when ever I make a big ship it busts into flame immediately and gets destroyed p.s I play this game on a craptop
Easy fix, don't build big ships.................
Although if you do insist on building a large ship there are a few ways to try to keep your overpriced vessel in one piece. Put fire doors around flammable modules, coal and ammo. Put fire points and fire extinguishers near those points and distributed across the whole ship. Reduce vertical weight, a very heavy and high ship will collapse in on itself easily. Use small Keels to increase the health and integrity of the ship overall. Find a balance of coal/ammo, don't put more or less than you need, too much means more money and higher fire chance, too little means a useless ship mid battle. Find a good average balance and build your ship around that amount. Use the right armor, don't weigh down the ship too much but if you have strong armor it's less likely shots can get through to start a fire.
Those are a few points that can help keep your ship intact a little longer. Large ships in general though (10,000+) are prone to self destruction so you have to be extra careful in their design or it will just become another pile of scrap on the battle field.
Don't use corridors. They spread fire like gasoline soaked cats. If you must use corridors, put in enough fire points and fire doors.
if you are not concerned about weight and cost, replacing ALL corridors with extinguishers are good to go. They have the same pathways.
you might experience crew problems though, considering you're making 10k+ ships.