Testing Stage Two, Prep #1

In this update I'll show off a few different things that have been happening in preparation for the second stage of testing, as well as changing up the blog style a little.

        Since the last update I've been stripping paint from the hull.  It was rather thick paint, probably enameled too.  I used paint stripping gel to soften each section, then cleared the majority of it with a paint scrapper, and after drying it with a rag I went over it with a wire brush attachment in the power drill.

        Then came the kill-rust undercoat, and once dry the first coat of kill-rust "ocean-color" top coat.  This paint will be okay for the all the testing, once the sub is finished, I'll sand blast the hull and coat with a marine grade paint.

        Also I've been cleaning and sealing all the threaded joins on the water pipes.  At the moment the front two sections are sealed and in place in the sub, ready to be bolted down.

        The battery brackets were also painted and this evening I bolted them in and took on the grueling task of dragging two massively heavy batteries into place.  Each battery weighs about 31 kg.  The terminal lugs have been ordered for both batteries and once they arrive I will begin wiring up the power and recharging system.

Mid section paint stripping.
11/01/2017

Cleaned with wire brush attachment.
11/01/2017

Under coat.
11/01/2017

Rear section paint stripping.
11/01/2017

Rear section cleaned.
11/01/2017

Under coat.
17/01/2017

Beginning the sealing of all water pipes.
23/01/2017

Front under coat.
23/01/2017

Under coat on the battery brackets.
27/01/2017

Top coat on the front..
28/01/2017

One of two batteries.
28/01/2017

Both batteries are in!
28/01/2017

Painting the brackets that hold down the front pipes.
28/01/2017

Pressure Test #4

This morning I completed the final pressure test and reached 8 meters down (11.76 psi).  Toward the end of this update I have outlined the reasons for stopping here.  The window gave no resistance to the pressure at that depth.  It was experiencing about 2,778 lbs/sq.in (1,263 kg/sq.in), even after hitting it all over with a rubber mallet, just to be sure.

Fig. #1.  5 meters down.

Fig. #1.
10/01/2017

Fig. #2.  6 meters down. 

Fig. #2.
10/01/2017

Fig. #3.  7 meters down. 

Fig. #3.
10/01/2017

Fig. #4.  8 meters down.

Fig. #4.
10/01/2017

Fig. #5.  Upon closer inspection I noticed that the ball valve had began to crack at 8 meters.  In case it suddenly failed whilst pulling a vacuum, and possibly damaging the pump if derbies went up the pipe, I decided to stop and replace it.

But after another look around the sub I saw that most of the plates making up the dome had began to go flat under the pressure.  These plates were actually made from a thinner steel than the rest of the hull.  I could go inside and weld more support for them but I'd have to stop at some point.

So I've decide that 8 meters is more than enough for a un-pressurized dive and will make it the maximum.  For safety I'll add a buffer below that of about 2 meters, so 6 meters un-pressurized.

I have also added these numbers to the Specifications page.

Fig. #5.
10/01/2017

Next will be Stage Two of testing.  As shown here.

Pressure Test #3

Yesterday evening I bolted and sealed the new front window in place and this morning I resumed pressure testing.  I managed to get it down to seven meters (10.29 lbs/sq.in [4.6kg]) today before a few leaks stopped it from going any further.  Besides the leaks, that are now fixed, an area on both sides of the hull directly beneath the conning tower began to give in (Fig. #2).

Over all though everything else was fine - including the window which would have had about 2,430 lbs (1,105 kg) across it.

Fig. #1.  Currently at two meters.

Fig. #1.
08/01/2017

Fig. #2.  It's hard to see, but the hull has given in a little at the places marked with an X.

Fig. #2.
08/01/2017

Fig. #3.  I'll be welding in some reinforcement over the next few days that will strengthen up the area shown in Fig. #2.  I originally had some here but it got removed when the tower went on and I forgot to put it back.   Hopefully I'll have both sides done tomorrow, but it'll depend on if I can replace my gas cylinder tomorrow or not.

Fig. #3.
08/01/2017

I plan to resume testing by mid week.

Pressure Test #2

Just a quick update today.  Yesterday I replaced both 3mm thick windows with 6mm thick ones and let the sealant dry over night.  This evening after work I resumed pressure testing.  At about five meters down (approx seven psi) the front window cracked and the hull lost its vacuum.

I made a crucial mistake with this window, and that was to use the old 3mm window's holes as a template to drill into this one.  I didn't think about the fact it would curve slightly different to the 3mm one, being a lot thicker, and of course some of the holes didn't match up toward the end of the window.  I then decided just to clamp it down, seal it up and test it anyway.

I concluded that it cracked due to a few reasons;

1. it didn't have any bolts in the last few holes so the forces may not have been equal across the window, also this section may have flexed more against the seal under pressure.
2. the forces involved in the straps holding the window to a curve would have not been there in the final build, and...
3. the main reason of using poly-carbonate is that it can be flexed quite dramatically and not break, so even under normal atmosphere pressures the whole window is under a lot of stress just simply being held in a curve.  That, coupled with the pressure difference would have added to why it cracked.

For next time, I plan to get the piece remade, and if possible have it heated and curved to the right shape.  I will make sure to drill the holes by holding the window in place, and I will put every single bolt in!

At least this will give it a good chance for next time.

Fig. #1.  The crack occurred when the window had approx 780kg across it at roughly five meters down.

Fig. #1
04/01/2017