Nomad

[Ian Dowlman 1Participant @iandowlman1]

Help!

I have built a couple of boats in the last 2 years and am currently building a third which is the Glynn Guest Japanese destroyer from MB plans last year.

All nice and easy so far, but I am attracted to the Nomad tramp steamer in this months MB and would like to extend it a bit, about 150 mm in length, which I have now drawn out.

I was thinking of using a geared electric motor, Maplin or similar, driving a 50 mm 3 blade prop, and there seems to be a suitable 50.1 ratio motor giving about 360 rpm at 12v, at £25 or so for which I can use a nice heavy battery to help with ballasting. While there will be no torque problems (I think the motor is a 540 can) is the prop actually going fast enough to create a reasonable scale speed of about 750 mm/sec which Glynn suggests.

Being inexperienced in the boat building art, please advise if I am on the right track, or is there a better way.

All help gratefully received

Ian

[Ian Dowlman 1Participant @iandowlman1]

Powering the boat

[Charles OatesParticipant @charlesoates31738]

50/1 is too great a reduction. I would suggest about 2.5/1 to get the revs and torque you need for a 50 mm prop on that model. Have a look at the MFA (model flight accessories) for some options. You need less power than you might expect in models of this type, many 540 series motors will be too powerful, the range of those is confusing to a newcomer. A geared 380 should be fine.

[Dave MilbournParticipant @davemilbourn48782]

Ian

Factors of ten.

I have to assume that your 150mm is a typo and that you mean 1500mm.

360RPM will barely move the model, if at all; 3600RPM would be closer to what you require. A 2.5:1 geared MFA Torpedo 500 running on a 12v lead-acid battery would give a top speed (no load) of 5890RPM, so you could sail happily at about half-throttle and have some left in reserve. **LINK**

Dave M

(Posted while Chas's reply was still in transit!)

 

Edited By Dave Milbourn on 30/05/2017 23:27:54

[Charles OatesParticipant @charlesoates31738]

Hi Dave and Ian, I read that as an extra 150 mm in length, but I'm not really sure. Dave's point about having a reserve is important, the throttle is there to be used.

[Dave MilbournParticipant @davemilbourn48782]

I read that as an extra 150 mm in length, but I'm not really sure.

You might be right. Perhaps Ian could clarify the matter. I have used those geared MFA motors and they are efficient but horribly noisy! I much prefer something 'softer' using direct drive e.g. the Mabuchi 555 or the 385/540LN type of MFA motors.

DM

[Ian Dowlman 1Participant @iandowlman1]

Hi guys.
Thanks for the useful comments. I have no experience in sizing motors which is why I went to the forum. The boat will end up about 1000 mm long (150 mm extension) and I think 4.5 to 5 kgs all up weight. Because of the tramp steamer nature of the boat it will not be required to move very fast as stated. I’ll have a look at the website as suggested.
Cheers
Ian

[Malcolm FraryParticipant @malcolmfrary95515]

A lot of beginners think that because the real boat had a prop that turned at a given rpm, so should the model. This results in a decorated drifting log.

For a truer figure, take the square root of the scale and multiply the assumed figure by that. Then add a bit for luck. Having extra performance on tap is a handy "get out of jail free" card when it is needed.

A 12-15 volt 385 run on a lower voltage with direct drive does a perfectly good job of producing the required power and speed quietly, and you can get bigger, heavier 6 volt batteries if the weight is really wanted. Or more than one if you feel the need to distribute the weight better.

[Ian Dowlman 1Participant @iandowlman1]

Hi Malcolm,
I already have 7.2v batteries and lots of lead so reading your reply no gearbox is needed provided I Am economical with the throttle control.
Have I got that right?
Sorry to pedantic, but this a learning curve for me.
Cheers
Ian

[Charles OatesParticipant @charlesoates31738]

I can't say that I would be happy running a 385 direct to a 50 mm prop. I have a pair in one of my models and they are just right on 3 blade 35 mm brass props. If you want direct drive on 7.2 volts, You could use a 540ln as Dave suggests. Performance will be adequate, they are torquey slow reving motors.If later you decide you need more speed, an increase in voltage is easy.

The geared motors are a bit noisy, whether this is acceptable depends on the model and your perception of what is ok. I know of one running in a Thames tug, the noise is well baffled by the superstructure and the bit that escapes is in keeping with the model….,… to my ears.

Lastly, don't forget the coupling, I don't like the popular huco style ones, rubber type ones as championed on this forum are quieter.

Keep asking questions Ian, it's the only way to find out.

[Glynn GuestParticipant @glynnguest59245]

Mr Dowlman,

You are indeed a brave man to not only contemplate building a model from a free plan and altering it but also not apparently reading the construction article that came with it. Still, I'm not sure if the people who offer advice without reading the article first are even braver?

The motor used in this model and found to perfectly adequate was a RE 540 LN obtained from MFA. This was described on page 18 of the magazine along with basic data of free running speed and current, stall current and the actual current drawn when directly driving the 50 mm diameter (with a pitch ratio of 0.85) propeller. Suitable alternative motors such as the RE 360/385 were discussed.

I think you will find that even with your planned extension to the hull, little (if any?) extra power would be needed on this model.

I do applaud your willingness to alter a design to suit your personal tastes or situation. Far too many people refuse to do this, probably from the fear of failure or lack of imagination? If you don't experiment, you don't learn anything and sadly too many people seem to prefer "alternative facts" these days. For them, the Internet has been a godsend.

Good luck with the model

Glynn Guest

[Ian Dowlman 1Participant @iandowlman1]

Thanks for the reply Charles, this clarifies it a bit better. Where do you source the rubber couplings. I've only used Huco in the past.

Also thanks for your comments Glynn. Being and aeromodeller in my youth I built among other things some of the Ray Malmstrom planes, and your straightforward approach to boat construction appeals to me in the same way, now that my aeroplane chasing days have passed. I believe in simplicity, and I have read the article but was trying to grasp what the changes I am making would have and explore possibilities in my inexperienced effort to get things right if I can.

My first effort was from your excellent small book introducing boat building and radio control, and I have to admit that you would probably recognise the hull but the superstructure kind of went its own way. It sails well though and creates interest from passers by on the canal where I sail it.

Thank you all for your encouragemant and advice. I'll submit photos when complete.

Ian

[Ian Dowlman 1Participant @iandowlman1]

Hello everybody

Ref the Nomad project I now have the motor Glynn suggested but would like some advice on the coupling. I have used Huco in the past but I recognise that a rubbed coupling would be useful to keep noise down in a direct coupling arrangement. Where do I source the rubber couplings based on the 540 motor with a 3.175 mm motor shaft and 4 mm prop shaft?

As ever all help gratefully received.

Ian

[Dave MilbournParticipant @davemilbourn48782]

Ian

I have sent you a private message and suggested a supplier.

Dave M

[Ian Dowlman 1Participant @iandowlman1]

Hello Dave

Thanks for your reply.

Don't see the private message. How have you sent that?

Do you need me to send my email address?

I am an old retired Dinosaur, and don't use Facebook or other new fangled methods of not talking to one another.

Ian

[Kev.WParticipant @kev-w]

Ian, if you look at the top, above the 'Model Boat' logo, there is an envelope, it will be in there.

[Ian Dowlman 1Participant @iandowlman1]

Hi All

Building now commenced and basic frame of hull almost complete ready for drive train, rudder assembly and planking. Have stuck with extending the hull length but I have reduced the material thickness to 9 mm from 12 mm to try and keep the weight down a bit and have used a marine ply for construction. This will be well sealed as construction develops.

I think that when handling the frame it seems strong enough and it will of course gain more strength from the hull sides. Because of the extended length I have introduced two more bulkheads into the forward structure of the boat.

Thanks for all the input from everyone. I will no doubt be asking for a little more help as I go on.

Regards

Ian

[ashley needhamParticipant @ashleyneedham69188]

Last year or so ago I sourced a length of silicone tubing to use as connector material to fit on the standard sorts of brass bits you get. It is thick walled stuff and about 6.3 I/d and 12.7 o/d (at a guess) and is a good stiff push fit onto the brass connectors. A metre for about £2…..

Perfect for 540LN and 385/300 motors. Not sure I would use it on anything more powerful though.

Ashley

[ChrisBParticipant @chrisb29081]

From memory ( definitely falable), silicon fuel line , unreinforced, 8mm , fit the hucko brass inserts fine.

Chris.

[Ian Dowlman 1Participant @iandowlman1]

THE SAGA OF THE TRAMP STEAMER PROJECT JUNE 2017

Part one

The boat I was planning was to be built up in pine,

Saw the wood guy to try and explain it.

He said that’s OK but he didn’t stock that size

And his machine had broke down that would plane it.

So we thought for a bit and he said yes that’s it

I’ve some nice marine ply, but not so thick.

And it looked to me about the same weight,

So I agreed that it may do the trick.

I’ve a five inch beam, deep water line,

And a lead acid gel battery moreover,

So I guess if I’m careful and make the top light

When it turns sharp it may not roll over.

I’ve extended the boat a bit from the plan,

Bought a brass prop and a tube with an oiler,

A dirty great motor and flex coupling too,

‘Cos I can’t justify a steam engine and boiler

So now I await the wood guy’s call

To say “Bits are cut to your templates, my man,”

Then I can start to build me a lovely strong hull,

Inside my Man Cave, beer fridge at hand.

Part two

So I’ve got the wood and some offcuts too

And some square bits as Glynn’s plan had listed

And the sawn up flat bits all seem OK

But the square sections all came out twisted

Well that’s no real problem, I need only short bits

And the framework’s progressing quite nicely

And the bottom and decks and bulkheads too

Fit together nearly almost precisely.

The motor’s gone in and the prop shaft too

And to my surprise they seem to align

So next I’ll buy and fit the rudder

Fingers crossed it will all go in fine.

Well it did nicely sit in a hole drilled to fit

With a fairing to extend the fin blade

And with epoxy for glue the prop shafts in too

And now some progress’s being made.

Part three

Well now for the sides of the hull we select

Some two milly ply stocked in the shed

And using the new scroll saw – a boon I must say

The sides were roughed out ahead

The straight bits for sure went in a treat

Glued with clamps and weights overnight

The transom end behaved with just a few clamps

But the bow was going to be tight

Now Balsa is generally forgiving stuff

And will most easily bend round if you try

But even thin ply I found to my cost

Is stiff and unyielding and quite spry

So the first side was glued and clamped and taped

But resisted my attempts to do it

So forgetting all the wisdom looked up and read

I decided to drill it and screw it

Well I’ve got to say it worked, and worked well

I must recommend this approach to you chaps

And flushed with success the other side was tried

But despair! I was vexed. The play snaps!

So you sit and look at the damage as wrought

How’m I going to get the side off, it’ll take ages

Until one of those light bulb thoughts Glyn sometimes reveals

I thought “lobster back the side in small stages”

Well this seemed to work and the side went quite well

Curving nicely around the boat’s bow

So panic is over at least for now

But the inside needs reinforcing a bit now.

[Author]

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