Where can I find the serial number on a late 1980's Nacra 5.8?

The number is not on either hull at the stern. We have looked in every logical place. The original owner said to "look on a hull under the trampoline". Huh? Any help will be greatly appreciated!
on one boat i had, the hull number was impressed into the hull in the curved recess underneath the rear crossbeam. you have to unbolt the rear beam and lift it up to see it. it seems to me that it was on the port hull (under the beam) while a second typical location was on the top rear of the starboard hull near the outside edge.
j

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Aquacat 12 (sold)...'87 Nacra 5.8 (sold)...'03 Nacra Inter18 (sold)
Venture 15 (sold)....'89 Nacra 5.8 (sold)...'91 Nacra 5.8NA (sold)
'99 Nacra Inter20 (sold)
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My 5.7 is etched under the rear crossbeam also. Could have been painted over a few times too.

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Dave Bonin
1981 Nacra 5.2 "Lucile"
1986 Nacra 5.7 "Belle"
Winnipeg, Manitoba, Canada
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Thanks very much for the responses!