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[Jimbob]

Hi I am a newbie just joined and I wondered if anyone can help me.
I am trying to help my brother in law finish and launch his model boat.
Its the HMS Invincible 2.2m long by 380mm wide.
We need to install lead weight as ballast in the hull but is there a way that this can be calculated and installed prior to sailing along
with the weight of the 12v 20A lead acid battery? as it is difficult to transport from home to the nearest lake or similar to try out.
From the waterline to the bottom of the hull is 140mm.


The other issue is with the radio control. Installed is a 12v 20A lead acid battery feeding 2 x12v 4A hectoperm motors and a 14A speed controller.
We have sorted out the 2 brass props and have them the right way round and we have them rotating correctly. However we need to reverse the direction of the
radio as up stick is reverse and down stick is forward.
Also is the speed controller safe to operate at 14A or could it have to draw a much higher current?
Many Thanks.

[HMS Invisible]

Hi I am a newbie just joined and I wondered if anyone can help me.
I am trying to help my brother in law finish and launch his model boat.
Its the HMS Invincible 2.2m long by 380mm wide.
We need to install lead weight as ballast in the hull but is there a way that this can be calculated and installed prior to sailing along
with the weight of the 12v 20A lead acid battery? as it is difficult to transport from home to the nearest lake or similar to try out.
From the waterline to the bottom of the hull is 140mm.

From volume of water being displaced at 1kg per litre.

The other issue is with the radio control. Installed is a 12v 20A lead acid battery feeding 2 x12v 4A hectoperm motors and a 14A speed controller.
We have sorted out the 2 brass props and have them the right way round and we have them rotating correctly. However we need to reverse the direction of the
radio as up stick is reverse and down stick is forward.

You need to say what radio it is but there shouldn't be a problem, unless it is a 1970s Futaba M series or similar.

Also is the speed controller safe to operate at 14A or could it have to draw a much higher current?
Many Thanks.

Again, you need to say what you have. 14A rings a bell as something really old. You'll generally find on the higher voltages that the power dissipation by a battery elimination component (BEC) to feed power to receiver and servos, is higher than from the motor drive components.
In short, hectoperms will be ok from a current rating perspective but what do you have and what powers the receiver?

[tonyH]

Hi Jimbob,

Which Invincible?

You can calculate the displacement from that of the actual vessel.
If you multiply the actual displacement by the cube of the scale, for example if the scale is 1:96 and the actual displacement is 20,000 tons, then the target weight would be (20,000 x2240) divided by (96x96x96) which comes in at about 50lbs.

This doesn't tell you where the weight should be of course.

Good Luck

[deadbeat]

When the TV show Supermodels made a 1/48 model of Fearless it too was too heavy to transport with ballast installed. To resolve this the ballast they used was bags of shingle from a DIY store, which easily took to the hull shape on loading. They ballasted the model whilst in the water so the hull had support so it wouldn't break. Just a thought, a fully ballasted model of that size may have strength issues in the hull whilst in transit. Even if you stuck to lead think about ballasting in the water at the pond side.

[warspite]

Also Transporting that much ballast is as difficult as the boat itself, some actually ballast with the medium its about to float in i.e. the pond / river water, its still weighs 1 kg for every I litre, so having a way of pumping in and more importantly out the ballast you use, remember if this is employed to always have the tanks baffled (plates inside that have holes that restrict the water from shifting).

[Geoff]

With a large model 78" long I used 8ft long x 6" melamine planks to build a test tank (just the sides). I used a large plastic sheet to make the whole thing watertight so I could carry out flotation and ballasting tests at home. If the lawn is flat you can use stakes to keep the sides in place if not I used external angle frames linked across the bottom to keep it all stable.


It worked very well and cost very little.


Cheers


Geoff

[chas]

Re reversing the motors direction. The transmitter might have a switch to change servo ( or ESC) direction, if not, just change round the confections to each motor. Obviously, don't swap the battery to ESC leads over.
 I strongly agree with comments about ballasting at the pond, the problems to the structure and your back can be nasty.
 I once did it by lining each area to be ballasted with cling film, and casing some concrete block to fit the hull area. When it set the cling film allowed it to be lifted out. I had set a handle into each block to make life easier. Don't make the block get too high in the hull or the model won't be stable. Thanks to Vic Smeed who told me about this some 40 years ago.

[Jimbob]

Thank you for all your replies.
HMS Invincible is the Aircraft Carrier. Its a Sirmar kit 1:96 scale 20,000 tons displacement purchased from Greenwich Maritime Models.
The Radio is a Futaba M series 27 2 servos powered by 4.8 v batteries and MFA 14amp speed controller. 2 Hectoperm 4amp motors powered by
12 volt 20amp lead acid mobility scooter battery.
Regarding the ballast calculated at approx. 25kg could we use 2.5 kg bags of sand or pebbles as used in small fish tanks.

[carlmt]

For ballasting, if you didn't want to go the route of pumping water in and out, I would choose the lead block method.
Cut Code 4 lead flashing sheet into 3 inch squares (a hobby guillotine is ideal for this), stack them into a block sufficient to weigh 1 or 2 kilos each, compress them in a vice between two sheets of ply to flatten them completely and then bind them together with electrical tape.
These can then be lifted in and out of the model at the pondside easily.  You could even leave a few blocks in the hull permanently, but not all of them.
Size for size, lead is smaller than bags of sand and gravel for the same weight due to the density of the material - think of all that air surrounding the aggregate in the bag that you are dropping into your hull.  The lead will take up far less space - both in the hull and in your car to the pond!!!
C
 
PS - this is what I do with my 8' long model of the SD14 cargo vessel - and she is primarily made of liteply and cardboard.

[HMS Invisible]

... However we need to reverse the direction of the radio as up stick is reverse and down stick is forward.

As it is the Futaba M series so you'll have to rewire the "motor confection".

Also is the speed controller safe to operate at 14A or could it have to draw a much higher current?
Many Thanks.

I knew it was the old MFA one. Modern processor based escs can iron out 27am radio glitches to the performance of pcm radio but this old one can't
It needs ventilation as the power transistor and heat sink gets warm. The 2-pole relay is made of thermoplastic and shrinks causing a direct short if it gets overheated. Both rotary trims need readjustment on change to a 2.4GHz radio.

[malcolmfrary]

The other issue is with the radio control. Installed is a 12v 20A lead acid battery feeding 2 x12v 4A hectoperm motors and a 14A speed controller.
We have sorted out the 2 brass props and have them the right way round and we have them rotating correctly. However we need to reverse the direction of the
radio as up stick is reverse and down stick is forward.
Also is the speed controller safe to operate at 14A or could it have to draw a much higher current?

The motors will take what they take.  As long as it is significantly less than the ESC can handle, things will be fine.  The current rating of the ESC is what it is capable of supplying before something goes "phutt", not what it supplies under all conditions.  The more important question is if it can handle the voltage being used.
If the ESC has a relay for reversing, it should ONLY operate to reverse since it can take a surprising amount of current.  Simplest way to do this is to look and check when it operates and use the servo reverse switch on the transmitter to get it the right way round, then rearrange the motor wiring to suit if needed.  Futaba transmitters used the opposite logic to everybody else, because they could and it made them a bit different, good quality or not.  Their "center/neutral" signal was also shorter than normal.  You couldn't tell once set up, but if you changed transmitter................

[HMS Invisible]

The relay coil runs off the main battery in this old speed control. The wasted power is minimal compared to the transistor loss.

[malcolmfrary]

Fair enough, but it still gets converted to heat, and low voltage relays are rarely intended for permanent operation.  Things should still be set up so that the relay only operates to reverse.
Perhaps this model is big and valuable enough to justify a couple of modern ESCs as well as an up to date radio?

[Geoff]

A couple of thoughts for you:

1) Ballast. Concrete is an excellent substitute if you don't have lead. It can be cast in blocks or directly into the hull. If the hull is lined with foil of clingfilm it won't stick to the hull so can be removed. Also you can cast an eyelet into the concrete to pick it up. Once dry it can be varnished to prevent powdering.

2) I always put a decent sized fuse between the battery and the speed controller, a little less that the rating of the speed controller to protect it. I then have separate fuses for each motor at about 50% of the speed controller fuse. This firstly protects the speed controller and secondly protects each engine. If an engine catches weed the current consumption can leap significantly and blow the main fuse thus leaving you stranded. With this system you only loose one engine. I have this arrangement with all my large models and it works well in practice.

Cheers

Geoff

[carlmt]

Be careful about pouring concrete direct into a plastic or fibreglass hull - the mix heats up as it cures.  Not enough to cause a fire but certainly enough to distort the hull.  Better to cast it in blocks outside of the hull.