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Oceanis 38.1 mast bend

mxwmxw

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Apr 9, 2021
7
Beneteau Oceanis 38.1 Greenwich, CT
My mast not only has an aft rake it is not straight, it clearly bends backward. There is no turnbuckle on the forestay to adjust it. The shape of my main does not look correct to me. Do other 38.1s have this bend? I do not have the in mast furler.
 
Feb 17, 2006
5,041
Lancer 27PS MCB Camp Pendleton KF6BL
I would recommend including a photo of what you see. From the stern and either side. This way those that have the same boat can give a better opinion if there is something wrong.
 

mxwmxw

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Apr 9, 2021
7
Beneteau Oceanis 38.1 Greenwich, CT
I don't have photos now, I won't be able to supply them until mid May. I'll post them when I can. A rigger did have a look. He measured the tension of the stay and strouds and said they were all in spec. He said the curve of the mast did not look right and the only way to straighten it out would be to cut the forestay. I wanted to do some research before cutting anything. Seems to me nothing should need cutting. This must be an indication something else is happening here.
 
Feb 21, 2013
2,363
Hunter 46 Point Richmond, CA
Ok then, cut OR replace the forestay with one with the required length and install a turnbuckle to adjust the rake to improve mail sail fit.
 
Jan 1, 2006
5,589
Slickcraft 26 Greenport, NY
I wouldn't cut the forestay unless absolutely necessary. It controls the rake of the mast which has a lot to do with weather helm. I can't argue with a rigger but I would look for another way - especially if you think the weather helm on your boat is correct. Maybe get a sailmaker involved.
 
May 17, 2004
3,155
Beneteau Oceanis 37 LE Havre de Grace
Some bend is generally desirable, especially with a conventional non-furling main. How many inches of bend do you think it is? Can you describe more specifically how the main looks wrong? Too much bend would usually lead to horizontal stress wrinkles from the midpoint of the mast back. The main sail probably has a certain amount of pre-bend built in. More bend will de power the sail a little extra. I wouldn’t go cutting anything until you’re sure there really is a problem that you can see visually and in the way the boat handles.
 
Aug 2, 2010
411
J-Boat J/88 Cobourg
Some bend is generally desirable, especially with a conventional non-furling main. How many inches of bend do you think it is? Can you describe more specifically how the main looks wrong? Too much bend would usually lead to horizontal stress wrinkles from the midpoint of the mast back. The main sail probably has a certain amount of pre-bend built in. More bend will de power the sail a little extra. I wouldn’t go cutting anything until you’re sure there really is a problem that you can see visually and in the way the boat handles.
David and others have it correct. In more performance oriented boats the backstay is adjustable to add curve to the mast to flatten the sail and reduce drag. The proper amount of bend is related to how the sail is cut at the luff as well.
 

mxwmxw

.
Apr 9, 2021
7
Beneteau Oceanis 38.1 Greenwich, CT
beside the rake there is a 6 or more inches of bend. When the sail is all the way up the boom does not sit as high as i would expect. so the stack pack and lazy jacks remain tight.
Here she is at the dock, the boom sits in about the same place under sail. Soon there will be two more 38.1s in my harbor so I will be able to compare. I'm wondering if anyone with a similar rig would say theirs is straight as an arrow. I never had a in mast roller, but i would expect them to be straight, so why not my rig?

Screen Shot 2021-04-13 at 4.07.02 PM.png
 
May 17, 2004
3,155
Beneteau Oceanis 37 LE Havre de Grace
A furling mast needs to be straight to accommodate the furling mechanism, so the structure of the mast and the cut of the sail are are pre-built for that assumption. A conventional main is cut very differently, with extra cloth in the luff to accommodate mast bend instead of a hollow there to furl tighter.

Looks like your boom sits pretty much horizontal. I would not expect it to move above that angle once the sail is raised. Having the boom above horizontal would just mean there is wasted area that would be better used as sail.

I’ll defer to any with more stack pack experience to say what adjustments may be possible there, but I don’t think the mast bend or sail are the problem.
 
Oct 27, 2010
115
E-22 e-22 Stratford
mxwmxw,
Do NOT cut the forestay. The 38 and the 38.1 rigs have about 19" of rake designed into it by the Finot, the naval architect. This is why the forestay is a fixed length.

You can measure it by hanging something heavy from the main halyard (bucket with water) when sitting at the dock on a nice windless morning. The halyard will be a plumb bob...measure from this line to the back of the mast at the boom height. Should be 16-19"\
The boom height in the picture looks about right..but that's not while it's flying...so hard for me to really say. Boom height is a function of the mainsail leech length and also rake...

The second issue is pre-bend. From the picture it appears you do not have the 38.1 performance rig...which is a very different rig set up with low spreaders...almost like the old B&R rig in some ways.
So I have attached our mast tuning guide for the more convential 38 and 38.1 rigs. As you have a classic mainsail, the amount of prebend can be adjusted to fine tune the shape of your mainsail. Typically we build ours for about 3.5" of prebend...but if you sail in LIS (as you do) you might tune to have less for a fuller more powerful light wind sail and if you were to sail in SF Bay you might tune it to have more to have a flatter main as you'll be sailing generally in more air. You can gauge your prebend by taking the main halyard to the gooseneck and pull it tight. Sight the line up the mast and at the half way point visualize how much bend there is relative to the mast section. In other words if the mast is 8" fore and aft in length, when you sight up the mast is the hayard about half a mast width behind the mast? If so you have about 4" of prebend. I would be surprised to find you have 6" of prebend...if so your mainsail is probably board flat...ie. no shape in it?

I have also attached our tuning guide for the boat, though it appears yours has Elvestrom sails...so won't really be across the board applicable.

Lastly, you can call me...I'm just up the road in Stratford.
Bob Pattison
Neil Pryde Sails.


 

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mxwmxw

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Apr 9, 2021
7
Beneteau Oceanis 38.1 Greenwich, CT
Thank you for the great info. I just sailed her from the BVI to USA. A few tweaks have fixed some of the shape, but more needs to be done. I'll look you up when I get to LIS