Fractional rigs on cruising yachts

[tmh900]

In the context of: 'fractional rigs are increasingly found on cruising yachts' I am trying to find out more about them.

I have two good books on rigs and sail trim:

Yachting Monthly Sail Power and Sail & Rig Tuning by Ivar Dedekam. Both cover the basics of fractional rigs, but I have a couple of questions I wonder if any 4-um-ites could help to answer:

1. Any recommendations for a good book/web site on the subject of fractional rigs?

2. I am confused by something in the second book above...

"The traditional fractional rig, normally with in-line spreaders must use running backstays (runners) to stabilise the rig. Checkstays are mostly used on racing yachts to control the mast bend in the middle and lower parts of the mast.
The runners have the same function as the backstay on a masthead rig. Forestay sag will decrease and the mast will bend to flatten the main, when you tighten the runner. The permanent backstay on such a fractional rig is primarily an insurance against rig failure when gybing"

How can the mast bend when the runner is pulling the mast at the point where to forestay is attached? You'd still need to tighten the backstay (at the mast head) to bend the mast forward and flatten the main would you not????

3. The simplest type of fractional rig - with swept back spreaders, no runners or checkstays, is only used on small boats - 35 feet or less. The problem here is controlling forestay tension. Are there any alternatives that don't suffer this problem that are easily handled?

TIA

 

[30boat]

You're correct.The backstay is used to bend the mast and flatten the main.The runners are there to tension the forestay and the checkstays will help support and shape the middle part of the mast.
I have a tall 3/4 fractional rig with aftswept spreaders.I wasn't getting good control of the forestay and the mast wich is quite flexible was bending too much in the middle thus slackening the rig.I fitted Spectra checkstays and runners and now I have a very controlable and safe rig.Too complicated for a cruising boat but that was the only way I could deal with the problem short of getting a new stiffer mast.
Modern fractional rigs are much better and should need no checkstays to stay in shape.

 

[dt4134]

They were very popular on IOR racers (I wonder when the book you were reading was written). For a start they allow you to have a lighter mast, which helps reduce weight, improves stability & reduces pitching. The runners also help to stop the top of the mast falling off to leeward so improve pointing ability slightly. However IRC over-penalises them (IMHO) so has tended to reduce their use.

Your book is right in that checkstays control mast bend - they can be used to reduce or limit it - which is significant when you have a lightweight mast.

Not sure I agree entirely about the runners being an important means of bending the mast, but it would depend upon the details of the arrangement. They help tighten the forestay which has an effect on foresail trim. With a keel-stepped mast they're bound to introduce some bend. However, most boats I've sailed on with runners & checkstays also have an adjustable backstay that is the primary means of bending the mast.

To be honest runner & checkstays over-complicate things on a cruising boat.

A fractional rig on the other hand, again IMHO, is perfectly suitable for a cruiser and I don't believe the 35' limit mention applies at all nowadays. There is a great deal you can do with a mainsail to flatten it as the wind rises when you have a fractional rig and know how to use the backstay, traveller, outhaul, halyard & cunningham.

It's at least as effective as a first reef on many boats, so you can save the reefing lines for a second and third reef.

I still think the North Sails book is the best book on sail trim. OK, it's aimed at racers, but that doesn't mean it won't help with cruising sail trim.

 

[tmh900]

Thanks for the replies. The book was written in 1999.

I think I might invest in the North sail trim book (I bought the tactics one to learn a bit about racing - woaoooh that's detailed)

P.S. I was interested to see what this guy said about cruising with a fractional rig: beneteau first fractional rig (although I think he is a bit confused about his nationality /forums/images/graemlins/ooo.gif)

 

[snowleopard]

A few other points- jumper struts can be used to transmit the pull of the backstay to the forestay and stop the upper half of the mast bending.

Many modern rigs, particularly on multihulls, have fixed stays in place of traditional runners. They greatly reduce the amount of travel of the boom and can be a menace when running in strong winds but are popular - with designers at least.

If you are stuck with a spindly mast as I once was, you need a lot of rigging to keep it the shape you want. If starting from scratch there are lots of options right up to my current extreme - 15 metres and no stays at all.

 

[flaming]

Fractional rigs do work in a different way from masthead rigs.

With a masthead rig the spreaders are typically in line, and so do not have any role in tensioning the forestay, this is all done by the backstay.

In a well set up frational rig the spreaders are swept back, and the shrouds don't reach the masthead, but are at the same height as the forestay. This means that the forestay tensioning is largely opposed by the shrouds, and the backstay has very little effect in this regard, being used instead to bend the mast and flatten the main.

And as another poster has suggested, the current rule in vogue, IRC, does penalise runners and checkstays. As a result they don't feature on modern race boats. Even the TP52s (which weren't designed to that rule, but their own rule) do not feature runners or checkstays on their fractional rigs, yet have no problem getting their forestay nice and tight!

Yes, setting up fractional rigs is harder than masthead rigs, but as a whole they are much easier to use.