Design Overview

 

Nordkyn on mooring

The sloop Nordkyn is a 13-metre (43′) round-bilge alloy yacht with a displacement of about 8600kg half-loaded in cruising trim. It features a fixed bulb keel with a draft of 2.35m (7′ 9”) and a single deep spade rudder.

The alloy construction is very robust without being heavy and the deck is integral to the aluminium shell. Three internal watertight bulkheads subdivide the hull into sections that can each be sealed and pumped separately, with the goal of buying plenty of time and allow a remediation plan to be implemented should some significant damage event ever occur.

On deck…

Clean, sleek lines, wide side-decks, nothing to carry away in heavy weather, low, narrow roof windows, a deep and well protected cockpit… profiled like a submarine for punching in all weather.

Nordkyn Completion 108 - Side deck

A clean and spacious deck plane without anything to be carried away. Headsails sheet well inside the lateral rigging.

The sloop rig is masthead with double swept-back spreaders. This arrangement, combined with some camber in the section and a slight rake back, results in excellent rig stability and strength without the need for runners or inner forestay. Fore-and-aft lower shrouds provide strong support in the lower section, which is the one most challenged with a deep-reefed main.
The keel-stepped rig is stayed wide, reducing compression forces, and headsails sheet well inside of the lateral rigging, the leech stopping before the spreaders. This limited genoa/mainsail overlap facilitates handling of the headsails and results in very easy tacking.

The distribution of the sail plan between mainsail and headsail slightly favours the main, keeping the foretriangle more manageable with a wider wind speed range.

Cockpit arrangements are simple and efficient

Cockpit arrangements are simple and efficient

The mainsail sheets down onto a track-and-traveller arrangement in the cockpit, from the end of the boom, well away from the companionway. This simple, classic arrangement provides the lowest mainsheet and boom loads together with the best sail control to harness the huge power of the mainsail and still leaves ample space in the large cockpit.

Tiller steering provides for the most efficient hook-up for a self-steering vane, the most dependable helm system for long-range voyaging. Very careful attention to rudder design and overall balance resulted in a boat that does not require the mechanical advantage associated with a wheel.
The rudder is also free to rotate over 360 degrees, which opens an option when reversing at speed under power.

Nordkyn Completion 109 - Companionway entrance

Companionway entrance

The companionway entrance is recessed underneath the sliding hatch. This arrangement is extremely effective at keeping the entrance dry down-below in the rain.

On the water…

Light wind performance is excellent and – to put it conservatively – the boat is fairly swift in all conditions, thanks to the generous sail plan, decent keel, long waterline and the characteristics of the hull itself. Balance and course stability are phenomenal at all sailing angles regardless of sea conditions.
Aft quartering seas have very little impact on steerage. The boat accelerates, heels a little and keeps tracking.

The sloop Nordkyn under sail

Nordkyn close-hauled in very light winds

Upwind, the hull balances with the helm close to neutral and remains balanced when a puff hits, unless heel becomes really excessive. Upwind speeds of up 7.4 knots were recorded under full canvas simply with good Dacron sails, and tacking angles can reach as little as 60 degrees in the right conditions.
The boat creates considerable apparent wind close-hauled in light breezes and one needs to think in terms of VMG, rather than pure boat speed on a beat in very light winds. Similarly, tacking downwind is very effective in light to moderate conditions, almost sailing a beam reach at times while only 15 degrees off the axis of the true wind. It also readily balances on a beam reach with a lashed tiller, including in strong winds and rough seas.

Heel angles are very moderate all round, very good speeds are achieved with little effort. The boat doesn’t pitch, cutting though small waves and otherwise following the contour of the sea. It shows very little inclination to slam upwind while sailing higher and faster than most, but can do moderately if seas are unusually steep and short, such as in tide rips. In such instances, the ride doesn’t get hard the way it used to on the Yarra that was deeper and V-shaped forward; it makes a bit of noise more than anything else.
The only situation that causes it to slam forward is a very faint wind unable to heel the hull, or a following wind, with short steep waves coming directly on the nose. This is so rare and abnormal that it isn’t really worth worrying about and changing course a little takes care of it.

On a run, the hull accelerates smoothly, the helm remains light and the sloop will punch through the 10-knot mark with a child at the tiller. The bow lifts as the boat accelerates before the sea and it gets on the plane with no noticeable transition, breaking the water at the mast and leaving a rooster tail behind. It is a startling feeling the first few times as it happens unexpectedly easily with a good breeze, full sail and a bit of a following sea running.
Course stability is such that one can often abandon the tiller for a few moments at sustained speeds of 9 and 10 knots with no consequences. With some 20-25 knots of true wind on a broad reach, boat speed hovers around 10 knots under full main and genoa, surging to 12 knots and more, the helm is light, the apparent wind just is just starting to get noticeable and we are still just cruising.

The reduction in apparent wind afforded by boat speed is often spectacular: a gybe in 15 knots true can be performed by hauling one strand of the mainsheet in by hand and “throwing” the mainsail across, as if sailing some huge dinghy. This makes for extraordinary manoeuvrability single-handed. Of course, with more wind, the picture eventually changes and the same manoeuvre involves significant work on the winch.

The sloop can balance under mainsail alone, achieving very good upwind speeds, or headsail alone, including upwind. It makes it very versatile and flexible, especially when handling canvas.

One striking feature is how incredibly dry the boat is at all times. Even at 8-9 knots in rough confused beam seas, there is very little water coming on deck. Headsail changes can be performed safely while still hauling upwind, just slowing down a little. Good freeboard, good buoyancy and a reasonably light vessel make for much more pleasant sailing. More importantly, having been designed in cruising trim, the yacht operates at its optimum rather than overloaded like most cruising yachts.

Offshore swell in light winds in the Southern Ocean

Offshore swell in light winds in the Southern Ocean. The ability to sail efficiently in such conditions is invaluable.

Lastly, if the wind drops completely, or the sea state simply doesn’t allow making any use of some faint residual breath, I drop all sails on deck and head down below. This is the course of action I had devised on the Yarra already, preferring to endure some rolling than the on-going slapping of the mainsail and shaking in the rigging. On boats with bulbed keels, flattening the sails to dampen rolling is even harder on the gear up there.
On Nordkyn, I had a welcome surprise. Very little roll with all canvas on deck, in most instances a cup of tea could stay on the table. This also means that the gear doesn’t crash rhythmically from side to side in the lockers and peace and quiet mostly reigns on board. The stability and inertia achieved in the design naturally oppose rolling most of the time, especially out at sea where the period of the waves is longer. Even the odd lurch taking place doesn’t go very far.

Down below…

The interior structure is built from PVC foam and E-glass composite for its light weight, faired and painted using a two-part semi-matt polyurethane. Hardwood trims, veneer tops and darker upholstery add contrast to create a bright, simple and classy finish on board.

A raised step separates the cockpit from the companionway, followed by a landing and a single step to reach the cabin floor level. The long windows at head height provide good view outside.

Two near-symmetrical aft cabins with standing headroom at the entrance and a double bunk each extending underneath the cockpit sides provide sleeping quarters.

The galley is located to the port side of the companionway and a vast chart table and navigation station occupies the other side, up to a partial bulkhead separating it from the saloon area.

Galley

Galley

Chart table area

Chart table area. The chart table is for navigation; on the other side of the partition is a small desk for writing or computer work, close to the SSB transceiver.

The saloon area offers a L-shaped settee to port, a good table and a deeper, strait settee that can be used in conjunction with a large folding flap on the main table. The starboard settee doubles as a day bed and a seat for a small aft-facing desk that services the communications area with SSB radio, laptop etc.

Saloon area and table

Saloon area and table

The mast crosses through the deck just aft of the saloon forward bulkhead and a watertight door gives access to forepeak that contains storage lockers, a toilet and shower compartment and a workbench with a vice.

Saloon forward watertight door

Saloon forward watertight door

Another watertight bulkhead leads to the sail locker, also accessible from a deck hatch.

Behind the aft cabins, the sealed lazarette houses the rudder stock, exhaust system, SSB antenna tuner and storage for fenders and various other light, bulky items. Access is afforded from a deck-style hatch from one of the aft cabins, or from outside through two hatches aft of the cockpit.

  15 Responses to “Design Overview”

  1. Yikes! What is under the waterline? !!

    PLEASE give us a picture of the boat out of the water!

    Tremendous article on sailing dynamics, but need to see boat parts relative position to each other.

    Thank you,

    Robert.

  2. Hi Eric,
    Are the coachroof control lines port: spinnaker pole and starboard: boom? And does the topping lift exit the mast adjacent the main halyard?

    Also, I can’t see any pole chocks on deck but note the pole heel track on the mast reaching to just below the lower spreaders. Do you stow the pole up the mast and if so, how do you square that with your desire to minimize top hamper?

    Regards – Peter

    • Peter,

      Yes, the spinnaker gear is on the port side, while the mainsheet and boom vang come back to starboard. There is no topping lift, the vang supports the boom. It saves one operation as well as little “accidents” when reefing. At the masthead, there are two sheaves side-by-side and the position for the topping lift is allocated to a spare mainsail halyard. They run exactly the same. There is also a spare jib halyard.

      The spinnaker pole is hooked onto the pulpit forward and lashed at the chainplates. It works fine. It can be stowed up along the mast indeed, it is just that I finished rigging up this arrangement quite some time after the photos were taken. There is a little more gear to enable that now. Many photos are construction era or a little post-launching.
      I prefer seeing the pole down on deck where it doesn’t contribute to windage and weight aloft, but being able to hoist it and stow it along the mast is useful when I am actively using the spinnaker gear, or use it to pole out the genoa. It saves manhandling what can be quite a dangerous instrument and you can use the long track to sometimes “push” the sail out by lowering the pole in a controlled way with the outboard end already attached to the sheet.
      Some of the things I could do on the Yarra are no longer possible or safe at all on a bigger boat, so I sometimes had to come up with new tricks.

      Best regards,

      Eric

  3. Hi Eric,
    Judging from the ‘profile’ photo heading the post “Too Fast On The Run”, there seems to be more side-deck camber adjacent the mast-shroud region. Or is it constant and what I see is the consequence of the modest sheer in Nordkyn’s profile.

    Thanks – Peter

    • Peter,

      That photo was taken from an inflatable dinghy from memory and the low view point combined with the hull beam is causing the sheer to look flatter than it is. Compare it with those on this page for example, especially the second one.
      The other thing to remember is that the deck edge is quite curved, while the line where the roof meets the deck is much straighter. The location of the jib sheet track is what determined the width of the roof forward and the sheeting angle is comparable to a racing yacht, no compromise there. What you see is the side deck getting wider.

      Regards,

      Eric

  4. Hi Eric,
    Looking at the cockpit photos above, can I see a drain hole in the port rear corner (I realise there are crossed drains forward) and where do the outboard sloping seats drain?

    In other photos I can see holes in the transom(gas bottle compartment drain?) and under the counter(exhaust?). And what about water intake and outlets? Where have you placed them and what sort of shut-offs did you use?

    Thanks – Peter

    • Peter,

      The seats drain back into the bottom of the cockpit, the drains are just there to remove the small amount of water that would otherwise remain in the corner of the seats. If you look into the aft cabins, the forward drain tubes act as handholds for moving in and out of the double berths.
      There are four cockpit drains, one in each corner, so the cockpit sole doesn’t need to be sloped. None of them are crossed, there is no need for that: when the boat heels, the whole cockpit rises further up from the water. The drains are plumbed back through the hull bottom aft, above the static waterline.

      The two outlets you noticed in the transom are associated with the bilge pumping system. There is one pump down-below and one that can be operated from the cockpit.

      There are two sea water inlets, one for the engine and one forward feeding the salt water circuit on board. The engine one is always kept shut when not in use. The galley sink has one outlet and the heads have another forward.

      I used Hansen fittings throughout for valves and skin fittings. They are very tough and completely impervious to corrosion.

      Best regards,

      Eric

      • Thanks Eric,
        Can you talk a bit more about the bilge pump system? Are both pumps manual and/or do you have a motor-driven pump as well or indeed electric ones in the bilges.

        There’s a photo in the Interior Construction post showing what looks like an in-line electrical
        pump in the bilge adjacent the galley sink – or is it a valve of some sort?

        Have you incorporated the gas bottle locker drain into the cockpit drain system and where have you run the engine exhaust?

        Cheers – Peter

        • Peter,

          Bilge pumping systems are another one of those things that sound important, but are of limited usefulness in the end. They are only good for removing small amounts of water and effectively finishing the job. If you have that much water in a boat that you need to do something drastic about it, you won’t be turning towards a bilge pump with a 38mm hose.

          This being said, there are two manual, double-acting bilge pumps in the system, two Y-valves and shut-off valves at the watertight bulkheads and it is possible to pump the two forward compartments even if they have been sealed off at the doors.
          In addition to this, I can divert the engine water intake to a hose inside the boat using a valve and use this to pump out as well. It is also useful for flushing the raw water side of the cooling system, etc.
          There is also a third bilge pump operating the Lavac head forward and something could certainly be done with it if ever relevant.

          I don’t have any motorised pumps. Not only they would never be of any use, but they probably wouldn’t work any more if I ever wanted to use them – short of putting them onto some strict testing and maintenance schedule, like flooding the bilge deliberately and pumping it out twice a year. I am not very interested in doing that.
          Driving a lay-shaft from the engine and coupling a mains alternator, a large capacity pump, a waterblasting pump, etc are all thoughts that had crossed my mind long ago, before I had sailed any long distances. In the end, it is just a lot of weight and complications for systems and equipment that hardly ever (or simply never) see any use and nevertheless deteriorate. I don’t need the deadweight and constant penalty going with it.

          It is a metal boat with a fully welded hull and the bilges are naturally dry…

          The LPG locker is part of the lazarette and is vented outside by itself. The engine exhaust runs into a water trap, through the watertight bulkhead behind the engine, up underneath the deck and then comes back down and through the hull, well above the waterline.

          Best regards,

          Eric

  5. Whilst for long distance sailing draft is not a problem it becomes more so if Coastal Cruising.
    However even with Coastal Cruising there are often some quite long passages of a week or more.
    For us going say to the Azores or the Arctic is about 13 days at 6 knots, the thought of being able to increase the average is very appealing,especially to my Crew( Wife )
    Speed also has the advantage that for those who cannot take long holidays enables one to consider cruising grounds further afield

    I wonder did you compute the trade off of loss speed /pointing ability and subsequent increase in passage time if you had opted for a shallower draft and if so what might it have been say in 10 cm increments.

    When we arrive in a Country we enjoy exploring which often means going up River. where a shallower draft is very useful.

  6. James,

    It is an interesting question and I had written a VPP code to investigate design trade-offs at the time, but this is basically a design that has been optimised towards one of the boundaries of the envelope and draft is one of the key parameters you cannot reduce without major repercussions.

    Less draft would require more ballast to maintain the same righting moment / stability limit. This would make the boat heavier, so either the carrying capacity would need disappear to the benefit of the keel bulb, or the displacement would need to be increased. In the second case, the performance objective becomes compromised, because it would be challenging to carry an even bigger rig on the same boat length. You would need to overlap the genoa past the spreaders to try and get more sail area and this would have negative consequences on rig weight and loadings if the lateral rigging had to move inboard, or on the pointing angle if the sheeting angle was opened up. It also makes tacking and handling a lot less pleasant.

    So a very small reduction in draft would be possible by reducing carrying capacity or using a lighter carbon rig to offset it, but the difference would be too small to change anything in terms of accessing shallow water. With a carbon rig, I would rather add another metre to the mast than reduce the draft. Any meaningful reduction in draft would make the design unfeasible and lead to a different kind of boat (one I don’t want), because everything here hinges on the low centre of gravity and light displacement provided by the deep hollow keel foil and bulb configuration.

    If you look at all the centerboarders and shallow draft designs, they are heavy, carry stubby little rigs and struggle to move in light airs. When a boat won’t sail in light conditions, the fuel tank gets bigger, a heavier boat needs a larger engine, which is also heavier and it becomes a compounding downwards spiral.
    In December 2016, I was sailing up the Northland coast on a light day. In the morning I saw a yacht coming out of an anchorage way up in the distance. It was just a speck, too small to see anything more. By noon I was near an Ovni ploughing through the water at ~2.5 knots with mainsail, staysail and genoa out on a beam reach. I sailed past it at 6 knots. Later in the afternoon, it was as small as it had been in the morning, astern. Sailing boats like that is a lot of effort for so little payback… I could have creamed it with my 30′ Arpege of 1968.

    In a few specific parts of the world only, deep draft can become an issue. There are some rivers and bar entrances I can’t access here, but you can always find a bar too shallow for any craft. In all my cruising, I can only think of two places where I couldn’t go back now due to draft: a bay in the South Shetlands and a shallow inlet inland in the West of Tasmania. Anchoring “on the beach” magazine-style is hardly ever a smart thing to do. If conditions suddenly change, it all goes wrong way too quickly. To me, the supposed benefits of shallow draft are an illusion in comparison with what a design intended for sailing delivers every day.

    I found draft to be a restriction for drying up on the tide for cleaning or even painting (it seems extremely difficult to find anywhere suitable for me in NZ). At the moment, the yard where I would like to haul out in the next few weeks doesn’t have any available cradles high enough for me (but I could readily go somewhere else) and not all slipways can accommodate me either. It just means that a little more planning or patience can be needed for these jobs. I can live with that.

    In marine design, the primary purpose needs to be primary, and everything else secondary by definition. Having too many “important” requirements just results in boats that are fundamentally good for nothing in the end. The worst are the so-called “expedition yachts”. I wanted an ocean cruising yacht that could really sail and carry a couple of tonnes, this was the primary objective. I fitted everything else within this envelope.

    Kind regards,

    Eric

  7. Thank you.
    Your comment about the Ovni is very apt,speed is everything when Cruising as narrower / shorter weather windows are generally the norm…we like to get the long and exposed journey over as quickly as possible so that we can enjoy the Cruise .

    I can see the problem of draft is a determining factor in Haul Outs but a quick review of yachts in the 55 foot bracket most have a draft in excess of 2.0 meters,so here in Europe would not be a problem.

    I wonder too if the” slim” keel precludes you from drying out against a wall to either scrub down or staying in a drying harbour.
    Your sonic anti fouling system seems to be a brilliant / effective solution to a continuing problem, one supposes that you do not have to scrub down very often.

    I cannot find the height of your mast complete with antennae etc., ,but much more that 20.00 m could start to cause problems,though I still, despite the cost, like the idea of a Carbon Fibre Mast and the possibilities that it gives to raising the height without the weight penalty of aluminium.Some argue though that Carbon Fibre Masts result in a more “jiggly” motion than their Aluminium /heavier counterparts because of the differences in inertia – any thoughts?

    Whilst I know that Copper and Aluminium do not mix,would or did you consider using Copper Coat type products as your anti fouling medium applied over a substantial barrier layer of epoxy?

    There is scant mention of the Heads department is it large enough and do you have a hot water and a shower or do you resort, as we did for many years to a very large plastic container to stand in (fish box),bucket of hot water and a sponge.

  8. James,

    Draft is no effective issue for me… as you say, some of the bigger boats can be just as deep and in some cases deeper. When you dry up, the boat rests on its keel bulb, which is very substantial at 2.6m long and up to 0.5m wide. It is much more manageable and stable than a straight fin that tends to sink into the bottom. I dried up once in the South to tweak the feathering propeller, but it was an uncomfortable situation as the bottom had too much slope and I had to hang the stern to a post to control the situation. The tidal range is not quite enough here.

    I have been told from a reasonable source that some big yards in Auckland paint alloy superyachts with high-build epoxy to insulate them and conventional copper-based antifouling on top, because the other stuff doesn’t cut it. I haven’t verified that myself. I know of a 40′ alloy yacht than developed a leak at the bow after burning a hole through from electrolysis after using copper paint and I also know of a major claim with a large aluminium workboat that had been painted with copper-based antifouling by the yard before launching… Realistically, considering the fairing and the number of layers of epoxy paint involved, I have a plastic hull and I could probably use standard antifouling, at least as long as I don’t scratch it down to bare metal anywhere. At the moment, I prefer to dive and haul out a little more often than take more risks.

    The mast and antenna just reach over 20 metres. I think you could expect a saving of up to 50% on the section weight of the mast by going to carbon, to be investigated. That would represent around 80kg at 9.5m height. The additional contribution to roll inertia is IXX=m x d^2, so about 7220kg.m^2. The keel bulb contributes about 12000kg.m^2. If we say that the rest of the rigging weighs as much as the alloy mast, all up it would give IXX = 2 x 7220 x 2 + 12000 = 40880 kg.m^2 for the alloy mast configuration. The reduction would be 17.6% and it would produce a somewhat different roll motion. The keel bulb and the rest of the rigging still dominate massively however. What would really change the picture would be moving the ballast up like in a conventional design. I hardly roll, even at anchor and when everybody is complaining and leaving.

    The head is opposite the workbench forward and you could make this space as big as you wanted and even redistribute the accommodation differently inside the whole boat. These are not meaningful design changes and the kind of thing I would expect from someone building a custom new boat. My head area is quite compact, so you can brace yourself easily at sea and it has a shower and draining floor. The water feed can be switched between fresh and seawater and runs through a gas water heater, so warm water is primarily constrained by LPG only. As long as you switch back to fresh at the end to flush the system, the water heater doesn’t care. Whenever possible, I prefer to use a solar shower rather than burn gas.

    The ultrasonic system was an experiment and it is not magic, but it has been doing an excellent job with regards to hard growth. With algae, it helps, and I am starting to see that I have improved it with the recent changes I made to it, a bit more power and higher frequencies. On any alloy hull, this should be fitted from Day One with the transducers epoxy-glued permanently to the plating. Scrubbing really starts once there is no antifouling left in places in order to get rid of soft growth. The experiment is not over however, when summer arrives, the unit will be operating at higher power levels again. It takes very little to keep the barnacles away, but weed seems to be a different proposition.

    Best regards,

    Eric

  9. Thank you.
    krs
    james

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