Build log #4
                                  by Ralph --- SSBN 598 

New Ballast Safety Tank.

After the last outing, the Skipjack is on my kitchen table disassembled.
Was looking for a leak that almost claimed my boat.
Turns out, the leak was caused by me not following the pre run check list.
I had not run the ballast tank water pump in both directions.
Most of all, I did not empty the ballast balloon completely before closing of the Schreader valve.
Pumping water in worked fine.
Pumping water out worked fine up until the balloon reached it's pre run state. Partly inflated.
As the pump removed the remaining air from the balloon, it pulled a negative pressure in the cylinder.
This was enough to pull water in through the propeller shaft seal.

Making changed to the Safety tank has nothing to do with what I caused.
While the boat and it's parts are sitting on the kitchen table, I wondered if I could find a better water pump.
The 3 minutes it now takes to fill and empty the ballast balloon is too long.
So, I searched for a new pump.
Ordered one and I am waiting for delivery.
Using the measurement numbers, I will have to make some changed to the tech rack.
Remove the water pump and decide once the new pump gets here, whether to put in at the back of the tank to in front of the tank.
Another issue is the battery. It currently sits under the safety tank which looks sort of like a "C" with the opening down that lets the battery slide under the tank.
Looking at the tech rack, it looked like I could move the battery under the rack once the water pump is removed.
Might have to relocate 1 servo.
Need the pump.

Now, with the battery moved, I could/can make the safety tank by making 2 water tight bulkheads with breather holes to equalize the cylinder pressure.

By using bulkheads, this will shorten the safety tank by as much as 1" or more.
More room in the cylinder for stuff.

Okay, think I will make the 2 bulkheads.
Found a piece of 5/16" clear plastic laying around the shop.
Put my short test cylinder piece over the plastic and scribe the circles needed.
Drill a 1/4" hole in center of pieces.
Put a bolt through and chuck it in the drill press.
Turn the circles to fit inside the cylinder.
Get out my Exacto knife, a couple of small files and a steel cutter I made for making grooves for O-rings.

15 minutes later, I had 2 bulkheads ready for the cylinder.

Test fit the bulkheads in to the short cylinder piece and I think I have what I want.

I put three 1/16" holes in each bulkhead to allow pressure to be passed to the entire cylinder when the balloon is inflated.

Once I have the new water pump, I will need to make an inlet tube that will hold the balloon in place and handle that the water flow rate. (thinking 1/4" brass tube and plastic parts.

I will also need to make something to keep the bulkheads separated so they can not move in or out.
Thinking 1/16" brass rods and wheel collars on both sides of each bulkhead.
This will allow me to adjust the length of the safety tank as needed.

This is the original ballast safety tank with it's parts and balloon.
I have since gone to a larger balloon (24") that when filled, does not put pressure on the balloon rubber but just fills it out.
There is no pressure trying to empty the balloon when filled.
Had the issue with the smaller balloon. (15")
The tube holds the balloon so it does not bunch up.
The new one will be larger. (this one is 1/8" tubing)

This morning, 
I tested the new water pump against the old water pump.
The Test.
Time to pump 450 ml when pump motor is connected directly to the 7.4 DCV (2650 mah) battery.

Original roller pump = 194 second.
New pump = 19 seconds in clock wise rotation.
                 18 seconds in count clock wise rotation.

19 seconds is perfect!

There is an issue I need to find a fix for.
The New pump is a gear pump and it will NOT seal completely and water will flow back through the pump when not running.

I need some sort of small electric off/on valve. 

Any and all suggestions would be appreciated on where to find a small electric off/on valve.
When testing this little pump, I sued the kitchen sink.
I was not careful the first time on pointing the exit fitting.
I did not put a length of hose on it but just let the outlet do it's thing.

This little pump shot water at least 8' across the room to the cabinets.
Had to do a quick wipe down of the cabinets and floor.
This pump put about 1/3 cup of water out before I got control and pointed the pump outlet in to the sink.

Note to self . . .when testing water pumps, make sure to use 2 lengths of hose to direct the water from the container to the sink.

 About the pump.
I bought 2.
1 to disassemble to see if I can put a brushless motor on it.
1 to test and run as is.

My total cost delivered to my mail box in town was $8.64 including shipping.


Inlet water valve.
This is one possible solution.

Work in shop has been suspended for today.
It has been raining hard for 2 hours and it has just turned to snow.
I am going inside the house. 
It's time for lunch anyway.
Doubt I will be coming back out to the shop.

Safety Tank rebuilt.
What can't be seen is the sides at the bottom tray are reinforced with black plastic sheet strips.
The joints where reinforced inside and outside of the tank. 
This is where the tank separated.
New ballast balloon installed on the inlet/outlet tube.
Balloon has been pressure checked with air filling the balloon to twice the size of the ballast safety tank.
The balloon when inside that safety tank will inflate to the size of the safety tank without putting pressure on the balloon rubber.
It is just a bag without stress.
The boat takes about 405ml of water to go from surface trim to slightly negative trim.
The safety tank worked out to about 500ml.
I should have plenty to work with when trimming.
The balloon with water in it without putting pressure on the balloon rubber holds about 475ml.

Tomorrow, I will start reassembling the tech rack.
Not much to do really.
Reattach the silicone tubing hoses to the original pump and the balloon inlet/outlet tube.
Slide it all back in to the cylinder then the battery pack.

I do need to repair the Sail Plane control rod connection magnets.
I took that a part to strengthen the magnet attachment to the end of the long control rod from the sail planes control horn.
I could see it twisting when manually operating the control rod.
I had depended completely on the solder for the connection.
I am going to make a brass strap to go around the wheel collar then drill a hole in it for a magnet shaft bearing. 
Sail Plane control rod repaired.
Actually a new fitting for the end cap control rod that holds the magnets.

Assembled the Ballast Balloon Safety Tank.
Cleaned the end cap o-rings grooves, o-rings and regreased them with silicone grease.

(I did not install the new pump. 
I have to make a few special fittings and one part has not arrived yet.
So, I put the boat back together as it was last time it was run.)

Connected all the water tubing and nylon tied.
Did the radio testing to make sure everything still works.

Slide the Safety Tank in to the cylinder followed by the electronics tray.
Connected the front end cap battery power plugs to switch.

Closed up the cylinder and installed the 2 long safety bolts.

Boat is now ready for trimming.
Plan to do that on Monday and Tuesday.
I have gathered up all my little trim lead weights so they are in one place when I get the boat in the water.

Here the boat is assembled and tested...several times. 

Note:  Matt, I did a water volume check on the roller pump this morning before reassembling the cylinder.
Did the same tests I did on the gear pump.
1 cup of water and timed it on both sides of the pump.
Water in = 170 seconds.
I looked at the Tx settings and increased it from 40% to 60%.
Then timed it again.
Water in = 25 seconds. Big difference.

Water out = 90 seconds.
Changes Tx settings from 25% to 40%. (pump runs faster one way then the other)
Water out = 27 seconds. (Again big improvement)
Will run time tests again during trimming.