My COVID-19 Project : Thomasson Panthera

JohnAbercrombie

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I had some materials and plenty of 'hobby time' so in early May I decided to build a shorter version of the Panthera, designed by Bjorn Thomasson.

I wanted a boat mostly for day paddling, with a rudder as I might want to play with a kayak sail in the future.
I decided on a LOA of 507cm (16'8").
Bjorn's plans can produce boats of different lengths as the mold spacing is varied, and 507cm is the LOA if the mold spacing is 39 cm.

I'm hoping that the lowered top speed capability and lower cargo capacity will be offset by the reduced wetted surface area, and less drag.

So, the plan was:
Panthera 'L' (higher deck version)
LOA 507 cm
Beam 53 cm (21")
SmartTrack 'Race' rudder with both regular and tandem (deeper) blades
Forward and aft compartments with SeaLect Performance hatches
Day compartment with KajakSport hatch
4mm Western Red Cedar strips
Epoxy resin - WEST and/or System Three (System Three Silvertip on the coaming and seat as it is almost colourless, not amber).
6 oz glass on hull outside, over Dynel strips on stem and aft keel
4 oz glass on hull inside, deck inside and out
Carbon fiber deck recesses for hatches and aft coaming
Alderson style deck recesses for lines (PVC pipe caps with 3/16" stainless bars, glassed on the inside)
Carbon/glass seat and coaming
Home-built footboard and rudder pedals
Painted finish (Valspar 2-part LPU)
Amsteel deck lines in 1/4" irrigation line
Building molds cut from 3/4" pine shelving from HDepot + 3/4 plywood from kitchen demolition
'T'- strongback from 2 x 8 s - same one I've used for years
Logos from Colin Franks at Signwave in Sidney
(more to follow)
 
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JohnAbercrombie

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May 16 - looks like I'll have more strips than I'll need....temptation for another boat!
:)
May 16 strips cut.JPG

No pics of tracing half-sections from plans to poster board, then marking and cutting forms.

I got the forms set up on the strongback and got to work stripping the hull. Strips stapled to forms, edge glued with yellow glue.
I wasn't working very intensely - a few hours mid-day then a few more in the evenings.

May 28 Hull stripped
Panthera 507 hull stripped May 28.JPG
Hull glassed on outside
June 6 Deck stripped and glassed
deck glassed outside June 6.JPG
June 10
Hull glassed inside
hull inside glassed June 10.JPG
 

JohnAbercrombie

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Glassed inside of deck and got to work on the foam molds for the cockpit recess aft (to keep the coaming plane flat) and the hatch recesses.
cockpit coaming recess foam June 10.JPG


Laid up carbon and glass over the foam molds
Joined hull and deck
hull and deck joined.JPG



Cut down from the deck outside to reveal the recesses.
cockpit and day hatch recesses June 16.JPG

June 19 Foam mold for cockpit coaming glued to deck with epoxy and Microlight 410 filler
Foam mold for coaming June 19.JPG

Coaming layup
coaming layup June 20.JPG
 
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JohnAbercrombie

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June 24 Deck line fittings
Deck fittings June 24.JPG

June 25 Bulkheads- glass panels laid up, patterns picked up from inside boat using cardboard and hot glue
bulkhead June 25.JPG
bulkhead June 26.JPG
June 28 Seat- Laid up seat on mold I'd made previously, trimmed it, and installed it.
seat June 28.JPG
Footboard anchor studs (1/4") - homemade - bonded to inside of hull
footboard studs June 30.JPG

footboard studs July 2.JPG

Glassed padeyes to cockpit sole and bulkhead behind seat
Built footboard and rudder pedals
Pic of finished pedals :
Footboard pedals.JPG
 
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JohnAbercrombie

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July: Lots of filling and sanding, then primer and paint.
After paint, the hatch rims were bonded to the deck.
Then a lot of 'detail jobs': thigh pads, rudder install, deck rigging, etc etc
I also added the sail mast step and the 'button' fittings for the side stays; the rest of the sailing setup (cleats, blocks) will come later.

July 18:
July 18 launch.JPG
July 18 (2).JPG
July 18.JPG
July 18 3.JPG
 
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JohnAbercrombie

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One reason I posted so many pictures is to emphasize that the hull and deck aren't the biggest part of the job!

It's all the 'other stuff' that takes the most time.

Oh, yeah - the boat works fine. :) Needs a better motor, though.... :)
The design (like all of Bjorn's boats) has beautiful lines - it's easier to do the work - sometimes tedious- when the boat shape looks good.

I had to sell that Coaster to make room for the new boat in the kayak shed!
 
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AM

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John, that is beautiful work! What is the final weight? And how did the sea trials go?

Cheers,
Andrew
 

JohnAbercrombie

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Thanks for the kind words.
As Bjorn's website says : "Build a better kayak than you can buy." It's fun to paddle boats that are different from what is available locally, or boats like the Panthera that may be similar to boats that I'm too cheap to buy (Stellar, Epic)....... though 'saving money' by building a boat is a bit of a myth.... :)

Weight- It seems that I want to make 'lighter' boats but when it comes to the crunch decisions, I choose heavier options. Commercial hatches that are convenient and seal 'perfectly' add weight, recessed deck fittings are heavier than P-clips, glass coaming is heavier than wood, deck recesses add weight, etc etc... "Perhaps I'll use heavier glass on the hull so I won't have to worry about hard landings". It all adds up, bit by bit.
So much for the excuses! This kayak (Panthera 507) weighs in the 'mid-40s' (pounds).
If, like me, you have been 'trained' carrying 60+ lb boats, it seems quite light! :)

Unfortunately :biggrin: I owned a 27# surfski for a while and that has skewed my ideas of appropriate boat weights forever!
 

JohnAbercrombie

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Sea trials - so far it's just been flat water with a few boat wakes and current whirls and ripples, so no test really.
It does feel really easy to move through the water and quite stable. The 'feel' is pretty much the same as my longer Panthera; my comments about that boat are on Bjorns web page for the Panthera (see link above, or search on the web).
To my mind, kayaks that 'need rudders' fall into two groups - some need the rudder to go straight (surfskis), some are so hard tracking that they need it to turn (more like K1). Panthera's surfski influences mean that it turns very easily with the rudder up, but really needs the rudder in the water for almost all paddling. That's why I chose the SmartTrack rudder which doesn't stow on the deck.
This build has a higher deck than behind the cockpit (compared to my Thomasson Frej, for example) and the seat is set a bit closer to the aft coaming so I expect it will be a bit more awkward to lay back toward the back deck for rolling. A 'centimetre here or there' can definitely make a difference in the 'feel'.
 

AM

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A boat in the mid-40s sounds awesome to me.

The reasoning you give for building is sound: kit boats are less expensive and lighter than commercially made options. I’ve often thought that my next boat would have to by something like a Pygmy due to both weight and price. What’s interesting about your new boat, however, is that it also incorporates some pretty advanced design ideas — that bow is not something we expect to see on a traditional sea kayak, let alone a home build.
 

JohnAbercrombie

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Bjorn has drawn some 'traditional'-looking boats - including the Black Pearl which typifies the Greenland 'rolling boat'.
His designs which I've built are all different from the boats I could easily buy.
The Current Designs boats by Danish designer Jesper Kromann-Andersen (Prana, Sisu) have a bit of the same feel to the sheer line, I think.
Panthera:
panthera-m-l.png


Njord
njord-lines.jpg


Frej
frej-lines.png


BTW, I built these with a Romany (NDK) shape cockpit. Small cockpits don't fit with my 'easy in, easy out' attitude!
 
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JohnAbercrombie

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When I sent a few pictures to Bjorn, he mentioned that there would be a delay in posting them on his website:
I am experiencing an all-time high in launching reports now (to some extent "helped" by the corona situation).
and
I think a lot of my customers, that perhaps for years, had been thinking of building a kayak, realized that their vacation plans for traveling or spending time in a summer house abroad just vanished – what else to do but ordering kayak plans ;-)
So I am not the only builder who has 'spare time' to thank for a new boat!
 

mick_allen

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Amazing work John! . . . and a million questions could be asked but here's a few: are your bulkheads bulged? what's the foam for under the ckpt rear [scuplting the drop?], and why the stain [coloured resin?] on the deck during the build before the painting [tinted epoxying?].
Just a whole host of fantastic details going on!
 

JohnAbercrombie

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Amazing work John! . . .
Thanks Mick! When you say that, it means a lot to me.
and a million questions could be asked but here's a few: are your bulkheads bulged?
I think you are referring to the commercial bulkheads which are pre-molded and have a flange around the outside? They just 'slide in'. My bulkheads are just flat glass epoxy layups which are bonded in place with epoxy fillets on each side. I've done a lot of those and they seem to work well, and stand up to abuse when packing gear, and use as a footboard.
The decision to put in a day compartment wasn't taken lightly! It's quite tricky to fillet the aft side of the cockpit bulkhead through the day hatch......
I've done a few of those so I should know better! :)
what's the foam for under the ckpt rear [scuplting the drop?],
I think you are referring to the 'sacrificial mold' which is used to form the recessed back end of the cockpit coaming?
Two reasons:
  • lower the cockpit rim for slightly easier layback (rolling), useful especially with the higher deck version I was building
  • keep the plane of the cockpit coaming flat, which is important to keep the sprayskirt on (and make it easy to put on)

and why the stain [coloured resin?] on the deck during the build before the painting [tinted epoxying?].
When the paint gets scratched, it helps to have coloured primer and coloured epoxy in the glass lamination layer.

I also wanted to make sure I didn't 'lose' the sheerline during the filling/fairing stages. That wasn't an issue in this build, so I needn't have worried. In the past I've often used bead and cove strips just at the sheer, so the hull and deck 'snap together'. On this build it was square edged strips at the hull-deck joint so I could shine a light from inside the boat to locate the sheer joint (sheer line). The epoxy in the joint lets enough light through to show. This can be quite unsettling in a clear finished boat if you stick your head into the cockpit or a hatch and see sunlight streaming through the joint. :)
 

mick_allen

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-My bulkheads are just flat glass epoxy layups . . .
Is it an illusion, or is this bulkhead 'bulged' to eliminate stress risers:


-the 'sacrificial mold' which is used to form the recessed back end of the cockpit coaming . . .
Aha, so the foam is just laid on top of the strips, sanded to desired drop shape, glass laid on that, and the strips cut out later for the drop.
simple and effective!

When the paint gets scratched, it helps to have colour in the glass lamination layer . . .

another good idea.
**
 

DavidDeWitt

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Beautiful craftsmanship as always. Thank you for sharing.
A few followup questions about the cockpit rim

1) What layup did you use?
2) Did you roll all layers to the underside of the deck or just a few?
3) Am I correct in assuming that you trimmed the foam to the sharpie line seen in the picture before laying up the rim?
4) Once the rim had hardened what tool did you use to cut to the final size?
5) Is there any place you have collected all pearls of wisdom?
 

JohnAbercrombie

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Mick:
Bulkheads are flat glass panels with fillets on both sides. It's an optical illusion, helped by the poor focusing of the phone camera. the fillets are concave; in the pics they look convex (to me) and more massive than they actually are.
I set the flat panels in place against a few (minimum #) of hot-glued foam blocks. Something solid to lean the panel against is essential when the bulkhead is the sloped/angled one at the front of the cockpit.
Once the panel is resting against the foam blocks I use small pieces of epoxy putty (QuickWood) to 'tack' the panel in place. Then I fillet using the zip-lock bag (like a cake decorating bag) to dispense the filleting mix (epoxy and antisag Cabosil). The fillet is shaped with rounded plastic tools cut from Bondo applicators (aka 'squeegees' in the strip building world).
All my pics of this are pretty bad, but here are a few:
Before filleting
before filleting.JPG
foam and QuickWood.JPG
One side filleted
far side filleted.JPG
Another blurry pic
bulkhead June 26.JPG

Breather hole in bulkhead
breather hole.JPG

Wood core glass construction (aka strip construction) makes a hull that's so stiff that I don't think stress risers at bulkheads are an issue. I have seen a lightweight (commercial) kevlar hull that fractured right at a rigid bulkhead, but that's unusual.
I think that the flanged ('bulged') bulkheads are actually designed to allow them to be easily installed (apply resin putty to flange and slide into place) with the stress riser idea being an afterthought.
 

JohnAbercrombie

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-the 'sacrificial mold' which is used to form the recessed back end of the cockpit coaming . . .
Aha, so the foam is just laid on top of the strips, sanded to desired drop shape, glass laid on that, and the strips cut out later
Exactly. The 'removal of unwanted bits' is done from the outside (top) using a 24 grit disk in a grinder, with a light touch. :) Then hand rasping and sanding. Using different colors in the fillers and laminations helps to indicate how close i am to the essential parts when grinding and sanding away the excess. Once the outside is shaped, I usually add some light glass and filler - for cosmetics and ease in finishing, more than for any structural reason.
 

JohnAbercrombie

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David-
Thanks for the kind words.
A few followup questions about the cockpit rim
1) What layup did you use?
The carbon is really there for 'appearance' as much as any structural reason. With hand layup carbon will be heavier than glass as it soaks up quite a lot of resin and is fairly thick. It needs to be vacuum bagged to show its superior strength and stiffness vs weight. Structurally ,the carbon should be on the outside with any glass layers buried in the middle of the layup. The coaming is just the opposite.
All the cloth is bias cut.
A couple of layers of glass go on first - generally twill about 6-8 oz.
Then a couple of layers of carbon - twill works much better.
Then at least one layer of 4oz or 6 oz glass over the carbon, to protect the carbon when sanding.
All the layers are wrapped under the deck by a couple of inches or more.
I 'overbuild' my coamings because people grab them to lift the boat and during rescues boats get slid over the coaming.
After the lamination is set up, I rough trim the coaming and then add a few layers of colourless epoxy (S3 Silvertip) and sand flat.
At some point the foam mold is removed with a wire brush in a drill (with vacuum pickup nearby - foam bits go everywhere otherwise). Acetone will get the final bits. Then hand sanding under the coaming takes care of the filler that was used to glue the foam in place.
After final trimming and shaping, I shoot clearcoat on the coaming (and seat, and cockpit interior in this boat).
2) Did you roll all layers to the underside of the deck or just a few?
All of them.
3) Am I correct in assuming that you trimmed the foam to the sharpie line seen in the picture before laying up the rim?
No, that's just a line to remind me to make sure all the cloth layers go beyond that line. I mask the deck beyond the form with tape and masking paper or plastic to catch drips. It's a messy process and it's necessary to work at a steady pace to make sure things don't set up too soon.
4) Once the rim had hardened what tool did you use to cut to the final size?
I use a diamond wheel (disc) in a Dremel type rotary tool. An improvised guide helps in some parts, the rest is hand cut to a scribed line.
coaming trimmer 1.JPG
coaming trimmer2.JPG

The edge is smoothed with rasps and sanding blocks.
5) Is there any place you have collected all pearls of wisdom?
No. Most the techniques I use have been picked up from others online. Kayakforum used to be a good resource and you can still find some of my build 'logs' there. I wouldn't assume they will be available for the long term. There's been 'a software upgrade' followed by a big decline in postings. Pic uploads are disabled there, now.
That's why I'll be posting build 'stuff' here from now on.
If you see something online that's useful, download it into your hard drive! Don't wait. :)
 
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