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TOPIC: Spreader Height

Spreader Height 8 years 2 weeks ago #287

Could someone please explain these two things for me.

1. What affect moving the spreaders up and down has on the mast. I believe the Holger boats have a lower spreader height than the west coast boats. Why?

2. What is the affect of longer spreaders vs shorter spreaders, given they have the same amount of deflection.
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Re:Spreader Height 8 years 2 weeks ago #288

  • JimE
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Not the best answer for your first questions, but in general, by moving your spreader up, you just change where you are attempting to limit the bend. Since, as you move up, you approach a smaller triangle w the shrouds and move further away from your other control point(the mast ram) at some point there is a diminished return by moving the spreaders too far up or too far down. There is a range of what works, everyone probably has differing opinions on what the "right" place is.

Second question...the outward deflection affects the side to side bend. You can tell you have too little outward poke if you find yourself sheeting the main to the middle of the boat even when sailing in overpowered conditions. You can tell you have too much poke if the end of your boom tends to be outside the corner of the transom when over powered. Optimum setting depends on your crew weight & your sails. In general, I think the boom should be just inside the corner of the transom in overpower conditions.

The thing to remember is if you only adjust the poke of your spreaders, you actually change poke and sweep. Longer spreaders increase sweep, shorter spreaders decrease sweep, even though you did not adjust the turnbuckle or screw on your spreaders.

The above is just some generalities.
A long day w access to a beach or floating dock and go out and make a bunch of extreme adjustments and you will feel and see what it is doing.
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Re:Spreader Height 8 years 4 days ago #294

  • usa7346
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I have a Superspar M2 with the lower height bracket(3048 mm / 10'0" above deck band) and I also have a Selden Cumulus with the bracket at the higher height(3150 mm / 10'4" above the deck band). I will have to check those numbers.

I have never been happy with my Cumulus and I have considered lowering the bracket to match my other mast. Generally speaking, I have run shorter poke on the mast with the higher bracket to achieve the same setup. I find that the mast with the higher bracket tends to be very sensitive to shroud tension in heavy air. I have never done much scientific testing on different bracket heights/poke/sweep settings. I feel the same way as you on this topic and would like to hear from some of the more experience guys on this. The problem is that there are a few key variables that cannot be removed from consideration before simply matching someone else's spreader poke/sweep setup:

1. Mast Butt Location: You want this to be at the minimum of 3048mm / 10'0" from Station 11(Transom Plane). Some people move this forward if the mast gate is not extended far enough aft to accommodate sufficient mast ram at max rake. Rondar vs Waterat mast length below the deck band is another variation that theoretically would make a difference, although I would say this is probably negligible.

2. Shroud and Forestay Terminal Locations: I have seen some variation in the shroud and forestay terminal height on the spar. I would argue that variation in the forestay terminal location(tack-forward/back) on the boat does not have a significant impact on spreader settings, while the shroud terminal locations on the boat have a major impact. In my mind, the new shroud tracks that have come into favor over the past few years even further complicate this equation. What is a good method for measuring shroud terminal location for comparison between different makes of 505?

3. Spreader Bracket Height: As discussed initially, there seems to be a ~100mm variation in bracket height which most certainly contributes to the spreader setup.

Can some people reply with their poke/sweep measurements along with the measurements for items 1-3 above for relevance? I will measure my current setup tonight and reply with those.
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