[PSUBS-MAILIST] Group Help Request

Sun Oct 27 16:48:06 EDT 2013

Not to throw any cold water on this parade, I should remind you that we went through this whole thing a couple of years ago. I spoke with some very nice folks (engineers) at Minn-Kota who were pretty clear about the design parameters. They don't use kort nozzles because they don't need them. The SP101 has the guts to shove a ton and a half of fishing boat against currents or breeze, and do it all day. The bearings are designed for the load they are under at full power with plenty left over for snags. The unit itself in their view is about as good as it gets. Taking it further would require a redesign for bearing lands and webs, the bearings themselves, and the rotating shaft to apply all that new torque. They looked into korts originally, but the penalties are too high for the projected results. Plus, the 101 as it stands simply doesn't need it according to M-K. From what I've seen, they are right. You want more in that design style then you have to do what they did with the 4 hp outboard--step up to bigger windings, magnets, bearings, shafts, etc. Dollars to pounds of thrust? It's hard to beat for light duty, which is what we do. 
Vance

-----Original Message-----
From: Alan James <alanlindsayjames at yahoo.com>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Sun, Oct 27, 2013 3:08 pm
Subject: Re: [PSUBS-MAILIST] Group Help Request

I am wondering whether it is a good idea to change the prop
size on the Minn Kotta. Or whether it would be good to get advice
from Minn kotta first. After reading the issues about sub sea motors & overheating
I am a bit wary of increasing the load, amps & heat in the motor by increasing
the prop size.
With regard to Kort nozzles.... I found a design on the internet, then tracked down a bucket of suitable size & slope, fiber glassed around a portion of it, then built up the thickness of the leading edge.
Alan

   From: Private <alecsmyth at gmail.com>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Monday, October 28, 2013 7:29 AM
 Subject: Re: [PSUBS-MAILIST] Group Help Request

Hi Joe,

Thanks for doing this. I have a Minnkota 101 here that I can measure for you, but I also have some suggestions for your consideration.

Oil or air compensation are both easy and trouble free, so I really don't see much value-add in the magnetic coupling. Or in a hard case. Ditto reverse, my trolling motor thrusters with 13 years on them have yet to wear out the reverse washer, and it's not like I don't use reverse.

Where I do see real room for improvement is with props and nozzles. The stock props are very short pitched, so if you put several 101s on a small sub for main propulsion, I suspect you would not get the cruising speed that their combined horse power would otherwise achieve. In other words, it would be like putting a big engine in your car but only having first gear.

Emile shared with me that the nice kort on his stern thruster is off a diving scooter. I researched those briefly and indeed they're in the ballpark of trolling motor prop diameters, and some appear to be true korts. Since kort nozzles are hard to make, ID'ing one that's a good match would be really useful. While looking at scooters, I noticed some have variable pitch props. By variable I mean adjustable with tools, not adjustable underway. That could prove a big performance booster for our application.

In summary, I'd encourage a focus on the prop and nozzle, as I've found the standard seals and reverse to be perfectly satisfactory. My trolling motors leaked for the first time in 2012, after 12 years of use. I've left the oil in them for years at a time. When I finally serviced them last year, there were cheap rebuild kits readily available. 

Do you need the measurements of the inside bits too? 

Best,

Alec

On Oct 27, 2013, at 8:29 AM, Joe Perkel <josephperkel at yahoo.com> wrote:

All Psubber Alert.

A handful of members in conversation off list are coming to the conclusion that perhaps a best solution to the thruster issues discussed, is to improve on what has been demonstrated to already be viable. That is Minn Kotas as demonstrated by Snoopy, Idabel, et al. Parts are readily available and inexpensive. Case in point here,.. http://www.northlandmarine.com/MinnKotaQuickRef.htm

Hank has graciously offered his efforts in modifying several he already has on hand, and I am willing to put in many hours of CAD work to come up with working drawings, with an eye on this armature in particular,.. http://www.northlandmarine.com/MinnKotaArmatureAssy92-100-216.htm

The goal would be to add a mag coupling, Kort nozzle, and true reversibility to a package that is compact, (4" dia) and field serviceable / replaceable. The end product result would be open source to the PSUB community.

Immediate problem that needs a solution.

I need a lot of information and detail in order to proceed. Particularly what I need is dimensioned section drawings of appropriately sized models. Unfortunately, Minn Kota does not make this information readily available as demonstrated here,... http://www.minnkotamotors.com/service/ascs.aspx

We need help accessing this information otherwise the effort is hobbled from the start. If anyone can help in this regard it would help tremendously. 

Joe

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