|Topic Review (Newest First)|
|08-08-2011 01:16 PM|
Originally Posted by sailguy40 View Post
If you want to sail on the jib alone, you should use an overlapping jib, about 130% or larger. If the jib is too small, it will be difficult or impossible to tack the boat, because a small sail, with all it's effort forward, will pull the bow downwind. A larger, overlapping sail will help push the stern to leeward, which will help the boat point to windward.
But, while either sail can be used alone under certain conditions to give a reasonably satisfying, casual sail, the plain truth is that sloops were designed to perform their best with a balance of mainsail and jib, and, if you need the boat to perform well in difficult conditions, the best choice is a balanced sailplan.
|08-08-2011 12:40 PM|
What most happened is 'fatigue failure' wherein the metal simply 'became tired'. Stainless steel is especially prone to work hardening or fatigue failure ... very common in boat design: spade rudders, rigging, etc.
When your boat was designed (70s & 80s) fatigue failure was little understood and the design 'safety factor' that was selected was probably underdesigned, basing the stress calculations solely on 'ductile failure' of stainless @ 90,000 psi. Fatigue failure for stainless needs to be designed at less than 30,000 psi or less to extend the functional service life of the material.
Once fatigue cracks (microscopic fatigue cracks) begin to form water can enter the cracks and cause a second means of failure: crevice corrosion; so, in boat design you get fatigue (because of 'underdesign') and crevice corrosion all at the same time.
Worse, a spade rudder is known as a cantilever (think of flag pole) and the stress design on a cantilever inherently causes the material, where its constrained at the 'root' of the cantilever to be 1/4 as strong as if it were a beam that is supported at both ends.
300 series stainless has a stress value of 90,000 psi; however, its fatigue endurance limit is ~30,000 psi. Requiring that the designer 'derate' the metal to 30,000 psi or less.
All things in nature eventually wear out or get tired, then they fail. So, probably your overstressing your rudder probably only accelerated the failure by a wee bit as especiallly spade rudders will ALL eventually fail ... a design problem, 'safety factor' problem and a materials problem, a 'cantilever' problem and especially when 300 series stainless steel is used. Your rudder simply 'got tired', developed fatigue/chemical failure ... and you were using it long after it should have been replaced. Periodic inspection is the only way to not experience 'most' of such failure.
|08-08-2011 02:08 AM|
@ RichH, you got me thinking about something now. In May while out sailing a trip in Lake Ponchartrain from Mandeville to Madisonville, when about halfway there my rudder snapped clean in half like a piece of weak thin wood. At the time, I had a 110 jib up front and full main even though winds were near 25. Wind was out of the southeast and I was on a NNW broad reach. A wave came from behind and I made a hard correction to steer, I pulled the tiller towards me nearly all the way, rudder was sideways for a few seconds and snap it went. The wind and waves hit it just right this time and my boat was hauling at full hull speed.
Reason I am saying you got me thinking is because there have been many times the past year after I bought my boat I was out sailing in higher winds and just hoisted a mainsail. As you mention about the rudder dragging sideways through the water, that did happen many of times and sometimes I had to do corrections. My boat seemed to sail fairly quick with just a main and not always pointing issues but it still had them. The bottomline now since you say that is, I am wondering if the stress I been putting on my rudder eventually caused it give in? Since I sailed with main only many of times and it was always in higher winds. When the boat is flying along and the rudder is nearly sideways, it puts it in perfect position to just snap like a stick. I do now realize it is possible to put too much stress on the rudder from making hard corrections. I also need to add, I oversailed the boat that day which is something I don't normally do. By that I mean pushing it too hard, two sails and full sails at that. Pushing her to go too fast in the conditions. I was able to keep healing down to just over 5 degrees since I was on a broad reach but nearly running as well.
|08-08-2011 01:36 AM|
Your lack of pointing ability is probably due to several factors.
1. your sails lack tell tales ... so there is no way to monitor or visualize the AERODYNAMIC FLOW across the sail(s). Strongly suggest you apply tell tales to the luff/mid-cord/leech of each sail.
An 'entry level' reference for use of tell tales would be: Sail Trim Chart and Sail Trim Guide and a more 'advanced' reference would be ArvelGentry.com ---> magazine articles ---> a 'sequence' of 4 articles ---> Checking Trim on the Wind, November 1973
Achieving Proper Balance, December 1973
Sailing to Windward, January 1974
Are You at Optimum Trim?, March 1974
2. a sails ability to 'point' depends on how much air is 'stacked up' well in front of it (upwash). The jib/main combo creates more 'upwash' and enables the combo to operate at a MUCH higher angle into the wind thus a jib/main (even reefed) combo is going to 'outpoint' a boat with only 'one' sail up.
3. HELM BALANCE. If because the sail SHAPE is bad and the 'balance' between the jib/main is out of kilter OR the shape of a single sail causes undue helm balance ... the result will be that the rudder will 'dragging' (held at a considerable angle off from being parallel to the centerline of the boat).
Your boat is a mast head rig and to make it 'point' with only the main alone (or jib alone), you will have to radically alter the SHAPE of the main alone (or jib alone) by halyard/outhaul/vang, etc. tensions so that there is 'dynamic' balance (interaction between sails and hull/keel) is in tune .... (radical) mainsail halyard/cunningham tension results in causing the point in the sail at which the maximum draft is radically 'moved forward' - heavy heavy tension of the luff (halyard) will move the location of draft 'more forward' (but will cause the leech to become more 'slack' as a reaction).
With only one sail up on a boat designed for jib/main ... your better option would be to reef 2 sails than suffer the poor 'upwash' conditions from the usage of only a single sail and the inevitable 'dragging the rudder through the water sideways', etc. How much to reef or exactly which to sail to reef, etc. .... the helm pressure will indicate which is more appropriate.
When I hear/read that someone "doesnt want to race", it usually tells me that they dont have any interest in sail trim and sail shaping. If you have proper shape and trim there is no 'requirement' that you have to race .... but you will have a better performing and SAFER boat that isnt so subject to 'sudden power-ups' and 'lulls' (and in this case bad pointing ability) ... plus you wont have the 'motor' on so often.
|08-07-2011 11:04 PM|
|sailguy40||I been kind of on the fence myself with sail configurations so maybe someone can give me some advice. I am still not sure if running only a full main with no headsail in higher winds (say 20+knots) is more effective then running a headsail only. Usually I pick one or the other and most of the time its a full main by itself because its just easier to deal with since I have not upgraded to RF yet. I sometimes think one headsail without main could be the better choice. Then I also wonder if a reefed main with a 110 jib is the better configuration. I do get satisfying speed with the full main alone. I guess I need to just keep trying different setups to see what is the most effective. Maybe someone else with an Oday 22 or similar can give some advice?|
|08-07-2011 10:17 PM|
Thanks for the update asdf38 , very helpfull threads like this with answers no less !
Reading your post I was thinking topping up not down was what you were getting at , now it doesn,t seem so intuitive , the more I learn the less I know
|08-07-2011 09:59 PM|
Thanks for the reply's. I wanted to follow up here.
My problem was simple and very foolish on my part; the topping lift. I had received the boat in the water from the previous owner last fall and had never needed to adjust topping lift. Then in the spring I replaced the line and just set it in place. By the time the boat was in the water I had forgotten that it probably needed to be adjusted and I think by chance it was very close to the right point. In my previous few sails this season I had sailed with the genny up and just didn't notice that the main was a bit out of trim. This all hit me at random a week ago and sure enough it needed to be dropped a few inches (so that it has a bit of slack with the main up). This mistake certainly reflects that I still need some more experience and probably more formal training at some point.
But thanks for the reply's. I do understand well the impact of sailing with main only (more weather helm) but on my boat it's not bad. However in the future I'll try to sail with the proper sails.
|07-11-2011 09:04 AM|
|imagine2frolic||Let's take the comparison of the car again. The sails are your motors, and when a motor is worn there is a loss of power. No matter what lack of knowledge you have of trim. Worn sails aren't going to give you the power you need. Just like a worn motor will not pull that load uphill. Sailing to windward is uphill...........i2f|
|07-11-2011 07:51 AM|
I totally understand that you are not interested in racing, but if you intend to sail at all, then you should care about sail shape. It's like saying "I'm interested in driving a car, but I'm not interested in ever changing the oil" and then complaining when the engine fails on you.
Nevermind the condition or age of your sails. As was said previously, if you have a masthead rig, and you're sailing on main only, the "center of effort" (where the wind is pushing against) is aft. CoE aft, creates bad weather helm, and reduces your ability to point. If you only want to use one sail, use the jib alone.
But really, a reefed main and a small jib in stronger breezes will give you the best helm balance and control. Then comes all of that fine-tuning stuff like tugging on the corners of the sails to flatten them or change their shape.
Hey, for what it's worth, I didn't know this a year ago. I went out in a stiff breeze, with main only any my weather helm was so bad that the boat just kept auto-tacking on me until I was nearly blown ashore.
|07-11-2011 05:55 AM|
Not a racing sailor myself but agree with the general consensus that the Jib is best for upwind sailing.
My Centaur has a furling jib so not great reefed beyond a few turns. I pull it as tight as it will go and she tacks through 110 or there abouts, generally need to be running above 3 kns or she stalls.
The main is roller boom reefing so not great when reefed either. Upwind its just to keep lee helm at bay. Still I,m happy to get out there and keep her moving in the right direction.
Its reported that the Centaur designer Laurent Giles recommends the Iron Main for progress to windward, and, unless I,m just messing around, I tend to press the start button.
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