Model Boat Mayhem
The Shipyard ( Dry Dock ): Builds & Questions => Navy - Military - Battleships: => Topic started by: DerekP on September 25, 2023, 10:01:33 pm
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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.
It’s a gorgeous example and has many working features, so after I’d 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 club’s 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 I’d won the battle, but it’s 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.
I’m 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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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 battery’s or current ballast lower in the model.
Any photos ?
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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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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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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 ? It’s 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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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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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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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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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
(https://www.modelboatmayhemimages.co.uk/images/2023/09/26/Avenger-4.jpg)
(https://www.modelboatmayhemimages.co.uk/images/2023/09/26/Avenger-3.jpg)
(https://www.modelboatmayhemimages.co.uk/images/2023/09/26/Avenger-1.jpg)
(https://www.modelboatmayhemimages.co.uk/images/2023/09/26/Avenger-2.jpg)
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Hi Derek,
Have you any photos of the model.
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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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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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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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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 ? It’s 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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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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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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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 didn’t seem to work.
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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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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 (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 (https://ibb.co/F7kR3fn) ps just click on the small pic an it will come up full size
chrisb
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how I fix it to the bottom and make any potential holes watertight
Blind threaded socket, two off, let into hull base.
Regards Ian
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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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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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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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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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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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%% %% %% %% two Bobs on this thread, confusing {-) {-) {-) {-)
Bob
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The superstructure on a Type 21 is usually removable in 1 piece just put it on some scales.
I have had some experience of these models having sailed 7 of them without external keels.
Bob
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Gorgeous build Frogman!
In answer to the question on dimensions, the length is 5 ½ ft and width is 19cm.
Inside the superstructure there is a motor and board, which I don’t have a clue what they are for (not the radar as that is on a separate motor) and a servo under the bridge, which again I have no idea about. These make the superstructure heavy, so I was thinking of taking them away.
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Gorgeous build Frogman!
In answer to the question on dimensions, the length is 5 ½ ft and width is 19cm.
Inside the superstructure there is a motor and board, which I don’t have a clue what they are for (not the radar as that is on a separate motor) and a servo under the bridge, which again I have no idea about. These make the superstructure heavy, so I was thinking of taking them away.
PITY Derek you cant put up pics why dont you log into IMGBB like me an post a linkpic as the site is free an i have over a 1000 pics on there an its easy to operate ? an regards them servo is it a full size servo ?
an the motor is that big an heavy ? but before you remove them make sure they are not essneishal to the model as you should be able to see what they do but pics if you can sir as love to help you if i can like the other guys
ATB
CHRISB
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Gorgeous build Frogman!
In answer to the question on dimensions, the length is 5 ½ ft and width is 19cm.
Inside the superstructure there is a motor and board, which I don’t have a clue what they are for (not the radar as that is on a separate motor) and a servo under the bridge, which again I have no idea about. These make the superstructure heavy, so I was thinking of taking them away.
Derek
Best thing for images is use the site system, easy to use and it is easier for readers as they don't have to keep opening links which is a real pain and the site is add free as well :-))
Bob
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I would agree about removing the motor and board and the servo from inside the superstructure as this may cure your problem.
Cheers
Geoff
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Yes removing the motor and servo will help but I don’t think the weight of a servo and assuming the motor is not of a 540 size will cure your problem.
If possible if you could post pics of the superstructure so we can see what and how it’s been constructed.
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I will add images of the superstructure over the weekend.[/size]Thank you
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I will add images of the superstructure over the weekend.Thank you
HI Dereck very bueatifull model an will look real good on the wet stuff when you get her to sail ok lovely just like my amazon F169
CHRISB
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Here are the shots of the superstructure
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WOW Dereck
i can see what you mean about all that top wheight an lookin at that servo it was suppoce to work 2 knock on switches but it wont as the arm of the servo will catch on the mirco switches they should have been fitted the other way around
chrisb
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Thank Derek,
As they say a picture is worth a thousand words.
I would remove the servo, motor gear box, there mounting plates and fixing and see if I would if possible lighten any of the wood parts by drilling holes.
I’d also look at doing as Chris and have done in using “D” plugs to make a breakable umbilical connection for the all the wiring in the s/s. This would allow you to have the servo, micro switch’s etc placed low in the hull.
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Is that what the plate and motor are for, a gearbox for the radar?
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I would carefully remove all the topweight I could and retry her stability.
She does look exceptionally top heavy.
Bob
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Josse[/size]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
Hi Bob,
Because the topic mentions stability issues and everyone is talking about ways to improve stability. Apparantly I missed the part about having replaced the battery already and that it improved the stability.
Greetings Josse
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Hi Jose
Think you missed my point, lot of posts about hanging lumps of metal underneath, I simply poste images of MY T21 that had no stability issues at all, built with the know issues for t21 models. Only ballast was the large 12 volt lead acid battery I never has stability issues. Post was to show you can built without lumps of lead or sailing fin keels.
Bob
Hi Bob,
Because the topic mentions stability issues and everyone is talking about ways to improve stability. Apparantly I missed the part about having replaced the battery already and that it improved the stability.
Greetings Josse
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Hi JosseThink you missed my point, lot of posts about hanging lumps of metal underneath, I simply poste images of MY T21 that had no stability issues at all, built with the know issues for t21 models. Only ballast was the large 12 volt lead acid battery I never has stability issues. Post was to show you can built without lumps of lead or sailing fin keels.Bob
Hi Bob,
I indeed missed that part, I'm sorry about that.
Greetings Josse
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HI Derek could you fit one pic at a time as it gets a bit tedious tryin to find the slide bar to move the pic over
cheers chris :-))
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an hi Derek did you get her balanced to sail ?
chrisb
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Chris, I think yes, assuming that one of your ESC's is also your BEC for your receiver.
I am surprised that you are having this issue. Your motors should not be maxing out a 320 amp ESC. Even if you run two motors off one ESC, there should be only one ESC supplying power to the receiver. Have you tried running her with just the outside motors connected to the ESCs? Do they still reverse at high throttle? If so, then I would look to the signal from the receiver.
I have run into the issue of having a motor go into reverse when the transmitter calls for full speed. I found that by reducing the servo throw setting in the transmitter( I am using FrSky with Open TX) the problem is solved with no reduction in the maximum speed of the motor. I suspect that this occurs because the digital radios are capable of outputting a servo control signal that is of greater range than the ESCs are designed for and this causes the ESC to reverse itself.I would try reducing your signal output before you re-wire your ESCs.cheers and good luckJonathan
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Jonathan, this is the Avenger thread - put your suggestion on the HMS Tiger one... you can probably copy and paste it?
Cheers,
Ray.
Edit: or ask Martin (Admin) to move it for you.
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My most humble apologies to all. My fingers had not received their morning dose of coffee. I have posted in Chris's thread.Cheersto allJonathan {:-{
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an hi Derek did you get her balanced to sail ?
chrisb
Not yet I’m afraid. Lots of other things have gotten in the way, so this might end up being a next year problem!