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Author Topic: HMS Avenger - Type 21 - 1/72 - ballast issues  (Read 3006 times)

DerekP

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HMS Avenger - Type 21 - 1/72 - ballast issues
« on: September 25, 2023, 10:01:33 pm »

I acquired an exceptionally nice working model of HMS Avenger, the Type 21 class frigate, which I believe is 1/72nd scale. The hull is wood and so is the majority of the superstructure.


Itís a gorgeous example and has many working features, so after Iíd modernised the ESC and receiver, it was pretty much ready to go. It weighs an absolute ton with all the ballast that was already in the boat when I bought it, so I went down to my clubís pond to try it out. Put it in the water with three Lipo batteries (one per esc and the third to power the lights etc) but without the superstructure and was nice and level, so took it out, put the superstructure on and lowered it into the water. This time it had a severe list to port. No problem, moved the batteries over a bit and tried again, now listing to starboard! Tried fiddling about, but could not get it balanced, so the safest thing I could do was surrender.


Today I had a go levelling it up in the big paddling pool I have to test out boats. Exactly the same problem as yesterday, all ok without the superstructure, but when I added it back on, it listed severely to port. I added a bag of ball bearing in a bag just loosely on the top starboard side, which with a lot of trial and error, got close to the right amount, so placed it inside the hull on that side. At first it looked like Iíd won the battle, but itís been windy down south today and as soon as a gust came through, I had to quickly grab the boat to stop it going over.


Iím in need of experience, as I know these type of models are prone to need ballasting right. Can I assume I need to put a lot more weight in the centre of the boat on either side of the hull to get it sat lower in the water? Personally I think it maybe too high in the water anyway, but I could do with the help of more experienced modellers please.
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T888

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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #1 on: September 26, 2023, 05:58:05 am »

Hi DerekP,

The type 21s can be a very unstable model if the builder does not kept the top as light as possible. It will require to have a lot weight added as low as possible, like a lead keel attached to the bottom of the hull.


Can you lighten any of the superstructure, fittings or move the batteryís or current ballast lower in the model.

Any photos ?
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frogman3

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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #2 on: September 26, 2023, 09:17:07 am »

HI DEREK
yes i had a type 21 IN i/64 scale hms amazon F169 AN yes very hard to get it to balance took a 8 pound lead whieght fitted on the bottom of the keel before she would sail but she did in the end  an my boaty m8 has also got his  avenger in 1/64 scale still an his also took that much wheight to get it to sail so dont give up just keep tryin but put the wheight on the outside of the keel for most balance
chrisb :-))
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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #3 on: September 26, 2023, 09:46:01 am »

Why try to load the hull with internal ballast? Warships are a pain, even with lightened topsides they tend to want to roll excessively. A rod extended ballast keel may not look pretty when on the pool side but you can't see it when it's underwater.


 Regards  Ian.
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T888

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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #4 on: September 26, 2023, 10:25:24 am »

If the builder of warship does not think about making to top side light you will always get a tender handling model. But putting an extended keel ? Itís a warship not a yacht  {-) {-)




But as you have inherited the problem then Ian option may be your only way to have a stable sailing model.
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frogman3

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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #5 on: September 26, 2023, 11:06:21 am »

WELL Dave an Ian thats what i had to do on my hms tiger as i built as light as poss but that big S/S still wheighed a fair bit so i fitted on her keel 2 half inch sqaure steel bar  just bolted on which not only gave her good balance an looked neat in my opinion an could hardly be seen but it also made the 8ft hull lenght stronger to carry her to the waters edge even with her 2 big batts in her  :-))
chrisb
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Geoff

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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #6 on: September 26, 2023, 02:01:37 pm »

what you are experiencing is a well known phenomenon and basically means the ship is unstable due to too much topweight. No matter where you put the batteries it will lean to one side of the other.


The only cure is to lighten the topsides, deepen the hull, increase the beam or increase the ballast low down. Not all of these will of course be practicable. In its current condition it means the model has an inherent lack of stability. I think its called LOLL and I read an article about it many years ago.


I would agree with the earlier suggestion a lead bar under the hull may be your best bet as this will have the most effect.


Cheers


Geoff
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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #7 on: September 26, 2023, 03:15:58 pm »

Basically what is going on is that the gravimetric center of the ship is above the center of bouyance, like demonstrated in the picture below. Since the gravity always wants to go down it will try to find a way to get past the center of bouyance causing the ship to list. To me it sounds like 2 steps would be best: both lower the weight topside and increase the ballast weight as low down as you can or indeed below the ship. Taking weight away as much as you can from the superstructure will make a difference.


Greetings Josse
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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #8 on: September 26, 2023, 04:50:52 pm »

here are my shots of /72 Avenger, she had no bolted on bits underneath, simply built with the T21 known stability issues taken into consideration, ballast was a single 12v battery and she sailed perfectly. so I think careful planning is the key, and she was built in late 80s from ply and plastic, was very happy with her.


Bob








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T888

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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #9 on: September 26, 2023, 05:00:06 pm »

Hi Derek,


Have you any photos of the model.
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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #10 on: September 26, 2023, 05:33:18 pm »

What are the radars made of because if metal they will have a disproportionate effect on stability as does any metal fitting high up, so, if they are metal replacing them with plastic or lighter fittings may solve the LOLL.


Cheers


Geoff
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Rob47

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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #11 on: September 26, 2023, 05:43:35 pm »

What are the radars made of because if metal they will have a disproportionate effect on stability as does any metal fitting high up, so, if they are metal replacing them with plastic or lighter fittings may solve the LOLL.


Cheers


Geoff
They were resin and incredibly light and that included the plastic wheels and rubber drive band to make them operational


Bob




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Colin Bishop

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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #12 on: September 26, 2023, 06:15:08 pm »

The stability issue doesn't just affect warships, it can apply to any model. Warships are however particularly vulnerable due to the mass of fittings above the upper deck. It is very easy to misjudge the amount of weight being added until the effect is seen on completing the model.

Another thing to consider is that even if the model is stable in the test tank it can still be affected by wind when on the pond and could even be blown over if there is a lot of windage in the top hamper. I have seen a lot of models affected in this way.

As already suggested, if internal ballast isn't enough then a flat steel bar attached to the bottom can definitely help as can raising the waterline. Water is fairly transparent on a pond so having the model floating a little deep is often hardly noticeable and can make a very useful improvement to stability.

Sometimes you are on a hiding to nothing though. When building my R/C conversion of Revell kit of the liner Queen Mary 2 the scale, weight of the superstructure and high windage conspired to make an external keel essential. You can't  ignore basic physics! In this case I used door handle spindles to get the weight I needed.

My recent paddle steamer needed motorcycle wheel balance weights attached to the bottom of the hull to achieve a comfortable measure of stability despite building the upperworks as light as possible.

Colin



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Rob47

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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #13 on: September 26, 2023, 06:36:25 pm »

If the builder of warship does not think about making to top side light you will always get a tender handling model. But putting an extended keel ? Itís a warship not a yacht  {-) {-)

Agree Dave  %% %% %% %%



But as you have inherited the problem then Ian option may be your only way to have a stable sailing model.
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Rob47

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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #14 on: September 26, 2023, 06:37:12 pm »

Basically what is going on is that the gravimetric center of the ship is above the center of bouyance, like demonstrated in the picture below. Since the gravity always wants to go down it will try to find a way to get past the center of bouyance causing the ship to list. To me it sounds like 2 steps would be best: both lower the weight topside and increase the ballast weight as low down as you can or indeed below the ship. Taking weight away as much as you can from the superstructure will make a difference.

no picture below except mine


Bob
Greetings Josse
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frogman3

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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #15 on: September 26, 2023, 07:42:47 pm »

DEREK fit a lead or a metal wheight on her bottom of her keel as i did this on my tiger an she sails well very stable
chrisb
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DerekP

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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #16 on: September 26, 2023, 11:00:21 pm »

Thank you all for your replies and I hear what you are all saying :-))


I need to find a lead /steel bar. Again, this is all new to me, so suggestions on how I fix it to the bottom and make any potential holes watertight, would be much appreciated.


I did try to attach a photo of this gorgeous model, but it didnít seem to work.
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derekwarner

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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #17 on: September 27, 2023, 04:25:25 am »

Derek


Sheet or stick lead will be found at Plumbers Supplies, or round shot [balls] from a Gun Club Shop


So the round lead shot is a little more expensive, however has quite a few advantages


1. Add a small number of wooden box's placed strategically around the hull, add lead and the final trimming can be 1 or 2 round shot balls at a time added to each box sub-compartment


2. After the total lead shot is achieved for each compartment, the total of shot pieces can be taken out & placed in plastic bags. however if the vessel trim is a little precarious, you may wish to fix the lead shot so that cannot move
Small wooden boxes with the height just enough to cover the mass of the shot with a flat top, these boxs can added to the hull in the location of each bag to contain the shot from moving


As an alternate to this, is casting the shot in the wooden box with an epoxy resin, but the box must be lined with Cling Wrap, so when set the squares/rectangles of cast shot are set, they can be removed from the vessel


Epoxy resin has SG of approx 1.5, or ~~ 50% heavier than water, so bear that in mind it you cast the lead shot
As a trial, add the shot to a box with the clingwrap internals, the pour water until the level of the water is just lapping over the lead shot.......tip the water into a measuring jug & you can calculate the volume and weight of the epoxy resin needed


Lead sticks can be shaved or lead sheet cut & rolled into pillow shapes to attain the correct trim


Plastic containers of water, or tins of Soup can be used as trial weights to achieve the correct draft, do the addition & find or source your chosen weight of lead & proceed to add the total ballast to the lowest sections of the hull.........for my money...the lead shot is the clear winner


Good luck......Derek


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frogman3

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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #18 on: September 27, 2023, 07:06:58 am »

HI Derek yes you have seen the ideas that you will need to do to get her stable  but so we can get an idea of the wheight you need how wide is her hull an lenght ? but for me my moneys on a steel half inch sqaure bar  just drilled out the holes only need about 4 holes an then fit them to the outside of the hull an then drill in an screw the steel bar to the outer hull an as its screwed on you can remove it till an cut it down till you find the correct wheight needed an the holes in the hull can be esayliy made water tight by makin a plasticene box up an then usein resin with talkum power in it to thicken up the resin just pour it in over where the screws come in an let the resin set an villay its water tight an you can also undo the screws an remove the steel bar an as i said cut it down till you are happy with it an i got my steel half" sqaure steel bar from B&Q
GOOD LUCK which ever way you go an a linkpic of my tiger front section showin the steel bars bolted on her keel as i had to fit two but it does not look unsightly as when the ship is upright it cant be seen
https://ibb.co/t8QZpRT
an a shot of her sailin to show how well them wheights work as she was very stable an hardley no rollin so she looks great as could your ship
https://ibb.co/F7kR3fn  ps just click on the small pic an it will come up full size

chrisb
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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #19 on: September 27, 2023, 07:22:44 am »

Quote
how I fix it to the bottom and make any potential holes watertight
Quote




 Blind threaded socket, two off, let into hull base.


  Regards  Ian
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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #20 on: September 27, 2023, 07:57:40 am »

here are my shots of /72 Avenger, she had no bolted on bits underneath, simply built with the T21 known stability issues taken into consideration, ballast was a single 12v battery and she sailed perfectly. so I think careful planning is the key, and she was built in late 80s from ply and plastic, was very happy with her.


Bob

What kind of 12V battery? May I assume it's a lead acid battery? Those are quite high and with their weight can easily have a huge negative impact on the stability. In that case you can easily solve the issue by replacing the battery by battery packs or LiPo batteries and lay these as flat as possible on the bottom. At some lead to the bottom (try the inside first) and I think you'll be fine.


With regards to replacing metal radars, this will most likely save you a few grams. Admittedly, those grams are where they matter the most but 100 grams in the superstructure will have more impact then replacing the radars. But personally I think your problem is the battery.



Greetings Josse
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Shipmate60

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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #21 on: September 27, 2023, 08:02:39 am »

Can you try her with a lower or lighter 12 volt battery or even consider 6 volts and run on buggy packs.
This might allow the internal ballast to be effectively lower and get her stable.
Could you weigh the complete superstructure in the running condition?


Bob
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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #22 on: September 27, 2023, 08:09:00 am »

What kind of 12V battery? May I assume it's a lead acid battery? Those are quite high and with their weight can easily have a huge negative impact on the stability. In that case you can easily solve the issue by replacing the battery by battery packs or LiPo batteries and lay these as flat as possible on the bottom. At some lead to the bottom (try the inside first) and I think you'll be fine.


With regards to replacing metal radars, this will most likely save you a few grams. Admittedly, those grams are where they matter the most but 100 grams in the superstructure will have more impact then replacing the radars. But personally I think your problem is the battery.



Greetings Josse


HI Josse an sorry Derek for cuttin on Josse post but ive built a type 21 frigate an i know how unstable they are an ive fitted in my tiger big SLA BATTS AN my tiger sails ok with them counter balance wheights fitted so i dont think that lipo batts will do any good to help your stabilty but just from my an my freinds an his an my exspereience its the same
chrisb
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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #23 on: September 27, 2023, 08:14:46 am »

Can you try her with a lower or lighter 12 volt battery or even consider 6 volts and run on buggy packs.
This might allow the internal ballast to be effectively lower and get her stable.
Could you weigh the complete superstructure in the running condition?


Bob


HI Bob not bein funny to you at all an all respect to you sir but just saw your post but i cannot fathom how you can wheigh the S/S when its on the water in running condition as you will have to take inertia into the eqation sorry not tryin to be a know all sir
chrisb
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Re: HMS Avenger - Type 21 - 1/72 - ballast issues
« Reply #24 on: September 27, 2023, 12:20:22 pm »

What kind of 12V battery? May I assume it's a lead acid battery? Those are quite high and with their weight can easily have a huge negative impact on the stability. In that case you can easily solve the issue by replacing the battery by battery packs or LiPo batteries and lay these as flat as possible on the bottom. At some lead to the bottom (try the inside first) and I think you'll be fine.


With regards to replacing metal radars, this will most likely save you a few grams. Admittedly, those grams are where they matter the most but 100 grams in the superstructure will have more impact then replacing the radars. But personally I think your problem is the battery.



Greetings Josse


Josse
Not sure why you are telling me to replace my battery, as it had a positive affect i.e. it kept the model stable, I had NO stability issues at all with and posted the images to show aT 21 can be built without hanging keels and lumps of lead, putting lipo in would have had a massive counter affect.  The model sailed 100%


Bob
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