Shrike, a lightweight sea kayak for home construction.^

[PlymouthDamo]

but Damian was there, and he'll know details of the damage.

I can do better than that Nick... The incident you mention above was on the maiden voyage of my Shrike-R when Paul M. managed to crack my deck with his elbow whilst we were getting him back into his boat after a swim. That was down to the excessive amount I'd bent my plywood deck around my goalpost shaped masik, which had clearly resulted in too much stress in the wood, which was looking for any excuse to split. Since then, I helped Paul build his own low-volume Shrike using 3 separate panels, rather than one panel bent round beyond its breaking point. The result looks brilliant - I think it's the best looking Shrike deck I've seen, and it allows us lanky buggers to fit our knees comfortably into an extremely low volume boat.

I've also had my hull holed when someone who shall remain nameless inexplicably rushed in to 'rescue' me after I failed an 'exotic' roll I'd been learning. When I rolled back up using a basic roll, I found their sharp, pointy end was embedded in the side of my boat.

Finally, I once found myself unintentionally running 1" deep white water in my Shrike-R which resulted in the sharp rocks knocking a hole in the hull under my backside.

Bringing it back to Simon's question: yes, I've proven you can hole these boats, but it takes some pretty careless paddling, and it's a doddle to fix them after. If I make another one, I'll definitely stick with 3mm ply without any glass cloth as that's proven more than adequate for normal paddling and general knocks and wear and tear. For the three incidents mentioned above, there have been hundreds more which have resulted in no more than minor scratches.

[ChrisJK]

Thanks for the robustness tests Damian.
My Shrike has now got I't's first coat of epoxy so getting near completion. I decided not to go for exterior glassing so hopefully I'll not regret that.
That does however keep the weight down. As does using a squeegee to spread out the epoxy. Forget those rollers, use a brush and recycle old membership cards.

From a cost/estimation point of view. I bought 6Kg of resin but if I had used a suitable device might have kept that to purchasing 4kg.

As a complete novice It is easy to either under or over estimate. I possibly have enough epoxyand glass fibre left for a third to half another Shrike.
As a reference for anyone just starting I think I used around 180g of resin mix to coat the entire external craft.
When glass taping the seams take great care to fully wet out the join and tape and make sure there is full contact or you will be left with voids which can be seen if not painted and will be weaker.
Read the manual several times.

[nickcrowhurst]

Joe in Singapore sent us this message and photo:
Today I did the maiden launch of my Shrike and it's a dream to roll. This is the only kayak I have built so far that I can static brace with. I built it out of 4mm Keruing/meranti marine plywood and weigh slightly above 15kg as a 3-piece sectional kayak with 40mm freeboard reduction. I have made my own spray skirt out of waterproof ripstop. My next step is to shift the seating arrangement forward as I was not getting sufficient thigh support. Thinking of adding a back band soon too! Once again, thank you for the plans and I look forward to getting more water time with it!

[eskapist]

Nice decor idea!

[nickcrowhurst]

Received yesterday from the Russian sea kayaking forum, news of 6 more new Shrikes from Asp:

‎Hi Nick! I hope that your back injury is curable and you will soon be able to enjoy kayaking again! Good luck and a speedy recovery! ‎
‎ I think you will be pleased to know that for myself and my friends I built 6 kayaks according to your project: the smallest length is 340 with a width of 44 cm, the largest is 548 cm and a width of 42 cm. Of course, for this I had to redo the drawings, but still they are all Shrikey! Thank‎
‎ you and Chris for this wonderful project, and good luck!‎ Asp.

The original message:
Привет, Ник! Надеюсь, что твоя травма спины излечима и ты скоро снова сможешь наслаждаться каякингом! Удачи тебе и скорейшего выздоровления!
Думаю тебе будет приятно узнать, что для себя и своих друзей я построил 6 каяков по Вашему проекту: самый маленький длиной 340 при ширине 44см, самый большой - 548см и шириной 42см. Конечно, для этого приходилось переделывать чертежи, но всё равно все они - Шрайки! )
Спасибо вам с Крисом за этот замечательный проект, и удачи!

And here's a lovely pic of Asp & child:

[nickcrowhurst]

Viktor is our first builder in Ukraine.This morning he sent me an email:

Hello Nick!
Finally the day has come where I
completed construction and carried out the first tests of the Shrike.
I admit, I have never kayaked until today, it is difficult to keep balance at first, but it's very cool!
Thank you very much, I enjoyed the construction and the first kayak trip.

[ChrisJK]

I wish that one could see and if necessary remove misplaced images rather than a string of numbers and forward slashes.

However hopefully amongst this there should be a view of the slot in ocean cockpit plus a wooden camouflage for the hatch covers with a view of the Kajaksport skeg box.
Hopefully there is a picture of the fitted cockpit which I found I could just about enter and exit when clothed with two boiler suits to replicate a dry suit and under layers but I thought probably too tight in an emergency so I will look at how to enlarge the opening. I do like the connection with the kayak the ocean cockpit gives but possibly for a full Shrike the Masik needs to be slightly further aft and with a steeper curve but I know very little. I am loving the problem solving nature of building this boat and the aspects of customising it. I can see that if bold enough one could chop out the cockpit section and play with it ?
Near the stern cover there is evidence of a leak in my garage roof with a streak of amine blush just by the hatch cover. Which indicated? that actually the whole ship was similarly inflicted and when I started sanding I would actually find the disks rapidly clogged with crap ergo I thought it might be best to wash the whole kayak which resulted in an entire amine blush this is following a coating of epoxy seven days previously. The photo was taken after three washes using a scrubbing brush and fairly concentrated sugar soap and subsequently concentrated washing up liquid and a rinse.
Help what is the next step? More of the same or a hard sand?
Thanks again to all contributors




I bounced back to preview and I think I have included most of what I to convey apart from the amine blush image, should I just sand over this and re apply epoxy or continue scrubbing with detergent,try a solvent like white spirit or take the boat out for a few paddles to wash off the problem and then apply a second coat?+

[Paul-C]

Is the surface still greasy or sticky, or is it just discoloured?
I've experienced amine blush that is either greasy or sticky, depending on the brand of epoxy, but in all cases it has washed off quite easily. Are you sure that the epoxy has cured properly?

If the epoxy is hard, but discoloured, that might be down to the working conditions. I think some epoxies can cure with a milky colour if it's used in very cold or damp conditions. That's possibly what's happened where your garage roof has leaked.

[nickcrowhurst]

Chris, are you still using that cheap epoxy from Amazon? I've never had a problem with amine blush. I use MAS epoxy as I recommend in the Build Manual, and as Chesapeake Light Craft uses. When another company sent me some impregnated cloths, gratis, with some MAS to "prepare the surface" I had a disaster as clearly the cloths were not compatible. I had to remove the mess with a Skarsten scraper, followed by coarse grit paper, down to the bare wood. Not a happy experience. I think Paul-C has it right. I'd hate to think that aspiring builders might be put off by this sort of problem.
https://www.epoxy.ltd/shop/epoxy-resins ... vis-resin/
I used WEST for many years, but now use MAS. This video is well worth watching:

[ChrisJK]

Thanks Nick and Paul
Firstly the epoxy wasn't randomly bought on line it is called professional epoxy coatings which i bought from Fyne boat kits. It it I assumed that it would do the job. I bought it as it claimed to be low in toxic vapours. Perhaps I should have bought something else but I thought it would be cured after a week so it would have happened if I'd gone for a test drive.
Re Paul's suggestion most of the kayak was covered it's just a shame that the drip found that bit of the boat or I would have been none the wiser. I may well have made a big mistake in scrubbing the boat but easy to remove is not how I'd describe it so possibly what has happened in that the partly cured epoxy has discoloured. As can be seen from the cockpit pictures it looks fine and dandy and one assumed it would stand a wash. If Paul is correct then I would hope that sanding and a fresh coat will do the trick probably with the proviso that I leave it for a couple of weeks before it gets wet. Making sure that drip doesn't make life hard for me. I had thought to wet sand it but given Paul's comment probably dry would be better.

[Chris Bolton]

Chris, the key thing to establish is whether it's cured fully. If it hasn't, it never will, and anything you put over it will be wasted. I hope that isn't the case. If it will scrape off, it hasn't cured. There's a thread on SOTP where a similar problem occurred, and the poster eventually found a solvent that would remove the uncured resin.

[ChrisJK]

Thanks Chris.
think I mixed the epoxy at the right proportions and I have spent an hour or so sanding the whole boat and was thankful I had bought that orbital sander and a pack of P120 disks..
The stuff was mostly powdery with a few waxy spots so possibly those washes were not in vain. So yes it it is a hard surface.

I think it might have been helpful to sand the ply before I epoxied as some of the stuff is wedged in micro pits.

I hope that as it now stands the sanding has helped and whatever has occurred will disappear with a fresh coat of epoxy or add a slightly distressed flair.

One of my customers who has built a canoe and have shared some of my progress when I mentioned I could have made use of his father's (101 in June) garage, he said please do. So for the next coat I think I will take up his offer.

I attach photos analysis please

[Chris Bolton]

whatever has occurred will disappear with a fresh coat of epoxy or add a slightly distressed flair

I hope so too. What I was trying to convey in my previous post is that, unlike some other coatings, you will never get uncured epoxy to cure by being in contact with a new layer as that's curing. Since you're down to a hard layer, that must have cured, and if there are any small pits that end up uncured, they should be small enough that they won't matter.

[simonballantine]

Those white deposits are probably a mixture of dust and wax from dry sanding the amine blush. It looks like they are stuck in all the tiny depressions. Best to go over the top with prep at this stage to avoid making a mess of it!
Since the boat it is now fully coated then it is a no-brainer to wet-sand the whole lot, whilst washing it down with lots of warm water and detergent. This will shift and wash-away any remaining wax and prep the boat for the next coat, all whilst making no dust.

[ChrisJK]

Thanks all.
It is probably a number of factors with the coat possibly not being fully cured I may also have got the proportions and mixing slightly wrong but have generally got on ok with this epoxy.
I talked to Phil at Fyne boat kits where I bought the epoxy from as they use it all the time with no great problems. He was helpful.
I will put the boat in a warmer drier place for a while give it a light sand and test coat it somewhere.
I would be reticent to give it a wet sand now as it might produce more of the same and there are now areas of bare wood. The coat is generally hard. It got washed with detergent about 5 times using a small scrubbing brush so I assume any wax will have gone
Thanks for suggestions.

[charleston14]

Skeg:
It’s easy to buy a kajaksport skeg slider and a 3mm wire but where do you get the “compression fitting” and a suitable tube from? You can’t get these from the karitek website any more

[Oisin]

I got all the parts from karitec, contacted them directly rather than via the website

[ChrisJK]

If this is Argyle Kayaks you are speaking of the main lady has been unwell so patience/perseverance may be needed. I bought the whole kit kayak sport skeg assembly including skeg,box,wire and slider as it was just £2.00 more than the Karitek 'Shrike kit' see my recent posts and they are included amongst the faff about uncured epoxy.

[Chris Bolton]

where do you get the “compression fitting” and a suitable tube from?

I don't know if it's the same, but on my Rockpool GT the fitting is a pneumatic connector, which is available on eBay - select "Male stud" and "6mm tube BSPT 1/8”" from the drop down. I assume pneumatic tubing to match but haven't actually bought that.

[nickcrowhurst]

https://www.ebay.co.uk/itm/113351940919 ... SwAThb4Fqc for the compression fitting.



6mm x 4 mm plastic pipe: https://www.ebay.co.uk/itm/380558137013 ... BM5sP43JVf

[on the rocks]

I’ve not read all the posts but are the Shrike and Vember named after two of the most beautiful rock climbs on Cloggy, rather than the Shrike just being named after the bird?

[nickcrowhurst]

I thought of calling them Llithrig and Octo, but then I remembered the lady who ran the café at the halfway house on the track by the mountain railway. She had a daughter called Vember, so it was meant to be. And Shrike was another dream.
Nick.

[nickcrowhurst]

It's great to have Simon, a highly qualified engineer, as a Shrike builder. At our request, Simon has prepared a paper on the theory of some practical means of enhancing the robustness of a Shrike for particular needs. We don't glass the Shrikes as they are strong enough for normal use, and glass covered plywood is much more difficult to repair in the event of a scratch. However, reading the paper makes us much better informed on future options. Good work, thank you, Simon. Here's the paper:

Maximising Strength Whilst Minimising Weight.

The standard Shrike is very robust and reports of failures or damage are very few. But if you are prepared to add some weight to achieve a particularly robust boat then here are some ideas to efficiently add strength without adding too much extra weight.

The most vulnerable parts of the boat are the plywood hull panels in the cockpit area, particularly beneath the seat. These panels are relatively wide and are vulnerable to localised impact damage under the full weight of the paddler.

There are two easy and lightweight options to significantly strengthen this area:-

Sheathing the inside and outside of the hull panel with glass cloth creates a very efficient composite ‘sandwich’ panel. Under a localised point load the outer skin of the composite panel is in compression and the inner skin in tension. These two forces are always equal, so it is important that both faces are sheathed with a similar thickness of glass to achieve the best strength gain. If we sheath 3mm plywood with a light 100g/m2 twill cloth on both faces we will increase weight by a third, but the bending strength of the composite panel will be in the order of four times that of the plywood alone. The strength to weight ratio is improved by a factor of 3.

It is very much more efficient to do this than to simply add glass cloth to one face of the plywood, which would give only a marginal strength gain.

Using 140g/m2 or even 200g/m2 glass cloth on both faces will give even better improvements in the strength to weight ratio. However, heavier weight glass cloths produce a coarser-textured finished surface. This is not an issue internally, but the external hull surface will need to be filled with (heavy) resin to get a smooth surface. For a high-strength job it is better to use 2 layers of a lighter cloth. My preference is to cover the 100g/m2 twill with 30g/m2 glass tissue to achieve a smooth surface whilst adding a little more strength.

To coat the full hull (not deck) inside and out with 100g/m2 glass twill wetted out with 120g/m2 resin will add 1.25Kg to the weight of the boat. However, this process offsets the need to epoxy-coat the hull inside and out, so the net weight gain should be about 1Kg. Not bad for a fourfold strength gain.

A super-lightweight option would be to sheath inside and out with just the 30g/m2 glass tissue. This would approximately double the plywood strength for a tiny weight penalty against coating with epoxy alone.

Loads on the hull tend to be greatest at the cockpit and reduce towards the bow and the stern. The panel widths also reduce towards the ends of the boat, making the ends inherently more robust. The most efficient arrangement would be to increase the sheathing thickness in the middle of the boat and to reduce the sheathing thickness towards the ends of the boat.

Another other way to strengthen the cockpit floor is to add a series of small transverse ribs to the bottom hull panels under the seat. Ideally these would be something like 10mm high*15mm wide foam strips glued to the inner face of the plywood before sheathing with glass. Proper foam is expensive and light timber could be used instead. For maximum benefit lay up 2 or 3 few strips of unidirectional glass along the top of the ribs, but 50mm glass tape can be used instead for a small weight gain. It would be possible to profile these ribs to form the shape of the seat… The ribs should connect to the side hull panels with the glass reinforcement lapped up the sides of the boat by a few cm to transfer the paddlers weight to the vertical sides of the boat.

The deck is not normally subject to the same impact loads as the hull, so the benefits of sheathing inside and out to convert the plywood into a composite panel are not so clear. The 3-fold increase in strength to weight ratio remains true for the deck and sheathing inside and out would give a particularly robust boat for a further weight penalty of about half a Kilogram. Sheathing the cockpit area between the masik and the rear bulkhead would be particularly beneficial since the cut-out for the cockpit significantly reduces the overall strength of the boat here.

So I’ve given a few ideas of how to make the boat heavier, but where can I save weight in the build?

The shear clamp is a big piece of wood. We can halve the weight of a rectangular section by cutting it into a triangular section on a table saw. This will have give significant loss of strength but it does mean that you cannot use the shear clamp to fix screws to.

Epoxy fillets are heavy. Taping the hull joints inside and out gives a joint 4 times stronger than the plywood, so there is no need to add a big epoxy fillet to make it stronger still. Use the epoxy just to fill the gap between the plywood edges and to produce a fair curve for the tape to follow. For best results wait about an hour for the fillet to just start to set and then tape over the joint whilst the fillet is still malleable. You will maximise bond and use a little less epoxy to wet out the tape.

Using glass bubbles as a filler for the filleting mix will give adequate strength and will be lighter than using silica. I use a mixture of the two to get the lightness of the glass bubbles and the non-drip properties of the silica.

It is very easy to add too much resin to the glass tape and this does not make the job any stronger. Cut the glass tape to lengths and then weigh it all; then mix up the same weight of epoxy plus 20%. Keep stippling the glass cloth with the measured amount of epoxy until the glass goes clear.

Also weight the glass for sheathing the hull so that you mix up the correct amount of resin. Spreading-out the resin with a squeegee as described in the build manual is an excellent method.

[Beryl]

Thanks Simon! That adds some great information to the build and is interesting in itself. The guide of tape to resin ratio is particularly useful to new builders as plenty of the taping is out of sight. I was heavy-handed here on the better safe-than-sorry principal. Similarly, the glass tissue alternative is intriguing. Trickier to lay?

[DavidDeWitt]

Agreed. Great post. Would you please explain your layup process when you use glass tissue in combination with twill. Do both layers go on at the same time?

[Chris Bolton]

Thank you for your ideas, Simon.

This will have give significant loss of strength but it does mean that you cannot use the shear clamp to fix screws to.

This doesn't quite read right - did you mean:

This will give no significant loss of strength but…

[ChrisJK]

Perhaps the sentence is meant to mean " significant loss of weight with little loss of strength but..."? please clarify Simon.
I'd be lost with out the help of screws. I suspect bending and clamping a triangular section might be a tad challenging. I used Paulownia for my sheer clamps which upped the cost but it is very light wood.

[Beryl]

I used screws at six inch intervals but I still had to use clamps to get the ply to follow the lie of the shearclamps. Then you have to fill the holes. I didn’t use them but the split drainpipe looks more promising as long as they don’t slide. And occasional srcew would help here. I’ve only built one kayak but I think another one would benefit enormously from that experience of the first,

[darylf]

Re fitting the sheer clamps, I used a combination of kerfing and tapering to encourage the bends, then used thickened epoxy with plenty of clamps, (a combination of spring clamps and cut up drainpipe), to fix the sheer clamps, I didn't use any screw fastenings in the whole kayak other than to attach the deck bungees. The drainpipe clamps work but I think you probably need at least a few proper clamps too.

[nickcrowhurst]

Daryl, neat work. Well done.
Nick.