A Skipjack in Ireland

[He Who Shall Not Be Named]

The only time you want long moments is to damp out wave action (a big deal on a diesel boat on or near the surface in foul weather). We called it the 'dumb-bell'. We got as much water into the forward and after trim tanks (and the torpedo rooms WRT tanks) as boat control would permit. We all still puked our collective guts out, but not as bad as if the boats longitudinal moment arms were short. On a model submarine, you want them short -- it gives the stern planes and rudder more authority.

David

[The Boattrainman]

Roger that Dave.

And therein lies the problem. At 1/72 scale, I can't pump ballast to fore and aft tanks to create a stable craft on the surface. It's a bit of a compromise really, the four larger metal bars in the photo are right under the piston tank (the heaviest componenet in the entire buld), so I really have a large 'moment' centred in the craft already by default.






Piling more weight around this central area had the sub bobbing like a cork, so I had to stretch out the weight down the longitudinal axis of the keel but still keep a centre of gravity around the piston tank, but I totally get that once submerged the best place to have the weight is in the centre.

Interesting that on the full size subs they moved ballast around to suit the sea conditions, I wasn't aware of that, I would of thought it's a risky business tricking around with the subs bouyancy, then again ballast shifting is practiced by all kinds of vessels. Also, I always wondered about submariners who never get to see the horizon, you must need a fairly steady inner ear to counteract motion sickness, at least on a surface vessel you can go up on deck occasionally.


Rob

[He Who Shall Not Be Named]

Roger that Dave.

And therein lies the problem. At 1/72 scale, I can't pump ballast to fore and aft tanks to create a stable craft on the surface. It's a bit of a compromise really, the four larger metal bars in the photo are right under the piston tank (the heaviest componenet in the entire buld), so I really have a large 'moment' centred in the craft already by default.






Piling more weight around this central area had the sub bobbing like a cork, so I had to stretch out the weight down the longitudinal axis of the keel but still keep a centre of gravity around the piston tank, but I totally get that once submerged the best place to have the weight is in the centre.

Interesting that on the full size subs they moved ballast around to suit the sea conditions, I wasn't aware of that, I would of thought it's a risky business tricking around with the subs bouyancy, then again ballast shifting is practiced by all kinds of vessels. Also, I always wondered about submariners who never get to see the horizon, you must need a fairly steady inner ear to counteract motion sickness, at least on a surface vessel you can go up on deck occasionally.


Rob

The trim tanks, axillary tanks, WRT tanks, negative tank and safety tank were not part of the main ballast system. The contents of those tanks were worked out before the first dive and fine tuned during the initial 'trim dive'. Once the boat assumed submerged trim (main ballast tanks full), the other tanks could be used to change the boats c.g. (for pitch management) or they could take on/off sea water to suite the desire of the diving officer, depending on if he wanted the boat light or heavy -- usually dictated by sea state. Keep in mind, I'm talking about a diesel boat, stuck near the surface for any number of reasons. (The safety tank stayed full of water as it was there to be blown dry in the event the conning tower flooded out so was not available for use). The main ballast tanks where there to change the submarines net displacement -- the other tanks were there to control trim and fine-tune the boats displacement.

I was the LPO in the TRUTTA's stern-room, the worst place to be on a submarine bobbing around in a high sea-state. And once the boat was stuck on the surface in bad weather, we had to stay there -- diving in such weather could roll the boat (if hit by an abeam trough the metacenter could invert in the half-full-half-empty ballast tanks as they flooded down -- sloshing water there could kill you). Such seas meant you rode the storm out on the surface. The stern room was a very special slice of hell as we not only pitched up and down violently, there was also a cork-screw motion to the boats ass end -- we were the tip-of-the-whip in bad weather.

A nuke boat simply assumes patrol depth and laughs at the sea-state topside.

David

[The Boattrainman]

Dave,

So the worst of all worlds, a machine designed to be at it's optimum submerged, stuck on the surface in a Force 7/8, I dount if any amount of 'sea legs' would be able for the battering.

I had a small river cruiser for a few years, and still use a mate's on the River Shannon, and the worst I've been out in is F3 -5, and I consider I've a strong water constitution (never been sea sick, yet!), but what you are describing is a special kind of hell. They weren't paying you enough man!!!!!!

Rob

[The Boattrainman]

Styrene surrounds for the ballast bars are constructed using 2 x 4mm square profile.








The bars are held in place by the surrounds and given the unique shape of the hull, they don't even fall out upside down. No Glue! Also their proximity to the WTC means they can't come out as their's no room.




Now I have one pet hate (two actually....decals, more on these later). I detest with a passion closed cell foam used as a buoyancy aid for submerged trim. Having used the stuff in my U-203 years ago, the constant trial and error, the fact it looks awful etc etc....I'd rather use rare earth magnets stuck to a ferrets ass!!!!

So I'm trying a few different approaches and to start I'm making small hollow buoyancy tubes. To make the tubes watertight, they are dipped in styrene cement.




The tubes are placed onto small squares of styrene which will be cut back and sanded flat at both ends. The trick is to turn the tube down hard onto the flat plastic to ensure it melts.




Here are just three tubes holding the sub on the level at periscope depth.





I'll need more and have to get them above the waterline inside the hull.


The Boattrainman

[He Who Shall Not Be Named]

Dave,

So the worst of all worlds, a machine designed to be at it's optimum submerged, stuck on the surface in a Force 7/8, I dount if any amount of 'sea legs' would be able for the battering.

I had a small river cruiser for a few years, and still use a mate's on the River Shannon, and the worst I've been out in is F3 -5, and I consider I've a strong water constitution (never been sea sick, yet!), but what you are describing is a special kind of hell. They weren't paying you enough man!!!!!!

Rob

My pay-off came in retirement -- retirement checks and excellent medical care. You get what you pay for.

But, back to your work here. You are going like a house afire! excellent Craftsmanship inside and out. And good sound planning throughout. One of my favorite WIP's here.

David

[The Boattrainman]

Here is the WTC separated from the hull, the piston tank is full in this shot. By keeping the motor and battery below the half way line it stays upright.



The WTC is perfectly level side to side with no additional ballast required, this is what made balancing the total sub much easier.





The WTC is just a fraction off level fore to aft, a bit heavy at the forward end, this was the compromise needed to get everything inside in a good position.


The Boattrainman

[The Boattrainman]

The immersion tests show the WTC is moving by about 1 - 2mm in the hull despite the keeper plate to the rear and the front coming up against the Caswell torpedo fittings.

So to set the WTC solid against the rear keeper plate, a 3mm knurled nut is set into the rear end cap and a long screw made of 2 knurled nuts and a 50mm bolt.




This odd shaped fitting is made to grab the rear keeper plate.




The fitting has a lip which sits over the rear keeper plate, a bit fiddly but the 1-2mm shift moves the pushrods and affects the trim.




I should have extended the keeper plate upwards when making it, but I didn't foresee this issue at the time, so a nod to Rube G!


The Boattrainman

[The Boattrainman]

The ballast bars get a coat of primer and a good coat of enamel rust proofing before re-instatement. I don't want a load of rusting metal lying in the bottom of the boat




The forward ballast bars presented a different problem tucked into the nose, I don't want to glue them in, I dislike a lot of fixed ballast especially in hard to reach areas, what happens if I want to re-trim the model should there be, for example,a different battery used or other changes.

Again surrounds are made from L-shaped styrene to hold the bars from moving sideways.




The bars are doubled up and stuck together with a protruding piece to fit the space. A clip is made from a small piece of flat brass bar.




The clip is a tight fit and slides over the centre bar of the Caswell fittings, and presses the bars downward, they are now locked in place.




Easy to remove if there are any changes.


The Boattrainman

[The Boattrainman]

To get the painting started, I'm starting with the sail.

It begins with a bit of colour matching, Humbrol 67 (which will be used for tips and scratches) is matched to a couple of basic grey car spray rattle cans. One can is a fraction lighter and the other a fraction darker then the Humbrol enamel.




There are loads of ways to apply the basic hull colour, here is my method. Before the final grey's are applied three basic colours Grey Primer, Red Primer and Black are used.


The whole sail gets a coat of the Grey Primer, then all over Black, then a light dusting of the Red Primer, this simulates the aging process of the paint.




I then give the sail a coat of the two grey matched cans, spraying lightly with one shade and then the other, never using too much of either, and trying to vary the areas that I hit with more of the lighter shade at the top of the sail. I never direct the spray at the sail, just trying to 'float' the mist onto the model.

You get these variations of shading and It also has that slight undertone of red primer, it's fast and cheap, with about 15 minutes between coats, not bad for a few hours and a couple of cheap cans of paint. A final coat of Matt Varnish applied to seal it all in will be allowed to dry overnight.

A bit of light weathering will come later.

The Boattrainman

[steveuk]

Hi. I enjoyed reading your build. I am just starting on a Skipjack conversion to RC myself and I have noticed your rudder posts are in a different position to the kit. (seen on page 3 of your build).

Am I right? Do I need to move my rudder post positions back?

[The Boattrainman]

Hi Steve,

Nice to hear from someone on this side of the world.

You are correct, the pivot point for the rudders has been moved. I followed David's instructions in his report on the adaption of the Skipjack for his fittings. A link to the the full report is here, you can ignore whatever part does nor suit.

http://www.rcuniverse.com/forum/m_10776725/tm.htm

Happy modelling.

Rob

[The Boattrainman]

The finished lower hull, I gave the inside a spray of primer, and the whole thing got a final spray of clear matt Rustoleum varnish.




The dive planes and rudders got the same treatment, the rear dive planes were a pig to mask and paint.




To my great surprise, the prop turned out well, I boiled it in white vinegar (etch priming?), and a cheap can of gold metallic paint was used after the primer coat. It's beside the brass nameplate for comparison.




The gratings look good,but will need work for definition, I prob should have put the wire mesh on the the inside of the model, you learn as you go!!




The Boattrainman

[Greevesman]

Amazing work. Could we see some photos of the painted assembled sub?
Thanks

[The Boattrainman]

Roger that Greevesman, I'll put up a full suite of photos on completion.

Here is as far as I've got, I can't paint the upper hull as I'm still trimming the model and adding flotation inside which will be painted over.






I'm taking my time on the painting as with only two basic hull colours this needs careful thought or it'll look like a grey featureless tube, and with applying multiple coats to try get some variation plus drying time and then going back over blemishes it's a time consuming process.






The Boattrainman