Backstay length question Ker 46

[mad]

FFS, get some info from the designer and or Spar builder before you start playing around any further!!

At the very least, get a decent rigger in, especially as you're not sure about the function of mastjacks and shims.

Either somebodies gonna get hurt or worse or at the very least, its gonna be expensive.

 

[ericrayl]

Thanks all for your thoughts, even the "don't be an idiot, hire a professional" which is exactly what we'll do for starters.

 

[french do it better]

one important thing: the mast and standing rigging were designed to be used with ALL mastjack shims in place, vene if you don't want to use the jack to tension the rigging.

on a 46 footer this is going to be something like 50mm + or - the fine tuning shims

sailing without the shims on will effectively make the backstay look 50mm (there goes your 2") too long

 

[Two Tone]

Don't go sailing and adjust the bottlescrews under load!

Having done plenty of miles on the boat, not using the mast jack is a good way of trashing the rigging screws! We would adjust the shims upand down from a base setting depending on the wind strength, that is how the system is designed, once we has the rig setup then nothing was really altered. The only proviso to this was if doing a v long offshore then the rig would be thoroughly checked and as it was normally setup pretty hard (don't want to be low on rig tension offshore and adjusting the jack offshore is a no no) then perhaps the D's were slightly tightened to allow for an increase in cap tension whilst keeping a straighter rig (you can reef offshore, not so much inshore).

I would suggest contacting the Broker/Previous Owner for rig tuning information - it exists and infact I am amazed that there is not something in the chart table, the rig tune was done in conjunction with the sail designer and the yacht designers and was tried an tested over 1000's of miles...

 

[markvannote]

Oh boy. So, firstly, your mast was designed to have bricks under the mast butt. In the case of the Ker 50 mast we made there are 63mm of bricks under the mast. It is pure luck that you were able to get any acceptable tension on the shrouds to even go sailing without them. The biggest issue is that without bricks under the mast to get the mast within a certain range of that height the spreader dihedral is completely out of spec and most likely creates a horizonal bow in the spreaders which greatly affect the safety factor in compression, so on and so on.

If the boat is in Seattle I would HIGHLY suggest giving Chris a call and hiring him to tune your mast as well as working with your sailmaker and spar manufacturer to set up a general tuning guide. If the mast is a Hall it was probably built over in our BV factory. I will be able to get the jack load sheet to obtain a base setting.

I would not sail this boat until this work is done. Also, it would appear your rigging lengths are fine and should not be adjusted.

Thanks.

Mark

 

[left hook]

You just can't write this shit.

 

[Monty]

Sounds like the rigging is fine. You need to put the shims in under the mast. your mast is essentially 2 - 3" lower than it should be, thus making the forestay and backstay slack. I shudder to hear that you are sailing with full backstay and no shims. It would be very wise for you to go and check the spreader roots in case they have cracked. I dont know who is available locally but it is wise to get a local pro main trimmer, or sailmaker to have a look. Riggers also if they have experience with this type of rig.

 

[Marko]

Dave lenz at north uk is a world class sailor and did a lot of time on this boat when she was hot. Drop him an email. Alternately Peter Bresnan built the boat when he ran vmg racing. Now with one sails Spain. Sure you could google either.

 

[ericrayl]

I was hoping to let this thread die, as my initial description wasn't that great and then I really forced the thread downhill when I wrote no shims were being used. What I should have said is no shims have been changed since the boat was set up stateside.

I got with Chris Tutmark today and we went at it. The cap shrouds were too loose, not by a lot. The D1's were way to tight so that 's a big part of the mast bend being so inhibited. The D2's are too tight as well and I'll fix that next time I'm at the boat. We moved the mast butt back a bit as well to induce some more mast bend down low.

The backstay is indeed too long to get the proper mast bend, even with the full shim stack in and the headstay turnbuckle dialed almost all of the way down, so we'll make a shorter cylinder to backstay tether.

I've reached out to 7 or 8 folks who were associated with the Fair Do's program, and gotten 3 replies. One of them had some rig tune info which was good but not complete. Anyway, we now have a recipe of 5 shim stack heights that make sense with respect to mast jack lift off pressures, and V1 to D1 load ratios that should be right across the wind range. Chris was great to work with, anyone who knows him already knows that.