David W wrote:

David,

with the buoyant and relatively high topsides and the well rounded deck I would imagine that neither Annie's version or the 7 meter version of SibLim will be inverted stable. Is this correct? If so then I would not question their ability to undertake moderate ocean crossings.

David.

I can't give a numerical answer to this, only to say that we're about as good as we can get with the deck shape, and the range of inverted stability should be small, and much less than boats with a wide, flat deck. Yes, the closer one can approach to "a barrel with a keel on it", the better for extreme sailing, but in reality, we have to be able to walk along the deck. Moderation in all things.

David W,

actually, when I wrote the posting #6010674, I neither had the Fastnet disaster, nor the Roaring Forties and ultimate stability in mind. I was focusing more on the ‘working stability’ at max 30° heel. This stability decides how long you can carry enough sail for windward work. This is something that coastal sailors really need (unless they have a good engine installation). I have had a few boats which in varying degrees could sail against a rising wind:

·        My 7.1m/1400kg Albin Viggen, Malena, was a surprisingly good seaboat and very easy to steer downwind. However, her blunt bow, light displacement and moderate keel weight and area made her tricky to sail against rising winds and waves. The junkrig helped me to give her just the right sail area, but on the other hand, I had fitted a way too heavy wooden mast, which did not help at all.

·        My 8.83m/3000kg  Alo 28, Johanna had a round bottom section, but also plenty of ballast, so could be sailed more on the ear than Malena. She could work to windward  in quite strong winds, but it was no use to press on downwind or she would just squat and start rolling.

·        My 6.5m/740kg Jollenkreuzer Frøken Sørensen was a very different animal. She had no ballast at all, and according to the datasheet, her point of no return was at 83° heel. On the other hand, she was 2.4m wide, with a flat bottom, and her bow was very fine. Max righting arm of 0.43m was at 25° heel. This made her sail like a witch to windward, even against a steep short chop and with only three panels set.

·        My present 7.87m/2150kg IF, Ingeborg is at the other end of the scale. Her narrow beam makes her initially tender, but her 1250kg(!) ballast and generous keel area gives her plenty of muscles at 25-30° heel. She can tack against a lot of weather for her size  -  but she is also quite wet, so the sprayhood is a must.

My posting below is just a mild warning when scaling down a design. I forgot to mention that a scaled-down boat should be given a relatively bigger keel area than the original, since the shorter boat is slower, and the lift of a keel varies with the square of the speed. If this detail is dropped, the smaller boat will be more prone to moving crab-wise under sail.

Arne

 

Thanks, David, I buy your reasoning, as long as the builders understand this.

Scaling a boat design down.

I know, in these days of CAD, it is very tempting to scale any design up or down from the original. It can be done with just a few clicks and keystrokes. However, with boats, one has to do this with care.
The problem with linear scaling a boat is that the righting moment varies with the 4^th power of the length while the healing moment from the rig only varies with the 3^rd power (..sorry, don't know the English  mathematical term for this…)

If a 7.9m boat is crimped in all direction to 7.0 m, the righting moment will drop to only 61% of the original,

David, how do you compensate for this, or do you reckon the original SibLim to have such ample stability that the 7m version will be all right, just like that? Or can the DeltShip program calculate stability?

In the sixties and seventies, a whole range of the Swedish Maxi-boats was developed. None of them was just a crimped or expanded version of a former design. The Maxi 68 (6.8m long) came after the Maxi 77, and it was proportionally beamier than the 77, probably to both preserve space and stability.

Arne

Now hang on a minute, Annie, you've entirely misunderstood what's going on here.

In fact, Gary and I went through the same process as I went through with you: I asked him for a design brief and his input on the methods and processes that he wanted to use and was familiar with. And then we worked up the design together, with me submitting drawings and Gary coming back with what he liked and what he didn't, and making an initial model using his local CNC firm so that we jointly understood how we could meet the design brief.

Which was for a shoal draught bilgeboarder, junk rigged, of a certain size, to be built in a certain way, because Gary likes doing things that way and wanted to take on this project.

And such a boat is not available on the market, either used or as a kit, or as a design for amateur build. As you yourself found.

Yes, if anyone just wants a boat, and any boat will do, I would strongly advise them to go to the current buyer's market and find something that's near enough. But if anyone wants *this* boat, and no other will do, then here it is. It may suit others, and they're welcome to build it, if that's the case. Those whom it doesn't suit will need to look elsewhere.

Let's go back to the early stages of your project. I distinctly said to you that I was going to provide the bare bones of the concept of the accommodation, expecting you to flesh it out and lay things out to suit you, and build to a standard and aesthetic that satisfied you. When we built the model together, we stopped at the stage where we had established that there was a blank canvas onto which you could create whatever it was was that you wanted to create, once you'd worked out what that was. Knowing that I couldn't possibly design an interior that would satisfy you because at that stage I couldn't possibly have read that in my crystal ball, seeing as how it's all developing organically as you've gone along. You haven't got the spatial awareness that develops in someone who has worked in a design field, so you couldn't possibly have done it in any other way than working it out as you went along. And so, it's turning out very well, and it's going to be the beautiful home for the next decades that you need it to be - but it couldn't possibly be anything other than an entirely idiosyncratic expression of your needs. Yes, you started out with a low level of woodworking skill, and now you have a much higher level of woodworking skill - that's the case with many people who fit out a  bare hull. It doesn't alter the fact that fitting out a bare hull takes an inordinate amount of time, whatever the level of skill - I know, I've done it. Just to take the example of Tystie, which is freshest in my mind, six weeks from first cutting wood to bare hull, with main bulkheads in, turned over - and then over a year to fit out and complete the boat. And that was mostly a professional build.

The case is different for builders with a different set of skills and life experiences to draw upon. Different people want and need different things from their boats. But again, in the present case, I'm not dotting all the Is and crossing all the Ts. I'm leaving the galley detailing and the filling in of other areas to be worked out by the builder, and I'm saying nothing about the standard of finish and general aesthetic that is to be achieved. I'm dealing with the structural aspects only, and expecting - nay demanding - that a builder should take up the baton and run with it, making the project their own as you have done with yours.

Size matters. In a boat of this size, 7m, there's very little scope for laying out the accommodation in a different way. Just make that small step up to the size of your boat, and more things become possible. So if I had a "client" wanting a CNC cut version of your boat, or larger, I'd go through the whole process again of establishing exactly what was wanted, and what constraints there would be.

Just because you build quickly, from precut components, doesn't mean you're not getting a bespoke boat, just the way you'd dreamed it. You are.