Hunter 37.5 - Bending Mast?

Bill Roosa · Feb 14, 2012

This is the price you pay for the "luxury" of not having a backstay messing up your cockpit area. The R&B rig cannot bend the mast "on the fly" as other rig designs do. this leaves outhaul, cunningham, and reefing as the major ways of depowering the sail.
The mast has a designed bend and the mainsail (at least the one on my 37.5) is cut for that bend. I'm of the impression that the sail was cut flat and the procedure was to add depth as the wind speed lessened instead of the normal concept of flattening as the wind speed increses.

Rick D · Feb 14, 2012

Know of Several...

neilleparkerjr said:
Just bought a 1995 Hunter Legend 37.5. With its fractional rig and tapered mast top, it looks like rigs on other boats that are made to be bent with a backstay adjusting tackle so you can flatten the sail in a stiff breeze. Would seem natural for such an otherwise performance-oriented boat. Yet there's no attachment point at the stern and no mention of this concept in the owners' manual that I can find. On the web I have seen a few, but not many, photos of this model with an adjustment tackle.

Does anyone out there have experience with this? Are the original full-batten mainsails designed for such a set-up? Thanks, Neill

I know of five legend-series boats with back stay adjusters. Three are 40.5's and two are 35.5's. Having said that, when I look at the geometry, it appears that without jumpers stiffening the top portion of the mast, you may lose some effectiveness. Also, when you bend the mast back, it appears you loosen up the side stays, so you would want to exercise some caution. At least that's what it appears from my feeble vantage point. I will probably install one when I re-rig if I can be convinced of the effectiveness. I got used to using them on my 26' T-Bird with bendy fractional rig and even with my 27' O'Day with the light pole masthead rig. Neither of these boats had swept back spreaders, however and the T-Bird had the forward lowers removed.

Rick D · Feb 14, 2012

You could do that, but all the one's I see have a block at the Y and tackle on one side only. You could always run a jumper around the tackle if you didn't want to trust the tackle too much.

s sauer · Feb 14, 2012

Split Backstay adjuster

I have a 28.5 with a B&R rig and long ago added a split backstay adjuster.
I don't have a catalog for the sheave assembly that rides on the split backstay but it has two sheaves on each side and one in the bottom center.
I made up a 10-12' long 1x19 cable with thimbles on each end. Attached a snap shackle to one end to fasten it to the same attachment 'u' bolt at the stern that attaches the starboard side lower end of the split backstay to the deck. I ran the cable up and thru the middle sheave of the split backstay car, back down parallel to the port side of the backstay and attached the upper end of a 4:1 purchase at the thimble with the lower cam cleat end attached to the toe rail.
This gives me an 8: tackle on the split backstay car and the 1x19 cable is right alongside the split backstay so nothing obstructs the stern swim ladder...and it works like a dream.

Rich M · Feb 14, 2012

I'd love to see a picture of the modifications on the 28.5.

Mariner356 · Feb 14, 2012

I own a 2000 Hunter 410. It does not have a backstay. Its rig design is B & R and the rollerfurled mast was made by Selden. I worked with an experienced fellow who tuned my mast prior to stepping on deck. It was "pre-bent" about 15-20 degrees before we set it on deck. There is info out there on how to do this. I would call Selden in North Charleston, South Carolina and they'll be able to tell you exactly what the specs are for your mast and how to do it. You'll probably need two different instruments to tune it as one instrument usually won't tune every shroud on the boat. BTW, You call Selden with any mast question including info on what and where to buy the deck lights that Hunter mounted at the factory. Also, North Charleston can manufacture a boom if you should need one. All this info is from personal experience.

robertsapp · Feb 15, 2012

neilleparkerjr said:
Thanks for the response! I believe, however, that my rig was made by Selden, not B&R. And there definitely is a backstay, with a Y-bridle that attaches to the two corners of the transom and leaves the center open. I figured That if i could take advantage of mast bend, i would add a car with sheaves on each leg of the bridle, that would tension the backstay when the tackle pulls the car down. This would still leave the backstay functional if the tackle fails.

Two comments. First, an observation. The B&R rig is a design, Selden is the manufacturer. Our '95 336 has a B&R rig, and the spars are from ZSpar. Here's some information you might find interesting:
http://www.cruisingworld.com/videos/hunter-tv/the-b-r-rig

Second, a caution. The B&R rig was not designed to use a backstay. You're messing with a highly engineered system, and applying loads that the designers did not allow for. So be careful. You'll undoubtedly find people who will say "I did it and everything's just fine." Good for them. Maybe they're right, or maybe they're just lucky. Only a naval architect could say for sure.

Rick D · Feb 15, 2012

There's Some Confusion

robertsapp said:
Two comments. First, an observation. The B&R rig is a design, Selden is the manufacturer. Our '95 336 has a B&R rig, and the spars are from ZSpar. Here's some information you might find interesting:
http://www.cruisingworld.com/videos/hunter-tv/the-b-r-rig

Second, a caution. The B&R rig was not designed to use a backstay. You're messing with a highly engineered system, and applying loads that the designers did not allow for. So be careful. You'll undoubtedly find people who will say "I did it and everything's just fine." Good for them. Maybe they're right, or maybe they're just lucky. Only a naval architect could say for sure.

The Legend .5 series is a swept-spreader conventional back-stayed fractional rig. It isn't a B&R design.

Rick Sylvester · Feb 15, 2012

Our '85 40

uses an Isomat mast and boom. It is a masthead rig but is also tapered. I just rebuilt it last summer. I would not assume yours is a Seldon since Hunter used several spar manufacturers over the years. It should have markings on it somewhere.

I'd like to make a couple comments:

The B&R design was done both with and without backstays. It can be a B&R rig and also have a backstay. The Bergstrom and Ridder design has more to do with the severely swept spreaders, the inclusion of diamond stays and a pre-bend in the mast.

I seriously doubt you'll bend that mast to any appreciable degree solely with backstay tension.

First of all, the entire idea behind pre-bend is to pre-tension the extrusion to stiffen it and prevent movement (pumping.)

Second, I'm willing to bet that over-tensioning the backstay will flex the hull to the point of doors and drawers not closing. Really bad things could happen. I can imagine hull to liner tabs popping loose. Or worse. Additional backstay tension will make the headstay tighter but I'd want to do a whole lot more homework with people with a pedigree before I'd risk severe damage to the hull. Keep in mind that it isn't just the extrusion getting bent when you apply that kind of force.

As some of the others have recommended I'd consult a quality rigger.

Rick D · Feb 15, 2012

No Diamonds

Rick Sylvester said:
uses an Isomat mast and boom. It is a masthead rig but is also tapered. I just rebuilt it last summer. I would not assume yours is a Seldon since Hunter used several spar manufacturers over the years. It should have markings on it somewhere.

I'd like to make a couple comments:

The B&R design was done both with and without backstays. It can be a B&R rig and also have a backstay. The Bergstrom and Ridder design has more to do with the severely swept spreaders, the inclusion of diamond stays and a pre-bend in the mast.I

The .5 series Legends do not have diamond stays; they are not B&R.

s sauer · Feb 15, 2012

Backstay Adjuster

Responding to Rich M.:
If you are into racing, you should check out the backstay adjuster for flatttening the main and tightening the headstay. The Kenyon mast section on the 28.5 was also used on J-29's and can take additional bend to flatten and de-power the main. Check out the Hunter 28.5 website : www.huntertwentyeightfive.com , go to Gallery / Celebration II / DSC00989 and 00991 to see how the backstay adjuster was set up including a Bimini.
Headfoil, decent sails, wetsanded bottom & folding prop complete the package.

Rick D · Feb 16, 2012

He walks out, scratching his head, wondering what all that was about...

Bill Roosa · Feb 16, 2012

Hey Neill
If you had used your secret wake-up word we would have given you the straight (not bent, get it?) answer. You do have a secret wake-up word don't you?

Rick Sylvester · Feb 16, 2012

I suppose I should've been more clear.

Rick D said:
The .5 series Legends do not have diamond stays; they are not B&R.

I'm sure you're correct but I wasn't saying which boats had a B&R. I was only pointing out that the B&R design isn't defined by whether or not it has a backstay as some of the posters were saying.

kemahflash · Feb 16, 2012

Yes you can use a backstay adjustor

neilleparkerjr said:
Thanks for the response! I believe, however, that my rig was made by Selden, not B&R. And there definitely is a backstay, with a Y-bridle that attaches to the two corners of the transom and leaves the center open. I figured That if i could take advantage of mast bend, i would add a car with sheaves on each leg of the bridle, that would tension the backstay when the tackle pulls the car down. This would still leave the backstay functional if the tackle fails.

I owned and raced a 35.5,37.5, and a 40.5 I installed cascading purchase on the backstay on all of these boats, on the 37.5 I had a 24 to 1 , I could almost turn the main inside out. I started with a stock main and eventually bought a Kevlar main. The ability to bend the mast to flatten the main is real and very valuable for racing. You also will get some tension on the headstay therefore allowing you to point higher! This is not as effective as it would be on a masthead rig but still you will see a big effect. This allows you to run a pretty loose rig for light air but also be able to tighten up when the wind picks up! Even on a stock main it still is good to be able to flatten, stock mains are built flat so with a adjustable backstay tension you can afford to set up the rig as loose and powerful as possible because you can tighten up. If you plan to race you really need to set up to adjust the back stay, a cascading purchase is the best and cheapest way. You have a bridle so go to the end of the single stay and put a beefy block there.then attach a length of no stretch line to the pad eye where the bridle turnbuckles attached, run it up thru the block you attached up at the end of the stay, attach another block to the line you put thru that block. Now go down to the other side of the stern and attach a line to that pad eye, run it up to that block at the end of the line you ran thru the top most block,attach another block on that line. Bring that down to a cam cleat. Now because the purchase doubles every time it turns thru a block you have a 10 to I purchase, do it again and it's 20 to 1. Etc best racing add on besides a folding prop. Sorry for the spenlling