A Skipjack in Ireland

[The Boattrainman]

Happy New Year!

So after a lengthy hiatus, I will be re-commencing my Skipjack build. I had to suspend the build and log due to work commitments and I used the small time I had available to finish the small details on my Ben Ain (Mountfleet Models), all those tiny details take a lot more time than you think.

Anyway, here is the Skipjack in primer, the hull is basically finished, with the all planes, rudders, lights etc working.




So I've spent a lot of the last few months mulling over the WTC and how to power and control the model, and I've decided to build my own WTC. This decision is based on a number of factors including the cost of buying a commercial product. For example, I had considered the Sub-Driver but the cost of delivery from the USA to Ireland plus the import taxes made the purchase prohibitive, the decision was taken out of my hands when production ceased anyway (for now at least).

Secondly, I want a challenge, having built the Robbe U47 (as U203) and converted it into a static diver with an Engel 750ml Piston Tank, I think it's not beyond my skills (hopefully). Also, I'm going to try to buld this for the minimum cost possible from items readily available to anyone (Ebay etc.) and be asthetically pleasing and more importantly watertight. So to get the ball rolling, I've mocked up on paper all the main WTC dimensions, with a 500ml Engel Piston Tank inside a 90mm diameter acrylic tube (3mm walls) plus various control items, Piston Tank controller, receiver, main battery, servos, drive motor, etc. etc.). Control items will be stacked on top of each other (i.e, in three dimensions), so I won't be 100% sure of locations till the WTC is complete.














I've ordered all the WTC components, I'll post the build when they arrive, the first hurdle will be to get this sorted. If I can make a watertight tube, I'll worry about other problems as they arise.

The Boattrainman

[greenman407]

Your model looks very good. Now that you have determined your course of action,success is easier to achieve. I look forward to seeing your progress.

[greenman407]

So some good and bad news with the first of many Primer coats, which will be done with acrylic spray cans (Humbrol range).

[ATTACH=CONFIG]n114091[/ATTACH]


The main seams have come out quite well and will need just a small amount of work, there's a seam running top to bottom here, nearly invisible.

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The Photoetched hatches and ballast vents add nicely to the main deck.

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The scratchbuilt inlet gratings look reasonable now they have blended in.

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However, there is a serious problem with the nose! As well as the obvious line where the two halves meet which can be filled, there is a dip along this seam resulting in the rounded shape having a flat in it around the entire nose, plus (to my eyes) the nose is slightly an odd shape, with the most forward part having a slight bulge outwards again spoiling the teardrop shape. It's not a biggy, but it will need some work to get it properly 'rounded', but it's the only flaw in what has been an excellent kit so far.

As for the flat meeting of the two halves, I can't see any solution other than some serious filling/sanding.

[ATTACH=CONFIG]n114096[/ATTACH]

If you enlarge the picture up a bit, you can clearly see a flat spot to the left of the torpedo doors at the seam.

The Boattrainman

Wow! Those inlet gratings look Fantastic! How did you do that?

[The Boattrainman]

Hi Greenman,

The gratings are detailed on page 1 and 2 of this log, all brass mesh and plastic strips.

There were some happy coincidences in going down the route of building my own WTC. The Caswell upgrades are suited for the 3.5 inch Subdriver, and there is 90mm Acrylic Tube (approx 3.5 inches) freely avaiable over here, plus the Engel Piston Tanks are 75mm in diameter with an additional 2.5mm for the motor overhang, so it will just fit in the internal diameter of the Acrylic Tube (84mm when you factor in the 3mm tube wall thickness).

Here is the Engel Piston Tank, a paper template is in the pictures above.





I've used these tanks before, they are 100% reliable and function exactly as Engel specify, plus they'll make one to any volume you want.

One step at a time, I'll get the WTC built and tested first before I purchase (as they are not cheap, but worth every cent for what you get).

The Boattrainman

[greenman407]

Looks like its going to be an interesting build.

[The Boattrainman]

While I'm waiting for parts to arrive, I'll have a go at making the end caps for the WTC. The key component will be a compressed 3mm nitrile 'O' Ring at each end of the tube

There are two ways to go here, threaded rod from one end cap to the other either inside or outside the WTC, there are disadvantages to both.

Inside rods will mean four extra holes in each end cap having to be sealed against water (four small circles inside the 84mm inner diameter), outside means extra width that the hull barely has to spare (the four dot points inside the semi-circles outside the 90mm outer diameter).

So here is a go at end caps with outer rods, the first job was to make a paper template to see if it would just fit inside the Skipjack hull.





The paper dimensions area transferred to a sheet of 3.2mm thick Evergreen Sheet (Plasticard), and then carefully cut out with a heavy duty blade.

The centre hole (which will eventually allow the motor shaft exit) and four outer holes were pre-drilled with 1mm pilot holes before the final cut out below. The outer holes are then opened a bit at a time with 1mm, 2mm and finally 3mm drills (for 3mm threaded rod).





All the tools to do this job are below, and more importantly it didn't require a lathe (I haven't got one!). The cap needed a fair bit of tidying up with various sandpapers as cutting 3.2mm styrene is messy.The completed end cap is seen with the paper template, now to make another identical one, plus the two round inner caps that will keep the sealing 'O' ring in place.




The end cap sits on a roll of tape to illustrate how it will sit on the end of the 600mm X 90mm tube.

The Boattrainman

[The Boattrainman]

The 84mm plain discs are again cut from 3.2mm styrene sheet, they will sit inside the 90mm tube. Making them perfectly round is tricky without a lathe, but the 'O' Ring itself should take care of any minor flaws.




I'll wait for the tube to arrive before bonding them to the end caps.

The Boatrainman

[The Boattrainman]

I will need a 'tech' rack, to mount motor, servos, piston tank etc. etc. I'll use the 3.2mm styrene to make a 587mm long (600 mm less 6.5mm each for the end caps). The rack is in two pieces which will be bolted together, a smaller one for the motor and servos and a bigger one for the battery and piston tank.




The rack which is 82mm wide, will sit on half round shapes to 84mm diameter, I'm using this handy circle scriber to mark out full circles which will be cut across at the 82mm points




This is the rear of the rack, the raised box will house the drive motor which will be mounted upside down to put most of it is weight at the bottom of the cylinder, as well as helping with buoyancy, it will give me a small bit of space on top for other items. The motor spindle is off centre due to the 6.1 gearbox which makes this possible.




The Boattrainman

[The Boattrainman]

Construction of the tech rack continues, another box (L145mm X W52mm X H25mm) is constructed at the bow end to house a 5000mah LIPO battery, this is located low in the rack again for stability, but also because the spindle of the Piston Tank must pass over the battery.

The section over the battery and moving spindle will have the Piston Tank controller and Receiver (Rx) for the servos (away from the drive motor), mounted on a little platform. The battery box is open ended so it can be pulled out of the WTC for charging without having to take the full rack out.




The Boattrainman

[greenman407]

Just a thought. What is the purpose of a 6:1 gearbox? Considering the size of the prop, a 3:1 would seem to be the more suitable, unless you will be satisfied with "creeping speed" all the time. Just sayin.

[The Boattrainman]

Hi Greenman,

Yeah, I'm still mulling the motor over, that MFA unit is my goto motor for scale models, it's powering my 40kg Ben Ain, so I was thinking that a much lighter vessel would fairly whizz along with the same configuration. That said, there is a 2.5 to 1 gearbox with the same motor.

The setup on the tech rack will mean any item can be swopped out, so I might go with the 6.1 gearbox first (as I have one in stock),and swop it out if the model is too slow.

Finally, I'm not a huge fan of models going way over scale speed anyway, I'll report back on this, thoughts much appreciated.

Rob

[The Boattrainman]

The acrylic tube arrived, and I'm really pleased with this, it cost just 30 Euro on Ebay and was flawless and beautifully packaged.

The only issue was that at the end where it was cut was a bit rough, so I sanded it down with my large sanding bar with 240 grit sandpaper, then 400 and 600 grit for a smooth end to take the O Ring.





The tech rack and end caps were trial fitted and are all a good fit.




So just a reminder the tube is 600mm long, 90mm wide (just over the 3.5 inches of the Caswell fittings), and made of 3mm thick acrylic. A small bit of sanding of the Caswell mounts inside the hull will be needed to get the tube to fit snuggly.

The Boattrainman

[The Boattrainman]

The Caswell tube beddings are sanded down at the end points so the 90mm tube can sit neatly in the hull




A spare half circle is used as a template for holes for three metal rods which will pass through the lower part of the rack, stiffening the unit and providing a bed on which the piston tank will sit.




A series of holes have been drilled in the battery tray and motor mount to allow air circulate around both.



The Boattrainman

[He Who Shall Not Be Named]

Hi Greenman,

Yeah, I'm still mulling the motor over, that MFA unit is my goto motor for scale models, it's powering my 40kg Ben Ain, so I was thinking that a much lighter vessel would fairly whizz along with the same configuration. That said, there is a 2.5 to 1 gearbox with the same motor.

The setup on the tech rack will mean any item can be swopped out, so I might go with the 6.1 gearbox first (as I have one in stock),and swop it out if the model is too slow.

Finally, I'm not a huge fan of models going way over scale speed anyway, I'll report back on this, thoughts much appreciated.

Rob

Yeah, this thing gets squirrely if it gets going too fast.

David

[The Boattrainman]

Hi David,

Congrats on the handover to Bob in Nautilus Drydocks, I'm a fan of Bob's U-Tube builds, and he seems like a nice guy.

So I've a small addition to the end caps, they now consist of the 90mm outer plate, an 86mm inner plate, an 80mm O Ring plate and an 86mm final plate.




They are bonded together with styrene glue, and the centre hole and a drill bit is used to make sure they are all in line. The 80mm plate will have an O Ring, and I can compress a larger one between the tube rim and the outer plate. Double O Rings, belt and braces!!!




Clamps hold the four layers together while the glue sets.




The rear (motor) end cap is bonded to the tech rack, the centre hole will hold the prop shaft tube and the location means it will lie along the top of the rack in line with the motor.




The tech rack is trial fitted with the 2mm metal stiffening rods inserted in the pre-drilled holes, where the piston will sit the rods are covered in styrene tube.




The Boattrainman