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34" Fire Tender - Propeller choice

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Tony Couch29/03/2020 02:29:40
13 forum posts
4 photos

Dear All

I am refurbishing a 34" Aerokits FIre Tender and would appreciate some advice.

A little background:

My brother purchased the kit (£3/19/-) and fittings kit (£2/5/-) by mail order from Roland Scott in Bolton in the 1960s. He partly built it before putting it aside. I picked it up in the 1970s, finished the construction and painted it.

fire tender 1.jpg

It was originally powered with an O.S. 30 marine. It performed very well with that engine but it was badly worn when it was installed and did not last long. I replaced it with an O.S. 40 4-stroke Marine but it was then overpowered and had extreme torque reaction - heeling over 30 degrees or more. For that engine, I used a 45mm propeller. I am not sure about the pitch but it is marked "45 63" so maybe the pitch is 63mm. The blades are 15mm deep. Here is a photo:

fire tender prop.jpg

I removed the 4-stroke and the boat then went into storage again for more than 30 years. A few years ago, I got it out, removed the I.C. engine mounts and big in-built silencer my brother had made. I then installed a 700 size electric motor.

fire tender motor.jpg

It goes well on this power, planing nicely, but also has a lot of torque reaction. That is using the same prop that I used for the 40 4-stroke. Another problem is that it is very noisy - I did not isolate the engine mount and the whole hull resonates.

I am now planning to refurbish the boat properly and finish it off. As you can see from the photo, the rubbing strakes need to be replaced, the paint tidied up and the fittings installed.

As part of this process, I want to install a brushless motor and use Lithium Polymer batteries. I have bought a Turnigy 3520-1700KV motor and matching 60A ESC - both are water cooled. I want to power this with 2S LiPoly batteries I have for other models.

The issue I now have is what propeller to use with this combination.

Once I have an idea of what to use, I need to source it. As the boat was built in the 60s, the propsahft is 3/16" rather than metric and uses a dog drive. If suitable propellers are not available to fit that shaft, I could possible thread it 4 or 5mm.

Your help and advice would be greatly appreciated.



harry smith 129/03/2020 09:31:01
976 forum posts
1270 photos

Hi Tony

The old prop 4563 is 45mm diameter with a 1.4 pitch which is a standard pitch prop.

For your new setup a 2 blade 32mm x 1.4 pitch would be a good starting point.

Banggood is another on line had sells props.

Your motor on 2S would be 12,240 rpm unloaded.

Harry Smith

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