Mike,

What I found was that a spinnaker pole cna easily be made strong enough to resist the spinnaker loads on normal sized beach cats. No strut is required. However there can be advantages using such a strut.

-1- If the strut is loaded up then the bridles can be taken higher which reduced the toe in bending moments in the hulls.

-2- It keeps the luff of the jib straight without alot of jib tension. Remember that tension in the forestay keeps the luff straight and no such tension is present between the bridle strop and pole. You don't want to load up the jib luff to much as that curves the leeach and may pull the draft to far forward.

-3- When the vectran / Wire support line run very horizontal then these line do not stabilize the pole in upward or downward direction. Today many try to get the pole as low as possible. Prebend can take care of this though.

-4- If the luff of the jib is tensioned than it will put a significant load on the pole which is far greater than the forces required to stabilize it in the vertical plane. Maybe the support wires run vertical enough to stabilize the pole but they will hardly ever run vertical enough to take the luff tension of the jib.

-5- A spi pole needs to kept up by at least one element. As all the support wires run downward it means the one element is required to pull it up. Often this is a ring or wires going down from the bridle strop to the pole. With an elongated jib luff this could be a wire also but why not have the advantage of at least point 2 and 4 as well ? In same cases it may pay to have point 1 too. If you are going to have an element there then why not use it to the max.

That is the reason why I use it. I made my boat wider and didn't want to load the boat up more so I raise my bridle strop and keep the angle to the hulls constant. In order to get the jib area in and keep the pole up I opted for a strut. I think I will load it up to medium level. I don't want to end up with a heavy thick road because of buckling considerations.

I don't know why the Tornado guys did it. I hear they changed nothing to the bridle height so I guess the answer must be found somewhere in points 2 to 5

Is it necessary ? I don't think it is. It can be done in other ways at well. May it be the msot attractive option ? That is likely.

Wouter