Rig design, will you check my Excel file?

[Gades]

First of all, I'm including my own Excel file to calculate the transversal loads on the rig.

I was about to do a preliminary scantling, but I needed some data from the rig. So, although I intended to do a three spreader rig (it's a 60 footer), I've started with a two spreader (just cause I wanted to make it quickly). But I have some doubts; for example, if the tensions are becoming too high, should I go for a thicker rig, or should I go for bigger spreaders? when do I go for one thing or the other? Doing the 45 footer was easy, because everything was smaller (in size and in loads), but the 60 footer is getting more serious

Anyway, if you'd please have a look; I'm just playing with the Linkked rigging (DYFORM*19).

I hope you guys could give me some feedback, both about the file itself and about the designing. Please, give me your opinion if you download it.

[Gades]

Any comments so far?

[Gades]

25 members have downloaded by now, any comments so far?

[Polarity]

Hi Fernando

Just had a quick look at work (must re install Excel at home!) I'm not at all qualified to coment on the calculations but I will work through them.

What I do like is the selection system that you built in to be able to see the safety factor, vs stretch of the different wire sizes.
You obviously put a lot of work into the spreadsheet, very impressive.

Paul

[Gades]

>> What I do like is the selection system that you built in to be able >> to see the safety factor, vs stretch of the different wire sizes.

I like that too. We were told to use a factor of safety of 4.0. But sometimes, you get really close (like 3.8) and if you try to get over 4.0 it goes a long way. So it's a quick way to check every little change.

I did put quite a few hours in there, though I cannot remember how many. But not as many as I'm putting in the Scantling's one I'm doing right now I'll send it to you once it's finished (give me a couple of days).

Thanks for the comments Paul!

[interlude]

Hi Fernando
Some comments from an interested novice on rig calcs only (the devil walks where angels fear to tread). I have been confused/educated by the following:
Skene's: bases his calcs on total pressure on the sail as you do.
Lars Larsson & Rolf E Eliasson: base their calcs on RM@30 for the dimensioning forces: Whatever the wind/sail combination, if it is strong enough to lean you over to 30 degrees, the rig must be able to hold the boat over in a bumpy sea. Different cases (fore sail alone, reefed main alone) are considered for their different action points.
See also hints on rig design at: http://ourworld.compuserve.com/homep...S/designhi.htm
Minor comments on calcs as such:
- D21 : fore triangle and main triangle calcs : mix of kg/m & kg
- G3 : RM@30 why multiply by Cos 30 as well?
- D28 : Shouldn't it be WindPressure*Area/2? Area at top<lower down
- D29 : etc.
- D30 : etc.
- Minimum factors of safety would be useful for different sections of rig in your shroud sizes tables.
Cheers
John Coates

[Stephen Ditmore]

Hi, Fernando!

I don't have time at the moment to review your calcs, but it occurs to me that whether you should add another pair of spreaders or lengthen the spreaders depends on whether you intend to use overlapping headsails, and whether your spreaders are already at their max length given your target sheeting angle.

I don't recall what angle we used from the headstay when I worked for Jim Taylor.... your best bet might be to talk to a sailmaker if you are going to use overlapping headsails upwind and are therefore planning to size the spreaders for a target sheeting angle.

[tonypearce]

Fernando,
after a short view of your work I see that:
your work looks quite good. your engineering appears sound.
but, there are a few basic details:
1)you show true wind speed. the sails will see the apparent windspeed.
2)it looks to me as though you may have read the work by Pierre Gutelle.
did you do a check of RMactual against the chainplate load? this will tell you whether you are correct at that stage.
3)your calculations for stretch are based on stretch from the no-load condition of each shroud.
You must know that you set the rig up with an amount of pre-load which means pre-stretch.
Normally the pre-load in each shroud is half of the load determined from the max RM condition that you have worked out. that way the lee shrouds do not go slack as you heel over.
also working out the mast shape at max RM is not where you will be seeing the rig for 99.9% of its life. A normal yacht will not be heeled past 25 to 30 degree.
you need RMmax to determine max expected loads. it is for normal sailing that you want the mast to remain fairly straight. This may mean the adjusting of the pre-tension in the diagonal shrouds, whilst sailing.
as a mast designer I have never overly concerned myself with the type of analysis that you have done.
we get it strong enough for the max condition and then fine tune the rigging whilst sailing at 20 to 25 degree heel to get our straight mast. Adjustung only the lee shrouds, tack over, see what it looks like, tack back , adjust, ...etc you can do both side at the same time.
It is very difficult to get the rigging to stretch the way you want to have the mast straight for the full range of wind conditions.

I hope that this is of some help to you.
you may ask questions if you need more assistance.

[Robert Gainer]

The spreadsheet is an impressive piece of work. Now I need to spend some time and really take a look at how it works and is designed. One quick question jumps out at me about the results you are getting on the deflection of the mast, particularly at the masthead. I would have thought that the stretch of the wire would be proportional to its length so why does the defection of the masthead show that continues conventional wire takes a jump in deflection compared to the other wires at the masthead and only at the masthead.
Thanks,
Robert Gainer