There's quite a number of free plans and kits... just keep searching.
I attach a zip with two Autocad files, just to give you a clean start. As for kits, contact this guy, he makes one of the best tunnels out there:
http://www.ml-boatworks.com/Page.asp?n=54897&snid=dKOE_6L4^&org=ml-boatworks.com

thanks for the files CornelP and i've been peeking at the ML boatworks site and drooling at the tunnel kit. it does look a bit big for my needs at the moment but if this obsession continues to develop who knows!

oh dear i've now started looking at outboard units, if i'm going to go tunnel i might as well do it properly!

has anyone used one of these before?

HOR Aluminium Outboard leg with outrunner motor.

Machine billet aluminum outboard drive with Topstar AE2815HL450-02A out runner motor. For use with 1/8" or 3.17mm unthreaded propeller with overall dia. less than 40mm

Motor spec:
Continuous Current(A) :38A
Output Power :420W
Voltage(V) :11.1V
KV: 3450



https://astecmodels.co.uk/catalog/pr...cffcf54d77960c

from reading a lot of posts the quality of outboard legs seems to vary wildly, no idea if this one is a lemon?!

Offshoreelectrics was selling these (or very similar), and seem to have good reviews.

another weekend, another sacrificial plastic coupling ready to snap! can't seem to find a metal 3mm to 3.2mm coupling, all i can find are various plastic. who knows how long this one with last!

Try here (only in german, unfortunately), you can choose any drill hole option:
http://www.ebay.de/itm/CMT-Alu-Kuppl...item7b6b94dd73

CornelP, has a full range of knowledge on rc equipment and is well respected.--- Ok, here's what i did on a 400 ADS watercooled motor with a 3 diameter motor stem. Now a gentleman on HK discussion site suggested said this-- use teflon tape used by plumbers and wrap it around the motor stem enough for coupler to slide on, yet make it kind of tough to slide it on and tighten set screw and don't look bback. I did this and under a microscope, it didn't wopple at all on 3S lipo at 33,000rpm. KEEP TRACK OF WHERE FLAT SPOT IS ON THE 3 PORTION .--------Rcraceboat.com site of Jeff Wholt makes couplers-- USA--The motor you have is a ADS motor from picture which is 3 diameter, so wrap tape around that motor stem.

thanks for your advice guys,

managed all of three mins today. boat wasn't running as well as last week, maybe i knocked the drive shaft a few degrees at some point or it just doesn't like any wind/chop, felt really skittish and soon blew over, boat flipped and took an hour and a half to drift in marginally better footage this time

object B - Run 5 (2 min 53 sec)