Knot Yet... if I remember correctly you ended up with a 5.4m Searider. Are you planning to do much cross channel / fog / night stuff? Whilst I think you should go prepared for fog etc anyway (horn, passive reflector etc), my gut feel is that an AIS transponder (2way) or Active Radar Reflector (e.g. SeaMe) is a significant chunk of cash... 10% of the purchase price of your boat? for something that you will probably not use in anger? Unless you are planning to regularly make night or fog crossings of busy shipping lanes.
If I was spending someone else's money on a medium sized boat (too small to fit your own radar to) I would go in this order:
- Echomax style Passive radar reflector mounted on your a-frame. Lets other people with Radar see you.
- AIS receiver that feeds into existing chart plotter. Lets you see other large vessels and take defensive action.
- Active radar reflector - to make sure you show up on the ship's radar.
- 2-way AIS transponder.
In reality most boats your size will only have a cheap (i,e, not the echomax one) passive radar reflector.