Somebody stole my fuel - locking gas cap ideas?


Member III
After filling the tank the last time I was at the boat, I came back down this past week and motored into Oriental Town Harbour. The area was pretty busy due to the Inland Waterway (chandlery) store going out of business with everything 50% off, so I had to tie up at the fuel dock. When I came back, I started the engine and it ran for about 30 seconds but then cut off, not to restart. After checking the carb and seeing it bone dry, I checked the tank and lo and behold - GONE! The bilges were completely clean, so no leaks, so some jerk came and stole my fuel likely during the night while it was on the mooring. Go figure I had just enough fuel left to motor through a channel with a submerged bridge on one side, the channel going through a newer fixed bridge, then getting into the harbour where I had to maneuver through some tight spots with the other boats, and finally having no where to dock but the fuel dock, where I finally ran out of gas (thinking I had a full tank).

In spite of the theft (about $80 worth of fuel), I consider myself VERY lucky. The engine dying during any point of the short trip to the harbour would have posed significant risk to me, the boat, others, and other boats. I hope would-be-theives consider the fact that they are not only taking what's not theirs, but putting other's in real danger by doing so. Lesson learned - always check your fuel level before heading out. I don't have a guage, but a stick will have to do....

So, what are some ideas to deter the theft in the first place? Locking gas cap, siphon preventer? It seems I would also need to a lock on the lazarette to keep them from just coming aboard and releasing a hose clamp to gain access. Probably should have all that anyway, but always liked the slow, trustworthy nature of the Oriental community. What a pain. Jerks.

Please excuse my rant, and thanks in advance for any ideas.


My sympathies.

I've worried about that for a while, both fuel and fresh water tampering. I posted a question on some forum to see if there were locking deck fills, but apparently there aren't. In our case it is up to $400 (today's price) of diesel that sits there unlocked.

I do seem to remember some device (ball of steel mesh ?) you could shove down the fuel pipe in a car to prevent siphoning. It was sold around the time of some earlier fuel crisis. It prevents the insertion of a siphon hose but doesn't interfere with filling.

You don't mention what kind of fuel/tank setup you have so I don't know if that idea could work for you at all.



Member III
Thanks Sven-

I've got the original Atomic 4 with the original aluminum 15 gallon gas tank. Fuel Fill hose goes straight up from the tank about 2 feet to the deck port on the port side of the traveller bridge in the cockpit. Vent tube is a 1/2inch line going straight back to the port-side transom. The rest is pretty straight forward - fuel line to Racor filter to engine...

I currently don't have any locks on either lazarettes or companionway hatches, though that is about to change.

Hadn't thought about fresh water tampering...


Member III
This is the only stainless solution I could find:

sea dog 351320L-1

It's about $50 with shipping.


Sustaining Partner
This is such an easy crime. Pull alongside and start pumping. I doubt they would bother to go below to get fuel.

2 ideas:

- An inline valve in your fill hose.
- Take the cap to a welder and have him fill the slots/holes and then have custom key holes drilled with a matching key.

You just have to make it harder so they goto the next boat.

BTW, I have also been thinking of this as my boat holds 210 gallons of fuel. That is nearly $1000 at the current price. I am living at a slip right now but it will be a concern when I go cruising full time and head south.


Sustaining Partner
There is a thing called a "spider" I think made by Vetus? that inserts into the fuel fill line, some ways down the pipe where it expands in the pipe. It is non-removeable, fuel flows around it easily but there is no way that a siphon/pump hose will fit down the pipe. If theives cannot get the hose down the pipe I'm guessing they will think that the hose is kinked, etc. and move on to another victim.

A powerboater in my club got popped last year for about 200 gallons of diesel. That ain't cheap.



Member II
Given that the fuel vapour keeps the fuel lines in an oxygen starved atmosphere there is probably no good reason to use a 'marine' specific device with it's associated costs. Back in New Zealand during the 80's when fuel was very expensive we used this simple coil/spring type device ( with very good results -others around us getting siphoned while we didn't. As always there are many ways to skin a cat....