HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Mar 26, 2012, 12:42 PM
Registered User
Joined Mar 2012
5 Posts
Discussion
I need a prop for a Dumas PT boat

It's my first posting so have a heart...

I have a Dumas 33" PT-109 which I built 30 years ago(!) which I am upgrading.
It's original setup was a Dumas 2004 6V motor, 3/16" shaft and a 1.75" plastic Dumas propeller and a Futaba 10amp ESC.
I have replaced the motor with a MACK 5045 (12,000 rpm 12V 5amp brushed motor.) No reduction gearing.
But now I am over propped.
I have tried both the Dumas 1 3/4" prop and an Octura 1240PL prop. Both are too big. (pulling 9 amps at 50% throttle.)
I need a smaller/lower pitch prop that will fit on a 3/16" shaft. (Replacing the shaft is not an option.)
I can't find a smaller prop anywhere.
I could take a dremel tool to the Octura prop and trim it down but I'm not sure that is such a good idea.
The MACK reduction gear set don't fit in the boat.
Is there anything anyone can recommend?
Thanks.
Overworked is offline Find More Posts by Overworked
Reply With Quote
Sign up now
to remove ads between posts
Old Mar 26, 2012, 02:38 PM
Registered User
United States, CA, Hayward
Joined Feb 2006
893 Posts
Drop down to a 1.5 3 blade it should help Dumas OK, but a Scale prop is the deal. 1.5" dia., 2.00" pitch is you goal. have been known to install NWSL flanged bushings and switched a 3/16th's out to 1/8th shafts. the OD of bushing is 3/16th's and green loctite will hold them in.
CaptLee is offline Find More Posts by CaptLee
Reply With Quote
Old Mar 27, 2012, 09:57 AM
Registered User
Joined Mar 2012
5 Posts
Thanks for the reply. I agree with your propeller recommendation.
But, I confess, I am a little uncomfortable with the idea of changing out the drive shaft in the manner you suggest. I can imaging all sorts of bad things happening, ranging from leaks to power robbing vibrations to total failure.
If I had the skill, I would turn down the end of the shaft from 3/16 to 1/8. If someone sells one pre-made, I have not found it.
.
Overworked is offline Find More Posts by Overworked
Reply With Quote
Old Mar 27, 2012, 01:10 PM
United States, FL, Lake Placid
Joined Mar 2012
81 Posts
If you do not want to make the shaft change then go ahead and begin to reduce the prop diameter say, 1 - MM at a time and test there after. Reduce .5 MM hub to hub on each blade and balance before using it. This will unload the motor and allow it to operate at a higher RPM range, and reduce the current draw. If the motor is a 540 type it will like to operate at a range over 12,000 + RPM's.
Pitch and diameter are relevant, however as you decrease the diameter you also decrease the forward motion per revolution, and there will come a point to where the increased RPM's of the prop will not be able to screw forward pushing the mass, ( boat ), and then becomes inefficient and slips, or "blows out". None of which effect anything more than the prop, so it is a cheap modification and well worth the efforts. Just a little at a time until you are satisfied with performance and of course full load current draw. If you go too far build a smaller boat or polish it good and gold, put it on a chain and wear it around your neck.
Good luck, Tony C.
P.S.- Don't tell anyone in the gas model boating business, but scale has always been a special place in my heart and passion for the hobby, and I have built many electric, steam, and of course gas semi and scale boats in my days.
whobbies is offline Find More Posts by whobbies
Site Sponsor
Reply With Quote
Old Mar 27, 2012, 03:41 PM
Registered User
Joined Mar 2012
5 Posts
Thanks for the reply.

Has anyone ever seen a 3/16" shaft that has been turned down to accept a 1/8" prop??
This would solve all my problems.
Overworked is offline Find More Posts by Overworked
Reply With Quote
Old Mar 27, 2012, 04:19 PM
United States, FL, Lake Placid
Joined Mar 2012
81 Posts
We used to make them many years ago, not very difficult. It's just as easy to go to a local machine shop and ask to have the shaft made from a 3/16" SS blank. Ask him to use SS and 10-32 threads on the 1/8" stub. You can use steel "music wire" however it will rust, but if you have an on-board lube it's not a problem, just spray the threaded end with oil when finished. SS drill rod is the better of the two. You will have to provide a simple drawing, and I would think that you could get one custom made for a half hours labor.
whobbies is offline Find More Posts by whobbies
Site Sponsor
Reply With Quote
Old Mar 27, 2012, 04:21 PM
United States, FL, Lake Placid
Joined Mar 2012
81 Posts
Don't forget to compensate for the drive hub placement, more than likely it will now be on the 1/8" dia. part of the shaft. If you have a hard time getting one made, email me a drawing and I will price one for you.
whobbies is offline Find More Posts by whobbies
Site Sponsor
Reply With Quote
Old May 01, 2012, 12:16 PM
Registered User
Joined May 2008
12 Posts
Hi Overworked,
Would hou be interested in selling your Dumas 2004 6V motor if you still have it? What condition is it in?
Nauset is offline Find More Posts by Nauset
Reply With Quote
Old May 02, 2012, 10:38 AM
Registered User
United States, TX, Frisco
Joined May 2007
1,543 Posts
Quote:
Originally Posted by Overworked View Post
It's my first posting so have a heart...

I have a Dumas 33" PT-109 which I built 30 years ago(!) which I am upgrading.
It's original setup was a Dumas 2004 6V motor, 3/16" shaft and a 1.75" plastic Dumas propeller and a Futaba 10amp ESC.
I have replaced the motor with a MACK 5045 (12,000 rpm 12V 5amp brushed motor.) No reduction gearing.
But now I am over propped.
I have tried both the Dumas 1 3/4" prop and an Octura 1240PL prop. Both are too big. (pulling 9 amps at 50% throttle.)
I need a smaller/lower pitch prop that will fit on a 3/16" shaft. (Replacing the shaft is not an option.)
I can't find a smaller prop anywhere.
I could take a dremel tool to the Octura prop and trim it down but I'm not sure that is such a good idea.
The MACK reduction gear set don't fit in the boat.
Is there anything anyone can recommend?
Thanks.
Here ya go...

http://www.harbormodels.com/site08/m...ers_rivabo.htm

-Rich.
RICH404 is offline Find More Posts by RICH404
Reply With Quote
Old May 02, 2012, 12:49 PM
Submarines, etc.
tsenecal's Avatar
Arvada, Colorado
Joined May 2005
1,583 Posts
1.5" x 2.0" 3 bladed octura prop for a 3/16 shaft:

http://www.offshoreelectrics.com/pro...d=oct-x437%2F3
tsenecal is offline Find More Posts by tsenecal
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Got a PT Boat engine, but no PT Boat? Kmot Dock Talk 16 May 10, 2012 03:15 PM
Question Motor control unit for Dumas 1/20th PT Gravman Dock Talk 13 Mar 17, 2012 12:40 PM
Discussion Dumas 1/20th FG PT boat. Gravman Dock Talk 5 Feb 09, 2012 12:29 PM
Discussion Motor / Prop Combination for 75" PT Boat mikgin Dock Talk 27 Apr 02, 2009 04:50 PM
Help! Need 1/12th figures for PT Boat CaptLee Dock Talk 6 Dec 11, 2008 02:53 AM