A Skipjack in Ireland

[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

[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

[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

[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]

David,

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

Rob

[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]

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]

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

[trout]

We are here to help each other. I am really looking forward to seeing your progress. This is exciting stuff!

[The Boattrainman]

A bicycle valve core is epoxied into a 9mm hole.





I found a nice stainless dust cap with an internal O ring that will be a bit of insurance if the valve fails.





The bicycle pump pushes 78ml of air per stroke, so seven strokes is over the 500ml of the piston tank (I know it's not exact as the air will compress, where the water in the piston tank will not).




Here is the WTC under water with seven pump strokes, the stuffing tube only has a small O ring tight up against the shaft, but still lets the shaft rotate. But this is where it gets a bit weird!




Tests with inner and outer O rings in place showed some small leaks around the rim. So to remedy this, I decided to start with the outer O rings only and fix these first. However, with just the outer O rings, there are no leaks (except a tiny leak around the outside of the stuffing tube, more epoxy).

So it looks like I don't need the inner O rings at all..................... have to do some more tests!!!!!

The Boattrainman

[The Boattrainman]

Here is the final arrangement, at the shaft end, the stuffing tube is filled with silicone grease and has a greased mini O ring at both ends that are compressed slightly so that the shaft still rotates. It a matter of getting the balance between enough compression of the mini O rings to keep the pressure in the tank and little enough so the shaft turns easily.




The forward end has the valve sealed with a box of styrene filled with two-part epoxy, that solved the tiny leak. The square of velcro acts as a bump pad against the forward caswell fittings in the top hull where the WTC rests.



The WTC now holds pressure with 750ml of air through the valve (50% more than the 500ml that the Piston Tank will disperse), so a good margin of safety.

Well pleased that it works, even though the inner WTC O rings are not required (note for the next build), on to the servos etc. which I have now ordered.

The Boattrainman

[Scott T]

put 500 ml of water in your WTC then see how much air can be put in

[The Boattrainman]

How about 600ml of water and 500ml of air!!!

The volume of the WTC with the water is now 3300ml minus 600ml, so 2700ml of space and pushing in 500ml of air is still around the 18% mark, beyond 25% there might be some issues alright.




Seals holding..........

Rob

[He Who Shall Not Be Named]

I like your style, Rod:

"I see your 500, and raise you 100... *****!"

I love this kind of WIP. Informative AND reactive!

David

[Scott T]

Sounds like a better test. Thanks for the update.
Scott T