Model Boat Mayhem

Mess Deck: General Section => Model Boating => Topic started by: shadysadie on December 14, 2018, 08:23:54 pm

Title: correct propeller size?
Post by: shadysadie on December 14, 2018, 08:23:54 pm

Some more advice please. I have been running my 1/24 scale (36") Vosper MTB Mk.2 for the last 3 yrs. on 2x 2836 1200Kv outrunners  powering the outer two shafts with the centre prop. freewheeling. Power is from 4S LiPo's the props. are 40mm., performance is good and the motors and Robbe Roxxy ESC's  run cool. In an attempt to reduce the weight of the boat, I've removed the two motors and fitted a single 3548 900Kv V3 thumper to the centre shaft and will allow the two outer to freewheel (thanks gra2 for giving me the idea over 3 yrs. ago!). I would like to use the existing 40mm. 3 bladed scale prop. ( George Sitek) but as I am still pretty hopeless when it comes to motor/prop. compatability, I thought I would ask here first.


Thanks, David.

Title: Re: correct propeller size?
Post by: canabus on December 15, 2018, 05:18:42 am

HI SHADYSADIE
I just trialled  my 37" Perkasa for the first time with a Turnigy 3639-1100kv(800Watt), 3S 5800mah(550gram) Lipo battery, 60 Amp car ESC and a 3blade 37mm prop.
I would say your new setup would be OK.
I have used this setup in a few boats and it works OK.
What mah's are your batteries???

Canabus

Title: Re: correct propeller size?
Post by: BrianB6 on December 15, 2018, 05:50:30 am

Props depend on pitch of the blades as well as diameter so what suits one motor / hull combination might not be right for another. When I was into racing boats even a small change could make big difference.   Props seem to be more an art than a science on models  %%

Title: Re: correct propeller size?
Post by: shadysadie on December 15, 2018, 09:13:48 am

Hi canabus, I have both 3S and 4S batteries and they are all 4250 mah.. BrianB6, you are certainly right about props. being an art form so I'll get a couple of plastic props. 35- 45 mm. and experiment.When the UK weather improves a bit that is.

Title: Re: correct propeller size?
Post by: canabus on December 15, 2018, 10:54:27 am

Hi shady
The batteries are no problem with running a  900kv on 3S or 4S .
 One battery only required with the other for backup.
Canabus

Title: Re: correct propeller size?
Post by: Hotglove on December 15, 2018, 01:41:51 pm

Hi Canabus, would be very interested to see some video of the Perkasa in action.
I have had a problem with cavitation from a 3 blade 38mm CNC prop on my Dumas 1930 Runabout but have found a temp solution.(discussed under cavitation on this section of the forum)
Our lake is now closed for the winter so will be able to give it some careful thought over the winter,

Title: Re: correct propeller size?
Post by: aeronut on December 15, 2018, 04:37:42 pm

A freewheeling prop will cause unwanted drag, why not just remove the unused prop(s)?  When the boat is on the water, no-one will know.  ok2