Wouldn't the 8" tapered pole you were looking at before, cut down to 24', be better than one of the four straight tubes you are looking at now?

I am staying away from the mathematics, but just a direct comparison between that and the 7" straight pole (no. 3 on your list that Dave refers to) it would come out slightly lighter, and with a lower c. of g.  The wall thickness is slightly less, but the outside diameter at the base is greater. And its tapered.

Its actually not that hard to make a mast from two parts. But if you can get a tapered pole which is a little longer than you need, and at a good price - well, I wish I could be that lucky.

The tabernacle will be an inch wider, but if that is a problem then you can make an aluminium tabernacle (from folded sheet aluminium) which may help.

With a proper tabernacle I think raising and lowering the mast is still a practical proposition even if the weight ends up around 35 kg. If it is too heavy for you to walk up into position (it possibly would be for me, these days) there are still ways, with or without a strut (sometimes called a gin pole), to apply a little bit of mechanical advantage and get the job done. Here are some examples of raising the mast on a 22' boat, using various forms of mechanical advantage (trailer winch, block and tackle - not shown here but a small electric anchor capstan will also do the job) - and using - and not using a gin pole. 

https://www.youtube.com/watch?v=Ve8lzTy-7JQ   no gin pole

https://www.youtube.com/watch?v=C5WdqdlB8Nc  no gin pole

https://www.youtube.com/watch?v=w0Sc1e3MXyA  gin pole

https://www.youtube.com/watch?v=l81rwc6-8SM  gin pole part 2

Not one of these guys has a proper tabernacle. A proper tabernacle is an advantage.

The junk rig is at a distinct disadvantage here, because of the mast position being a lot closer to the stem head where a turning block would be. If that turns out to be a problem you just have to figure out a  way around it - in one of the examples above, the person pulled from the trailer winch instead of the stem head. There's always a way.

I think that whatever mast section you choose, provided you decide it is going to be strong enough, you can just stop worrying too much about other issues and push on, confident that you will find your own solutions to the other problems as they arise (and they will arise.)

Next on my 'bottom up' build plan is a tabernacle. I am a little stuck on that until I can decide on the diameter of the mast. I would very much like to use a tapered pole and avoid having a two-part mast that will need assembly. I looked at the 8" pole available at a great price nearby -- to me it is clearly bigger than what I want.

I am trying to find something that meets all the calculations and rules of thumb I have read. So far nothing meets the criteria.

I will need to fall short of one, or more, of the goals I typed up:

1. Mb_yield greater than 1753 kpm

2. Wall thickness between 2.5% and 5% of the outer diameter

3. Mass somewhat under 30kg

If anyone is willing to look at the summary I attached and provide feedback I would appreciate it. At the moment I think going with 'too heavy' might be OK. I am not sure how literally I should take the 'between 2.5% and 5% of OD' rule.

My 7in mast is 36kg bare tube weight, around 40kg after completion and with rigging added. I can just about lift it, but transporting it single handed needs some wheels strapped to one end. Imagining it to be in a tabernacle, I think I could live with raising and lowering it once a season, but doing that every weekend would be a deal breaker for me. It would be sad to have to pass on a bargain, but in this case, it does seem more sensible to hold out for a 6in or 7in mast, somewhat under 30kg.

Scott,

if the price is good and if the boat were mine, I might still jump at it. There are three reasons for it:

• The boat is not to be crossing oceans or win races.
• The boat is so light that body weight will have a significant effect on keeping it upright.
• This mast will still be much lighter related to the boat than the wooden masts of my Malena (her about 85kg mast was 6.1% and her hollow 70kg mast was 5%)

The solid mast really was too heavy, for sure. The 70kg mast (1400kg boat) was still not ideal, but I could live with it in lack of anything better.

I would therefore not call a 35kg mast a show-stopper. However, you are to raise and lower that mast before and after each sail, right? Then I guess 35kg would feel on the heavy side.

Arne

PS: When cutting down the lamp post to fit your rig, I think you can safely cut from the thick end. Leave a mast about 1-2 feet longer than you think you need, and then trim it down after having gone for a few sails. It's easier to subtract length from a mast than adding more to it...

If I remember correctly, Roger Taylor put a 8in mast into Mingming II, and was a bit nervous that it would 'look' too big, but when the boat was launched and sailing, he no longer thought that.

I'm happy that my 7in mast can take anything that I can throw at it, so there's no need for the extra diameter in your case. That said, if you were to make an all-wood mast, it would be about 8in at the partners, and probably heavier than the tube that's available to you. If that tube complies with Arne's "% of the displacement" rule, it should be OK. My only other thought is that the tabernacle will have to be large to accommodate it, and take up more room inside the cabin.