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[neilthebus]

Hi everyone.

I am sorry for yet another question but I really am new to all this and I have found the forum helpful beyond belief.

Is there a rule of thumb that determines size of motor/propellor combination for a given size of hull?

[dougal99]

Hi Neil

I copied the following from one of the many modelling books I've read. Yours for a starter of ten:


Scale Models  (all dims inches)

Length                  Prop              Motor Watts (Volts x Amps)
     16                         1                      5
 14-20                         1.25                 5
 18-28                         1.5                   7.5
 24-32                         1.75                 10
 27-36                         1.75                 15
 30-48                         2.0                   20


This is just a general guide. You will have probably noted that the tug towers use bigger motors and props for a given hull size. Of course racing boats are a different ball game altogether. Hopefully some one who knows will give you an answer.

HTH

Doug

[neilthebus]

Thanks Doug.

Thats very much what I wanted. The xouple of model boat books I have so far aquired are very general and didn't have specific details such as this.

Much appreciated   

[tigertiger]

Scale Models  (all dims inches)

Length                  Prop              Motor Watts (Volts x Amps)
     16                         1                      5
 14-20                         1.25                 5
 18-28                         1.5                   7.5
 24-32                         1.75                 10
 27-36                         1.75                 15
 30-48                         2.0                   20

Doug
I have a saill boat (Mary J Ward) about 34".
I only want the motor for rescuing her if she gets becalmed.
could I get away with a 1" or smaller screw/prop?
If so do you recomend a motor?

[CAD2]

Tigertail
Graupner list a special unit with a geared Speed 400 and folding prop, exactly for this sort of application. Details are on their website (hope your German is better than mine) but I'm sure the serial number 1175 will be relevant if you contact Westbourne Models:
http://shop.graupner.de/webuerp/servlet/AI?ARTN=1175
Good luck.
CAD2

[GOGSAMWE]

On the above Graupner page..

  Click on the Union Jack Flag at bottom left of page.. and all will be revealed .....
In English 


Steve 

[CAD2]

Thanks, Steve. If I'd bothered to check the whole thing I might have spotted that one................... Darned cunning, the Hun!
CAD2

[dougal99]

tigertiger

Your question has been answered I hope :)

Cheers

Doug

[tigertiger]

tigertiger

Your question has been answered I hope :)

Cheers

Doug

I really want to know if I can get away with a 1" screw.

I want to cut it into the keel stock so it will look semi scale and won't look bad as a static model. The keel is about 1/2" so drag will not be too bad I think.
The folding prop will be too big and will look odd on the display stand.

Getting her back in at speed is not an issue.

[dougal99]

I would think that a 1" prop on a 34" hull is about the smallest you could go. However, I suspect it would have to be dead flat calm or it would probably be overcome by whatever wind there was in the sails.

Doug

[tigertiger]

I would think that a 1" prop on a 34" hull is about the smallest you could go. However, I suspect it would have to be dead flat calm or it would probably be overcome by whatever wind there was in the sails.

Doug

Thanks for this
doug.

If I got wind in the sails there is no problem, I can sail her back.


I saw something about people frying motors sue to overloading them. Is this another potential problem?
Is there a certain type of motor I should be going for?

Mark

[dougal99]

Martin,

I am aware that you can sail if there is wind. I was thinking that if you start out in a wind it is unlikely that it would suddenly drop to flat calm marooning your boat in the middle of the pond/lake so your prop/motor is likely to have to cope with some wind.

As far as motors go, if you buy one that can cope with 3-4 amps on 6 volts (that's 18-24 Watts) you should be ok.

Doug

[tigertiger]

I was thinking that if you start out in a wind it is unlikely that it would suddenly drop to flat calm marooning your boat in the middle of the pond/lake so your prop/motor is likely to have to cope with some wind.

Believe it or not, it can drop to flat calm, with sails completley lifeless.
I have had to sit and wait 15 minutes to bring a Victoria back 15m on occasions.

Unfortunatley the lake is in a hollow between high buildings, a slight shift in wind direction (when winds only light) can leave you devoid of wind.

On the plus side, I have got very good a searching for air.

[cbr900]

Yes we on rare occasions over here sometimes will have the breeze fade away to zero, the yacht is left like a ghost ship, occasionally you will get enough to flex the sails but no forward movement, so have a smoke sit and wait have lunch and the breeze will come back and your off again, next ketch will have a small prop and motor fitted to at least allow you to move to a better location for a breeze shift....



Roy