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Assess my Z-Spar mast (H23)

Jun 19, 2014
33
Hunter 23 Twin Cities
After reading this forum last season and getting some tips on rig tuning and reducing weather helm I decided that I had too much rake in my mast. Armed with the knowledge I gained here I tuned my standing rigging, which basically meant loosening the shrouds and backstay, tightening the forestay very tight, and then tightening the shrouds (to a lesser extent than the forestay) firmly and evenly.

My forestay is now tighter than it's ever been, I can feel the difference in reduced weather helm, but I feel like my mast still has too much rake. I realize that Z-spar masts have a natural curve to them, but I still feel like mine has more than it should.

In the pictures below my forestay is very tight and the shrouds and back stack are only tight enough to have the slack taken out of them. In the 2nd pic, mine is the mast closest on the right (took this one as a reference to other boats with straight masts).

My questions are as follows:
1) is this amount of rake normal for a Z-spar mast and
2) is it possible to overtighten the forestay, even as performance increases?


 

Doug J

.
May 2, 2005
1,192
Hunter 26 Oceanside, CA
I could be wrong, but I don't think Z-spar masts have a natural curve to them, never heard of that. At the very least it does look like too much rake. I had to adjust my mast, it once had too much rake as well. While on the water in very calm water, put a weight on the main halyard and let it hand down to the boom. It should be about 4 inches away from the mast.
 
Jun 19, 2014
33
Hunter 23 Twin Cities
I could be wrong, but I don't think Z-spar masts have a natural curve to them, never heard of that. At the very least it does look like too much rake. I had to adjust my mast, it once had too much rake as well. While on the water in very calm water, put a weight on the main halyard and let it hand down to the boom. It should be about 4 inches away from the mast.
Agreed that it looks like too much. I will do the halyard test next time I'm up but if and when I do confirm that there is too much rake then my next question is how do I get rid of it?

The forestay can't get much tighter and the backstay is only tight enough to take the slack out.
 
Feb 21, 2013
2,941
Hunter 46 Point Richmond, CA
Rig tuning advise per Z Spars Rig Tuning Advice (zsparsuk.com)

General:
A. Ensure a straight mast athwartships.
B. Control sail shape.
C. Achieve proper helm balance in a variety of conditions.
D. Spread loads appropriately on spars, rigging and boat.

For a single spreader, fractional rig tune as follows:
1.1 Mast Rake
  • Mast rake is determined by forestay length. Rake affects helm balance - raking the mast increases weather helm.
  • As a starting point, use the designed rake on the sailplan (ask the boat designer, not the mastmaker). If no information is available, start at 1:30. (e.g., 33 cm (13 inch) rake on a 10 m ( 32.8 ft) mast). To measure rake, tension the backstay approximately 60%, then check rake with a weight attached to the main halyard. (Boat must be floating level when you do this!). Adjust forestay as necessary to obtain the desired angle. For a Hunter 23 with I = 26.0 then rake = 10.3 inches
1.2 Mast Bend
  • Check that the mast is upright athwartships in the boat. Use the main halyard to measure from the masthead to the chainplate each side. Adjust upper (cap) shrouds to get identical readings each side (but use minimal tension in the shrouds).
  • A certain amount of pre-set mast bend is desirable, to stabilise the middle part of the mast and thus minimise rig pump in a seaway.
  • Ensure the lower shrouds are slack. Induce the required amount of pre-bend in the mast by tensioning the backstay. (Make a note of the amount of pre-bend by using the main halyard tensioned down to the foot of the mast, and measuring the amount of bend at the spreaders). Tension the cap shrouds equally, a few turns at a time, until the fore and aft bend starts to increase. Check that the mast is still straight athwartships.
  • Now tighten the lowers in the same manner as the caps, until the fore and aft bend starts to decrease. At this stage the caps should be tighter than the lowers.
  • Release the tension in the backstay, check that you are happy with fore and aft and sideways deflections.
  • (Once the rig is set up as described here, tensioning the backstay whilst sailing will affect the curve in the upper part of the mast only, as the area around the spreaders is fixed by the opposing forces of the shrouds)
2. Transverse Tune
  • Go sailing! Set full sail to windward in smooth water in enough wind to induce 10-15 degrees heel when sailing to windward.
  • Tension the backstay just sufficiently to straighten the forestay.
  • If the leeward shrouds are slack, tighten them, but NO MORE THAN TWO TURNS AT A TIME. Go on the opposite tack and do likewise, then tack again and check if the lee shrouds are still slack. If so, repeat the operation. DO NOT OVERTIGHTEN the lee shrouds, as you may bend the boat or break the mast when you tack!
  • Back at the dock, check that the mast is still straight athwartships.
 
Jun 19, 2014
33
Hunter 23 Twin Cities
^^^Based on this post it appears I have too much bend (not rake) and tightening the cap shrouds will increase the bend, while tightening the lowers will decrease it. The dilemma I face is that with the shrouds and back stay loose I still see a bend (with forestay tight).

Following the advice above and also the rule of thumb that the cap shrouds should be tighter that the lower shrouds I don't see the bend situation improving.

I'll just have to play around with it some more and see.
 

Doug J

.
May 2, 2005
1,192
Hunter 26 Oceanside, CA
If you loosen the shrouds does the mast still have a bend? Meaning it is actually bent? If so, not sure but maybe you could straighten it some with the proper headstay and shroud adjustment. But I would think the mast should be straight prior to any shroud tensioning. True, after shrouds and headstay are properly adjusted there should be a slight bend, but that looks somewhat extreme, making it hard to tune out weather helm.
 
Jan 1, 2006
5,820
Slickcraft 26 Greenport, NY
It looks like too much prebend.
I don't think you can judge rake by looking at a photo. Or at least I can't. I think the amount of rake is determined by how the helm feels. 3 to 5 degrees of weather helm is considered good.
I agree with sail sfbay regarding forestay length - it sets the rake.
If you want less mast prebend you can loosen the backstay. It looks like the top of the mast is where a lot of that prebend is. So far as I can tell the top of the mast is un-supported (By the cap shrouds), so I would definitely straighten it out a bit. But while sailing that rig will bend some and thereby depower the main. I think that's why the taper is notable there. It's part of the design. I think of it like a auto-reef feature.
The amount of prebend should match the luff curve of your main. You can take the main off and stretch it out on a lawn and measure the luff curve in several areas - say 25% of luff length, 50% and 75% 85% and 95%. (More points up high where it looks over bent). Record those numbers. Then on the boat use the main halyard stretched from the mast head to the boom gooseneck. Sighting up the mast from off the boat you can see if the bend conforms with your numbers from the sail.
Is your backstay adjustable?
You have a fractional rig with swept back spreaders and a tapered mast. So mast bending is a way to depower the mainsail. Cranking on some backstay (If it is adjustable) will flatten the middle part of the main reducing power. That may be important in your weather helm situation. The sail could also be blown out which would create weather helm as well - particularly in gusts.
Tightening the forestay and setting forestay length are different. Tightness of the forestay is determined by the size wire you are using - usually 20% of the Safe Working Load. The length of the forestay is determined by the length of the wire and terminal fittings. Try to find that number and start there.
 
Jun 19, 2014
33
Hunter 23 Twin Cities
It looks like too much prebend.
I don't think you can judge rake by looking at a photo. Or at least I can't. I think the amount of rake is determined by how the helm feels. 3 to 5 degrees of weather helm is considered good.
I agree with sail sfbay regarding forestay length - it sets the rake.
If you want less mast prebend you can loosen the backstay. It looks like the top of the mast is where a lot of that prebend is. So far as I can tell the top of the mast is un-supported (By the cap shrouds), so I would definitely straighten it out a bit. But while sailing that rig will bend some and thereby depower the main. I think that's why the taper is notable there. It's part of the design. I think of it like a auto-reef feature.
The amount of prebend should match the luff curve of your main. You can take the main off and stretch it out on a lawn and measure the luff curve in several areas - say 25% of luff length, 50% and 75% 85% and 95%. (More points up high where it looks over bent). Record those numbers. Then on the boat use the main halyard stretched from the mast head to the boom gooseneck. Sighting up the mast from off the boat you can see if the bend conforms with your numbers from the sail.
Is your backstay adjustable?
You have a fractional rig with swept back spreaders and a tapered mast. So mast bending is a way to depower the mainsail. Cranking on some backstay (If it is adjustable) will flatten the middle part of the main reducing power. That may be important in your weather helm situation. The sail could also be blown out which would create weather helm as well - particularly in gusts.
Tightening the forestay and setting forestay length are different. Tightness of the forestay is determined by the size wire you are using - usually 20% of the Safe Working Load. The length of the forestay is determined by the length of the wire and terminal fittings. Try to find that number and start there.
Yes I have an adjustable backstay and in the pics above it only tight enough to take the slack out. New mainsail as well.

I'm thinking I'll have to play around with the shrouds a bit more...but as long as I've had the boat I've tried all kinds of variations (tight/loose) on the standing rigging and have never been able to get rid of that bend in the mast.