Combat Boat 90H, the Hull

This article was published May 17, 2012.

cb90

First things first. I surfed the net, phoned friends and acquaintances, sent emails to people with info about the CB90 on their sites... Early on I had to make my own blueprints, since I didn't know how long it would take to get the real thing from FMV. I printed out the closest picture I had to a blueprint and, after several printouts of varying sizes I decided to split it up in parts so I could get as big a schematic as possible on a paper. After that, out came the pencil and calculator. I knew the correct prototype measurements and compared these with the drawings; thus I could calculate the scale, 1:14. When I knew how much I needed to recalculate all measurements I started to write down the most important ones on the plan.

Templates

Since I didn't have a clue what the frames looked like, I had to give up the idea with a perfect scale model and settle for a robust lookalike model instead of a floating display model. It was not easy, but I had to - I was so eager to start building. My marine modelling skills had been dormant since my teens, I had to start! Getting started, I went down to the kitchen and collected all the old pizza and cake boxes I could get my hands on. Out of these I cut out my frames with scissors and put them together with clothes pegs, then cut out the skin in thick art paper. When I then bent the 'skin' over the 'frames', I could clearly see where they looked rubbish and needed modifications. Heavy work with the scissors and try again, and again... Finally my paper frames looked the way I wanted them, and I could use them as templates for the real ones in 1.5mm aero-plywood. For better stability I glued on balsa spars along the edges. Most big parts were also done this way.

Jig and Preparations

All the jigs I found were too small, and I didn't like the idea of building standing up and adding one tiny piece at the time, as I suspected it to be very time-consuming and error-prone. After surfing around and looking at different jig types, like Graupners, I decided to build my boat upside down instead. This way I was sure of getting a straight deck, and it would make it much easier to add the skin. Instead of adding planks one by one, I could make the skin in only four parts! If my hull had been like a sailboat, with very rounded edges both in front and rear, planking would be a must, but since CB90 has very sharp and straight lines this was OK.

In retrospect, I have realised that I made far too few frames; I have had to add extra wood to hold up the skin. It started with the engines, which I of course should have put together before the hull was done. Since the intakes for the waterjets are rather long and close to the stern frame, I put a second frame after the intake instead of dividing it in two parts with a bar over the engine. Also I didn't know exactly how much space the radio and battery needed, so I estimated. That's something to remember for next time, as well as having both the battery and the radio on hand to measure. First projects always have a very steep learning curve, I think.

Details on deck

I was very early surfing for finished small parts on the net, but not much out there really is alike those parts needed for CB90. So I did starting to make my own. Working in brass is something I done before with my model trains, so this was not difficult for me. All parts except the gun-barrel on middle-deck is done with very simple tools. A small saw-blade attached to my DREMEL, soldering iron, cutting nippers, several small files. Not much more. For the gun-barrel I did go to a friend at the club, who helped me to fix the top-ring with a lathe. All parts are soldered together. Rails, gun barrel, mast and radar will be fixed with screws and the rest small things will be glued to the deck.

I started searching the net very early on for small detail parts, but not much out there is really right for the CB90 so I realised that I�d have to make my own. Working in brass is something I had done before with my trains, so there was no significant difficulty involved. Everything except the foredeck gun barrel was made with very simple tools; a small saw-blade attached to my Dremel, a soldering iron, cutting nibblers, several small files.. not much more. For the gun barrel I went to a friend at the club, who helped me to fix the top-ring with a lathe. All parts are soldered together. Rails, the gun barrel, the mast and radar will be attached with screws and the other small details will be glued to the deck.