So, what have John and Charlie done with their spi pole here?

Picture is from the "Delta Loyd" regatta, formerly known as SPA regatta

Have a look at some photos of 12' skiff prods, they all have a dolphin striker. It allows for a reduction in tube size, and probably takes some load off the bows.

When I rigged up a spin to my 6.0 I did something similar to the 14 foot windsurfer mast I used as a spin pole. I think it would have assumed an s shape if I hadn't rigged up a pole dolphin striker.

On a skiff I understand the usage of a dolphin striker: the pole is not end supported as on a cat, hence it will see high bending moments and hence it needs a structure, which transfers the bending moment in compression loads on the tube and tension on the wire. If not, the bending moment would destroy the pole.
On a cat however, the pole is supporte at the end (where the spi is attached and at the jib. The pole will not see bending moments, but only compression: The spi up and side forces are taken by pole shrouds. Since they are in a forward direction, they produce a compression load in the tube. The efficient buckling length of the pole is reduced by the bridle wires at the jib.
So I do not understand why they are using a dolphin striker.

Cheers,

Klaus

I noticed this on Mitch's T also.
I will be in town later this afternon, if the guys are still there I will go and ask.

Spot on Smithscat !

Wouter

If I see correct, the tack halyard of the spin also runs differently, or is this common to run it via the bridle?

I can imagine the forces on the hull are quite high when you run the halyard in that way.

Gill

The way I see it, they are trying to improve strength and stability at the pole end. The luff loads on the kites is quite high and there can be a quite a bit of movement up and down at the end of pole. Easily demonstrated by lifting a boat on the beach by its spinnaker pole. A F16/F18 would have 5 to 10cms of movement quite easily. So by minimising this movement then it could give them that extra x% needed. It is an Olympic year and Booth/Lovell both tried exotic sail material in the lead up to Athens. And with it potentially being the last time for a multihull gold to be offer, trying these kind of things could be difference.

Have you tried lifting a Marstrøm Tornado by the tip of the spi pole?

Taipanfc,

I'm sorry to say that your comments are utter nonsense.

First of all the pelican striker (as the setup in the picture is called) is whole fitted to the pole itself and therefor can not improve the displacement of the pole tip under load. The shown setup still wholely dependents on the pole tip and bridle support wires to limit tip movement and as such is absolutely no different from a setup without the pelican striker.

Secondly, I have no seen a F16 yet where the tip is displaced 100 mm under (spi) load. If that is the case for a given F16 spi setup then an error has been made in constructing it. A simple 40x2 mm alu tube with 3 or 4 mm dyneema support line to the tip and midsection of the pole is enough to lock the pole up in quite a stiff sense.

Wouter

The only reason I can think of is that it adds some additional stiffness.
Something they would probably want for the light winds at Qingdao.

You are hilarious Wouter. I guess I just know nothing and should give up sailing.

That isnt my experience or understanding..
On an 18teen the pole end is supported by side wires from the wings. I am not sure if they still do but they used to run a tripod as well as wing lines. A third line runs through a dolphin striker to the tip. I believe the 12s still use a tripod still as they have no substantial wings. So to gain lateral stiffness there is a lower dolphin striker and two spreaders. These take the side forces and the under takes the lifting forces.
Now understanding the pole on a "12" is 14 foot past the bows and they have up to 30" of mast above deck the forces on the rig tend to extreme. Even a small rigged 18 pole being around the 14 foot level past the bows is extreme in cat terms. Also the poles on a skiff is generally straight out not lifted as on a cat..


Cats have tiddlers for poles (past the bows) then the forces are far less (for the size) but still significant. Placing things into 12 foot perspective a T would have a pole that would be 20-24 foot past the bows.

What I suspect is they are increasing the luff length by bending the pole down with a striker..

Tornado spis are already at ~max luff length as defined in the class rules, so I dont think that is it?

Wouter,
Have you forgotten about the compression strut above the pole that goes to the bridle wires?

The way I see it this set up will allow the spi pole to be carried lower or make the setup stiffer for the height the pole is carried.

As the pole is lowered the spi pole bridle is less affective at taking the vertical loading while quite adequate at handling the horizontal loading. So the striker below the pole will help transfer the vertical loading on the tip of the pole to the standard fore stay bridle wires via the compression strut above the pole between the spi pole and the normal bridle.

Just the way I see it.

Regards,
Phill

We sailed with less mast rake than most, mega rake did not work for us, and probably the lowest spi pole in the fleet. What Phill describes was an issue solved by fine tuning the lower bridle wires for good performance to windward. It was quite visible when beating if these were not perfect, but not while using the spi as far as I remember. Pre-bend in the spi pole was our way of lowering the tip while keeping the compression strut at the same length.

Will be interesting to find out where the advantage is and how well it works.

Explained it better than I Phil. The lower the pole at the bow, the less effect the front bridles will have.

Perhaps they are also using new cut kites that are flatter and closer to a Code Zero and require extra assistance in keeping the luff tight and consistent. The Pelican striker is a good option to assist in achieving this.

Rolf, Not sure what you mean by tuning the lower Bridals for windward work. Surely they are D12(or similar) so streach more than the wire of the upper bridals?

I dont remember what line we used there. It was some synthetic line (4mm, no uncover, silver colored) but I do remember the need to tune them to make the lower part of the jib set properly going to windward. Lining up the spi pole so it was straight and perfecting tension and length of the lines was a chore. The hulls also flex to a certain degree, so you rarely get perfect trim on the lower part of the jib even if perfections is the goal.

I think a flatter kite would give better VMG around the course, but there are limits due to measurement rules. Spis have been the area for most experimentation, but it is still the Gran Segel MK4 which is the choice. The sail John and Charlie use in the picture is a Performance cut. Interestingly enough, the reason the Gran mark 4 is the weapon of choice is that you can go quite high with it. Gran themselves say a slightly deeper and different cut will be faster VMG wise around the course if there are no other boats there. Contradicts my opening statement of course but that is part of the fun with sailing.

If the question is "do a flatter cut spi need less movement of the tip of the spi pole?" I would say the movement is so small already today that it dont make much of a difference.

That picture turned into an interesting discussion for us gearheads <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

Ah; OK, so it was positining of pole / tensions to get the best set in the jib correctly.