Nordkyn Project

 
Nordkyn in Foveaux Strait (1)

The sloop Nordkyn gliding at 6 knots in very light winds

The 13-metre alloy sloop Nordkyn is the outcome a personal design and build project. In short, I wanted a new ocean cruising and voyaging yacht suitable for the type of sailing illustrated by the voyage of the sloop Yarra.

The project had a long gestation period and involved development far beyond what would have been commercially viable for a one-off. The result also reflects this.

The sloop Nordkyn was not designed to meet a long list of requirements. It was designed for sailing and shaped by experience at sea

Seakeeping performance and survivability considerations led to the design of the hull, appendages and rig. The rest is mostly details and, while those received plenty of attention, they were not allowed to interfere or compromise the essential.

I wanted…

  • An awesome sea boat first and foremost, superb seakeeping characteristics, a boat to go to sea, stay at sea and live at sea for extended periods. Long passages often go hand-in-hand with high-latitude sailing, they take you there in the first place and get you out once the season is over – unless you tuck away for the winter.
    Conditions at sea in the high latitudes are not always good, and can be terrible on occasions. The opposite is also true, some areas are under the influence of the polar anticyclones and are notorious for endless very light and variable winds, and this prompts for a boat that is also able to excel in light weather.
  • A boat fun and rewarding to sail, sharp, precise and responsive to tuning. A boat that would handle like a thoroughbred.
  • A boat structurally strong and resilient in terms of construction.
  • Good carrying capacity for food and supplies and decent room on board. The sloop Yarra could carry over a year’s worth of provisions for myself in addition to sailing gear, documents, tools and spares, but it was somewhat overloaded and couldn’t have accommodated another person on board.
  • A comfortable boat: good motion at sea, no insane rolling or pounding, moderate heel under way, good living space, good insulation, a bright interior and a view outside from down-below.
  • A simple, reliable, practical boat throughout: simple to manoeuvre single-handed, reduced interdependencies, no complex systems. In short, as little as possible that could go wrong, cause grief or require maintenance.

I didn’t want…

What I didn’t want was a huge boat

There is a relation between boat size, usability and enjoyment. It is not a case of bigger is better, there is an optimum that varies with people and the intended use for the boat. I would also suggest that – for hands-on owners undertaking personal cruising programmes – the peak moves to the left with experience and difficulty in the intended voyage, but it does remain a personal measure.

I like sailing short-handed to areas that are sometimes difficult and I designed Nordkyn to be as small as possible while still being everything I was after. It started at 14 metres, at some point I tried to bring it down to 12.5 metres, but I needed 13 metres to make it work. I gained a metre towards my optimum and I am glad I did.
The metre I lost was prompting a larger rig, larger sails and winches, without adding much of actual value to me.

Seaworthiness

Seaworthiness, understood here as dynamic handling or seakeeping performance, is still the non-quantified factor in yacht design.

The amount of attention that goes into the design of hull shapes today is often insufficient or inadequate

Since the early 1980s, systematic quantitative experiments have been performed to understand how hull resistance relates to shape over a range of speeds. This work, mostly carried out at the Delft University of Technology in the Netherlands, is still one of the most practically significant advancements in yacht design today. However, it deals with resistance of upright hulls mostly, in flat water or head waves mostly, and it has limited correlation with the seakeeping properties of the hull out at sea.

In other words, the geometric constraints over the volume distribution of a hull set out by the Delft Systematic Series are necessary conditions to obtain an efficient design, but they are not sufficient in themselves. They are extremely useful for developing potentially fast hull shapes, but the outcome at sea in terms of dynamic handling goes beyond this.

One key issue is that, once a hull heels, its properties can change dramatically from the design figures achieved in the upright condition. Heeled or upright, we are still dealing with an object travelling at the surface of a fluid and creating pressure waves while displacing it. The work from Delft University does not specifically quantify what the heeled hull should look like, but this is not to say that it doesn’t matter or should be left to inspiration.

Some design initiatives, such as the so-called and inept “powerful stern sections”, in fact result in hulls that misbehave significantly in a seaway, typically because they trim down by the bow as they heel.

The Nordkyn Project involved designing an ocean cruising yacht with a hull where the gradual change in characteristics due to heel would be deliberate and contribute positively to seakeeping, while promoting both excellent upwind performance and course stability downwind.

Anchored inside Oamaru Harbour

Nordkyn at anchor in Oamaru Harbour, New Zealand

Performance Considerations

The sloop Nordkyn was designed with no regards whatsoever for racing, ratings or top boat speed, it was developed for seaworthiness and ocean voyaging. However, it was designed to fall into a certain performance class of boats as explained in much more details further and this condition was going to take care of the matter.

In terms of sailing performance, the point is not how fast you can go; it is how slow you don’t go

Speed offshore is a matter of average daily mileage over time. The 9-metre (30′) sloop Yarra was not extraordinarily fast, it just had an insidious way of outperforming a lot of boats over time, most of them larger, even though it would often only travel at around 6.3 knots and practically top out at about 6.8 knots only.
The difference was that it got there quite readily, it climbed upwind quite well and very seldom stopped completely. Over an ocean passage, it often achieved enviable daily averages.

Long ago, I read in an oceanographic magazine that the average wind speed over the oceans of the globe is below 15 knots. It doesn’t sound like much, but there is a huge proportion of light winds and gentle breezes out at sea. When it comes to designing a cruising yacht, it would be absolutely foolish to ignore this detail.

Yarra left northern British Columbia bound for New Zealand non-stop, 6600NM away and averaged over 140NM per day until hitting the Variables coming out of the SE Trade Wind. Some slow days ensued, interspersed with near calms almost all the way to New Zealand afterwards. We made land in Tauranga, after 55 days out, having averaged exactly 5 knots, or 120NM per day. Now, even though a lot of larger cruising yachts are capable of sustaining speeds of 7 or 8 knots, they need more wind than what we had to get to 6 knots and they stop much sooner when conditions soften. This commonly resulted in lower averages on ocean passages.

Daily averages on ocean passages suffer much more from light and variable conditions than bad weather, which is comparatively rare. Sailing ability in light conditions is primordial to achieving good passage times in comfort. A boat under way is much more stable and liveable than one rolling in the sea making no headway or motoring. Concepts such as autonomy under power or fuel carrying capacity are hardly relevant on an efficient sailing yacht.

Specifications

General  
Hull Length 13.00 metres
Beam 4.00 metres
Draft 2.35 metres, bulb keel
Displacement 8600kg half-loaded, ballast 2600kg
Shell material 5083H3 welded marine grade aluminium
Interior construction PVC core/E-Glass sandwich
   
Sail area Up to 105m² upwind
Propulsion 40-55HP diesel, shaft drive and feathering propeller
   
Miscellanous  
Watertight bulkheads 3
Subdivision Lazarette, two aft cabins, galley, navigation station, saloon, toilet/shower, workshop area with bench, sail compartment
Berths 2 aft double cabins, 1 day bed
Ground tackle 45lbs CQR, 80 metres 12mm chain

 

  10 Responses to “Nordkyn Project”

  1. Hello Eric.

    Thank you for this site, for the information about the design and build of Nordkyn and for your technical articles. I’ve enjoyed reading through almost all, along with the comments, which you are most generous in replying to. I do wonder if you provide commentary elsewhere on the web; I would go looking if you did.

    I’m in the process of building my knowledge on yacht design and approaches to sailing, with the prospect of heading out cruising with my wife when we’re both retired in a couple of years. I’m intrigued by the similarity of a couple of recent yacht designs to that of Nordkyn, as far as my inexperienced eye can tell, that is. These are the Hallberg Rassy 44 and in particular, the Garcia Exploration 45. If you are in a position to offer comment on those designs, relative to Nordkyn or as stand-alone assessments, I would find that to be most interesting and helpful for my education. They are on my shopping list, but might have to fall off, for funding reasons. Which makes me think – do you know what Nordkyn ended up costing and what might a new build come in at, approximately?

    Thanks for your input, if you are indeed able to engage.

    Regards, Rick.

    • Dear Rick,

      First of all, my deepest apologies for not replying earlier. Your message was caught by the spam filter and went unnoticed until now.

      I don’t partake in too much else on the internet, the lack of time being one reason and the other is that forums are not always very constructive. It is one of the drivers for having this site up.

      Those are interesting comparisons. The short answer is that while they seem a little similar, they are not.

      The HR44 is 5 tonnes heavier without any more sail area really and the hull shape entirely precludes obtaining the same kind of performance. The buttocks have a lot of curvature located quite far aft and the deepest point is underneath the engine (!) Nordkyn’s hull is deepest in front of the keel, close to the mast step, with a very straight run from there into the stern. Curving the streamlines in the stern region causes a trough to form, the stern to get sucked down at speed. While the HR44 will “cruise” fine with sufficient wind, overall it is a slow, sluggish cruiser in comparison. The deep body and limited draft also mean quite a short keel foil, which won’t do it any favours upwind. The somewhat distorted hull seems to have been designed with an eye on what was going to be possible in terms of interior fit-out, and this is always a very bad start. Boats are sold from the inside-out however, and this is unfortunately what it leads to.

      The Garcia 45’s hull is also very curved aft of the keel and much the same comments apply, but it is not as deformed as the HR44. The displacement is about the same again. It is a centerboarder, which means internal ballast, less righting moment and less sail carrying ability. The specs from the yard don’t even quote the sail area.

      When Nordkyn heels, about half of the hull comes out of the water and you are suddenly sailing a much narrower boat with a huge righting moment and a small wetted surface. This won’t happen anywhere near the same extent with those hulls, which are quite rounded compared to Nordkyn. Both certainly are from yards that are known for quality of their construction, but I wouldn’t envy either of the boats. I want this ability to get speed out of almost no wind, steer the boat with just one hand on the tiller in nearly any conditions, point so high into the wind that almost no one can follow… I designed the boat for sailing and everything else was secondary, which was not much of an issue because there is plenty of volume in a 13-metre hull. The problems arise when “more becomes better”, when people start comparing the number of berths and the number of heads (!), as if one couldn’t be enough… it becomes silly and the outcome is no longer about sailing at sea.

      I reckon that having a Nordkyn 13 built today in a yard might set you back around NZ$1M finished and ready to go in New Zealand, in part because of the inefficiency/high margins of small building yards. A yard using its own in-house marine engineers, electricians, riggers etc should be able to do better and if it had to be competitive it could come down to something like NZ$750K. It should generally be cheaper to build one in NZ than Australia at the moment due to labour rates, but there are some big efficient boatbuilding firms in Australia. Building small craft in Poland is far better than New Zealand these days and this could see prices around €300K. I designed and built that boat because I wanted something I couldn’t otherwise find or get. It only cost me in materials and I was fairly ruthless in sourcing everything. Since I truly enjoyed building it, it was a very good deal, but this meant 5000-6000 hours of labour.
      The only areas where you can reduce costs are mark-ups on materials and external labour… and this means doing things yourself basically or building offshore where labour rates are much lower and quality is high.

      Kind regards,

      Eric

  2. Really impressed with your site and Yacht. I would be interested in the scantlings, plate thicknesses etc. Did you consider leaving the topsides unpainted in the French fashion? Nice looking rig, simple, efficient easily handled be interested in measurements.
    The articles are well presented and informative.
    I shall watch this site with interest.

    • Hello Terry,

      Thank you for the feedback. I could have mentioned the scantlings in the construction pages… The hull plating is 5mm, the deck 4mm. The plate around the keel and underneath the mast step is 8mm. The frames are 60x60x6mm T extrusions and the floors are mostly made out of 6mm plate.

      I am not very fond of the bare aluminium look, especially for the topsides where doing the work once results in a much nicer result forever. The coating seems to suffer more on the deck and leaving this unpainted would make more sense to me than the topsides. Either way, it is a matter of preference, but the bottom has to be painted anyway and fairing it to perfection is also a good idea for hydrodynamic performance.

      The mainsail has P=15.5m and E=6.2m with an area of 57m^2. From memory, the foretriangle height is I=16.8m and J=5.5m. The top of the mast is 18.6m above the water. The rig is really easy to handle, I can tack up a narrow channel under sail single-handed without any issues and do just about anything under main alone too. Sail handling takes a bit more time than on smaller boats, but it is fundamentally manageable and sometimes easier than it was on my 30-footer. It is very powerful and really responsive to tuning.

      I have been working intensely on projects and not writing much lately. I have had another go at the Wild South concept, but targeting higher speeds and outstanding economy for commercial applications like fishing. That hull would make amazing launches as well from around 13 metres up.

      Best regards,

      Eric

  3. Hi Eric,
    thanks for your reply. Could not agree more about painted decks , do you think tread plate would provide sufficient non skid properties? or I would even accept the weight penalty of teak overlay.
    Having faired a 12m hull and decks once before, cutting down on the amount of fairing by 70% has a lot of attraction.
    I agree with your concept of hull form, so many have been previously driven by rating rules and the distortions they encouraged and heeled waterlines. A moderate beamed hull with clean lines is going to give a faster passage time especially when short handed rather than a super beamy harbour racer that needy constant tweaking and a football team on the rail. High averages and good windward ability are high on my list.
    Your rig looks pretty bullet proof and easily handled, what section did you use?

    Good luck with the Wild South project.
    Cheers,
    Terry

    • Terry,

      Alloy thread plate is a horrible material, very abrasive, very aggressive (try walking bare feet on new thread plate) and to make things worse it is usually not available in heat-treated marine grades, so it is lacking strength and it is not as corrosion-resistant either. It buckles and dents very easily. My deck is covered with TBS non-skid. Even if I decided to leave it unpainted, I would still paint the walking surfaces and glue TBS on it for the non-skid and cushioning properties it has (or use some recoatable non-skid paint). What would benefit from staying unpainted (up to a point, maybe) is the toe rail, and definitely the areas around the chainplates. Now, I would anodise all my chainplates before bushing them in stainless steel and welding them in and I would keep the paint completely away from them. The presence of the stainless steel causes localised blistering. Putting wood on top of metal would be asking for serious trouble down the track. Aluminium pits very quickly in the presence of trapped moisture. Sooner or later, water will get underneath the teak and you won’t know it until it is too late.

      For me, fairing was nowhere near as bad a job as people seem to think. I used long boards with 40-grit paper and cut into the filler really quickly and efficiently. Of course, there is additional work painting before and after filling and preparing the surface for the topcoat, but it only needs done once. There is an initial time and cost saving in not painting, but it is probably more a matter of preference than an absolutely clear-cut decision.

      The mast section is a Selden C264. Interestingly enough, I could only find two suitable production mast sections for this boat. The combination of the height and high righting moment from the deep bulb keel made it quite challenging. Determining which section to use is a bit of a process in itself and it is driven by the stability curve and staying arrangements.

      If you look at recent production cruising hull forms, with a blended chine, very wide stern etc, they are only different in the topsides. The designers had to fit these “features” in while trying not to screw up the hull. They haven’t changed underwater. The stern is only wide at deck level, the bottom is in fact quite curved and narrow aft to stay away from drag, balance and bad behaviour problems. Increasing the stern beam increases the deck area and weight aft, where it is rather unwanted, so it is quite silly to try and “follow the trend” here.
      The ones that carry a lot of waterline beam aft have to go to twin rudders and incur the penalty of a higher wetted surface until they can heel (if they are also very flat, and therefore light). When they heel, they immerse the corner of the transom, which is not desirable. Lowering the transom down to the water generally is a bad design idea. It adds to the wetted surface at all speeds (very bad in light winds), adds drag at all but very high speeds and still gives no more waterline length at relevant speeds. To make this work, you need to be able to almost guarantee that the boat will be sailing extremely fast all the time. In practice, it just doesn’t happen. The overall result in cruising conditions is slower, sometimes also in racing conditions.

      Passage time really is a function of how slow you don’t go, not how fast you can go. On Nordkyn, the mileage comes from the ability to still do 6 knots in very light conditions. It becomes 4-5 knots faster than the 1-2 knots you might otherwise get if you can’t get the boat going.

      Regards,

      Eric

  4. Hi Eric,
    Couldn’t agree with you more about stern shapes, I think a lot is due to Fashion! Dragging sterns is slow and does horrible things to helm. The chine question interests me. It seems to be a cheap way of increasing waterline beam hence form stability without a big penalty in wetted area and displacement. I do have a gut feeling flattish aft sections and chines would benefit planing stability.

    Know what you mean about masts, all of the scantling formulae use a myriad of approximations and arbitrary safety factors. Since I abhor huge overlapping genoas and would plump for a max 105% headsail so I would have a wide staying base which cuts down on the transverse inertia considerably. Not knowing your righting moment even allowing for your displacement ( bigger than my proposed but different requirements) your rig must be bullet proof with a C264 section which is of course highly desirable for where you sail.

    I started looking at aluminium construction on a what if basis because of the durability and impact resistance. It seems to me not to be too much heavier than strongly cedar glass sandwich.
    Thank you for the valuable observations on decks.
    Cheers,
    Terry

    • Terry,

      Fashion, yes. The aft chine is a good idea fundamentally, but it requires a light, shallow flat boat to be able to gain from it. Production cruisers are a long way from that, so the chine needed to be moved up quite considerably, where it basically doesn’t interfere with the hull shape… Also if you generate righting moment aft, it means buoyancy developing astern with heel and it becomes very difficult to prevent a negative heel-trim couple from developing.

      Flat aft sections benefit downwind speed, but the run of the lines into the stern must also be correct. It often isn’t. I can’t see the chine doing anything for course stability. Once the flow exits perfectly cleanly, the stern has done its job. Course stability is much more complex and involves the interaction between the hull and rig as well as the appendages.
      Flat hulls have more righting moment, but also more wetted surface, at least upright. Hulls with the least wetted surface are completely rounded. Hull design really is the most interesting part and makes the biggest difference in the end. I had spent about 4 years on and off developing the Nordkyn hull.

      The rig is bulletproof with the C264 section, but the numbers don’t support going down one size, it isn’t the result of being conservative. Both Selden’s and my calculations got to the same result. It just shows how unconventional the boat is. Keel-stepping the mast is what made the biggest difference to lowering the required transverse inertia. The first span from the deck to the lower spreaders is usually the determining one for Ixx. A wide staying base and small overlap makes a huge difference in the amount of sheeting coming out of a tack, it is night and day.

      Aluminium seems to basically weigh about the same as a cored hull with strong, durable skins. Cored hulls can be lighter if you overlook impact resistance for the outer skin and just meet the tensile stress requirements… but it can be an unhealthy choice and fails to meet standards. At the limit, an alloy hull yields when a cored hull breaks, so it seems to be quite a good material choice for sailing to beautiful bad places.

      Eric

  5. Hi Eric,
    you are so right about tacking and effort, however it is the ease of trim I like. Sailng with an overlapping (say 150%) genoa in anything other than very light breeze requires constant attention or the choking of the slot actually slows you down, a smaller headsail often gives a better average and considerably less fatigue. Keel stepped should result in in 30% approx reduction in required inertia according to what I have read.

    I had been thinking along the same lines regards cored hulls, ( I have built 2). Aluminium trailer power boats seem common enough yet not sailing boats. Building a one off cored boat is not inexpensive so I was thinking Al might be an option worth exploring. Then I found your site.
    All the best, early night for me so as to get up early to watch the racing in Bermuda.
    Cheers
    Terry

    • Terry,

      I won’t be up much longer either now…

      Keeping the displacement in check is the key. Many boats end up with an overlapping genoa just to try and get enough sail area. It doesn’t do them much good upwind and these headsails get very heavy to winch in. The old IOR boats with ridiculous mainsails…

      Building alloy yachts is nothing unusual in Europe, like in France. Round bilge is less common as the skill is not so widespread, but it is nowhere near as difficult as it looks. Circa Marine in Whangarei does round bilge alloy here in NZ. I have designed both for alloy and cored laminate and I have used both processes. Building in alloy is fast, you work with big pieces of material and there are no curing times: weld and move on immediately. The work is quite clean, the material is no problem to cut and nothing is too heavy, quite a pleasant way of making a boat. Gouging seams and grinding is noisy, but there isn’t all that much of it.

      In fact, this is exactly why so many powerboats are made out of alloy. Those hard chine hulls can be thrown together very quickly from CNC-cut panels with just a basic attention to detail and having a jig is not essential. The small ones have very little internal framing, often too little.

      Eric

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