Design

Here are some computer generated graphics of various design concepts. Images were rendered using Blender 2.71.

Basic Design

Fig. 1.  The first proto-type. The original idea was to have the ballast tanks as 44 gallon drums cut in half length ways and welded directly to the hull, but their displacement wasn't enough, which led to the using large PVC pipes instead.  (at the time I thought it would be less work too - I was wrong)

Fig. 1.

Fig. 2.  The second prototype with PVC ballast tanks and a concrete keel.  In this one the plan was to have three sets of tanks per side, so all of them could be used as a trim tank too.

Fig. 2.

Fig. 3.  The third, refined and more to scale prototype. Separate trim tanks were added for a more precise control of the subs angle and weight in the water and the main ballast tanks were extended to the length of the sub.

Fig. 3.

Ballast / Trim Tank Brackets

Fig. 4.  I spent about three days designing the bracket system for the tanks, all together going through about three different designs until I was happy.  The one below was one of the first, it didn't quite make use of all the space available, you can see the trim tanks are too far away from the main ballast tanks.  The closer I could squeeze them together, the more space there would be for the concrete keel.

Fig. 4.

Fig. 5.  This was the best design for bolting the brackets to the sub.  Having the four bolts going length ways with the sub meant I could move the trim tanks closer toward the main tanks and still be able to get tools in to do them up.

Fig. 5.

Fig. 6.  All four sets of brackets are on.  It may not look like it but they are very strong.  Each of the trim tanks have four 8x20 mm bolts holding them to the sub.  The total force exerted on each bolt will only be about 4 kg (an upward force when the tanks are empty).  The total force on each bolt for the main tanks will be about 3 or 4 kg (also an upward force).  When out of the water the only weight the brackets have to hold are the weight of the pipes themselves, which isn't much.

Fig. 6.

Concrete Ballast

Fig. 7.  There will be twelve blocks of concrete ballast in which will have second hand steel embedded into it for strength and density improvements.  The density of the concrete is about 2.4 g/cm³, and the density of the water is about 1 g/cm³, so when I put a block of concrete in the water it's overall weight diminishes by 1 g/cm³, which means I'd have to increase the volume of concrete even more to make the sub neutrally buoyant - so that's why instead of increasing the volume of concrete I increase its density by adding the steel.

There are eight 16 mm x 200 mm bolts welded into the bottom of the sub to hold each block into place.  The reason for making the ballast into twelve blocks was to make them easier to make and lift into place.

The four green shaded blocks are able to be dropped in case of an emergency; like if the ballast tanks won't flush; the air system has a leak and can't provide enough volume or pressure to the tanks; the water inlet is blocked; or there is a leak in the hull and the empty ballast tanks don't provide enough buoyancy to bring the sub back to the surface.  Each block will weigh in at about 50 kg (submerged in water), so dropping the four blocks will give about 200 kg of buoyancy (out of the water the blocks will weight more than 200 kg), which is about the same as the empty main ballast tanks.

Fig. 7.

Fig. 8.  One of the four concrete ballast release mechanisms.  The inner shaft can rotate whilst the outer bracket remains stationary, being embedded in the concrete.  The shaft has three key-ways machined along its length and the outer bracket has three teeth that slide along the key-ways.  When the shaft rotates about 30° the teeth then slide down the key-way under the force of gravity (see the videos below for how it works).

Fig. 8.

How it works.

Operation prototype.  This is the first idea for how to release the ballast (the handles linkage will release all four blocks).  I'm not overly happy with this handle design though, it's too big and requires a lot of movement to get it to release, not to mention the fact that it'll have 200 kg of force against it.

Fig. 9.  What the release mechanism should end up like.  This makes much better use of the space than the previous design.  Also it should be easier to release.  The handle will sit just forward of the seat between the operators legs.

Fig. 9.

The Hatch

Fig. 10.  A quick design of what the hatch might look like.  It will have two turning handles that will lock / unlock the hatch in a few turns.  One of the handles is on the outside and the other on the inside linked by a stainless steel shaft.  The two light gray shafts in the hinge both pivot so that the hatch can be lifted directly upward about an inch before rotating backwards where the hinge will then hold it from falling to far back.  This is just a prototype and is not to scale.

Fig. 10.