Working load on Mainsheet, E30+

[tilwinter]

I am in the process of upgrading the mainsheet traveler on my E30+ with a Harken system.

I thought I would also at the same time, go from 4:1 to 6:1 on the mainsheet itself. The current 4:1 system is a little worn looking, and I would also like to make it easier for my wife to sheet in the main when I am at the helm. I could just upgrade to a 4:1 system with all ball bearings, but I thought why not go to 6:1 at the same time; it's just a little more line in the cockpit.

My question is: what is a good estimate of the working load on the mainsheet? (the sheet is not quite end-boom; more like 3/4 boom)

The Harken Midrange system has a safe working load of over 4000 pounds, but is horribly expensive (list > $500) relative to the other systems on the market.

My friend just put series 60 Garhauer blocks on his end-boom sheet for a Hylas 44; the 60 series has a SWL of 3500. I would have to think that my smaller boat, even with 3/4 boom sheeting, could get by with the series 50 (SWL 3000), or even the 40 (SWL 2800). The Garhauer blocks are all similar in price, about half the Harken. So the issue is partly one of size; I think the 40 series would not look so massive on my boat.

I would love it if someone actually could tell me the approximate load on my sheet, or has real world experience to share.

 

[gareth harris]

There was an article in SAIL magasine last year that had the necessary formulae to figure that out, I will see if I can find it over the next few days, but I will need to know your mast height and boom length, and position of the mainsheet on the boom.
You might be able to find the formulae online, but I just had a quick look and it didn't jump out.

Gareth
Freyj E35 #241 1972

 

[Geoff Johnson]

I got the formula off the Harken site and converted it to an Excel spreadsheet which I posted to this site last January. You can find it here:

http://www.ericsonyachts.com/infoexchange/attachment.php?attachmentid=179

 

[tilwinter]

Swl

Geoff:

I couldn't get your link to load, but I did go to the Harken site, and got "the formula"

Using the numbers for an E30+ (I had to extimate "X" at four feet, as I haven't been out to the boat yet), I came up with the following:

20 knots, load = 1152

30 knots, load = 2592

40 knots, load = 4600

These calculations to me do not account for the boat heeling, or for the point of sail. I assume the loads are assuming I am beating?

It seems to me that I would be OK with a block that has a SWL of 3000, although in a sense, I guess I would be reassured, knowing these numbers, with the Harken blocks that have a SWL in the 4000's.

Comments?

 

[Geoff Johnson]

When you click on the URL you should get a dialog box asking you if you want to download a Zip file (the format this site requires) which can be unzipped to the spreadsheet. (Works for me.) The spreadsheet allows you to play around with the four variables of the formula. I attach a picture of what it looks like.

On my 32-3 with mid-boom sheeting, I figured the maximum working load is about 2500 lbs. (remember, with higher wind velocities you are going to be reefing (i.e. reducing the luff length). I used the formula to check whether the OEM towers had sufficient strength after I switched to a Harken track.

 

[tilwinter]

Geoff:

I am surprised at your P and E.

My 30+ has a P of 38.5 and an E of 12.8

could a 32 have a sail that small?

 

[Geoff Johnson]

So it would appear. Your boat is fractional rigged, I believe. So while the 32 has a larger sail area overall, it carries more of it in the foretriangle. My main is 40 sf smaller than yours and the foretriangle is 66 sf larger. The PHRF difference is 168 (E30) vs. 156 (E32).