The Saga of the PBK 27 (sea scout)
by ROB BROWN
Forward by Rob Brown
Regarding the CECONITE 101 covering material the name CECONITE is a trade name for a heat shrinkable dacron that has been certified for use on aircraft.
The 101 stands for the weight or strength of the material 101 being the strongest.
There are lighter weights of CECONITE available but they are used on gliders and in my opinion are not suitable for covering a kayak. As to the availability of the material in the UK. I would start with the smaller aircraft maintenance facilities that carry out fabric covering near you. They should be able to help you and the 2” inch pinked finishing tape will be also be available from them.
I don’t think that covering with a heat shrinkable fabric would be the most cost effective way to cover a kayak as apposed to covering with the material recommended in the P.B.K construction manual as the tarp material does not have to have any finishing coats applied after the covering has been tacked on.
Dacron does have a few advantages though, it is light, strong, easy to apply by one person and a really slick finish can be achieved with a little care.
I first decided to build the 27 in early June 1993. The plans were purchased from www.clarkcraft.com. I had at that time intended to build this kayak for my children as I had been involved in the construction of a similar one whilst a member of a local Scout troop in the mid 1950s. At the time, if my memory serves me, it was a PBK 13, but there is no mention of this in the catalogue, the 27 is 13ft long with a 27’ beam, 45’ cockpit and a normal load of 350lbs.
Why build a skin on frame kayak in this day and age? With plenty of plans and kits available for stitch and glue, strip building, fibreglass etc to mention a few, and I must add, with perhaps superior performance in the hands of an experienced paddler and no doubt due to the evolution of the competitive aspect of kayaking, there are a few reasons in my mind at least.
Let me try and explain.
Firstly, I have two sons, who at the time had grown out of the small eight foot kayak that I had built for them and I was going to try and pass on to them a few of the skills that I had picked up as an aircraft engineer working on wood and fabric restoration jobs over the years, and a long history of aero modelling behind me, instilled in me by my elder brother and his like-minded friends. Apart from the frames being sawn out of 3/8 exterior ply and a local sawmill going under with the loss of my materials list and instruction sheets, that was the extent of the progress. My boy’s interest changed to sailing and surfing so a stitch and tape dinghy was constructed along the lines of a sabot and the lads were introduced to sailing. A lot of fun was had by all for a few years.
Due to the normal pressures of life and work, the completion of the 27 was put on the backburner until the last couple of years. Guess what? It’s now being completed for my grandchildren. As you can see from the photos the construction of the 27 is not rocket science, just a little thought and careful construction is all that is required, along with reference to supplied plans and the old adage - measure twice, cut once.
Full size patterns are given for the frames, stem and stern profiles along with other items. I might mention here that the stem and stern profiles might be better cut from 1/2” ply but this will mean a slight alteration to the taper of the keelson. The keel is dead flat if built to the plan but a little rocker might be nice for maneuverability, but please yourself. Whatever you do,do not let hog creep in to the keel as it can over time, believe me, it did with mine, but easily fixed by laminating a1/4 inch strip of wood to the keel and tapering out to both ends. Hog is not going to improve the performance of your pride and joy.
Please use the best timber you can get, I used Hoop pine and some nice straight grained Douglas fir, both quarter sawn for my stringers, keelson etc. I only had to steam bend the cockpit opening stringers and the outer beadings of the cockpit coaming. The 1/8th ply coaming rear section was only soaked in water for a day or two. The coaming is not shown in the photos but will be in part two. Epoxy glue was used at all times during construction. The double bladed paddle carved out of Douglas fir with the blade cheeks glued to the shaft. No offset was put into the blades as it only confuses the issue with young children and can be added to the paddle at any time in the future.
The seat base was carved with two cheek indentations that will help to make them sit in the centre. Four coats of marine varnish has been applied to all wooden parts.
Covering is the next task to be considered as time permits. I shall be covering the kayak with Ceconite 101 aircraft fabric with 2” pinked tapes over all stringers, keel, stem and stern etc as per aircraft practice but at this stage will deviate from aircraft practice in using water based undercoat and finishing coats as aircraft dope is very expensive and water is a much cheaper thinner and a lot less toxic, believe me.
Okay let’s get into the finishing of the kayak. You may recall earlier in this article that I mentioned the coaming this was manufactured from three pieces of 1/8th marine ply the rear piece, with vertical grain to better resist the loads imposed by your back during paddling. Make up cardboard patterns as per photo 1 also note the adjustable footrest and modified seat cushion fitted to the duckboard.
Soak the ply in water overnight then fit to cockpit opening using the handy little clamps shown in photo 2. These clamps can be made in various sizes from poly pipe with differing diameter and wall thickness to suit the job at hand. Wall thickness = pressure that is applied by clamp. I use circlip pliers to fit these clamps but any home made expanding tool will do. Let the ply coaming bits dry in place with the joints overlapping.
Now mark out the scarf joints. Glue joints with the coaming refitted into cockpit opening not forgetting a small piece of Gladwrap between coaming and cockpit stringers we really don’t want these glued together at this stage.
Now make up the coaming nose block from a nice bit of hardwood of contrasting colour. Fit nose block to coaming nose with the block checked to match ply. Make the coaming beads and fit to the upper outside edge of the coaming. These will have to be steamed. Contrasting coloured beading looks nice here as well.
Remove coaming from kayak, clean up, varnish and hang out of harm’s way for now. Next job, manufacture and fit the hardwood rubbing strips temporarily to the bottom stringers of the kayak as shown in the plans. I had to steam the outer strips, as this would be a cow of a job after the kayak is covered. It also allows you to space out the fastening screws, the holes of which can be picked up easily after the covering process. Remove rub strips and store with a bowstring attached to the steamed rub strips to retain curve.
Now the covering of the kayak. I stated earlier in this article that I would be using aircraft covering fabric in this case Ceconite 101 and two inch-pinked tapes. Ceconite is a trade name for one of the fabrics that are available but they are all heat shrinkable woven Dacron. This fabric can shrink about 10% in all directions with the application of heat from a household iron. Caution should be used during the shrinking of the kayak skin as the power of the shrinking can distort your frame very easily. I have seen steel tubing in an aircraft fuselage badly distorted with the over-enthusiastic application of heat, so be warned.
There is another reason why we in the aircraft industry don’t like to overshrink the fabric and that is adhesion of the finishing coats. Dacron, as a manmade material is very smooth and slippery. So adhesion of subsequent coats of the finishing system can be a little difficult if the most important first coat can’t key into the little holes between the weave of the fabric. This is very important.
Sneak up with the heat settings at all times until you gain a bit of experience. Dacron will melt at too high a heat setting, nothing worse than seeing the household iron vanishing through the brand hew skin of your pride and joy. Enough to make the Pope say Golly Gosh.
Never set the temperature of the iron above COTTON even then, because iron’s temperature settings vary between irons. Please test a few pieces just to check. In all reality you should not be at this critical temperature at any stage of the job, just to be careful.
Now after the little lecture, let’s put a nice smooth strong dress on our little lady. Drape the fabric over the inverted frame refer to photos three and four. Mark a centre line along keel. Allow a couple of inches of fabric at one end. Staple or tack this end just at the transition of the keel to stern curve. Put staple or tracks through a small piece of thin ply or cardboard, this helps to remove them later.
Now pull fabric very firmly along the keel keeping the marked centre line to the centre of the keel. Now fasten this end with a couple of staples or tacks at the keel to bow transition. Apply a few more staples or tacks along the keel as per photo three, as this keeps the fabric centered as we apply tension down to the gunwale.
Now, starting at the centre of the gunwale, apply fasteners through a strip of cardboard toward one end, alternating from side to side. Repeat from the centre to the other end.
You should now have a skin looking like photo four with very few wrinkles or baggy spots. Don’t fret if it’s not as smooth as the photo because, I have had a lot of practice at this sort of work and remember the shrinkage factor will hide a lot of sins. Just do your best, stand back and make a few adjustments if you really think it needs it.
We now trim the fabric using pinking shears, allowing enough fabric to go across the top of the gunwale and up the inner side about one inch, remembering we have the kayak inverted. Let us now turn our attention to stitching around the bow and stern centre line. First pull one of the flaps over the centre and mark the fabric down the centre line of the bow or stern as the case may be just around the deck line. Repeat on the other side, allow and mark a half-inch sewing allowance inside these marks.
Remove the ‘V shaped bit of fabric from between the inner marks, fold under the sewing allowance and then hand stitch from the keel to deck line using a baseball stitch. I used saddle makers’s thread for this job, but dental floss will do just as well. Repeat this stitching job at the other end of the kayak and that’s about all the hand stitching that is required.
Now, let me take a moment to explain why we use pinking shears on fabric work. Well, the zigzag cut they produce gives a longer line to bed down into adhesive and helps stop fraying, and, at the finishing stage holds a lot more paint or other finish at the taped or joint lines that will rub down a lot easier to give a slick finish. Don’t get adhesive all over the pinking shears, the wife will not be pleased, as these shears do not sharpen well and blunt shears will not cut synthetic materials. Very simple mate, keep them clean and look after them because they are not cheap.
Now the stitch lines at the bow and stern should look like the bow in photo five (missing - sorry. Ed). Now turn the kayak over and prepare for gluing down the fabric at the gunwales.
Now at this stage of covering my kayak I deviated from aircraft practice and used clear UV resistant water based paint, manufactured in Australia by VIPONDS under the name of TautFlex as the adhesive. This worked well in the end, but required a different technique as, being water based and even with the thickener supplied it lacks the initial tack that you get with let’s say, contact cement or, in the aircraft industry, a nitrate based fabric cement.
What I had to do was prime the inside face and the top of the gunwale with Tautflex, then staple the fabric down over the inside of the gunwale and then iron the fabric along the top and down to the staples on the inside of the gunwales with just enough heat to remove any wrinkles in these areas. Refer to photo six and note the great big hypodermic needle I am using. That would make a brave man sit up and take notice if the doctor produced one at his next visit.
Anyway it’s just the thing for the next step, injecting adhesive under the fabric along the top and the inside of the gunwales in a back stepping action. Now using your credit card or something similar squeegee the adhesive up through the weave of the fabric, stand back, wash your card in water and let the adhesive dry overnight.
Removal of the staples on the outside of the gunwales is the next little job. This is when the cardboard strips help. Now heat up the iron to about synthetic setting and give the fabric a gentle iron all over, working from the centre to each end. Remember, there is still that row of staples or tacks down the centre of the keel and this is when the centre line marked down the middle helps you to keep the tension of the fabric equal both sides of the keel. Now that we have the fabric nice and t not tight, remove the staples from along the keel.
Now get out that big needle and credit card again and inject some adhesive under the fabric at the gunwales and along the keel. Use the credit card again then let the adhesive dry. Roll the kayak right side up, and from the off cut fabric cover the decks from the bow to the cockpit opening and then from the stern to the rear of the cockpit opening. Please refer to photo 7 and note the simple marking gauge made to give a neat line to trim to the deck panels to. This lap is 1 1/4”.
Now that all the edges on these two panels have been adhered down and dried, heat up the iron to about the synthetic setting and run the iron slowly along all the pinked edges. You will note that those pesky pinked edges that have not adhered down will, with the gentle application of heat. Now cover the panels beside the cockpit giving a lap of at least 1 1/2” over the rear and front decks When adhesive is dry tighten up the fabric skin in gentle stages increasing temp. settings of your iron untill a 20-cent coin dropped from about 6” will just bounce off the fabric and then stop.
Next step is to apply one good coat of UV clear all over, working carefully to get a good penetrating coat into the weave of the fabric. This is the most important coat as far as adhesion of any finishing system to synthetic fabric. I like to use a foam brush at this stage, coating the bottom and the deck as two separate jobs to avoid runs. Finishing tapes are now applied along all stringers and overlapped seams.
Finishing tapes are two inches wide with pinked edges and are applied to help protect the fabric skin from abrasion in areas where the underlying structure is in close contact with the skin and to add strength to lapped joints. Applying the tapes is simple, just rule a line offset half the width of the finishing tape from the centre of the underlying structure, fasten one end of the tape with a staple or tack then lay the tape into a bed of wet adhesive with gentle tension applied at the other end of the tape.
Use that credit card again and bring the adhesive up through the tape. Ends of finishing tapes that are visible look nice and trimmed to a convex arrowhead. I suggest that you tape the keel and around the bow and stern last, keeping the laps in the right direction to the water flow or airflow as is aviation practice where airflow speeds can be high.
May I also suggest that the bow and stern finishing tapes be cut from an off-cut piece of fabric cut at 450 to the weave, this is known as bias cut, and really helps fitting tapes to tight curves. Photos eight and nine will give the general idea of fitting tapes as in photo 10 the bow tape.
Remove all tacks and stapes. Iron down all tape edges. Spray or brush another couple of coats of clear with very gentle sand between coats with 350 grit wet and dry and you should have with the cockpit coaming sitting in place a kayak looking like photo 10. If you like a clear finish just apply more clear about six to eight coats in total or apply colour of your choice until the weave of the fabric is nearly filled.
I might mention that aircraft practice requires at least one coat of silver be applied between the clear and finish coats to protect the fabric from UV light but I don’t think the amount of time the kayak will spend out in bright sunlight will be a big factor in the life of the skin. Try and keep as much sand out of the interior of your kayak by fitting a close celled bath mat in the cockpit because sand between the fabric and the structure will in time cause major problems. Now all that is required is to fit the rub strips to the keel and bottom stringers as per plan and the gunwales. I used varnished shelf lipping for this.
Well that’s the saga of the PBK27 the way I approached it anyway. Launching took place on Easter Sunday all in the traditional way except they poured a bottle of home brew over me or was it in me. Anyway, a great day was had by all.
It paddles great.
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