, heightened abrasion resistance, and extreme temperature differential capabilities above that seen in other uses. House paints are very good at sticking to houses, automotive paints are very good at coating sheet steel, and marine paints are particularly suited to immersion (not all of them, top side paints are not for below the waterline). Coatings for airframes are specific to that industry, and not generally used outside that - there is some crossover but you will not consider aviation coatings generally due to cost and application requirements. What is the hull built of, current condition of the hull and any coatings on your boat? If it has a few layers of whatever already painted on then just sand back and blow some of the same on, perhaps an epoxy based single pack enamel could look o.k. - it will last for a few weeks and months before it falls/floats/rubs off. Use a lot (25%) of Penetrol instead of turps and several light coats a day apart. If it has gel coat without too many chips and gouges you might just give it a light cut and polish after filling and fairing all damage. The critical thing with GRP hulls is to keep the water out of the fibreglass structure at all costs. As the preparation for any paint job is 80% of the total cost, trying to save money by using cheap products is meaningless, and in the end simply wastes all that time and effort. If you want to paint the boat without putting the preparation time in then use whatever you want, the result will be temporary at best regardless of the products you choose.

I have an older sailboat, Hand Laid quadruple Fiberglass layered. It is a tough boat. I used Imron paint on it two years ago, it still looks nice. I sail in Salt Water and the vessel is usually kept on a trailer. I have to wax it every year. Topside and Bottom paint is different. Then there is Deck Paint. All are different. As was stated by a few, it is all in the preparation of the Hull and or the surfaces that are to be addressed. I bought a 14'sailboat for $80, stripped the house paint off of it, repaired the damage to the fiberglass and gel-coat, applied proper paint in a proper fashion, took two months, I sold that Laser for $2000. I just bought a Cal 20, it needs the same thing, but this one is a keeper, until someone offers me what she is actually worth, to me. So although the buying price may have seemed low does not mean the vessel is cheap. Two Part Epoxy, do it right, do it once. You should have 5 hours of prep for every 1pint of paint applied. That is hard to figure out unless you have restored other vessels, and that is not written in stone. That is just a rough estimate of time and labor. I am talking performance racing sailboats, you may be talking flat bottom jon boats, huge difference. Sure i have used Spray Paint on the Bottom, but that was temporary protection until I could get the proper chemical applications, paint. Then that temporary cover is stripped/sanded off , then surface area prepped, primed and painted, properly. Have fun,read all instructions, wear safety gear and always wear a PFD.

Use the marine paint. It is formulated to withstand the conditions unique to being submerged in water. Regular outdoor paint will repel water from rain but it isn't designed to be used IN the water.

The primary difference is quality, and you get what you pay for. If you want a decent finish, which will adhere properly, will withstand the harsh marine environment, will smooth out properly and produce a decent gloss, and which will last reasonably well, then you need a top quality marine paint. And the surface needs to be properly prepared, as per the paint manufacturer's recommendations, and you need to use the recommended primer/s and undercoats, and the recommended number of coats. If you are happy with a rough job, producing a lower quality finish, which may well need to be repainted frequently, and which may not adhere anything like so well, then you MAY get away with house paint. This applies whatever the material of your boat, and in particular whether wood or GRP. If either GRP or reasonably new wood with absolutely no movement of the wood, 2-pot polyurethane is probably the most durable paint and will probably also give the best gloss, but because the fumes are carcinogenic it absolutely must not be sprayed without using the proper professional equipment, which includes appropriate masks and ventilation as a minimum, and I would expect the breathing apparatus would be specified. Recommended application for amateurs is either by brush, using the best quality brush that you can afford, or by roller but followed immediately (i.e. before it even starts to set) by "tipping" it smooth with just the very tip of a top quality brush. International Paints' Perfection is one excellent headline name product, which I personally use on my modern wooden boat, but other top manufacturers have equivalent products. If older wood, or if there is any sign of movement in the wood, then two-pot paint is unreliable because it is not sufficiently flexible; it cracks where the wood "works", and that lets moisture in beneath the paint film, which then lifts the paint off. Conventional marine paint (i.e. NOT polyurethane) is more flexible and is the recommended choice. International Paints' Toplac is again one excellent headline name product, which I personally use on my older wooden boats, and I have also known people use it very succesfully on GRP. This can safely be sprayed, but again brush or roller followed by "tipping" brush are excellent alternative means of application. Again, other top manufacturers have equivalent products. Avoid the one-pot polyurethanes; they are an unfortunate half-way house, which share the limitations of both true (2-pot) polyurethane and conventional paints, without properly having the advantages of either. They are not as durable as either two-pot or the best of the conventionals, neither do they have the same gloss, they are not as flexible as the best of the conventionals, and when touching up minor blemishes they are almost as hard to rub down as the two-pot paints. One vitally important point; you absolutely MUST NOT apply two-pot paints over existing one-pot paints. If you try to do so, your very expensive paint will turn into very expensive (and not particularly effective) stripper; it will attack the paint underneath, and produce a very rough "bubbled" surface that is not even durable, so it will all have to come off again. If in any doubt, either strip right back to bare wood (or GRP), or test several small areas with two-pot thinners (and if the paint reacts adversely then you will have to repair the damage, but at least that damage will be localised), or assume that the existing paint is one-pot so use conventional paint. At the end of the day, 95% of the work lies in the preparation, and the value of your time is probably far greater than the cost of the materials, so if you want a decent result it is likely to be a very false economy to use cheap paint.

Many of the marine paints in the market are actually brought over from the aircraft industry, some are high end automotive paints. They are used because they last. I would paint you 16ft boat as cheaply as possible. You might want to look at Easypoxy by Pettit about $125 per gal. You can roll it, brush it on or spray it. Lots of colors and it comes in quarts. Seagloss is another paint that you might consider about the same cost but the colors are very limited. Now if you are really cheap and just want to get the boat in the water and have some fun, try a good quality oil based house paint and just roll it on. It'll do the job and will be easy to repaint as needed.