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I was rather pleased to find out that my motorsailer's 6 x 9 inch "tree stump" mast was in fact a Selden, so I purchased a Selden pole lift ring to fit in the handy grooves. Now, of course, I have to tap in holes for cheek blocks (or cut rectangular holes for sheeve boxes) to move the thing up and down.

I have a further question out of these Selden pages, though, Alex: See here?



Everyone I know tightens the turnbuckle with a screwdriver. Why a wrench/spanner?
 

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Discussion Starter · #62 ·
Everyone I know tightens the turnbuckle with a screwdriver. Why a wrench/spanner?
I'll keep it simple...

That type of turnbuckles are designed to support tension forces only, and has very little torsion strenght, mainly because there are very little lateral efforts they need to support.....it's made that way when the turnbuckle is made, when the metalurgists make sure the grain of metal is more oblong, making it tension resistant, harder, but less resistant to lateral forces.

In using a screw driver, you are stressing the legs of the turnbuckle with lateral forces, (for which the piece was not designed for), and even twisting the turnbuckle legs, wich then get stressed, and the integrety of the intergranular structure gets compromised, possible causing it to fail at a later stage.

For this reason, the turnbuckle manufacturers make 2 flat surfaces, like a nut, to use a wrench, that will in turn provide rotational forces without stressing the legs of the turnbuckle.

Hope it was simple.

Alex
 

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Yes, that explains it perfectly, and I will change my habits accordingly.

Although I am lucky enough to have old Merriman turnbuckles in chromed bronze and they seem a little more robust than the current types.

This is Merriman "style":


They aren't made anymore, as far as I know.
 

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Keel, I am not going to argue this anymore.
Was not trying to argue anything Giu; I was simply trying to add some information to your excellent post of how to adjust your rig tension.

Since there was confusion on what your post was saying I tried to determine why it would be 1mm extension for 1 meter or 2 meters; but it is off by ~50%. The calculation is correct; so it must be a problem with the published breaking strengths. So I was doing some more research on 316 stainless and it turns out that the published breaking strengths must not be actual ultimate breaking loads; they seem to have a safety factor of 2 built in. The 15% breaking strength calculations I did earlier were based on the published breaking loads; while the Selden formula is based on the true Utimate Tensile Strength of stainless wire (actual failure strength).
 

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I have an in-mast furling for main sail. Therefore when I bend the mast during sailing the furling system operation is adversly effected. Is it a good idea to bend such masts or to keep them straight is better?
 

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All good info but really...it's not that difficult to do.
Lay on your back, feet facing the bow, looking up the mast to see the straightness of it port to stbd. Adjust until straight with moderate tension on the shrouds or stays. Next lay on your back with your feet off the beam while looking up the side of the mast to check for bend for and aft. Adjust acordingly until straight with moderate tension on shrouds and stays...done. I've been doing it for 15 years this way.
 

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Rod Rig Tensioning

Anyone,

I have NavTec rod rigging on my 40' boat. Should the lower shrouds have the same level of tension at rest as wire shrouds or should there be more tension? I noticed this summer that the lee shrouds were flopping around when we were sailing.

Hank Tully
 

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Anyone,

I have NavTec rod rigging on my 40' boat. Should the lower shrouds have the same level of tension at rest as wire shrouds or should there be more tension? I noticed this summer that the lee shrouds were flopping around when we were sailing.

Hank Tully
Usually, the uppers are tightest, next the intermediates and then the lowers. This can vary with the type of rig. A good rule of thumb is that the larger the diameter, the more tension.
Your lee shrouds, in my opinion, should not be flopping around.
 

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I used the folding method as Selden explained to tension my rig last year since the 1x19 wires were larger diameter than the standard tension gage available. It was easy to do and the boat now points better. Good explaination.

Another thing I did which may or may not be right is to replace the old spartite around the mast. It's keel steped and I was getting some leakage through the deck and when I went to replace the mast boot I saw that the original spartite(not sure if it wa spartite) was cracked and crumbling. I dug it all out and then just used the best silicone caulk that I could find to fill the gap. The silicon may not be as hard as the epoxy based spartite, but it does limit movement of the mast at the deck. Not sure if there is much movement anyway since the mast is thick walled. At the Annapolos boat show I asked the spartite people about this, but they really didn't have any good response. The one problem that I see is that the cure time for a thick ribbon of silicon to comletely cure might be excessive?? days..weeks ...months
 

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Shroud length/tension problem

For people still struggling with the length issue look carefully at the image posted before by "Valiente" at post # 61. (Sorry I'am not alowed to post images so I can not show the image myself)

At first I will say that I also was confused and could not believe what "Giulietta" was saying about this. Plus I had to agree with what "KeelHaulin" was saying about length of the shroud. :confused:

Then I saw this image and everything became clear. :D :)

If you look good at the tape measure in the drawing you will see it is attached, at the top of the tape measurer, to the shroud with adhesive tape. What this means is that you are indeed lengthening the whole shroud but only measuring the stretch over 2 meter.

If you keep this in mind the whole explanation makes sense.
 

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2) Longitudinal Adjustment. (Rake)

(NOTE: this has to be done in a day with no wind with the boat perfectly horizontal, shift weight if you have to balance the boat).

Rake will help increase or decrease Weather helm. Aft Rake increases weather helm, improving pointing, forward rake does the opposite.

Normal rake is 1 to 2º degrees aft for cruiser boats and up to 4º deg aft for high performance racers.

a) Install a bucket with water under the boom by the mast.

b) Attach a heavy object to the main sail halyard and dip it the bucket but it should not touch the bottom of the bucket. (The bucket and water are used to dampen the swinging of the halyard.)

c) Measure P, which is the distance from the boom to the top of the mast.

d) Measure the distance from the halyard to the edge of the mast, at the gooseneck.

[
2) Mast Pre bend

Once the masts are where you want them to be, and before we tension the shrouds, we need to set the masts curvature, or pre-bend.

For this attach the halyard that was in the bucket so it ends at the mast foot.

Now adjust the baby stay and or forestays so that the belly of the mast goes forward. Takes a few tries.
The max bend at rest should not exceed half of the mast diameter.

Have fun.


Alex,

Still a little confused about mast rake and mast bend and how to put in one without effecting the other. I've seen the diagram showing the difference between the two so that is not what I'm questioning, just implementation of it with a mast head rig, a keel step mast with "spar-tite" around the mast at deck level, cutter rig with furler on the forestay(Pro Furl), bow spirit with bob stay, and heavy dispalcement cruiser. (A Tayana 37) Even with putting somewhere near 25% tension on the backstay, the mast remains vertical using the method of the halyard hanging from the mast head. It seems that in order to get aft mast rake, I would need to adjust the keel step such that the mast sits at an angle fore and aft using shims. If that is the case then there can be no adjustment to the mast rake once the mast is installed on the boat. Is my understanding correct on that point?

The other question is the tension in the forestay with furler. I did look for some way of accessing the wire like you suggested, but I can't locate anything in the Pro Furl. The only thing I can figure is to assume that whatever I put into the backstay gets transmitted to the forestay.

BTW Your videos are great!

DB on the Cheaspeake Bay
 
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