By continuing to use this site, you agree to our use of cookies. Find out more

Member postings for Gareth Jones

Here is a list of all the postings Gareth Jones has made in our forums. Click on a thread name to jump to the thread.

Thread: Shemarah II
28/11/2010 18:38:14
 For the past few months I have been debating what to build next.  The choice came down to two possibilties, Shemara II (plans bought for me as a Christmas present by my wife last year) or the Spurn lightship (original builders drawings supplied by the Hull Maritime Museum).
I like to work in 1:24 scale and both would be big models but they would fit in the back of my car (a Honda Jazz with magic seats!), although I will probably need a hand to lift either of them in and out.
I have only built one previous plank on frame model (a TID tug) and in the end the decision was made on the basis that the Shemarah plans have all the hull sections so it will be easier to make all the frames accurately and quickly.  The plans are in 1:25 scale which will make the model approximately 1045 mm long but its very deep and wide so it will certainly be heavy when complete.

I have been inspired by Paul Godfrey's excellent built sequence of a Mountfleet Sir Launcelot, so hopefully this is the start of the Shemarah II story.  My personal target is to have the model on the Goole MBC stand at the CADMA show in 2012.  However my project manageress has just reminded me that I have a narrow boat model to finish, a porch to build, a GMBC newsletter to write and probably lots of other jobs as well so I may not meet the programme.
First thoughts are that the motor will be a Graupner Speed 900BB torque driving an 80 mm 4 bladed prop via an  MFA 2.1:1 belt drive reduction gearbox. If anyone has any experience of this combination (or of building Shemara II from these plans) I would be interested to hear their views.
Over the last few days I have traced all the hull frame half sections on to greaseproof paper, reversed the paper and repeated the exercise so that I have a full frame outline for each section.  I have 19 frames to cut out, the majority in 3mm ply but a couple will be in 6 mm.  These two thicker ones will be either side of the main hull opening to provide hand holds to lift the hull in and out of the water. 

The centre section under the main superstructure and centre trawl winch will be removable to provide access to the inside of the hull.  Although its not a very long, its wide and deep so there should be plenty of room for the systems and the ballast.  The hull section for most of its length is around 13 inches wide and deep so I cannot cut the frames from the normal model shop pieces of 4 ft x 1ft ply sheets and will have to order some 4 ft x 2 ft from SLEC.  I made up a dummy 4 x 2 sheet from newspaper, laid it on the desk and then played around overlaying the traced frames to work out the best layout with the minimum waste.

I have now ordered 3 sheets of 3 mm ply for the majority of the frames, 2 sheets of 1.5 mm for the skinning and 1 sheet of 6 mm for the thick frames which should give me plenty of spare stock to cover any mistakes.
Not much is likely to happen for the next few weeks until Father Christmas will hopefully bring me a scroll saw and I will start cutting the frames - if he doesnt it could be a long job with my coping saw.
Thread: Motor and Prop Survey 2020 Update
22/11/2010 13:32:52
And heres the last one for now.
Name   Onion barge E
Type    Springer tug
Kit   Scratch built (by my wife Elizabeth)
Length   460 mm
Breadth   200 mm
Draught   85 mm approx
Weight   3.9 kg
Number of props 1
Motor   Graupner Speed 500E (type number 1788)
Prop type   3 bladed brass Rivabo general purpose
Prop diameter   40 mm
Direct drive, no gearing
Battery 7.2 volt NiMh, 4300 mah
Duration around an hour
Performance   A little underpowered but fine as a 'have a go boat.'
Motor gets a bit hot after long periods, prop is a little too large for motor.  At full power prop rpm is 3250 compared with motor free running speed of 7200 rpm.
22/11/2010 13:22:33
Its fine by me Colin. I agree, the more information there is in the database, the better the possible match and the greater the number of people who will benefit.  Heres the next one then.
Name    PT602 Snogg
Type      PT boat
Kit         Originally I think the hull was a Keil Kraft or Aerokit
Length   1020 mm
Breadth   280 mm
Draught   40 mm approx
Weight   6.3 kg
Number of props    3 but only 2 are driven, the other freewheels
Motors    2 off, Graupner Speed 700 (type number 7307)
Prop type      3 bladed brass Rivabo general purpose
Prop diameter      30 mm
Direct drive, no gearing
Battery      2 off NiMh, 9.6 volts, one is 2600 mah the other 3300 mah, the only reason they are different is because they happen to be what I already had available
Duration    around 15 minutes, depending on how much space there is to plane around the pond.

Performance      Excellent, planes well,  now better than with the 2 Speed 600 motors as originally described in Model Boats.  Present motors run much cooler.  Motors are well matched to propeller size, prop rpm at full throttle 9240 compared with motor free running speed of 14600.


Edited By Gareth Jones on 22/11/2010 13:35:40

22/11/2010 08:41:52
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)

22/11/2010 08:26:35
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

22/11/2010 08:14:41
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

Thread: stanchions
20/11/2010 12:34:22
I have found it much easier to bend the rails to near enough the correct shape first.  I have always used brass wire/rod as the rail material and never bothered to heat treat it.  Then thread all the stanchions on to the rails.  Finally locate and glue each of the stanchions in turn, making any further small adjustments to the rails as you go.
I found that if you fix the stanchions first,  then try to thread the rail through, it jams in the holes and the stanchions get bent or broken. 
Thread: Method for choosing the right prop and motor
11/10/2010 19:41:01
All of it, a Speed 500E is a pretty weedy little motor.  Its another story with my TID and a Speed 900BB torque which is why I had to do that one in the pond.
11/10/2010 19:34:14
They were measured statically, either in the pond or the domestic test tank.  See below for the Springer in the bath.

Note it was not necessary to bolt a bracket to the bath, its just a couple of rubber suction cups!   The wattmeter is on the side of the hull, the digital scales are resting on the back  against a small wooden bracket..
11/10/2010 15:06:49
Heres the example I was trying to illustarte earlier.

11/10/2010 13:02:23
Your child has got its first fan, I am sure it will be very useful. 
I am not sure how best to illustrate this but here is an example and you will have to work it out and see for yourself.  I have run a Springer tug with a Speed 500E motor, 7.2 volt battery and no gearbox (1:1 gearing).  I ran it with three different propeller sizes and measured the performance at full throttle as below :-
Prop size (mm)        30            40            50
Voltage                     7.8         7.75         7.75
Current                     3.1         4.1            5.1
Prop rpm                  4700      3250         1900
Thrust (grms)            229         234           236

My conclusion before seeing the Billysugger Motorcalc programme was that the 30 mm prop is the best of the three but the Motorcalc programme makes it very clear.  Input the above motor parameters, i.e. Speed 500E motor, 7.75 volts, and 1.1 gearing.  Look at the charts and using prop rpm as the reference datum,  see where the three prop sizes sit relative to each other and it clearly shows how much influence prop size has on the efficiency. 

As a guide I will provide the prop rpms I have measured for a few other motor/prop combinations and you can see whereabouts on the performance charts you would be operating for that size and get an idea where you would be with a bigger or smaller prop.  I will try and put the data on this evening.

Edited By Gareth Jones on 11/10/2010 13:28:59

Edited By Gareth Jones on 11/10/2010 13:30:48

Edited By Gareth Jones on 11/10/2010 13:33:05

04/10/2010 16:33:06
Maybe I am a bit odd, too as I have been experimenting over the past few months to try and achieve the same aim as you.  I began building my first model boat about 5 years ago (a TID tug) and I was surprised there were no recommendations on matching propellers and motors.  In the electric model aircraft world there seems to be much more information with advice on thrust available from various battery and propeller sizes for a given motor.  My second boat was a three motored PT boat (Snogg as described in the Sept issue of Model Boats) and that turned out to be a bit of a disaster initially.  Even the second attempt has not turned out to be very good after about a years running with ever higher motor temperatures.  I have done some testing and research and now I am much more confident that I have a good working match of propeller and motor, at least for Snogg.  I have already written to Paul Freshney and suggested a follow up article on the work I have done, Snogg the Sequel perhaps.  I am also supposed to be giving a presentation on my experience to the club that I sail at, (Goole MBC), probably in November.
Essentially I have gone down two routes.  I have compiled a spreadsheet for our limited fleet of models (I say our because my wife built some of them).  This documents the build standard details, size, weight, type, battery, motor, propeller size etc.  I have also measured performance using a wattmeter to measure the power into the speed controller, a tacho to measure prop speed and a digital set of fishing scales to measure thrust from the propeller.  I have put this data into the spreadsheet and rated all the combinations I have covered, ranging from a 1:12 narrow boat through Springer tugs, Steam drifter, TID and PT boat. I have come to the conclusion that the best performance is with a propeller that lets the motor run at around 60-70% of the free running speed,  i.e. somwhere between the max efficiency and max power points on the motor performance chart.  I have also done some experiments with different propellers and found some surprising variations as you can see if you look on the forum under R/C and accessories of a few weeks ago.  I am not an expert in electric motors but I spent nearly 40 years as  a Flight Systems engineer with BAE Systems so I have a lot of experience with collections of equipment connected together and being forced to work together.  
I would be interested in collaborating in some further work as you suggest.  I thought it would be relatively easy to come up with some analytical tool to predict performance but as Colin Bishop has said its not as easy as it looks and there are more variables than is first apparent.  If you would like to get in touch I could send you the spreadsheet as a starting point.
Thread: Variation in thrust and propeller pitch
25/09/2010 17:33:47
I have now done some more work on Snogg's propellers and here are the results.  Firstly I measured each blade tip height as shown below using the 'penny washer'.  For my best propeller, which was originally the LH side one, I took an average of all three blades, which came out as 10.5 mm.
Then I carefully bent the blades on one of my RH propellers to match, setting all three blades as symmetrically as possible.  I also made a minor adjustment to the LH propeller to match the blades to the 10.5 mm setting.  Note, in bending the blades I dont think I am changing the pitch very much, just evening up the circle which is swept by each blade.
To avoid bending the blades again when I refit or remove them I made a tool from a couple of scrap ply disks, three small bolts and some heat shrink as below.  The tool can be held in my fingers with the bolts up against the edge of the blades, reducing the chance of bending them.

I then repeated the performance measurements as before.  The figures below show the way in which a fishermans digital scale is used to measure thrust and the Wattmeter measures the power into the speed controller.

I ran the tests twice, firstly with the propellers in their original position.  Secondly, with the props swapped over side to side and the motor wiring swapped to provide the correct rotation.
Just to remind you originally before matching the blade heights I had:-
LHS motor 8800 rpm, thrust 900 grm   RHS motor 9000 rpm, thrust 550 grm

After resetting the blades

LHS motor 8700 rpm, thrust 930 grm   RHS motor 9400 rpm, thrust 740 grm
After swapping props side to side
LHS motor 9350 rpm, thrust 870 grm   RHS motor 9300 rpm, thrust 1065 grm
My conclusions are that matching up the blade heights has improved the performance of the propeller.  The penny washer method seems quite effective as a way of measuring the differences between blades.
I think I probably bent the blades myself originally when fitting or removing them and the tool should help prevent this happening again in future.
There is still a significant difference between the two propellers, even after they have been matched and swapping them from side to side shows the effect persists so its not the motors or prop shafts.
Overall changing from a 7.2 volt Speed 600 motor to a 9.6 volt speed 700 has roughly doubled the thrust and the motors run much cooler and more efficiently.  The current at max power has increased from about 17 amps to about 20 amps so the original speed controllers are OK.
The propellers are now fitted so that the RH side rotates anticlockwise, when looking from the back, LHS rotates clockwise.  I think this is the opposite of what is normally recommended but since it seems to give the maximum total thrust they can stay where they are. 
Its been an interesting few weeks.  Maybe if I can find some good looking 30 mm propellers at the Blackpool Show I might have a go at repeating the tests to see if they are better matched or more efficient.


19/09/2010 10:52:02
I thought about this a bit more last night and I dont think that the pitch of the blades is that much different.    I think that when the propellers have been fitted or removed the blades have been bent along the line of their roots which is the weakest point when you are holding the propeller and tightening up the lock nut.  It would be very difficult to twist the blades and affect the pitch.  Consequently its perhaps the efficiency of the propeller thats been affected somehow.  I will stick to my original plan and try and set one of the RH side propellers (Left hand pitch I think, always get confused over this), so that all the blades are set at the same tip height.
I am thinking of writing 'Snogg the sequel' as the test results from various different motors (and propellers) has been quite interesting and enlightening. 
18/09/2010 20:14:24
I have been experimenting with Snogg, the PT boat featured in the September edition of model boats.   I decided to try fitting a Speed 700 motor to replace one of the Speed 600's and this showed a significant improvement in speed and ran much cooler so I purchased a second Speed 700.  I retained the original 30 mm propellers but increased the battery voltage from 7.2 to 9.6 volts.  I measured the speed controller input volts, amps and watts using a Wattmeter, the prop speed using a laser tacho and the propeller thrust using a set of digital fishermans scales. (all very nerdy but I like to be methodical!)
The interesting point that came from these tests was that I had much more thrust from the left propeller than from the right.  Both were doing near enough the same speed, LH 8800 rpm, RH 9000 rpm  with similar input power, LH153 watts, RH 142 watts at full throttle.  However the LH propeller gave 900 grammes of thrust, the RH only 550 grammes.  I tried an alternative propeller on the RH side and it gave about the same thrust as before, around 580 grammes.  I then put the propeller from the LH side on the RHS, reversed the motor direction of rotation and got around 850 grammes of thrust.
The only logical explanation is that the pitch of the propellers is different so I decided to try and measure the pitch.  The photo below shows the original LH and RH propellers.

 I fitted a penny washer over each one and used that to try and measure the height at the tip of each blade

The photo below shows the best of my propellers, the one that was originally on the LH side.  While it was slightly more evenly pitched than the others, it still varied quite a lot and on average seemed to have less pitch than the RH blades.  I plan to try and set one of the RH propellers to a similar but even setting to see the effect.

Has anyone noticed anything similar or got any ideas, I assume all three blades should be symmetrical or is the design more complicated than that?

Thread: Lightships I want to build one
12/08/2010 21:35:33
The Maritime Museum in Hull have a print of the Spurn Lightship drawings in 1:24 scale.  There are two sheets showing a side elevation and a plan view but no hull cross sections.  They can supply the drawings as a jpeg file or you can go in and trace the originals if you wish - Bill Jefferson who built the model you saw traced the drawings in the museum.
I also have a long term plan to build the Spurn lighship but have not got round to starting yet.
Thread: Speedline 1:16 Severn Lifeboat
09/11/2008 21:42:00

I have seen a part built example of the Speedline 1:16 Severn Class lifeboat at a recent model boat show.  I have only built woden model boats up until now and I wonder if anyone has built the above model in perspex and has any information or advice on how it went?

Magazine Locator

Want the latest issue of Model Boats? Use our magazine locator link to find your nearest stockist!

Find Model Boats!

Support Our Partners
Premier March
Tony Green Steam
Restorers Wanted
Pendle Boilers
Shopping Partners
Social Media

'Like' us on Facebook

Follow us on Twitter

Pin us on Pinterest

Member Contributions
Distributors of Model Boats for our overseas readers

Make sure you never miss out on the latest news, product reviews and competitions with our free RSS feed

Make your own contribution to the Website

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.

The Member Contribution area offers space for short informative mini articles which would not normally find a place in Model Boats magazine. It is an opportunity for Website Members to freely share their  expertise and experience but I am afraid that virtue is its own reward as there is no budget to offer more material recompense!

I look forward to receiving your suggestions.

Colin Bishop - Website Editor