16 February 2009

SHOP: kayak mods_ retrofitting a ruddered kayak with a skeg

My SeaBird Designs kayak came with a rudder.
While probably a faster proposition for the racer a rudder in my opinion hinders good sea kayaks. I have paddled the kayak for a while now and always with its rudder stored on deck. The kayak does weathercock slightly.
In winds of 15 knots or stronger some effort is needed to edge the boat and use corrective strokes to keep it from turning into the wind.
The rudder has been removed and I have embarked into the daunting task of fabricating my own adjustable skeg.
Pricing a ready made kit from a local kayak manufacturer made me think that I can probably make a better one possibly cheaper.
Greg Schwarz has been my inspiration and his work is truly outstanding and after some consultation with him I decided that it must be done.

The trickiest part was sourcing high quality housing for the stainless steel wire/cable needed to adjust the skeg.
I found what I needed at an industrial hose supplier. The exact product is a high density polyethylene hose used for compressed air. The fitting for the hose is brass and has a neat "olive" to securely attach the hose to the skeg box.
The next step was to decide what shape and what size I wanted my skeg.

The skeg does not need to be very large and a sloped triangular one was going to be the least obtrusive one inside the rear hatch. I cut a piece of "smoke" colored 5 mm tick polycarbonate (Lexan®) to the slightly oversized shape of my desired skeg. Note the slightly oversized; we will come back to that later.

I waxed up the skeg with mould release wax and placed it on a smooth flat surface. Mixed up some epoxy and tinted it with black die: I don't like the look of semi transparent fiberglass. I used 2 layers of double bias cloth (available at most marine chandleries) and draped it neatly over the skeg.

top half ready, bottom is freshly laid
Once the resin hardened enough (10 hrs approx) I trimmed the excess cloth away with scissors and left a flange of about 2 cm. I repeated the same operation by flipping the skeg and making the second half of the skeg box. The two sides were flat and matched well.

I roughed up the flange surface with coarse sandpaper to create a good mechanical bond. This time I mixed up some epoxy (tinted again with black) and some microfibre filler (extender) to create a thicker glue that would not run. I joined the two skeg box halves allowing for a slightly wider gap at the bottom/entrance of the box to create a slight taper.

the two halves are joined

the bottom of the box was separated slightly to create a taper
The joint was filleted with the tick epoxy paste to create a strong joint line.
Once the joint cured the excess fibreglass flange was cut away and the ridge line made smooth with sandpaper.
A slot was cut to accomodate the brass housing fitting.
The fitting was fibreglassed into the slot with epoxy paste.

slot cut into skeg box
fitting before fibreglassing
fitting with fibreglas and resin
The skeg pivots on a stainless steel 5mm bolt secured with epoxy in the skeg box. A washers was cut out of nylon (or polyethylene) for each side of the skeg to prevent friction between blade and box.
cutting the washer
washers in place, excess bolt still to be cut
A slot was cut into the skeg blade to allow the skeg to be attached/removed without undoing the bolt.

The skeg wire was attached directly to the polycarbonate blade. A hole was drilled into the blade, a slot cut for the cable, the cable end was frayed a bit to ensure a better grip for the resin.The cable was resined in with epoxy paste and a laid on baking paper to create a smooth surface. The excess resin was trimmed once cured.
cable before resin
resin before baking paper
skeg dimensions (in mm, sorry metric only) click on image for larger view
The skeg is controlled by a stainless steel wire.
A control box with a knob attached to the wire was fabricated.
I used a piece of PVC conduit to shape a plug for my control box.
I cut the PVC pipe in half and after heating it gently on a flame I pushed it into a “U” shaped section.

I used West System 105 resin, 207 hardener (UV stabilized) to impregnate some carbon weave cloth.
Draped the resin rich cloth over my plug and overlaid it with cling wrap (Glad Wrap®) to prevent it sticking to the two blocks of wood keeping close shape to the sides of the cloth/plug.The box once cured needed end “walls”. I cut a small section of plastic and used it to “dam” the ends.
control box with ends in place
A section of the deck had to be cut out to have the control box recessed flush with only the knob slightly protruding.
Would you believe that after all that careful measurement and attention I cut and installed the skeg control box in the wrong position?
I took great care to make sure it will be out of my legs and knees' way but forgot to allow for the cable that would protrude past the box.
And of all places I did align it perfectly with one of the deck fittings.
The cable would run into the fitting!
After much cursing (you can imagine) I had to cut out the carbon box, clean up the resin and repair the massive hole left by the box. A new box was fabricated and repositioned.
The deck was repaired (I kept the section of deck that was cut out) and the gap left by the cutting blade filled with color matched gel coat.
skeg control knob (slider)
The control knob was fabricated from a piece of clear polycarbonate.
The knob was shaped to fit neatly inside the box and a hole drilled at the base to allow the sleeve to fit through.
The sleeve is drilled to allow a bolt (or grub screw) pinch the cable and keep it in the desired position.
The whole assembly has to run smooth and care must be taken to ensure that there are no bends where the sleeve runs inside the housing or a jam will occur.
control knob secured onto the brass sleeve.
The skeg cable runs inside the housing until it reaches the control box.
Here it enters a stiffer tube (stainless steel is desirable, brass will do) that would act as a sleeve.
The sleeve has to fit tightly around the cable and still be able to fit inside the polyethylene housing. The stainless steel cable is never exposed and therefore the chance of kinking the cable is reduced.
gel coat repair still to be sanded and buffed
skeg box view inside under the deck
It was time to assemble the skeg blade into the box.
You should end up with the blade well inside the box allowing trimming for the hull thickness and curve of stern keel line.

Once I had my parts ready it was time to prepare the hull for cutting.
This is the most critical part.
Measure twice, cut once! (yeah right...:-)
A perfect centre line is needed along the keel.
I selected and area as close as possible to the stern of the kayak but not too far for being able to reach from the hole of the rear hatch. I would need to work through that hole and be able to glass the skeg into place!
I masked the area with masking tape and draw lines on it to have a very visible cutting line.

masking and marking
checking for gap width
Once I was positively sure that all was good I fired up the Dremel®.
You will need a high speed cut off wheel. Wear a mask and goggles.
I cut less than needed and enlarged the hole slightly as required to fit the skeg box.
I managed to cut away a very tight fit and my skeg box had a gap of only 1 mm in places.


the scary part
The box fitted well and with the blade in place I made sure it would not protrude once trimmed.

skeg box before glassing
The skeg box was then perfectly aligned vertically in the kayak
A spirit level helps.
I removed the skeg blade and inserted a piece of wood the width of the box protruding about ½ meter.
I used that to align the skeg box.
The skeg box was then glassed into place with epoxy paste first (to create a watertight seal) and fiberglass tape later for strength.
Once cured I trimmed off the excess of the skeg box. A flush finish is desirable.

I masked a small frame around the box, sanded it and applied some West System 105/207 epoxy since my hull is clear and I wanted to have a non visible joint line. I did two applications for wear abrasion.

skeg blade retracted

pivot point
the skeg fully extended
skeg box view inside hull

housing attached to skeg box.
Loop/guard of fibreglass to prevent damage to housing when loading kayak with camping equipment

I hope I have not bored you with my account of retrofitting a kayak with a skeg.
I also hope that I have not omitted something and made the instructions not clear enough.
Feel free to comment and I might try to amend/update the document.

18 comments:

  1. Sulla pagina dello skeg ho notato molte visite da lettori italiani.
    Se vi fosse piu` facile ed avreste domande specifiche, vi possos rispondere in italiano.

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  2. Nice work! Thanks for sharing. This gave the guts to cut up my own kayak in order relocate the skeg control box.

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  3. Good evening. Nice post. I have a Riot Britany built with a skeg placeholder. I was wondering if I should go for it or go for a rudder...

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  4. David, I can't decide for you and I don't know what kind of kayaking you do to make a suggestion.
    I used to paddle ruddered kayaks but for the type of kayaking I do now I prefer skegged ones.
    I find that rudders limited my skill building (I would rely to heavily on the rudder for directional stability) and were prone to damage too often when in the surf zone.
    I like skegs.

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  5. Hi I was wondering if you know of any information or anyone who has done this with a polyethylene kayak? I have just bought a secondhand poly sea kayak which has the option of adding a rudder, but a) they're damned expensive and b) I prefer the idea of a skeg.

    Thanks.

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  6. Gremmut, I had trouble finding info on retrofitting a skeg to a fiberglass kayak but I have not seen any on a poly boat.
    Trouble with poly is that (almost) nothing sticks to it so performing a mod like the one for my carbon/Kevlar boat would probably be impossible.
    A different approach could be taken where the skeg box would be fabricated with a frame that would then be bolted onto the plastic hull and sealed with polyurethane (similar to some retro fit hatches).
    The skeg box would be a bit more complex (box with integrated lip and separate frame for inside the hull that would distribute side loads of the skeg).
    Not sure if it would work though.
    Kati-tek makes a cartridge type skeg box, that apparently works on poly boats too: http://www.karitek.co.uk/kbyre/acatalog/Skeg_Systems.html

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  7. Hi. Thanks very much for that. I've had a look at their site and I've e-mailed them to see how they recommend bonding the skeg system to a poly boat. I can only imagine it would have to be by plastic welding, like you said not much sticks to poly. But then that's assuming the plastics are similar and able to be welded together.

    I'll let you know what they say.

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  8. Had an answer from them, the skeg kits are made from HDPE, and need to be plastic welded to fit them. Instructions on how to fit to a plastic kayak are included with the kit, as long as you specify that it's for a plastic boat when ordering.

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  9. Nice article, and well done!! Very clean. Haven't done any modifications to that extent yet w my boat, they will come...
    Just puttin' it out there I was wondering if you have heard of anyone that has built a skeg deployment system that uses a PULL (similar to rudder deployment) with a cord instead of the typical PUSH of a cable? I feel (hope?) that I could lay the tubing down on the hull of the boat and by wrapping the cord around the pivot axle of the skeg be able to pull it down as I would a rudder, then pull it back up too, there by getting rid a kinkable cable and reducing field problems. This might also increase the access to storage in the stern of the boat too.

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    Replies
    1. Paul, I have not seen up-close any rope skegs but I believe there are several documented articles on the net. As for the skeg wire kinking I think it only occurs when the manufacturers of kayak use inferior material for the housing of the skeg wire. With my kayaks, I have a couple of factory skegs that are very sticky; the one I have made myself is however very smooth (I used quality HDPE stiff tubing).
      Of course one could kink a cable if a pebble jams the blade in the retracted position and tries to lower the blade with a "ham-fist" on the slider. If it doesn't slide easily something is jamming it and it should be addressed without forcing anything.

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    2. yes there are options to do this. You will likely need to make sure that you pivot around something larger than the axle to ensure that you have some mechanical advantage or leverage.

      A drop-down rudder works the same way though a rudder is either up or down. In a skeg, you want it infinitely adjustable. With this setup there are challenges to establish some reliable retaining/adjusting mechanism that will also retract on impact. Thats why most people use a shock cord & static cord combination.

      I am currently copying gnarlydog's (thanks !) construction for my new skeg and using shock cord and dyneema for the control line.

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    3. Chesapeake Light Craft sells a kit (also available as plans) for a rope pull skeg. It is designed for their wooden kayaks but I believe that it can be retrofitted to a plastic or fiberglass kayak.

      I bought a new (but never built) CLC Chesapeake 18 kit that the previous owner ordered with a Feathercraft rudder. I am currently building the boat and I am debating whether to install that rudder or just go with a skeg because I have never paddled a kayak with a rudder before. All of mine have skegs and I rarely deploy them.

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    4. I like skegs and all my current kayaks (5) have skegs. Just recently however I have paddled a kayak that has a rudder that I could consider, if the rest of the boat would fit me: the Hybrid550 (http://gnarlydognews.blogspot.com.au/2013/02/video-hybrid550-project.html )

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  10. Thanks, I have a north shore, atlantic LV. Made by valley. I am fully aware of skeg issues as I have delt with them many times. coming around a point out of some following seas recently, the rocks adjacent to the point were much shallower than I expected (should have anticipated!). anyway jamed the skeg, brand new boat!
    I have been thinking about this rope idea for some time but it will take some diagraming and some idea sharing with others (like yourself!) before I attempt it.
    You think that the stiffness of the tubing has something to do with it, eh?
    Paul

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  11. Gnarlydog, great write up! How did you address leaking around the pivot bolt? I just picked up a 13.5' old 1980s fiberglass whitewater kayak. I have wanted one since a friend of mine bought one a couple of years ago. It will be used for weekend trips on rivers. I plan to add a skeg, either retractable or fixed, although i am really leaning towards retractable as the kayak is fun and challenging to paddle as is. I also plan to add bulkheads and hatches as well. Seriously thinking of building hatches out of fiberglass as well, but want to see how a skeg comes out first. Actually got some great ideas on how to do it after this write up!

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    Replies
    1. I covered the bolt head with epoxy paste/glue and totally encapsulated it. Notice the skeg blade slotted so it can be inserted over the bolt's shaft (pivot point).

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  12. Hello Gnarlydog,
    I have studied this skeg section a few times. I have a half built Guillemot Expeditions single which will be 18ft=5.8metre when finished. I have read they go a lot better with a skeg. I also have a 16ft riot Brittany and just gave up fixing rudders and paddle it with neither a skeg not rudder.
    I just bought a set of skeg plans from guillemot and his skeg looks a bit small compared to what I see poking out the bottom of some new boats.
    Is there a sort of ration between the area of a skeg and the length of boat you are trying to keep straight? (does size matter?)
    He recommended placing the skeg an inch off the centreline to reduce exposure to sand/gravel, Can you see that having much effect?
    How come everyone seems to go for a single cable rather than a push /pull arrangement?
    Cheers
    Vere

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    Replies
    1. Vere,
      size does matter, but it's in relation to the hull design.
      Of the many skegged kayaks I have paddled each one requires a different amount of skeg when paddled in beam wind conditions. I can be paddling side-by-side with somebody else and they will have a different amount of skeg deployed than me.
      Some of my kayaks have a very small skeg and very little is needed most times, other more rockered kayaks ("loose") need a bit more.
      I don't know if there is a formula to calculate the size of the skeg needed as often trim will also dictate how much will a kayak weather cock.
      When in doubt, I usually go big and maybe then deploy less if not all of the skeg blade is required.

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