|Topic Review (Newest First)|
|10-25-2007 09:54 PM|
SEMI...I'll give it one more pass.
Here's a link to a discussion about inboard tracks http://list.sailnet.net/read/messages?id=177663#177663 for the P30 . The thought the guy put into the linked analysis for the P26 , extended to your P30, indicates a pointing gain of 3.2 degrees for a working jib - not as much as I would have expected, but still worth a nice chunk of CG's VMG. I have seen some P30s with a short track inside the chainplates...
I don't understand his measurement for a 150%, it seems to have been affected by the cockpit coaming. You can determine what benefit there may be for a 150% simply by looking at how far your sail is from the spreader when close-hauled. Anything more than 2 inches represents some opportunity for gain.
I raced a C&C 30 for about 6 years against a group of P30s and T30s, and I can tell you that on my C&C the 150 trimmed well inside the lifelines (2 inches off the spreader in fact), and the 110% trimmed inside the upper shroud.
|10-25-2007 06:29 PM|
The "inside tracks" issue came up some time afterward.
|10-25-2007 03:14 PM|
Chris Gee Windex vanes allow for different tab angles to be set....
The tacking tabs should be set depending on your boats pointing capabilities.
It can vary from 65 to 50º.
On my boat they are set at 50º, but I can point pretty high, so its not a good example.
On the average boat these should be set at 60º for cruisers or 55º for race boats.
Rember they point apparent wind.
My boat does'n have inside genoa sheets because the deck is wide, but due to another reason, somehow related to beam....pointing ability.
My boat is very beamy, therfore it suffers in pointing when comparing to a boat with a narrower beam. My boat was designed to be a good downwind sailer.
Therefore, when designing the deck, and the cabin, we needed to improve its pointing ability, so the tracks locations on the deck were decided based on moideling. Once the track locations were established, we built the cabin width around these limitations. But in my case we even played with mast location, and that made us change keel location and CofG and CofE....
Deciding if a boat should have inside or outside genao sheets really depends on pointing abilities, the gap between main and genoa and other factors sich as momentum, bow design, keel location etc.
Technically if the boat was not designed for it, and you narrow the gap between the genoa and main, you will be able to point higher, yes... but you won't go anywhere because you wont move....
This is because the gap decrease will "deform" camber on the main. These things are all related.
Jim, I am also sorry I didn't read the whole thread. So I might be missing your main question here.
|10-25-2007 02:55 PM|
I thought the Windex indicators were fixed. I don't know the angles but they are probably around 30. If as I suspect you are looking up the mast you won't be working to the last degree, but yes 30 seems the figure.
I am not familar with the boat but thought possibly the number 3 might go inside. For any sail that is outside I don't see how an inside track as one picture showed is going to work. Possibly on the number 3 the clew is high enough to clear the rails and be pulled in but that is going to hook the leech in which is not desirable as you want a clean runoff.
When I suggested trying an inhaul as an alternative, this was in the context of saying I suspected you could not sheet inside but if you could then it was a simpler alternative.
Some of the advice you were given was that you should be using an inside track and that the PO was an idiot.
"Inboard tracks are essential for racing - your PO was a dummy. The basic trim guideline for a 150% should be a few inches off the lower spreader - you won't get anywhere near that close with rail sheeting. It's even worse with a small jib that you are trimming to the fattest part of the boat - you'll give away 5-10 degrees of pointing."
The sheeting angle in part depends on the boat. Clearly Giu has much wider decks, and I suspect comparatively smaller genoas which can be sheeted in tighter. Older boats have bigger overlaps and are often narrower and get more power from the genoa, so the scenarios are different.
I am no expert on wind tunnels etc. I imagine like anything else they have constraints but have proved useful. I suspect that people often overtrim, and confuse sideways force with forward drive, ie we are heeled right over so we must be going fast. Forward drive and VMG are what interests me.
Because there are many variables involved in trim for conditions, my feeling is that while knowing what adjustments you can make is part of the deal, often it comes down to listening to the boat and getting it to where it feels sweet, and the sails look right.
When you start adding in windshifts, current and tactics etc you see how fascinating it can become. Nothing like beating your mate by a second after a nail-biting finish when the lead has changed a few times over the race.
This is all part theory, part practical experience. That is why I suggested racing helps you learn even if you are in the tail end in a private battle with one or two others, because it gives you feedback and encourages you to try different things.
|10-25-2007 02:18 PM|
This main sheet system is called the Admiral's main sheet control, beacuse it was first used in the Admiral's Cup boats. Mainly it consists of a looped main sheet. as I drew bellow. If you need more help, let me know.
A good thing about this system is that I can swap the main sheets with the genoa winches and use the main in the forward winches and the genoa in the rear winches so I can tack alone.
Bellow I swap the main sheets with the genao sheets to sail alone
You will need 2 blocks in the front of the boom...
One on the deck to bring the sheet from the boom aft....
and one to direct the sheet to the winch....
Tom, if you need I will gladly calculate the bill of materials and the block sizes for you.
|10-25-2007 01:33 PM|
And to think: The Admiral wants to repaint the decks, destroying her patina.
|10-25-2007 01:24 PM|
|10-25-2007 01:20 PM|
You gave me a lot to think about (and figure out!) and digest with this one, Chris. Obviously you've devoted quite a bit of study to sail trim. Have you generally found that computer modeling and wind tunnel experiments produce results that are reflective of real world behaviour? (Within limits, of course.)
|10-25-2007 12:57 AM|
WOW, verrry clever, how's it work out Alex? Is this a fifth, dedicated sheet winch? Should it work with a mid-boom sheet?
|10-25-2007 12:19 AM|
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