Mast stiffeners

What are you guys using for mast stiffeners on the windsurfer composite masts?

For standard diameter windsurfer masts, the maximum length of 48mm x 3mm wall aluminium that will fit, before the internal mast diameter tapers. (knock out the plastic or foam plugs that are up the mast first.)

Some slightly smaller diameter masts we have to use use 45mm x 3mm.
All glued in with "roof and gutter" silicon. ("No more gaps or liquid nails", wont dry in the enclosed space and was still wet 3 months later.)

Make 4 cuts into the sides of this new stiffener, 150mm down (90 degrees apart) to make flexible fingers so as not to have a stress riser. Deburr the sharp edges.

The alloy we have used is softer for bending and after a few years it does take on a curve, so we are now looking at using a higher tensile scaffold tube.

This let go this weekend after 2 years use. I am using it on my Mini Skeeter with a 82'' runner plank which puts more stress on the mast than the mini 5.6. I'm thinking 1.875'' aluminum stiffener tube. What length are people using?

Not sure about the strength of the scaffold tube yet. Haven't be able to track some down yet. Local fellow is away.

The shortest internal total stiffener length has been 650mm (just over 25.5") including the fingers inside an old fibreglass mast that tapered very quickly at the bottom.
It's curved but still serviceable.

The longest has been 1200mm (4') in a 26 IMCS mast that was 30% carbon.

I have broken 2 masts now at the top of the mast step, (like you) as this is where the max loading is. There is no way the internal aluminium stiffener will come out when siliconed in.
The last mast that broke I couldn't pull the bottom broken bit away from the rest of the base as there was still a collapsed aluminium joiner bonded in, holding it all together. I had to hacksaw it to bits.

I have now followed "Greg S's" lead and gone to internal mast supports on our minis. These bolt on with 4x 12mm cap screws and can be reversed for different angles. The threaded anchor plates welded to the chassis are at 3 degrees and the mast "stems" are from 1degree to 6 degrees. So we can now get the mast to a negative rake to allow for the mast curve and keep the sail low over my head.

The mast can now be shifted up to 350mm for and aft along the chassis in a couple of minutes.

This means the boom can now go to within 100mm from the bottom of the mast if needed. This gets the overall height down as well for a lower CofG. It also means the mast can be wrapped with carbon to get the exact curve IMCS to suit the sail. The leverage on the front of the boom sheeting is also better transferred to a chassis component rather than just the mast with this setup. Centre sheeting doesn't work with the sails we use.

Greg is experimenting and has just 2 screws (through the mast and stiffener) at the very bottom of his mast, just to retain the internal stiffener so it can be removed if bent. So far so good.

This is the chassis I won the West Australian state titles with. I'm a much bigger fellow (108kg) than Greg, so I only have 2 mast anchor points.
I use a 6.7m2 sail up to 25knots. Then reluctantly drop back to 5.6mt2 with wind above that.

Yes "Hiko" I've come back slightly with the mast from on top of the steering head for our rubbly local conditions. It was bulldozing the front wheel in the large gusts with it so far forward and a big sail.


In the pic below you can see the 2 internal mast stems drying. They are machined out of 51mm x 31.6mm 4140 hollow bar and pass through a 12mm thick plate before warming it up and welding it. Then 4 gussets are then built up with the welder. The anchor mounts on the chassis are 75mm x 75 mmx 16mm thick flat bar.

If you look closely you can see the top and bottom bearing surfaces that contact the mast stiffener. They are 30mm wide top and bottom of the mast stem. (it's machined down 1mm thinner in between these bearing surfaces so the mast doesn't contact them.)

This means the mast and boom rotate together as one piece. Most of the sail no longer has to rotate on the mast. We use a lot of downhaul.




I have also added another becket pulley to the rear of the boom and another pulley to the rear of the seat.
I have a lot of trouble with my carpel tunnels and this eases the wrist strain.

I also use blue coloured dimpled silicon faced gloves that are bonded onto stretchy fabric ($6 from Bumblin's) The yellow ones are too grippy and the sheet won't slip through your fingers. Now with a ratchet block I can hold a full sheet pressure with 3 fingers.

Cheers Chook

Haven't got to the ski's yet.

I have 3 pair in the shed that "sn" got me, when I first got into sailing and they are still on the to do list.
There is no end to this guys scrounging ability. I'm not sure how you find a pair of snow skis in Perth our hot WA capital city, let alone 3 pair.

Most of the time the Hiko step worked really well, just when I got hit with our coastal gusts with huge sails it pushed the front end down wind when at high speed. It never ever lifted the front wheel though. My mast was adjusted to very upright as you correctly said.

Still busy sewing/altering new to me sails and loving it.
We were out Sunday with gusts to 28-30 knots with 6.6m2 of sail having a ball. Greg was on 5.5m2.

connect.garmin.com/modern/activity/704085186

I can only dream the top speed is true. If you expand the graph you can see it's a phantom reading.
Bit hard to believe I can accelerate 80kmh in 7 seconds.

Thanks Chook. I like your chassis and movable mast step. Burton has been using an internal mast support too for a while. I'm going ahead with the aluminum pipe. I'm guessing that it will suffice.

Hi John,


What was the wind speed (mean & rms) when it broke? Do you think that it was a structural (i.e. overload) failure caused by a gust? or, a fatigue failure from 2 years of use?

I haven't been to Ghost Lake in several years. The population of Alberta is growing faster than the national debt. What once was a long but manageable day trip is now a driving nightmare. Fortunately, now that I have perfected my sailing skis, I don't really need to go there anymore.

Cheers,

Barney

Barney, It was gusty and the ice was sticky. The day before in no wind I was sheeting in and heard a cracking noise. I think the wood dowel just gave up after 2 years. Going the aluminum route now. The stiffener thickness is about the same thickness's and diameter Ive seen in five square meter masts. I just ordered a 20' stick of it today. Should be here tomorrow.