relays going out

Ok, first time poster. Dont know much about electronics thats why Im here. I have a boat, we pump water in ballast bags to get a nice wake. I have 3 pumps that fill and empty the bags via one swith. I open or close the valves as needed. Switch up fills , switch down empties. There is a 40amp 12v relay near the pumps. There is a power wire from the battery, power wires from the pumps and two other wires(switch?). The relay is a four prong, automotive realy.  Ok, I bought the boat and this is the set up. It worked fined for a couple outings then went out; I bought a new realy and it worked again for only two outings and its out now. What can be causing this relay to go out?? Also I had to replace my battery yesterday. When I jump the relay the pumps work. But just curious, could a bad pump kill the relay?? Is it a short somewhere?

help!

Thanks!

Are you using waterproof relays?  Most relays are not hermetically sealed, but a few are.  If using a relay on a boat I would highly recomend ONLy using sealed relays.

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=330-079

You may also want to consider adding 1 relay per pump, instead of 1 relay for all the pumps.  This will decrease the current going through the contacts and should increase life.