[PSUBS-MAILIST] Motor Modification

Tue Dec 6 11:55:49 EST 2016

Hi All

Parts number 40 on this diagram are the seals.  I just packed both the
seals and void with loads of marine green propeller grease.  Not sure if
that is ok or not.  They don't leak.  I just have a real pain filling them
up.

https://cdn.shopify.com/s/files/1/0191/7628/files/2013-N-Minn-Kota-riptide-motors-rttransom-Riptide-80t.pdf?6255360441529777455

All parts numbers etc for the motors are here by the looks of things.

https://northlandmarine.com/pages/minn-kota-riptide-transom-mount-motor-diagrams

On 6 December 2016 at 15:27, Sean T. Stevenson via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> You would also ideally reverse the inner seal to preferentially resist the
> bias pressure inside the housing (even though it may easily seal against 4
> psi in the normal orientation), and leave the outer seal orientation alone
> to preferentially resist seawater incursion.
>
> Sean
>
>
> On December 6, 2016 7:23:56 AM MST, Cliff Redus via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>>
>> Thanks Sean.  The dual lip seals on the MK-101s are spring energized to
>> handle this zero differential pressure issue.
>>
>> Cliff
>>
>> On Tue, Dec 6, 2016 at 7:11 AM, Sean T. Stevenson via
>> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>
>>> One caveat to the embodiment that I described:  As seals are generally
>>> energized by pressure, when you employ a seal to separate two fluids at the
>>> same pressure, you must pay attention to the seal contact in the absence of
>>> that pressure differential - possibly opting for a spring energised seal if
>>> there otherwise isn't sufficient force on the seal lip.
>>>
>>> Sean
>>>
>>>
>>> On December 5, 2016 9:06:33 PM MST, Cliff Redus via
>>> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>>>
>>>> I can give you my experience with the seals on the Minn-Kota 101 I have
>>>> on the R300.  Much of this was covered in my Psub presenation at Watkins
>>>> Glenn earlier this year.
>>>>
>>>> The OTS Minn-Kota lower unit (MK part number 2886289) consist of a
>>>> center section that contains the permanent stator magnets, the plain end
>>>> housing assembly (bow) that contains two radial roller bearing that support
>>>> the shaft and armature assembly, a brush end assembly that holds the
>>>> brushes, a bronze flange bearing and two lip seals with a carboard spacer
>>>> between them each oriented to expect higher external pressure than
>>>> internal.  There is a static o-ring seal between the center magnet section
>>>> and the plain end housing assembly.  On the brush end assembly, the dual
>>>> lip seals are design for approximately 10 feet submergence but have been
>>>> known to work to a depth of about 30 ft.  To modify this MK-101 for the
>>>> four thrusters on my boat, I reverse engineered! the brush end assembly so
>>>> that I could machine a replacement  brush end assembly that beefed up the
>>>> part so that I could screw three 316-SS supports to hold a nylon MARLIN
>>>> Wageningen nozzle 37.  This modify part was made of 6061-T6 and hard
>>>> anodized.  This new part uses the same two lip seals in the original part
>>>> design and the same static o-ring seal beween the brush end addemlby and
>>>> the center section.  In the nozzle that is welded to the center section
>>>> that the two 10AWG conductions exit from , I inserted a 316-SS adapter that
>>>> would accept a Subconn BHB2M bulkhead connector and a Swagelok 1/4" NPT to
>>>> 1/4" tube fitting.  I use a single pressure reducing/ releaving regulator
>>>> that Hugh Fulton specified for his Q-Sub for air pressure compensation of
>>>> all four thrusters.  The regultor is adjustable and I have mine set to hold
>>>> a pressure of 4 psi over ambient water pressure.
>>>>
>>>> For both the original MK-101 brush end assembly and my modifi! ed
>>>> version, there is no barrier fluid other than air beween the two lip seals
>>>> and their is no compensation line.  As Alan mensioned in an earier post, it
>>>> is likely that this arrangement would cause the the outer lip seal to
>>>> collapse againsit the cardboard spacer beween the two lip seals because the
>>>> initial pressure beween the two seal is initially 1 atm.
>>>>
>>>> On Jan 24th this year I took my boat to Lake Amistad and did a manned
>>>> dive to 155 ft. I had no issues with the thrusters either before or after
>>>> the deep dive. They worked great. When I was ascending from the deep dive I
>>>> did note that the pressure regulator was releasing air from the thrusters.
>>>> When I disassembled the thrusters after the dive, they were all dry.
>>>>
>>>> As to Sean's idea of using a positive bias pressure inside the thruster
>>>> and filling the space beween the two seals with oil that has ambient
>>>> pressure via a compensation line, I think this could be done fo! r both the
>>>> original MK-101 brush end assembly and my modified version.  Might be
>>>> tricky to machine the hole beween the two lip seals but I think it might be
>>>> possible.  Not sure how you would keep the oil place as there is no room
>>>> for a bladder. Might be able to use some kind of plug that would transmit
>>>> ambient water pressure to area between the seals.
>>>>
>>>> Before I take my boat out again, I am going to call the  *Parker
>>>> Hannifin* guys and get their take how to modify this seal
>>>> arrangement. In the spirit of KISS,  I am leaning towards just removing the
>>>> outbound lip seal and relying on the pressure compensation system and a
>>>> single lip seal. We don't put a lot of hours on this seal so duty cycle is
>>>> light.  A single lip seal with pressure compensation might be all that is
>>>> required.
>>>>
>>>> Maybe we c! ould get Jon to post the PP file on the MK 101 thruster
>>>> project to the PSubs web site.
>>>>
>>>> Cliff
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>   Late year I reverse enginnered
>>>>
>>>> On Mon, Dec 5, 2016 at 8:01 PM, Sean T. Stevenson via
>>>> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>>>
>>>>> Do the Minn Kota motors have! a dual seal arrangement that would
>>>>> permit you to run a compensation line to the void between the two seals? !
>>>>> I am not familiar with their design. In designing mission critical sealing
>>>>> arrangements, I have always stuck to the rule of thumb of using any single
>>>>> seal to change fluid, or to change pressure, but not both simultaneously.
>>>>> Thus an ideal arrangement with dual seals would be to run bias compensated
>>>>> oil in the housing, unbiased compensated oil in the volume between the
>>>>> seals, and then the seawater outside. This way, leakage across the inner
>>>>> seal is immaterial because the fluid is the same, and leakage across the
>>>>> outer seal is unlikely because there is no delta-P.
>>>>>
>>>>> Sean
>>>>>
>>>>>
>>>>> On December 5, 2016 3:58:49 PM MST, Alan James via
>>>>> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>>>>
>>>>>> Rick,
>>>>>> one method Psubbers were using to compensate thrusters was to have
>>>>>> two nipples
>>>>>> in the thruster with a piece of PVC tube leaving one, wrapping around
>>>>>> the thruster
>>>>>> & joining the other. The idea being that the oil filled PVC tube
>>>>>> compressed to equalize the thruster.
>>>>>> It's easy to squeeze the tube with your fingers, but when you have
>>>>>> water pressure
>>>>>> squeezing evenly, it's collapse pressure! is quite high. Also lights
>>>>>> are compensated like
>>>>>> this with the wiring running through oil filled PVC tu! be from the
>>>>>> back of the light fitting
>>>>>> to the through hull. Again, the tube needs to be crimped to initiate
>>>>>> it's collapse.
>>>>>>    With the addition of a bladder there is no need to worry about
>>>>>> this, as the bladder collapses
>>>>>> easily. If you semi fill the bladder then it can take any expansion.
>>>>>> As long as there is enough
>>>>>> oil in the bladder to cover the compression of any air at the depth
>>>>>> you are going, then
>>>>>> you could have quite a bit of air still left in your thruster. But
>>>>>> the ideal is to have
>>>>>> as little as possible.
>>>>>>    I know Cliff mentioned the problem of the dual seals when he was
>>>>>> doing his Minn Kotta
>>>>>> modifications. I think he built a new end section to the motor, but
>>>>>> aren't sure.
>>>>>>    I have heard that the Minn Kotta seals are rated to 15-30ft but
>>>>>> have been tested
>>>>>> to over 100ft in some cases. I have only looked at them from an
>>>>>> obscure parts diagram.
>>>>>> There may be such a small void between them that it would be a non
>>>>>> issue if the seaward seal
>>>>>> fails. Sometimes in thrusters with dual seal arrangements the seaward
>>>>>> seal is regarded
>>>>>> as sacrificial because it sees all the grit! etc.
>>>>>>    Today I am emailing manufacturers to try & find a cheaper version
>>>>>> of the Parker PR364
>>>>>> relieving regulator that Cliff is using for compensation.
>>>>>> Cheers Alan
>>>>>>
>>>>>> ------------------------------
>>>>>>
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>>>>>> Personal_Submersibles at psubs.org
>>>>>> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles!
>>>>>>
>>>>>>
>>>>>>
>>>>> ____________________________________________! ___
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>>>>> Personal_Submersibles at psubs.org
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>>>>>
>>>>>
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>>>>
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