Anonymous wrote:

I know that Mingming II, a larger boat, has a 200mm mast, but can't find the size of the original Mingming's mast (Eric A will know).

Mingming mast :

-diameter at mast head 60 mm

-diameter at foot 100 mm

wall thickness at foot : 3mm

the inside tube seems to have a thickness of 1mm

Mast lenght : 8,25m

Partner tube outside diameter 130mm inside diameter 105mm wall thickness 10mm

Partner's stainlesssteel  reinforcement plat parts thickness 4mm tubing diameter 25mm

Distance from the center of the bermudian mast support to the middle of the partner 370mm.

Mingming is a Corribee that has been changed to Junk rig. The mast is in the middle of the forward hatch. The hatch was replaced by a cover and reenforced by a heavy tubing that is fixed to the side of the coachroof. (see photo).

Roger has a rather conservative sailing but Mingming mast survived to a full capsize (mast down and keels up) bare pool while Mingming was rolled by a rogue wave.

Mingming mast is chambered (there is an other tube inside the mast at partner level).

I hope it helps.

Eric

I've found this...looks like it could work.  It's 7m tall in total, 3mm wall thickness, tapered starting 2.8 m from the bottom, from 145 to 76mm dia, so would need a small extension according to Arne's sketch, which I think is 7.7m in total. I don't know how the access door would affect strength.  I could weld it to seal it and strengthen that area.

- Jes

Jes, it would be a pitty to buy a mast weakened by any holes. Even if welded shut, those areas will be where fatigue appears first.

It might work for you to directly contact that supplier, and ask them if they would sell you the raw mast - of a production stage, where they did not cut any holes yet. At least, that worked out when I bought the mast for Ilvy. It was cheaper, too.

Cheers,

Paul

Any holes in a tube, or anything other than an entire round tube,  is less than optimal for an unstayed mast - fatigue cracks always start and propagate here. I would only use the length above the access door. But at 145mm dia, there's a good chance that it will fit into a 6" x 10 swg (152.4 x 3.2mm) tube, using the top 4 metres as a topmast, instead of timber. 

When David Tyler speaks, I listen, in particular about mast scantlings for offshore sailing, where I have no experience to speak of.

The term Jester Challenge was also thrown in by Jes, and I realise that I should be a little more conservative when suggesting a mast section for this sort of sailing.

In my Chapter 6b of TCPJR articles, I recommend keeping the wall thickness between 2.5 and 5% of the mast’s diameter. Now I tend to drift towards the lower end if possible. The problem in my world is that I cannot just dream up a mast section, and then have it. I must pick tubes from what is available, so have to compromise.

The fact is that older British junks from the eighties and nineties had very thin masts, probably with quite thick walls. Some of these masts appeared to hold for over 20 years, and then suddenly snapped due to fatigue. Photos of these early rigs in use clearly show quite some mast bend, even in moderate conditions (photo below). In contrast, the mast of my 2.15 ton IF Ingeborg (Ø150 x 5mm 6082T6) doesn’t appear to bend at all, even when dipping her toerail.

From a windage perspective, I am not so afraid of increasing the mast diameter with thinner walls. I have had quite stout wooden masts (Ø250mm on my Johanna), and it worked well enough. However, I still try to avoid building taller masts than strictly necessary. Just imagine what that top metre of the mast does to increase whipping as the boat is dancing about in an offshore gale.

Arne

( see last page of JRA-NL 20 or my Member's Album, Photo Section 8-17)

May I come in on the mast size, Jes?

My preference for offshore sailing was to go for a larger, thinner wall section, so as to get more stiffness for a given strength. Particularly in tidal overfalls, a mast that whips around is most unpleasant. My last boat before I quit sailing, a 22ft 6in Hunter Duette, Weaverbird, has a 177m dia x 3mm tapered aluminium mast, which didn't look too large, and I was glad of its stiffness in rough going. These tapered sections are a little softer than the 6061T6 of a hybrid mast's tube, so for sufficient strength and stiffness for offshore sailing, you can certainly come down to 152mm dia x 3mm, possibly to 127mm dia x 3mm, but as you mentioned The Jester Challenge, I really wouldn't want 100mm dia of any wall thickness. Dirty weather in mid-ocean causes one to have enough to worry about without the mast behaving like a fishing rod!

I know that Mingming II, a larger boat, has a 200mm mast, but can't find the size of the original Mingming's mast (Eric A will know).