Proper measurement to get mast centered for tuning

Hi,

I had to pull the mast on our 1984 E30+ to repair the electrical connections for mast lights, and want to get the rig tuned right after re-attaching the shrouds.

I know the general process for tuning the rig, but am having a bit of trouble getting the mast absolutely centred on the boat. The reason is that everything I'm measuring is a bit off--from the centre of the bow back to each cap shroud is not identical; from the mast base to the port/starboard lower shrouds is different, etc.

I have been trying to centre the mast using the halyard pulled taut to the toe rail, adjusting the cap shrouds til the halyard length appears the same. But this is a challenge and of questional accuracy, as to pull it taut over the length from masthead to the toerail, I need to exert some pressure on it to get it into a straight line, and then I'm estimating whether the amount of pressure I'm exerting on each side is the same, at the same point on the toe rail.

I spent quite a while yesterday trying to get it as identical as possible, then tightening the intermediate and lower shrouds to keep the mast in column with no "S" bends along the length of the mast. It all looks reasonably straight, but eyeballing it over the height of the mast doesn't seem to me to be too accurate. I know I need to do the final tuning under sail to ensure the lee shrouds don't go slack and the mast doesn't bend to leeward, but I want to get it as close as possible on the dock first.

Two ideas that won't work: 1) Counting the threads on each of the turnbuckles to ensure they are are same on each side won't work because the shroud attachments to the deck are not in precisely the same spot on each side, which means the shroud length needs to be slightly different; 2) Using a loos gauge won't work for the same reason, I think. With the shrouds slightly different length due to the different placement, the tension needs to be slightly different to accommodate for the different length. As I don't know how much different, this is also a crapshoot for me. And I don't have a loos gauge.

Does anyone have any better method to suggest?

Thanks,
Frank

Attach the end of a tape measure to the halyard shackle. Attach a spare line to the shackle(in case your tape measure fails). Hoist all the way to the top of the mast. The tape measure should give you a more accurate reading. Do it on a day with no wind.

shock cord

I use the halyard method also. I don't measure to the top. The North book suggests holding the halyard with a shock cord attached to the shackle and measuring point. Measure the length of shock cord until you are centered. This keeps the same pressure and I have found it quite accurate.

I may be doing the same thing soon. My intermediate shrouds are being replaced and I will need to re-tune. This won't solve your initial problem of differing measurements, but from what I have been reading a more accurate way of getting the initial static tensioning of the shrouds is to measure the amount of stretch of the wire. Brion Toss in his rig tuning video shows a device called the Rig Stick; basically a two meter length of tape measure that is attached to the shroud with an indicator at the bottom end that allows you to measure the amount of stretch as you tighten. I tried calling the phone number that was visible on the device in the video with no luck, and sent an e-mail to Brion Toss to try to find out where I can get this device and have not gotten a response.

Once the shrouds have been tensioned at the dock and the mast is straight then, as you point out, the on-the-water tuning has to be done, which seems to be a more by-eye procedure.

Wow... You guys are making this really tough...

1> The masthead shiv for the halyard is automatically on one side of the masthead.
2> The halyard is indeterminate stretch and will stretch more depending on how you pull on it.
3> If you use a tape measure all the way up the windage on it is going to make it bow really badly.


So the answer is.... Measure up about 6 feet on the mast. Place a mark in the middle of the mast measure from there as precisely as you can to either the chain plates or the toe rail depending on the boat.

Less windage, better measuring easier to do. And gives more honest results.

This is a lot easier, a lot more precise than using a halyard.

Guy

Frank Langer said:

I spent quite a while yesterday trying to get it as identical as possible, then tightening the intermediate and lower shrouds to keep the mast in column with no "S" bends along the length of the mast. It all looks reasonably straight, but eyeballing it over the height of the mast doesn't seem to me to be too accurate.

I know I need to do the final tuning under sail to ensure the lee shrouds don't go slack and the mast doesn't bend to leeward, but I want to get it as close as possible on the dock first.

2) Using a loos gauge won't work for the same reason, I think. With the shrouds slightly different length due to the different placement, the tension needs to be slightly different to accommodate for the different length.

Click to expand...

There are a lot of comments in here that confuse me. The Loose and CO strain gauge is going to give you the loading on the wire. It is a tuning tool good for use doing a static tune if you understand the forces on your rig. If you have two cap shrouds they should be at the same static tune load.

Sighting up the mast can be a very accurate method for determining if the mast is straight or not. Actually it is the only method.

I would recommend getting Brion Toss video on how to tune your rig... Also reading the section in The riggers apprentice on the subject.

The only thing that we are really working on here is keeping the mast roughly in the center of the boat and not allowing the mast to bend out of column to leeward when we are sailing.

As for the lea shrouds going slack when you are sailing they should.... Really there is no way to make it so that they do not..... Trying to make it so they do not has destroyed more boats then I can even speculate on.... A couple of them I am consulting on with very large repair bills right now.

Guy

Playing devils advocate here Guy Do you just eyeball the top of the mast once the lower section is in column?

I like your method but it makes me think we should be measuring the mast at each set of spreaders and the top.

Ah I see where the confusion is

Start with this...

Lay on the deck with your cheek against the mast dominant eye against the mast. Sight up the mast. This is much like sighting down the barrel of a gun. And you will notice every little tiny thing about the mast. You may even notice that there is a lack of compression sleeves in your spreader area, and that the mast seems to narrow a bit there.

You will definitely notice any curves, bends, or the like.

Really it works great you can get a mast perfectly straight in this manner.

To relate it to another concept. You can fire a rifle and be within 10ths or less of a degree of alignment with a target, otherwise you would never hit anything more than about 10 feet away from you. Same concepts function here. You will see any mast bends etc.

Remember the goal is to keep the mast straight, so that it is always in Column. It breaks when it goes out of column.

Guy

Guy,

Thanks for this helpful advice. I will try this "6' up the mast measurement" to see how close I came using the halyard, and make any necessary adjustments.

Regarding the lee side being slack, what I have read (and I've tried to do alot of reading, including the write-up on tuning the E30+ from Ericson) says that the lee shroud should feel slightly slack but not look slack when the boat is heeling about 20 degrees, ie. not show any looseness, with the mast remaining straight with only very slight bend to leeward in a strong blow, if at all. The Ericson write-up says that fractional rigs should be tensioned more than masthead rigs, with the cap shroud tightest as it has the greatest length to stretch. Does this all make sense?

Frank

That is a confusing write up

The verbage on the tuning write up you are quoting seems confusing at best to me.

The leeward shrouds on most boats should not be swinging wildly in the wind... They should not be tight however.

Each of the wire ropes on the boat support a different amount of load depending on their function. The longer wires support more load and a generally higher loaded and therefore more tensioned. The fact that they are longer is not what sets the tension. The tension is set more by the thickness of the wire in a static tune than anything. That is why we don't want to upsize the wire for "safety" it actually makes the rig less safe. (That however is another thread and I don't want to hijack this one, because this is a great thread!)

You can actually calculate for every given wind condition what load each of the wires on your rig is loaded at. I am not going to go into the forumla here, although it is not hard, because Brion Toss has a wonderful write up of how to do it in his book "The Riggers Apprentice".

You are asking the correct questions and seem to me to be grasping the whole purpose here. Keep working at it and asking questions till you are sure you have it. I am happy to answer them.


Guy

Thanks, Guy. I appreciate your patience with this. I understand not increasing the size of the rigging as this can place more stress on the boat, and most designers will have built in enough "extra" or safety margin so that the existing rigging size should be fine (especially if not going offshore).

But I have read that if the upper and lower shrouds are both the same diameter wire, the upper one should be tensioned a bit tighter, as it has more length to stretch than the lower one, so needs a bit more tension to avoid becoming loose. Is that not correct?

What makes this a bit more challenging is that the upper is 1/4", the intermediate is 3/16" and the lower is 9/32". The intermediate being the smallest, I'm hesitant to put much tension on it, yet anticipate that it will be too loose once I get on the water. By feel, I am putting slightly greater tension on the upper, a bit less on the intermediate and perhaps slightly less on the lower (although it is higher diameter, it has the least length to stretch). Or am I being too finicky on this?

Frank

FWIW, I use a "survey tape" or long flexible tape measure to center my mast. I understand the windage factor but I also only do something like this in WINDLESS conditions. I'm talking about when the anemometer ain't even spinning. Then the tape works great. RT