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[John-T]

Hi,


I'm considering building a Mobile Marine Models Damen Stan 1605 tug, OAL 20", beam 6".


I have the following to hand:

• 2 x 555 motors
• 2 x 40mm 4-blade Kortz-nozzle-type props

and

• 2 x 385 motors
• 2 x 35mm 3-blade brass props

Any ideas as to which would be the most suitable combo?


The 40mm Kortz props would be true to scale, but I'm not too fussed about that. I'm more concerned with a suitable performance (I won't be towing with it).


Cheers,


John

[Fastfaz]

Hi John,
      I would go for the 40mm Korts combo, this will look right and, should you wish to start towing at a later date, be ideal for the job. Most Tugs have 4 blade props but the choice of prop is doan to the builder, after all it is their boat. Hope this helps.
           Regards,
               Pete.

[Fred Ellis]

Hi
I would have a word with MMM, and see what they would recommend.

[John-T]

Hi again,


I emailed Mobile Marine Models, and they advised that the 40mm props and the 385 motors would be the ideal combo, so that's what I'll go with.


As you state, Fastfaz, I'll have the ability to tow if I decide to at a later date.


Thanks to you and Fred for your replies.

[Colin Bishop]

See my comments on the Model Boats website. Prop Shop might be the way to go.

Colin

[HMS Invisible]

Hi again,


I emailed Mobile Marine Models, and they advised that the 40mm props and the 385 motors would be the ideal combo, so that's what I'll go with.


As you state, Fastfaz, I'll have the ability to tow if I decide to at a later date.


Thanks to you and Fred for your replies.

We've all got our opinions where test instruments give a reading.
Do you have access to a multimeter or an infrared tachometer?
Either can show if your loaded, full throttle revs have fallen below 50% of the free running speed of the motor.
That's not my opinion. It's a fact that can't be argued with.

If you test, I predict the 555 will cope with both. It's rated torque is about four times that of a 385!
MFA 385 will need gear reduction for the larger option, and probably for both.

[John-T]

Hi HMS,


I have a multimeter, but it doesn't have a frequency-measurement function, which I understand is necessary to measure RPMs.


MMM said that the 555 was "really too big" for the 20" 1906 hull. They MMM supply their own motors for that model, but they're expensive at ?14.80 each, and their can diameter is only 0.5mm larger than the standard 385.

I did think the 385 would be a bit underpowered with the 40mm 4-blade kortz props.


Would the MFA 385LN be more appropriate, anyone? Its torque is rated at 110g-cm as opposed to 79g-cm for the standard 385.

[John-T]

Hi Colin,


I've checked your comments over on the Model Boats website; thanks for that reply.


I have no idea what the Prop Shop reference numbers mean in terms of size.


I think I'll go with the 385s - I might even splash out and buy the more torquey 385LNs -  and 35mm 3-blade props. As you say, only the fish will see the difference - although those diving ducks tend to be a bit fussy, and might make some rude remarks! I have already begun to fabricate suitable nozzles myself. I'll post some pics of them when they're finished.


Originally, I was even considering fitting just a single prop sans Kort, then I progressed to a single Kort/prop, and I've now moved on to two of the latter. I always start off deciding to keep things simple, but it never ends up that way!

[HMS Invisible]

Hi HMS,


I have a multimeter, but it doesn't have a frequency-measurement function, which I understand is necessary to measure RPMs.


MMM said that the 555 was "really too big" for the 20" 1906 hull. They MMM supply their own motors for that model, but they're expensive at ?14.80 each, and their can diameter is only 0.5mm larger than the standard 385.

I did think the 385 would be a bit underpowered with the 40mm 4-blade kortz props.


Would the MFA 385LN be more appropriate, anyone? Its torque is rated at 110g-cm as opposed to 79g-cm for the standard 385.

Multimeters often require an attachment. Testing by me was suggested because it ends a pointless neverending argument. Our currency exchange rate is more favourable so a hanheld infrared tachometer can be bought quite cheaply.
 But your prop to motor torque  mismatch is glaring so you'll see by the current draw and how blisteringly hot the 385s get in a water basin check that you can see if the LN version is worth considering.
  We all sussed the dimensions would mean a 555 would be a tight squeeze, as well as their weight when ballast is best sheeted round the lower hull. It looked like you suggested them as a realistic option, however. If you can shoehorn 555s in and the model ballasts then they are the optimum. You'd run at near peak efficiency as your meter and basin test will tell you.

As for esc, look up "dual brushed esc" on Aliexpress. You can get a small esc, small single Lipo and connect together with the minimum of fuss.