TEV Wahine by Richard Dunn - Radio - scale 1:35 - 1965

[mtaylor]

Richard, 

 

You might consider asking about ballast tank "design" here:: https://modelshipworld.com/forum/13-discussions-for-ships-plans-and-project-research-general-research-on-specific-vessels-and-ship-types/

 

Nor everyone reads all or even most logs but a lot of those with tech knowledge on ships read the Shop Notes, Research area.

[lmagna]

You might consider just adding a flat "top" or internal lid to the tanks that travels up and down with the level of the water while resting on the surface. This would prevent the water from sloshing around and the constant shifting of ballast as the ship rolls and pitches. Once you know the level of water needed for proper ballast then you can lock the lids in place and vent any excess through vents over the side to show that they are full. These same vents can be used to allow air back into the tanks when pumping dry for transport.

[Kuparu]

In response to Imagna's suggestion I would wish to avoid contentious arguments in this forum but I must express doubts about his concept while fully agreeing that the tanks must have air vents capable of permitting air flow eqivalent to the rate the water is pumped in or out.  I must cast doubts on the idea of a floating tank top however, unless Imagna has proven the concept in practice, since it cannot restrict the free surface if it is floating.  A tank without baffles can only prevent free surface problems if pressed full or in such a state where "pocketing" occurs.  

Once you know the total displacement of your complete model you can work out the amount of ballast required to bring her down to her marks, and thus the volume of your tanks.  Calculating the required contents for each tank to get the trim right will be "fun".  Good luck, Kuparu.

[mtaylor]

Given that once the fully loaded weight is known and then testing for the amount of balllast needed, could a solid material be used instead of liquid?  Or does this really need to be dynamic?   I'm thinking something bricks or scrap steel blocks that can be removed .

[Roger Pellett]

You can either add ballast or reduce displacement.  The effect is the same.  Submarines use both techniques.  They have “hard” tanks inside the hull designed to withstand full sea pressure.  These tanks are used to maintain diving trim; neutral or slightly negative buoyancy, by pumping water in and out. 

 

To dive and surface “soft” tanks located outside of the pressure hull are used.  These have holes in the bottom and vents on top.  To dive, the vent is opened and water flows in through the bottom hole.  The submarine loses buoyancy equal to the volume of the tank x the density of the water.  To surface, the vent is closed and the water is blown from the tank with compressed air.  You could use a similar system but with wing tanks located inside of your hull.

 

Free surface effect in partially filled tanks can be minimized by one or more vertical baffles within the tank.

 

Another idea would be to add a double bottom with vertical baffles within the hull. This would add ballast down low.

 

Roger

 

 

[lmagna]

All of the above methods are viable and have been used. I have used several of them including the moveable lid ballast tank I described above. When the "free floating" lid is is dropped to the level of the water and locked then the "tank" becomes a solid weight were the medium no longer moves thus becoming a solid weight. My method of locking the floating lid was to use two threaded rods that lay across the top of the lid and when it was resting on top of the correct amount of water, run the end out so that it locked the lid and prevented sloshing about and go ahead for the day. As the weight of water is a well known factor and the cubic inches of the ballast tanks can be deduced then it is easy to tell just how much weight would be needed for a given depth. I prefer to just stay with using water as it does not normally have to be transported to the running area and back. I have used this method in two barges that I used along with my RC tugs years ago. That way I could adjust the weight of the barge to suit the power of the tug I was using and not make it so light that it was too easy to be a challenge. No additional baffles were needed as the tank tops themselves were adjustable. I have also seen submarine style ballast tanks used and of course solid weights they all have their pros and cons as well as limitations depending on the size of the model.  

 

Richard is not building a barge and may never have the desire or need for variable displacement in which case it is also relatively easy to figure out the needed weight with mathematical formulas and build to suit.  I was just offering one possible solution. YMMV

Edited May 22, 2022 by lmagna

[Veszett Roka]

Forgive me, i'm a newbie in RC scene. Ok then, why liquid ballast for a surface ship model? I do understand that liquid ballast needed in real life because it is everywhere around, needs to adjust to current load, weather, sea bottom and million things. But in model ship life those aren't factor, do they are?

Maybe to reduce dead weight of model during transportation, its easier to simply fill or empty a tank than transport a couple of brick among with the ship.

If so, the air vents could be simple: fill the tank and when its full just close the opening with a cork. Since it is full, no free surface effect.

Also, triangular tanks could help, more filling means more weight and less free surface. We are pleased with huge space inside the hull, we can adjust the tanks freely.

[Veszett Roka]

Nah, during i typed my note, Imagna just answered all the questions above

[Roger Pellett]

The reduced displacement idea has been studied for full sized ships as a means of reducing the spread of invasive species from ballast water.  With free exchange of water from the outside to inside the tanks, contaminated ballast water is not hauled from one port to be discharged at another.

 

Roger

[Richard Dunn]

Thanks guys.

Too many quotes so will just answer in text, the disp weights were posted a while ago but this has both static ballast in lead as well as water, why? because it reduces the amount of stuff I have to carry to the lake. that's it pure and simple.
I  have no problem with baffles, I  will probably just have 3 vertical longitudinal bulkheads with elongated holes cut in them, with the middle ones holes offset from sides so there is no direct line. glassed into the tank.
Ballasting will not be a huge issue, I have a tank to test in in back yard.

Well I have started the long process of gluing plates onto the model.
I struggled to find a way of holding the side plates on the hull until today I discovered these massive rubber bands,

The plates with windows are just taped in position for now with only one plate here being glued with epoxy, once done 2-3 can be done off it.
The windowed plates here cannot be glued yet because the strake above it is a rivetted joint and behind the plates, there as a slot where the plates go down behind the plates in grey so they have to be glued first and of course the glass added before that.
the recess can be seen at the extreme left of image next to grey plate.

Superstructure plates glued on, the slots above it are to receive the deck above the promenade, also the vertical slots in the plates are to receive the deck beams for the deck.
Below they can be seen in red, also the framing for the promenade can be seen and is ready to cut.
note the very subtle distortion sanded into the primer, I think you can just make it out, the hull also has this to.

A shot of the bow before final shaping.

 

 

 

Edited May 23, 2022 by Richard Dunn

[yvesvidal]

Impressive. You are getting there. It will be interesting to see that beast in your test tank in your backyard.

 

Yves

[KeithAug]

As impressive as ever.

[Richard Dunn]

On 5/25/2022 at 6:33 PM, KeithAug said:

As impressive as ever.

Thanks Keith, I hope my fittings and details are as good as yours.

I finally can show the effect of the plating and seams....well sort of. It's a long job, made longer by the fact that the pressure switch on my compressor has  died so have to wait a week before I can spray again.

 

Hull plates, some glued, others temporarily taped.

Weld seam, this will get widened when softened and rolled into groove.

Deck panel glued down forming waterway, the 1mm thickness replicates the 1 1/2 Semprene deck. the mast base can be seen as well as the various vent holes.

The 2mm holes in the waterways are the scupper positions.

Plates on the Fan Room roof being glued, these have not been sanded for distortion yet..

Edited May 29, 2022 by Richard Dunn

[KeithAug]

The plating is very impressive - did you say earlier that you had checked that water would not get behind it and delaminate it?

[Richard Dunn]

1 hour ago, KeithAug said:

The plating is very impressive - did you say earlier that you had checked that water would not get behind it and delaminate it?

No I had not, but it can't happen, the plates are glued on with a liberal layer of marine grade (5 min) epoxy, and prior to that the plates are soaked in Everdure which impregnates the wood plasticising it.
Aside from that only topsides are plated.

The effect will be over whole hull but bottom sides will be totally done in he sealer.

Once I have a section complete I will airbrush prime the plates one more time to check for sanding scratches and blemishes, and remedy all that before sanding with 320 and doing the weld beads

Edited May 29, 2022 by Richard Dunn

[Richard Dunn]

More plates to prime and fit, showing the slots to locate the framing and bulwark stays for the structure.

[Richard Dunn]

Getting the lower hull ready to laminate with glass.
Seachests and bilge keel fitted.

Hull finished and sanded ready for glass.
Bilge keel is recessed 8mm into hull into a slot cut with saw attachment on Dremel and run along a batten screwed to hull.
Grain run across width of Bilge Keel to keep it strong, it will also get 25 gram cloth glassed onto it.

The most fussy thing here is getting the razor shape edge along the top where it flares out I don't want what should be a sharp edge to be at all round so feathered it out with scrapers etc.

Full Size Shell Expansion to plot everything on shell, openings, discharges and weld beads.

 

Edited June 9, 2022 by Richard Dunn

[ccoyle]

Man, your 'model' is as big as my canoe I finished last year!

[KeithAug]

You could put a seat in it - just like they do at Peasholm Park in Scarborough. I think that was where I was introduced to ship modelling over 60 years ago. I bet someone knows what I am on about!!!!

[Richard Dunn]

Next up is to do the bilge keel on the other side.
I then have to laminate the frame for the bow rudder and have the arduous task of fitting and setting up the whole bow rudder arrangement.
The lateral thrusters fore and aft have been fitted and are ready to be installed and I also have to make the rudder horns and rudders.
The shaft bossing's will be made  after I have built the engine mounts and glassed them into hull so I have the exact shaft centre inboard and a jig at rudders to keep the outboard centres, the A brackets carry very little load with my new design  as the shaft which is nothing more than a 16mm dia 800mm long outer brass shaft with bronze bushes each end with the 8mm SS shaft carried through middle running from motor compartment all the way to the aft end of the A bracket.
The A bracket just keeps it from vibrating but no longer needs to have bearings in it as it was last time.
Then a large number of false discharges and intakes to do, about 160 2mm ones for various things like scuppers and valves and some larger ones that are 11mm for boiler intakes etc on ships side. once all this is done i can  glue the topsides on and paint the lower hull in VHT red oxide.

Question
When making twin dagger type rudders does it matter if they are solid or should I make them from a frame and cover in 1mm ply?
They are about 90mm deep and 55mm wide.
Just not sure if light weight is an advantage with rudders given the servo etc. of course I could just make them from glassed balsa

Edited June 9, 2022 by Richard Dunn

[Richard Dunn]

I have done some think this morning and am considering dropping the water ballast in favour for lead. I need to stiffen the ship up and need to lower the CG and I can only do this with lead as it is 11 times heavier than water for the same volume.
yes its $500 of lead but is the stability of the model worth it....YES
 

[Veszett Roka]

5 hours ago, Richard Dunn said:

I have done some think this morning and am considering dropping the water ballast in favour for lead. I need to stiffen the ship up and need to lower the CG and I can only do this with lead as it is 11 times heavier than water for the same volume.
yes its $500 of lead but is the stability of the model worth it....YES
 

Richard,

 

here in my local shipmodeling club the RC guys use very thick copper rods as ballast: they stating that it is much cheaper than lead and easily available anywhere in the metal parts shop.

[Richard Dunn]

Lead is $2100 per ton here and copper just over $9000

Edited June 10, 2022 by Richard Dunn

[KeithAug]

1 hour ago, Richard Dunn said:

Lead is $2100 per ton here and copper just over $9000

Eye watering - I think I would be considering dry sand sealed in heavy duty plastic bags - but then again I'm a bit of a Scrooge.

 

 

[Veszett Roka]

You will install 250kg lead in the model? Thats the 500$... so wow.

I believe the difference comes because the amount of metal. They are sporting with much smaller boats, mostly around 150 cm - 1:100 scale. don't know exactly how many kilograms they need for ballast. Plus they need to pay for environmental tax too for lead.

 

[Richard Dunn]

I only need 90kgs of lead but some of that is casting cost, I am happy with price no need to be a scrooge about it.

[lmagna]

90kgs? That is almost like carrying an extra body to the lake and back! My back aches just thinking about it!

[mtaylor]

4 hours ago, lmagna said:

90kgs? That is almost like carrying an extra body to the lake and back! My back aches just thinking about it!

But with a body you only need to carry it one way.    I suggest some sort of wheeled dolly or cart and with tires to match the terrain.  Might even need a small crane attached to the cart.

[Richard Dunn]

The plan is to leave it at the clubhouse.

It's only 18 bars

Edited June 10, 2022 by Richard Dunn

[Mercator]

What about the weight used by divers, I was able to find them cheap at garage sale. But that is in the US and at a landlocked State where most people had no clue what they were used for.