Didnít notice this and half answered this in the current Kolibri Cats thread.
We currently run an Elling tunnel hull sib that has a solid transom, put about 40 hours water time on the open transom Boatworld Katsport 330 we recently tested, and helmed a couple of 340 and 380 Takacats in the past.
Must admit really like the sporty look of the Takacat open transom. Sheds water instantly, no worries of soggy ply and makes the dismantled folded boat more compact. Despite popular belief water does not flood in as the stern wave catches up when stopping.
Downsides would be concerns long term of the tube fixing pockets and only limited to using the OEM transom wheels which are good but on the small side and have heard some welding failures to brackets after a few years.
As open bow cats have to be considered wet boats and rapid water drainage a must for safety, then difficult to fault the open transom solution in this respect. In practice weíve found very little water actually comes over the bow in general use except when launching in surf or playing around punching through large surf at speed. In reality not dissimilar to any closed bow sib.
Iíve no real issues with solid transom cats either if honest. In fact if I was going big bucks on a Kiwi cat then it would be the 4m TrueKitÖaluminium solid transom with a cool permanent rapid drain grill system. No problem either with say the traditional plywood transom on the Kolibriís as Iíd just fit a couple of large dia. transom drains to supplement the woefully inadequate standard bilge drains. A couple of these 42mm jobbies from Ribstore would be more than adequate:
Already fitted a couple of similar smaller diameter drains on our Elling. Open drains on cats, even low on the transom, are well above the waterline and have found not even flooded by the stern wave when coming off the plane.
Also keen to try the Kolibri SeaCat and not phased by the closed transom as easily modified to rapid drain.
Still think the stainless steel open transoms look way cool though.