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>> Home > Forum > Boat Specific Chit Chat! > What is the optimum prop shaft angle?
What is the optimum prop shaft angle?
Author Message
(Fleet Admiral!)

Forum Posts: 189
21st Aug 2018 01:12  
>> Permalink

This is a Norstar Kingfisher design. I want to place the motor beneath the rear hatch where the batteries sat. The CG was far to forward and this is a heavy model so it never ran very well. the motors ran hot even with a water jacket.

I am moving the motor back, using a shortened prop shaft ,but what shaft angle will produce the optimum performance?


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(Fleet Admiral!)

Forum Posts: 189
21st Aug 2018 02:10  
>> Permalink

12 degrees according to this PDF but I may need to go a bit less say between 8 & 10.

These photos give an idea of where I am going with these modifications. The prop shaft is too steep in this photo...

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(Fleet Admiral!)

Forum Posts: 2527
21st Aug 2018 08:14  
>> Permalink

Mornin' Ron,
If you put the motor where the batteries are now - where will the batteries go? They weigh far more than the motor so moving them forward will push the CoG even further forward😲
Re shaft angle; as flat as you can get it for the size of prop you want to use.
This is to reduce the forward rotation moment of the thrust which tends to push the bow down. The further back you fit the motor the larger the angle will inevitably become due to the space needed for the motor and mount!
BTW: Why two NiMh batteries?
I would be tempted to change the set up to a brushless and a single LiPo.
This will significantly reduce the total weight as well👍
You did say the boat is 'a heavy model'! 😉
Doug 😎

Young at heart - slightly older in other places 😉 Cheers Doug

Forum Posts: 30
22nd Aug 2018 00:26  
>> Permalink

You could reduce the angle by rotating the motor 180 & using gear or belt drive to the shaft, so the motor is sat over the shaft.

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(Fleet Admiral!)

Forum Posts: 42
22nd Aug 2018 01:17  
>> Permalink

Ideally the centre of the weight needs to be near the middle of the boat.
The original plan looked OK, maybe it required the batteries a little further back. The whole propulsion system did look a bit heavy for the boat.


Forum Posts: 64
22nd Aug 2018 18:30  
>> Permalink

The Nor Star Kingfisher is a heavy boat for its size and the positioning of the motor and prop shaft angle certainly matter.
I built one in 1972 powered by a DC Sabre marine diesel (1.5cc) and the engine was in the cockpit which made it heavy at the bow.
I was disappointed by its poor performance in relation to other boats of similar dimensions, in some cases these being powered by 1 cc diesels.
It never crossed my mind that I could have used "ballast" and the boat was sold on 7 months later at a greatly reduced price.
"Fools rush in where experts fear to tread."


Dave Keech