H16 TuneUp Features 2


Vol 3 - Issue 1October 1998
What's All This About Weather Helm?
Exploring One of Life's Great Mysteries.
By Kim Miller

     Part 2

The How-To Guide

Adjusting Mast Rake, Rudder Rake, and Toe-In

This article follows on from Part 1 which deals with the theory behind the termWeather Helm.

Mast Rake

Mast Rake refers to the angle of attack of the mast. If it upright is has no rake, if it slopes backwards so that the top of the mast is over or behind the rear cross beam is has extreme rake. If it points forward, well, it shouldn't point forward. One of the discoveries of the racing world is that having extreme mast rake makes the boat go faster. Extreme mast rake causes unwanted side effects, but the speed gain is worth it. Some of those side effects can be compensated for by adjusting other boat parts, particularly the rudders.

When your Hobie left the factory it was set with the mast at a pre-determined angle. As with many things, that angle might not be the most suitable for your kind of sailing. The angle of the mast is controlled by the length of the forestay. As the forestay is lengthened the mast tilts backwards. And as the mast tilts backwards the side stays become loose and have to be adjusted back to a suitable tension by shortening their effective length.

How far should I rake my mast?

If you want to get maximum speed from your Hobie the mast will want to be raked back as far as possible. This is not as radical as it sounds. There is a limit to how far you can rake it anyway. This limit is caused by the mainsheet blocks. As you rake the mast the outer end of the boom tilts towards the deck. This makes the mainsheet blocks come closer together. You can't rake the mast beyond that point of the blocks touching each other.

However, you still want some control over mast bend with the mainsheet, so you can only have the blocks touching after you have maximum operating tension on the mainsheet. This limits the mast rake again. If you have too much rake the blocks will touch before any mast bend is induced. This limit is measured when the boom is centred.

The most extreme rake you can put on the mast is when the blocks are just touching when you have pulled on the mainsheet as hard as you ever need to while sailing, generating maximum mast bend in the process.

How do I rake my mast?

You rake the mast by lengthening the forestay. The easiest way to do this is to add a short length of rigging cable called a strop at the top or bottom of the forestay. It is not a difficult process to get the length of the strop.

You will need two people. One stands on the trampoline and holds the mast from behind. 
Rig the mast as normal. 
Take some strong cord, like very heavy blind cord. Braided cord is better than twisted stuff. 
One person holds the mast upright and the other person undoes the lower forestay shackle. 
Tie the cord onto the bridle centre point and loop it through the lower forestay thimble. 
Loop it around these two points three or four times. This makes it easier to manage the adjustment. 
The mast-steady person then lets the mast lean backwards as the cord-tying person takes up the slack with the cord. 
Rake the mast until the mainsheet blocks are about six inches apart. 
Tie off the cord. It should be strong enough with 3 or 4 loops to take the load. 
Centre the traveller. The mast-steady person has to hold the mast from swinging sideways. 
Pull on the mainsheet and check how close the blocks come to each other when the mast begins to bend. 
Adjust the cord length until you have good mast bend and the blocks are just starting to touch. 
The cord now represents the length of the strop you need, less the shackles needed for attachment.

You have now reached the maximum mast rake point. There is no value in going further than this. However, you could easily decide in the future that you want to reduce the rake, so you can add adjustability by shortening the strop and added an adjusting plate while maintaining the overall length. Remember that the plate will have to begin life at maximum length so you can adjust it shorter if necessary. Instead of a cable strop you can add a stainless steel strip with adjusting holes in it.

Now you have to get the new length of the side stays. Your existing stays will have to be shortened, or you might like to have new ones made. The shortened length is easily worked out by measuring the amount of slack that has developed as the mast tilted back. Just cut that slack out of the stays and swage new thimbles onto the lower end. Remember that if you decide to reduce mast rake the side stays will lengthen, so cut the new length so that with full rake the adjuster plates are at their shortest. This way you can lengthen them as the mast moves forward if needed in the future. Keep both stays as equal as possible when measuring and cutting.

If you are not familiar with how to cut the stays, or with how to swage new fittings, or you do not have the proper tools, (parrot beak cutters and a suitable sized swaging tool) do not do this work yourself. It is easy to measure it up, remove the stay, and have the sail shop do it for you. And it is a lot safer as well.

How long should my stays be?

Unfortunately there is no real answer to this question. It will depend on your desired angle of mast rake, on the length of the bridle, on the length of the shackles you are using, on whether you have a jib furler or not, on the position of the mast tang. There are too many variables to give a set length. Two boats coming from the factory are the same, but in a year or two one of them could easily have had some modification that makes a difference. Even just replacing a lost shackle with a longer one floating around in the sail bag can make a difference. 

Adjusting rudder rake

Unfortunately, one of the side effects of extreme mast rake is that the rudders become harder to manage because of the extra weather helm and "tiller tug" induced by the new boat balance. You can make the boat easier to control by raking the rudders forward. There are several ways to do this.

Rudder rake adjusting screws. 
If you have a newer model Hobie the adjusting equipment is built into the rudder castings. In the lower casting there is a grub screw which maintains the rudder position. On the top casting there is an adjuster to lock the rudder into the cam properly. To rake the rudders forward screw the grub screw into the casting and allow the rudder to move forward. You will need to experiment with the position, but with extreme rake you will probably have to screw that screw fully into the casting. 
As the lower tip of the rudder blade moves forward the part that locks into the cam moves backward. You adjust that back into position with the top adjuster. With the rudder pushed forward against the lower casting, loosen the top bolt enough to that it slides back and forward. Push it as far forward as it will comfortable go and lock the bolt. Test that the rudder unlocks and locks without any slack in the cam. If there is slack, adjust the bold forward a little more.

Re-drilling rudder positioning holes. 
If you do not have the adjusting system on your rudder castings you need to move the positioning holes in the rudder. You do this by filling one hole with resin and drilling it again in a slightly different position. This process has been dealt with in an earlier edition of On The Wire. It is not difficult, but you might get nervous drilling into the rudder blade.

Taking up cam slack. 
Even if you do not have adjustable castings, and you have a certain amount of fore/aft slack in the rudder, you can rake the rudders forward as well as take up that slack. If your rudder moves more than a quarter or half inch at the lower tip it needs tightening. All you have to do is fill the space between the cam and the locking bar under the top casting. This space will be about the size of the head of a self-tapping screw. Just drill into the cam from behind the boat (lift the rudder cross bar) and screw in a short screw so the head rests on the cam material and when the rudder is locked the locking bar rests on the screw head. 

Adjusting rudder toe-in

The go-faster guys tell us that the boat works best with a slight amount of toe-in to the rudders. Here's how to measure it. With the boat on the trailer lock the rudders in the down position. Get a tape measure and a helper to steady the rudders. Tie the tiller cross bar so the rudders can't move sideways too much.

Measure the distance across the boat between the leading edges of the rudders. Now measure between the trailing edges The measure point is where the rudder has the widest fore/aft distance. The leading edge distance should be about a quarter inch shorter than the trailing edge distance.

The adjustment is made at one end of the tiller crossbar, where it fastens to the little casting joints. It is more likely that you do not have toe-in and the tiller crossbar has to be shortened. If you already have excess toe-in the crossbar has to be lengthened. This is a headache, but not impossible.

Once again, the newer boats have an adjustable system, and the older boats don't. If you have an adjustable tiller crossbar you can unlock one end and screw it in or out until the toe-is is set correctly.  If you do not have an adjustable tiller crossbar you will need to drill out the pop rivets from one end of the crossbar, cut it to length, and replace the rivets. 
Cutting the crossbar might make you nervous. That's OK, join the nervous club. Then do it.

If you you need to lengthen the crossbar you need a piece of tube that neatly fits inside the existing piece. Then you cut your crossbar, fit this new piece inside and pop rivet one end. Then measure again to locate where the other end should be pop riveted together. Doing things this way can leave edges that your hand will not like to run over when sailing, so put this extra piece as close to the center of the crossbar, not at the ends where you are more likely to hold on to it. Tape it over with duct tape when you are done.

Lubricating the Rudder Cam Plunger

By David Hall

I use Super Lube spray. I hose it first with WD-40 as a cleaner. After that I spray with the SL. I'm sure there are others that work. Remember that anything you spray attracts crud, so depending on how much crud you sail in or are exposed to, you'll have to clean and relube to keep it working. 

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