B&R rig tuning take 1

[SteveHughessails]

After what some would call a mild winter for us, which included a lot of reading, I am going to attempt to tune my B&R rig on my 240. I have already had one scare. I ordered a Loos gauge when she was wrapped. I used data form the manual plus a quick look under the tarp to determine what model I needed. I unwrapped her last week and went oh no, that’s larger than 5/32, it isn‘t. Phewww

Step 1: diagonals, I have one spreader with just one upper and one lower set of diagonals labeled D2 and RD1. D2 are not adjustable only the lower diagonals RD1 are. With the mast laying flat across the crutch and pulpit, I can see a gentle bend (athwartship) to the right just above the spreader. I checked all 4 lines with the Loos gauge. All of them are coming in around 4% accept the one lower is a bit looser at roughly 3%. Ironically if I tighten that RD1/loosen the opposite side, it will/should pull that bend out. My goal is to have all 4 diagonals at the same tension with a straight mast (athwartship).

Question: standing rigging lines are tightened to 10% of the breaking strength. My lines are 5/32 and 1/8 1x19. Roughly 2800lb break strength. I have a nice bend in the mast and all is (will be) more or less even. If I go 10% on the diagonals I feel my bend would be too great. Would you be ok with 4%? (It’s a grey area for me).

 

[SteveHughessails]

Answered my own question. 5/32 is 2800lbs. 1/8 is 1700 lbs. I can’t go tighter.

 

[colemj]

I'm not quite sure what you are describing. I'm assuming it is the prebend fore-aft in the mast, and not a side-side bend? If so, then the prebend is set to whatever you need it to be. It's purpose is that a bit of prebend is necessary to stabilize the mast, but the amount after that is set to match the luff curve of the sail. A good ballpark is usually 35-50% of the long dimension of the mast extrusion.

If it is side-side bend, then that needs to be removed by lengthening one side and shortening the other side until it is straight, then putting in the correct prebend by tightening both sides the same number of turns until the bend is correct.

Setting the prebend doesn't require paying attention to the percentage of the wire break strength because you are just bending the mast, so the tension will remain fairly low like you are seeing. Don't worry about the different size wires and their relative breaking strengths.

Setting wire tension to a preset value (usually higher than 10%, but I don't know your rig) is for the headstay or main shrouds (probably called V1 or similar). That is where your gauge will help.

Mark

 

[SteveHughessails]

Thanks for the reply
Athwartship (side to side) above the spreader the mast turns to the right a bit. That’s what I am trying to pull out without going too tight on the diagonals. I’m going to stay with the 4%. This keeps the mast with the same prebend. Once I step the mast I will run a plumb line with the Jib halyard and make sure my mast is standing straight.

If it doesn’t start raining again I am going to go run a string line and attempt to measure the prebend. I agree, lots more detail and need for the Loos gauge once the mast is stepped.

 

[SteveHughessails]

1. Tuning diagonals for equal tension and prebend.
Well that was darn near impossible by myself. I will have to wait until I have another set of hands to help with measuring the prebend. Ultimately I may have better luck once the mast is stepped and I use the Jib halyard to measure side to side and for and aft. I am a tad bit concerned though, if the prebend is too much relaxing the lines to reduce it may leave them too loose. (Guessing)

2. Once I was up high looking down on my string line, the mast actually looks straight, side to side.

Came in just in time, raining again.

 

[colemj]

There should be no worry at all about diagonal tension because you are loosening one side and tightening the other, so it just stays the same.

Mark

 

[SteveHughessails]

I agree, lots of rain here now; no complaints though we need it.

I am confident I will make more progress tomorrow. I was fortunate, I found a small bottle of Boeshield T9 locally. (Bike shop)
Today was a good day.

 

[SteveHughessails]

I spent my time on Wednesday cleaning and oiling all the turnbuckles etc. By the time I was finished doing that, I was 2 beers in and decided not to step the mast.
I replaced one T bolt that was bent on a shroud. There is another one with a slight bend. I decided not to change it (yet) giving me one extra one.

Yesterday I stepped the mast. I rigged the gin pole with the sheets nice and high (long), that let me stand mid gin pole. I pulled the mast up (alone) very easily, what a slick system. I thought I pulled the mast up just enough, time to check the shrouds, too tight. Dang it, I put a 40 degree bend in a T bolt. I replaced it with my one extra. That won't happen again. I loosened off all 4 shrouds and gave the mast a final pull.

I was able to attach the forestay in the proper spot with no issue. I hand tightened the side shrouds and looked at the mast. I am quite happy. Nice and straight to my eyes.

 

[SteveHughessails]

Today I will be attempting to confirm the position of the mast using the halyards etc. and tighten the shrouds and forestay to spec. Gentle concern here though. Everything I have read says, tighten the upper shroud and then the lower shroud. I only have an inner shroud attached the mast (D1) and another outer shroud roughly the same height (V1) attached to the end of the spreader.

I would assume one should set the initial tension on D1 first then V1? Maybe more tension on D1 and slightly less on V1 to not pull the spreader too much?

I am procrastinating, hesitant to measure the pre-bend and rake. lol

 

[SteveHughessails]

OK, attached some open end wrenches to my halyards and was shocked to see them swing out a foot past the mast. I thought, ok this is really dependent on the vessel being level. Not so easy but I believe I got it pretty level. Both halyards are laying very very close to center. The main halyard is close to the top of the mast (of course) and very close to the bottom of the mast with a 4-5 inch ish gap from the middle of the mast to the halyard.

The jib halyard is close to the mast up top (of course) touches the mast down to just below the spreaders then starts to move ahead of the mast. At the bottom it is roughly 4-5 inches forward of the mast.

 

[SteveHughessails]

I checked all of the rigging tension. I was almost on the scale lol. I started with the forestay. I attached the Loos gauge and started tightening. With both T bolts almost touching I was still only at roughly 3-4%. I checked the shrouds too make sure I wasn't going too tight again, roughly 10% ish. I am going to wait until I get advice re D1 or V1 tightening options (post #9) as I don't want to over tighten anything. Chances are I will have to back off the forestay before I tighten the shrouds up.

I am hoping for some advice guidance now.
Now I want to: tighten D1 to 10% then check forestay and set to 10-12% (checking D1 again likely loosening back to 10%.
Then set V1 to 10% and check all again.

 

[colemj]

Does the camera mess with perspective, or is your mast actually raked forward? You don't want that.

Mark

 

[jssailem]

is your mast actually raked forward? You don't want that.

This is a fact that is valid for all boats.

Ease the forestay. That will allow you to increase the aft shrouds.

This is a balancing act. You want the mast to be “In-Column” and with a slight prebend aft of center. It is important to achieve the correct shape even if the numbers are not exact on your loos gauge.

Try sailing then adjust as needed.

 

[SteveHughessails]

That’s her, standing tall. I took another picture from the other side tonight. The mast follows the lines of the manufacturers formed deck/plates.

 

[SteveHughessails]

So maybe I am looking at this wrong. I see the forward lean in the mast and the forward leaning seat the mast sits on. Makes it look fast. I’m thinking if I achieve the right tensions, I will have to shim the base as there will surely be a gap

If I look at the hanging weighted main halyard. I would have to say it looks much better. Changing my thinking to yes perhaps I can achieve a few degrees of aft rake adjusting the tensions.

How/what/where are you guys looking at?

 

[colemj]

This picture. It looks raked forward, but that might just be perspective.

This line drawing shows it with a small rake aft:

 

[SteveHughessails]

Thank you
So you’re looking at the mast itself. I see no pre-bend in the stock image. If I can pull our mast that far back, our main halyard will be over the rudder.

Ok, I will loosen the forestay to the absolute max length. Then I will tighten D1’s to spec then I’ll check rake.

 

[colemj]

I don't understand your comment about the halyard being over the rudder. The halyard comes down the side of the mast - no?

I looked at images of Hunter 240's, and they all had varying degrees of prebend and rake, but none of them were raked forward. At most, it was plumb.

But I would probably expect that if these boats have their masts regularly removed and restepped.

Mark

 

[jssailem]

I’m looking at the vertical angle of the mast plus the bend. When the middle bend is ahead of vertical there is too much. Releasing the forestay and adding a little to the aft shrouds would provide balance. The mast is intended to be in column with a bit of “pre-band” to the upper third.

 

[colemj]

For a fractional B&R rig, the prebend is necessary for stability, and should be centered around the spreader, not the upper third. Prebend will always have the middle of the mast ahead of the ends.

Rake and prebend are independent parameters.

Mark