My Nighthawk IOM

Already owning a Marblehead yacht that I built over forty years ago, I joined a local radio model yacht club.

The predominant boats being sailed were IOMs. I soon found out that my old MH was no match for the lighter, slimmer IOMs. What was I to do about it? Being a model builder, I was not going to spend the many dollars needed to purchase a new or even a second-hand yacht. 

I was made aware of a kitset, plywood construction, IOM. Then I learned that the cross sections and full-size side panel shapes were available on this forum, post 87. Now armed with an A0 print out of the panels, and a sheet of 2mm plywood, already purchased for another project,      I made a start.

The panel shapes were pricked through the print onto the plywood, and roughly cut out using a hand saw.

A sanding disk was then used to bring them to their correct shapes. Left and right side panels were done as a pair, held together with double sided tape.

An indication of the required edge bevels was given. I did these with the disc sander too, but put more bevel than was needed in some places. I became aware of this when I started to assemble the panels.

The bow piece, transom and a mid profile were mounted upside down on a base board. Each panel was temporarily screwed to the transom and bow piece, and held in place with rubber bands at the mid profile. Masking tape was then used to hold the joints together, while super glue was run into each joint.

Some of the temporary screws had to have their heads ground off; the glue did too good a job. This was a messy process, and I got stuck by the glue on a number of occasions. It’s amazing how far it will run. I should have worn gloves.

When taken off the base board, it was all one piece; however, the gunwale line was a bit uneven in plan view. To rectify this, I constructed a plywood sub deck, with most of it cut away, and glued this in.

In hindsight this was a bad move, and added unnecessary weight. Gunwale strips with some cross members would have been lighter.

The internal hull seams had been glued with Gorilla, Bond It On, which I found out later is only water resistant, not water proof!

A number of coats of a clear sealer to the inside of the hull will hopefully keep water away. The fin box and mast step were assembled and glued in with epoxy glue, as was all future gluing.

I liked the look of a curved cockpit, so developed a cardboard template for this.
It’s amazing how much bend is attainable in the ply with steaming.

The fore deck was cut out, only partially cut through at the centre angles. I used a longer pot life epoxy for this.

The aft deck was similarly glued on with the hatch holes pre cut. Recesses were created for the hatch covers to sit into.

I was disappointed with the surface finish of the plywood. It took a lot of finishing off. Also, in some places the chine lines were not smooth curves. I had to do considerable sanding along them to get true curved lines.

The rudder was laminated from three layers of ply. The changing layers within the ply help when shaping the fore and aft profiles. The middle layer was cut out to take the rudder shaft.

The fin, also laminated from three layers, has an aluminium strengthening section inserted down its length. The overall stiffness of the fin is a bit lacking.

The winch is out of my MH yacht and is probably heavier and slower than what is available now. It weighs 217gm.

Once again, I added more weight than needed. The battery box and servo support are overkill.

The copper tube for the return winch line.

Push button on/off switch, return line, shroud attachments and mast slot.

I have made keel bulbs before, so decided to make a wooden plug and casting boxes. Two pieces of wood were temporarily bolted together to give the two halves required.

A friend’s lathe was used to turn the bulb shape.

The dimensions were scaled from an A4 print out of the yacht elevation. Post 160.

Final hand shaping and dowelling finished the plug.

The molding process was a bit messy. I spilt some of the lead, and ended up with an incomplete fill.

I managed to top it up, but had to screw the two pours together.

Because the back end of the bulb is very narrow and soft, I turned a brass piece to insert into the cut off end.

The A rig is all home built. Aluminium tube from the local hardware shop, and sail material, A2 sheets, from a drawing supply shop. The jig made for sail shaping.

The completed yacht was about 200gm over weight, (4200gm) certainly not what I had intended. No provision for balance weights. The use of 2mm ply probably did not help.

I have shaved 100 gm off the bottom of the bulb.

The fin and bulb now weigh 2410gm. The centre of gravity of the whole yacht was too far forward, so I have moved the bulb backwards 25mm on the fin. Flotation is now better.

I am currently considering ways to reduce the hull weight as much as I can. These include cutting out part of the fore deck on each side and covering the holes with sticky-backed vinyl. While I am doing this, I will remove as much surplus ply from inside the hull as I can (the sub deck). Also doing away with the plywood hatches and as much of the aft deck and sub deck as I can. Vinyl will replace these areas too.

I will report on the results of this, once completed.

The bow being lightened.

The finished hull

Part weights as measured.