Folding Mast - Hollow, Sixteen-Sided (will end up round)

In Woodenboat Magazine #237 of March/April 2014, there is an article written by David McCulloch about building an "In-Mast Hinge" which he has designed and developed. I urge you to purchase a digital issue of this copy if you don't already have it, as Mr. McCulloch has written a good article, and there is an excellent coloured illustration.

 https://www.woodenboatstore.com/product/WoodenBoat-magazine-issue-237-march-april-2014-DIGITAL

David McCollough"s photograph of his "In-Mast Hinge" from the Woodenboat Magazine article. Note the detail in the upper-right corner.

This article inspired a customer of mine to inquire about including such a hinge in a replacement mast for a large, open daysailer he had recently purchased. After some discussion, and an inspection of the boat, I agreed to attempt the project. It was necessary for me to make modified drawings for the plates to fit the mast I was commissioned to build due to its different diameter from that shown in the article.

The location of pivot holes, and the radii of cuts made to all three plates alter depending on the geometry, which is itself dependent on the diameter of the mast. However, this is not at all difficult to work out, and just requires attention to detail.  For those who may be interested, here are some early progress photos: -

One half of the mast being laid up in a female station mould mounted on part of my 12 metre (40 ft)-long bench. The mast is made up of 16 staves, so this half-shell comes from 8 tapered pieces.

All eight staves glued up in the female mould. The first stave was fixed along a marked centreline in the bottom of the female stations, using 18 gauge polymer brads fired from a pneumatic branding gun through the stave and into the plywood edge of the station mould. Subsequent staves were laid up on either side of the "master" and glued using epoxy. The overwhelming reason for using epoxy is that it only requires contact pressure to form a good bond. Careful attention must be paid to priming the gluing surfaces with un-thickened epoxy before applying the thickened mixture. This method allowed me to fire polymer brads into the SIDES of each successive stave to hold it to the one before, because the epoxy did not require clamping pressure. The polymer brads stay inside the shell of the mast, and will of course never corrode. The bradder and polymer nails were purchased from Duckworks. After being glued-up, the inside of the half-shell was given three or four full coats of epoxy to ensure that the inside of the finished mast would always be protected from moisture.

Here is the station mould after the removal of the first mast half-shell. I used adhesive tape applied to the inside  of the cut-out section of each mould to prevent epoxy squeeze-out gluing the mast components into the mould. Alignment of moulds is very important, and you can see the blue chalk-line "snapped" onto the bench surface (now covered with epoxy drips!)

Two half-shells of the mast after being removed from the station mould visible in the top/right of the photo. The outer surfaces are still rough-looking due to epoxy marks. When first removed from the mould, the half-shells had lots of thickened epoxy squeeze out, which I largely removed using a heat-gun and scraper. Any gaps were filled with additional epoxy.

Here you can see the two shells clamped together with cable-ties and hose-clamps. The extra length of the staves has been roughly cut off using a handsaw and you may just be able to see that there is no glue on the opposing faces of the two shells. Note the heavy layer of sealing epoxy on the inside of the hollow mast.

This is a similar photo, but taken from the mast head. The trimming of the extra length  was done quite roughly, and the un-glued faces of the staves still need to be sanded to remove dags of cured epoxy, so the gaps in the un-glued faces are a bit open. This will change prior to final assembly. Note that the taper of the mast resulted in a reduced outside diameter, but the thickness of the staves has reduced as well. The idea is to keep the percentage wall thickness of the mast constant at about 20% of the diameter. This is something which can't normally be done with a "Bird's Mouth" mast. (see photo below)  

An off-cut from the tip of  "Bird's Mouth" mast I made. a while ago. Note how the wall thickness, which started off at the base being 17% of the diameter, has ended up being so large it almost makes the mast solid.  Compare with the previous photograph.

Three stainless steel plates to make up the hinged section of the mast (refer to the inset in the David McCulloch photo at the beginning of this post to see how this works). These plates are quite heavy, with the outer pair being 6mm thick, and the inner one being 8mm. I had these laser-cut, which saved a lot of time, and was not expensive.

This sketch shows the stainless steel plates extended and folded. The black lines depict the 8mm plate which is buried for half of its length into a solid mast stub which runs from a mast step near the keel to a short distance above the deckline of the boat. The red lines show the two 6mm stainless steel plates, which are fully buried in the base of the mast you can see in this article.

Here is a close-up of the insert from the heading photo in David McCulloch's article in Woodenboat Magazine #237.
 https://www.woodenboatstore.com/product/WoodenBoat-magazine-issue-237-march-april-2014-DIGITAL 

There needs to be a solid section at the base to hold the stainless plates. On the free-standing hollow masts which I normally make, I always insert a solid section from the base of the mast, to a reasonable distance above the mast partners. In both my normal free-standing mast inserts, and with this one, I terminate the solid insert with what is often referred to as a "Swallow Tail", the purpose of which is to ease the transition in stiffness from where the mast is solid (i.e. the hollow shell combined with the solid inset) to where it is a hollow shell. Here is a view of the early stages of the solid insert for this mast.

As you can see, there is the "Swallow Tail" section, and at the base, a cut-out slot to accept the stainless steel plates and an 8mm hardwood inset to hold them apart and allow the 8mm tongue of stainless from the mast stub to fit between. At this point I have planed a square blank into an octagonal section - it is on its way to becoming round!

At this point the blank has been planed from octagonal, to 16-sided, and them planed further to 32-sided, and then hand sanded to a round cross-section.. All of this sounds complicated and difficult, but if you start with an accurately cut square blank, and then mark carefully for the 8, to 16, to 32-sided planing work, you'll find that the work goes quickly, and is actually a satisfying and relaxing job. As with most boatbuilding work, it just a progression of simple steps. I can tell you I'm finding it more difficult to describe than it is to achieve on the bench. Other than the initial sawing of the square blank, I did all of this with a low-angle block-plane you can see in the photo before this one. It did not take long.

The hole you can see drilled through the filler block at the apex of the "Swallow Tail" is just something I do to prevent a crack propagating from the apex. This may be an over-kill, as the block will be contained within the mast shell anyway, but it only took a moment to drill - so better to be safe than sorry... 

Here is where the stainless steel plate assembly will eventually reside. Matching slots will have to be cut in the mast shells.

Checking the fit of the insert. The actual fitting will be done with the two half-shells of the mast opened up, and the plug will be laid into a bed of epoxy in one half, before the pair of shells are finally glued together to form a round, tapered mast. The tip of the mast will receive a similar (but smaller) plug to distribute loads from the shrouds and fore-stay, and to carry the attachments for the halyard blocks

I'll write more about this interesting folding mast experiment as the job progresses.

View from my office

I've had a few exhausting days of work lately, and a lot of it hasn't been fun - just hard, messy, dusty and physically demanding labour.

But tonight after a shower, a drink, and something to eat I glanced at this sight from the verandah outside my office. Gentle rain falling in the darkness - sort of makes it all worthwhile...

She is 15 years old, and has encountered many hurdles in her life. She has been back to my workshop plenty of times, but she still looks great to my eyes - especially in the quiet of an evening after hard work.

Some of Phil Bolger's designs are an acquired taste, but none of his work should ever be underestimated - particularly those designs up to around the mid to late eighties. Trust me when I tell you that Micro is a masterpiece of design. It is such a pity that so many people fail to understand the subtleties. As Phil Bolger said about the designs of L. Francis Herreshoff, and William Atkin said about his own work -  do not ever alter anything - build exactly to the plans - that way you keep the treasure.

More Detail on the Micro Repair

My recent post http://rosslillistonewoodenboat.blogspot.com.au/2015/04/micro-repair.html about repairs to a Phil Bolger Micro generated quite a bit of interest, and the following comment from Dave is an example:-

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. 

Well, after taking initial photos of the damage, I didn’t many more during the repair process, simply because of time pressure – but here is a brief look at some aspects of the job: -

Initial job was to do a rough paint removal around all of the damaged areas to get a clearer idea of the extent of the damage, and to remove components/timber which had been destroyed. It also allowed ventilation and thorough drying.

Initial job was to do a rough paint removal around all of the damaged areas to get a clearer idea of the extent of the damage, and to remove components/timber which had been destroyed. It also allowed ventilation and thorough drying.

A small puncture wound on the forward/starboard topsides on the outside, and

....the corresponding spot on the inside

Brutal removal of paint, damaged timber, and broken epoxy fillets 

Brutal removal of paint, damaged timber, and broken epoxy fillets

Paint removal from around the forward bulkhead on the interior of the cabin, where the floorboards had punched through.

Most of the work shown above was done using a heat-gun and a variety of sharp scrapers. The paint was all two-part epoxy primer/undercoat and two-part polyurethane topcoat (I know, because I built this particular boat myself fourteen years ago!) and removal was not ever going to be easy. However, the heat-gun and scraper combination is a good choice as long as you are very careful about never overheating the material and damaging epoxy adhesive and paint in locations which are not part of the repair. Other primary tools include chisels, 4" angle grinders, drills, sandpaper - and elbow grease!

Next stage was to carry out a more gentle sanding  using (in this case) a 5" random orbit sander, going down through the grits to about 120 or 180. On the internal areas, the job is more difficult to achieve, and I made heavy use of a Fein Multi-master detail sander and plain, simple sandpaper on a sanding block, or folded triple. Hard work!

See above comments

See above comments

I don't have many photos of the next stage, but it mainly involved pulling usable components back into position using a variety of improvised tools such as lengths of purpose-cut steel angle-iron with holes drilled at strategic locations, and also temporary through-bolts and backing pads. This work can be very satisfying if done properly, and with attention to detail. The key is to have an open mind, and to be prepared to be bold with your surgery.

Once I was happy that my bracing would all work, and that all interfering debris was removed from joints, I opened the whole lot up again, and even spread damaged components further apart (using wedges and chisels etc). With the components held apart, it was relatively easy to treat all surfaces with un-thickened epoxy resin and hardener in order to prime the mating and damaged joints using disposable bristle brushes. This is a very important step if you expect to achieve a good structural repair. With the work area well primed, it was then a matter of applying a rich mix of epoxy/hardener combined with the recommended structural glue/filleting powder additive.

With the structural epoxy  mix worked into all joining areas, I screwed, bolted, or clamped the repaired sections together, which is why the previous work dry-fitting the bracing and jigging was such an important step. Where appropriate, I applied structural epoxy fillets at the same time.

The above two photos show steel angle braces screwed into position over the epoxied repair. In the case of Micro I had the luxury of using straight sections of steel to hold things in place, but on more conventionally shaped boats the same thing can be done using shaped and bent timber splints. I'll show an example of this in an up-coming post on a Whitehall repair.

Interior shot of the repaired bow transom, topside planking, and forward bottom planking. This was taken while the initial epoxy work was still wet and ugly. This work was followed by additional cosmetic epoxy filling.

Exterior shot of the starboard, forward topsides repair taking place. The actual puncture damage is quite a small spot underneath the centre of the plywood pad.

Matching plywood pad on the inner surface of the topside panel. As you can see from the exterior shot above this one, I placed twelve screws through the hull and into the internal plywood pad and pulled them in tightly over the epoxied repair. Note that both pads have been covered in a film of plastic to prevent them being glued to the hull permanently. All of those screw holes had to be repaired later, but the repair turned out well. The plywood pads were large enough to take up the curve of the topside planking when screwed together.

Structural work complete, glass applied where required, fill and cosmetic work done, and the two-part epoxy primer/undercoat applied (the white paint - three or four coats)

Topcoat (two-part polyurethane) applied, with just some minor black line work to be done between the green topsides paint and the off-white bottom paint (that is my little step ladder relected in the paint by the way).

Because of a lack of photos, time and space, this has been a very brief overview of the job, but it may give you some inspiration. Unfortunately, I have no photos of the way I repaired the forward watertight bulkhead of the cabin - a job involving more steel angle bracing and numbers of temporary through-bolts, nuts and fender washers.  In a post in the not too distant future, I'll show the repair of a glued-lapstrake Whitehall tender which suffered very serious damage to her hull in an accident. Most people considered her a write-off, but we were able to give her a new life.

Just a word about repairing screw and bolt holes. Many people simply fill the holes with thickened epoxy and sand the surface smooth after curing. I do not do this because the "cylinder" of hard epoxy in the screw hole intersects the surface of the repair at 90 degrees, and is sure to result in a circular crack in the paint after cycles of expansion and contraction due to temperature changes over time.

My approach is to heavily chamfer the hole on the inside and outside surfaces using a wide countersink or by dishing-out the surface using a sander. Then I fill the hole and the chamfered areas - this gives much less of a stress-riser where the epoxy fill intersects with the surface. However, if the repaired holes are going to be covered with a layer of fabric set in epoxy, this step is not necessary.

Several Videos added to bottom of Website Footer

I've added several videos to the bottom of the listing on the video page of my website - see video link on the footer of the home page.

Image Galleries on Website

After a lot of time spent learning about the intricacies of the dashboard on the new website, I have now been able to expand the list of picture galleries, and I have some images on every gallery.

This is very time consuming due to my ignorance when it come to working with Wordpress, but I have made significant learning progress over the last couple of days, and the site content will continue to grow.

The next thing I'll be doing is getting captions onto the gallery images, but it will be a gradual process over a week or so. Also coming in the near future will be extra pages in the 'Designs' section.

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.

Website and Blog - Making Progress Slowly but with Determination!

Those of you who have been patient enough to be checking back to see how progress is going on the new website and the blog deserve an explanation about what is happening.

Due to an excess of work and looming deadlines, I've been caught between devoting time to the workshop and to development of the new website and the blog. Jobs in the workshop are well in hand (and must take priority), but by September my contracted work will be complete, and I'll then be turning my attention to fun jobs in the workshop, and lots more writing and design work. With good luck and sensible management, this should result in lots more articles and the publication of a stack of designs I have sitting in the wings waiting for finishing touches. Yes, I know you may have heard me say such things before, but I really am ploughing through the work at the moment, and I have for many months now had a moratorium on taking on any new building/repair work.

Tomorrow I'll post some photos of recent work, and a list of current jobs. One particularly interesting project is the building of a sixteen-sided mast for a large sailing dinghy. This mast is unusual in that it is not only hollow, but the wall thickness tapers as the mast tapers, so the wall-thickness as a percentage of mast diameter remains constant. Another interesting feature of this mast is that it incorporates an 'in-mast' hinge - sort of like a tabernacle without a tabernacle (see Woodenboat Magazine #237 for the idea)

Here is a slice off a test section of my mast construction method. There is a very good reason for the angle being cut into one side of each stave, rather than half the angle being taken of each side as they used to do it in the old days. Maybe I tell you why some day...

The sixteen-sided method is probably too labour-intensive to be practical without a production set-up, but the experiment has provided me with valuable insights, and has been R&D time well spent. Maybe eight-sided next time? The method does have advantages over the Bird's Mouth method, mainly in providing the ability to taper wall thickness as well as diameter - all in a home workshop.

I'm just beginning to come to grips with some of the complexities of the website program and associated plug-ins, so there will be gradual (but accelerating) addition of content and pages. Further down the track will come video tutorials on some interesting stuff.

Facebook and Twitter have me somewhat stumped at the moment, but that will improve with time - especially after workshop commitments are complete.