Panthera

Oh no, of course not. I am still working on translations, adding numbers and the never-ending task of proofreading ;-)

No need for that. I believe in keeping all comments (but spam) as part of the work process, and I don't mind sharing even my silly mistakes ;-)

Besides, I am grateful for the help...

(I should perhaps add that I have deleted a couple of comments over the years at the request of the commenteer.)

Thanks Etienne, another translation error ;-)

Hunter och Panthera har snarlika stabilitetkurvor (eller snarare potential – eftersom stabiliteten beror mer på tyngdpunktens läge än på skrovformen). Wave har aningen mindre initialstabilitet med ungefär samma slutstyvhet, beroende dels på den mindre totalbredden och dels på att den smalare botten tvingar upp sitsen en aning jämfört med de andra båda.

Panthera bär sig åt ungefär som Wave i sjön, medan Hunter är en grönlandskajak som kontrolleras bättre med skädda än med roder. Titta även på Njord som är min favorit i skädda-gruppen, både för lek och långfärd.

Thanks Walt, there are two sizes indicated on the drawings (as can be seen on the thumbnail images on the Panthera page): one small (54x40 cm) indended for kayak control, rolling, bracing etc, and one large (78x39 cm), more standard sea kayak cockpit. These are simple to adjust to your own criteria.

Thanks Sukru. Yes, the suggested numbers for Panthera are calculated with a low waterline, which I in retrospect believe is too conservative (and I am going to recalculate). A waterline comparable with most of the other kayaks would indicate a designed load capacity of approx 135 kg. Above that every 17 kg sinks the kayak by 1 cm. With a higher freeboard than kayaks like Njord, Frej, Nomad, Najad etc (the surfski influence – surfskis with their open cockpit normally have a higher sheer to keep water out) there is a healthy margin on top of the theoretical numbers.

A though provocing example of kayak's (and paddler's) capacity is Jim Danielsson who started his famous round-scandinavia trip 25 years ago in an Icefloe (load capacity 150 kg) loaded to 240 kg! And did this at the Finnish-Russian borded in the Barents Sea in early April, launching in freezing temps, ice, snow, severe winter storms, along an uninhabited and dangerous coast.

So Panthera will be fine for touring, excercise and play ;-)

Thanks Daniel. Yes I think the Panthera would be fine for you, shortened to approx 500 cm. The capacity decreases from 130 kg to 116 kg, which means that you will have a net load capacity of 20-25 kg to the design waterline. And should you for some reason stuff it with 50-60 kg gear it would still float and be maneable, but a bit wetter in waves ;-)

Bear in mind though that Panthera is of surfski origin and thus need a rudder to perform the way intended.

If you (like me) prefer an adjustable skeg, you might take a look at Frej instead.

The Panthera would be fine, but with a capacity of 130 kg it would float a little high in the water when you have no cargo. But most kayaks commercially available are also designed for paddlers around 80 kg, so that is a problem you will face with most kayaks.

You can shorten it slightly (perhaps down to 533 – 2 cm less distance between the molds when you attach them to the strongback). The obvious consequence with this is that you loose approx 2% of the top speed, but you will also benefit from a slighly better maneuverability.

The Panthera is deigned to be used with a rudder (the surfski influence).

If you prefer to handle your kayak with an adjustable skeg, the best alternative would be a Njord.

Hello Dragos. No order yet from your Romanian countryman (I will pass on your contact data).

I have no final data yet for speed and stability, since I worked over the hull shape a little further after the software had done its share ;-)

But here are the files from the software (drag/speed and stability), which are very close to the final result.

Ännu oprövat, men det bör fungera. Jag kan dock tänka mig att det kräver lite mera aktivt pillrande med skäddareglaget än man är van vid.

Ett surfskiskrov, som Pantheras. är normalt helt beroende av ett effektivt roder för att vara hanterbart, dels beroende på att skrovet i stort sett saknar kursstabilitet och dels på att sittbrunnen är placerad rakt över skrovets mittpunkt (centroiderna LCB och LCF ligger mycket nära den geometriska mittpunkten). I en havskajak som Frej ligger dessa centroider en bit akter om mittpunkten vilket ger ett lugnare rörelsemönster (mer av kajakens beteende sitter s a s i skrovet istället för i rodret), men gör det också att havskajaken är svårare att kontrollera i surf.

Gissningsvis betyder det att du får jobba mer aktivt med skäddan för att få tillgång till hela prestandaprofilen: skädda upp lite för att gira, ner lite för att hålla kursen o s v. Men om detta är ett problem är svårt att bedöma utan att prova.

Som potentiell HBB-kajak skulle jag föredra en förlängd (för att kompensera för mindre packvolym) Njord: teoretiskt lika snabb (men i praktiken kan det bli längre dagsetapper eftersom den är lugnare och kräver mindre aktivt jobb i besvärliga förhållanden), liknande lastkapacitet (men mindre känslig för var lastens tyngdpunkt hamnar). Njord surfar sämre än en roderförsedd Panthera, men hur ofta har man grov sjö akterifrån under en långtur?

En roderförsedd Panthera och en stark paddlare kan förmodligen komma till Haparande någon dag snabbare än motsvarande Njord-ekipage, men det sker inte automatiskt. Det krävs en hel del råslit...

Panthera is designed for rudder, as it has a lot of surfski in the lines and hull configuration.

As with surfskis a lot of the tracking depends on a rudder, and without a rudder, you might have to work the skeg a lot to control the kayak.

Going against hard wind is no problem with Panthera. The pitching in short waves is reasonably easy to manage – again the surfski inheritance.

Panthera L would do fine for fast long distance touring, of course depending on your own weight.

With its surfski heritage, Panthera doesn't have a built-in tracking like sea kayaks. With a rudder, you can control both steering and tracking – with a skeg you can just add tracking. This means that you probably will have to use the skeg control a lot to maneuver the kayak: skeg down to go straight, skeg up to turn, down to go straight, up to turn etc – which I would consider annoying in the long run.

Both Nanoq and Panthera will be fine for long-distance touring: Nanoq with a skeg and Panthera with a rudder. Nanoq with an advantage in precision maneuvering close to cliffs and rocks, Panthera slightly faster on long distances.

But you should consider Njord as well. Almost as maneuverable as Nanoq and as fast as Panthera – to me the perfect long distance cruiser.

A shortened Panthera L would be significantly different from the Njord. Slightly faster overall than a Frej, comparable to the Njord, and more efficient surfing than both. Stability on par with a Frej, and maybe (guessing here) as maneuverable as a Frej, but probably not more (more maneuverable than Njord though). Much more room in the cockpit, which I would see as a drawback, but that is debatable (if you excuse a worn expression, Njord is a kayak you wear, but a surfski is a boat you sit on, or in – in that respect, Panthera is quite surfski-like). Furthermore, the Panthera is rudder-dependant but Njord/Frej are skeg-dependant. You may only occasionally use it with the rudder lifted – the reason being that a surfski hull is a thorough-bred with an efficient rudder replacing the directivity that keeps sea kayaks calm and easy on track.

So, compared to the Njord you get approx the same speed overall (but you have to work a little more with control), more room, more maneuverability and more stability.

Compared to the Frej you get more speed (especially off the wind), slightly more room, approx the same stability and (with the rudder up) the same maneuverability (rudder down you have more control surfing but at low speed Frej will outperform a Panthera).

Det hade jag missat – men nu finns den!

I have not built a kayak in sections. But others have. Look fx at Rune Eurenius' Sea Racer (a very good technical solution) or Dan Caouette's Black Pearl (as always, fantastic overall quality).

Of course, the kayak will gain one or two kilos in the process (doubled bulkheads, strong wooden members to take the sturdy metal bolts).

But well constructed the strength is not noticeably affected.

Thanks, Noel. These are two fast tourers, designed for rudder, with a good and predictable behavior in open sea, and with a decent room for supplies – Najad slightly more, Panthera slightly less (my kayaks are generally fast tourers rather than full-blown expedition kayaks and I support the idea of fast and efficient cruising in a lighter kayak, rather than providing volume for the load needed to compensate for the slow going of a big and heavy kayak).

To me, the Najad is good for a week on the coast during May-October, a couple of days more in inland waters where the water is used for cooking, a couple of days less in the winter months with more clothes and sleeping gear – Panthera typically one day less.

It is possible. Just shorten the C/C distance between the station molds (and of course the distance stem–sta 1, and sta 13–stern).

You will lose some top speed (approx 3%) and gain a little maneuverability – but most importantly: the load capacity will be approx 95 kg instead of 120 kg.

Hi Jacob

I have three partners that build kayaks on order from my plans: one in Sweden, one in USA northeast, and one in Finland. In other parts of the world, you have to find someone yourself; a local boatbuilder most likely, or a competent amateur will kayak building skills.

You can use an aft-hung retractable rudder (fx SmartTrack), but more efficient is a surfski-style under-the-hull rudder – both are easy to attach to the Panthera and are indicated on the plans.

Petruskajak i Tranås och Tunarps Kvarns båtbyggeri.

Panthera was designed in response to a couple of requests for a surfski with kayak deck. The first one to build wanted a not too long but initially stable kayak and that became the starting point for the hull shape.

If I were to design an optimal speed machine I would have reduced the beam to approx 50 cm and increased the LOA to somewhere around 580 cm.

A surfski-style hull doesn't have the directional stability of a sea kayak and, thus, needs a rudder to be controllable. Of course, a fixed sked turns it into a sea kayak, which may improve the flat water speed, at the expense of the surfing qualities.

My experience is the opposite – the width, 50 cm, means that you have full control of how the hull moves in the waves, while in a wider, more initially stable hull, the waves will control the hull. What you need in waves is a lot of secondary stability, not initial (you don't capsize from an upright position, if you capsize, you will do it from overtaxing the secondary stability).

The hull will get slightly more weight in the front end since the foredeck is higher, but since this is a surfski type of hull (designed that way, to improve speed and maneuverability on big waves) the seating position is above the turning center of the kayak, not behind it, as is the case in most sea kayaks. This means that the kayak lacks the tracking that is an important feature in sea kayaks calm movements in waves – a surfski is more maneuverable and relies on an efficient rudder for both tracking and turning, and can thus perform on waves in ways that would be impossible in sea kayaks.

Due to this hydrodynamical arrangement, a fixed skeg would be counterproductive and will turn a high performance surfski hull into a more middle-of-the-road sea kayak. I recommend that you try such a skeg (tape it in place) before permanently attaching it.

For an additional SEK 350, I can make whatever adjustments you want to the dimensions, to provide Petrus with a correct set of plans – with the caveat that if you want changes that goes beyond my design criteria for the kayak, the responsibility for its performance is yours ;-)

Contact info in the left col of the about page

...and here:

bjorn@thomassondesign.com

Tel +46 (0)46 139416

+46 (0)721 979390

Pantheran har ungefär samma initlastabilitet som Frej.

Fördäcket behöver vara högre än på Njord och Frej, för att ett surfskiskrov behöver ett effektivt roder och ett bra pedalsystem – och för att kunna manövrera pedalerna krävs höjd.

Liten sittbrunn kan användas, men för Panthera kan det bli lite svårhanterat eftersom det blir besvärligt att nå pedaler och linor för justering framme under fördäck. Så jag rekommenderar en större sittbrunn.

Jag har laddat upp en mer utförlig version av roderidén på download-sidan, inklusive några bilder från mitt prototypbygge.

På min testmodell är lintrissan tillräckligt tjock för att bara kunna röra sig vertikalt ca 3-4 mm innan den slår i "taket". Men under testerna laminredare jag dit en fals som stoppar rodercylindern uppåt. Lintrissan med sina styrlinor ligger lös i det övre cylinderfacket och man kan släppa på lyft/sänk-linorna och dra ut rodercylindern med roderbladet för service (t ex dra ut roderaxeln och byta roderblad), medan lintrissan ligger kvar under däcksluckan. För detta behövs inga verktyg – roderaxeln hålls på plats i roderschaktet och rodercylindern av lyftlinorna.

Det här fungerade bra vid de tester jag gjorde. Däremot var roderbladet på prototypen för litet för att fungera som tänkt – blev ett racingroder istället för ett surfskiroder ;-)

Det blev sedan inga fler rodertester. Jag fick andra kajaker och utveckla, bygga och testa – kajaker med justerbar skädda istället för roder.

Så rodret får nog tills vidare betraktas som en tämligen otestad idéskiss – en som fungerar bra mekaniskt men som är oprövad i en relevant storlek.

Ja, det är viktigt med fotstöden. Precis som när man cyklar är det främre trampdynan som skall ha stöd, så att man kan jobba även med vadmusklerna. Annars finns risk för kramp i benen vid vid längre paddlingar.

Den numera vanliga lösningen för pedaler är att göra merparten av pedalen fast och bara en övre tå-manövrerad del rörlig. – en tämligen välfungerande kompromiss mellan bra avstamp för foten och rodermanövrering.

Jämfört med de gamla pedalsystemen (helfotspedaler, fästa i nederkant, eller ännu värre, glidande fotstöd direktkopplade till styrlinorna!) är det en riktigt bra lösning.

Bra är också VKV:s gamla "svängel" – en fast, högt placerad fotbräda med ett spår i mitten där en "rorkult" sticker ut. Denna skjuts i sidled med fötterna för att styra. Finessen är bland annat att fotbrädan kan justeras fram och tillbaka utan att styranordningen behöver röras. Detta fungerar förstås bäst i en racing- eller maratonkajak där man använder rodret främst för att hålla kursen, men lite sämre i en surfski där rodret används kontinuerligt för att kontrollera kajakens hela beteende.

Magnus, det går alltid att anpassa. Längden är inga problem att ändra, men på bekostnad av lite fart. Höjden på däcket är också relativt enkelt att få till – men det behövs förmodligen inte. Pantheradäcket är lägre än de flesta motsvarande kajaker och inte högre än vad som behövs för roderpedalerna. Bredden är däremot knepigare. Generellt behövs en omritning av hela skrovet för att ändra bredden utan att det uppstår formfel som påverkar egenskaperna. Men ett "fulhack" som funkar hyfsat bra är att köra de relevanta partierna av ritningen i en kopiator där höjd- och breddimensionerna är individuellt justerbara. De småfel som kan uppstå är lätta att korrigera under slipjobbet.

Jag kan också om du vill justera måtten efter dina önskemål. Ritningen kostar då 1500:- istället för 1000:- (justerjobb + extrakostnaden för en ritningsomgång (ingen mängdrabatt från tryckeriet)) och en eller två dagars extra leveranstid .

Men kan du tänka dig en surfski, tror jag att en kortad Spindrift skulle vara tämligen idealisk för dina behov: enkel att använda, snabb och utmärkt i vågor.

Hi Baldwin,

The internal height of the L version at 122 cm from the backrest is 31 cm – but for a little margin, it is quite easy to lift the foredeck slightly (build up the molds with veneer/cardboard, starting with the center strip, and then just make sure the strip layup looks nice longitudinally and transversely).

The weight of the extra strip area if you lift the foredeck will be negligible, but you might want to move the seat approx 20 mm aft from the indicated position since you seem to have longer legs than I have.

Frej is designed for a different paddling culture than Panthera. It is a skeg kayak meaning that you don't need the height to work a pedal system, and it is intended for long-distance touring and play in waves where you may want a lower, more relaxed stroke geometry, rather than a higher competition style. The low deck is also beneficial for rolling – Frej is as easy to roll, even the more complicated Greenlandic rolls, as a dedicated Greenland rolling kayak.

Yes, the Panthera L is a good starting point – it was initially the answer to a request from a paddler of your size.

Hello BJ, Panthera is special in that it in essence is a surfski with deck, and as such it balanced somewhat differently than ordinary sea kayaks.

The main difference is that a sea kayak hull tracks more or less efficiently – more of it is intended for rudder, that overcomes the tracking for turning, and if less, there is an adjustable skeg to improve the tracking when needed. In a reasonably maneuverable sea kayak, I also prefer to lift the rudder or pull up the skeg to have full control over that boat in big surf – hard work to steer during surfing but enough control to avoid a perhaps dangerous broaching.

A surfski on the other hand is balanced to have minimal tracking, and an efficient rudder system to control both the course and turning. This gives it maneuverability on wavefronts that a sea kayak can never match – and of course, it surfs with the rudder down at all times (compare with fighter planes of gen 5, that lacks stability I free flight and must be controlled by fly-by-wire and a computer – giving them unparalleled maneuverability).

But to be really efficient in big surf you should have an under-the-hull surfski rudder some two feet from the stern. Most Pantheras has been built with aft-hung rudders, which is fine for touring and in shallow waters, but such a rudder risk hanging above the water when surfing steep waves and thus occasionally of no use – but on the flip side, no particular risk either).

Talk to surfski paddlers for tips. I don't know much about the surfski circus on your side of the Atlantic, but the best youtube video I have seen is Oscar Chalupsky's (google "Oscar Chalupsky surfski clinic"). But apart from being more rudder-dependant than most sea kayaks, you paddle the Panthera just like any other kayak. It has though a potential that most sea kayak lacks and to take advantage of those, you need to practice surfing skills and competitive paddling techniques. But that is optional ;-)

Panthera M har en 40x80-sittbrunn, och L en 42x83 cm, vilket i båda fallen är realtivt stora sittbrunnar. De kan utan att tappa styrka och hållfasthet ökas lite grann om det skulle finnas någon anledning till det.

Men funderar du på en betydligt större sittbrunn är det bättre att bygga en Spray, där sidoväggarna i brunnen ger den styrka som behövs.

Men det handlar om två olika funktioner. I en havskajak bör sittbrunnen inte varav för stor, eftersom tryggheten och kajakhanteringen bygger på att man är ett med kajaken, och kontrollerar den genom kroppskontakt med däcket, knästöden, fotstöden ocxh svankstödet – och att en mycket stor sittbrunnssarg gör det svårt att få ett kapell tätt. En öppen surfskisittbrunn sitter man i utan annan kontakt än sittytan och kontrollerar därför kajaken i högre grad med paddeln och rodret och det vatten som oundvikligen hamnar i sittbrunnen sugs ut när man öppnar bottenventilen i fart. Två olika system där mellanvarianter löper risk att vara varken eller.

Förr fanns det kajaken med väldigt stora sittbrunnar, men det var antingen tävlingskajaker avsedda för rakbana på plattvatten och ett enkelt nylonkapell för att hålla skvättandet från paddeln ute eller gamla skärgårdskajaker med så hög sarg att man paddlade utan kapell mellan öarna i fint väder, och med armarna högt för att inte slå i den höga sargkanten. Det har hänt en hel del sedan dess.

Det minskar bredden på sidodäcken en aning, så jag hade nog för säkerhets skull lagt ett extralager glasfiber på undersidan av däcket längs med sittbrunnen.

Thanks Jenny, I hadn't seen this. Very nice that he set this record!

Yes and no ;-)

It is a standard Panthera L but stretched to 572 cm, by positioning the molds +1 cm further apart. The drawings show how this is done for different LOAs.

As mentioned above, the kayak was initially built for a long-distance expedition, which required extra room for provisions, and was later repurposed and repainted for this record attempt.

Hej Thomas, Panthera är väldigt mycket surfski, vilket innebär två delvis motstridiga egenheter: dels att den är ritad för goda prestanda inom ett lite smalare spann av lastförhållanden, till skillnad från vanliga havskajaker som klarar sig bra med både för lite och för mycket last, men aldrig riktigt når surfskins potential, och dels att surfskiskrov generellt har lite högre däck (för att minska risken för vatten i den öppna sittbrunnen: på surskis för att minimera vatten på däck – på Panthera för att få plats med surfskipedaler under däcket) – men det högre däcket innebär också att fribordet är större och därmed att det finns en större marginal för "överlast".

Tillsammans innebär det att kajaken kommer att fungera utmärkt även med din fulla last – naturligtvis med de nackdelar som alltid följer med tung last; att kajaken går lite tyngre i sjön, får lite större levande massa att hantera vid accelerationer, inbromsningar och girar, och tar mer vatten på däck om man pressar på för hårt i krabb sjö.

Men du kan kompensera för detta om du har plats i bygglokalen till att öka längden lite; t ex 1 cm mer per spant till 572 cm total längd eller 2 cm per spant till 585 cm. En sådan ökning förbättrar beteenden med full last på bekostnad av egenskaperna med liten eller ingen last, men utan att skrovet blir ett besvärande vindfång. Det krävs ca 18 kg för att ändra flytläget 1 cm upp eller ner.

No, scarphing is quickly and easily done without any disadvantages. Scarphs are, of course, visible when looking close, as they are on all beautiful wooden yachts out there. Very few kayaks are built with full-length strips. Building time isn't affected noticeably and the strength and durability are the same. Staggering is, of course, important

I have not had the opportunity to try out a modern Inuk, so it will be mostly guesswork based on the dimensions. Inuk and Panthera cater for the same paddlers and the same usage and are similar in dimensions. I have spend some time discussiong kayak hydrodynamics with Rob, and we have similar views on design/function. But, still, I would dare a guess that Panthera has slightly more initial and secondary stability, based on the assumption that there is a higher seat in Inuk 18 (indicated by the higher foredeck and Rob's preference for racing seats(as I remember it)), which means a higher center of gravity. The lower seat and foredeck in Panthera means more overall stability without the disadvantages of beam-induced stability in bumpy seas, and a lower profile to catch wind – and of course slightly less load capacity.

On all my designs I outline two optional cockpit sizes: large (approx 40x80cm) and small (approx 38x58). Most paddlers chose the large while I prefer the small. The large is more convenient getting in and out of the kayak (which takes a few seconds) while the small is more comfortable, safer and offering better kayak control and a better seal with the spraydeck during the long hours of paddling. Aquired taste I believe ;-)

The intermediate sizes are thought of as relevant one-size-fits-all solutions – suiting a large share of the paddlers, while being managable for those who find it too short. Tall paddlers will have to use it as they would a small cockpit, but without the benefits that comes with that.

It is not very inconvenient for tall paddlers, just a bit annoying. You hold the paddle on one side as a stabilzing float while embarking or debarking. and sit on the inboard blade while sliding into the cockpit with straight leg. It takes no more time than getting into a large cockpit and can be done everywhere: beach, rocks, high or low piers etc...

The compromise is not a Scandinavian tradition, but an industrial mass-market consensus. Older Scandinavian touring kayaks often had very long cockpits of 90-105 cm, and those built in Greenland traditions had small cockpits.

It was not my intention to convince you, but to discuss the complexity of the issue. I agree with you that a compromise is not always a good solution – and you'd prefer a bigger, I a smaller cockpit hole.

I am also too tall to be able to use a compromise cockpit as intended (183 cm/83 kg) and have tried and used all kinds of cockpits during my 35 years of paddling, designing and building kayaks. Eventually I ended up favoring small, so called, ocean cockpits, that perfectly suits my main usage (long distance touring along the Swedish west coast and southern parts of the Norwegian).

I could go on about the advantages I find (as I have elsewhere on the site ;-) but that is not the point. Everybody has to find the way that works best for him or her, based on experience, preferences etc...

Hi Kreso

I have only the plans for strip construction. The files for S&G belong to PetrusKajak in Tranås, Sweden, and are sold as a kit (CNC-cut panels, epoxy, fiberglass, fittings, etc), as an 8-day building class, or as a finished kayak.)

Calculating average speed over days is often a depressing experience. As you mention, pauses, food and drink, other pressing matters requiring going ashore, currents, headwinds, waiting for commercial traffic to pass, waiting for an opportunity to pass an unprotected cape in bad conditions, etc, all take their toll on the efficient speed over time.

Furthermore, those who make surprisingly fast long-distance trips (Erik B. Jørgensen, Jim Danielsson, Petri Sutinen, Freya Hoffmeister etc), are often not the fastest paddlers or have the fastest kayaks. They are well-prepared, stubborn, and efficient ashore, minimizing the time out of the kayak.

Panthera is a very fast and efficient cruiser for long-distance paddling. But for me, I get farther in varying conditions in my Njord than in any other kayak I've tried – but the important thing here is not hullspeed, hydrodynamics, or drag. Rather, the initial stability is low, meaning that the hull moves calmly and efficiently in seas, letting me handle the conditions without the kayak getting in the way. Furthermore, the hull is low, with a very low center of gravity which means less resistance in a headwind and a rock-solid secondary stability. Together this means I get farther with less work and never waste time on support strokes or feeling insecure – my strength and stamina get me more kilometers than in many faster kayaks.

But the choice of kayak is personal. You have to find what suits your preferences and purpose best.

For a HBB, I would use my Njord, or build a new, slightly longer one...

Of course, something happens if you make significant changes in a unified design like Njord, where every design decision points to a narrowly defined performance range.

Your suggested 5 cm higher deck will, if loaded with proportionally more gear, increase the wetted surface and thereby the friction, and the added displacement will increase the wave-building resistance – adding up to more power needed to maintain the intended touring speed. But that, of course, will happen regardless of the kayak type.

For the interior volume other things happen. If you sit on a low seat you will have a less comfortable paddling position with arms higher, and you will need to raise your knees to reach the thigh supports or underdeck (which raises the center of gravity). If you raise the seat you lose much of the initial stability of Njord and may find it too tippy (to some extent countered by heavy load in low position). But you may want to widen the hull to get back the proven balance between initial and secondary stability that Njord is designed for – and in the process get even farther from the original Njord design.

The Njord construction is a proven long-distance cruiser, but of course, it can be tweaked in different directions – but you can never get away from the fact that the total weight of the kayak, paddler, and load, displaces the same amount of water, which has to move away in seconds when the kayak glides through and has to flow back after the passage. How the hull conversion is handled defines how much of the original performance characteristics will translate into the adjusted version.