Bergstrom & Ridder Rig Problem

[CAM]

1st, how does the boat balance while sailing, with the current rake? I suspect most folks with in-mast furling don't care about a well tuned rig, but if the helm is light or neutral now, raking forward could make things very unbalanced.

2nd, you seem to be using rake and prebend interchangeably. You *should* be able to remove lots of the prebend without changing the rake through adjusting the D's, mast step, and partners. Most swept-spreader rigs need some prebend, but you may be able to tune some out for the base setting, and allow the topmast backstay to be used for upper-range sail flattening. It would need to be eased during furling operations, naturally. For a new boat, the rig designer should have prebend numbers for you.

Significantly changing the prebend will likely require a trip to the sailmaker for a luff curve recut.

[Mark Prymuszewski]

Cam,
Thank you for your response. I spoke to the captain and he said the handeling was pretty neutral. There is no adjustment in the backstay and once the rig is set there is no further adjustment. The captain said there is a small amount of adjustment at the mast step. Not really enough to effect the rake of the mast. The issue is the pre-bend destroying the mains'l furling motor and the mains'l itself. I apologize for not being clear on that. The sailmaker has the sail and needs to remake it anyway and is waiting to for us to determine the pre-bend first. There is a warranty issue with the owner and the designer so pre-bend numbers are not available. I will have to do this from scratch. The mast is currently on the hard and we have a chance to make changes to the rig tune now. What I have read about the B&R rigs say the pre-bend should be 1% of the mast length. What we have now is much more than that. Is changing the fore stay length still a viable option? The captain told me that there was no sea trial after the launch and the only thing done to the rig since the builders touched it was tightening the fore stay. He said there was about a meters worth of flex in the stay when under sail. I will try to take the prebend out of the mast with the D's. It will be an experiment from the start because nothing seems right. The captain said there was quite alot of movement in the spar before we got a hold of it. Pulling the pre-bend out would seem to loosen the rig more. It is quite a mess. Any further thoughts would be appreciated.

[davidsamuelson]

I believe that in-mast furling, pre-bend and, to a lesser extent rake do not belong together on a boat unless you are looking for the eternal problem. David

[Brion Toss]

Hello,
I have been around this barn a few times. The B&R is meant to be bent; that was Lars' intent. But the demographics of Hunter ownership has slid things almost exclusively into in-mast furling, which is most intolerant of bending. The standard recommendation is less than 2" of bend along the entire mast length. This is a fairly arbitrary number, but you get the idea.
Getting a sufficiently straight stick is tricky, at least if you want to avoid overloading some of the components. There's way more to this than I could possibly go into here, but the short form is: back everything off, and gradually work up the opposing wires -- some are trying to induce bend, some to arrest bend -- keeping the stick as straight as you can without exceeding 10% or so in load on anything. And keep clear of whoever "tuned" this rig in the first place.
Fair leads,
Brion Toss

[Joe Henderson]

Dear mark,

I feel for you and the skipper!

In- mast furling, a bloody good idea on paper!

I had a similar tuning problem way back in 1973 when I was presented with what must have been one of the first B&R rigs to have been made by Kemps. Two spreader, deck stepped on an IOR one tonner, nowhere near as big as yours, it must be said.

Neither Kemps nor the owner of the boat knew what was needed and I was only 17 and two years into my apprenticeship when I was thrown in at the deep end with this funny looking rig that none of the other riggers in the loft wanted to touch.

Not knowing quite what I was doing, I did no pre-tensioning prior to stepping, just connected everything loose as per S.O.P. and then, with the rig in the boat, I found that I just could not get enough pre-bend in it to satisfy the sailmakers, despite what I thought of as the correct tuning method.

I was getting it too straight, completely the wrong end of the stick, so to speak.

What I was doing was tuning the caps and diagonals aloft, the same way as a "normal" discontinuous swept spreader rig, and then snugging-up the reverse diagonals to just take the slack out of them.

This "incorrect" method which produced a straightish mast for me, may work for your mast.

The provision of the backstay would seem to remove the normal B&R tuning requirements and flavour from this rig.

If you have no adjustment on the backstay, I would suggest fittting an hydraulic ram.

Then, as Cam says, you can load up the forestay for sailing and. hopefully, get a bit of bend in the rig to help the main's shape and then release the backstay to straighten the mast for furling.


Regards,

Joe Henderson.