SHOP: DIY sea kayak sail

SEA KAYAK SAILby Damiano Visocnik © 2008

My first sea kayak (used) came with a sail.
I loved the thing. My background is windsurfing therefore using the wind was obvious.
The sea kayak had a step mast sail rig that I soon found out had several limitations over a windsurfer.
I realized that I will not be able to use as much wind as I used to on the windsurfer: the kayak lacks a dagger board and unfortunately drifts sideways a fair bit.
The rudder would prevent some drift and would give me some directional steering.
My step mast set up was however preventing me from paddling while I would sail: the boom was too low and close to me.
Never satisfied with a commercially available product (that's my motto), I set to design and fabricate my own sailing rigs.
After 8 sails and a few modifications I am getting closer to what I can be happy with.

A sail must be:a) light
b) easy to deploy and store
c) sturdy enough to take a stiff breeze (desirably around a max of 35 knots)
d) allow me to paddle when under sail.
The original design inspiration came from Sea Mongrel’s sail on his Polar Bear kayak.
In my opinion that sail could be improved in a few areas and therefore I set out to redesign it.

1) MAST
I started off with a mast and boom made from 16mm Ø aluminium tubing.
The tubing can be purchased from most hardware stores.
(MAY2008: After extensive research I discovered that generic aluminium from the hardware store is not good enough. A 6000 series alloy possibly anodised would be the preferred material.)I reinforced the tubing with a core of timber dowel. Unfortunately the mast would still bend under winds of above of 25 knots.
The second generation mast was made from thin walled stainless steel. I am not sure if this mast was any stronger but it still bent at 35 knots wind.
I am now using a custom made carbon fibre mast that has a thick wall.

Ready made fibreglass tubes are available from CG Composites.

The mast has an anchor point for the stays (rope/cables that hold the mast in position) at about 2/3 of the way. The anchor point is a stainless steel welded ring that is attached to the mast with a small shaped strap of stainless steel (alternatively a strong nylon strap will do). Drill the mast and pop rivet the strap into place.

The base of the mast is anchored to the front of the kayak very close to the bow. I found that this position neutralises weathercocking and the kayak could be sailed in any wind direction even with just a skegged kayak (a step mast rig requires ample use of the rudder).

2) REINFORCING THE DECK
The deck of the kayak must be most times reinforced.
Most kayaks have a relatively flexible deck and are not designed to be loaded with the force of a sail.
If the deck is peaked (not flat) then sometimes is possible to forego the reinforcement.
I prefer to have a very sturdy set up that won’t give me grief down the road… err, sea (?)
If the deck is very light I prefer to reinforce mine with a couple of layers of woven fibreglass (or carbon) and epoxy.
I usually create a ridge (with PVC tube cut in half, foam core material or half moon dowel, slotted) contoured to the shape of the under deck.
I use a heat gun to make the PVC soft and place it hard against the kayak to give it the desired shape. For the foam core or dowel I just slot them and shape to suit the undeck.
I place the woven fibreglass cloth with the resin already infused and drape it over the ridge.
The kayak is hanging belly up (hull side up) and I work through the tight confinement of the front hatch opening. Be prepared to get your hands dirty.


3) MAST ANCHOR TO DECK
The mast is typically attached to the kayak with a tiller extension device.The device allows easy attachment and removal of the sail kit.

A ) Ronstan makes a stainless steel model that is sturdy enough for the loads that the wind generates on the mast base. http://www.ronstan.com.au/marine/product.asp?ProdNo=RF1127


The base must allow the mast to be lowered and stored on the deck of the kayak while remaining attached to the kayak.
The base must also rotate on its axis to allow the mast to swing left to right according to boom position when trimming a sail (if boom is fixed on mast).
What the Ronstan stainless steel tiller extension unit does not allow though, is vertical side to side movement. Potentially this could cause some problems.

(PS MAY08: in high winds there is the chance to crack the deck when lowering the mast sideways)
B ) Alternatively a tiller extension that uses a polymer (rubber) knuckle can be used. Although promising, I am still testing the effects of side loads on the unit. (PS SEP08: after several months of testing this version is now the preferred one)

Base in epoxy resin and carbon fibre to spread the vertical load that is exerted onto the deck

C ) A third version of the mast foot can be made from the Ronstan tiller extension above (RF1127), a saddle and a D-shackle as base on deck.

I like this last version since it allows vertical and lateral movements of the mast.
Deploying and taking down the sail while at sea can create at times side loads that the standard tiller extension base (RF1127) transfers to the deck of the kayak.
(MAY 2008: THIS VERSION IS CURRENTLY UNDER REVIEW; some odd side loading issues with hardware)
4 ) BOOM ATTACHMENT TO MAST
The boom is attached to the mast with a Ronstan tiller extension. The base of the tiller extension (rotating knuckle) should be welded and attached to the mast with 4mm bolts.
The mast should be reinforced here since most of the wind load will be exerted to this spot.
A sleeve or internal reinforcement (dowel) is recommended.

The alternative is a canopy fitting but this will not allow the use a tubular boom.
A boom made from a fibreglass batten (canopy fitting) is in my opinion too weak. I have seen several fail.
In version B) and C) the mast does not rotate on its axis and the boom must be attached to the mast via a collar that will freely spin around the mast.
I have been unable to find such fitting (for a tubular boom) and I had to fabricate my own one out of a stainless steel strip.
At the top and bottom of the collar you can install a sleeve that keeps the boom in the correct position and prevents it from sliding up or down the mast.


collar for boom on mast

5 ) DECK RIGGING
The mast and the boom must be controlled from the cockpit of the kayak.
You have to be able to deploy the sail while paddling and be able to trim the sail for various wind direction.

The mast is hoisted with a sheet (rope) that is attached from half way up the mast (forestay) to the front of the kayak, through a little pulley, and then back towards the cockpit.


The sheet is then held to the deck with a cleat or a cam cleat.

All cleats should be fastened to the deck close to the cockpit and be easily operated but should not interfere with paddling.
Make sure that your knuckles will not bump into the cleats!
All fittings should have a decent size washer under the deck, especially if the layup of your kayak is light.
Every kayak deck is different and the perfect position of the cleats will be determined by the user.
Use only 3-4 mm size cord since it is more then sufficient for the loads of the sail. Use a sheeted polyester cord that will offer a decent grip on the cleats or slippage will occur especially on the forestay cleat.

The rope that trims the boom (main sheet) will pass through a small pulley attached to the deck of the kayak with a little saddle. To secure the sheet into position, a cam cleat (RF5001) is better then an ordinary cleat since the boom might be adjusted frequently while sailing.

6 ) STAYS
I have used stainless steel for my stays in the past but I found that the cable is too rough on the sail.
I prefer to use now 3mm Dyneema (Spectra) cord. The sheet is unbelievably strong (rated at 650 Kg) and very easy to work with.
The anchor points for the stays are two stainless steel saddles bolted to the reinforced deck of the kayak. Large washers are used under the deck and nylock nuts to prevent unwanted loosening of the fittings.
On some kayaks you can use the fitting that attaches the perimeter line as stay anchors (image below)
A D-shackle (with a wing (flared) pin end will allow install and removal without tools) connects the stay to the saddle.

7 ) SAIL
The sail design itself is obviously the most important element.
The sail should not be too large or it might be overwhelming in high winds.
The whole rig, when folded on the deck, should not intrude over the cockpit area.
The top of the mast should be somewhere in the vicinity of the front of the coaming.
When specifying the length of the mast, boom and battens it is best if all 3 end up being the same length when folded on deck.
The mast will need to be slightly longer while the boom and batten should be of the same length.
The sail has a sleeve where the mast slips into.
A small cut off is needed where the stays are attached to (halfway up the mast).
A clear PVC window is desirable to allow you to view ahead of you when sailing.
The sail should have a slanted boom to create enough clearance for paddling or you will be hitting the boom when paddling.

sail for a mast of 1400 mm

sail for a mast of 1350 mm

The sail is not of my manufacture since it is a science and an art to create an efficient sail.
The sail must be shaped correctly to have enough draft and “catch” the wind.
Since I have very little knowledge in sail making, I have not bothered sourcing the materials and sew the sail myself.

Mick MacRobb from Flat Earth Kayak Sails (http://www.flatearthkayaksails.com/) is my current sail maker.

He can sew just the sail or he makes complete sails with all the necessary hardware.

Admittedly not everybody wants to spend the time (and has the knowldge) to make the hardware for the sail.

Mick's complete sails are ready to install often requiring little more than a cordless drill.

JUL 2012: Updates on the sail set up here
Notes:
- I have used all Ronstan fittings references because they are available locally. I am sure that other fittings of similar description are quite suitable for the job.
- Pacific Composites from Coopers Plains in Queensland, Australia have fabricated the carbon fibre tubes of the desired specifications.
- Despite my best efforts to engineer the sail rig and specifying my findings in this document I assume no responsibility if anyone replicates my design. It is the sole responsibility of the user to make sure he/she is totally satisfied with the design before they set out to the seven seas.

Flat Earth Kayak Sail on left, my design on right

For more images of sails used in the field (or should that be sea :-) check http://www.flickr.com/photos/gnarlydog/sets/72157600524255302/

Damiano Visocnik