Busy few weeks always around Christmas time in college for us! We thought we should share a few thoughts on basic boat tuning, particularly for RS’s. We definitely aren’t the experts at this but here goes!
The first point is that boat tuning only accounts for around 20-30% of boat speed with most boats, so it’s normally not worth worrying about if you’re new to a fleet. However, at the front of a fleet it can a big difference! Also, there is no “perfect” way to tune a boat. Different settings will suit different types of crew and different weather. For example, we like to tune our boat for high pointing upwind as it can be major tactical advantage in starts and up the first beat.
There are 4 main areas that can be played with for tuning: mast rake, mast ram, spreaders and rig tension.
This is an important one for getting the boat balanced. The idea here is to line up the centre of pressure on the sail with the centre of lateral resistance in the water. These two forces are in opposite directions and if they are not in line they can cause a twisting moment on the boat. In extreme cases, this leads to weather helm resistance when trying to bear away. Most of the time the resistance isn’t noticeable via the tiller, however, this is still slowing you down as the rudder has to be turned slightly to counter act the twisting moment which causes extra drag in the water, ultimately slowing you down and hinders pointing! So the idea is to get the balance such that the boat goes in a straight line when the rudder is straight.
Mast rake is quantified by measuring the length from the top of the mast to the top of the boat's transom, with the jib on and tensioned. The general rule of thumb is if you’re strong upwind and slightly weaker downwind, the mast needs to go forward (longer mast rake). The recommended numbers can normally be found on class associations websites.
A really good example of all this is seen in windsurfing. Next time you see one out, watch how they vary their mast rake, forwards and back, to steer the boat.
The theory here is that a straight mast produces more power than a bent one. So this area of boat tuning is very focused on the crew weight. A heavier combination like ourselves normally aims for a straight mast for maximum power! One thing to bear in mind here is that sometimes a change in mast bend can cause a change in mast rake so be sure to only change one thing at a time.
The bend can be varied via the mast ram and the spreaders. With the spreaders, increasing the spreader deflection and increasing spreader length increases mast bend and reduces power. Similarly, increasing the spreader angle and decreasing the spreader length normally decreases the mast bend and increases power. One thing to watch out for is making the spreaders too short as this can result lateral(side to side) deflection of the mast in gustier conditions! It’s a good idea to set you spreaders first as you’ll rarely change these and then move on to mast rake.
The mast ram is only present in some boats such as the RS400’s. The ram pushes against the bend of the mast to keep it rigid and straight. The more the ram is set to push the straighter the mast and hence more power!
The rig tension is another key area of boat tuning. The rule of thumb here is that more tension results in a stiffer mast and more power. The helm and crew will need to provide the flexibility to handle the different wind changes that are often experienced. With less tension things are more flexible, but with possibly less power and less pointing. The mast can help the helm/crew with the “gust responses “ which can be very useful when sailing in gusty spots!
A good place to start is to visit your class associations website and find the numbers for your boat type and from then on experiment and see what works for you and your crew. For RS400’s this can be a good starting point -> http://www.rssailing.org/docs/RS400/tuning/RS400NickCraigGuide.pdf
Sean and Tyner