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What is the ideal setting for the mast step

Postby David on Fri Jun 11, 2004 11:02 am

I understand the rules take measurement from the transom to middle of the mast, but there is quite an allowance in the placement of the mast step.
Where do the top boats have their mast steps and for what reason.
David
 

Mast Step and Mast Rake

Postby Stephen Early on Wed Jun 16, 2004 11:22 am

I noticed the questions on mast position and Mast rake. Over the past 28 years in the class I have noticed many variations amoungst the top boats. Some such as David Wood (a past Victorian champion and consistent performer) has his mast step forward and carries a fair amount of rake. Another is Maree Early who has the mast step well back and very little rake. Both have reasons for what they do and both go fast.
I have concluded that what is important is that the rake must match the step position. The difference is dramatic and I have a great photo taken at the finish line of both boats crossing together and you can easily see the difference in rakes.
What is more important once the rig is balanced is the way you sail the boat and how you set the sail.
Never say Never 1437
Stephen Early
 

My mast position

Postby barrye on Thu Jun 17, 2004 2:33 pm

Until recently, my mast position (centre of mast) was 2710 mm from aft of the transom. That was was on my old boat 1439 and my current boat 1611. I have recently experimented by moving it to the minimum allowable position ie maximum aft. The boat is still perfectly balanced...using the same rig tension, but the mast is raked slightly straighter (haven't actually measured it).
At this stage, I think upwind speed and pointing ability are about the same but because the shrouds and mast are more in line, the mast has the ability to flop forward downwind.
Barry Eastgate
:D
barrye
 

Mast rake

Postby Shane 1668 on Thu Jun 17, 2004 8:10 pm

Could you please be more specific with how to sail the boat? If the mast step is forward with more rake, will this help the boat point higher and how do you sail it for different mast and rake positions?
Shane 1668
 

mast step. rake and pointing.

Postby barrye on Thu Jun 17, 2004 9:26 pm

This is a bit complicated and perhaps we will put a more detailed article under "Sailing Hints".
Ultimately you should be aiming for a 'balanced' feel on the tiller upwind when the boat is sailed flat. The reality is that you will probably have a little bit of weather helm. I suggest you also look at the sail control article under Sailing Hints... particularly the effect of leech pressure, twist etc on pointing ability.
Balance (in tune) occurs when 'centre of effort' (CE) lines up with the 'centre of lateral resistance' (CLR). Too much rake aft moves the CE of the mainsail aft and gives the boat weather helm. Moving the mast step forward, but with some rake will overcome weather helm and contribute to perfect balance.
Moving the centreboard aft will also have an affect.
Obviously, the converse ocuurs if you have lee helm.
The mast maybe raked aft in strong winds to lower the CE. As I said before, this is complex and there is no straight answer. What I can say from experience is that the majority of Sabres have their mast step somewhere between max aft and the midpoint allowed by the rules.
barrye
 

pointing

Postby phillip on Fri Jun 18, 2004 8:39 pm

Pointing or not, that is the problem.

The ability of a sailing boat is dependent on three things
1. Balance
2.Sail shape
3.Skill

The first item has been thrashed enough so lets condider the other two.

Sail shape

Pointing is the ability of a sail to generate adequate power to drive the boat forward with the lowest angle of attack between the apparent wind and the chord of the sail. This is basically determined by the sailmaker when the sail is made but it is important that the crew get the best out of the sail by adjusting the trim of the sail. This is done by adjusting the luff tension to keep the angle of attack low by not over tensioning. Flattening the sail with the vang also helps to flatten the sail and this helps to reduce the angle of attack. The downside of using the vang is that it is easy to overvang and close the leech and by flattening the sail too much the available drive is reduced. As is evident above there is no easy answer and each skipper work out the solution personally. This can only be done by sailing the boat. In this world you get nuthin for nuthin.

Skill

When sailing to winward the boat must be constantly kept at the correct angle to the wind.This is done by constantly luffing the boat into the wind by just enough to stop the winward tuft from streaming and the steering the boat back on course. This goes on constantly and assumes that the boat is properly balanced as previously discussed. Any hint of lee helm must be eliminated as it makes pointing impossible, slows the boat and increases leeway.

Phillip Johnson
Sabre 1644
Illegitimatti non carborundum

PS Just get out there and do it
phillip
 

Another 2 bobs worth

Postby Guest on Sun Jun 20, 2004 3:57 pm

If you watch the top boats they have one thin g in common. In almost all conditions - (except for very very very light) they sail the boat flat. If the boat is heeled then the shape becomes asymetrical. This causes the boat to want to round up. What you do is pull the helm up a bit to sail it straight. The end result is a HUGE amount of drag on the rudder and the boat goes slower. Unfortunately all this drag makes you think the boat is going faster as you can now feel the water moving past the rudder blade as the water moves past it. To increase this feel instinct tells you to heel more and as a consequence you go slower. With the water turbulence you also tend to drift sideways hence not pointing.
I agree with what has been said beforeabout pointing but there is another quirk that comes about. What is important is the relative wind not the actual wind. so if you are going faster you have a higher relative wind speed and can go faster. So you need to keep up speed to windward if you are going to point high. Boy does this get confusing.
A number of things you can do is this.
- Balance rake and step position
- set the vang so that the top leach telltail strams about 90% of the time. (This will mean the leach is as tight as it can be without causing turbulance and loss of height and speed)
- Sail the boat FLAT and when you think it is flat sail it flatter.
- Practice and Practice so that you can keep it flat and quick

Never claim you are too light as Maree Early and David Wood are both in the 60kg or just above division and both finish towards the top in a breeze.

Stephen Early 1437
Guest
 


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