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dorgan

Too much mast bend?

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How much should a mast bend under no load? When does it become a problem?

This is an older model Beneteau first 30 with a cascading backstay system. The mast is an Isomat NG-37. As you can see in the picture from the base of the mast, there is at least 100mm of bend when you hold the main halyard taut.

When I loosen off the backstay the curvature in the mast does not change. So the mast has undergone some permanent deformation. When we're beating upwind with a few waves the mast does not appear to be flexing significantly. Shroud tension seems not to be either super tight or too loose. When going upwind, the leeward cap shrouds are less tight but still have enough tension not to go slack.

Not really sure how this could have happened to the mast. It seems that the PO may have been playing around with the baby stay because it is still hanging there at the base of the mast. The bend is also causing the cap shrouds to rub against the aft part of their slot at the top of the mast. It has obviously been like this for a while as you can see from the galvanic corrosion. This might not be due to the mast bend and could possibly mean that the spreaders are not original. I'm still trying to piece together the mystery. 

Is a bend like this some kind of sign that there was an accident with the mast in the past? Is this amount of curvature just a disaster waiting to happen or is it pretty normal for older masts to take on a bit of bend? Maybe I should jury rig a checkstay around the spreaders and crank the mast back into shape, but maybe that could make the bend pop out the other way instead...

IMGP3839.jpg

 

IMGP3842.jpgIMGP3839-2.jpg

lines.jpgIMG_20180421_124055.jpg

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i imagine that the prebend is due to tension on the cap shrouds. even with the minimal spreader sweep you have it wont take a huge amount of tension to achieve the bend you have there. You can test this by marking the cap turnbuckles with tape and slackening some tension off. Or dont bother, it looks perfectly fine. Nice boat.

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How's the headstay feel?

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Were is the cap shroud attach fittings. should there not be a internal tang ball fitting in the slot that the shroud is running thur. where is the shroud attached does not look right you have a DIY botch job. that is why it is wearing on the slot. 

https://drive.google.com/file/d/1ZA0-4v6IIXpDGlmWBgVWfTVwCq3JpGzf/view see page 22

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30 minutes ago, Overbored said:

Were is the cap shroud attach fittings. should there not be a internal tang ball fitting in the slot that the shroud is running thur. where is the shroud attached does not look right you have a DIY botch job. that is why it is wearing on the slot. 

https://drive.google.com/file/d/1ZA0-4v6IIXpDGlmWBgVWfTVwCq3JpGzf/view see page 22

No, there should not be.

Isomat spar the shroud terminates on the mast cap, slot in the mast is for the wire to pass through. I saw a rig the other day with the same slight wear marks.

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Most boats that have a rig with swept spreaders have some prebend.

Depending on the amount of the sweep.
My rig has 24 degrees I think and I have around 3" of prebend to keep in column in light ait.
We use runners and checks all the time except in > 5 knts of wind.
I'll try to get you a shot.

You need upper tension or you rig will fall to leeward. tension gives you prebend and then you need check stays.

 

Sorry if you have swept spreaders.

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With the mast raked aft, the shrouds will rub against the cut out in the mast

Go sailing, see if the helm balance needs adjusting. If it doesn't, thank the PO and keep an eye on it as part of your regular maintenance.

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5 hours ago, dorgan said:

How much should a mast bend under no load? When does it become a problem?

This is an older model Beneteau first 30 with a cascading backstay system. The mast is an Isomat NG-37. As you can see in the picture from the base of the mast, there is at least 100mm of bend when you hold the main halyard taut.

When I loosen off the backstay the curvature in the mast does not change. So the mast has undergone some permanent deformation. When we're beating upwind with a few waves the mast does not appear to be flexing significantly. Shroud tension seems not to be either super tight or too loose. When going upwind, the leeward cap shrouds are less tight but still have enough tension not to go slack.

Not really sure how this could have happened to the mast. It seems that the PO may have been playing around with the baby stay because it is still hanging there at the base of the mast. The bend is also causing the cap shrouds to rub against the aft part of their slot at the top of the mast. It has obviously been like this for a while as you can see from the galvanic corrosion. This might not be due to the mast bend and could possibly mean that the spreaders are not original. I'm still trying to piece together the mystery. 

Is a bend like this some kind of sign that there was an accident with the mast in the past? Is this amount of curvature just a disaster waiting to happen or is it pretty normal for older masts to take on a bit of bend? Maybe I should jury rig a checkstay around the spreaders and crank the mast back into shape, but maybe that could make the bend pop out the other way instead...

IMGP3839.jpg

 

IMGP3842.jpgIMGP3839-2.jpg

lines.jpgIMG_20180421_124055.jpg

What year/model exactly do you have?

First 30E (1981-84) Had a cast iron keel and single spreader masthead rig with inline spreaders 

First 30ES had the same hull, lead keel and fractional rig with single swept back spreaders

First 305 (85-??) had the same hull, but a double spreader masthead rig with inline spreaders

First 300 (94-97) has a single spreader masthead rig with swept back spreaders.

your boat looks like a First 30E, but looks like someone “retro-fitted” swept back spreaders to be able to induce more mast bend...

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Take and bend are different things.

some have addressed the bend, probably just fine. The rake might also be fine, and is more about where the CE of the sails are in relation to the CLR of the foils. Generically speaking, more rake means a bit more weather helm. Maybe the PO wanted more helm going upwind? Is the adjuster at max length, or is there an extra link at the forestay tack or top-of-mast?

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18 hours ago, Overbored said:

Were is the cap shroud attach fittings

The shroud terminations look like this:

IMG_20180421_125727.jpg

 

19 hours ago, Alcatraz5768 said:

even with the minimal spreader sweep you have it wont take a huge amount of tension to achieve the bend you have there

Thanks, I hadn't considered that the cap shrouds could have caused much bend really. I'm curious so I think I'll mark the turnbuckles and loosen them off just to see what happens.

 

15 hours ago, Rushman said:

Go sailing, see if the helm balance needs adjusting

15 hours ago, Raz'r said:

Maybe the PO wanted more helm going upwind?

The balance is quite nice when sailing and only when heeled over more than 30 degrees it becomes a bit hard to manage on the tiller. So they did well in that respect. The backstay adjuster is a 48:1 system adjusted to a reasonable tension between slack and too hard to pull anymore. I haven't played around with the tension much while underway because the boat is coming out of a period of disuse and I don't know the state of the ropes. So at the least I would like to add a new safety strap on it before playing too much.

 

15 hours ago, Crash said:

your boat looks like a First 30E, but looks like someone “retro-fitted” swept back spreaders to be able to induce more mast bend...

 I think you've got it pretty spot on. It is the 1984 First 30E with a cast iron keel. That explains the strange placement of the cap shrouds in the slot in the mast. The boom seems to have been shortened by about a foot as well so maybe this was done to counteract the CE moving forwards a bit. Thanks for the info.

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With a masthead rig the back stay won’t have a huge affect on mast pre-bend. It’s really a forestay tensioning tool. How does the main look with the pre-bend you have. Mine is designed for 4” of pre-bend do your mast looks about like mine.

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7 hours ago, dorgan said:

 

 I think you've got it pretty spot on. It is the 1984 First 30E with a cast iron keel. That explains the strange placement of the cap shrouds in the slot in the mast. The boom seems to have been shortened by about a foot as well so maybe this was done to counteract the CE moving forwards a bit. Thanks for the info.

I used to own an 84 First 30E as well.  Other give away that someone put swept back spreaders on an inline rig is to look at where the chainplates are.  In your pic, and on my (most, all?) First 30Es, the chainplates are inline with the mast.  I.e. a straight line drawn from one chain plate to the other would pass thru the mast.  On most boats with swept back spreaders (my J/109 for example) the chain plates are aft of the mast, and a line from one chain plate, to the mast and back to the other chainplate would have an angle equal to the sweep of the spreaders.

You'll note as originally rigged, the boat had a "babystay" to induce some bend in the mast...also helped keep the mast from pumping in big waves with a lot of backstay on.

The First 30E also has on IOR-ish rig.  The boom was already pretty short.  Hopefully, no one shortened yours even further...thou it looks like maybe they did to clear the bimini???

First 30 E (Beneteau) drawing on sailboatdata.com

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If your chainplates are in line with your mast you will always get a bent mast if you use angled spreaders. When you tension the stays the spreaders will push the mast forward. Normally (when the chainplates have as much angle back as the spreaders) you can counteract this by tensioning the lowers. Since your lowers don't pull backwards they have no effect on your mast bend....

edit: Just looked at your pictures again, and judging by the red line you drew the stays are perfectly straight and have pushed the spreaders (and mast) forward.

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Not sure if you did this or not, but in the photos it shows a snug topping lift with a snug mainsheet. Did you take the weight off the boom? When I tune a rig the boom is on the deck or resting on a rigid vang

 

WL

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