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Motor and Prop Survey

Article in forthcoming Special Issue oif Model Boats

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Colin Bishop, Website Editor18/11/2010 11:39:25
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MyHobbyStore have commissioned another Model Boats Special Issue for next year and this one will be a combination of recycled plan features going back to the 1980s plus a series of articles on what might be termed ‘Model Boating Basics’ which will be aimed at giving people advice on the issues which come up again and again on internet forums from new or less experienced modellers.

I’d like one of the articles to be about Choosing Motors and Props as this is something which a lot of people find difficult. There is no magic solution to this and any ‘scientific’ based method involving calculations could be a turn off, people basically just want to know what will work in their boat. So the idea would be to give some general advice on things to take into consideration supplemented with a series of ‘benchmark’ setups for actual typical boats drawn from practical experience. If your boat is very similar in its characteristics to one of these benchmark model setups then you can be reasonably sure it will work for you too. If it is somewhere between two benchmarks then at least you will have bracketed the range of possible options.

So I am inviting Members to use this topic to post details of their boats where they have a good working motor/prop/battery setup. If possible, also post photos of the model in action and of the interior layout as some of these could be published in the magazine. If you would prefer to PM me with details of your boat, that is OK too.

Assuming that I get a good response, it will be summarised in the magazine for the benefit of all.

The list of parameters that I have identified is as follows. We need all of them to do an effective job.

Boat Name
Type:  ie. tug, destroyer, cabin cruiser etc.
If a Kit – which kit?
Length (mm)
Beam (mm)
Draught (mm)
Weight (Kg)
Number of propellers
Motor(s) used. (specific rather than generic i.e. Not just ‘540’ but ‘Dean’s Kondor’ for example so we know exactly which motor is being referred to.)
Propeller type and description: i.e. 2 blade/3 blade/4blade etc. conventional or racing
Propeller diameter.
If geared drive what is the reduction ratio and are gears or belts used?
Battery type and capacity.
Approximate average running time obtained.
 

Please don’t use this topic to ask questions about which motors to use, it is intended for gathering information only!

 I look forward to lots of responses!

 Colin

Robin Lee18/11/2010 15:24:52
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Hi Colin,
I'll have a go at this request. One of my favourites a Dean's Marine HMS Kelly.
 
Boat Name: HMS Kelly
Type: Destroyer
Dean's Marine Kit (more or less!)
Length: 1120mm
Beam: 125mm
Draught: 50mm
Weight: 3.8Kg
Number of propellers: 2
Motors: Deans Marine Kondor
Propeller type: 3 blade conventional (kit parts)
Propeller diameter: 30mm
Drive: direct
Battery type: one for each motor Sanyo 7.2volt Nicads 2000mAh
Running time: at least 2 hours at half throttle
 
Some photos:
 
 

 
Quite difficult to get all the info together but can do more if wanted?
Robin



Colin Bishop, Website Editor18/11/2010 15:44:43
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That's great Robin, exactly what I am looking for.
 
Colin
Robin Lee18/11/2010 17:25:06
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Hi Colin,
Another model:.
 
Boat Name: Tsekoa ll
Type: Navigation Aid maintenance
Model Slipway kit
Length: 840mm
Beam: 228mm
Draught: 60mm
Weight: 6.8Kg
Number of propellers: 2
Motors: 545 type - Electronize 545-12 (marginally underpowered but is very subjective)
Propeller type: 4 blade conventional Prop Shop 1517/4
Propeller diameter: 38mm
Drive: direct
Battery type: one for each motor Led Acid Gell 6volts 4Ah
Running time: 2 hours 
Some photos:
 
Mark Beard18/11/2010 22:46:48
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I don't want to clog this thread up with non-data posts, except to say how excited I am to see this info being published.  If enough people post their info as Robin has, we are going to get a superb database of empirical results which will really help new builders (like me) to get their models correctly powered from the outset.  Although I don't have results to post, I look forward to offering some analysis or reduction of the data to some sort of usable form.
Francis Macnaughton20/11/2010 20:54:04
65 forum posts
Colin,
 
I would suggest that at least some indication of overall performance of the model with that power installed in comparison against the performance of the prototype would also be useful.  This especially true for higher speed types like warships, speed boats and MTBs.  Perhaps something along the lines of either:
 
   a)  Achieves prototype maximum speed    or
 
   b)  Exceeds prototype  maximum speed    or
 
   c)  Cannot match protype maximum speed
 
Ideally this should be done by comparison of the model wake pattern with the original's but I would suggest that even a subjective estimate such as Robin's above would be better than nothing.
 
Francis Macnaughton
Gareth Jones22/11/2010 08:14:41
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Since I have started to keep a very similar database of my own models for the same reason I suppose I had better submit the details.  (Maybe Colin has borrowed my idea?)
Here is the first one then.
 
Name   TID13 (I know there never was a TID 13 in real life)
Type       Tug
Scratch built, ply plank on frame hull
Length    900 mm
Breadth    230 mm
Draught   70 mm
Weight   6.4 kg
Propellers   1
Motor   Graupner Speed 900BB torque (type number 6373)
Propeller type 4 blade Rivabo brass general purpose (apologies to Glynn Guest, I dont know the pitch)
Propeller diameter 55 mm
Direct drive, no gearing
Battery 12 volt 7 amp hour lead acid
Duration not known but well over an hour
Performance    significantly over powered with this motor - it will almost plane.  However the propeller is slightly large for the motor, prop speed at max power is 3150 rpm. free running speed of motor is 6500
 


 

Edited By Gareth Jones on 22/11/2010 09:01:20

Gareth Jones22/11/2010 08:26:35
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459 forum posts
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Here's the next one
 
Name    Daisy II
Type      Armed drifter
Kit    Mountfleet Osprey
Length   1100 mm
Breadth   250 mm
Draught   90 mm
Weight   8.5 kg
Number of props 1
Motor   Graupner Speed 720B torque (type number 6372)
Prop type 4 blade brass Rivabo general purpose
Diameter 70 mm
Direct drive, no gearing
Battery 12 volt lead acid, 5 amp hour
Duration over an hour
Performance,  good realistic scale speed.  Propeller size is a bit large for the motor. At full power prop rpm is 1530 compared with free running speed of motor which is 4100 rpm


 

Edited By Gareth Jones on 22/11/2010 08:43:06

Gareth Jones22/11/2010 08:41:52
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459 forum posts
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And here's another.
 
Name     Walbut Dream
Type    Narrow boat
Kit      Scratch built using Deans marine hull (still work in progress as the photo shows)
Length   1060 mm
Breadth   180 mm
Draught   60 mm
Weight   8.3 kg ballasted to estimated completed weight
Number of propellers   1
Motor   Graupner Speed 500E (type number 1788)
Propeller type 3 bladed brass Rivabo general purpose
Prop diameter 40 mm
Direct drive, no gearing
Battery    7.2 volt  2600 mah NiCad
Duration not known but probably about an hour
Performance   slightly over powered for a narrowboat.  Propeller is slightly large for motor size.  At full power, prop rpm is 3040, free running speed of motor is 7200 rpm.
The model has a bow thruster but in practice it is not required as turning performance is excellent using rudder alone (surprisingly perhaps)



Colin Bishop, Website Editor22/11/2010 11:03:21
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Gareth,
 
No I didn't pinch your idea it's a case of great minds think alike. I have had this in mind since July but your posts pre empted the formal decision of MyHobbyStore to go ahead with next year's Special so I wasn't in a position to 'launch' before then!
 
Obviously the more boats we have then the more useful the data will be. My proposed article will cover general advice and publishing the benchmark data but wlll stop short of attempting to draw any theoretical conclusions for selecting motor/prop setups. If the data helps you and Billy move forward in this area then I'm sure Paul Freshney would be interested in publishing it in the regular magazine.
 
Francis, you have made a good point but the assumption will be that we are looking at benchmarks where satisfactory 'scale' performance is a given. Defining this can be a bit of a minefield in itself and can be somewhat subjective to say the least.. The wake patterns in Robin's excellent photos demonstrate satisfactory performance very well which is one of the reasons I asked for photos.
 
Thanks for your help to date everyone, and keep them coming!
 
Colin

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We welcome well written contributions from Website members on almost any aspect of Model Boating with a particular emphasis on practical hints, tips, experience and builds.

In order to maintain a consistent standard and format, all suggestions should first be sent to me by Personal Message for approval in principle. Only a very limited amount of time is available for editing contributions into a suitable format for placing on the website so it is important that the material is well presented, lucid and free from obvious spelling errors. I think it goes without saying that contributions should be illustrated by appropriate photos. I shall be happy to give advice on this.

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I look forward to receiving your suggestions.

Colin Bishop - Website Editor