shroud and spreader placement

Hi, I'm designing a homebuilt skiff of my own design (built out of marine ply). I was wondering if anyone on here could help me out with some mast and rigging questions. how does one go about figuring where to locate the attatchment point for the shroud/forstay, and location/sweep/width of the spreaders? and how do you know what a good starting tension is for the shrouds?

 

A lot of the answers to your questions can only come from the hull you have in mind. You have not given us one single detail on this dream ship of yours other than it is to be made of plywood and that you intend to build it yourself.

What type of boat is this to be? A racer? A day sailor?

How tall do you want the mast to be?

What's the maximum Beam and how far forward is it located?

These are but a few of the questions that need answering before anything near an intelligent response is possible.

I would suggest that you pick up a book on yacht design and learn the basics.

Or, failing that, look at other boats that are similar to your design and see how they are arranged. Then you will have a fairly close idea of what you will need to do.

 

Well, he did say a homemade skiff, out of plywood, and since he's talking spreaders I would guess he's talking a high performance skiff, not a utility row/sail/motor boat with a flat bottom.

If you mean skiff in the high performance sense, it depends on whether or not you are intending to fly a masthead spinnaker or not. Your rigging is determined by what you intend to do. Uppers, lowers, spreaders and such are derived from your rig plan, and also from the proposed materials for the standing rigging.

I build a high performance single hand skiff over the past couple of years, and the rig has evolved as testing drove us to modify it to meet performance demands. If you search on "Homebuilt single hand skiff" here, or check out Sailing Anarchy for "Eric McNicholl design single hand skiff" you will find out some of my thoughts.

My boat has a cat rigged main, and a 3/4 fractional asymmetrical spinnaker (29er sized). I have uppers, spreaders, lowers and on-the-water adjustable forestay tensioning and tuneable shroud chainplates. I can alter the rig rake and tension to meet conditions.

Basically, a rule of thumb I use is to have the spreaders in a neutral position between the hounds and the chainplates, neither forcing bend into the rig (avoiding longer spreaders) or increasing rake (shorter spreaders). They are right on the fore/aft line drawn from the hounds to the chainplates, avoiding rig stress again.

Rig tension and rake are important, and need to be adaptable to the conditions. Higher winds require more rake and higher tension. Lowers help keep the rig powered up in light winds, and can make the rig more flexible and forgiving in heavier winds by easing off.

My boat is using a Proctor D section mast for now (cost was a factor), but a carbon mast will be a far better choice. Masthead spinnakers need added support to avoid rig inversion under pressure.

--
Bill

 

It all depends on whether your boat will tend to be overcanvassed or undercanvassed - hunting power or losing power, and also on the conditions you will sail in. Excess power and or gusts means that a more gust responsive rig is desirable, so shrouds and jib down lower and spreaders raked back more, and vice versa. But its a huge subject with an enormous number of variables. The easy option is to commission a rig from a mast/sailmaker combo with good experience in an active development class as near as possible to your boat...

 

All good thoughts. I used a Proctor D mast section as there is a world of tuning info out there in the 505 class. My main is the same size as a 505 main, and I had a 505 world champion sailmaker (Ethan Bixby - North Gulfcoast) design the sail for the tube and he worked with the naval architect (Eric) and I to get things right.

The result is better than I had any right to expect.

--
Bill