I just started sailing a Nacra I20 and am curious to what extent do bottom and daggerboard imperfections affect speed for the recreational sailor. I have a couple of long indentations on the hull bottom from the previous owner sliding the boat over a rock and recently repainted one of the boards, leaving minor brush marks in the finish. What seems to limit speed the most is the boat becoming overpowered, even when double trapped. I was wondering if a better bottom would translate into more power being converted to speed. I suspect that the answer he is going to be that imperfections slow the boat but only enough to notice over the course of a two hour race. Thanks!
Edited by traphappy on Oct 12, 2016 - 04:34 PM.
Bottom and daggerboard imperfections and speed
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Posted: Oct 12, 2016 - 03:28 PM
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Posted: Oct 12, 2016 - 04:19 PM
Typical imperfections in the bottom - imperceptible. If the indentations are rougly aligned with the fore/aft axis of the hull, you will not even notice them. The only real reasons to do anything about them would be 1) the hull is structurally compromised or 2) they cosmetically bother you.
Defects on dagger boards or rudders are a little different. Since the rudders and boards need to provide lift, surface imperfections can disrupt the flow to the point that the rudders or boards stall prematurely or simply don't point as well upwind. Again, there's not likely to be an perceptible reduction in max speed, but you may notice handling issues at higher speeds or when you're pushing the boat hard. I would use a sanding sponge to knock of any brush marks and then wet sand to 600 grit or higher for best performance.
You are correct that proper tuning and boat handling will have MUCH more effect on performance than minor imperfections in the hulls and boards.
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Posted: Oct 12, 2016 - 04:26 PM
Basically neither matter. Some of the fastest I20's locally, in racing conditions, are really beat up. Don't do this on purpose, i.e take care of your things, but your energy is better focused on replacing worn out line (trapeze hardware especially), building better systems for sail control (copying the F18 style rigging) and learning how to sail properly.
The stock EP N20 sails are cut fairly deep and its a tough boat to de-power in over 15kts. If you already have mast rotation back, downhaul cranked, and are thinking about dropping traveler, raise boards 6". Boards half up reaching and downwind. The other thing to note is diamond wire tension does matter, IIRC ~38 was base and we'd run 42 in big breeze Tybee 500 conditions.
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Posted: Oct 12, 2016 - 04:35 PM
Thanks for the great responses. I went out solo in 8 kts the other day and had the downhaul reasonably cranked, outhaul pulled in all the way, mast rotation limited quite a bit, and boards up halfway all the time. I wonder if I should not sail with the boards halfway up to depower when sailing upwind because I heard popping sounds at times from the rudder area. Should one be concerned about loading up the rudders to much? Everything back there seems to be in really good condition. It was an awesome sail, super fast, two super near flips and one capsize. Saved by the 150 lbs righting bag! Incidentally, how much should one pay for a mid 2000s Nacra 20 (mid pole snuffer and self tacker) in great condition with new trailer, lines, tramp and new EP main and jib?
Edited by traphappy on Oct 12, 2016 - 05:46 PM. -
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Posted: Oct 12, 2016 - 04:45 PM
Traphappy,
No, I can't recommend sailing with the boards up halfway to depower all the time, just a little upwind. "Popping sounds" at times from the rudder area, well I would be fully inspecting that, the gudgeons and lower castings are know to fail from time to time. Make sure you ease traveler when transitioning between upwind and downwind especially in a blow or you can overload the lower castings really easy and that's a $500+ mistake...
Lot of variables in that question, like location of the boat and who the previous owner was. Last year of build in the U.S was basically 2006 for the Alter Cup, though a couple of later models were built. Does it have Gen 1 (narrow, skinny) or Gen3 (Infusion) rudder blades? Trailex or steel trailer? A new trailer is basically $2k+box costs, new main and jib is roughly $3k, tramp is $600+, so I'd say $8k is a great price for the setup, if the hulls are in sold condition and late vintage, and the spinnaker is new, $9-$10k isn't a bad price. $10k is the most I've seen one go for in recent memory and that was one of the fastest I20's in the country, two sets of sails, on a $4k double stack trailex trailer with lots of spare parts and meticulously maintained. -
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Posted: Oct 12, 2016 - 05:08 PM
Thanks samc99us for your reply and great info! I really appreciate it! Not sure about the blades and the trailer is aluminum. You gave me a good sense about the going rate!
Incidentally, I got the boat insured for loss (minus $500 deductible) and liability for $56 a year through All-State. I am about to call them to ask how they insure the mast. I feel like that is what half of the policy is for! -
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Posted: Oct 13, 2016 - 11:06 AM
How much liability? Are you insured while racing? Are your sails insured? What did you insure the boat for? I insure my race boats for basically new replacement cost; if you can source a carbon N20 mast (unlikely), we are talking $8k plus. The aluminum replacement rig is ~$4k BUT requires a new mainsail cut ($2k for the sail plus another $400 for battens). The way to deal with this is to make sure your insured value is double the value of the rig, so they don't total the boat instead of buying a new mast. Incidentally I pay state farm $280/year for $2million in liability and $30k insured value.
Edited by samc99us on Oct 13, 2016 - 11:08 AM. -
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Posted: Oct 13, 2016 - 02:14 PM
I am with Gowrie for insurance... $500 deductible, $12k replacement, includes the mast/trailer/sails for $150/year (or so). -
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Posted: Oct 14, 2016 - 07:11 PM
I've got a different perspective than sam99; hull dents don't bother me as much as board/rudder fairing. Yeah, maybe the current fast guys have beat up boats, but back when I was racing I20's, we took VERY good care of our boards and rudders. The efficiency of a foil decreases dramatically when imperfections are introduced into the shape, not to mention the noise that they start to make when they aren't faired well.
As far as pulling the boards up, I wouldn't worry too much about it so long as you have gen 1 or gen 3 rudders. Back in the Worrell days, we would use extra long forestays and shorter shrouds so that we could rake the $#@$@ out of the boat. If I remember correctly, the "normal" rake measurement (not when it was really blowing) was somewhere around the tip of the rudder blade (when in the up position). Keep an eye on the castings as they have been known to break since they are cheap cast metal. If the rudders don't fit nice and snug, use some shims to tighten them up and make sure that the blade is well supported. Also check your gudgeons and make sure that they are appropriately tight and make sure that the gasket material in the bottom of the dagger board slot is in good shape (reduce drag and protect trailing edges of boards).
Remember, lift (and drag) of a foil vary by the square of the velocity, so you need less board to produce the required lift as you go faster. Running too much board results in excess "tripping" force, so to speak (longer board, greater lever for the sails to push against and fly a hull) and is slow. We'd sort of work in small increments as we pulled the boards up; handle height, 3".... all the way to half way up when conditions got crazy.
As far as the main goes, get some stiffer battens if you feel like you can't flatten it out enough, that can make a huge difference. Also, those Omohundro/Southern Spars masts are like a tree trunk, you've got to get some prebend going in them for the downhaul/Cunningham to have much effect. Remember here though, that pulling the rotation too far aft will increase the tension on the leech b/c you are now pulling against the stiffer axis of the mast and the leech can't open as much. -
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Posted: Oct 15, 2016 - 06:47 PM
I think in simple terms.
If your boards or transoms or rudders are making noise, that is slow.
Boards should always be filling the opening and not allowing noisy cavitation.
Transoms should be out of the water enough to be quiet.
This is controlled by weight distribution.
If you are in heavy air and your heartbeat is louder than your transoms, that is OK too.
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Sheet In!
Bob
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Prindle 18-2 #244 "Wakizashi"
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Arizona, USA
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Posted: Oct 15, 2016 - 09:38 PM
Huge difference for me this year since I fared and refinished the rudders on mine. I don't race, but the boat used to have a lot of harmonics at speed. That is gone since I got rid if obvious and bad imperfections and the boat seems faster...I dunno but it was kinda fun when the boat was howling over the water.
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Posted: Oct 17, 2016 - 09:53 AM
Raw speed matters in distance racing. I take care of my equipment and generally fair my boards and rudders several times a season, but the reality is on a shorter course buoy race, one missed tack, or picking the left side vs. the right side matters far more than how perfect your foils and hulls are. New sails make a much larger difference as well.
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