I am building the 3-in-1 boat.
I found some 2" scrap aluminum tubing, but the inner diameter is about twice as thick as what is called for in the plans (.125" inner diameter). Is this a problem? Is the added weight (probably twice as much as expected) going to rip the sail apart?
If so, should I choose a smaller diameter for the boom and leave the mast at 2"? They also have 1" aluminium tubing, which, obviously, weighs the correct amount, but isn't as wide.
I would go for the 2" tubing, even with the thicker wall dimension, if you can't find the specified tubing. Your mast is the second to the last thing you want to have to worry about (the first being a breech in the hull :lol: ). It isn't THAT much heavier, once cut to size.
I'm only a little worried about the mast. Since the weight is basically 16 feet in the air, it should create a little bit of extra moment which should make it harder to stay upright, but that's probably not much of a big deal.
The bigger question is the boom. It's 12' long, and doubling the weight might create a change in the sail performance. I'm just not sure how strong 6 mil poly really is I guess. Instead of a total of around 6 pounds for the boom, I'm looking at 12. I guess I'm also not sure how much stress is put on the boom as compared to the mast; seems like it would be less.
The mast takes a fair bit of stress mainly from the weight of the rig. The gaff and boom could quite probably be fine with lighter tube. A Sunfish rig uses quite small tubing for those.
On my MiniCup - which had basically the same rig - I used the same sized tubing for everything but I was lucky with the supplier. I know as well that for the Triad, which has a very slightly smaller rig, that the Stevensons specify wooden spars.
I did find the correct weight 2" tubing for the gaff and boom. The problem is they only have them 12' long so I need to stick with the heavier one for the mast.
Thank you for your help!
Hey Ron,
I'm glad you were able to find lighter tubing. Never fear little variations in weight, these boats aren't really engineered to exacting specifications... Thank Goodnes, or I would be doomed!
As long as your rig weighs less than you do, you will always stay at the bottom if you just let the sail out when she starts to tip.
Just a heads up, the 6 mil visqueen is part of the old design, the Stevenson's recomend using polytarp, they just never reprinted the plans for the small boats (I had to ask for my Skipjack, those were designed with visqueen too) Just something to think about if you haven't bought the visqueen yet (if you have, don't worry, it worked when they designed it, it will work now)
Good luck, and have fun!