A Skipjack in Ireland

[The Boattrainman]

So pressure testing begins, the unit passed the immersion test with no pressure, it doesn't leak, big deal. But blowing down the stuffing tube, it leaked like a sieve.

First job was to tighten the inner O ring with a bit of tape.




That sorted out, I the bevelled the edge of the WTC, not an easy job. I decided around a 30 degree bevel, and used a mini sanding drum..........




.....followed by 120 grit sandpaper on a round pole.............




.......and finally 400 grit by hand.




This was a tricky job, as the outer rim must not be damaged or the seal will be lost, the bit to remove is from the inner rim. The mini sanding drum does give a bit of a wavy line, the trick is to keep checking and going back over bumps.




Putting it all back together and giving it a good amount of air down the stuffing tube (as a trumpet player I can get a fair bit of pressure up), the seal at both ends was intact.

Many thanks to Trout for the tape and bevelled edge ideas, the final pressure test will be to get the WTC up to piston tank level of stress.

The Boattrainman

[The Boattrainman]

This fitting is made from 3.2mm styrene, and with two brass bushes will hold the WTC down in the hull.




Glued to the hull, the fitting acts as a backstop to the rear of the WTC, and the 7mm hole at the bottom accepts the lower threaded rod with the brass bush attached




The front part of the same rod gets a brass bush and fits into this 7mm hole drilled in the Caswell fittings in the front hull.




The WTC is now anchored when in operation, pinned at the rear by the backstop and at the front by the Caswell fitting, but can slide out of both when the hull parts are separated.

The Boattrainman

[The Boattrainman]

I've built my own prop shaft, I found a tube of 6mm brass in the spare box, a tiny pilot hole was drilled from one side to the other, opened out to 2mm and a piece of 2mm rod inserted.




The rod is trimmed to make a dogbone and soldered in place with the torch (soldering iron not powerful enough).




The finished tube exactly cut to length with a 5mm rod inserted and glued in place, with a flat filed for the coupler.




The prop shaft is in line with the shaft from the WTC, it's so accurate I prob don't need another coupler, but will use one just to iron out any tiny misalignment.




I never made a prop shaft from scratch before....cool.

But I've now got four shafts, one coming out of the gear box from the motor, one through the stuffing tube, one from the stuffing tube shaft to the mini shaft on the prop with the U connector!!!!! Must fail some ergonomic rules............................


The Boattrainman

[The Boattrainman]

David,

Wow, much obliged, will keep you posted............!

Rob

[He Who Shall Not Be Named]

Hi Redevil and David,

To be honest, I haven't a clue if the stuffing tube will work, I'm just going with what I know and what worked before. My water trials will begin now, because the WTC is finished.

When the piston tank arrives, I'll test under pressure and get report back, if there's a problem, I'll sort it at that stage.

And many thanks David for the words of encouragement.

Rob

If you have problems with your seals, I have a selction of 1/16", 1/8", and 3/16" Pushrod and shaft seals here if you need any.









David

[The Boattrainman]

So here is the finished article, just out of the bath from two hours immersion, totally dry inside.




Now of course there are servos, electronics etc. etc. all to be sorted, but they are 'add ons', the WTC as a solid unit is finished bar trimming the 3mm threaded rods.




I thought it would be worth detailing the time/cost on this, and I don't mean any offence to professional suppliers, I hope non is taken.

The cost was as follows:-

Acrylic Tube 90mm X 600m X 3mm..........30.00
Styrene Sheet 3.2m X 2............................24.00
Nitrile O Rings...........................................15 .00 (3 X packs of 5)
3mm threaded rod X 5 (1 spare)...............14.00
2mm steel rods X 3.....................................5.00
Stuffing tube and shaft .............................13.00
M3 nuts X 10...............................................2 .00
Misc styrene bits from spares box...................0
Glue/epoxy/sandpaper etc. (negligible)...........0

TOTAL 103.00 Euro

Hours to date 20 approx. (and very enjoyable hours they were)

What's not detailed is postage/delivery, some items I found in the local hardware store, others were shocking expensive (given their size) to deliver to the house, but different builders will find this cost varies depending on availability.

The Boattrainman

[The Boattrainman]

Hi Redevil and David,

To be honest, I haven't a clue if the stuffing tube will work, I'm just going with what I know and what worked before. My water trials will begin now, because the WTC is finished.

When the piston tank arrives, I'll test under pressure and get report back, if there's a problem, I'll sort it at that stage.

And many thanks David for the words of encouragement.

Rob

[He Who Shall Not Be Named]

Though I've been silent for much of this thread (I rather keep silent than chime in with useless complements), I want to assure you I am examining your excellent, exacting work with deep appreciation. You are a Craftsman, sir. Keep slugging away on this project.

I'm particularly interested into your approach to the WTC. New, thought provoking stuff.

There! Enough ass-kissing for the day. Carry on.

David

[reddevil]

One question about the shaft and its sealing Are you sure the method you're using is really watertight? Because I once asked ENGEL about using that kind of drive shafts with sleeves, and the answer waas that they weren't watertight

[The Boattrainman]

A 3mm slot is filed in the centre of the rest points to hold the lower outer rod on the WTC.




The lower rod sits in this groove and doubles as end cap holder and keeps the WTC in place.




The steel pushrods are all replaced with brass rods and brass clevises and checked again for straight alignment.





The Boattrainman

[The Boattrainman]

Hi Albion,

It's a prop tube from Model Bits, I suspect you might be right, I'll stuff it with silicone grease and there will be a mini O ring compressed against a thrust washer, that's why I've cut the shaft to exact length. The photo is just for demo purposes, the O ring will be on the inside.

Worked for the 750ml piston tank on my Robbe U203, I just replaced the O ring every 3/4 sessions, the few bubbles coming out of the shafts told me the O ring was toast.

so



Those markings are the lines along which the servo arms can exit the WTC so that they line up the arms from the rudder and dive planes.

Rob

[Albion]

What seals are in the stuffing box tube ? The piston tank is going to pressurise the etc when you dive, if that just a close clearance tube, I suspect it's going to leak badly as the tank fills.

[The Boattrainman]

This fitting can now be sorted, it will carry the throw of the dive plane servo, reversing it's direction out of the WTC. It's held in place by these styrene fittings, one at the bottom of the hull another at the top.





The fitting is installed and removed, by pressing the hull inwards and as it's not glued in, it drops out.




The Klik On magnet is installed on the servo arm, the other magnet is on the end of the snake rod going to the front dive planes.





The plastic snake will bend downwards when the hull is opened up, and you just pull the magnet off (a safety ring ensures it stays on during operation).




This is the top hull in place , opened up at the breakpoint, the lower arm of the servo rod will go to the rod coming out of the WTC from the forward dive plane servo.




The Boattrainman

[The Boattrainman]

A stuffing tube (3 inch, the shortest I could find) is pushed into the shaft hole, a surround of styrene is filled with epoxy to seal the joint. Not my neatest work, I'll be filling and sanding this later.




The inner shaft is cut down and a flat filed into it to take the outer coupler.




A plastic gauge is made from scrap styrene to set the linkages from the rudders and rear dive planes as they are on slightly different levels, in preparation for installation of the servos and linkage holes.




The Boattrainman

[HardRock]

Wasn't Menendez the man who brought the left handed screw driver to America?