Moebius Skipjack with R&R WTC question

[redboat219]

https://www.amazon.com/SI-A0050-Windscreen-Washer-Keenso-Universal/dp/B07GN3ZT89

Or this one

https://www.amazon.com/wrtgerht-Power-Small-Self-Priming-Hydraulic/dp/B0B7QKT42S

[Subculture]

It's unusual for those pumps to leak in my experience. They can sometimes shed their key on the driven pinion if they're run hard, but in the R&R system they're under fairly low strain as the tank is aspirated, so they don't have to pump against pressure. To have a pair leak seems really odd, are you certain it's the pump itself leaking and not one of the connections to it?

Fitting other pumps is going to be a faff, as the tech rack is designed to take that pump, and to be frank unless you use a Kavan, which I doubt will fit anyway, they're all much of a muchness quality wise.

[redboat219]

As diaphragm pump are non-reversible you could use 2 pumps, 1 to pump water in, the other to pump water out of the ballast tank but would take up space inside the WTC. https://youtu.be/mQC4nxo3G8g?si=Si-5Bh7bpfAFWp-b

[g2tiger]

Subculture, I agree. Yes, I am reasonably sure its the pump. I am able to run the intake and output to long tubes while the cylinder is off the internal frame. I watched water accumulate under the pump while I ran it. To me it looked like it was coming from the area where the tan part meets the orange housing. I admit that I did not check it very closely so it may be one of the tubes leaking down the case and just showing up at the joint. It can be difficult when the water is clear, I will check it again and pay more attention. I do have tie wraps on each point where the tubes connect to the fittings on the pump and also the others in the frame and ballast tank so I thought they would be less suspect.
Redboat219, Thanks for the information on the pump. It looks like it will do the job. Do you know how much it pumps per minute at 6 volts? Those specifications are not listed.

[Subculture]

Check the pump on the bench with the rack out of the tube, use a bowl of water to feed the pump, and watch it carefully.

[biggsgolf]

I purchased two of these cylinders, both had tiny slit cuts in the tubing where they connected to the nipples, in both cases caused leaks

[redboat219]

Nate He uses one of those 3-12v gear pumps on his 1/96 Blueback maybe best to ask him as I can't find any info online about it's rate.

[redboat219]

Just talked with Nate, he says with his Type II Uboat the pump can fill a 600ml balllast tank in under a minute.

[Albacore 569]

Several small comments for what they are worth. I remember Dave Merriman balanced my D&E skipjack USS Scamp out perfectly. The WTC ballast tank was on the center of Gravity. So then where is that? (CG)? - aft of the sails trailing edge. in a narrow range. I could release the controls, and it fly hands off steady as a rock at periscope depth

But also, in turning. Dave had the nicads in the forward part of the wtc, a shorter moment arm, forward, the moment arm aft of the CG was considerably longer aft. this made for excellent maneuverability with that all moving scale rudder. Keep that in mind too. Once you have a good CG point balanced in, then follow Bob and Daves advice I suggest. Weigh of a arrow, with long body and tail feathers farthest aft.

I watched a recent you tube video of one of Bob Martins video programs restoring a Trafalgar class boat with a pump jet. I was surprised pleased impressed how maneuverable the Trafalgar was in the water despite the fixed shroud aft.

Seen other pump jet models and the one I saw turned abysmally (that is the owner/ operator's description not mine).

Was it because of the CG was more forward on the boat in Bobs video allowing a longer moment arm aft? Why the difference.? Similar hull design, both had Pump Jets, but what made for the huge difference in turning ability?

I can only guess the CG was bit more forward, and the dive module set longitudinally to that new balance point accordingly?

[Subculture]

Hull aspect, control surface area and distribution of mass within the hull will make a great difference to how the boat handles.

If a boat is a bit sluggish in pitch and yaw, you can try moving the mass more towards the centre of the boat and lowering the metacentric height a bit. There are limits to how far you can push this, but with modern batteries and electronics, packaging and weight distribution is much easier than it used to be.

[g2tiger]

Good information team, Thank you.
I was able to run up the pump (the replacement) and I saw no leaks when filling or emptying it as installed in the frame without the cylinder. I took the frame out of the cylinder and ran the pick up and discharge tubes into a small tub of water. The current pump empties/fills the tank in about 20 seconds. Anyway, no leaks as tested, ran it full and empty about 8 or ten times. I will need to get the WTC into the tank and figure out how to locate the leak. One area that did catch my attention some time ago was the prop shaft seal, I thought I saw a drip or two on the end cap directly under the shaft at one point. But I do remember seeing the water accumulating under the pump when it was tested as a complete unit. Perhaps replacing the pump and new tie-wraps may have fixed the leak at the point where the tubes are plugged into the pump? Also, I may need to add a fitting to the WTC to allow me to put pressure into the WTC and see if the leak is a bellows or the Shaft seal or a end cap seal.

[Subculture]

You can add a new fitting or you use one of the existing exits e.g. remove one of the control rods and replace with a small diameter metal tube with a hose on the end that you can blow through.

[type7]

Have you tightened or loosened the shaft seal and put threadlocker on it? Mine were loose when I got them but are adjusted easily.

[Subculture]

On Ron’s earlier offerings the motor gland used to have a locking ring/nut to prevent loosening. It seems that part has been removed from his newer designs.

[g2tiger]

Team, I have been out of town but hope to get back to her this upcoming week. I plan on checking the drive fitting. I guess worst case is a pump to pump out the WTC, ha ha I also have been working on a 1/77 Disney Nautilus from Master Model Work I think it is. Man, I need some money! I do have a twin motor 2.5 or 3 inch R&R WTC and VEX radio I think I can part with.