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motor size suggestions needed

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John S:
Can anyone suggest a suitable electric motor size for a 4 feet long, 12 inch beam boat with 6 inch diameter wheels? In case the length/beam proportions seem odd they are more or less true to scale  for a 16 feet long full sized boat.  Seven floats per wheel 2 inches wide by 1 inch deep. Hull draught 2 1/4 inches, overall beam over sponsons and paddle boxes 18 inches. Preferred power a compound steam engine with Scotch return tube boiler but if problems getting it accepted by a club then an alternate bed plate ready for electric power. Hope someone can suggest suitable motor from a UK supplier. john.

 :whistle....many people 30 years ago, utilised a 12 volt automobile windscreen wiper blade motor [from the auto wreckers] ......with a 2:1 sewing machine V belt pulley increase in speed to the paddle shaft

Running this on 12 Volt lead acid battery [usable ballast] with a Bobs Board or Tamiya Speed controller provided say 180 RPM down to near zero, reversible control and proved absolutely adaquate  :clap

A 4' x 1' hull follows the displacement family of a Barge with the hydrodynamics of a floating brick.. :sunglasses, but hey...many Paddlers were built on such concept lines

The 2" x 1" individual blade surface area are is certainly in the ballpark for the vessel size you mention, however the worm + worm wheel electric motor drive as explained has massive torque would also power a 6' long model of the same lines without any issue

However this drive torque would also be able to sever a finger  :ranting so care is needed


John S:
Having despaired of fiddly bits that get knocked off while putting a model into the car I cast around for a simple prototype to base  a hull on. Firecrest came up not so long ago and I had previously seen it for sale but at that time was embarked upon thoughts of Medway Queen later superseded by Monarch then by a stretched Strongbow until Firecrest came up on the forum. For those not familiar with the vessel she is but 15 feet 9 inches long, 4 feet beam plus sponsons, draws 9 inches of water with a 9 inch freeboard at paddle position. Seats 3 in comfort or two in easy chairs in the cabin plus stoker, driver  sitting outside at the stern doing the fun bits with scorched fingers and being able to blow the steam whistle when feeling like it. Virtually no delicate detail to get broken off in transit and being so small I decided on 3 inch scale as being the largest length I could fit in the back of the car. Naturally no plans as she was a one off project back in the early 1970s so using photos  and the basic details bits have been made. I have not really attempted to produce a scale model, more an interpretation of how David Garrick might have built a second version using the same basic design as he used for Firecrest. So I hope the present owner will not look too unkindly upon my variation when I eventually mail him a photo of my effort.
John. PS She is pointy at the front and square across the back and to me has a nicely curved plan view.

John S:
Following on from pointy barge shapes. A few pics of assorted bits and pieces, pointy deck blank sheet included.


--- Quote from: John S on August 07, 2021, 07:07:37 AM ---Can anyone suggest a suitable electric motor size for a 4 feet long, 12 inch beam boat with 6 inch diameter wheels? (...) Seven floats per wheel 2 inches wide by 1 inch deep.
--- End quote ---
Just a few very rough estimations on your given specifications:
Maximum hull speed would be 1,4 m/s. With neglected wheelslip, this corresponds to a max wheel speed of 173 rpm.
A wheel of the given dimensions acting at this speed against stagnant water whereas would need a drive torque of 0,19 Nm and a mechanical power of 3,4 W.
So a high-torque steam engine is needed for direct drive.
A twin cylinder Regner 12/36 (12 mm bore, 36 mm stroke) for example at 2,0 Bar pressure, 80% cutoff and an (estimated) mechanical efficiency of 50% possibly could reach these data.



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