My first exposure to pre-bend masts. I decided that the diamond wire belongs in this part of the spreader. (Apologies for the poor focus).
When I go to tighten down the cap, the screw starts binding on the wire before the plastic cap sits down snug. Do I take 3 mm off the screw? Or is the wire meant to be in the caps notches?

This is how I did mine.

No you didn't do this right.

Take it apart and use the notches. Well, just one of them obviously. To be exact my spreader (same brand but 3 years older then yours) has only 1 notches and that is all you need. So partly I don't understand why yours has two.

Best is to tighten the diamond wires first and then pull them onto the ends of the arms. There should be small corner or ver shallow notch at the very end of the silver coloured part of the arm. The silver coloured part is the slider that allows a sailor to adjusts the length of the spreaderarm. In your case your want the arm at minimal length, it looks like you've done that.

You can tighten the diamond wires ones they're on the spreader arms but your risk cold welding of the nuts to the threading and pulling the threading of either the nutts or the terminals. This last issue seems to be less frequent these days, maybe the threading has been improved on the terminals/nutts. The first issue can best be solved by (properly) greasing up the threads before assembling. An extra safeguard is, as mentioned, not tightening the wires when they are in the spreader arms or at least minimize that action.

Actually what I do myself is as follows.

-1- lay the mast horinzontally on two sawhorses or chairs. One at the base and one just above the hounds. Make sure that it is at knee height.

-2- I put on wire on the spreader and secure that when fully as if I was going to sail with it. I leave the other wire off. The mast will bend sideways noticeable by that is okay. The load on the threading is pretty small now and you can just turn the nutt on this wire without any worries. Have the pre fitted wire on the underside of the mast.

-3- Shorten both wires by the same amount (turning the nutts on the mast base plate). Same amount = counting the threads or turns when you tighten the wires. That is AFTER you checked wether the wires are of the same length to begin with. If not then count the turns needed to correct this and add them to longest wire.

-4- When you feel that you are close then put the second wire on the spreader arm by placing your knee on the mast next to the spreader arm and putting your weight on it. Then pull the wire ONTO the spreader arm with two fingers of either hand. Don't secure this wire. If the wire is under tension it will stay on the spreader arm under its own loading if you don't do weird stuff.

-5- Measure the prebend of the mast by measuring the distance between the sailtrack and the line you tesioned between the top of the mast and the goose neck. Make sure the mast is on its side to take gravity out of the equation and that you use a thin and very lightweight line. This line mast be just on the backside of the sailtrack at the mast hook and gooseneck. I just run the line under the hook fitting and gooseneck fitting as these are right on the backside of my sailtrack.

Note if you have to much prebend or two little prebend.

-6- Take the upper wire off the spreader arm by using the knee trick in reverse. Now adjust BOTH wires so that you come closer to the desired prebend setting.

-7- Repeat the above steps till you are pretty close to the desired value

-8- With both wires on the spreader arms turn the mast 90 degrees so the front of it is laying on the chairs. Have somebody hold the mast while you look along the masttrack from base to top. Try to see whether the mast is bend to one side at the spreaders. If so then losen one of the wires to take THIS curve out. Loosening a nutt is far more safe in the way of cold welding and breakage of threading then tightening. This is obvious.

-9- When the mast is straight then lay it on its side again and remeasure the resulting prebend. It should still be pretty close to the desired value. If not then take out the upper wire again and adjust both wires by equal amounts.

-10- repeat the above step till everything is as it should be

-11- Once satisfied secure the uppper wire to the spreader arm and make the mast ready for sailing.


Don't check for straightness of the mast when it is on the boat in any good amound of wind. The mast will already bend noticeable under windpressure in these conditions.

Good luck


Wouter

Bobcat....Wrong
Pete......Right

Ken

I took a picture of mine - as far as I know you can put it on either notch. It doesn't seem like it is very stable, but mine have never slipped off. The first pic I unscrewed the cap some so you could see where I position the wire.

Actually, mine came from the factory this way. I had it all apart and, fortunately, remembered how it went back together.

I started off the "right" way but as things got tighter I had the easy one jump into the deeper groove while pulling the hard one on. So I said to myself, Hmmm. It just seemed like the little ear on the plastic cap wasn't substantial enough. But that is why I asked.

After setting the diamonds to the default values I was given for prebend and rake, I ended up with a tension of 39 on the Loos Pro 1 gauge. (And about an inch of the stud sticking down below the base plate.) I did have a couple millimeter bend to the right but I guess I'm adjusting everything a bit more anywise.
The two holes are different sized. 1/8" and 3/32 or something. Thank you for your quick replies and photo's.

At first, I thought I had two options, but really the notch at the rear is the only feasible option as the wire will stay in this position without the caps. The front notch would require the caps to hold it in place, making it more difficult to adjust and putting sideways force on the plastic caps. You can spin the caps to fit 3mm or 2.5mm cable.

While adjusting the cables, I found it quite easy to just lay the mast on the grass, and while sitting, push against the mast with my feet holding onto the wire. And just leave the caps off while making the adjustments.

That looks like dyform wire, does anybody know what diameter is used on the Blades ?

3 mm or 2.5 mm.

Or can anybody measure it with a vernier ?

Wouter

No vernier, just a wooden rule laid out in mm. Looks like 3mm, certainly not 2.5.

When you get the chance can you also measure the effective length of your spreader arms ?

I'm guessing 390 mm.

Wouter

"Effective length"?

Center of sail track to center of wire 15" exactly = 25.4(mm/") x 15" = 381 mm.

Center of leading edge of mast to center of wire 17 1/16"= 25.4 x 17.06= 433.3mm

"effective length" = the full length of the spreader arm including the the little slider and the eye on the mast. So from foot of the spreader on the mast and directly under the pivot point to the very end of the arm where the wire is attached.

Sorry I should have more clear about this. Can you remeasure ? Thanks alot.

Wouter

I suspect 3mm as the 2.5mm end of the cap would not fit onto the wire.

16" x 25.4 = 406.4