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[Flatspin7]

Is there a table or information source for determining the corrrect size prop  for a given setup ?
I imagine it's a difficult situation to give an exact size but are then any general rules to help make a start?


Thanks

[Shipmate60]

From the plan.
That should give you a good idea then match a motor/voltage to the prop.

Bob

[Flatspin7]

Thanks for that Bob


How about from a given motor spec and battery ie matching a prop to a known combination?


Are there any general rules?

[Shipmate60]

Rule of thumb for direct drive the motor case should be at least the same diameter as the prop (or larger).
This is not for geared motors.
What type of ship is she?

Bob

[Flatspin7]

That's a very easy to understand guide for diameter : thanks.


What about the pitch choice ?


I have not decided on a specific boat type but it will almost certainly be a cabin cruiser type, probably something like the Fairey Swordsman.


I already have a selection of various brushless inrunners/outrunners from aircraft use hence trying to understand what may be suitable


There are various resources/references for aircraft to match motors to props etc and I wondered if there was such a  thing available for boats   

[Colin Bishop]

There is a Masterclass build of the Swordsman on here:

http://www.modelboatmayhem.co.uk/forum/index.php/topic,7668.0.html
 
and also a topic on the Model Boats Wesnsite Forum here:
 
http://www.modelboats.co.uk/forums/postings.asp?th=48826&p=1
 
Both well worth a read.
 
Colin

[Subculture]

I don't recommend using can size, it does give some indication but is very loose indeed.

MAP published a brilliant book called 'Model Boat Propellers' back in the 1970's. It gave all the information a modeller is likely to need to calculate the correct size of prop for a given RPM. Unfortunately out of print. I have scanned it into an ebook, but can't distribute it, as it's probably still under copyright.

[Colin Bishop]

I have scanned it into an ebook, but can't distribute it, as it's probably still under copyright.

I doubt if anyone would mind, the information will be almost totally out of date by now anyway.
 
Colin

[bj]

 

Is there a table or information source for determining the corrrect size prop  for a given setup ?
I imagine it's a difficult situation to give an exact size but are then any general rules to help make a start?


Thanks

Incorrect link back - apologies
Try again -  http://www.modelboatmayhem.co.uk/forum/index.php?topic=37609.msg377048#msg377048

[Subculture]

I doubt if anyone would mind, the information will be almost totally out of date by now anyway.
 
Colin

Well if I get nasty letters, I'll quote you!

The information is not at all out of date, and it doesn't matter if you're running steam, brushed, brushless etc. The information is the same. There is still a bit of empiricism in the process, as factors like blade shape and area have an effect, and this book only really deals with pitch and diameter. However this will get you 90% of the way there, and certainly makes it much easier to choose appropriate props, and motors.  Note that for those who hate formulas, nomograms are provided in the book which give respectable results.

Here is the link- http://document.li/P86z

[RAAArtyGunner]

 
Here at Least, is one nice letter
 
       

[Colin Bishop]

There is certainly some interesting material there which could be helpful in choosing a prop for a particular application. However, prop choice these days tends to be made on an empirical basis by trying several alternatives until you get the best match. The information given in the article could certainly point the way towards the best options though.
 
Colin

[Flatspin7]

Thanks for all the response and useful information : already I have a better grasp of the basics
and can make a semi educated guess rather than a pure one!

[Colin Bishop]

Getting the right motor/prop combination has always ben something of a black art so don't be afraid to experiment.
 
Colin

[Walney Col]

Well if I get nasty letters, I'll quote you!

Here is the link- http://document.li/P86z

Thanks for that Subculture, it's just come in really handy for verifying my calculations, and as you say the laws of physics seldom become outdated

Col.