Rounded Bow Modification and Navigator Progress
(also read: Micro “Oink”, conversion to Navigator)
by Don Baldwinson  oink@paradise.net.nz 

Before hauling out to build the Navigator conversion, “Oink” had suffered damage while lying neglected on an exposed mooring. Thousands of slaps and bangs under that flat bow had caused ongoing damage, culminating in the mast coming down due to wear around the fid and mast step. Extra inertia caused the tabernacle supports to rip out the top layer of the marine ply side, and down she came, splitting the main bulkhead clear across. There are often posts to the Bolger Group,

Micro "Oink"
Oink as originally built

requesting ways to reduce flat bow slaps and gurgles, which keep people awake at night, and it seemed to me a permanent solution was best, and now was the time to do it. By the way, the flat bow is fine while sailing, and people with less difficult conditions have no problems with damage, except getting some sleep!

A false rounded bow underbody seemed the best answer. I wanted to leave the ply bottom in place so she would stay in shape, and first thought of a molded ply fabrication, but this would have been difficult because there would be no access to the upper side. A solid lightweight shaped addition appeared to be more practical. Bolger has shown ideas for solid timber shapes glued in place for larger boats, but their roundness was limited and probably inappropriate for lightweight Navigator. Newer designs have sacrificial ply bow extensions filled with foam, and this would be a very good method for a new boat. Styrene and epoxy, surfboard style looked practical for my situation, and questions to rec.boats.building popped up some very helpful advice from a surfboard maker in Asia! Ah, the miracle of the Net.

Round bow keel framing
stem piece first then keel battens
 faired to hull with fitted hardwood deadwood infill

To achieve a rounded softer entry, one is limited to the space between the existing chine line, and a new lower keel line; any deeper and one would end up with a Yorkshire Coble, and the bow would take charge of steering the boat. Measurement showed I could add onto the existing bow, a new stem, extending 250mm (10”) below the present stem/chine/bottom, and a keel line could run aft and blend with the deepest point of the existing chine/bottom. The stem was glued in place first, followed by a false keel, 150x20 (6”x1”), slotted to fit the existing keel and tapered to the new stem. The space left was filled with solid deadwood as pictured.

Blue Styrofoam in sheets was the recommended base material, because it can be epoxied without melting. The first sheet, 35mm thick, was glued flat against the ply bottom for the full length of the new shaping, and subsequent sheets were shorter each time to match the new bottom line, and to reduce wastage. Epoxy was used for bonding the first layer to the flat ply bottom, and here the most difficult part of the whole operation reared its head - working on your back applying glue, goo and pressure upwards. All epoxy had to be thickened to stay up. A system of cross-timbers, vertical struts and wedges gradually forced the gluey sheets (one each side) firmly into place, but it was a real struggle, involving every curse known to civilised man. As one wedge was tapped into place, inevitably the previous wedge, or two wedges ago, strut and caboodle would drop out, due to the flexible 6mm ply of the original bottom. Every one of the 40 wedges on each side was re-jigged 2 or 3 times. Then when I had finished, struggled out and leaned against the boat in relief, the whole damned ship swayed and nearly toppled! She was now floating above the cradle on many little hands. I was very relieved when the epoxy set and the boat could be sat down again.

Round bow fairing
Sheets stepped towards bow to follow keel line
and glued with contact adhesive for easy fairing.

The first life-saving tip from my surfboard friend came next – fix subsequent layers of foam with contact adhesive, never epoxy. Fairing is fun enough, without hard lines of glue sailing across the fairing lines. One quickly learns just how soft the foam is. Even a swipe with the back end of a plane will gouge a chunk out. Contact adhesive worked well, but you must force yourself to wait for the glue to “set” before you place the sheet, as the manufacturer states. And when it is ready, the sheet must be held exactly square before pressing upwards, because you get only one chance. No clever sliding fits! But with care it went well.

Round bow roughly faired
Faired with saw electric planer
and sandpaper boards

Fairing. Uggggggh!!!!!! Sawing the side projections took seconds. The rest took hours and hours and hours. I tried all possible tools, and found the best tool to form the basic shape was an electric hand planer. I hate this effective but most dangerous of electric tools, and swinging the plane above my face, blinded by a snowstorm of blue confetti was no fun at all. But very effective. It shaped cleanly with little tearing, though if the day had been windy, the whole neighbourhood would have been blue! Earlier, I had drawn a measured and faired drawing of how the bow would be shaped. In the end it was all too difficult, and I threw the drawing away and shaped by eye. This was not as hard as it sounds, because the layers of styrene could be faired evenly by comparing the curved joints on both sides – rather like shaping a plywood centreboard. Sanding blocks and boards were tried, but were not greatly useful because of the tight curves in this bow region.

The second life-saving tip came next – don’t try and fair the styrene to perfection before filling, glassing and epoxying. It will drive you mad, because you will damage the surface everytime you go near it, and cause further damage trying to correct the first damage. If you try and fill raw styrene, the softest filler is denser than the foam, and sanding rips away the surrounding styrene, leaving a lump of filler! When the shape is reasonably fair, with no major lumps and bumps, coat the foam with epoxy and glass cloth. This gives a firm base to which you can then apply and sand filler. Overhead glass and epoxy was another trial by fire, but I got there in the end.

Round bow faired
You cannot completely fair the foam because it is very soft.
A nudge with the plane will dent it

First I epoxied wide tape along the chines and keel, in case the fairing ever decided to come off in one lump! Two layers of the heaviest cloth stocked by the boatshop were used for the main surface(10oz I think), and two further coats of epoxy. The amount of fairing you can do towards achieving perfection is infinite, and as my surfboard man said, you will know when you reach the balance between perfection and condemnation! For the larger concavities I used epoxy thickened with microballoons, and on wider thinner areas, house type exterior white acrylic paste, applied with a plasterers steel float. I have used this before, and found it to be just as durable as much more expensive and unfriendly materials (epoxy), but only in non-structural applications.

Round bow glassed and primed
Bow rounded primarily to stop noise
and destructive pounding while moored.

I think the bow will work. It is certainly much more solid than before; hitting it with your fist sounds more like a Rolls Royce door closing than a kettle drum! Probably the stem will be an inch or two below water. If not, ballast may have to be added inside to compensate and adjust the trim. If we hit anything, I would expect collision damage to be less than before the addition. The foam may be dented or chewed, but should be easily filled and faired. Extra floatation will be a benefit in the unhappy event of a hull breach.

I also hasten to add that I have not asked, and don’t have the blessing of Mr Bolger for this change; it’s at my own risk. The more I work at changing this boat to meet my needs, the more I admire Bolgers original concept of Micro - extreme simplicity and economy. Every change I make seems to involve yet more sheets of ply and expense. But hey, we are supposed to be having fun.

Other Progress

Top view
windows in roof to come,
rear deck tiller enclosure to come,
extended stern floatation both sides
and future hinged motor hatch

The photo from above the boat shows the main rear deck completed. This space is really just for access and a platform from which to tend the outboard. Bolger intends Navigator to be steered from inside the cabin, where crew weight is best positioned for the trim of such a short boat. My added low deck extension aft, is to provide protection for the motor; also Micro though a tiny boat, when approached in choppy water can be dauntingly high above a small dinghy. The low rear decks should provide an easy boarding point, with the stanchions right there to heave oneself aboard.

I connected the stanchion tops with a hardwood plank, to provide a base for a mainsheet traveller, and to help support my standard Micro mizzen mast. The plan showed a heavier alloy tube, because the chinese mainsail sheets are sheeted to it, but I reused my old mast to save cost. The plans are short on detail about the sheeting in this area, but seem to show them running into the cabin above the rear deck at cabintop height. Stumblebums like myself would be prudent to lead them under the deck and through the tiller slot, to cabin cleats. Angled uphill so water will not run down them and into the cabin!

Front view
gunwale cut down and bow extended, bowsprit for possible extras

The front shot shows the new mast support in place. A fly speck below the yellow boot top is actually a drain from the forward well. The bottom of the well has been lifted towards the rear by floating in an epoxy/concrete reinforced mix. This was to avoid drain tubes through the styrene layers to exit through the bottom, which if disturbed may have allowed water penetration into the foam, and would also be vulnerable to blockage by marine growth. I once bought a 30ft trimaran for a good price, because the owner was sick and tired of mysterious flooding. I later found that an underwtaer cockpit drain would block with marine growth, and at a certain point the main hull filled with a rush through a toilet fitting, sinking the boat down to the level of the bunks.

Next job, the cabin interior and rigging.

Don Baldwinson  oink@paradise.net.nz