There is definitely a trick to getting the centreboard in or out while the boat is on its trailer. So before I forget (and to remind me next time) this is how it went back in…Continue reading
Following on from my previous post I’ve added angle brackets to the top of the clamps.
The plates were bending under clamping load, so these brackets allow much better and more reliable clamping. I’ve also painted the welds.
One widely used way to extend an aluminium tube is to use a wooden topmast. This way we get the strength of the aluminium where it counts and we can use wood where the ability to taper is more critical.Continue reading
Here’s an idea for a simpler wooden mast:
|Item||Height above heel (m)||Notes|
|Circle base||2.4||70 diameter|
This mast uses rectangular sections at the base to provide the strength. It gradulally transitions to square section, then circular sections when possible. The rectangular and square sections next to the sail aren’t ideal – the junk rig works better on a circular section mast as this allows the sail to rotate freely. However this design would be easier to make.
I’m not going to show the strength calculations here. If you want more detail please ask!
Weight isn’t too bad. Adding up the weight of each mast section we end up with 10.3kg.
A couple of extra points:
Finding suppliers for tubes that will definitely fit is proving harder than I expected. In particular I’d like a 70mm diameter by 3mm wall thickness tube for the main tube, as this should fit a 2 1/2″ inner tube with everything at its nominal size. However 70mm is very close to 2 3/4″ so 70mm is hard to find.
I’m also struggling to find suppliers who will measure what they have in stock.
Adjusting the size
I found a discussion on using Car Exhaust Tailpipe Expanders to adjust the size of an aluminium tube. Neat idea but rather scary – I’m not sure what that would do to an aluminium extrusion with a T6 temper.
- It might be possible to make the internal diameter 0.1mm larger, should that be necessary;
- I could always wrap abrasive paper around the tool and use it to make the internal diameter larger using an electric drill on low speed.