Translated this post for you Trimmen van de mast - Technical Matters - sportinaforum.net
Last weekend I ticked off a job I had been looking forward to for a while, trimming the mast. I had no experience with this before and was a bit apprehensive about adjusting it differently from how the previous owner had delivered it.
With this Guide 17 in hand, it is quite doable but it is a precise and time-consuming job.
loosened stays completely and checked for wear.
Check whether the stays are the same length, as this is important for adjustment. If they are not the same length, I think you have done a bad job and it seems difficult to tune them according to this guide…
Equipment: 2-metre folding rule, some painter’s tape, a small piece of string and a caliper.
my rigging is all 4mm, main rigging 6.90m long measured between the rollers, baby rigging a little less than half as long, 3.36m. Backstay also 4mm thick, not measured how long.
guide well read, contains important details on how different types of steel wire behave, maximum load, stretch per metre etc.
Baby and backstays
First ‘reset’ baby stays. Fore, aft and main bows fixed and the bolts turned all the way out of the tensioners. Screw in bolts exactly the same distance and hand-tighten, remembering at all times to fix the forestay itself and let the tensioner do the turning. Note the number of half turns to hand-tight.
First apply the folding rule method to the backstay. Taped one end of the folding rule with painter’s tape about 200.5cm from the underside of the backstay. Kept the other end near the stays with a piece of string, Do not tighten as you use this to measure the stretch of the wire rope.
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manual, 5%, 10%, 15% and maximum 20% backstay load marked with a marker on top of the delay. You’re going to need this later when tuning the main stay.
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key point: 1mm stretch per 2m of cable gives 5% of tov max load, regardless of cable thickness.
also screwed completely out of the tensioners (so the baby stays first hand-tight so the mast stays up!)
reinsert the threads and hand-tighten with the same number of turns on both sides (fix the stays and turn the tensioner).
Secure one end of the folding rule again at about 200.5 cm with masking tape, loop at the bottom for the loose end of the folding rule.
tension both sides alternately in steps of 3 mm = 15% of maximum load.
then from the mast foot up, check that your mast does not bend. In my case, there was a slight bend to starboard. Give port side babystay 5 extra turns and the mast curvature was gone. So babystay is mainly there to straighten the mast widthwise and lengthwise to prevent pumping of the mast under sail.
Then tension the main webbing to 20% max load. So another 1 mm of stretch added and with my tensioners that meant 5 extra half turns. This fact is nice to remember if you want to do some tuning later: 1mm = 5% = 5 halfstrokes. (The baby rigging is shorter so this does not apply there!)
then trim the mast straight again with the baby rigging
then the backstay full to 20%. This curves the mast and thus relaxes the main rigging.
then tighten the main rigging again to 20% load, this time 7 turns needed on both sides.
then the guide tells you to fully relax the backstay again and then check that your main rigging has come to no more than 25% of maximum load. In my case, I just had to relax them a few turns to get to 25%.
The mast really stands like a house now, can’t say otherwise. The rigging really is adjusted much tighter.
Not that it was unsafe before because I went through a rough 24 hours with it.
However, I think the mast is now much more under control under sail and that will improve performance, I am convinced.
However, the hull will now have a completely different load from the stays, but I assume that is designed for it and will not cause any problems.
Furthermore, I learned a lot and mastered this unknown area.
I now know how to adjust the backstay quite precisely, which is something I can benefit from when sailing.
The guide also gives instructions for fine-tuning under sail, so I’ll let you know what comes out of that.
The boat is ready to sail again, enough work, now let’s go sailing!
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