Does Anyone Have A Rig Tuning Guide?

[robertsapp]

Specifically, I'm looking for a rig tuning guide for a B&R rig Z-spar furling mast. This is for a 1997 H376. I'm trying to find out exactly how much prebend there is supposed to be in the mast. I know it's not as much as you would set in a conventional mast.

 

[Dan Johnson]

Robert...

Here's what I have for tuning the B&R rigging...

 

[robertsapp]

Re: Robert...

Thanks. This is pretty much the same general guidance that's given in owner's manuals, so it's not the specific information I'm looking for that speaks to the limits of mast prebend on a furling mast. I appreciate you sending it along though!

 

[Charles Erwin]

This is a guess but - in-mast furling gear need to be as straight as possible otherwise it will not work or will work poorly. That means you want as little pre-bend as possible.

But you do need whatever pre-bend the luff curve of the sail requires while keeping the furling gear as dead vertical as possible.

Whoever made your sail will have considered this problem and will have cut either very little (maybe no) luff curve in the sail. So - it seems likely that the sail maker that made the sail you are using will be your very best source of information.

Charles

 

[Scott B]

1% is correct, page 51

http://www.seldenmast.com/files/595-540-E.pdf

 

[robertsapp]

1% is correct, page 51

That's too much prebend for a furling mast. Here's what I've learned so far.

The 376, 380, and 386 are all pretty much the same boat and rig, with some evolutionary differences.

The tuning guide in the owners manual for the 380 and 386 both distinguish between the standard and furling mast when setting prebend. It calls for 8" of prebend in the standard rig, and no more than 2" of prebend in the furling rig.

1% prebend on a 56 foot mast would be a little less than 7". That's obviously way too much when the manual says it should be no more than 2".

The 376 owners manual makes no such distinction between masts. I guess it was so early in the life of in-mast furlers (1997) that they didn't cover it in the manual. The tuning guide calls for 4" of prebend.

The 380 and 386 (the ones where the owners manual says to not set more than 2" of prebend) used the Selden mast and furler.

The 376 used the mast and furler from Z-Spar. Same basic funtion but a completely different internal setup. So I'm not quite sure if I can use Hunter's guidance for setting prebend on a Selden mast on a boat with a Z-Spar mast.

Hence my dilemma. I am unable to find a guide from Z-Spar that speaks to tuning a B&R rig with a furling mast. I'll have the mast down and it will be easy to set the correct prebend. Once the rig goes back up, it's going to be a major PITA if the sail won't furl properly and I have to readjust it. So I'm hoping that somewhere out there is a 376 owner with a Z-Spar furling mast who knows the correct answer!

 

[robertsapp]

So I decided to go straight to the source and contacted Eddie Breeden at Marlow Hunter. He replied that you put no prebend in a Z-Spar furling mast. His words were "the straighter the better." So I guess I have my answer.

It's good to know that you can still get this kind of response from the manufacturer. I'm so glad we own boats from a company that's still in business and able to provide support.

 

[Scott B]

So I decided to go straight to the source and contacted Eddie Breeden at Marlow Hunter. He replied that you put no prebend in a Z-Spar furling mast. His words were "the straighter the better." So I guess I have my answer.

It's good to know that you can still get this kind of response from the manufacturer. I'm so glad we own boats from a company that's still in business and able to provide support.

Very good information. Never thought to contact Eddie, he's been very helpful with inquiries in the past. I stand corrected.

 

[Franklin]

Sorry...late to the conversation but thought I would add my 2 cents:

It is true that not only does the manual not talk about inmast furling main when talking about tuning it, but later it does state that the standing rigging is the same on both the standard and furling main masts.

I also want to point out that "straighter is better" is half right and half wrong. The straighter the mast the less problems you will have with furling but the straighter the mast the less stable it is from mast pumping, which is the whole point of the pre-bend.

My furling mast has 4 inches of pre-bend and it works just fine. The only time I had a problem with my current sail is when I put too big of a shackle at the bottom which caused the top to rise too far and get caught on the bolts for the mast head. That has been fixed and all is great now with 4 inches of pre-bend just like the manual says to do.

I came to this thread because of a discussion I had with another Hunter owner who said they are supposed to be different.

 

[JamesG161]

My furling mast has 4 inches of pre-bend and it works just fine. The only time I had a problem with my current sail is when I put too big of a shackle at the bottom which caused the top to rise too far and get caught on the bolts for the mast head. That has been fixed and all is great now with 4 inches of pre-bend just like the manual says to do.

Mine too!

So I decided to go straight to the source and contacted Eddie Breeden at Marlow Hunter. He replied that you put no prebend in a Z-Spar furling mast. His words were "the straighter the better." So I guess I have my answer.

Ask Marlow/Hunter to post that information in their website please, along with the mast designer's detail calculations of mast stress. So if my "straighten" mast cracks from moving stresses, or as...

but the straighter the mast the less stable it is from mast pumping, which is the whole point of the pre-bend.

Marlow/Hunter will pay me for a new one.

There is 2 separate issues here.
1) Mast stress under a beam reach with full sails and gusting winds.
2) Furling the Main sail (little wind in the sail) or minimum Mast stresses.

Here's what I have for tuning the B&R rigging...

That was almost the same as my Hunter 430 manual. My 57' boom to mast head height calculates to ≈5" prebend, yet my total "no stress" bend ≈7". Why? My fractional rigging head sail pulls the mast forward.
This is exactly the same as "pre-stressed" concrete beams. If you look at a "no load/stress" beam, it is curved. Under load the beam straightens. You would not to "pre-bend" so much if you have a "back stay" (oops... B&R rig).
Remember, the entire force, to move your boat, is transmitted through your mast, which in turn, stabilized by your 3 stays.

What does Mast "pre-bend/pre-stress" have to do with furling the main?

With my berthed boat, with its properly furled main, there is 2" clearance between the inside of the mast and the maximum wrapped main sail diameter. Therefore, with my ≈7" bend, there is no, none, nada, zilch, drag by the furling foil/sail and the inner mast walls.

Last thought. Your mast is not circular but oval (fore/aft). The diameter of the mast is much much greater at the deck than at the unfurled leech point.
Jim...

PS: @Franklin and @Dan Johnson this now make at least 5 members that run in-mast furling with pre-bend.