Backstays touching the akas?

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EarthBM
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Backstays touching the akas?

Post by EarthBM »

Hi, just going over the questions as they come up on the new to me DF 35... Are your backstays touching the beams? Mine are, not too bad, but at that tension the rubbing is real -- can see some paint wear on the aka and a (very little) rope chaffing. It looks like it is just about 2-3mm off the straight line. Does it mean I should add 10mm or so to the forestay to bring the mast backwards enough for the backstays to clear?
EarthBM
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Post by EarthBM »

This (mast too much forward) could explain the fairly heavy weather helm I've consistently experienced on my two sails so far... Thoughts?
Mario
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Post by Mario »

Backstays should not touch the akas. Is tension of backstays correct? More tension on backstays gives more distance to the edge.
EarthBM
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Post by EarthBM »

Thanks Mario -- is there a way to measure correct tension (like with a torque wrench at the winch)? The previous owner put some tape on where the backstays should level with the akas, so I just went with that.
gminkovsky
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Post by gminkovsky »

Mast forward = lee helm
Mast aft = weather helm

More sail pressure forward = lee helm
more sail pressure aft = weather helm

A few other comments: on my 920 if the backstays are too lose they touch the akas. In addition to adjusting them correctly, I put a short piece of fire hose as a chafe preventer around the backstays. It is from the top of the blocks to some height above the aka. It really helps when the backstays are slack.

To check for correct tension, follow the manual. On 920 in light wind the backstays are adjusted by hand. In heavy weather they are on a winch with only one hand winching. That gives a pretty good indication how much effort is required for an average person.

As far as the weather helm is concerned, there can be a number of reasons. Here are some that are easy to diagnose and fix:
1. poor sail trim - main oversheeted or not enough jib.
2. make sure that both the rudder blade and the centerboard are completely down.
3. make sure when the rudder is down that the rudder downhaul wire is not jammed between the blade and the housing. This happened to me and caused really bad weather helm on one tack, but not the other. In fact, make sure that there is nothing between the blade and the housing.
Mario
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Post by Mario »

No, unfortunately there is no objective tension measurement, not in manual book at least. JQ says that the tension should not be higher than that you can obtain by turning the winch handle max you can by one hand. Well, not very precise description. What I do is tightening the backstays so much that they go away from akas… Sometimes I have to use both hands; sometimes my wife has to do it…, but after 4 seasons sailing 35’er I must say that it fits very well. Have you got a manual book with the boat? Is not perfect, but still better than nothing.
EarthBM
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Post by EarthBM »

Thanks guys. The manual is on the boat (and the boat is a 2hr flight away), so next steps take place on weekends.
Mario wrote:JQ says that the tension should not be higher than that you can obtain by turning the winch handle max you can by one hand.
Just to be sure when you do this in plactice, max you can do means on the more torquey winch direction, without much bracing with your legs etc, right?

gminkovsky wrote:As far as the weather helm is concerned, there can be a number of reasons. Here are some that are easy to diagnose and fix:
1. poor sail trim - main oversheeted or not enough jib.
2. make sure that both the rudder blade and the centerboard are completely down.
3. make sure when the rudder is down that the rudder downhaul wire is not jammed between the blade and the housing. This happened to me and caused really bad weather helm on one tack, but not the other. In fact, make sure that there is nothing between the blade and the housing.
Well I was unable to get rid of weather helm by playing with trim, which doesn't mean it can't be done, but I did try several things... The rudder in fact does not go in with a satisfying thud. The previous owner says he had to grind a few mm (starboard side, from memory) from the rudder because it wasn't fitting into the slot. How do you make sure the rudder is all the way down -- can you hear the thud?

Same for the centerboard - do you feel when it hits the fully extended position?
EarthBM
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Post by EarthBM »

Actually now that I said this, reefing the main to the first reef solved the weather helm issue and didn't affect speed at all. But I was trying to go faster, would be good to find more power from the genoa.
Ivan -- DF 35 #29 "Lykke"
gminkovsky
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Post by gminkovsky »

The rudder is fully down when it hits the stopper - the rudder housing. After that you have to make sure that rudder downhaul is taut and properly cleated. Any stretch or slack in the downhaul will let the rudder back.

Reading what you said about the prior owner grinding down the rudder makes me think that that must be the first area to investigate. If the rudder is off center your handling will be impaired.

The board down position is trickier. On 920 we usually have a knot tied on the uphaul line that will let the board fully down but not past vertical. The only way to adjust that knot properly is with the boat hanging from a crane or in a sling - let the board down, pull it to where the leading edge is perfectly vertical and tie a knot at that position. You can also dive under the boat and look at the board position.

If I read your last post correctly, you reefed the main but kept the jib full and the weather helm went away. This sounds like your jib is on a small side. Is it a genoa (115% or larger) or more of a working jib (100% or less)? Was your jib already furled? With the full main oversheeted and the jib furled to 2nd reef, you probably will have some weather helm.

To tighten the backstay use the slow speed on the winch with one hand and some bracing of the legs. Don't strain too much :). It will be fine.
Mario
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Post by Mario »

In practice: I have el-winch only on the portside; therefore, first I fold out the starboard side and tight the starboard backstay to the tape-mark which level with the aka. There is no tension on the other side, so it goes easy, you can do it just with hands, without the handle. Then I fold the port side out and tight the portside backstay by the el-winch up to the tape-mark. Both backstays stay about 1 cm from the akas edge.
During folding out it is good idea to tight the backstays constant (just slowly by hand) as they can be clamped if they swing loose.
The rudder has to go 90 degr. down, and you surely can hear the thud when it comes on place. I cannot hear the centreboard, but the knot on the uphaul (or: “board-up” line) has to come closly to the clutch (remember to open for this clutch when taking the board down!).
EarthBM
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Post by EarthBM »

Well yes, this is the thing, the rudder downhaul is taut, but I can't feel a distinct stop. Anyway this looks like a boat-specific issue, need to investigate more.

There is a knot on the centerboard uphaul. When I inspected the underside at the yard, the centerboard wasn't really vertical when fully extended (more of a triangular shape). Probably designed this way to be kicked up easily if you hit something. Is there a picture on the internet where I can see a fully extended DF centerboard and compare to mine?

Yes, the main was on the first reef, and the genoa (think it's 110% or 115%) was not reefed (furled) at all the helm was perfect. So my gut kept telling me I needed more power on the foresail.
Ivan -- DF 35 #29 "Lykke"
gminkovsky
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Post by gminkovsky »

Your board is NOT all the way down. The leading edge must be vertical. I think you have to adjust the board and investigate the rudder.

As far as sail balance goes, especially in stronger wind, check your sheeting angle, adjust traveler - move to leeward, adjust your genoa track. Also, maybe play with with barberhauler to adjust the slot. You should probably also look at the main shape. I suggest inviting a good sail trimmer for a sail to help you diagnose trim issues. I learned a lot from just two outings with a really good sail trimmer!

On a separate note, on my boat I find that the main sail shape is (was) dramatically better on Reef 1 than on full - the sail was fuller and more powerful. As a result, after 7 years of not touching the outhaul, I moved the outhaul a couple of positions forward and made the sail fuller. So the last season of sailing (before the main disintegrated) I finally achieved correct shape!
EarthBM
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Post by EarthBM »

gminkovsky wrote:Your board is NOT all the way down. The leading edge must be vertical. I think you have to adjust the board and investigate the rudder.
Great, now I have the new owner "my centerboard is not all the way down" angst... Not sure if the image would show, and it wasn't taken at the right angle anyway, but it doesn't look vertical... Now I have to dive and take another pic from abeam.
Image

But my intuition tells me that apendages (both centerboard and rudder) being aft of where they are supposed to be would create lee helm, not weather helm, am I wrong?
Last edited by EarthBM on Wed 23 Mar 11, 4:23, edited 1 time in total.
Ivan -- DF 35 #29 "Lykke"
gminkovsky
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Post by gminkovsky »

I think the issue with rudder is different from the board. If the rudder was filed on one side, it may be off-center. This may cause weather helm on one tack and lee helm (or balanced helm) on the opposite tack. Read more on this here: http://www.dragonfly-trimarans.org/phpB ... highlight=

If the rudder is not all the way down, the effort required to keep the boat on track and the load on the rudder blade increase and may give you an impression of increased weather helm. In other words, the default trim of a DF is to have a very slight weather helm for safety - without helmsman or autopilot the boat will go into irons with the sails sheeted. This translates into slight pressure on the blade and the tiller or wheel. When the blade tilts back the pressure on the blade and what transmits to the feel on the tiller or wheel increases very quickly. That will feel like much more of a weather helm. As soon as you reefed main and left full jib, the trim became less weather and reduced the apparent pressure on the blade, tiller or wheel.

Did you look at the actual rudder position in relationship to the boat's centerline when you experienced strong weather helm?

I can't figure out the physics of the centerboard and will leave to others to comment.
Steve B.
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Wx helm vs Lee helm

Post by Steve B. »

As the board is progressively lifted going upwind, there will be a progression from weather to lee helm.
EarthBM
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Post by EarthBM »

Yep, I understand how the pressure would increase quickly if the rudder is lifted off vertical. And yes, the autopilot was showing 3-4 little bars off center before giving up by the end of the second day (MOT STALL error code, S1 tiller pilot)

Went to see the drawing on Quorning website and it shows 35 centerboard swept back a little, I can't really say that mine is different.
Image

Hi Steve!
Ivan -- DF 35 #29 "Lykke"
gminkovsky
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Post by gminkovsky »

I think I jumped to a premature conclusion regarding the board. (I will also double-check the board position on my 920 when I launch this spring.)
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