Building a Strip Planked Petrel Kayak [video series]

Petrel Build: 01 Making Forms for Strip Planked Kayak:

Nick Schade writes:

This is the first in a new series of videos showing the steps of building a wooden kayak using the "strip-planked" or "strip-built" method. This particular boat is a high performance sea kayak design called the Petrel by Guillemot Kayaks.

Cutting the building forms for a strip-built kayak. The forms are cut out of 1/2" thick MDF (medium density fiberboard).

 

Petrel Build: 02 Milling Bookmatched Cedar Strips

Cutting strips is always a little tedious. It is primarily a matter of feeding the wood through the saw. When you intend to bookmatch the strips on the boat you also need to keep the strips in order.

The process starts by planing the boards smooth. I'm using western red cedar siding that is rough on one side. I run the boards through my planer removing just enough wood to get it smooth. I run a few test boards through the planer and then run all my boards through to be sure they are all the same thickness.

The strips are cut on the table saw set up with a zero tolerance insert. This assures that the strips don't get caught in the gap around the blade.

I wax the table top to make it more slippery then buff off the excess. I use a power stock feeder which power-feeds the wood through the blade. This results in more consistent results than pushing by hand and is safer, but it is a luxury and not required to successfully mill your own strips.

I set up the cut a little larger than 3/16" thick and check the results with dial calipers. I'll plane it down to final thickness later.

I mark up each board with diagonal lines so I can get everything back in the same order if I should get the shuffled. As I cut the strips I lay them out on a large table in order and then carefully bundle the results together with stretch wrap so they stay in order as I move them around.

After the strips are all cut I move my plane into place and run a few strips through to dial in the thickness. To save time I'll run several strips through at a time. The results are all numbered and reference lines are drawn on all the strips to help align the grain.

 

Petrel Build: 03 Assembling Forms

The easiest way to set up the forms for wood-strip kayak is using an internal strongback. Here I use a 2" x 4" x 13' aluminum extrusion with 1/8" thick walls. The bow end has been tapered so it can reach farther into the bow of the heavily rockered boat.

I chose to slot together the sectional forms near the end onto the end or stem form. This is a simple method that allows the forms to be disassembled easily when the boat is done.

The stem forms are also slotted to fit up inside the hollow strongback. I've planed down some pine pieces to fit inside the strongback on either side of the form to keep it centered. The end forms are screwed in at each end so they will not slide off the ends. Pre-cut spacer between each form define the form location and a pair of wedges at the center of the boat secure the form in place.

 

Petrel Build: 04 Installing the Sheer Strips

All the strips follow the first one in one way or another, therefore it is important to get the first strip along the sheer right. On most of my plans I include a mark that indicates the location of the sheer. This mark is typically placed at an angle to the side of the form. This angle should bisect the angle formed between the deck and hull. By beveling the edge of the sheer strip to match this angle you will get a smooth, tight deck-hull joint that maintains constant thickness across the seam.

I start by clamping some scrap strips on the sheer marks. These scraps will hold the sheer strip in its proper location as I bend it in place and I can use them to determine the bevel at each form.

I look at the gap between the strip and the scrap and then hold my block plane to match that gap. Holding that angle constant I plane away the edge until the gap disappears, rolling the angle from one form location to the next.

I am not using staples on this boat so I am hot-melt gluing the strips to the forms. The hot-glue is chosen to be easy to break free when the time comes to release the boat from the forms.

The Petrel has a lot of curvature along the sheer. To make the sheer strip easier to bend I am tapering the ends down to be narrower. A smooth even taper is made by planing with short strokes at the beginning and then using longer and longer strokes.

I don't want to taper all the strips, so the second strip is allowed to run on its natural curvature.

 

Petrel Build: 05 Installing Cheater Strips

In the previous video I installed two strips, the Sheer Strip which follows the shear line and then the second strip which follows a more natural bend. Between these two strip there is a gap at each end. This gap needs to be filled with what I call "Cheater Strips". These strips are tapered at one end and run off the stem of the boat at the other.

The tapered end needs to be fitted to match the gap defined by the shear and the second strip.

Cheater strips can be run in a variety of patterns as shown to the left. I' m going with the "Top-Down with Sheer" as this requires the minimum bending of the cheater strips which makes the fitting easier. I also think this pattern looks best for the boat.

The first cheater has a long, fine taper where the sheer and second strip merge together gradually. I clip the strip off a little longer than necessary because getting the right fit may require a fair amount of adjustment. I want the grain to line up on adjacent strips so I first align the marks on the strips and then back off a bit. I align the end of the strips with the end of the tapered gap and mark where the edge of the new strip crosses the edge of the sheer strip. I connect this mark with the end of the strip with a straight line. The actual line will be curved but it will be concave so a straight line will not remove too much material. For this long taper I bring the strip over to the bandsaw.

After sawing off most of the scrap, I plane the edge smooth and make a first check on the fit. It will need a lot of work. I do this planing on the work bench which provides support for the long flexible strip. Initially, most of the wood needs to be removed from the middle of the taper so I concentrate most of my planing there, attempting to make a smooth curve along the length of the taper. I check the fit frequently to be sure I am working on the right place. I remove wood where ever the strip binds up when I insert it into the gap. Eventually I get the taper right, but the length is wrong so I work on adjusting the length, using the reference marks on the strips to gauge alignment. Due to the curved taper of the strip, length adjustment requires removing more wood on the wide end of the taper than at the narrow end. When I get the grain alignment right, I glue the strip in place using masking tape and clamps to assure a tight joint.

All the rest of the cheater strips follow the same process. Because the length of the taper becomes shorter as I proceed I end up removing the scrap wood from the strip with a jack knife because it is quicker than walking over to the band saw. Initially I need to support the back of the strip with a scrap strip while I plane the taper, but with shorter tapers where the tip is less flexible I can start planing in the air with no support.

 

Petrel Build: 06 Stripping Past the Chine

The Petrel has a hard chine. This creates some issues specific to the boat that must be dealt with. You want the strips to reach the chine evenly. I.e. you don't want the first strip to hit the chine to be high on it at one point and low on it farther down the boat. This would make a situation where part of one strip is on one side of the chine and part on another. Since the chine is a sharp angle, the strip itself would have to incorporate a sharp angle somehow. This just isn't reasonable. There are ways to make it happen, but the easiest is to have the edge of one strip coincide with the chine line along the full length of the chine.

Back when I installed the sheer strip I made a point of following one of the diagonals lines I had drawn on the forms. I had two diagonals drawn, one that followed the chine and another parallel line that followed the sheer at the middle of the boat. I installed the sheer strip to follow the sheer, but the second strip followed that second diagonal. I could have had that second strip follow any smooth curve but I wanted it to follow those diagonal lines. The reason for this was to cause the strips to run parallel to the chine when they reached it.

I wasn't sure that the edge of the strip that hit the chine would be exactly the right width, but it worked out well here. I could have ripped a narrow strip if it had not worked out. But, what I have here is the edge of the strip sticks up slightly above (approximately 3/16") the chine line. This is good because I need to put a bevel on it so the inside edge of the bevel is directly on the corner of the chine.

What I want to make is a miter angle so the next strip that is on the other side of the chine line has a tight joint from the inside corner out to the outside corner. I used my rabbet plane to create this bevel. The rabbet plane has a blade that reaches all the way to the edge of the tool, allowing me to shave right up tight against the forms.

As I cut this bevel I tried to approximately bisect the angle between the side and bottom of the boat created at the chine. I didn't need to be perfect, but I wanted a smooth rolling bevel down the length of the strip. The chine does not run the full length of the boat, at the bow and stern the shape is quite rounded and I found I did not need to bevel the strip at all at the ends.

After I had beveled the strip that was on the boat already, I set up to install the next strip which would be on the far side of the chine line. This strip needs to have a rolling bevel cut to match what is already on the boat.

As with other rolling bevels, the drill is: Dry fit the strip, mark the form crossings, look at the gap at each form crossing, hold your plane to reproduce that gap, plane until the gap disappears, check your work, adjust as needed and then move down the boat, rolling the bevel as needed along its length.

After the bevel is formed, do another dry fit to double check that the seam is tight and then glue the strip in place.

A note to people building with Cove and Bead

It may be possible to get past the chine using just cove and bead strips, but I would advise ripping or planing the cove off one strip and the bead off another and planing the bevel along the chine as shown here. This will produce a smoother, tighter, stronger joint.

A note on Music

The music on this video is by my friend Peter Wortman and his trio Montage of Three.

 

Petrel Build: 07 Installing the Keel Strips

On this Petrel I chose to do a "side herringbone" stripping pattern on the bottom. This involves running strips down the keel line and then filling in on either side.

The first step to this pattern is installing the keel strips. These strips run down the centerline of the bottom, one strip on either side. They run all the way from the stem at the bow to the stem at the stern. Near the middle the meet at a relatively shallow angle and at the ends where the keel is more deeply "V"ed they come together at quite and acute angle. These different angles need a rolling bevel to produce a tight seam along the keel.

To determine the angle of the bevel, I started by installing some scrap strips vertically on the center line. By butting the side of the strips against these scraps I get a visual on the necessary angle. By matching the gap between the top of the strip and the scrap I can plane the appropriate angle. I did this most of the way down the length of the boat, but at the ends where the angle is more severe and I can not clamp the scrap strips due to the end forms, I have to freehand the angle.

I twist the strips to their approximate orientation and then holding the face of the block plane on a vertical plane I shave away the edge and inner surface of the strip until I get a smooth tight joint between the two adjoining strips.

Due to the severe twist of the keel strips near the ends it helps to pre-form the strips into their final twisted shape. I accomplished this with a hot clothes iron. You could use a heat gun, but I've found the iron transfers the heat faster and gets the job done sooner. A little water spread onto the strip accelerates the heat transfer a bit but is not required.

After the strips are twisted to shape I adjust the bevel some more. Actually, you could pre-twist the strips before doing any beveling, it is up to you. Once the bevel is about right, I trim the ends to fit together with the existing strips at the stems. More beveling and shaping may be needed before gluing in place.

I clamped one strip in place temporarily, check it for straightness and then used that as a guide as I hot-melt glued the other strip in place. Then I came back, unclamped the first strip and glued it to the second strip, using tape and clamps to hold it in place.

 

Petrel Build: 08 Stripping up the Bottom

Stripping the bottom is much like installing the cheater strips, with the major difference that you need to shape and fit both ends of the strip so the length is correct. Since I am book-matching these strips I also need to do this while maintaining the grain alignment.

This is all done through a series of reference marks. Back when I milled the strips I was careful to draw lines across the faces of all the strips. These lines serve to align one strip next to the other with the grain lining up. I used these lines to place the strip properly on the forms, then I go to the end of the strip I am going to fit first and make a mark across the seam between that new strip and the existing strip it will sit next to. These marks are close to the end that I'm fitting so I don't need to look around to much.

I cut the strip a little over-long with some anvil cutters that are quick and easy. I then side the strip so the first end is a little over-long based on the reference mark. Usually about 1" (2 cm) extra length is plenty. I now mark the taper. This mark is not meant as the exact fit you will want to achieve, it is merely a guide to assist in the initial fit. A jack knife makes quick work of removing the excess wood, then plane the taper parallel to your mark. Don't worry yet about precision. Do a trial fit. Note where the taper binds up in the space. If it binds up at the "toe" or pointy end you will want to concentrate your planing on the pointy end, if it binds near the heel, or inside end of the taper, you will work on the heel first.

If you have a large gap start by holding the block plane to reproduce the gap and then plane away the taper until the gap is gone. If your taper is close already but it binds slightly at one end or the other, take one short cut with the plane on just half the length of the taper plus one full length cut and then try the fit again. Keep fitting and adjusting until you get a tight fit along the full length of the taper simultaneously.

If you left enough extra length your length marks between the strips should not yet line up. Use even, full-length cuts with your block plane on the taper to gradually shorten your strip until the marks ling up. Don't try to remove too much at once and keep checking the taper to assure it stays tight. With a long, gradual taper one cut of the plane can make a large difference in the length of the strip.

Once one end of the strip is fitted, you need to measure the length for the other end. Dry fit the strip in place with you new taper set in place. Use clamps to hold the strip tight in position along its full length if necessary. Make a mark between the two adjacent strips close to the unfitted end. This mark will let you remove the strip at the first end while you work on the second and still get the correct length. Fit the second end in the same manner as the first.

 

Petrel Build: 09 Fitting the Closing Strip

After working diligently on stripping the bottom you eventually come to a time when there is just one strip left. If you are using cove and bead strips you will want to have removed the cove from the second-to-last strips so you have a nice straight-sided hole to drop the last strip into. I use the hole as a template and trace the shape of the hole from underneath. I then cut off the majority of the scrap wood being sure to leave enough excess to work on as I refine the shape.

Working on the pointy end of one end at a time I refine the taper to get a tight fit in the hole. As you get the end to fit start working back along the length of the strip. Start out over long because as you refine the shape you will likely end up making the strip shorter.

As you get close to the middle, stop and go work on the other end, again starting at the point and slowly working towards the middle.

By pressing the strip down into the hole where it fits and allowing it to rise up as it gets tight you can then take a pencil and mark the edge you are planing. This mark will travel diagonally across the width of the strip edge. It will start on one side near the pointy end and end up across on the other side. At the pointy end you don't need to remove any material with your plan because it is fitting correctly there. At the other end you will need to remove more material. Take a couple strokes at the wide end of the taper, reducing the strip width there, and the one longer one to just remove the pencil mark. In this way you will remove more wood where more needs to be removed, but little or none where the width is good.

A very sharp plane will set at a very fine cut will remove material slowly allowing you to dial in a very snug fit.

 

Petrel Build: 10 Flipping the Forms and Releasing the Hull

After the stripping is done on the hull, it is time to flip it over. I got Robin to help and rested the now-upright hull on some foam saddles.

Since the hull is glued to the forms with hot-melt glue, I am taking this opportunity to break that glue. I could wait until the hull is complete, but is a lot easier to access the forms now. The first step is to remove the spacers between the forms so the forms are free to move. This starts by tapping out the wedges at the center form and then just lifting out the spacers.

If you noticed while watching the previous videos, I did not use much glue. On the first strip I placed one small dot on each strip, but until I got to the keel strip I used almost none. There were several occasions where I felt the strips were lifting off the forms and could use a little help staying in place so there are probably about 10 or 15 spots between the sheer and keel.

This makes it pretty easy to break the glue. A light tap with a mallet or hammer directed towards the middle of the boat will generally do the trick. Hammer towards the center or wider side of the form just keeps from driving the forms into the smaller part of the boat.

The stems can be a little harder to pop free. First the sectional forms here are secured to the end or stem form and secondly the space to fit a hammer gets tight. Finally, the keel line may get a little carpenter's glue dripping on to the stem form that needs to be de-bonded.

I first flexed the sides of the bow and stern a little to help crack some glue and then drove a chisel down between the inner stem and stem form. I was able to use this to lever up the forms just enough to crack any remaining glue.

I double checked that the forms would lift out when I get there, and then put the spacer back in and tapped home the wedges. This puts the forms right back where they are supposed to be, ready for the deck.

 

Petrel Build: 11 Repairing a Split Strip

The first part of this video make look familiar. While releasing the hull from the forms in the last video, I ended up splitting one of the strips. This happens sometimes but could have been avoided if I had glassed the hull first as I did with the microBootleggers I built this spring. On this boat I chose not do glass because it is easier to do the fairing when doing the deck and hull at the same time.

The fix is not a big deal. Squirt some glue in the crack and tape it back together.