From my research it would seem tha a Xebec carried a much larger crew than other ships of its equivalent. This was to enable vastly overwhelming boarding parties and to provide crews for prizes.

To this end I reflected on what would be the result in the ships abilities to fight.

Would the numbers mean that small arms results would be better than a regular ships Marines?
I felt that the numbers of less well trained musketeers would allow about the same fire as a smaller trained body, so left that as it is on the cards.
As Dobbs pointed out, the Xebec hulls were known to be less robust than other warships, so I reduced the hull strength by one.
Casualty rate was more of a conundrum. More men on deck croweded together would suggest a greater attrition rate than a warship with the crew spread throughout the ship, and yet if too many were removed it would prevent the boarding advantage. I looked at a 50 gun ship card which had a crew of 350 as the nearest approximation and saw that it actually differed very little from a 36 Frigate. Crew actions being reduced pretty much in the same way, and crew attrition also similar excepting near the end where the 50 held out a bit longer where it dropped from 3 to two actions. So I decided to leave things alone and go with a regular Frigate's card, but give an extra chit to the Xebec for boarding except after it lost more than half its crew when it reverts to an ordinary number of chits.

Any comments on this will be taken onboard for consideration. However, I do favour the Kiss method when working out the stats.