Thursday, March 17, 2016

Pre-coating Plywood

Recently, I was contacted by Phoenix III builder, Jonathan McNally regarding some persistent cracking he has noticed in his boat where the garboard strake (i.e. the plank closest to the keel) overlaps, and is glued to, the keelson.

Photograph of the keelson of Jonathan McNally's Phoenix III , where you can just see a feint crack in the outer edge of the epoxy fillet on the inside surface of the garboard strake.
According to Jonathan's report, he has re-epoxied this section several times, but the slight cracking keeps coming back. He and I have discussed the matter by 'Trans-Pacific' email, and have diagnosed the problem, tracing it back to (we believe) the high-quality, but unusually flexible plywood used - that is another story.

However, Jonathan's story brings up several matters which I'd like to discuss regarding the use of epoxy as an adhesive, and as a surface sealant i.e. epoxy encapsulation. For those who have missed it, here is a link to a recent blog post I put up about the hull structure of Phoenix III after Jonathan first reported his problem.

Two of the possibilities I had considered in regard to Jonathan's cracking problem were: -

  • perhaps the planks had been pre-coated with epoxy, and when glued into position on the boat, the cured epoxy coating may not have been adequately sanded; and/or
  • the pre-thickened epoxy glue may not have been laid onto a freshly primed gluing surface.
Neither of those possibilities were to blame as it turned out, but they do bring up issues about which people need to be aware.

Epoxy is my favourite marine adhesive by far, although I do make use of a number of other glues for specific jobs. But epoxy is the most versatile adhesive I use, and the vast majority of my gluing is done using epoxy and suitable additives. Epoxy is gap-filling in a truly structural sense, and that is the key to its versatility.

 When using epoxy as an adhesive and/or as a filleting agent it is really important that all of the gluing surfaces be primed with an application of un-thickened epoxy resin/hardener. This relatively low-viscosity application will penetrate the surface of the timber and form an excellent foundation to which the thickened adhesive mixture will bond chemically. For this to occur, the priming application should be applied no more than a few hours before the adhesive, so that it will still be chemically active when the adhesive mixture is applied.

Here you can see how I have primed (or wet-out) two adjoining surfaces prior to laying down thickened epoxy which will be formed into a fillet.

In this photo, the joints on the left have had the epoxy formed into a fillet over the primed surfaces of the joint, and glass tape has been placed over the fillet, and wet-out with another application of un-thickened epoxy. The lady on the right is brushing epoxy through glass tape which has been laid into the still wet epoxy priming coat and the wet thickened epoxy fillet.

On face grain, epoxy does not penetrate a long distance - I've heard various distances mentioned, from fractions of a millimetre to as much as a millimetre in the case of some very porous timbers - but on a molecular scale it is a very substantial distance, and the epoxy adhesive will adhere tenaciously. In end-grain, epoxy penetrates a much longer distance indeed.

Now this brings me onto the subject of pre-coating plywood - or any wood for that matter - and what I see as being some stumbling blocks. Pre-coating sheets of plywood laid flat on a bench is certainly convenient, and efficient from the coating application perspective. But the problem is that when the components are cut from those pre-coated sheets, all surfaces which are going to be glued MUST be very well abraded so that the epoxy adhesive (and its priming coat) have a 'key' or 'tooth' to which a mechanical bond can be established. This represents an extra step in the building process, and detracts from gains made through the pre-coating. Also, the mechanical bond between the fresh epoxy and the previously applied pre-coat represents a 'secondary' bond - good if well executed, but not as good as a chemical bond.

I also have concerns about the cured epoxy on pre-coated sheets being subjected to tension and compression when components are bent into position. In my mind's eye, I see micro cracks forming on the tension side of the material, and crushing occurring on the compression side. Unfortunately, I do not have the engineering or chemical qualifications to claim that I know what I'm talking about!

Under some circumstances there may be a place for pre-coating - an example would be the under-surface of a cabin-top or a deck, where subsequent sanding would be very difficult. In that situation, the under-surface could be pre-coated, and then sanded to the point where it is ready to accept adhesive where it sits on deck-beams etc, and it would also be ready to accept paint.

Other than in the cases mentioned in the preceding paragraph, I much prefer to build the boat structurally, and then apply any epoxy coatings. I have fairly strong opinions about where epoxy coating is of value, but that can be the subject of another post.

Saturday, February 27, 2016

Phoenix III Hull Structure

Glued-lapstrake is a wonderful method of construction for small-craft - the appearance is elegant (as long as the lining-off of the planking is tastefully done), the interior of the boat is relatively clear of structure, making maintenance of the paintwork easy, the method makes efficient use of sheet plywood, and the amount of epoxy work is relatively low. In addition, the plank overlaps on the outside of the hull perform very effectively as a series of spray rails.

Periwinkle showing the 'spray-rail' effect of the plank laps....

...and Phoenix III doing the same
In addition to all of the benefits I've mentioned above, what I think is the the most important element of the glued-lapstrake method of construction is that each overlap in the planking produces what is, in effect, an integral stringer! This stringer effect is caused by two characteristics - firstly the thickness of the hull planking is almost doubled where the planks overlap, and secondly, on a round hull, the adjacent planks are at a different angles relative to each other. The angular difference gives additional stiffness in exactly the way that corrugations in roofing iron add stiffness.

The structural benefits of the overlapping planks mean that a lapstrake hull can (within limits) be built with reduced internal framing, and in the case of 'Phoenix III' I specified no transverse framing from the semi-bulkhead at the forward end of the centreboard case through to the bulkhead at the forward end of the stern seat (i.e. 'sternsheets') - a distance of 2280mm or 7-1/2 feet. However, there is other structure present in the form of a substantial transverse thwart structure, the keelson, and the centreboard case.

I had some minor misgivings about whether I was taking the matter of a structurally clean interior to an extreme, but until very recently I have had no reports of problems. In fact, the very first Phoenix III built is now more than nine years old, and has been used heavily, going on the water weekly for that entire time, and having travelled long distances on a trailer (trailers damage boats more than anything else).

Despite the lack of structural problems reported, in 2007 I placed this entry into the instruction manual which accompanies the plans:-


One of the design aims with Phoenix III was to have a clean and uncluttered interior. This has the benefit of making sanding and painting easier, makes cleaning easier, and produces a smooth interior hull surface for sleeping aboard.

Another design aim was to make the boat as light as possible. The lighter a trailer boat is, the more she will be used. The clean and frameless interior is in line with the quest for light weight.

There are no transverse floor timbers (frames) specified in the plans between the half-bulkhead at the forward end of the centerboard case, and the half-depth bulkhead at the forward end of the stern sheets (seat). Between these two points, the hull relies upon the strength of the planking, the glued plank laps, the keelson (or hog), the centerboard case, and the main thwart.

The resulting structure is strong, clean, and slightly springy. But, it is very important that the builder pays close attention to the standard of gluing – particularly along the plank laps. Use of epoxy fillets along the internal lap lines will prevent water sitting in the laps, and will add considerable strength to the joint. This is only really important in the lower planks.

 For those who prefer additional strength, or who need a base upon which to place raised floorboards, transverse floor timbers can easily be added during construction. Consult one of the suggested test books, or contact me for details. My preference would be for bent floor timbers (steam-bent if necessary) glued across the top of the keelson, extending out to cover the first two laps. Size is arbitrary, but I would be thinking of 9mm x  22mm/ 3/8” x 7/8” as recommended by John Brooks for his design, ‘Ellen”. 

When Woodenboat Magazine asked me to write a 'How to Build' article about 'Phoenix III', I re-drafted the plans to make them better suited for magazine publication, and while I was at it, I drew a pair of half frames to go under the main thwart, on either side of the centreboard case. That would deal with any lingering concerns about the expanse of unsupported planking once and for all, but at the expense of the clear interior.

Now, having told this overly long story, I have to tell you that my customer and friend (email friend, that is - we live on opposite sides of the globe) Jonathan McNally, has reported a persistent cracking problem in the joint between the garboard strake (i.e. the plank closest to the keel) and the keelson on his 'Phoenix III'. Jonathan's boat was built without any extra framing structure, and is a good example of the 'pure' original design. The cracking is minor, but it does indicate a potential problem - as I had feared. 

Very fine crack in the paint work on Jonathan's boat just above the keelson in this photo
Jonathan believes that the cracking was initiated by heavy foot-falls on the planking, and he intends to put in some steam-bent ribs and light floorboards to distribute human foot pressure. This is very similar to my comments listed above in the except from my building instructions.

I'm hoping that this whole business is a case of me worrying too much, as nobody else has told me of the problem. I asked Jonathan about the eopxy products used, and they were all perfect for the job. However, the plywood came from a very highly regarded European manufacturer, but there is a twist. A very good friend of mine who is a Naval Architect conducted engineering tests on a range of plywoods on the Australian market, one of which was this fancy European brand. The results of the testing were surprising. This particular 'super high quality' ply came out as:-
  • lowest bending strength;
  • lowest peak load at breakage;
  • lowest modulus of elasticity;
  • lowest strength-to-weight ratio;
  • 2nd lowest stiffness-to-weight ratio;
  • lowest structural efficiency (adjusted)
So, many lessons to be learnt. If building a 'Phoenix III', I am now changing the status of the two half frames under the main thwart from, 'Optional' to 'Recommended', even if they may not really be required.

Monday, February 8, 2016

Builder's Discussion Group Established

My email load is quite heavy, and I find myself caught in the difficult position of writing lengthy explanations and giving lots of advice - but it only goes out to one person at a time.

I've got literally thousands of email responses to queries, and I'd love to be able to show them to everybody, but I'd have to get permission so that people's privacy was protected.

A frustrating spin-off of this situation is that with my email workload, as well as building and design obligations, I don't have time to write regular posts on this blog.

So - Chuck Leinweber has helped me by setting-up a Group page on Facebook. I'm still very much a novice when it comes to using Facebook, but I'm hoping that builders will be able to address questions to my via the Facebook page, and that way everybody can take part in the conversations.

I'm happy to accept any suggestions about how to develop this page, and I hope that people will be able to help each other and not have to rely on emails from me.

the address is:-

Look forward to seeing some messages!

Sunday, November 1, 2015

Fleet - Videos of performance with Two Different Motors

As some of you already know, Fleet is a planing-hull derivative of my very successful Flint design. For some background you can look at this post and at this post.

Fleet awaiting more trial runs
Fleet was designed from the outset to perform well in the very speed/length ratio spectrum in which normal planing hulls are at their worst. By that I mean the so-called "semi-displacement" or "semi-planing" range - widely thought to be in the S/L ratio range of 1.5 to 2.5.

Speed/Length ratio is basically the speed of a boat (expressed in knots), divided by the square root of the waterline-length (expressed in feet) of the boat. So let us take Fleet as an example: -

  • LWL (length on the waterline) equals 14 feet
  • Assume S/L ratio of 2.5
  • Speed divided by 2.5 equals 3.74 (i.e. square root of 14 ft LWL)
  • Therefore, Speed in knots equals 2.5 times 3.74
  • Speed equals 9.35 knots (10.8 mph, or 17.3kph)
Now those speeds sound modest, but for a small boat like Fleet it represents a very satisfying speed indeed. More importantly, because this hull has been proportioned to operate within this S/L ratio, the boat trims well, instead of pointing her bow in the air like the standard planing hulls, which chew fuel at a high rate just to pull a large wake.

So far I've been able to carry out several test runs in Fleet using both a 9.8hp Tohatsu two-stroke and a 2hp Honda four-stroke. The 9.8hp Tohatsu is based on the powerhead from the 6hp and 8hp models, so is suitable for this light-weight boat. My next test will be using a 4hp motor, which I think is about the optimum size from an efficiency perspective. In my part of Australia, 4hp (2.9kW) is the largest motor allowed without boat registration.

Here are two Youtube clips - firstly using the 2hp Honda, with which I achieved a consistent 7.9 knots measured by GPS with my weight aboard, and 7.1 knots with my wife joining me (she only weighs 60kg/132lbs. The 9.8 Tohatsu gave 15.5 knots (17.8 mph or 28.6 kph) with two heavy men aboard plus gear.

Saturday, October 31, 2015

Flint and Alby Sailing Videos

I've written a fair amount about a group of my designs which make use of a very simple boat-building method, know by a range of names including "Stitch-and-Glue", "Taped-Seam", "Tack-and-Tape", "Composite-Chine", and so on.

A taped-seam hull under construction - in this case a hull made from my First Mate design.
There are some significant advantages associated with this construction method, with notable ones being:-

  • if properly designed, hull panels can be marked directly onto the sheets of plywood used in the boat's construction;
  • the builder can produce a "flat-pack" kit ahead of time, which allows those who have limited building space to get a head-start on the job;
  • again, if the boat has been properly designed, accurately marked, and carefully cut, the hull can be built without a fixed strong-back and station mould assembly - a very significant saving in time and resources;
  • the amount of timber framing in the hull can be reduced to a minimum, saving cost, reducing weight, and avoiding rot-traps - all without sacrifice in strength;
  • the vulnerable edge-grain of the plywood is exceptionally well protected within a cocoon of thickened epoxy and glass firbes;
  • sanding, painting, and maintenance are all made easier due to the clean interior (and exterior) of the hull.
Please do not get me wrong - I am not advocating this system over other methods of construction. All construction methods have advantages and disadvantages, and every boat design and building project must be carefully considered in the light of many compromises. What I am saying is that taped-seam/stitch-and-glue/composite chine should be given the respect that it deserves.

I continue to design boats to be built glued-lapstrake (glued-clinker), glued-strip-plank, cold-moulded, and taped-seam. Frequently the design itself determines which method will be the most appropriate, and it is very important that the builder understands the design, materials, and application very clearly. Education is the word!

Here are two video clips of taped-seam (stitch-and-glue etc) boats under sail.

The first is a clip shot by Paul Hernes, a Phoenix III owner-builder, showing a boat built to my Flint design by Paul McShea. Flint was designed primarily to be a rowing boat, but her hull shape assumes that some will feel the need to sail her, and/or mount a small outboard motor. The plans include details for a sailing rig, daggerboard and rudder. However, Paul McShea had a Heron rig on hand, and it happens to be just about the right size and shape for Flint.

I've also been able to shoot a short clip showing my Alby design under sail, showing-off her tanbark-coloured balance lugsail. There are plenty of eight foot long pram dinghies in the world, but what is important about Alby is that she has an unusually large carrying capacity, and due to the design of her chine-line, she is still able to travel quite fast while leaving a relatively flat wake. Both Alby and Flint have easily-driven hulls for their size.

This particular Alby carries a short foredeck, which is a variation from the plans - something I do not recommend.

Tuesday, August 4, 2015

First Mate Capsize Test.

As I have mentioned on several occasions, First Mate is one of my favourite designs. For those who don't already know, she was designed to be a stitch-and-glue version of Phoenix III in functional terms, with an internal layout, rigs, centreboard, mast, and rudder all virtually identical to those on the glued-lapstrake boat.

First Mate  

Phoenix III  (photo - Paul Hernes)
Each of these boats share a selection of rig options, and both use the same emergency floatation arrangement, which is a combination of a large buoyancy tank under the foredeck, and a corresponding buoyancy tank under the aft deck and stern sheets (i.e. aft seat).

Many people have asked me why I don't have side seating incorporating side buoyancy tanks. Well, the answer comes in two parts. Firstly, side-seating which is fixed is a real thief when it comes to space. When cruising in small sailing craft, my favourite seating position is down on the bottom (on floorboards if you like) with my upper back supported by the side-deck carlings, or the hull topside planking if side-decks aren't part of a design. You can see this position nicely displayed by my son, David, in the photo of First Mate above.

This seating location is comfortable, and is particularly effective for human ballast positioning when the boat starts to heel. In a racing boat, where comfort is a secondary consideration, hiking-out on the side-decks is effective. But it is tiring and uncomfortable. For cruising, where the boat has to be sailed for longer periods and in difficult conditions, the comfort and protection afforded by sitting in the weather bilge is more seaman-like, and safer. Not only that, but as the boat heels, human ballast in the weather bilge becomes more effective, while human ballast on the side deck becomes less effective.

That is me sailing my 1956 International Finn in very light conditions. Even though the weather is pleasant in this shot, the hiking position becomes tiring after a relatively short time. Good for the stomach muscles!
Getting back to the original discussion, fixed side-tanks rob you of the best space in the boat, but they do prevent much water coming aboard in a capsize. The problem is that the side-tanks mean that a capsized boat floats so much higher, that the mast points downwards towards the surface of the water significantly, and it is easy for the mast to submerge completely. The boat will then turn-turtle. This is a really serious problem! Unless they are provided with very significant foam floatation, alloy and carbon-fiber masts try very hard to turn themselves into keels at the first opportunity!

I do make provision for removable side seating for those who want it, and my design allows the seat to be removed completely, or moved into the centre of the boat to form a servicable sleeping platform raised above the bilge water.

Phoenix III removable side seating (First Mate has the same arrangement). Photo - Paul Hernes

Side-seating and stern-sheets in casual use (photo - Tom Pamperin)

Seats moved together on the centreline........ be used as a bunk-flat (photos - Paul Hernes and Tom Pamperin, respectively)
This seating/bunk-flat arrangement only works because of being incorporated with the generous stern-sheets and the main thwart.

So, I keep being asked to design-in side-tanks/seating in cruising dinghies, and in cruising dinghies I refuse to oblige (I do put side tanks in several powerboats though, because they don't have the option of using buoyant wooden spars as makeshift outrigger floats). Apart from the space issue, I want a capsized sailing dinghy to float a little deep while on her side, as it means that the mast, sails, and (if they are present) yard/sprit/gaff float fairly flat on the surface of the water. Getting at the rig is simple while swimming, and it is easier to reach up to the centreboard when it comes time to pull the boat upright. Once upright, it is quite practical to sit inside the partially flooded hull to set things right, and do some bailing - after all you probably won't have been in a race.

Gerry Lavoie built a First Mate and he has used her a lot, it seems. One of the pleasing things I note from Gerry's emails is that he has found that she is very effective when being used under oars - something I aimed at with the design of both Phoenix III and First Mate.

Gerry recently sent me three images showing the results of a capsize test he carried out, and I'm happy to see that the built-in buoyancy worked as I had hoped:-

Note how the buoyant wooden mast is nearly flat on the water. Combined with the yard and boom, the mast makes an excellent outrigger. Gerry has easy access to the interior of the boat while he sorts things out.

Here Gerry has climbed up onto the topside planking, and the boat is carrying his weight without a problem.

Next, he appears to have placed a foot down on the centreboard where it protrudes from underneath the bottom of the hull, and the boat has rolled upright. Another approach when the water is warm (and you aren't being chased by sharks!) is to simply swim around to the bottom of the boat and pull down on the protruding centreboard.
If there is much wind blowing, always try to swim the bow of the capsized boat around into the wind before righting - otherwise you may lose control and find yourself in another capsize situation.

Here is a little video from Gerry's collection...

Saturday, July 18, 2015

Website Being filled with More Content - At Last!

Have been working too hard in the workshop, and blog entries have suffered. However, paid building jobs are almost finished, and the website is being populated with several design page entries, and an increasing number of items on the "Shop" page.

After mid-September, I will be working predominantly on designs, website content, small video production, and more regular blog entries. I've got a stack of material from workshop jobs over the last year or so - have just been lacking time to edit photos, write copy, and publish material.

Much more to come very soon.