I’ve made myself a swept back rig without a backstay and have had it out a couple of times in different ranges and am absolutely wrapped with it.
i thaught i was going out on a bit of a limb because all photo’s and rc’s i’ve seen are’nt swept back and being used to building full scale thaught i’d give it a go.
it’s marblehead size 3/4 rig one set of caps (with spreaders 10mm wider than b-max)and one set of D1’s (lowers) no backstay but about 18mm of pre-bend. Admitadly my section (alum)might be a bit heavier than the top boats but i have little if any mast falling away. And no problems down wind.
“question” is this -
Why do all the boats i see not use swept back with prebend to induce headstay tension? I
n full scale everyone was in love with inline/runner rigged boats years ago but now have come to the obvious conclusion of “keep it simple stipid” lets go swept back!
Is it that most people make their own sails therefore it is easier to cut a straight luff so they make their masts to suit? From what i know (which is probably not alot) a curved leading edge for an aerofoil like what you produce with prebend is more efficient. take a look at a windsurfer!? Or is it different with theese high aspect rigs?
Have’nt been out to play with the “big” boys yet but it’s working fine for me and i’m carring .98m2 off it and it has’nt budged.
surely i’m doing something wrong or everyone’d be doing it! so straighten me out! (or you could give me a bit of prebend???)
sodium,
I looked into this as well on a boat I was working on for a while, but I came to the following point and stopped.
In big boats, even when sailing downwind, you hardly ever sail DEAD down wind. However, in most model boats, the fastest way to get these boats down hill is by heading straight down wind with the sails perpendicular to the centerline of the boat. By going with a swept rig and even a set of D1’s, depending on how far bac you have your spreaders and shrouds, you can only sheet the boom out to say 75 degrees. This will lead to a boat that is fast on all points of sail EXCEPT dead down wind. It is my belief based on several years of racing RC that the competative line down wind is straight down wind.
Whats the benefit in the class you are sailing? You can carry a “traditional” rig with more induced bend, and or prebend just as easily.
Yeah i did think of the sailing 180 to the breeze thing but as the hull speed increases the aparent wind angle starts to creep aft so you do need to sheet on a bit(though i suppose not as much when 180), my boom angle is more like 80 degrees and it is also possible to put a “hinge” in the boom at the shroud point in order to moove the clew further forward although the shrouds and spreaders does disturb the optimum shape of a sail going 180… another thaught by hinging the boom at that point it would also “automaticly” ease the outhaul therefore bellying up the main at the points outboard of those annoying shroud lines and still getting use of 90 odd percent of your sail area. Hmmm… think i’ve been thinking about this too long.
The “class” I’m sailing is - design a boat, put a mast in it, whack some sails on it and sail it! … though i have tried my best to adhere to the marble rule. my keel is only about 50mm too deep and my sail area is WAY too big (.98m2) but apart from those main points i’m at marble length,rig height,etc. I will get around to cutting the fin down and making a set of sails that measure so i can race with my local group. By the way I weigh in about 3.2kg fully rigged ready to sail am i under weight??
My MultiONE design I am working on has a designed mast rake of 13 degrees, instead of the “normal” 3 degrees or less. Since I plan (hope?) to be creating my own apparent wind, I have no intention of barn-dooring it downwind.
With the exception of “floaters”, the slightly longer DMG by very deep broad reaching is usually offset by a much higher VMG. Balancing the two and rounding the leeward pin first is the experience factor.
For monohulls - generally limited by lead weight/hull speed, unless you carry an asy chute and are able to “heat up” on the off wind legs, dead down wind may be the fastest point of sail and hopefully at least equal to the actual wind speed. Coupled with classes that aren’t allowing spinnakers, (which could encourage off-wind speed and deep reaching) there is little reason to develop off-wind mast/rig research if you spend most of your downwind time running wing and wing.
Consider that downwind the most (usually only) 3rd. r/c channel is being used for backstay tension. Nothing is controlling vangs, downhaul or outhaul, all of which would also be “tweaked” if one were aboard a real boat.
At that sail area and weight on a 50" boat if you don’t have a canting keel than you’re light for sure. Weren’t you building a canting keel boat?
I like the hinge idea; how would you make it work?
A number of boats (particularly IOM’s with aluminum masts and swing rig Marbleheads) without an adjustable backstay use pre-bend in the rigs. In the Marblehead class, though, one of the principal reasons for having a backstay is the ability to adjust headstay tension underway via servo control. Upwind and in heavy air you crank on the backstay, downwind or if the wind lightens you let it off. Proably the most useful and important third channel that can be added to a boat. The benefit is awesome.
What about the old dinghy rig? - no backstay! some without kites at all. all tryied and tested and all out there still having a blast! without too many headstay tension problems. BTW you can cut a headsail to allow for a bit of headstay sag if your happy to live with it not sure of performance loss though.
I’m sure when i do go and race with the local group they’ll chew me up and spit me out because of the fine adjustments in every control they can possibly play with. but i keep wondering “by how much will they beat me?” my idea was simple enough i wanted to build a marble size rc and not spend the earth. wanted it easy to rig and easy to sail but most of all eveything had to built by me right down to the turnbuckles.(xcept the radio gear) at the end of the day i’ve not done too bad it cost me about AUS$250 including radio gear and it weighs only 3.2kg can have it from the back of the ute in bits to fully rigged keel and rudder on ready to sail in about 3 mins. And it is very easy to sail, two channels “steer with this and sheet with that” i can hand the control to anyone in the club and they can sail it well straight off the bat (even the missus picked it up in about 1 minute! i don’t let her drive anymore in case she shows me up which is likely).
It’s just my nature to look at a boat and think “that could be easier” I’m a firm believer in the theory that the less you have to play with the more windshifts and tactical advantages you’ll notice and make use of. “keep it simple stupid” and i prefer to sail my boat than spend half an hour on the dock setting it up. Though it’ll all change with my next hull which i plan to make a bit more “compettitive” with all the trimmings so let’s call this hull a trainer where i try out systems like the swept back.
So no-one else uses swept back without backstay??? OK must be doing something wrong. (doh!) Might follow the flock with my next hull if this turns out to be a dog.
Doug: I was going to go canting but decided against it because of cost and this is the second hull design of this length i’ve built because the first was a dog and would’nt tack nicely and etc etc… so i didn’t want to outlay all that time to find this hull was no better! as it turns out i’m extremely impressed with this hull and will probably have a canting system on the next one. MichaelB on this forum is the apprentice at work and he’s taken a hull from the same mould and has installed a canting system on his and should be in the water soon. Will be a great test for the canting system versus the standard. two (close to) identical hulls one with one without racing one on one. will keep you posted on results.
The hinge is something you’ve prob already thaught of - at shroud line a hinge without vertical movement boom vang attached at same point. sheeting angle led for’ad to maintain outhaul tension when close-hauled. LOTS of problems with it though if you just want to reach. maybie a spring external to the section to add resistance untill boom reaches 90deg?? dunno doubt i could get it to work probably just a pipe dream.
I have done about 3 seasons on a naval architect’s boat, & he said that “Backstay’s actually loosen the forestay, cause when you pull it on the mast bends, which means that the point at where the forestay is attached to the mast is actually bent forwards, thus loosening the forestay.”
I don’t know if this is correct on model boats, but it might be, I suppose what the backstay really does is let the top of the main twist, depowering the rig.
Regards
Rob
no backstays tighten forstays. when you pull on backstays it bends the mast yes but where is the bent and how is it created? by pulling on backstay you bend the mast below the forsatay point thus creating forstay tension by pulling the forstay back
When the Apprentice knows more than the Mentor its time to quit!
Unless you have a leech line on the jib the jib leach will also become tighter and shift the balance of the rig slightly ahead so when a puff hits you the leach of the main is spilled a little but the leach of the jib is tightend thereby shifting the center of effort forward which is exactly what you want when a gust hits you. Better control, less rounding up etc. If you have a leach line on the jib there is no effect on the leach of the jib but the principle of shifting the effort forward is the same - I think