I would suspect that an 18teen pole is actually closer to the water than a cat pole when sailing in "flat" mode.. Since the poles on the standard skiff classes are parallel to the waterline..

Then the assy on a skiff seems to lift the bows far greater than the cat... Not sure if this is just the cut?

John a quick query here as I have also the same spinnaker and will have the same problems when I get around to fitting mine, have you maxxed out the length of the pole as the early Stealths had a shorter pole than later models ? Also the later models tangs maybe lower but also angle foward more than our tip wires which go through the bow ? putting them at a worse angle than ours.

Sorry guys I hate seeing people getting kicked in the goolies for simply stating engineering fact, I reckon Wouter is right and in theory the tip should not move a mm up down sideways whatever if all dimensions remain constant, it will only change if one of the 3 dimensions of the triangle change. <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />

It appears the Spi made as an evolution from my last Spi has been polular!


Hopefully the same will be true from the Mainsail Grant and I are working on. I'll hopefully have evolution 1 at Rutland and be in a position to take orders.

Simon: How does that process work? (developing/improving a mainsail).

Hi Wayne,
Pole is not quite max (measures at 3.47m). Also all of the pole lines and bridle come off the same tang on the top of each hull. IIRC later versions of the same hull had the forward pole wires separate to the bridle.

I'd prefer not to separate the wires and have to create an additional mounting point on the bow for the tip wires.

Tony,

I've known Grant for ages (we’ve grown up sailing against each other for the last 30 years or so) and I trust his skill in making sails totally. He's made my last 3 kites for my Inter 17, and my last kite is the one Grant is now selling as his "F16 Kite". He's also made other sails for boats I've used and they have all been good.

I've always just given Grant what I am trying to get from a sail and he has delivered. So the kite spec was basically:

1, bit flatter overall
2, similar luff length to my previous one
3, Ability to carry high, yet still power for low


Now having sailed with it a couple of times, both in about 12kts of wind, I can say that it feels faster and has improved in the consistancy of my speed. Initially I thought while out sailing it was crap as I did not get "kicks in the back" I was getting from the Landy as the boat accelerated, but when I looked at the GPS, I noticed that the speeds were more constant around 17kts and I reaslised that the boat was just not slowing down as much.

I also feel that the kite needs more trimming to get the best out of it. Its more effort, but the GPS is (I think) showing that it's faster as boat speed is more consistant.



Now the mainsail development is more complex. Again Grant and I have discussed what I want from the sail, we’ve made some decisions on Luff length and curve, foot length, head length and profile of the leach. For the record, luff will be longer but the overall luff curve will be very similar to my current Landy. The head will also be longer. Foot will be shorter as we plan to add area to the top of the sail, draft will be a bot further forward and the sail will be very slightly flatter.
we are yet to be 100% certain about the leach profile, and we’ll be looking at some different battens.

I have to say that most of this, again, has been me explaining what I want for the sail to be able to do and Grant giving me options.

I do not expect we’ll get it 100% right first time, so we’ll evaluate it and then (maybe) make a few changes if needed. Should be right well before the GC.

If people are interested in sails from Grant, either drop me a PM and I'll get in touch and can keep you up to date as to how developments are going or contact Grant directly at his website, Google "GP Sails" and mention my name when you do.

A really simple test to prove whether or not the pelican striker as shown in the photo will reduce tip movement is to remove the bow to pole tip lines, while keeping the pelican striker setup normally, and then try to move the tip up and down.

Looking at the original photo, it appears as though the whole pole with pelican striker will pivot about the main beam connection, just like a normal pole without pelican striker would do.

If the pelican striker wire went through another "spreader" under the dolphin striker and continued to somewhere like the rear beam, then it would influence the tip movement because the pivot point of the pole is separated from the wire. This is how skiff poles are setup.

What the pelican striker does at mid pole is another matter and probably more to do with the jib than the spinnaker.

Gero,
You may not have noticed it but the Pelican striker is beneath a compression strut going to the bridle apex. This will stop the pole in its upward movement.

Don't all tornadoes already have that though? Wouldn't it negate the need for the pelican striker?

Wouter,

Given that there are physical constraints such as keeping the mast in one piece (therefore limiting the height of the halyard hoist) you will still see a gain in performance by lengthening the luff length, even if it means dropping pole tip height.

Been tested and proven.

Actually the strut is a standard item on F16's ever since the beginning of the class.

And Phill is right Ncik, your test won't work well because of this strut. You reasoning with regard to the difference between the pelican striker on cat pole and skiff poles is correct again. On skiffs the pelican striker setup is fixed to another point then the beginning of the pole itself and thus secures the pole in the vertical plane. On the cat pole this is not the case and all is dependent on the importance or not-importance of the strut under the bridles relative to the influence of the tip support wires.

Additionally the strut does indeed negate the need for a pelican striker in the way of shoring up the spi pole in the buckling failure mode. In fact, the strut and bridle support wires to the pole are even more effective in this way then just the pelican striker on its own.

The only way out of this situation is to just rig up the boat on land and actually measure the spi pole tip displacement of both setups when sheeting in the sails relative to the top of the decks. The difference in flexing (if large enough to be measureable) can be scientifically attributed to the pelican striker setup. When devided by the total amount of flexing one can surmise the relative contribution of the pelican striker setup.

Wouter

How about some examples

Ok, if the pole tip lines AND the strut is removed, but the pelican striker is left in place, the whole pole will still move. Therefore the pelican striker is not designed to reduce pole tip movement.

So there's either some other reason or it is useless/over complicates the pole...

I believe the pelican striker assits with the pole tip flex. If you remove the pole tip lines, the peican striker will offer more resistance in the vertical movement of the pole tip, then if it was not fitted at all.

Steve, think through it again. If the problem is hull flex, it will not matter how stiff the pole is as the geometry will change anyway. If the problem is pole flex, then it is different.

Ok I must be missing something.. If the hulls toe then the prod lines must slacken and allow movement of the tip.. The pelican would stop vertical movement at least.. Lateral movement isn't such an issue..
Guess I'm missing something..

If the hulls toe in, they do it not only at the tip but also at the bridle wires. Hence the bridle wires slacken as well and the pole is turning around the beam and not the jib tack.
However they are slacken not as much as the foremost pole shrouds, hence there will be a bit, but not much, bending in the pole and the pelican striker may help a bit, but not much, depending on the pre-tensioning and wire diameters.

The point I am missing is, if you dont want -let say- 50mm of displacement, why not just rig the pole 50mm lower as already suggested? Or retension the spi halyard? And actually doesnot the halyard stretche as much as pole tip, or even more?
Anyway, better spend the time on the water than discussing on the internet. Tomorrow will be a great sailing day in northern Germany, 4 to 5 Bft, sunshine and 20 to 25°C., Sunday as well...

Cheers,

Klaus

Hey Rolf,

Remove both the bow lines and lower bridal wires, leave the pole supported at the front beam and at the bridal strut. With the pelican stricker, you will still have prebend and will still have resistance in the vertical.

Without the pelican striker the pole tip will flex greatly in the vertical..... Therefore the pelican striker must offer some additional resistance in the vertical to the bow lines.

Steve,
I do not disagree with your statements but just for fun lets complicate the issue by also considering the movement
of the hull bridle fittings.

Lets assume the hulls are flexing around the main beam when they tow in.
This will mean the bridle fittings on the hulls come closer together.
So the apex of the Bridle wires between bridle fittings on the hull and forestay will move up.
This in turn will allow the compression strut above the pole move up which will allow the pelican strut to move up.
Which in turn will allow the pole tip to move up.

I asked myself how does this influence the situation?

Intuitively, I don't think very much.

But I don't know so I dug up the Tornado rules to get some dimensions to do some rough calcs.

Supposing the Tornado bows towed in 30mm under load.

The movement of the apex of the bridle wires will allow the pole tip to move vertically by approx 22mm with the pelican strut.

However without the pelican strut the pole tip lines would allow the pole tip to move approx 60mm.

As I said the calcs are rough because I don't have the exact height of the pole above the bow attachment point but this would be close.

So just for fun they maybe minimising the pole tip movement to 1/3 of what they would get without the pelican strut.


Regards,
Phill

Phill,

From memory our marstrom T flexed around 12mm toe in from unloaded to fully loaded - measured at the bow tips.

Whatever the end result on the pole tip, the reduction will equal stable luff length which = performance.

Marcus