Wouter,

I have an AHPC mast base casting similar to what you have on your F16. I have the stock diamond wire configuration where you can only add tension by dropping the mast. I recall that you said you added closed-body turnbuckles to your diamond wire configuration so that you can adjust diamond wire tension without dropping the mast. I have a question regarding your diamond wire configuration:

Did you do anything special to prevent the wire that feeds into the bottom of the turnbuckle from turning in the mast base casting when you turn the turnbuckle?

Geoff
Boyer Mk 4

Geoff,

Another item about the tension setting on the turnbuckles. Please do not let any tension on the wire before you are turning anything on the turnbuckle otherwise it will weld itself and you have big trouble. Take always the wires off the arms before you are changing tension.

I appologize if my comments offend anyone, but I fully disagree with the necessity of taking the wires of the arms.

Plenty of boat designs turn on the diamond wire tension using turnbuckles with the wires in the arms. For example on the F18's it is standard practice and on yeachts as well as in architectural rigging it is almost the only way to do it. Turnbuckles are designed to be used like this while maybe threaded terminals and small nuts (as used on A-cats) aren't. Often suppliers will use slightly different materials for the different parts of their turnbuckles to make cold welding alot less likely as the metals structure of the two aren't then really compatible anymore.

Cold welding is definately an issue to keep your eye on (it happened on one of my rearbeam bolts once) but with some care it is not an issue that prevents adjustment with the wires in the arms.

Cold welding is pretty much related to :

-1- Cleanness of the threading. Very clean (and new) threading will more easily cold weld.
-2- Stress on the threading. The higher the stress the easier is will cold weld.

With these two things in mind I made sure that my threads are well greased up with (in my case) silicone grease. I do the same with my beam bolts when they are very new. Of course the grease must be water proof.

Also my turnbuckles are not highly loaded because the size I'm using are designed to take alot higher loads then my diamonds have as pretension. Then I got more then a few turns on them so the load/stress per turn is pretty low, certainly significantly lower then when using only a nut.

Additionally my diamond wires costed only 50 Euro's the pair including turnbuckles so if one ever seizes up I just cut it off and replace it. In the past I choose to take the risk, have been working it for 2 years now and it has not seized up yet.


Geoff, I have a true aluminium base plate casting. Alot of AHPC A-cats are coming with a much thinner stainless steel plate. So in my boat I could drill tapered holes in the base plate but I guess that is not possible with the stainless steel plates.





Anyhow, the best to use is what AHPC themself are using on the Capricorn. The terminal that goes throught plate is a T-end terminal. Its head will rest on the bottom of the base plate and because the diamond wires are slightly angled the T shape will keep the terminal from turning as long as the diamond wire is under tension. Think about this. Additionally you can decide to more or less glue it into place by adding some silicone sealant, glue or isolator like duralac. You don't need that much holding force there.

I couldn't get these T terminals when I had my diamond wires made so I just decided to use plain fork terminals, the fork acting as a T-head somewhat. Of course these forks have a pyramid shaped widening of the stem before it shapes up like a fork. So I just used the head of a larger drill bit to taper my holes accordingly. Now the tension in the diamond wire is magnified by this taper to a much higher surface tension on the pyramid shaped widening that is also has a larger radius from the centre. This appears to be more then sufficient to just jam the fork terminal in the base plate and work up a large holding torque. I have never had any fork turn on me.

Either way you do it, I think, you'll be fine.

My turnbuckles are very similar to Ronstan RF220 for 3 mm wire diameter. These weight 95 grams each (less the 1/4 of pound) and have a breaking load of 1630 kg (over 3500 pounds). This means they have a garanteed working load of some 800 kg at the minimum (over 1700 lbs). I don't believe my diamond wires tension ever goes over 200 kg (over 450 lbs) so I think my setup is well protected agains cold welding. In the ronstan catalogue it also describes how one part of the turnbuckle is SS of the 316 variety while the main body is a high grade brass based material so the dissimilarity between the materials protects the turnbuckle from cold welding.


Additionally I was more then willing to accept 200 grams (1/2 pound) extra weight in order to have easy adjustment of prebend and diamond wire tension even when the sails are up. Also I have a much large range of adjustment and is really nice. I can tell a few stories of boats running out of threading on their threaded terminal/nutt setups and what do you do then ?

Those 200 grams additional weight won't loose me a race when the wrong prebend for the conditions might. I also think this setup looks very clean as well and it won't take away from the general feel of "simple and clean" that your A-cat has. I much prefer this setup to a large turnbuckle on the front of the mast.


I hope this all helps you.



Wouter

About loosing up the wires from the arms, it will be working with Wouter but my advuse will always be : take the wires of the arms. You have better control over what you are doing and when the housing of the turnbuckle is stainless and there is only a slide deforming or on the thread or in the housing or you are not turning the rightway you will have for sure a problem and to prefent this it is always better to take them loose. When you are using your hands by turning the buckles you can feel what it is doing and you always feel if there is a deforming on the thread, when you are using tools you can put much more force on it so you can damage things and you do not feel it.It is only a 1 minute job and it can save you money and it is more acurate because you can measure better the lenght you want to have.
And why should you add 200 grams extra and if you are doing this 10 times you have already add 2 kilo's to the boat which is maybe not needed.

Thank you Hans and Wouter for the information.

I didn't mention it in my first post, but I stripped the threads on one of my diamond wire terminals yesterday while turning the nut under tension. So I am very interested in the cold welding discussion.

I want to be able to sail this weekend, so I am hoping that cutting off the stripped terminal and swaging on a turnbuckle similar to Wouter's will get me back on the water fast.

Geoff

This typical of the threaded terminal and nut setup. And it is also one of the reasons I changed the Taipan design in this respect when I build my own F16. I'm not the only one, several others have done so too. The biggest validation of this setup came when I saw that the AHPC Capricorn F18's were using it as well.



Just make sure you get some well designed turnbuckles and you'll be fine. Cold welding can largely be prevented by making proper design choices.





I'm sure of it. Another big advantage of the turnbuckle system is that even when a dummy misreads his ruler and cuts it off too sort then the much larger range of the setup can correct it again.

Wouter

The turnbuckles are installed. I think they are working fine. I didn't have as much clearance as you did between the mast and my downhaul cleats, so I had to remove the bottom lock nut. I am hoping the top lock nut will be sufficient to keep the turnbuckles from rotating while sailing.

You can even use a tie wrap or small diameter line, lead through both turnbuckle openings, to fix the turnbuckles in place.

Wouter