Join Date: Nov 2008
Location: Victoria, BC
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Stick to the marine quality
I recommend you only consider a marine 30 Amp cable from the dock to a 30 Amp receptacle on the boat. Household extension cords, even exterior rated, just can't handle the exterior marine environment. The higher standard is for good reasons. Marine power cables are more UV tolerant due to the light reflected from the water. They have much greater insulation which protects against stray currents should the cable ever droop into the water. The marine cables are also designed to protect against oil, gasoline, diesel fuel, acids, and other chemicals that are on the water the cables are drooping into. They are designed to handle greater abrasion and temperature extremes, as they must flex with every wave for months or years on end.
It is very dangerous to have an extension cord run into the boat. It should go to an on board receptacle which in turn feeds the boat. Again the standard is written for a good reason: The ability to disconnect a boat from the shore power cable, while on board, allows the boat to be removed from an inaccessible dock. If the dock or neighbouring boats are on fire, your boat can be towed away to safety. Someone can slip or cut your docklines from on board, but they cannot cut through an extension cord without risking electrocution. They may not be able to pull the extension cord out through the closed hatch. Not having an exterior receptacle could force a good samaritan to abandon your boat and move on to rescue others.
This marine grade stuff is a considerable outlay of boat bucks, but as a starter at least run a marine cord onto the boat to an exterior rated cord that goes inside. That way it can be unplugged from on board. Keep the total lengths as short as possible to avoid voltage drops. With a set wattage load, as the voltage drops the current goes up, often to an unsafe extreme.
Household exterior rated cords are usually fine for temporary-attended use. Once the job is done they should be removed. Having a proper marine cord will make it easier to travel. Marinas don't ban proper shore power cables, but many ban household ones. Insurance companies don't stop payouts because you used the correct equipment, but they could slam the file shut if they found out a non-marine cable contributed to the fire. In the long run a couple hundred boat bucks is worth the peace of mind.
Sorry for the long reply. But once I get started...
"Navigare necesse est, vivere non est necesse."
- Gnaeus Pompeius Magnus, 81 B.C.