WTC FOR AKULA II

[u552]

After a lot of tests and trials, I've finally finished the WTC for my SCALE SHIPS AKULA II. First of all, forgive me for one thing: Although there's plenty of job to do so far, I've applied a coat of color (after one of coachbuilder primer) to the sub because she looks very much better tha in grey. The ballast system is with a 750 cc ENGEL piston tank. And of course is clearly insiperd in the thread by Ramesh. By the way thank you for your answers to my questiosn about.
After dry checks, made one complete test in water. Everything right at the begining, but leaks detected through the shaft seal and one of the rear plate nuts when started a cycle of ballasting and deballasting. Perhaps one of my mistakes was that to avoid the build up of pressure inside the WTC, closed it with the piston tank in the "ballasted" position.
Here you have some images of the WTC, the linkages of the rear planes, rudders and propeller and how the WTC sits inside the hull. Also a pic of the fore planes fittings, which are operated by the servo and manget mounted on the fore closing plate of the WTC. ALso in the fore plate is the "trigger" for switching on and off.
The WTC is closed with nuts, washers and o rings; o rings are also mounted between the tube and the closure plates. It's fitted with ADC (linked to the fore planes) and APC (with the rear planes). ENGEL piston tank has a safety system which blows the tank in case of signal lost.
I have no lathe, and the plates for the WTC were made from a plank of PVC, rounded using a drill and tested for fitting inside the tube. The "quality" of the results are clearly visible so, please be indulgent.
Regards from Madrid

[Wheelerdealer]

Re: WTC FOR AKULA II

You done a really good job on the Akula. I will be interested to see where your wate line ends up. I had to place the WTC right on the floor for it to work right.

[greyakula52]

Re: WTC FOR AKULA II

Your Boat Looks Great!
Test It!
Submit Some Running Pics..... Please.

Captain Andrei

[u552]

Re: WTC FOR AKULA II

Thank you all for you answers. But there's a big mistake in my concept of sealing the WTC. As I haven't a lathe to do them precisely, cut PVC discs and rounded them with a drill to , let's say, "roughly" fit the outer and inner diametre of the tube, and joinned to complete the end caps. But doesn't have a slot for the O ring. It's pressed between the edge of the tube and the outer plate of the end caps, as you can see in the pictures, resulting in a smaller and less effective sealing with the logical consecuence of air scaping and water leaking. So I'll have to make aprropiate end caps with.
Other surprise was a leak through the shaft seal. It was mounted with the spring facing out side the WTC; I've been suggested to turn it to face inwards. Seems that it sits a little "tender" in the tube; Hope won't be popped out when the WTC gets pressurised.
The rest of the system works nicely. Ballast tank is a 650 CC ENGEL TA one. Tube is 55 cm long, 10 cm OD and 9,6 cm ID.
Haven't done any floating test yet (and due to the need of new end casps, will be a little delay on it), but for sure will have to adjust lead ballast and foam.
I've tried to sit the WTC inside the hull as low as possible, but will have to make tests to verify how she sits in the water.

[skip asay]

Re: WTC FOR AKULA II

1. With a piston type ballast tank, it's best to use O Rings for seals since these will seal in both directions.

2. When sealing your WTC prior to putting it in the water, position the piston as close to the mid point of travel as possible. This is the best compromise as far as pressure/vacuum is concerned. Putting a pressure port in the WTC isn't worth it since you'll never be able to pressurize it enough via lung pressure.

3. There's nothing wrong with your method of sealing the end caps as long as the end of the tube is clean, smooth, and straight. I've been doing that for several years with absolute success.

4. Use "acorn" nuts on your threaded rods which hold the end cap in place with an O ring and no washer. There's no way to seal the threads reliably. I'd be willing to bet this is where your water is getting in.

Hope this helps.

Skip Asay

[JWLaRue]

Re: WTC FOR AKULA II

4. Use "acorn" nuts on your threaded rods which hold the end cap in place with an O ring and no washer. There's no way to seal the threads reliably. I'd be willing to bet this is where your water is getting in.

It is possible to seal threads.....but you'd need something like this which uses an o-ring][/url]

This is similar to the acorn nut, but seals with 100% reliability. I use these on my Seehund dive module which uses an Engel piston similar to yours.

-Jeff

[bill rogers]

Re: WTC FOR AKULA II

Jeff, What are they called so I would know what to ask for at the hardware store?
Bill Rogers

[JWLaRue]

Re: WTC FOR AKULA II

Hi Bill,

...I've not seen them at a hardware store. (At least not one near me)

I either get them from OTW or make them myself. OTW uses them for their dive modules.

-Jeff

[Guest]

Re: WTC FOR AKULA II

Other surprise was a leak through the shaft seal. It was mounted with the spring facing out side the WTC; I've been suggested to turn it to face inwards.

Is that the Engel motoro mount, it looks like it is. You have the seals facing the wrong way, the spring should be on the inside, as the pressure rises the seal will tighten. make sure you havent damaged the seal at all with sharp edges on the shaft, and also a little lubricant on the seal helps prolong life. Other than that the shaft seals and bellows is the same deisgn i use with piston tank.

on one oy other boats which is RCABS and not subject to the same pressure changes i use a similar end cap design, with capped nuts. I plan eventually to get some mdae like Jeff shows with a captive o ring to seal the face of the nut. But for now i have found that tightening the nut down, then a pplying small amount of silicone sealant is suffienct to keep it air tight

[skip asay]

Re: WTC FOR AKULA II

"This is similar to the acorn nut, but seals with 100% reliability. I use these on my Seehund dive module which uses an Engel piston similar to yours."

Potato....potahto. The net result is the same. The important part is that the end of the nut is closed off. My way is cheaper. Your way is more elegant (and more expensive). Truthfully, I like your way a little better since with the O-ring "captive" you have less chance of losing it.

Actually, my way as used on the WTC in Albacore and Marlin is a little different yet. I don't use nuts but long screws with the holes in the end cap countersunk slightly to prevent the O-ring from being extruded on compression. There's more than one way to skin a cat! (God, I hate that expression. I had to make sure neither one of my cats was in the room as I write this.)

Skip Asay

[u552]

Re: WTC FOR AKULA II

Thank you all for contributions. I've turned the shaft seal spring side inwards and applied silycon gease to it. Nuts have O rings under the wahsers, but silycon "topping" will also aid in sealing. By the way, nuts are self - blocking type.
Yesterday made new joints for the WTC from a rubber sheet. These new joints are now between end cap discs (I'll take pictures and attach): the outer and the inner. After this all, re - mounted and re - sealed everything. New batch of tests is scheduled after silycon is completely dry.

Regards from Madrid
Juan Carlos.

[u552]

Re: WTC FOR AKULA II

I've consulted with ENGEL:
1. Shaft seal: His web says the spring must face OUTWARDS, but they say it also could be mounted facing inwards to avoid its corrosion
2. State of the ballast tank: Must be EMPTY when model is closed.

J.C.

[u552]

Re: WTC FOR AKULA II

More from ENGEL: Perhaps the size of the tube is too small in relation wit the piston tank, so the build up pressure is too high for the gaskets, even the simmering in the shaft seal. They say that the piston tank volume must be around 10 - 15% "net" WTC volumen. Any previous experience about?

Juan Carlos.

[Guest]

Re: WTC FOR AKULA II

Could be. I think Ramesh used a 500ml tank in his WTC.

The Simmerring used for the motor shaft should be able to withstand a bit of pressure- that is the purpose of the little circular spring on these seals. However I would be cautious about raising the pressure beyond about 5 psi, and Engel are being cautious in recommending about 1.5-2 psi.

If the tank can handle the pressure inside the boat e.g it isn't straining hard when retracting, and you still get leaks around the shaft seal, there are a few options.

1. Mount the motor within it's own little cylinder within the module, so it's effectively sealed off from the rest of the larger cylinder- you're using a metal mount for the motor which goes outside to the wet, so it's already well cooled by conduction.

2. Fit a pressure relief system.

3. Make another small cylinder and place that forward to increase the volume.

4. Shorten the piston tank.

What size is your module?

[Wheelerdealer]

Re: WTC FOR AKULA II

Yes the piston tank in my Akula is 500ml, I have the 'spring' on the outside, no air or water leaks. I used brass domed nuts and soldered on a brass washer.