Model Boat Mayhem - Forum

Dry Dock / Shipyard: Builds & Questions => Working vessels R&D: => Topic started by: ZZ56 on May 02, 2009, 01:12:42 AM

Title: Prop Sizing Question.
Post by: ZZ56 on May 02, 2009, 01:12:42 AM
Hello Mayhemers,

I am building a model freighter based on a hull plan of the M/V Canadoc.  The model will be powered by a six-volt system with direct drive.  The final model will be fairly large, displacing about fifty pounds by my estimates. 

The propeller i have on hand happens to match the size on the plans perfectly, but i am concerned it won't be enough, as these are builder's plans not modeller's plans.  I believe the next largest size is 2'' diameter.  Should i step up the diameter and possibly look for a four-bladed propeller?  I'd like to make sure i have some extra power.

(http://img.photobucket.com/albums/v323/DestructorBot/IMG_1242.jpg)
Title: Re: Prop Sizing Question.
Post by: DickyD on May 02, 2009, 09:16:39 AM
Try the one you have first as it might be OK.
Title: Re: Prop Sizing Question.
Post by: ZZ56 on May 04, 2009, 12:46:01 AM
Thank you sir.  I know there will be at least 1/8th inch clearance on the bottom and top, if need be.

is this the right forum to also post pictures of your build or does that go above, in Dry Dock?
Title: Re: Prop Sizing Question.
Post by: DickyD on May 04, 2009, 10:46:43 AM
Your build photos go in the dry dock section and you needn't call me Sir, I haven't been knighted and I'm not that old.
Title: Re: Prop Sizing Question.
Post by: Pat Matthews on May 08, 2009, 04:53:02 PM
My experience: Many scale displacement boats can use bigger rudders, but more than adequate power can be transmitted to the water with a scale size prop... one of those mysteries of scaled hydrodynamics.
Use the scale size prop.

Extra credit: Build a working variable pitch unit just as used by your prototype!
Title: Re: Prop Sizing Question.
Post by: BJ on May 08, 2009, 09:05:06 PM
The propeller i have on hand happens to match the size on the plans perfectly, but i am concerned it won't be enough, as these are builder's plans not modeller's plans. 

It might be from Prop Shop's 1992 catalogue but it is still valid - refer to the attached chart for a suitable prop for your vessel.
Title: Re: Prop Sizing Question.
Post by: ZZ56 on May 10, 2009, 01:25:38 AM
Thank you both.   Think I'll stick to fixed pitch as my machining skills are on the level of 'remember not to lick the lathe while it's running'.

For the Prop Shop catalogue, it seems to say 3580/3/4 for my category.  Is that a product code?

(I will try to get some build photos up ASAP... progress has been slow while i wait for good weather to prepare planking)
Title: Re: Prop Sizing Question.
Post by: BJ on May 10, 2009, 02:55:39 PM

For the Prop Shop catalogue, it seems to say 3580/3/4 for my category.  Is that a product code?


That means ****/3/4 means a 3 or 4 bladed prop and I think you meant to say a 3540 not 3580