Recommendations for halyard sizing

[Avocet]

I'm looking to replace my halyards, which are currently 10mm diameter. The boat is a Cutlass 27 - modestly canvassed masthead rig, about 3 tons displacement. They seem a bit big for the sheaves that they run in, so I was wondering if I could go down to 8mm (without going over to fancy materials). I'd be grateful for any thoughts!

 

[LittleSister]

Yes (in a word). I have a similar sized, but heavier boat, with, i think, a slightly smaller mainsail than yours. When I researched this a while back I concluded 8mm would be plenty strong enough, but would stretch under load very slightly more than 10mm. As your sheaves are tight for 10mm presumably the boat was rigged with 8mm at some point.

For that size/rig boat, fancy materials for halyards will only buy you a modest reduction in stretch, I believe. You can't save a lot of weight, and the line becomes too thin for easy handling unless you fit thicker tails (more cost and complication). Reducing stretch to the nth degree may well be important if you race (or plan to be out, with sails up, in very strong winds?), but for cruising our venerable MABs I would have thought a long way from the front of the queue for additional expenditure.

A rummage around on the internet will find various guides on halyard sizing (recommendation varied a bit, I recall), and rope loading specifications. I thought Jimmy Green had a useful one, but I can't find it now. (They have some good info, but it's a bit randomly distributed in bite-size chunks around their site, and lacking links between related material, so you keep having to back out of rabbit holes to the start again.)

p.s. I have just found, on Jimmy Green's site, this page about Liros' basic cruising halyard rope, which for 8mm suggests a maximum sail area of 20 sq m. I think a Cutlass main is about 10 sq m (but could be mistaken).
LIROS Braid on Braid EVO Halyards - Jimmy Green Marine

 

[Avocet]

Thanks for that. Online data suggests that the main is 13.0 square metres and the genoa, 18.4, so maybe 8mm will be OK. I have a boat data book (quite old) which has a sizing table in it that suggests 10mm (three strand) for a 25-30' boat though.

 

[RupertW]

I moved down from 12mm to 10mm for a 42 footer and the strength is fine from the research I did so 8mm for you sounds fine. . Much more slippery up and down - partly I think because the old ropes were stiffer but also the reduction in diameter.

 

[dansaskip]

Sure 8mm will be fine from the strength viewpoint. My only concern would be the handling - 10mm much better to handle and haul on particularly if your hands are cold and wet. Which is why I use 10mm on my similar size boat.

 

[RupertW]

Sure 8mm will be fine from the strength viewpoint. My only concern would be the handling - 10mm much better to handle and haul on particularly if your hands are cold and wet. Which is why I use 10mm on my similar size boat.

I completely agree for a sheet but for a halyard on a winch then I don’t mind a thinner line. That might be because I winch almost all the way so might feel differently if I was able to get the sail up mostly by hand.

 

[Stemar]

I use 10mm on a 24ft Snapdragon. Not because I need the strength - I could almost get away with parachute cord, but for ease of handling. However, if you think 8mm might reduce friction, I'd beg or borrow a lump of 8mm and try it. Even if you had to buy it, it isn't a lot in an annual sailing budget

 

[TernVI]

Consider the stretch.
There is a lot to be said for the head of the sail staying where you put it.
A low stretch halyard avoids the sail being over-tight if the wind drops.

There is a lot to be said for a stripped dyneema halyard, fat enough at the bottom for the winch and clutch to work well, thin up top to go around the sheaves nicely.
Dyneema is expensive, but plain old polyester is not exactly cheap either.

 

[dansaskip]

I completely agree for a sheet but for a halyard on a winch then I don’t mind a thinner line. That might be because I winch almost all the way so might feel differently if I was able to get the sail up mostly by hand.

Ah but then I do hoist my sails by hand and only use the winch to get the tension for the last few inches.

 

[Avocet]

Consider the stretch.
There is a lot to be said for the head of the sail staying where you put it.
A low stretch halyard avoids the sail being over-tight if the wind drops.

There is a lot to be said for a stripped dyneema halyard, fat enough at the bottom for the winch and clutch to work well, thin up top to go around the sheaves nicely.
Dyneema is expensive, but plain old polyester is not exactly cheap either.

What's stripped Dyneema? I hadn't heard of that!

 

[TernVI]

What's stripped Dyneema? I hadn't heard of that!

A typical dyneema rope will have a polyester cover over a dyneema core.
Removing the cover where it is not needed gives you a 'stripped' or 'tapered' rope.
Some people ever splice cheaper rope into the tail where stretch does not matter.