Motors/prop for model warship

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Motors/prop for model warship

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29 August 2020 at 13:52 #91172
T Thurlow
Participant
@tthurlow33205
Hi, New member here.

My soon to be 9y old son has asked for a model warship for his birthday that could go in the bath/lake and be remotely controlled (having watched too much youtube on historic sea battles…). I'm not shelling out for an expensive plastic thing so having done some dabbling in modelling in my youth I've decided to use this as an opportunity to build something with him.

I've purchased plans for HMS Embling (https://www.modelboats.co.uk/news/article/hms-embling/7577) from Sarik Models (although not the wood kit). The plan is to make it free running now and upgrade it to RC later if he is still interested – is this a viable route or should I be planning it all in one go?

I was looking at this motor https://www.modelboatbits.com/MFA-280 and a 5" shaft. Would I be better with something else?

Thanks

Toby
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29 August 2020 at 13:52 #2957
T Thurlow
Participant
@tthurlow33205
29 August 2020 at 16:53 #91175
Chris E
Participant
@chrise
Welcome

Have you seen this article

HMS Embling Build
29 August 2020 at 17:27 #91176
Ray Wood 3
Participant
@raywood3
Hi Toby,

Looks like an ideal model, radio gear is so cheap these days, I'd put the steering servo in when you build the hull, fairly awkward to retro fit.

Good luck with the build 👍

Regards Ray
29 August 2020 at 20:48 #91182
T Thurlow
Participant
@tthurlow33205
Thanks Chris, It was the article which made me choose the HMS Embling – something I could follow along to. Considering my last boat (and effectively only) was a Vic Smeed plan from the book 'Model Magic' back in the late 80's I need something to guide me.

Ray – if fitting the steering servo is preferable now, what is a good option to go for?

thanks

Toby
29 August 2020 at 21:30 #91184
Ray Wood 3
Participant
@raywood3
Hi Toby,

Just a standard servo, no more than £5.00 should do the trick, some Carson radio sets I use come with a standard servo for around £40.00 for the whole thing rx & rx on 2.4mhz.

Regards Ray
30 August 2020 at 09:05 #91186
Malcolm Frary
Participant
@malcolmfrary95515
My first go at building from a plan was HMS Quickstep, probably a GG plan. A few changes were made as it was built from ply panels recovered from a dead kitchen door. It ened up a bit shorter (missed out a set of torpedo tubes) and a bit deeper (about 1/2&quot which heped stability and payload. The ply probably helped make it strong enough to minimise bank damage.

With a free running boat, you don't get to choose which bit of bank its going to slam into. You have to guess and get there first. Remote steering helps. Getting a speed control as well was a revelation.
30 August 2020 at 11:46 #91189
Charles Oates
Participant
@charlesoates31738
Hi Toby, you asked about the motor and shaft. As long as the shaft is long enough to get the propeller in the right place and at a gentle angle to get the motor to align with it, it will be fine.

As to the motor, it's an old joke on here that if you ask 5 people about the best motor for a model, you'll end up with a choice of 5.!

I noticed on the model boat bits web page, the 280 motor they sell is rated at 12 to 24 volts. The 280 designation just refers to the motor length, and many motors are made to different voltage ranges. The 280 motors I've used in the past were rated to 6 volts, which would work in the model, but not ideal as it would be running at the top of it's range. My personal choice would be a 385 motor, they're rated 6 to 15 volts, and are quite touquey so will drive a decent propeller. You'll only need to use 6 volts to make that model go well.

With that motor, a 30mm or 35 mm propeller will be fine, check for sufficient clearance at the stern. As to a coupling, you can buy a huco or similar one, but with low powered models like this, I just use a piece of neoprene tubing, such as is sold for model fuel tubing or fish tank pumps. It's cheap, forgiving in the alignment, and lasts forever. My 30 inch Corvette has had the same piece in for 20 + years and is still fine.

I hope that helps a bit.

Chas
30 August 2020 at 11:52 #91190
Chris E
Participant
@chrise
Toby

You have picked an interesting model with lots of detail to keep you occupied.

Having had a look at the article I note that the model is quite narrow at just over 3in. This is absolutely fine bit it does mean that if you build the superstructure heavy it could be very "wobbly" and even possibly unstable in the water. Add lightness and it will be just fine. I know that "beefing up" can be seen as a good idea by a new builder but in the superstructure of this model it is not. The extra cm of under water hull depth mentioned above by Malcolm seems like it might be a good idea although if Glynn posts I am sure(??) that he will say that it isn't necessary. Just make the bow 1cm deeper and extend the ramp at the stern until it is 1cm deeper. The bottom of the hull will now be 1cm deeper in the water. You will obviously need to make all the bulkheads1cm deeper than the plan. When fitting out the hull keep any weight as low as possible.

If you go with this idea I would suggest fitting a 385 motor and allowing space for a 35mm prop even if you fit a smaller one to start with. You can regulate the speed of the model by both the propeller fitted and the voltage applied to the motor.

Edited By Chris E on 30/08/2020 12:11:01
30 August 2020 at 16:01 #91196
Ray Wood 3
Participant
@raywood3
Hi All,

Having just finished Vic Smeeds Tribal class destroyer which he deepened for stability, it's not really required, it just needed 4 lbs of steel plate as ballast, and anyway destroyers lean over quite a lot when turning 😀I

Toby I guess you built Sea Rider back in the 80's a Leander class frigate, I have the plan.

Regards Ray
31 August 2020 at 11:14 #91207
Malcolm Frary
Participant
@malcolmfrary95515
The main reason that the one I mentioned earlier wound up shorter was the free wood panel size. The reason for it being that bit deeper was that in that magazine issue there were two plans. One for a retro Bowman look-alike launch, the other the Quickstep.

I started on the launch and decided that I would rapidly get bored with it. A bit of pencil work, a few bits missed off and there was a slightly shorter, wider and deeper "frigate". It got called "Troutbridge". Despite the lack of any actual prototype, it didn't stop the occasional passer by claiming to have served on one, or something very similar. At least, until they got a close view. They were all polite enough to not mention the missing rack of torpedo tubes.

A boat this size will work well with a 385 on around 3/4 the volts it says on its label. A much smaller 280 will be working far too hard. A longer shaft lets you position the inboard end higher, hopefully above the water line, while keeping the angle shallow.
1 September 2020 at 09:02 #91212
ashley needham
Participant
@ashleyneedham69188
Yes, my vote for a 385 as well. Smashing little motor. I have no qualms about using a 40mm prop and 9.6 V on them. Was not aware that the 280 came in 12-24v ….I may get one for the Sans-P which has an unsuitable speed 280 in it!

I almost always add extra depth to anything of a (roughly) scale nature that I am building, as it makes the boat sit much better in the water. A pet hate is “bobbing”….no battleship or liner bobs….they need a bit of weight which you can add with a deeper hull.

I know that it may not be an option for Toby, but my TBD and a couple of other narrow craft have a ballast strip glued lengthways underneath the hull and this works wonders for the stability, as do adding fixed bilge keels.

Ashley

Edited By ashley needham on 01/09/2020 09:04:14
1 September 2020 at 09:27 #91214
T Thurlow
Participant
@tthurlow33205
Chris, Charles, Malcolm, thanks for the motor correction to a 385. I did wonder what the numbers mean, length is not what I guessed. The plans show a 180mm length of motor (as I think that is what the author used), but the article says 280/380 should be fine. So 385 it is.

On the plans the prop shaft is 5" and the propeller (assuming we are measuring diameter) is 25mm. This size prop doesn't seem to be regularly available (although that could be my completel lack of knowledge of model boat hardware), but I should be easily able to find the extra 2.5mm in radius to put in a 30mm. I'm debating whether to go for a 6" shaft which would flatten the angle out. Currently the motor mount is about 25% of the way in from the stern, but I assume it's all a matter of sorting th ballast out.

Ray – the boat I built was called the Ulsterman, an oil-rig tender style, and came as free plans in his book 'Model Magic'. I have the original book in front of me now, and it tells me that it supported the Channel 4 TV series, which I never saw. I was about 13 or 14 when I built it and I remember getting bored trying to get the balsa strips to bend round the hull and I ended up using some card to finish; which ended up never being totally waterproof even after sealing…
1 September 2020 at 09:47 #91215
Colin Bishop
Moderator
@colinbishop34627
These 385s from Component Shop are excellent..

**LINK**

Colin
1 September 2020 at 10:25 #91219
Charles Oates
Participant
@charlesoates31738
Hi again Toby, if the 6 inch gives you a flatter angle without any problems, go for it.

I wouldn't recommend a 25 mm prop for this, try and arrange things so you can use at least a 30 mm, and space for a 35 if you can do it without major alteration. Three blade props will suit the model and motor better than 2 blade and plastic ones are very cheap and strong enough.

We all forgot an often given warning, don't get a 380 motor thinking it will be similar. It looks the same but is utterly different and very unsuitable.

I too enjoyed the model magic programs back in the day, they used to be on YouTube, I'll have to have a look and see if they're still there, a bit of nostalgia to do me good.

Enjoy your build, chas.
1 September 2020 at 11:04 #91220
T Thurlow
Participant
@tthurlow33205
Thanks all,

Charles, reference your comment about 385 not being the same as 380. I've seen two motors with very similar characteristics (and price) that I can see, the 360 and 385.

360 – https://www.cornwallmodelboats.co.uk/acatalog/mfa-re360.html#SID=2304

385 – https://www.cornwallmodelboats.co.uk/acatalog/mfa-re385.html#SID=2304

Aside from being about £1 more expensive, and having a slightly faster 12v RPM, the 385 is 5 pole vs the 3 pole on the 360. I assume that in general the higher number of poles the better. I'm going to go with a 385 because everyone is pointing me this way, but for future knowledge is there a reason why I would choose the 360 over the 385 (other than I needed a smaller size and weight).
1 September 2020 at 11:22 #91221
Charles Oates
Participant
@charlesoates31738
You've pretty much got it, the 5 pole motor has more torque than the 3 pole motor. It will run more smoothly especially at low revs. That's very useful with scale models if you decide to put radio control in it.

Chas.
1 September 2020 at 16:43 #91224
Chris E
Participant
@chrise
Firstly the motor to avoid for this application is the 380. With 7.2v the spec says maximum efficiency is 19000rpm which isn't what you need at all – far too fast meaning a very small propeller which might work with a small planing hull but definitely not your model.

Unsuitable 380 Motor

The 360 and the 385 are much more similar. The 360 numbers are 12v 8320rpm whilst the 385 is 12v and 9280rpm. The 385 thus gives slightly higher rpm but is a bigger heavier and more powerful motor to support that. The only real reason to choose a 360 would be that the 360 weighs 51gms compared to the 385 at 66gms. If that matters then choose the 360 but the extra 15gms doesn't matter to you & the 385 is really the standard motor for models of this type. There is a lot of experience here with the 385 but the 360?????.

A final word of warning. Don't assume that all motors of a given description (eg 385) are the same. It is worth going onto ebay and entering "385 motor" as a search. The wildly different specs of motor that you will be offered, all 385's, are frightening.

Compare this to the precision of description that you get with brushless.

Edited By Chris E on 01/09/2020 17:07:35
1 September 2020 at 21:47 #91234
Malcolm Frary
Participant
@malcolmfrary95515
The much quoted rule of thumb for sussing out a combination of motor and prop is "motor can no less than prop diameter, prop should have fewer blades than the motor has poles." Not scientific, but it works. Having the precise definition of a brushless motor is great if what is actually wanted, or needed, is known.

A very common question that crops up is "Why is my motor too hot to touch after only a few minutes?" The answer is always "There is too much prop". If going for a 360, go for a smaller prop with fewer blades. A 385 with a 30mm 3 blade prop works well and will not melt the solder off the terminals (yes, seen it done)

Most of the 385s that turn up in model shops say 6-15 volts on the label, running one on half to 3/4 the max gives the right performance for a surprising range of models.
1 September 2020 at 22:02 #91235
ashley needham
Participant
@ashleyneedham69188
A 360 is a weedy motor and nothing like a 385 at all despite the possibly similar looking specs. If 15gm makes a difference I would say you are in big trouble!

Can’t go wrong with a 385.

Ashley
2 September 2020 at 10:33 #91242
Chris E
Participant
@chrise
I thought that you might like to see how you model would look with the 385 (standard MFA type) and a P35 two blade prop on 7.2v that I recommended.

IJN Kirisame is by the same designer and about the same size / construction as your HMS Embling model.

Click on the photos below to get the full size image.

IJN Kirisame

Edited By Chris E on 02/09/2020 10:37:28
1 October 2020 at 21:45 #91692
Dave Cooper 6
Participant
@davecooper6
A few random thoughts :

I once saw a boxed set of "Model World" for sale on an internet auction site. Price was on the high side, but, I'm kicking myself now.

Hmm, 3" beam sounds narrow(ish). I suppose if the CG is low enough it should be all right.

I have a 385 in a fast, planing hull with a 30mm /3 blade prop. It doesn't seem to get hot at all – I expect this is breaking all the 'rules' though.

Nice choice of subject. I think I can visualise a rotating scanner and (randomly) moving turrets. Arduino maybe ?

Dave

(ps I did say they were random !)
1 October 2020 at 22:01 #91693
Ray Wood 3
Participant
@raywood3
Hi Dave,

Those magic mushrooms are really working 😀

Regards Ray
3 October 2020 at 10:06 #91717
ashley needham
Participant
@ashleyneedham69188
A warship with a 3 inch beam that long….dodgy…tender, not good in bad weather or any sort of wind. Becomes a fair weather sailer.

I know it’s not scale, but sticking a strip of steel under several of my long thin boats works a treat and allows operation in almost any weather. I depends if you sail all year, as we do in the wilds of Bushy park.

As below (minus crew at the time) (and not shown in rough weather)(powered by a speed 480…boy does it go!)

Ashley

hooligan
14 March 2021 at 23:22 #94251
T Thurlow
Participant
@tthurlow33205
Hello all,

A few(!) months on, and as expected the work is going slow. However, the basic hull is now shaped.

I've now also cut and fitted the removable rear deck. I still have to add the transom and shape the hull properly but this shouldn't be too much work. The rear of the bottom hull is still loose, I decided that it would make it easier to fit the running gear to keep it free for the moment.

This leads on to a couple fo questions. I was going to make this a free runner, but my son is keen on fitting remote control, and I'm assuming it will be easier to do now rather than retrofit later. On the principle of keeping it cheap will something like this do?

https://www.ebay.co.uk/itm/2-4GHz-3-Channel-3CH-Radio-Remote-Control-RC-Car-Boat-Transmitter-Receiver-UK/383864211142?hash=item59601706c6:g:Q3gAAOSw6K1f3F3m

I assume I would need to add an ESC and a battery unit. I already have a servo.

And the second question relates to finishing. The instructions I am following suggest thin glossy card of the type used in birthday cards and brochure holders, to line the upper deck and two part epoxy coating resin of the type used for sealing wooden surfaces on model aircraft to seal the rest of the hull. Any suggestions for alternatives, or should I just stick with these?
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