In reading the various tuning info sheets on the 5o5 web site, I see
that many specify the "rake" measurement as ~25' 7" as measured with a tape
measure from the top of the mast , over the transom, and down to the hull-transom
intersection. I know that most of these measurements are to be taken as starting points
and that it is only important to always measure it the same way each time as you
"dial in" the right setting for your boat; but it still seems it would be more
helpful to the new folks if rake measurements were reported on the web page in a way that
does not depend on the shape of the top of your transom. There can be about three inches
difference in this measurement, at exactly the same rake, for boats with different transom
heights. Can those of you who post this kind of information plese measure the rake and
report is as measured through the cut-out in the transom directly to the aft edge of the
hull?
Thanks
John Dean
US5518 "Miss Scarlet"
Seattle
I have a better question. Why do we use these arbitrary measurement
standards? What is the reason for measuring rig tension at the shrouds. Rig tension
primarily controls headsail sag, so why don't we measure it on the forestay? Different
spreader lengths, angles, or heights can cause the same shroud tension to give very
different headstay tension. Furthermore, why don't we measure mast pre-bend directly: hold
the end of the main halyard against the mast at the gooseneck, tighten it so it is
straight, and measure the distance between the halyard and the aft edge of the mast. That
is the prebend. Now we all report spreader length and sweep, but a slightly different mast
foot position or spreader bracket height will result in a different amount of pre-bend for
the same spreader set-up.
If we measured headstay tension directly and mast pre-bend directly,
tuning would become much easier. We could understand what we were really doing when we
changed something and it made us go faster. For a given set of sails, headstay sag and
mast pre-bend are the single most important set-up parameters. For example, right now, if
I change my spreader angle and leave my shroud tension and rake the same; and i find that
it makes me go faster, I don't know why. Is it because I've changed my pre-bend or because
I've changed my headstay tension? The same question applies to changing shroud tension. If
it increases my speed, is it because it changed my prebend or my headstay sag? If we
measured headstay tension and prebend, ideal rake would be a measurement that was a
function of the boat set-up only (CB position, launcher or bags, hull shape, etc). All we
east coast 505ers who use Norths could quickly determine what is the best prebend/sag for
those sails, and it would be transferrable to every boat that uses those sails.
Stergios Papadakis
US 7199
Princeton, NJ, USA
John,
I am not going to try to steal any wind from the people who REALLY
know whats up with tuning guides on this list, but it was my undertstanding that this
measurement was taken from the inside corner of trans/hull.
Either way, I will make my point. The probability of you having a
boat (Parker?) and having a suit of sails, foils, etc. that would "mirror" those
of the boat on the tuning sheet is low.
For what little I know, I do know that these things can make a
difference.
BUT BUT BUT BUT BUT
That is not to say that those numbers aren't EXCELLENT starting
points and can save you TREMENDOUS ammounts of time tuning.... I like to get a boat
(whatever kind) "dialed on paper" , but then go out on the water w/boats, races,
etc. and see how it is going - from there, I slowly make changes - but keeping track of
them in comparison with the original numbers.
I guess what I am trying to say is that even whether it is over or
under, you still have to 'improvise' a considerable ammount.........
Cheers
"T" Brockenbrough
USA8316
Charleston USA
John,
I think you misunderstand. The measurement is from the top of the
mast to the intersection of the transom and the hull on the *inside*. You pass the tape
measure through drain ports (cutouts) on the transom near the floor. Not over the transom,
at least for NA boats.
Ed. I measure over the transom on my Waterat... I believe the difference in the
measurement between through the drain port - if you have one - and over the transom is
actually quite small.
So a measurement of 25'8" is from the main halyard, raised to its racing position,
down the intersection of the hull and the transom. It is a straight line. The Aussies
measure to the top of the transom (according to the North Australia sheet), but they all
sail Kyrwoods and Kulmars.
Ed. which have very similar transoms and transom profiles... boats appear close to
identical
Bill Green
Denver, Colorado, USA
Sterg raises some good points here, but I think we must not lose the
big picture when it comes to tuning. I think it was already stated that the tuning guides
are only a good starting point for a campaign that wishes to experiment and get that extra
edge. For the casual 505 sailor, they are tried and true numbers that enable an infrequent
sailor to go relatively fast without having to think too much and get distracted while
sailing. It is my experience that detailed tuning beckons the type of questions that Sterg
has asked, but I would warn against changing convention for fear of losing simplicity.
The Bixby tuning guide which most NA sailors use is fairly specific
with respect to where all the major rig components should be (i.e. mast step, ram,
spreaders, CB pin, etc). However, I can see that it may not be specific enough for people
aspiring to get to the top of the class. This is where multiple boat tuning can help.
Barney Harris and I on #8643 have decided that the best way for us to gain an edge is to
duplicate our rig settings to that of another Waterat launcher boat. This means having
identical rig parameters AND identical measurement systems. I know the west coast sailors
have been doing this with success for some time. In this way, two boats tuning together
can easily see the difference that adjustments make while sailing. Moreover, they are
quantifiable to a certain degree. Perhaps the prebend measurement that Sterg recommends is
best applied when attempting to discover the measurement differences between two boats
with supposedly the same settings while on land.
One last point here. As important as it is to quantify settings,
never underestimate you're power to perceive better performance through feel. Too often I
have gotten caught up with numbers and neglected my sense of feel. The only way to develop
this sense is to get out on the water and try some of those settings you've been
painstakingly measuring. Ed. Those numbers were developed by feel in the first
place....it felt fast, so someone measured it and wrote it down....you can - and should -
do the same.
Jesse Falsone
505 8643 crew
Annapolis, MD, USA
I think that measuring pre-bend and forestay tension directly will
give you a better feel for the changes you are making, because those measurements directly
affect the shape of the sails. They will help prevent "sailing by numbers". If
you are doing some two boat tuning, here is what you do: you set up the two boats to what
you think is fast, then go out sailing. You speed test side by side all day, changing
settings one at a time, until you are going faster than you were at the beginning of the
day. Then you come off the water and measure everything again. If you use the North tuning
guide standard measurements, you won't be able to link an individual measurement to some
physical effect. If you measure prebend and headstay tension directly, you can come to a
conclusion like: "Our mainsail needed to be flatter (more prebend) and our jib needed
to be fuller (less forestay tension) than we originally thought, but our rake hasn't
changed." Or, you may find that your prebend and forestay tension are the same, but
your rake is different. This means :"our sail shape was good but the whole sailplan
was too far back. Changing the rake changed the center of effort and now we are
faster." If by some blind luck you are faster than everyone at some regatta,
measuring prebend and headstay tension directly (and rake, of course) will make it more
repeatable, plus you can spread the knowledge more readily to other boats.
When I get a chance, I will set up my boat as the North tuning guide
suggests, and then measure the headstay tension and prebend directly, and post that.
Stergios Papadakis
US 7199
Princeton, NJ, USA
Howdy Sterge, I'm looking forward to the end of May.
How do you propose we measure headstay sag with the jib up?
Cheers,
Bryan Largay California, USA
Measuring Jib luff sag? thats easy -
We are not allowed to adjust shrouds in the Albacore class, so
measuring jib luff sag in response to jib halyard adjustments is key. We have a separate
wire rope forestay and a wire luff jib. The jib takes the majority of the tension, and is
adjustable while sailing. To measure jib luff sag I have my forestay tensioned by a shock
cord thru a bullet block on the tack fitting and lead to the jib halyard where it exits
the mast below the deck level. In this way it automatically compensates as the jib halyard
is adjusted, maintaining relatively constant tension. I have a one inch length of tape
stuck to the jib luff. It is easy to get 1/2 or better inch accuracy and resolution by
eyeballing the distance from the wire forestay and comparing with the 1 inch tape. This
only gives relative measurements since the forestay will sag in response to the wind also,
but it is repeatable.
Barney Harris
505 8643
Albacore 8011
Annapolis, MD, USA
Hey People,
Don't forget that raking (angling mast to the rear), does more than
just move the center of effort to the rear. Assuming no other adjustments are made, raking
the mast loosens the jib leach (ie twisted off), increases the middle mast bend (due to
the effective change in spreader position), and increases the lower mast bend due to ram.
The later two flatten the main and open its leach.
Graham Alexander
Sail fast but sail smart.
US7685 and US4593
Columbus, Ohio, USA
I'm sorry if I wasn't clear, but I meant that tuning guides should
record forestay tension instead of shroud tension. Then you would mark the rig tension
controls in your boat to correspond to forestay tension numbers. I don't want to
permanently add another forestay to my 505, so I'll be unable to measure forestay sag when
sailing upwind, but by knowing the headstay tension, I have a setting that is repeatable
from boat to boat as well as day to day. I can tell someone, "In ten knots of breeze,
a North jib should be set with XXX lbs. of forestay tension." That will correspond to
a certain amount of headstay sag. That measurement is independent of anything else in the
boat.
Stergios Papadakis
US 7199
Princeton, NJ, USA
I have a '78 Ballenger with fixed shrouds (chain plates) and a jib
halyard adjusted by an 8:1 magic box. Sooner or later I will re-rig the boat with
adjustable shrouds and a fully adjustable jib halyard. But I want to learn to sail the
boat first. Since I only have 8:1 mechanical advantage I can't pull much rig tension on,
maybe 400 lbs or so, and if I choose to rake during a race, the shrouds (hence the jib
luff) will slacken. Since it is a jib halyard and not a seperate forestay how do I measure
forestay tension and jib luff sag? I am trying to figure out how to set up the boat, but
I'm not totally sure how to do it. I am thinking about increasing the jib halyard purchase
to 16:1 or possibly 24:1 with a small cascade between where the jib halyard exits the mast
and the magic box. I would rather spend my time and money learning to sail and race not
re-rigging the boat. Any advice on where to start. If it matters, I have a raggedy Danger
main and jib and an even worse North (not Bixby) set. I'm not too concerned about the
condition of the sails as the boat is much faster than I am.
Thanks for your help.
Bill Green
Denver, Colorado
US 6491
Hi all,
I was racing 5o5s in Bermuda for the past week (watch this space for
an e-mail report) - without my laptop - and am slowly catching up on the approximately 140
(no, not an exaggeration) sailing e-mail messages I received in the 6 days I was gone...
Sorry about jumping in late, but I did want to comment on the tuning sheet measurements
discussion...
The good thing about the current measurement system is that it is
easy to use. The bad thing is that it is not perfect as Sterg points out... We can develop
better ways of measuring.
It was not designed by engineers after lots of careful analysis....
However, it is useful as a starting point. The numbers WERE ALL DEVELOPED BY FEEL... all
that happened is someone went around the dinghy park measuring fast boats, and wrote down
the numbers.
Whatever system we use, and whatever numbers we come up with THEY
ARE NOT GOSPEL!!! They are merely a starting point... While you are sailing and racing,
make adjustments and notice if the boat FEELS better, or if you can see the difference
relative to other boats... this can be done while racing but is best done during two - or
more - boat tuning sessions.
Don't worry about how exact the numbers are.... I never know exactly
how hard it is blowing anyway, so I start out with too little rake, and slowly rake until
the boat FEELS GOOD and the combination of pointing and speed look good compared to the
boat I am lining up before the start with.
I always measure rake with the main halyard hoisted to the usual
location, a tape measure shackled or tied onto the main halyard, and measuring OVER the
top of the transom to where the back of the hull skin is (if the transom is sligthly
forward of the back of the hull skin (as on Rondars, Waterats and probably Kyrwoods and
Kulmars), measure to the edge where the hull stops at the back (the edge that gets ground
off when the back of the boat hits the ground 'cause you lifted the bow too high on the
trolley). Go just enough off centerline so that the tape measure goes to one side of the
center of the transom pintles/gudgeons. Yes, this number will vary slightly depending on
the height of the transom (which does not differ by much), but drain ports differ markedly
in shape, some boats have open transoms and some have no transom drains at all. If you do
measure it both ways, I think you will find that the measurement is not far off, and is
well within the tolerance of the measurement... What matters is that once you figure out
what feels good and works for you, you can reproduce it, not that 25' 8" on one boat
is actually the same rake as 25' 7.5" on another. I very much doubt you can tell the
difference between 25' 8" and 25' 7.5" on the water... so don't worry about how
exact the measurement is.
So..... check the measurements... set up your boat to them... GO
SAILING... change the adjustments and note what works for you... measure what works for
you anyway you like, as long as you can reproduce it.
The engineers amongst us can in the meantime develop a better
measurement system (I would particularly like to see a way of measuring mast bend on the
water, and am thinking about streching whipping twine from mast head to gooseneck as an
indicator).
By the way, I once compared headstay tension to shroud tension
through a range of tension settings... Headstay was approximately half that of shrouds
through most of the range. Obviously, if you have low tension and lots of pre-bend, the
forestay will be much looser than the shrouds...
Now a question.... since we have access to Australian North and
Pinnell & Bax tuning sheets on the web, I would like someone to tell the list how rake
is measured in Australia and in the UK.... This is particularly important for the four
people who just imported used UK 505s into the US...
Cheers,
Ali Meller
5o5s 7200 & 8263
Annapolis, MD, USA