These guys have pretty "bendy" masts and spins up - besides all the capsizes, collisions, and running into tankers, they do pretty well
https://www.youtube.com/watch?v=fFYGJ6ox6DI
MN3
MN3, totally different load cases and rigs. Those 18' skiffs mostly have carbon rigs in the air which can take enormous deflections before failure. In either case, keep the mainsheet on and you should be OKAY, the stiffer rigs I mentioned would probably work fine with 100% masthead spinnakers and enough mainsheet.
totally different load cases and rigs
Oh i know - i was just being cheeky.
i actually have RonStan Skiff race VHF (where i think this video is from)
pretty wild watching those masts curl and flex
MN3
Yes, there are differences. It comes down to different ways of depowering the rig.
If you have a 'bendy' mast, you over rotate the mast in order to induce camber on the minor axis, and also creates drag/turbulence in the forward part of the sail.
Stiffer masts use prebend tuning, which combines with extra downhaul purchase and bends the mast on the major axis, with less drag.
The sails are cut different for each approach
IIRC, wither White or Fragale discuss the different modes in their books.
I can state from personal experience that older NACRA Squares had bendy masts with little, perpendicular spreaders and the upgrade was to either install swept spreaders or get the stiffer mast which usually had swept spreaders installed.
Jay
Ex-1981, -82 and custom Squares
Now cruising in my old Catana
Yea so the previous owner who got second at nationals in 87 with the boat says he always ran the stock perpendicular spreaders and pretty loose diamonds. Can touch them to the mast about 18" up.
Then I talk to the guy who won nationals most of the time in the late 80s and he says to go prebend for sure on the bendy mast. I'm gonna try it both ways and check the sail shape. The diamonds attach to the front of the mast up top so there is essentially some spreader rake built in to the setup already and since the previous owner has a 12:1 downhaul on the thing he's already depowering the rig just like a prebend setup anyway. I think with the downhaul I should easily get the mast to bend on the primary axis enough to work given the flexibility of it.
Question is which spreaders should I use. I could use a H18 set and just buy some longer aluminum round bar. Just from looking I think the square has slightly wider arms. Some other boats have a turnbuckle adjustable type which I like. I could probably weld a setup that would use that but not sure if I need that fine of adjustment really.
Edited by tamumpower1 on May 17, 2017 - 12:57 PM.
Tip:
Pay attention to anything Jay says about 18 Squares.
____________
Damon Linkous
Thank you, Damon. Hope you're doing well!
FYI
"TUNING THE NACRA EIGHTEEN SQUARE METER
John Brink - 1980 Class Secretary
The NACRA 18 Square Meter is one of the fastest sailboats in the world. However, it is very sensitive to sail and rig adjustments. While there is no guarantee that you will have the fastest NACRA 18 Square Meter on the water, if you set your boat up as follows, you will have a good starting point for further adjustments and your boat will be very pleasant to race.
Believe it or not, the best starting place is at the top of the mast. The NACRA 18 Square Meter is set up so that, if you wish, you may convert to an internal halyard by adding a sheave in the after side of the section near the top. Consequently, the geometry of the rig is based on the premise that the sail doesn’t go all the way to the top of the mast section. Make sure that when your halyard lock is engaged, the sail is a few inches shy of being fully hoisted. If the sail goes up all the way, the boom will be too short.
Now, to adjust the rest of the battens. The theory behind modern (1980) sail batten combination is to use relatively flexible battens and tie them in without much tension. Because the battens are flexible, the sail will take a nice shape in light air without much tension, and when the breeze comes up the sail will flatten itself as you sheet harder and as the wind blows the leech open. If you tie the NACRA 18 Square Meter battens too tight, the sail will be hopelessly full.
Let’s go back up to the top again. The three upper battens should be very loosely tied, perhaps not even quite taking the slack out of the line. The fourth batten down should be slightly tighter, perhaps just barely taking the slack out of the line but no tighter than that. With the fifth batten and on down, tighten the lines just enough to take out most of the vertical wrinkles along the batten pockets. However, sometimes even this may be too tight. Loose is better than tight!
Next, adjust the diamond wires until you can touch them both against the mast about three feet up from the lower diamond tangs. This is a good starting point. There is some give and take between the tension on the lower battens and on the diamond wires. The diamonds can be looser with tighter lower battens. Finding just the right combination is a matter of trial and error.
Now let’s rake the mast back to where the sail is sheeted as hard as you ever want it and with the sheet blocks almost together. Set the shrouds up with plenty of tension so that the mast won’t jump around when going through the waves. The shrouds will stretch some when new, so you might as well sail the boat hard a few times before you get too concerned with rake adjustments.
Another adjustment that is critical to both good handling and speed is rudder alignment. It helps to bend each tiller arm inboard about six inches. Whether you do this or not, you should check to make sure you have the rudders set with a slight amount of toe-in. That is, the leading edge of the rudders should be slightly closer together than the trailing edges. If the reverse is the case, besides slowing the boat, they will make the boat difficult to steer.
Now, to steer it fast. When sailing a sloop, most good sailors will pay very little attention to the main. They sail by the seat of their pants and keep an eye on the jib. With a uni-rig, there is no jib to keep an eye on and many sailors may make the mistake of transferring their attention to the main. If you look at the main, you will inevitably end up sailing too high and going slow. Sail the boat by the seat of your pants and direct your gaze ahead. You don’t have too pinch the boat (sail too high) as the extra width that comes with a NACRA 18 Square Meter allows you to drive off and build speed – perhaps covering more "ground" but at a much faster rate of speed. But, on the same hand – don’t be afraid to sail high to cover an opponent or force them over the line early. The uni-rig NACRA 18 Square Meter will out-point and sail higher and faster than most boats, especially those that are sloop rigged. You can pinch, you can foot, but either way you will be the fastest one out there after some practice and experimenting with different setups."
Did you personally play with mast rake very much for different conditions. I'm assuming the reason the little guide is calling for rake is to help out with the bows givin how hard you can drive the boat. I got the rake position the previous owner used and he said he more or less always ran it in that position but I haven't stepped the mast to see what rake that is.
Edited by tamumpower1 on May 17, 2017 - 08:51 PM.
Be conscious of one thing on spreaders for that mast. The old style round ones from before pre-bend do look crude now BUT since the shroud is not fixed to the spreader tip (seizing wire and tape do not count) it is essential that the spreader tip does not move up and down because if it gets started doing that it will collapse rather than spread. One of the original engineers and Roland had a big fight about that. You do not want to lose that mast. If I were you I would stay with the original spreaders (which were round for a reason) but if you choose not to be careful.
I don't understand what you are saying to do. My current spreaders are indeed one solid piece inserted through the mast with wire holding the diamond to the tip. I guess I can wire the crap out of them?
I'm a bit confused as well. Even the modern spreader arrangements are free to move, and you are correct that seizing wire and tape don't prevent the tip from sliding on the diamond wires. One solution is to put epoxy hardpoints on the diamond wires to stop them from sliding.
What i meant was that the circular cross-section spreaders that go through the mast will not move up and down at the tips. the cross-section makes it hard for them to flex that way so the setup with the shrouds sliding up and down as needed, seized and taped to the tips, is safe. the problem could arise id your get modern spreaders which are 1) not thick walled tubes going through the mast and 2) lacking in vertical cross-section and strength at its base to prevent it for sliding upwards or downwards and collapsing against the mast. I have never seen, only heard. But what I heard was that the first time a mast buckled the guy who raised the issue with Roland said "I told you so." With the set-up you have just keeps the shrouds seized to the end (I always used copper Easter egg dippers for this purpose when i fitted out every year in the spring). Remember you have a bendy mast that has successfully lasted with those spreaders for 40 years. And BTW, no spinnaker, that is another bad move.