Ding, ding, ding, we have a winner - or at least a well narrowed down 
time frame.
To summarize:
1981 advertised but not quite available yet at least not when Mike 
purchased his 1981.
1983 Chris Geankopolis purchased ENOSIS with IMF

Note that not all boats had IMF once it was introduced - it was always 
an option. I believe some recycled boats may have started life with 
standard and then when recycled became IMF and possibly vice versa.

Mary Lou
ex R22
now Rosborough RF-246

On 7/16/2019 12:33 AM, Chris Geankoplis wrote:
> My 83 not refurbished has imf. Replaced all the plastic parts 10 years ago
> , still going strong.
> Chris Geankoplis
> ENOSIS
>
> On Tue, 16 Jul 2019 at 04:14, Shawn Boles <shawn.sustain at gmail.com> wrote:
>
>> I have a refurbished 86 with IMF.
>>
>>
>>
>> Cheers
>>
>> Shawn
>>
>> s/v Sweet Baboo
>>
>>
>>
>> On Mon, Jul 15, 2019, 6:58 PM Stephen Staum <snstaum at gmail.com> wrote:
>>
>>
>>
>>> My ‘87 had IMF, my ‘83 did not.
>>> Stephen Staum
>>> s/v Carol Lee 2
>>> On Mon, Jul 15, 2019 at 6:18 PM Mary Lou Troy <mtroy at atlanticbb.net>
>>> wrote:
>>>> There is a brief history in the FAQ on the owner's site. At the time
>>>> someone speculated that IMF was introduced in the 1980s.
>>>> http://rhodes22.org/blew_skies/history.html
>>>> Our boat was a 1991 and I always thought IMF predated her. by several
>>>> years, so maybe mid-to late 80s?
>>>> Mary Lou
>>>> ex- Rhodes 22
>>>> now Rosborough RF-246
>>>> On 7/15/2019 5:25 PM, CKLang--- via Rhodes22-list wrote:
>>>>> I looked on the website, but couldn't find the answer.CynthiaSent
>> from
>>
>>>> my Samsung Galaxy , an AT&T LTE smartphone
>>>> ---
>>>> This email has been checked for viruses by Avast antivirus software.
>>>> https://www.avast.com/antivirus
>>>> --
>>> Stephen Staum
>>> Pariser Industries, Inc.
>>