Estimating mainsheet load?

[prv]

As built, the new boat's mainsheet has only a 2:1 purchase (single moving sheave) with the real advantage being provided by a winch. I don't like this approach, and would rather have a larger tackle with a cam cleat, like a scaled-up dinghy sheet. I've already removed and repurposed the winch, so there's no going back - but now I need to sort out a suitable tackle. The boat is a fractional-rig 34-footer. According to the manufacturer's brochure, the mainsail is 28m².

What purchase would be appropriate, do you think? Gut feel leads me to 6:1, but suitably-sized blocks are expensive so I don't want to buy them and then find that the load is too great in a breeze.

If anyone can suggest a rule of thumb value for max load that would be handy too, to make sure I buy something suitably sturdy. I'll probably end up buying online where scale is hard to judge, so just weighing it in my hand and saying "that feels strong" isn't an option. Obviously it's difficult to allow for shock loading etc, but there must be some guideline that riggers follow.

Cheers,

Pete

 

[AngusMcDoon]

My main is 37 square metres and the purchase is 24:1. I wouldn't want it to be any less. The cost of the tackle is high though to achieve this, about £1200 last time I looked.

 

[Stork_III]

I have HR34 with similar sized main sail, total with furling genoa 62m². My mainsheet is 6:1 with Lewmar 72 triple blocks, plain bearing, would not want smaller.

 

[Salty John]

Harken calculator is here:http://www.harken.com/content.aspx?id=9094

A rule of thumb is mainsail area in m x 25 gives load in kgs for boom end sheeting in 20 knots of wind. So, 700 kgs in your case. Load diminishes rapidly as wind drops but 6:1 is very borderline.

 

[prv]

Harken calculator is here:http://www.harken.com/content.aspx?id=9094

Ta. Don't have any of the necessary dimensions to hand, but I'll measure up next time I'm down. I do know the total height of the mast, so only need to measure the height of the gooseneck to get that one.

I do like the "Mainsheet load in meters" option . Wonder if it's meant to be newtons or kilos - I guess converting from the pound one would show which.

A rule of thumb is mainsail area in m x 25 gives load in kgs for boom end sheeting in 20 knots of wind.

Ok. Obviously I want to be able to sheet the boom in more than 20 knots of wind, but of course load would be reduced by reefing.

6:1 is very borderline.

Hmm, ok. I'll see who else chips in for comparison . Stork, above, seems to have a similar boat and do ok with 6:1.

Or perhaps I could use one of those continuous-loop two-speed mainsheet systems, offering a choice between 8:1 and 4:1...

Pete

 

[wotayottie]

first question is where does the mainsheet attach to the boom.If your boat has that (awful) cruising set up of main sheet half way up the boom in front of the sprayhood, then the main sheet load doubles compared to a sheet attached to the end of the boom.

My main is 26 square meters and with the main sheeted from the end of the boom. Bowman fitted it with blocks with 3 pulleys each top and bottom. Particularly when racing I wouldnt mind a bit more gearing - its manageable as it is but can be hard work in high winds.

That said you can do a lot with a track, hauling in the main spilling wind and then pulling the thing up track. But its an awfully cumbersome way of doing things. I hesitate to suggest you luff up to sheet in the main since you likely are doing that for the genny already.

 

[sailorman]

I have the easy block 3:1/6:1 system on 37` ( 260sq ft) its more than adequate

Ta. Don't have any of the necessary dimensions to hand, but I'll measure up next time I'm down. I do know the total height of the mast, so only need to measure the height of the gooseneck to get that one.

I do like the "Mainsheet load in meters" option . Wonder if it's meant to be newtons or kilos - I guess converting from the pound one would show which.



Ok. Obviously I want to be able to sheet the boom in more than 20 knots of wind, but of course load would be reduced by reefing.



Hmm, ok. I'll see who else chips in for comparison . Stork, above, seems to have a similar boat and do ok with 6:1.

Or perhaps I could use one of those continuous-loop two-speed mainsheet systems, offering a choice between 8:1 and 4:1...

Pete

 

[Salty John]

I do like the "Mainsheet load in meters" option . Wonder if it's meant to be newtons or kilos - I guess converting from the pound one would show which.

It's a typo on their site - load is in kgs.

 

[AngusMcDoon]

Or perhaps I could use one of those continuous-loop two-speed mainsheet systems, offering a choice between 8:1 and 4:1...

Mine is a Frederiksen setup and has a continuous loop in 2 speed arrangement offering 6:1 or 24:1. When it's fully loaded I can't pull in the 6:1 with one arm, but then I am a bit weedy.

 

[prv]

first question is where does the mainsheet attach to the boom.If your boat has that (awful) cruising set up of main sheet half way up the boom in front of the sprayhood, then the main sheet load doubles compared to a sheet attached to the end of the boom.

Nope, it's OK, the main sheet is at the end of the boom where it belongs. We have a sort of vestigial aft deck rather than running the cockpit right up to the transom, and the sheet comes down onto this.

Pete

 

[Salty John]

When deciding on a mainsheet system using the various calculators there is plenty of potential for over-design. You have to think carefully about the wind strength you are likely to be operating the mainsheet in - at what strength do you usually reef? If you put the first reef in at 15 knots, put that in the calculator and you'll see a dramatic reduction in load compared to 25 knots, say.
If you design for unrealistic conditions you'll end up with an under-utilised, but very safe, system.

 

[prv]

Mine is a Frederiksen setup and has a continuous loop in 2 speed arrangement offering 6:1 or 24:1. When it's fully loaded I can't pull in the 6:1 with one arm, but then I am a bit weedy.

Your main is also substantially bigger than mine

I can't envision how a 6:1 / 24:1 continuous system would work, only a coarse and tweaker which I think would be too much fiddly string and gear for my boat. Do you have a picture or a link to a page about it?

Pete

 

[prv]

You have to think carefully about the wind strength you are likely to be operating the mainsheet in - at what strength do you usually reef?

Mm. Trouble is, new boat to us, haven't sailed it yet, so don't know

Pete

 

[AngusMcDoon]

This is Barton rather than Frederiksen, but it's the same idea. On mine the blue and red rope are the same one with just a loop between the two cleats.

 

[Deleted member 36384]

31 m2 on the Rival 41C main, 6:1; in a F4, going onto close hauled, I have to sweat the main sheet in, tailing round the cleat, mast head rig.

 

[prv]

On mine the blue and red rope are the same one with just a loop between the two cleats.

Thanks - I'd consider that a coarse and tweaker rather than continuous, even though the two ends are spliced together. Difference is that you need to pay attention to how much of each end has been fed through - if you let the red rope all the way out till the boom was on the shrouds, you wouldn't be able to use the blue rope to pull it all back again. With the Easyblock type continuous systems, you can use either speed from any position.

I think my mother would get into a muddle with a coarse and tweaker system

Pete

 

[wotayottie]

Nope, it's OK, the main sheet is at the end of the boom where it belongs. We have a sort of vestigial aft deck rather than running the cockpit right up to the transom, and the sheet comes down onto this.

Pete

In which case you'll be OK with 3 pulleys top and bottom but not less than this. And even then it will be a hard pull in 25 / 30 kn over the deck hard on the wind.

What size winch was it?

 

[prv]

What size winch was it?

A self-tailing 16. Now moved up to the coachroof to handle the reefing pendants.

Pete

 

[Ian_Edwards]

I had a 6 to 1 main sheet on the end of 5.25m boom and 41.6m ^2 of main sail, on my last boat.
A couple of comments, most of the time it was OK, but upwind in a blow I couldn't sheet the main in tight.
So I added a tweaker, a 4 to 1 on the inboard end of the main sheet, giving 24 to 1. That worked OK and it doesn't have the be a heavy block and tackle on the tweaker because it's only handling 1/6th of the load (or there about).
At 6 to 1 it was an lot of main sheet to haul in when going from a dead run to close hauled and a lot of rope to stow in the cockpit, so I wouldn't want to use more than a 6 to 1 there's two much main sheet involved.

 

[Rossynant]

If you want simple tip: 4:1 tackle, 12 mm line, to the boom end of 50 sqm main - I found it bit difficult to harden the full main max in F7. I'm 50, weight 60 kg, had broken back and muscles ruined by being paralyzed.
So anything more powerfull than this I would say might be OK

PS remember the more sheaves, the more line in it - the more friction... better to ensure you have good position in cockpit relative to tackle so to put your weight into or reach conveniently, than worry about "purchase power" which is in fact lost. Worst setup is when you have to pull up from cockpit sole, best - pulling towards you from coachroof or at least horizontally.