Skipjack
     Build log #2
                                  by Ralph --- SSBN 598 
 
A few modifications.

I had a lot of issues with the main motor.
I used the motor programing to reduce the RPMs to 20%.
I used the Tx menu to program the motor to 20%.

This did reduce the RPM but not enough.
I tried reducing the Tx down to 10% and this resulted in a sever cogging of the motor.
Not acceptable.

It was suggested that I try the Engel's 300 with the SubCommander ESC.
Both of these items are purpose made for submarines.

I removed the Rock crawler motor and Esc and installed the Engel's parts.
What a difference! ! !
The Engels is setup to run on 12v and my system is 7.2v.
On the high side, I have far more RPM than I will ever want to use.
I set the Tx down to 50% and this is so much better.

On the low side.
OMG. I can slow the propeller down to where I can count the RPMs as it is running.
No cogging at all.

I did a fast trim on the boat and took it to the pond.
The boat run so much better.
So much more control over the speed.

Only issue was my hurry to trim, I made the worst mistake.
I balanced the boat opposite of what I knew to be the way to do it.
I added more ballast to the stern to compensate for the smaller motor and ESC.
About half the weight and volume.
This caused the lost of weight and the increase of air volume in the cylinder.

The mistake was, I put the new ballast weight near the stern to replace the weight lost in the stern.

What this did was move the surface center of gravity forward and the submerged center of gravity rearward. 

The boat ran really well as long as I kept in mind that the trim was not correct.
In forward, I could control the pitch with the stern planes and the depth with the sail planes.

Where it got ugly was in reverse.
The pitch controller tried to correct the pitch but the controller is set for forward motion and not reverse.
The rear planes activated to bring the stern up in forward motion but the boat was going backwards so the stern dove to the point the boat was bow straight up.

This is something that causes extreme concern. (panic)
First thing I did as this happened very quickly was turn off the Tx.
This shuts off the main motor and centers all control surfaces.
And the biggie, this turns on the ballast pump to empty the ballast tank.

The boat surfaced and I was able to drive the boat back shore.

Took it out of the water and brought it home to be retrimmed correctly.
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Got side tracked by an Akula II assembly.
That is complete and I can get back to the Skipjack modifications.
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Opened up the Skipjack this morning.
Pulled the electronics tray out and put it on the work bench.

Before I start any trimming, I plan to make some changes to the electronics tray.

The new motor/ESC combination is much smaller than the original items.
The motor is shorter in length.

Took some measurements and cut the electronics tray under the motor location.
Currently waiting for plastic cement to cure so I can do the hole drilling.
The long tray mounts to the motor frame with 2 small bolts.

This will allow me to move the ballast tank back 1.75" from the bow.
This will position the ballast tank under the rear of the sail.

The battery pack will remain in the bow.

I will remove the lead ballast blocks and start over with trimming.
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Trimming is under way.

I have move the 3 small ballast blocks three times.
I think I have it very close to where it needs to be.
I have siliconed in 2 of the blocks and have left 1 in place using tape.

This photo shows all the ballast blocks. 
There are 7 total.
You can see 3 in the center of the photo. (not painted black)
There are 3 on the front (left end)
And there is a small 200 grain weight in front of the propellor shaft support. 
(under the white silicone that holds the shaft bearing)

Here are the 3 weights I have been moving around.
The left one was moved forward from center of the flood ports to right next tot he left one.
The far right weight, (a 200gr lead 45 cal bullet actually) was moved from aft of the propeller shaft support to 1" in front of the support.
The weight in the middle has been moved forward about 1".
You can see where the silicone smear is.

At this point, I am going to work with the weight here.
I can still move the battery pack, 3/4" aft and 1.50" forward.
I can also move the balloon ballast tank back 1" and forward 3".

I have plenty of options to balanced the boat should it need it.
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Another modification...Safety Tank needs to be enlarged.

Here the safety tank can be seen in the cylinder.
There is room to lengthen it.

Safety tank removed from cylinder and taped for the cut.
I am going to use the clear tank shell to hold the extension in place.

End cut off.

Making plastic pieces to lengthen tank.

Bonding the bottom shims to both the tank and the tank end.

Bonding the bottom piece to the end.

Fit and bond the tank extension to the end.

Test fitting the extension to the tank to get a look.
Will bond align and tomorrow.

The safety tank extension, complete.
This gives me 1.75" more length.

Here is what I have now.
Comparing the original 12" balloon to the newer balloon.
The larger balloon is a 24" balloon.
In it's collapsed state it almost fills the safety tank.

A test on the table using a bucket of water, the pump does not strain to fill the balloon to when it starts to stretch the balloon material.
At this point the balloon has already filled the safety tank.
Time to fill is about 30 seconds, instead of the 2 minutes I was seeing before.
Emptying is the same as before and is acceptable.

The issue of the pressure pushing water past the pump rollers was fixed by removing the tubing in the pump which is different than the tubing you see going to the balloon and intake tube through the rear cap.
The tubing in the pump has a thinner wall to give it more volume to pump.
Looking at the removed tubing, I see that the tubing has worn to the point it stays flat in the area that the rollers contact.
I replaced it and the pump moves more water and when stopped actually seals.
But this may also be because the balloon does not apply pressure to the water in the balloon.

I found a couple of very small leaks in the safety tank and filled them.
Testing will continue after the tank sealant has cured.

Moved ballast weights

  
Ballast weight after moving.

 
Paint touch up of ballast weights and bottom of hull.

  
Nicks and scratches need touch up.

 
After touch up.
The spots on the end of the rear planes are the small screws showing