Most Footy masts are crude tree trunks. Sorry, folks, but that’s the honest truth of the matter.
If you can push your Footy down to having its masthead in he water in the bath, the mast is too strong: the boat cannot develop that force in real life. Something like 60 degrees of heel is probably going to give you a big safety margin. For most boats a thin-walled carbon tube of around 4mm diameter at the deck should be plenty.
I’ve got more thoughts, butl let’s get some feedback on that one.
Agreed…Even a 4mm tube can be pretty stiff. I’ve been thinking of experimenting with the tip end of a couple of fishing rod blanks that I never got around to building. The progressive taper would seem to me to be an advantage in gusty conditions, but I haven’t yet tried it. I’m also intrigued with the idea of a “modern gaff” rig that was in Wooden Boat magazine a while ago. It seemed to allow more flexibility than a marconi rig.
Bill H
i have a super secret mast lined up for my next footy… but i’ll suffice to say that it isn’t fancy, in fact, it wasn’t even designed to be near the water… should be sweet!
Angus,
For the uninitiated amoungst us, could you elaborate a bit on your mast bend criteria ?
Do you mean that an acceptable mast stiffness would give a hull rotation of 60 degrees with the mast head just touching the water ? This would presumably be with deflecting the mast at its tip and not at the height of the sail centre of effort.
Cheers,
Trevor T
No, sorry. Not very clear. Sufficient bend to flatten the sail and/or free off the leech as much as you want with with enough foce on it to heel the boat to 60 degree. Masthead should be well clear of the water. Jusy how much bend you have depends mainly on how full you want the sails (mast straight) and how flat you want them when the wind blows. Try having a look at a full size Laser, Finn or OK dinghy.
Hope this helps.
So, would you advocate the use of shrouds in Footys if you are using a much thinner mast? The tapered end of a fishing rod can be rather flexible
Bob
Sorry people. Had a long weekend in Belgium, came back to my own thread, forgot what it was about and started spouting total B…S… !
What I should have meant to say in the last post was that you should be able to heel the boat to about 60 degrees in water by applying force to the mast alone. The weakest point unless the taper is very extreme will usually be where it comes through the deck.
No bod - no need for sgrouds - and no need to force it down by the masthead either - apply the force say half way up and you should be well OK unless you are doing something very exotic.
Sorry about that, folks!
don’t use shrouds! it is pretty silly on a boat this size, since you will never load the mast to a point where it needs that much extra support. also, since you are not able to adjust them while on the water, your maast’s bend characteristics will suffer.
Thinking laterally as I often do…
Rather than concern about a fully tapered mast and getting that ‘just right’ why not us a 4mm OD carbon tube (4x3 is common in pultruded) and top that with a small socket into which 1mm, 1.2mm, 1.5mm etc carbon rods can be slipped. Then use a head boom (whatever it is called) in the manner of a modern gaff. The bend of the tip and hence the easing of the head of the main will then be isolated from the mast itself and easily tuneable to boot!
Unless this is laughed out of court I may well experiment in the near future.
Graham
I think that if you did use a mast that was sufficiently bendy, shrouds attached at about half-way will be enough to support it. Having the top part bend a little in a gust will be benificial, but can you actually design & make Footy sails that can make use of that much pressure? Like it’s been said- a Footy doesn’t have that much pressure on it to need a stronger mast. And probably the same goes for most of the Footy keels I’ve seen.
I’m using carbon arrow shaft because they’re convenient to buy; I’ll pick up a couple on the way home from Saturday morning bagels.
Angus-
In addition to the strengthg issue, are you also interested in scale appearance to dictate the mast diameter?
my Tuppence
Graham, join the queue. If you make both the length and angle of the snotter that holds to gaff up adjustable, you have almost infinite control of twist and leech tension. However, you still need mast bend to actually flatten the sail as the wind speed increases.
Tomohawk: I can’t see much point in making the mast anything but a cantilver - particularly if you use some sort of pocket luff, which has considerable aerodynamic advantages.
A.
I suspect that after various times you have raised this Angus I still do not understand what you are aiming at.
So, visualising a boat on a reach for instance, if a sudden gust hits it what do you intend to have happen?
As a very practical modeller I am finding I do not see what part of a typical triangular mainsail is going to impart a bending force on the mast. I imagine that the loads on the mast decrease from mast base to tip, based on the local area of the sail. Taking my pocket luff main as an example, as the wind increases (holding the boat in my hand) the pocket luff pulls tighter against the mast but clearly imparts an even pressure… so no apparent possibility to induce bend.
I must be missing something so can you explain it in actual effects and how they will come about?
Graham
In princiiple, you have two different mast bend effects.
First (mainly to windward) you can flatten the mainsail. The most of the camber in a sail (all of it in a single panelled one) comes from setting a curved luff sail on a staright spar. If we then bend the mast forward in the middle, we will take the camber out. This requires mechanical application of force - kicker (vang to Americans), mast ram, main sheet tension, swept-back spreaders, backstay - the list of posdiisible mechanisms is long. Probably the only ones of great potential importance to a Footy are mainsheet tension pulling the masthead aft and (possibly) swept-back spreaders pushing the middle of the mast forward. .
Second, we can let the mast bend sideways at the top as the windspeed increases. This will spill wind from the head of the sail. It is much easier to achieve than sail flattening: all we have to do is to make the mast flexible enough at the top. The downside is that the relationship between the rig, the mast and stability is fairly critical and, in a conventional sert up is really only adjustable with sandpaper!. The beneffit of the system you propose is that the extent of lift dumping is much more readily adjustable. The penalty is greater aerodynamic drag and more weight high up.
Hope this helps.
A.
OK so I did understand that… somehow I thought you were expecting more of the wind/sail’s ability to bend the mast.
Hence the ‘twitcher’ idea. Weight should be minimal, the twitcher will most likely be less tham 1.5mm (even that is stiff) more likely 1mm. The same material in a pocket would be enough to give a broad top to the mainsail and attachment to the twitcher. I am imagining the twitcher to be under some constant tension, curved back, held there by the leech tension via the kicking strap. Once a stiffness/length of the twitcher is found for the rig I think it may be able to be fixed?
The carbon rod could be sanded to have opposite flats if you wanted to dump more with sideways bend than for and aft bend… I suspect. Interesting as ever…
Graham
This is great stuff, but I am afraid I can’t visualize what either of you are recommending.
Angus, in your reply to TomoHawk, are you advocating a unarig style mast like Brett’s?
Would you mind making a sketch of what you are proposing?
And further to Graham’s comment in another thread: How does one put a curve in a pocket luff?
–Doug
the quick answer is yes. they are advocating cat rigs. the longer answer is that htey are advocating rigs that bend off when they power up. i don;t have drawing software on this computer yet… so try this.
get a piece of paper, and draw a mast. just a stick will do. you are looking at the back of the mast. [if you want to get draw a sail you will get things more complicated, so wait on that!] now, on the right hand side of the paper, draw an arrow going towards the mast. that is the wind. the mast is straight up and down. now, make the arrow bigger. the wind just got stronger. the mast is going to react accordingly. draw the top of the mast bending away from the wind. the mast has just depowered. the leech of the sail is spilling wind, and becoming less effective. this is one form of mast bend.
now, new piece of paper.
draw a mast. this time, you are looking at the side of the mast. so draw a main sail on the mast. now, point your finger at the sail from straight above the picture. your finger is the wind. now, “pull” in the main sheet. the boom comes down, and the sail tightens. it also applies pressure on the top of the mast. [you might draw an arrow following the leech of the sail down fromthe mast tip to signify this tension.] now, as you tighten the sail, and put force on the mast, you pull it down. redraw the tip of the mast, so that it is bending back towards the stern. you have just depowered the rig again. the leech is spilling wind, and the sail is less effective.
now, last drawing.
draw the sail looking down on it. [this is pretty much a curve that looks sorta like an airplane wing.] now, thinking o the last drawing, bend the mast. when the mast bends aft, and pulls down at the tip, the front pops out forward. this pulls the leading edge of the sail forward, so do this on your drawing. as the leading edge comes forward the middle of the sail flattens out. the edge spills wind, the sail depowers.
there! now you know all there is to know about mast bend. [within reason that is] please don’t find this condisending, i had to put it very simple step by step terms to visualize for myself!
now, as for adding luff curve. that is a much larger topic. i would suggest Tom Whidden’s “the art, and science of sails.” really good book, writen by a nice guy who knows his stuff.
:zbeer:
barrett
Thanks, Barrett. I pretty much understood the theory, though your description clarified a lot.
I was, and am, looking for a better understanding of the mechanics of the implementations. I realize that they are just ideas, and won’t have detailed construction plans.
For example, in Graham’s twitcher idea, how far down does the thinner section reach? 70% up from deck? 50%? Is the masthead crane rigid, or designed to flex as well? Again, ballpark figures will do; I can experiment to fine tune it.
I was also told way back when that the Bermuda rig was the most efficient way to implement a given sail area. Was this obsolete data? Or based on other rule restrictions, such as maximum headboard width?
–Doug
Mate, luff round inside a pocket luff is a prick of a thing to get right.
I eventually gave up and went to 10mm luff attachments.
I had tried a single piece and a two piece pocket…sorry too hard.
Ian , it is. We’re working on it.
Doug. I’m not necessarily advocating a una rig. However, as you’ve obviously sussed the straightness of any forestay must be independent of mast bend. The anseer to this is to have a tubular forestay, if necessary further supported by shrouds and spreaders, that ‘floats’ at the top end (i.e. is allowed to slide freely in a tube attached to the mast). This means that the mast can bend as it will without affercting the shape of the headsail.
Our experiments in Gary’s back yard tend more and more to sails that are completely double al a Stollery. Given this, it looks like a tubular forestay of dia 2mm (thin walled pulltrusion) is man enough for the job without spreaders - and is aerodynamically very clean indeed.
As to dimensions, I’m currently trying to use continually tapered tubes. I’ve got some rod rips waiting to be tried. Troubble is getting anyuthing that bends enough. For a sectionasl mast, I would guess that the fuirst taper step at 1/3 height (i.e. at height of centre of area) would make some senses.