VIC
741 posts
I got an old 460 mast from a friend, which I suspect had been cut down.This in turn snapped again near the base so cut down again to 400cm. I've been using this mast on my smaller sails 5m and down and after doing some internet research i'm a tad concerned. Most people say you should only cut approx 20cm from a mast not the 60cm I've had to cut. What do people think. I'm getting a tad nervous when I'm offshore now not knowing whether the mast is a potential timebomb.
for peoples reference: Kilwell 460 carbon 30% original spec.
QLD
7436 posts
Boy! If its 60 cm shorter then its probably got the stiffness of a 490 ie IMCS approx 29. You could measure it using the standard IMCS test to confirm this. In a 400 that kind of stiffness may suit one of those old Gaastra F1s but no other sail on earth. Heavy too. It must be God awful. I suggest you borrow a decent 400 and take it for a test sail. My guess is you wont want to give it back.
QLD
7436 posts
ARgh. Got that wrong but true in principle none the less.
VIC
741 posts
funny, i'm using that mast and have been rigging an arows impact 5.0 m and its rig well. loose leech between 2-3 battern and good twist... feel ok to me but don't have an comparison...
WA
12885 posts
Cutting the tip off the mast increases it's stiffness, but cutting the base off doesn't.
Cutting the base off, creates the risk of the boom being in an unreinforced area, especially if you're tall and have the boom high.
I have killwell 70% carbon, these are unground and the boom reinforcing area is visable, if yours are unground you should be able to see if there's a problem or not.
Not sure if we can assume the 70% and 30% are constructed the same way, but I can measure where my 460 reinforcing is if you like.
WA
8894 posts
Watched some of the International Pros recently cut down masts(even helped one) to fit their new sails they were using as they didn't have the right sized mast.
They cut from the base. It is also important to clean up any imperfections in the cut by cleaning up with a file and sandpaper
Alby
VIC
741 posts
cheers decrepit... If I could get a rough idea where the boom reinforcment is meant to go I'll look at giving the mast a bit of a beef up in that area..
WA
12885 posts
Boom reinforcment starts 900mm from base and goes all the way to 1880mm from base, there's 1.25 laps and it's tapered so that a stress point isn't created.
What hasn't been mentioned of course is the base reinforcment!!!!!
Even more important, that goes to 270mm and is 2.25 laps, again tapered. So that start of first lap is 220mm from base, and end of last lap is 270mm.
What I can't tell you is how thick each lap is, looks more than 100gm cloth guess it could be around 200, may be more. Probably a good idea to err on the side of safety, I'd give it a good few wraps.
You'll probably find it's not that easy to do, I've reinforced these masts, where the boom has started to wear the outside layers, it's very difficult with wide cloth, you can't keep an even tension over the width and you get loose spots, if it's going to do any good the fibers need to all be tight. The base area can be done with narrow strips because the strength there is only stopping the extender expanding the tube, so the fibers only need to go around the mast not along it.
The boom area is different the reinforcing is stopping the boom clamp crushing the mast as well as taking the bending tension downhaul, so you also need length-wise strength.
So good luck with hope you get it to work.
I've got a good finish by wrapping a plastic strip (about 100mm wide) around the fiberglass/carbon nice and tight after it's wet out.
