Thursday, April 2, 2015

Micro Repair

Phil Bolger's Micro design is a favourite of mine, and of many other people around the world.

To the uninitiated, the boat looks somewhat like , well..., a box. The hull cross-section is, in fact, perfectly rectangular - something which leads many observers to underate the design and write it off as a crude and simple piece of work.

Well, Micro is a very simple boat to build, but only a genius - someone like Phil Bolger or Naval Architect C. Raymond Hunt - could design such a hull and make it work well (Phil Bolger was heavily influenced by C. Raymond Hunt, among others). It takes understanding to get the best from Micro and her free-standing cat-yawl rig, but if treated properly, she is an exceptionally good performer, while at the same time being cheap and quick to build, self-righting and self-bailing, roomy, and comfortable - all in a 15-1/2' x 6' x 18" package.

Cricket - a Micro which I built back in late 2001/early 2002.
In this photo you can see some of Micro's unusual features - flat bottom, extreme rocker, and rectangular sections. Very few people could design such a boat and make her a success. Very few people understand why the hull and rig work so well.
I'm not going to go into detail about the design aspects of the boat, but I will say that on one occasion I sailed her against a well-handled Navigator and an equally well-handled Penobscott 14, and even though I had two passengers, we beat both boats to windward, and pointed just as well. Now, the conditions were ideal for Micro, in that we were on a lake with about 10 knots of breeze and almost flat water, but her performance was superb, surprising me as much as anybody. It might have been different in a steep chop....

This particular Micro has been back to my various workshops on a number of occasions in order to have cockpit modifications made, and to have repairs carried out. Most recently, she came back to me after having been in collision (head-on) with a concrete floating walkway/wharf beside a boat ramp.

The damage was fairly localised around the bow transom and forward topsides, but Micro has a wonderful self-draining well, right between the bow transom and the forward bulkhead of the cabin, with a strong set of floorboards filling the space between the bow and the cabin bulkhead. The floorboards are at approximately the level of the painted boot-top (i.e. the division between the green and cream just above the waterline in the photo below).

My youngest boy, Steven, standing in the forward well back in 2002. He is standing on the forward well floorboards.
When Cricket hit the concrete walkway, the point of impact was head-on, almost exactly at the level of the floorboards. This not only damaged the bow transom, but also forced the floorboard panel back through the forward cabin bulkhead with great force. Micro is not a particularly light boat, carrying 195kg/412lbs of cast lead in her keel, weighing-in at around 500kg/1/2 a ton - so the damage was substantial.

Winch post pad covers most of the external damage. The paint is the original Hempel Polybest two-pack polyurethane which I applied in 2002! Notice how the plywood of the topside panels has de-laminated and split away from the bow transom framing. The damage is much worse than it appears.

Photograph of the inside of the forward well, looking towards the bow transom. The two large holes in the transom are the steps of the boarding ladder! (there is a hydrodynamic reason for the transom at the bow, but that is another story). You can see how the bow transom has been driven backwards through the topside panels, and that the framing has suffered serious structural trauma. In addition the planking-to bow transom epoxy fillets have been more or less destroyed.

Looking aft at part of the damage inflicted to the forward cabin bulkhead by the floorboard assembly. The boxed opening at the far left of the photo is the cabin ventilation opening - lets air through but keeps water out...

External damage to the starboard side of the bulkhead after initial paint removal...

......and the same on the port side. Doesn't look too bad, but represents serious structural damage on close inspection from inside and out.

Micro has a primary structure made from 6mm/1/4" marine plywood for the most part, with a substantial amount of 3/4" framing timber throughout in various widths. The boat relies on her large volume and surface area for her structural strength, and is well designed from an engineering perspective. However, like many aircraft, she is structurally strong, but vulnerable to point impacts.

Bulkhead damage

Damage to the bow

Damage to the bow.
The point of this post is to let people know that with careful planning and execution, a wood/epoxy boat can almost always be repaired to as good a standard (or better) as when she was built. Do not skimp on the process and avoid any temptation to "plaster over the cracks" so to speak - attention to structural detail is essential.

I may write more about the repair process use on this boat in a later post (no promises), but here are a couple of photos of the structurally complete repair, with only a few remaining paint details to be finished.

Just some painting to be done over the white two-pack epoxy primer/undercoat visible at the forward end of the keel, and some black boot-topping to be painted as well.
The repair process involved a lot of debris removal, fabrication of simple jigs to regain the correct hull shape, re-lamination of damaged plywood sheeting, plenty of epoxy, epoxy fillets, and glass fabric reinforcements - but the boat is alive and well!

The moral of the story is to build your boat properly in the first place, and repair her with care if the need arises. Have an open mind and be prepared to be inovative and to improvise. There is no reason why a home-built plywood boat should not last several lifetimes, even if damaged along the way. In fact, if you are not under too much time pressure, the process can be both challenging and rewarding.


  1. Thanks Ross -

    A great tribute to well built epoxy/ply boats and their builders.


  2. Thanks, Simeon. It is my opinion that for trailer boats that can be built in a sensible amount of time, quality plywood and epoxy make a potent combination. My own boat (designed and built by my Dad, and subsequently maintained by me and one of my sons, is now 45 years old and going as strong as ever!


  3. Thanks for the blog post, Ross, but you left out the details on the very parts I'd be most interested in seeing!

    So if you do a future post on the nitty gritty details of truing up and patching the damage, I'd be most interested in that.

    Thanks - Dave

  4. Dave, I would have done it last night, but I simply ran out of hours in my working day. My plan is to write a number of short (illustrated) posts about repair work and simple day-to-day workshop techniques. One interesting repair was to a 12-1/2' glued-lapstrake Whitehall which was in davits on the stern of a 12 ton auxilliary , and got caught on a marina pile on the way in. That was an interesting job!

  5. Yes, I totally understand the running out of time thing! I think a series of posts about repair work would be very interesting, and I'm sure others could also benefit from that.

    My primary interest would be how to fix accidents affecting plywood/epoxy /fiberglass boats. I've made a couple kayaks, a canoe, and now SCAMP using those materials, and have not had the occasion to make any major repais, but would like to be prepared with some knowledge in the event it would happen some day.

    Thanks - Dave

  6. This post really helps other boat owners know more about inspecting and repairing their boats. Fixing (or even building) wooden boats could sometime be troublesome and stressful, but with a lot of knowledge and perseverance, one can truly see the wooden boat’s full potential once it is fixed or properly built. Thanks for sharing your experience in fixing your wooden boat!

    Boyd Caldwell @ Hays Hydraulics