The US rep for Permatrims (shipyardisland.com) had no info about Permatrims and broaching in following seas, but here's what the manufacturer of Permatrims (in NZ) says about broaching in following seas:
Permatrims work differently to trim tabs and should not make a boat more susceptible to broaching in a following sea, they will help to stop your boat from broaching by giving your more trim control so you can hold your bow up, this is one area were permatrims differ from trim tabs, trim tabs cannot lift your bow only lower it.
I hope that helps explain the difference. If you need any more info please email me and I will try to help out.
Thanks for your enquiry.
Regards
Colin Chapman
I did some research on the Net, but couldn't find anything directly linking trim tabs (or accoutrements like Permatrims) to broaching in following seas, but numerous references (Bennett and Lenco owner's manuals) state that trim tabs should be kept up (retracted) in following seas "to improve handling" and/or to prevent the bow from "digging in" (to the next wave). My personal experience is that extended trim tabs in large following seas (6-10 feet) WILL cause a boat to broach -- and it happens very violently and rapidly, without warning and is uncontrollable. Colin's point above makes sense. If kept trimmed down in a following sea, a Permatrim equipped outboard should function to really keep the bow up - important to prevent digging in to the next wave...