straighten my mast

[KAIROS]

Hey Forumites,

My mast is bent. It's solid spruce and in cross sectoin is glued up in quarters. It's 33 feet long. It has a bend of about 6 inches to port above the spreaders.....that means a curve resulting in the top being 6 inches to port over the 16 feet above the spreaders. No idea how it got there. When I bought the boat, the upper shroud turnbuckles were wound in to starboard (and wound out on the port side) to straighten that top part of the mast.

I'm thinking 'jumper stays' on the sides of the mast (so in this case 'jumper shrouds') would straighten it so that the upper shrouds could then do their typical job rather than also have to hold that upper part straight. My worry is that these 'jumper shrouds' would make the upper half of the mast too rigid especially since the 'jumper shroud' on the starboard side would need to be kept relatively tight to accomplish the straightening.

THOUGHTS - SUGGESTIONS?

Thanks.

[oakman]

Well Kairos, here is where I think some pics would really help with the diagnosis.

The only input I have for this situation is that taking the bend out with rigging tension can't be good for the hull. But I really don't have that much experience with rigs that need a lot of tension or tuning, I sail an old gaff rig cat which is set up pretty loose by todays standards.

Here is a crazy suggestion: perhaps you could steam the bend out, However, this would probably mess us your glue bonds. Better minds should be along soon.

Good Luck
Oak

[jackster]

KAIROS,

I'm having trouble visualising the condition.
It seems to me that the upper shrouds, if properly installed and adjusted, will keep the mast top centered over the step, and if there is any deformation, it would be a bow in the length.
If there are lower shrouds, they would be adjusted the straighten the mast, but if that were the case, you would know that and say so, hence my confusion. I must be missing something here.

[merlinron]

i'm by no means an athority here, but i would think jumpers are the only way you're going to pull that bend out without an overly-tight starboard upper shroud. over a long period of time, that extra tension will pull the shape out of the sheer( i can't recall what that's called right now). i don't think i'd worry about the upper mast being too stiff, you can always shape the upper by adjusting forestay/backstay tension bias, i would think.
think you are correct in thought about getting the job away from the upper/lower shrouds, allowing them to do thier proper job. it will take allot of stress off the chain plate area. it must be a fairl big mast, so corrections of this type take allot of unnesessary tension and imbalance the rigging.
i'm sure someone with more knowledge will chime in, maybe Ian MacColgin?(sorry for butchering your name, ian, if i did)

[Woxbox]

I'm no expert either, but I can't believe that the force on the rigging required to pull the mast straight is even 10% of what those shrouds see when the boat heels hard over in a blow. I've only worked with a couple of rigs with wood spars, but it seems to me that they rarely stay straight with age. The turnbuckles are there to properly tune it up, which may include a little straightening. But if you can't get it straight, bigger problems may develop, since it will tend to flex more under stress.
As stated, what we really need is a good photo or two.

[merlinron]

consider "roaminaway's thread and the 600 lb. tree on one of the posts. how much do you think it would take to bend that 6 inches.
the loads on a shroud are really almost in collum with the mast. so any increase in tension to move the mast sideways also puts allot into collum as the mast tries to remain straight, up on the chainplates, down on the mast step. one of the purposes of spreaders is to convert all that downward shroud tension into sideways pull against a blow, without them, tension needed would be higher still. they also transfer wind load to the mid section of the mast, which is stronger and the angle of the lower shroud is better situated to handle a sideways load because the shroud angles are further from being in collum with the mast.

[George Ray]

Solid section laminated from 4 quarter pieces.

Hard to imagine that all four pieces agreed find their 'natural set' and the result is what you describe. Seems more likely that lack of care/attention in setting up the rig pulled it out of shape and it took the new shape over time. Having said that it seems reasonable that it can be pulled back to it's original straight shape with the rigging and not over-strain/wrack the hull. The lowers will hold the bottom of the curve in place and the upper shrouds & stay will move the top to straight. Borrow a rig wire tension meter from some racing hot shot person to satisfy yourself that the rigging tension your exerting is not so different/extreme when compared to similar rigs. Don't do it all at once but if it seems an extreme move but do it in steps over a summer season.

[KAIROS]

The Solution:

On the boat, the starboard upper shroud had been twanging taught while the port one was slack. The starboard turnbuckle was wound in to it's limit, while the port was out. Still the mast was curved above the spreaders. The lower part of the mast was in the right position (straight and vertical and centered).

Ashore, with it well supported from heel to masthead, it had a bend of about 8-inches to port, but only above the spreaders. That's 8-inches in about 17 feet.

We rolled it on it's side well supported for it's whole length EXCEPT the upper part where the now upward bend was. For months we hung 75 lbs on the masthead hoping the upper mast curve would be straightened by the relentless force. We had a yardstick for reference affixed next to the masthead so we could see and record where it bent to initially. We expected over time that the solid (actually 4 glued up quarters in section) spruce mast would slowly give in and relax toward straight.

After months of weight on the unsupported masthead, it hadn't budged. The reading on the yardstick hadn't changed one little bit. I was thinking of various complicated schemes - some involving steam.

My friend (a complete lubber) says to me....."how about using an electric blanket wrapped around it covered with a space blanket, where you want it to bend." He'd bent some wood for some lubberly application, and had the impertinence to tell me to skip all that steaming and moisture nonsense....heat alone will relax the wood.

It worked. It was amazing. Sure you can see it work on a stick heated all around over a campfire, but I never held a mast over a campfire.

Imagine the mast laying on sawhorses, the lower mast well supported, weight hanging from masthead, a sawhorse under the upper mast where we wanted to focus the bend. The yardstick was still standing there telling us nothing had changed in months, and when we removed the weight the upper mast would spring back into it's curved shape.

Now wrap a 7-ft section of the mast with the electric blacket, straddling where you want to focus the straightening force (drawing, below). We put a digital thermometer inside the bundle against the mast to keep track of the temperature.

For the first bend we used sawhorse #1 (only, no #2) under the upper part of the mast, so that we were trying to straighten the lower part of the bend. We set the blanket on heat setting 8 of 12, and watched. The temperature inside hovered at about 150-degrees (F). Within 2 hours the weight had brought the stubborn masthead down 3 inches according to our yardstick.

Next we added saw horse #2 to focus on the upper most part of the bend. The blanket was moved so it was nearer to the masthead than shown below.

Tips:
1. Be careful that the electric blanket kindling temperature is not reached....the space blanket apparently really holds the heat in.
2. Allow the mast to cool before removing the weight. It will spring back more if it cools unfettered.
3. The mast will spring back SOMEWHAT after days, in the direction of the original curve. So, you need to 'overbend' it. How much? Good question. Our first 'overbend' concerned me since I thought we had gone too far (how much can you torture a mast?). We just bent it and let it cool then bent it again.

When it is ashore laying on saw horses, it still has a slight bend. By rigging the upper shrouds to the mast as it lay there, we could see that by tightening the turnbuckle on one side 1/2-inch more than on the other side, the upper mast would be straightened. On the boat, this worked as expected.

Now the mast stands straight with only slightly more tension on the upper shroud on the one side. We'll see if it continues to behave.

http://www.yachtflyers.com/forum_images/mast_bend.gif

[peter radclyffe]

i would not apply heat or steam to glue,
unless i wanted to prise a musical instrument or other apart
it may ruin the glues strength

[floatingkiwi]

My mast is the same as yours in material, construction and length. From the top spreaders upward it bends to the side about 4 inches over 8 feet. I am not even worried about it. I know what caused it too. Before I owned the thing someone had put a bondo filled plug under a fitting where and older one existed. Water got in behind it, and rot spores and their immediate and loving family, had their merry flourishing way.
Since repair it has a kink. Most masts are probably not 100 percent straight anyway.

[KAIROS]

My mast...bends to the side about 4 inches over 8 feet. I am not even worried about it. ....Most masts are probably not 100 percent straight anyway.

Thanks for not posting this 2 years ago. My partner Deb would have used it as another bit of evidence of my slipping mind, and the mast would still be bent.

I took the pains to straighten it for several reasons. First, it was straight when the boat was designed and built. A straight mast is not a bad thing and probably better than a bent one. Second, it was an interesting challenge. Third, we were taking care of every little problem we encountered during this 3-year restoration. The completely stripped mast was laying out in the shop right along my path to the car. I had to look at it there, bent and forlorn, for 2 years.

Then, the excitement of seeing how quickly and simply that stupid electric blanket worked was worth it all.

A mast bend that requires one upper shroud to be twanging taught while the other is loose, can't be good. Anyway, we left it a little bent just for you.;)

[KAIROS]

i would not apply heat or steam to glue,
unless i wanted to prise a musical instrument or other apart
it may ruin the glues strength

Good point! There was a thought about this at the time. This is one reason why we kept the heat relatively low....I don't know if 140-degrees-or-so breaks down resorcinol. I'll update the thread if it comes apart (!)

[Peerie Maa]

Good point! There was a thought about this at the time. This is why we kept the heat relatively low....I don't know if 140-degrees-or-so breaks down resorcinol. I'll update the thread if it comes apart (!)

Resorcinol is a boil proof glue, so if you are talking degrees F you are definitely OK.