SOME NOTES ON BOAT TUNING
by Derek Wilkes some time ago but still a very good read..
Most of the following pointers and settings tips have been gleaned from
various tuning guides and watching and noting how other people do things.
If you intend changing anything then do the whole gambit and do not do it
piecemeal as the whole rig needs to work in synchronization.
Most of the comments refer to the October 1998 Pinnell & Bax tuning guide
and for ease of reference I will start at the bow and work aft.
1. It is important to realise that all the newer boats have the roller-furler
mounted on the foredeck which is extended to the bow in a straight line
unlike our boats which have a stepped section on the bow. This means
that the clew of the jib is 100mm above the deck which is according to
regulations. Our practice of fixing the jib directly into the roller furler
actually lowers the profile of the jib which gets it out of synch with the
main and upsets the balance of the overlap. Therefore you should put a
longer shackle into the furler onto which shackle the clew of the jib.
2. The overseas guys shackle the eye of the clew to the eye of the luff wire
which does two things: firstly it gets the sail fixed as low as possible onto
the deck but more importantly it prevents the sail from twisting around the
luff wire when you furl the jib. In order to set the luff tension of the jib with
this set up you simply hoist the jib upside down set the tension and then
re hoist it the right way up. When changing jibs they keep the same luff
wire and simply feed it into the luff of the next jib and repeat the process.
This keeps all your tension settings exactly the same as well as your rake.
3. The mast heel position is very important as it sets the relationship
between the CE ( centre of effort) and the CR ( centre of lateral resistance
of the keel and rudder). The measurement is 93 mm from the centre of
the front keelbolts and the aft mast bolt in the mast step. This is required
irrespective of where your keel is positioned within reasonable tolerances.
The keel should be +/- 3939 mm from the transom to the forward edge of
the keel measured along the hull.
4. The spreader set up is important and you should adhere to the tuning
guide. For the older masts (gamma) I would recommend a length of
420 mm and the spreader angle of 21 O mm to allow the mast to bend
more because they are very stiff masts.
5. Rig tension on our boats should not exceed 350 to 400 lbs maximum
whilst at 200 lbs the rake should be a maximum 7500 mm moving forward
with increasing tension to a minimum of 7570 mm The rule is the lighter
the conditions the higher the tension makes you think eh!
6. Jib car (fairlead) positioning is also very important for pointing. The
distance from the transom and the centerline is critical. On our Windibank
Mark IV boats the angle of the side deck is such that at the very bottom of
the side deck the distance from the centre line is 400 mm whilst at the top
of the side decks the distance from the centerline is 440 mm. This means
that you should angle the tracks between the 2850 mm and 2950 mm
measurement from the transom. The rule here is that the lighter the
weather the closer in you sheet the jib and the converse when the wind
pipes up. Remembering to get the telltales streaming and lifting together
as per tuning guide.
Without doubt what we have learned in Esperance is that boat speed is about
tuning the rig above the deck. The only requirement of the hull is that it should
be stiff and flex under tension. I must stress there are others who will disagree
with me but even with bicycle boats we will still not be competitive unless we
get to grips with the rig and learn what can do with it.
SOME COMMENTS:
Derek suggested a few measures to improve the sailing speed of your Fifteen.
It is generally recommended that you make only one change at a time and try
out its effect on the water. The setting up of a Fifteen is governed by the Class
Rules which do not leave you much choice in the positioning of the main
components of a boat, such as keel, rudder, mast, side stays, etc.
Certain measurements can be changed. The rake of the mast is a much
discussed subject and so are the positions of the fairleads in various wind
conditions. More rake creates more weather helm which can be counteracted
JJ.y moving the foot of the mast forward (if the Rules permit). More influence '6n the helm has the CR (see Derek's article). Not only the position of the keel
and rudder but also the underwater lines of the hull at any given time make
a big difference. A heeling Fifteen has more weather helm than one which is
sailed upright. Keeping your Fifteen flat is the first step everybody can and
should take before embarking on changes in the current set up of your boat.
Most of our Fifteens have come out of the same mould and all were built by
the same builder. They are likely to differ somewhat from the overseas boats
on which the tuning guide by Pinnell & Bax is based. So don't rush in getting
your boat to fully comply with the guide, make changes step by step.
