strain on mast

[JeffM]

Broke the mast on my Michalak pram a few weeks ago.  Was taking it into an open bay in 10-15kt winds to see whether (1) how it would handle the chop and (2) how dry I would be behind the dodger I made for it.  Running along at up to 5kt (who said this hull can't plane?) my crewman heard a cracking sound.  We hove to, jiffy-reefed, and continued.  (Only because I had a little motor, mind you.)  Maybe 10 minutes later the whole thing went into the water.  We made it back okay under motor, the mast the only casualty.

Now I am making a new one: 2" diam laminated from pretty-clear pine 1x3.  I got the clearest I could, pretty muck kept the knots out of the lower end where the leverage would be greatest, and staggered the knots as best I could.  Even so, the mast will be a bit stronger in some directions than others.  Not wanting to loose another mast (especially since I don't usually carry a motor on this little boat), I am wondering what the orientation of the greatest stress will be.  Is it likely to be greatest reaching?  close-hauled when the sheet forces multiply the stress?  Maybe it will be greatest downwind since I wouldn't feel the need to ease off?  By the way, it's a balanced lug rig.

PS: it also occurred to me to wonder if the mast wouldn't be improved by a layer of strips of 6oz glass running lengthwise.  (It would mean thinning the mast a bit to make room for this in the step & partner.)

[JeffM]

Actually, Ray, I toyed with the idea.  But a wood mast is pretty, 'specially on a traditional hull carrying a traditional rig.  Besides, Online Metals won't ship tubing over 8' long except by common carrier--kinda silly expense for one piece of aluminum.  Or even six (which is why my cs20 mast sections are all 8'). 

[PAR]

On a free standing lug mast, the partner and just above/below it will be where the most strain is. Orient what you feel are the stiffer sections fore and aft, because close hauled will be the biggest test. It'll still spill wind with leeward bend, just not as much fore and aft.

Regular 'glass will not add much stiffness to the mast, unless you use a lot of it. Biax will add some stiffness and conform better. A spiral wrap of 6" six ounce biax tape, one in each direction will do a good job of stiffening up the stick. I don't think it's necessary, but it will help.

You original mast likely broke from an unseen internal defect, located in an unfortunate spot. Since you've taken steps to insure the lower portion is relatively defect free, you'll probably have good service from the new one.

[JeffM]

Thanks, Paul!  I'll orient accordingly.