Category Archives: Hull Build

Building a Strip Plank Hull
Below are posts concerning the building of the hull for Steam Yacht Befur. This hull is s strip-plank built design by Selway Fisher (see link on right of home page) and is constructed of Western Red Cedar planks clad in woven epoxy-impregnated glass-fibre cloth.

It’s the first boat I have built, so your watching a learner!

Providing some Direction – Befur gains a rudder

Rudder ready for fitting and varnish

The rudder with pintles ready for varnish and fitting

One of the major outstanding jobs on the hull was to build a suitable rudder. As Befur is meant to sail (as well as steam) we wanted to make sure we provided some thing effective.

Researching the subject covering everything from historic articles on Chinese Junk development to the Steamboat Associations’ handbook and designers from Selway Fisher to Dave Gerr’s excellent book on ship design and lots of trawling of the Junk Rig Association’s web site we discovered some important facts:

  • Traditional Junks had “rudders the size of barn doors” – so delicate little daggers seemed inappropriate.
  • Aerofoil profiles work best – the NACA profiles are well documented.
  • A balanced rudder would reduce the requirement for Charles Atlas courses for the helmsperson.

Balance and Profile choices

Balance: The idea of balance is that the rudder is built with part of the blade ahead of the rudder-stock, so as it is turned some of the force of the water helps with the turning, off-setting the tendency of the rudder to want to return to the straight-ahead position. This reduces the effort needed to steer the boat.

Clearly, there is an upper limit to the amount of balance included in the design, or the rudder will continually try to swing into “full lock”. Reading up we concluded we would aim for 20% of the rudder surface area to be ahead of the rudder stock. We failed to recognise that of course the actual pivot-point of the rudder is not in the centre of the rudder-stock but on the centre line of the “hinges”/pintles.

So our actual balance is somewhat less than this intended 20%, so we will see. in time. if Befur is easy to handle. Of course handing is likely to vary considerably between steam and sail, so it’s probably going to be a compromise.

We will initially just fit a simple tiller to control the rudder, but the plan is to also install hydraulic wheel steering, as it will not be possible to control the engine and reach the tiller from the same seat – so some “drama” will probably ensue as we attempt to pick up a buoy or dock.

Profile: While a flat plate rudder will work, they produce more drag and deliver less “turning moment”. The better plan is to make the profile of the rudder an Aerofoil (Aquafoil?) shape. This causes the rudder to produce sideways “lift” helping to pull the stern around.

It emerges that standard aircraft aerofoil sections are appropriate, and the most well known are the NACA profiles developed by the American National Advisory Committee for Aeronautics. This is because water and air can both be considered “fluids” (Hence all the work on Fluid Dynamics in Formula 1 car design).

These profiles are identified by 4 digit codes, the first two numbers indicating the “camber”  of the section and the second two numbers indicating how “thick” the profile is. As the rudder needs to provide “lift” in both directions (port and starboard) the camber is zero producing a profile that is symmetric about its centre line.

The “thickness” of the profile determines a) how much lift the rudder will produce for a given speed through the water (larger profile = bigger lift) and b) how much the rudder can be swung left and right before it stalls and the lift is lost.

Clearly this is also a compromise – but we settled on a NACA0015 profile – this meaning that the thickest part of the profile is 15% of the length (chord) of the rudder. Again, time will tell how good this decision was.

Manufacture

An old friend Nick Pilbeam from Aberdeen volunteered to come and assist in the manufacture – thank-you Nick.

We adapted the design to take advantage of the contents of my boat-building timber store. I have become a considerable fan of epoxy-composite structures and of laminated timber designs, so we started with a rudder stock of 75mm square Iroko and a blade core of 25mm thick plywood.

These were jointed via a “cross-halving” joint (with the blade inserted into a slot cut in the rudder-stock. This was then built up with lamination of Iroko and Douglas Fir.

The whole rudder was to be wrapped in epoxy-soaked glass cloth (in the same way as the hull is built), but this time finished in the clear (with varnish to protect the epoxy from the Sun’s UV radiation). This approach means that at least a small part of the boat will look like the wooden boat that it is!

Having laminated the components together with thickened epoxy, we then undertook the initial profiling with a router running on a pair of slides which had been cut to match a set of co-ordinates computed using this rather helpful web page.

In practice (after having repeatedly struggled (and failed) to correctly copy the measurements from the spreadsheet to the template) we concluded that it was not possible to accurately route the leading edge portion of the aerofoil from the template. This was because the rate of change of thickness is so fast at the leading edge, and as you need to keep the router normal to the template to get the correct profile, it was very easy to make a BIG mistake.

So we settled on making another template for the leading edge and using the trusty power plane and belt sander to profile the leading edge of the blank 🙂

Some pictures:

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The Final Push to the North

Well, as I may have mentioned we have decided to relocate to Cumbria (330miles north of current location) – this of course means moving house and more significantly relocating the workshop and boat! This decision has resulted in the gap in posts and also a final push to get Befur in a state ready to hit the road.

Continue reading

Paint!

A day we thought we might be never reach, has arrived ☺.

Today we put the first paint on Befur,it’s only primer but it is a milestone.

We have decided to use Epifanes 2-pack polyurethane for the hull cockpit, decks and topsides (and something cheaper for inside)! So £480 later we have the necessary under and top coats.

Onwards! (You can tell we are excited by all the exclamation marks!!!)

Collecting the trailer tomorrow and the mast on Tuesday – real progress.

 

Fitting Out

Louise (having retired) has joined as a full-time worker now, and progress is much improved… She has become an expert epoxy filleter, and having two people to hold a job, or get the pencil you left on the bench when you’re up-side-down in the cabin saves a huge amount of time.

We have fitted the cabin roof, and almost completed the initial fit-out of the cabin and started on the seating (which also provides a deal of strength to the hull in the cockpit), so feel like we are moving quicker.

We compiled a (slightly daunting) list of outstanding jobs, ~80 of them, and are actually ticking some of them off!!! Cumbria is feeling closer!

A selection of recent pics:

A Chart Table!

A Chart Table!

Cabin Roof - well screwed!

Cabin Roof – well screwed!

Cockpit combing in place

Cockpit combing in place

Under the Cosh!

As we move inexorably towards August I am feeling the pressure to finish Befur ready for the move to Cumbria!

We have ordered a trailer from Gecko Trailers in Cornwall, (who’s spelling is worse than mine)! that is due to arrive in 6 weeks, so I think it’s defining a definite end date :-/ Continue reading

More fitting out – and symmetry

Just a quick note, the last week or so have been dedicated to the building of the cabin on Befur, and the first stages of internal fit-out.

This has involved the fitting of the cabin sides (as seen in the last post’s pictures), and the fitting of internal bulkheads, (e.g. the walls of the loo and heads for the bunks.) This has involved more “spilling” to get the shapes from the hull for cutting of the bulkheads (a remarkably accurate process) and fitting these too the hull using epoxy filets. Continue reading

Sculpture in Epoxy and Wood

Boat building for botchers!

I have returned to work on finishing and fitting out the hull, and in the process come to the conclusion that boat building using strip-plank/epoxy is mostly a process of sculpture using wood and epoxy as the constructional elements. I must confess that this approach really rewards the botcher, as there seems to be no need for the kind and quality of woodworking skills traditionally needed – in fact I think they may be a disadvantage. 🙂 Continue reading