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How to make a geocache for extreme conditions


Do you get tired of finding poor quality geocaches with containers that don't keep out the moisture?  Often these are sheltered locations as well.

You end up with stinking, sodden logbook and contents. YUCK!!  Not a pleasant experience.

How to make a floating geocache buoy

Floating Geocache Buoy

To to see if it's possible to create a waterproof geocache that stays dry in the most extreme environments, I created a Floating Geocache Buoy that is placed in open water. It  is constantly being pounded by wind, waves and every passing storm.

The cache is called "Buoy Oh Boy" and the GC code is: GC33XG0

OK, to you Americans, that name doesn't sound very good (Boo-ee Oh Boy).  However here in Australia, it's pronounced "Boy Oh Boy"!

The video below shows how the  geocache was created and placed.

Also because of all the quality geocaches that have been shown on Progeocaching I was inspired to create a high quality one of my own. Hopefully it will give you some inspiration as well.

How to make a geocache buoy

So how do you make a geocache buoy?  In essence it's a waterproof container inside a waterproof container.

The outside container is made from a 5 inch plastic drainpipe cut to 450 mm (~18 inches) in length.  It is sealed at one end with a plug and a screw top at the other end. The inside container is a 4 inch plastic drainpipe that is sealed in the same manner. The overall length is about 500 mm (~20 inches)


To float vertically a buoy needs to be weighted in the bottom.  To determine how much weight was needed, I kept adding sand (in ziplock bags) until the buoy floated at the right height in a water tank.  It took about 2.5 kg (5.5 lb) of sand to achieve that.  I then took a short length of 5 inch drainpipe, sealed it at the bottom with sticky tape and measured out 2.5 kg of Quickset concrete.  This was mixed with water in the tube and allowed to set overnight.

Surprisingly, after setting hard, it still weighed 2.5 kg.

Because concrete expands slightly, I needed to use an angle grinder to take off some of the concrete from the circumference of the block so that it fitted inside the geocache.

Cavity Filler

Once that was in place, the cavity above the block was filled with expanding foam (Space Invader), up to the bottom of the inside container.   This is so that even if water does manage to get in, the buoy will still float.

Some expanding foam was also put inside the screw-top lid to give flotation, just in case it's dropped into the water. The thread of the lid was masked with sticky tape and given enough room around the foam to be able screw the lid on.

Attaching points

The buoy needs to be anchored, so it needs an attachment point.  How do you attach a rope to the geocache without breaking the waterproof integrity of the container?

To do this, a stainless steel screw clamp was attached to the bottom of the buoy.  A couple of brackets from a bike rack were used as the attachment points.  A screw was inserted into each one, then the brackets were slid under the clamp, and the clamp was tightened.

2 Nylon cable ties were used on each bracket to attach a loop of chain.

2 carabineers (for redundancy) were used to attach the rope to the chain.  This is to allow finders to remove the buoy from the rope and bring it into their boat so that they don't drag the anchor. A slice of pool noodle was attached to the carabineers as flotation when they are removed from the cache.

The anchor

An 11kg (24 lb) concrete garden block was used as the anchor.  A hole was drilled through the middle and a long bolt inserted.  An old pulley from a sailing dinghy was attached to the bolt and secured with a couple of nuts that were locked together.  This setup allows the pulley to swivel around the bolt as the buoy drifts with wind and tide.

Waterproof Geocache Logbook

OK, so if it all goes to water (ha ha), then the last line of defence is to have a waterproof logbook.  I found one at the local Office Depot.  The pages are made from some sort of polymer and shouldn't mind getting wet.   It was cut down to size to fit inside the inner container.  I inserted 3 different writing implements - a normal ballpoint pen, a retractable ballpoint pen and a mechanical pencil. The purpose is to see which one survives the best in such a salty environment.

Placing the buoy geocache

Finding a secluded location

Because it will be in plain site, the most important thing is to find a location that doesn't get a lot of passing traffic.  We found a spot in the backwaters of a bay near some old oyster leases.  Not many boats come here because there are so many submerged posts from the oyster farm.  Even if you know the GPS co-ordinates, it's not easy spot until you are about 30 metres (100 ft) away.

Tide watching

The other benefit of this location is that the water is fairly shallow, so it doesn't need a lot of rope.  However the anchor block was still lowered over the side very carefully in case it disappeared into the depths and took the buoy with it.  It turned out that there was plenty of rope - even taking into account the highest tide of the year.

In this location, maximum tide height variation during the year is about 1.5 metres (5 ft).  Average variation is about 1 metre (3ft).  So it was important to check the tide tables for maximum height throughout the year to make sure there was enough rope, otherwise there was a risk that the buoy would be completely submerged at some times.

GPS co-ordinates were marked at the anchor point. This is because the buoy will move around with wind and currents. It was difficult to keep the boat located in one spot long enough to average the co-ordinates.  However they don't need to be that accurate because the cache is easy to spot when you get near GZ.

Anchor drag

Cache finders need to be careful not to drag the anchor.  There is enough weight in the block to hold the buoy, but any sort of boat will pull the block along the bottom. Talk about a bad case of cache creep!

This is why it is recommended that people remove the cache from the rope when they sign the log. There is an instruction in the cache description for this purpose. If they do drag the anchor they will need to bring it back to the original co-ordinates.

I'll check back in a few weeks or months to see how it's faring in the environment.  Hopefully it's still there!

The cache page for "Buoy Oh Boy" is here.

My thanks to Usat31 for helping me to place it.  It was quite windy and choppy on the water that day which made it difficult to place it by myself.

Check out the video.  If you aren't interested in the construction details, skip to 10:45 on the video to see where and how we placed it.



How to Geocache with great containers

Ammo Can - ideal container for geocaching

Ammo Can - ideal container for geocaching

As you become more experienced in learning how to geocache you'll find that one of the rewards is the pleasure of finding the treasure at the end.  After you expended considerable energy to find the thing it's something that makes it all worth it.

... unless it's a wretched micro!  Man, I hate those things.

Not only are they hard to find but it is a pain to unroll a tiny scroll and find a space on it to jot your signature in microscopic letters. There is no joy at the end, only pain.  A lot of people think the same.  Check out what people DON'T like about some caches here.

Unless you're going to be very creative with a micro, just don't put them out. Unless you're going to be very creative with a micro, just don't put them out. Unless you're going to be very creative with a micro, just don't put them out. Unless you're going to be very creative with a micro, just don't put them out.

Did I just repeat myself?

Go for quality.

If you're a creative type who can design and construct unusual containers, then my choice of container is an ammo can. These things are relatively cheap, rugged and totally weatherproof.  They last for years and you rarely have to maintain them.  Stuff it full of quality goodies and find a fabulous location in which to hide it.

Sometimes an ammo can is too big and obvious for the location you have chosen.  This is where you get to use your imagination. There are so many creative ways to hide things that will avoid using a nano or a micro.  In fact you can purchase all sorts of camouflaged containers (e.g on eBay) that you don't need to think up something yourself.

By being unique and creative you will enhance your reputation in the geocaching community and people will look forward to doing your caches.  You never know, they may come and ask you for advice on how to geocache.