Originally Posted by hoppy
Prior to getting one of those bowsprits I had the Selden and either way I could not have a roll bar anchor.
To accomodate this (big, & or, roll bar anchors), there are several options. The most common ones being; retractable sprits, like on J-boats. And detachable deck mounted sprits. Such as on Eric Goetz's (former I believe) boat, "Katie G". And there's a link to images of her, & also her sail & hull plan, in one of the above posts.
Plus, there's the option of sprits with more offset, them being set at more of an angle, or A-frame sprits. Some of which hinge up vertically, when not in use. As seen on some of the boats made by www.rm-yachts.com
on the SWL, I noticed that the SWL of most units is 2500kg covering different boat sizes. Perhaps an issue for Dockhead's size of boat?
How do you know the SWL required for a C0?
Last year I watched the VOR inshore race in Auckland
in light winds and most of the yachts used their C0 for most of the race, beating into the wind and tacking and then on a deep reach.
Regarding sprits. No they're not mandatory. But the longer the sprit is, the bigger the sail which you can fly, as it increases you J dimension. Plus, it puts the leading edge of the sail out away from the turbulent backwash of the furled jib. By a few feet at least, which is where the worst of it is.
And as stated before, the further forward your sailplan's center of effort when you're not beating, the less load there will be on the rudder
, & less tendency to want to round up, or get pulled into the right harmonic to start a boat rolling. Especially downwind.
This is also true when on the wind, to a fair degree. At least up until the boat's righting moment becomes the limiting factor. And then the boat heels over enough so that again, the rudder
loses it's grip, & the boat's nose (typically) spins up to weather
Though, even without a sprit, you need to get everything for the Code 0, out in front of your headstay, & everything else. Just like with a normal kite. And you also need to ensure that whatever you attach the tack/furler to, is strong enough to handle the load.
As, from time to time, bow rollers have been ripped out... along with some pieces of fiberglass
But usually cruisers fly these sails in lighter winds than racers do, & also tend to put less load on their hardware
& sails. Unless caught by a squall, or front. Which can be pretty common in some locales.
To figure the load more precisely, you'll want to work with your sailmaker (& possibly your rigger too). Not that the math is necessarily complex. But you have to think it through, & run the numbers. Followed by adding in a safety/fudge factor.
Particularly if you'll be carrying the sail in any real breeze, & or waves. Where shock loads really start to become a real factor, too.
Though by my reckoning, the load calc's are something like this. Let's take a hypothetical 40' boat as an example:
Say you have 50:1 halyard winches, & you're running the sail on a 2:1 purchase
. Then, with a big double handed winch
handle, you can input 50lbs of force. And with a decent sized rig, your Code 0 is 1,200sqft +/-
With frictional losses, you're inputting about a 4,000lb load onto the anti-torsion cables
. 40x for the winch x2 with the block on the halyard, & 50lbs input by you.
And in addition to that, there will be some load from the sail too. But to be safe, I'd figure on adding the full wind loading in addition to that of the winch, & 2:1 purchase
. With the thought that I'd be shifting down to a different sail when the breeze picks up.
Thus, I'll use 15kts for wind. Which equates to 1lb/sqft. Or, 1,200lbs in this case. Thus, by combining the two, you get 5,200lbs.
In the real world, even with 15kts of breeze, I doubt that the system would see 1,200lbs of additional vertical load from the sail. Or not consistently anyway.
But when you figure in what happens as you sail though waves. Or anything else happens which causes the AWS or TWS seen by the sail, & thus everything attached to it, to go up abruptly. Then so do the loads on everything which is connected to the anti-torsion cables
, furler, sprit, tack fitting, halyard, etc..
And all it would take for the load on the sail to double, would be for the breeze it's seeing, to go from 15kts, up to 22kts.
Plus, if the breeze is building, & you want to depower the main via the backstay...
And on a racing
boat, or a cruiser which has a tunable mast
, the above is entirely reasonable. As, when trimming the main, I spend FAR more time using All of the controls when the wind is in the low to mid ranges, & variable. Than I do once it's consistently well into the double digits.
And a key shaping control for the main is the backstay. Which, on a boat with a tunable rig, it's easy to move the masthead on a 40'er 18" (1/2m) or more. Albeit, that's the range of the spar's movement, from say 3kts to 30kts.
If you then scale up those kinds of loads to something like a VOR boat, where the loads on the "small things" are measured in tons. And the backstay loads are well into the double digits tonnage wise. Then the loads generated by Code 0's get Big.
As the anti-torsion cables are taking the same loads as headstay would see, if not more. And on a 40'er going upwind, sometimes thats 3-4 tons. So, yeah, Big on even mid-sized boats.