To Firstfooty. A reperat the ceentre of EFFORT must be precisely above the centre of LATERAL RESISTANCE. Otherwise a turning moment will arise. I mean the actual physical points of action, not geometric proxies such as CLP.
What is not apparent from any of the other contributions is what lead is for. It attempts (by quite parbarously crude methods) to iron out the problem of dealing with a 3-dimensional problem by a 2-dimensional solution.
As the boat heels, the centre of effort moves to leeward. The centre of forward resistance probably moves a bit too, but by far less. We therefore get a couple ACROSS the boat, which is trying to turn the boat into the wind. In order to overcome this, we need to move the rig further forward. That is fundamentally what lead isfor - and if we are of such a turn of mind an ideal lead for any given angle of heel is quite easy to calculate.
Where the witchcraft comes in and people start shaking their bags of bones is that the ideal lead increases as the angle of heel goes up. This means that boats that can operate at high angles of heel need to have a big lead - except in light weather when the CE needs moving aft by some means (or the boat will carry lee helm - common problem). Lead is also used to overcome problems of ill-balanced hulls - ones that are intrinsically directionally unstable when heeled. This really is bag of bones country and clouds what is basically a simple issue quite hugely - hence the wide range of suggested values for the lead.
I suggested the knife-edge method for a basic determination of CLP for one very simple reason. What we are primarily interested in is the fore-and-aft position of CLP. The knife-edge method will always provide this. The disadvantage of the pin balance or pin and plumb-bob methods is that when we are looking at the full profile of a Footy including rudder it is quite possible that the actual 2-d rather than 1-d (flat land as opposed to lineland) centre will fall outside the profile. This is a bit awkward!
The ghosts of the ‘its only a Footy’ philsophy have not yet been completely laid. I quite agree that it is possible to design excellent Footys by purely empirical means - suck, spit out and adjust. I tend to calculate things because I come from a (hobby) background in big boat design where serious mistakes can be expensive, and because I am a poor builder. This means that I rely on other people to build my designs. These tend to be fairly radical (if you’re not doing it for your living,what point is there in following the guy in front at this stage of the development of the class?), so it seems grossly unfair not to minimise the uncertainty before asking someone else to put their time and effort into the building.
HOWEVER, this is not the same thing as saying ‘it’s only a Footy so these physical details do not matter’. Because a Footy is small and at the bottom end of widely available sailing boats that do actually sail properly, tolerances are tiny. Absolute errors tht would be insignificant in an IOM assume giant significance when reduced to Footy size.
That’s exactly what I felt in the begining of all this. Due to the small size, errors are magnified, not reduced! A 2%-5% error in a large ship is easier to comp than a 2%-5% error on a very small ship. The smaller they get the more precise it has to be…
Interesting to me was that I read the information that [i]Bill Hagerup[/i] has provided for the Razor and figured the mm to inch conversions. [i]Where he states the Center of Gravity for Fin/Bulb from Bow 165mm.[/i] I took the inverted bare hull (which I had finished) and used a thin straight edge. I set the inverted hull across the straight edge and moved it till it balanced perfectly fore/aft (no small task) and when I marked and measured it, I was just about dead on his dimension. I was just a tad aft of it due to the fact that I used a thicker piece of Balsa for the transom. Had it been the original thickness, it would have come out dead nut.....
When you read the Norwegian stuff, remember that their Class 1 were knocking on for 2 metres long - persued by men in rowing boats!
P.S A reminder to the Luddite school - apart from being probaly the most successful yacht designers of all time, the most obvious common charateristic of Nat Herreshoff, Olin Stephens and Bruce Farr is an exceptional talent fo ‘medium level’ maths.
I’m still here in spite of my stroke in 2004 and decided that if I had to give up big catamaran sialing due to the “scramble” requirement, I can still build and sial the little ones. Go ahead and visit the club - according to my feelings, most clubs are made up of “old men” with a variety of maladies.
Seriously, I’ve helped a family friend’s son who was born with a range of physical issues, build and learn to sail his Seawind. Likewise there are some on the internet community who have found ways to “wheelchair” their boat and themselves to pond’s edge for some quality sailing. And don’t overlook the “privilege factor” of being able to park close in the handicap spots of it was a serious one.
Not to make light, but depression is there, and getting back out and enjoy what you make of it is also important. I lamented the fact of reduced big boat sialing after mine - until the grandkids came over. It’s part of the reason I’m building four RG-65’s - for son, grandson and son-in-law. I plan on going sailing with them and am looking forward to it. Living here in Minnesota, I watched closely when Kirby Puckett (Mn Twins outfielder) succumbed to a massive stroke - and from that I came away thinking how really lucky I was.
I urge you to visit your local club. If you have the chance - tell them of your stroke, and I wouldlay odds, they will try everything they can to accomodate you if you show an interest in sailing.
This psychological moment brought to you by “others like you” - don’t take offense - get even and join us.
Seriously, email me off line if you wish to talk further. It’s slowed me down, and on certain days I get cramps trying to hold small parts - but dang it - it’s fun when you see a boat under YOUR control on the water. Just do it - as the saying goes.
ADDED: apologies for going off-topic on tis one guys. Back to the regular topic at hand.
No apology needed Dick. I’m into Footys because I will never sail a boat on an offshore race again. I have heart disease and crippling arthritis to the point of being virtually bed-bound- hence the reason why I prefer other people to build (and sail) my boats.
Model yachting (and Footys in particular) is full of the ancient and the cripples. Get in and do it. If you need an advice, you have my email.
Yes and my apologies for making the initial comments in my post, which had nothing to do with this topic. I’m new to forums too and those comments were way off topic.
knowing what we know, just helps with responses. And as for feeling uncomfortable - until you show up and make the effort, you will never know - but just assume. In the end, I believe that in most clubs there are the "quiet guys, and the boisterous ones. Somewhere in the middle you might also find guys who, for health reasons, have moved into the hobby. THEY are the ones that will understand and assist. I urge you to give a visit or maybe three, to a local group if circumstances permit. Somewhere out there someone is just waiting to give advice or help you enjoy the hobby even more.
Feel free to ask questions - many are knowledgeable and very willing to share.