[PSUBS-MAILIST] Group Help Request

[Jon Wallace]

What is the cost of having a true Kort nozzle machined by a CNC? I think 
a 30% improvement in thrust for $30 would be great but I suspect 
machining a Kort is going to equate to many hundreds of dollars, if not 
reaching beyond a thousand.  When I look at the Snoopy underwater videos 
it is difficult to imagine a kort nozzle really making any difference in 
the operational experience given that the motors are operating very 
slowly and pushing Snoopy around at about 2 knots (estimated).  The 
props are designed for power, but that's what we want underwater.  True, 
a kort nozzle would increase that power but what is the return on the 
cost?  In other words, on a road with a speed limit of 30mph and no 
passing zones it doesn't matter whether you have a 1.6 liter or 5.4 
liter engine under the hood does it?

Like Vance, I don't want to rain on the parade and I do "get it" that 
the challenge of coming up with a "home-built" alternative can be 
rewarding.  I just think that production cost will be the determining 
factor on practical use.  Like going from T-Rex back to minn-kota, I 
can't help but wonder if the ultimate conclusion will turn out to be 
that the stock minn-kota's are good enough for 99.99% of our applications.

I can think of many things that your CAD experience could offer to the 
group if you are interested in providing some designs.  For example the 
K350 plan modifications that have been talked about by a few people.  We 
could really use help in that area.

Jon


On 10/27/2013 6:20 PM, Joe Perkel wrote:
> Alec,
> I've gone round and round for the past two weeks in depth on the 
> issues of propulsion and have come full circle back to the trolling 
> motors. I was on hiatus for the discussion mentioned by Vance ref 
> contact with the manufacturer as I would have remembered that.
> So, I'm with you on the prop and nozzle. While the 101's may indeed 
> have plenty of guts for the job as is, the Kort data shows a 30% 
> improvement in Bollard thrust at low speeds for any given prop 
> diameter. That and the added benefit of protecting the prop, are 
> significant enough reasons to forge ahead. This is actually good news, 
> less work by not mucking around with the guts of the motor.
> You guys are the builders with recent hands on, I'm behind in the 
> trial and error business because I cant get started tinkering yet. But 
> as you well know, I developed CAD capability for this purpose only, so 
> time to put it to real use. Where I need help is deciding on materials 
> and manufacturing processes. I can give you guys the cutting files 
> needed to whittle a Kort out of a block of solid titanium, but that 
> would not be practical. That's my limitation and where hands on 
> experience counts.
> Now these nozzles are reverse foils with coordinates in percent of 
> length. I can generate a NACA 4415 on my airfoil generator and 
> transfer that to the model.  I can give us accurate 3d models and 
> eventually CNC cutting files for whatever the group wants on these 
> Minn Kotas, nozzles and attachment hardware. I can do both Nozzles, 
> Marin 19A, and or 37, with the latter being optimized bi-directionally.
> Finding something off the shelf would be ideal, but I suspect given 
> the nature of the business and the quote I recieved it would likely 
> prove problematic.
> You need a new square tip prop to optimize the duct. I've had custom 
> props made for my boat in the past, so that should not prove 
> insurmountable. I should be able to do the prop as well.
> Can we post pictures on this forum?, I forget. It would be helpful to 
> point things out. If I could post pictures of the various exploded 
> diagrams, I can point to where I want dimensions with red 
> arrows. Eventually, I'll start a web-page.
> So for now, I need some detail on the shaft and prop as is., what have 
> you done with that washer and where it is in the drive, as well as any 
> other modifications.
> I think this is a decent group effort project, and one that can pay 
> dividends in the end.
> Joe
>
>

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