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125 Discussion Forum
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Return to the Forum List  Mast Spreaders | We have adjustable spreaders on our recently purchased 125. Could someone please explain their effect? Should we be looking at adjusting them each time we sail to suit the conditions? If so what setting should we be looking for? Is this also something that should be adjusted in combination with the mast step setting which also has 6 different positions?
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| | Re: Mast Spreaders | G'day Shane,
I find spreaders and masts and their controls one of the most complicated things on boats. As far as I can tell spreaders adjust the amount of prebend you have in the mast. I’m sure they have a number of other affects I don’t yet know about but this is what I’m finding on the 470 I’m sailing at the moment:
Spreaders work by deflecting the sidestays (making them go round a corner) and pushing the mast forwards. The amount they push can be changed in two ways: adjusting their length or adjusting their angle with the mast.
Changing the angle with the mast is the primary way of increasing or decreasing the amount of prebend (generally because it’s the easiest to do). Adjusting the spreaders so they are more swept back towards the back of the boat will increase the prebend because they are pushing the mast more forwards. Winding them forwards so they are closer to 90o to the mast will decrease the prebend because they are now just pushing into the mast.
Their length changes the sensitivity of changes you make to their angle. Longer spreaders will get a bigger change in prebend for the same angle adjustment. They will also increase the amount of prebend the longer you make them because they deflect the stays more and more.
Generally, the amount of prebend you want should match the amount of luff curve the sailmaker has cut into you main. To measure prebend generally you run a string from the bottom of the black band at the top of the mast to where the tack of the sail is held or attaches to the mast. Pull this tight and measure the distance from the outside of the mast to this string at the spreaders. On the sail run a string from the top of the sail at the inside of the bold rope (ie the spot on the sail that would line up with the spot you measured from on the mast had the sail been there) down to the tack. Find the place on the sail where spreaders are and measure the distance from the inside of the bold rope to the string. This is the measurement that should be the same.
Spreaders will also affect the tension in the forestay so when you play with them keep checking the forestay tension so that it stays in good ranges (see earlier discussions)
Changing the mast step changes the prebend also. Shifting it aft will increase it and forwards will decrease it. I’ve no idea where the best spot is on a 125 as I’ve only just learnt all this on a 470 and I’m yet to apply it to my 125. Hope this all makes sense and helps a bit!
Darren
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| | gucci homme
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gucci sac
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