# Changing to square top high roach mainsail



## cousineddy (Nov 27, 2011)

I would like to switch to a square top sail to add some efficiency to my underpowered boat. I am concerned about the square top interferring with the back stay. Has anyone upgraded to a square top? What did you do about the backstay...if anything?


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## Faster (Sep 13, 2005)

What boat? Any boat with a standard fixed backstay is not going to work with a modern 'square head' main. Typically these rigs (on small boats) and going to be swept spreaders and no backstay, or a moderate 'square' head with a backstay whip, though I suspect most such rigs that actually work will rely on running backstays.

Without knowing what boat you're thinking about modifying it's tough to say much more...


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## cousineddy (Nov 27, 2011)

Its a US 25. It has a smaller J and E than the higher performing boats of that size. So, I have a flammin case of SA/W envy. It may not be worth the trouble, but I was thinking dual running backs, or maybe an upper split backstay with a wishbone mast head. I really think those square tops are sweet....I always thought that the top third of the rig was basically useless.


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## Faster (Sep 13, 2005)

That's a tough one... you'd definitely need twin runners to run such a sail on that rig. I'd wonder about excessive weather helm too, as a result of moving the center of effort aft with the extra roach in the main. That rig has in-line spreaders, IIRC, so you couldn't afford to forget a runner on a gibe or a tack.

Probably not a practical thing to do, but fun to consider isn't it?


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## captbillc (Jul 31, 2008)

a square topsail on a yard has two sheets , two braces to swing the yard & a halyard to raise the yard. the minimum lines for a small one. not a practical conversion for this boat.


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## cousineddy (Nov 27, 2011)

Its not that extreme of a square. I think I just need a bracket that mounts to the masthead and sets the backstay aft about 18 inches. Ill send pics when done.

Will my rating get docked?


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## mitiempo (Sep 19, 2008)

That is not what he is referring to. He is thinking of a racing type main with a square top held by a batten and a whip for the backstay or runners and no backstay like shown below. Here's a link discussing the problems you can encounter: Fat head, or square top mainsails, in one form or another, have been around for what seems like forever, but have of course come into vogue of late in a fairly broad spectrum of boats. Harry Pattison, of E/P Sailmakers takes a closer look.


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## mitiempo (Sep 19, 2008)

cousineddy said:


> Its not that extreme of a square. I think I just need a bracket that mounts to the masthead and sets the backstay aft about 18 inches. Ill send pics when done.
> 
> Will my rating get docked?


If I was one of your competitors I would hope so.


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## cousineddy (Nov 27, 2011)

You can add a full batten high roach sail as long as you dont change standard measurements, right? Thats kinda what this is.


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## mitiempo (Sep 19, 2008)

I guess that would be up to the PHRF committee.


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## Faster (Sep 13, 2005)

PHRF will recognize the extra area.... your division rivals will for sure. Sails are measured for girth now as well as P and E.

.. and 'Just an 18 inch extension".... think about the forces on that in a good breeze. Not a simple engineering item.


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## jackdale (Dec 1, 2008)

You might be able to use a backstay whip, if you replace your backstay with a high modulus line. You just need to use the core. I sailed Beneteau 36.7 with that setup. Just ease the backstay to get head through. There was no need for running backstays.


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## sailingfool (Apr 17, 2000)

jackdale said:


> You might be able to use a backstay whip, if you replace your backstay with a high modulus line. You just need to use the core. I sailed Beneteau 36.7 with that setup. Just ease the backstay to get head through. There was no need for running backstays.


I race on a boat with the same setup, and we have recurring difficulty getting the big roach under the eased backstay, I think a square top is a whole different configuration and would be not amenable to use with a backstay, the back corner of the square would be hitting the whip, let alone the leech.


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## Faster (Sep 13, 2005)

sailingfool said:


> I race on a boat with the same setup, and we have recurring difficulty getting the big roach under the eased backstay, I think a square top is a whole different configuration and would be not amenable to use with a backstay, the back corner of the square would be hitting the whip, let alone the leech.


Agree with this... we have a dyneema backstay with a whip to clear a roachy (but otherwise conventional) main w/ full top batten and it works fine, but getting a whip that will lift enough to clear a fathead would be very difficult


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## jackdale (Dec 1, 2008)

SF and Faster

Good calls.


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## cousineddy (Nov 27, 2011)

As for forces, the loads should be about the same, Im just attaching at different locations that changes load angles just slightly. But, i will put a larger bending moment on top of the mast....which could be good for flattening the main. But I suppose the mast could have an undesireable bend load off the wind, flying the chute? Could even fail. Below is what im thinking....


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## cousineddy (Nov 27, 2011)

If I shorten the foot to compensate for the fathead, so the sail area is little changed, I should still create more lift, right? But yeah, fellow racers may not like me, huh.


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## WDS123 (Apr 2, 2011)

To do this correctly, you'd want to change the entire rig - likely carbon mast plus all sorts of adjustements to rebalance the center of effort 

But why the effort & money when other boats are so inexpensive ?


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## jackdale (Dec 1, 2008)

Will the bigger main result in more weather helm?


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## cousineddy (Nov 27, 2011)

No, this boat is REALLY inexpensive. Like garbage inexpensive. LOL Plus, its gotta nice hull shape, fin keel, lots of ballast, trailerable, volvo saildrive, and a 216 PHRF. Comparing specs to other boats, it looks like it will perform closer in the 170 range if I can give it more SA. Its seems a bit underpowered due to small J and E. Also, lee helm is a complaint on this design, so more main power could balance it out. If it need to change the mast, then I will drop this idea quick. I gotta put kids thru college in a few years.


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## mitiempo (Sep 19, 2008)

I don't think it is as easy as you are thinking - and I don't think the benefits will outweigh the costs.


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## cousineddy (Nov 27, 2011)

I am thinking the only cost right now is the cost of the backstay extender bracket. Maybe I can get by with a 1 foot aft extension? I do tend to over simplify.


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## Faster (Sep 13, 2005)

cousineddy said:


> I am thinking the only cost right now is the cost of the backstay extender bracket. Maybe I can get by with a 1 foot aft extension? I do tend to over simplify.


Prior to installing our backstay whip I considered a similar, but smaller crane extension for our rig.. A local rigger would have done it with no guarantee and strong misgivings had I insisted... for around $700. He did not think that it would stand up to the task. I took his advice and went with a whip, which has worked fine, but we just have a particularly roachy main with a std headboard.

I don't think that this is a practical plan for increased performance.. rigs intended to support and use a 'fathead' main are generally designed around the concept.. not the other way 'round.

Have you talked to a sailmaker about this??


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## cousineddy (Nov 27, 2011)

OK. I hear yall. I think I will look at adding 2 feet to the boom then. Ill just take my rating hit. I dont have a feel for how many seconds they will knock off my rating. Do you guys have any guesses? I found this curve fitted PHRF formula below where you could plug in your boat specs like draft, displacement, LWL, JIPE and it spit out your rating. Adding 2 feet to my "E" only knocked like 1 second off. It seems like the committe would hit me harder.

R' = 610-8.36*(SA/Disp^.333)+0.0000511*(SA^2)-55*(P/(J+E)) -30.8*(LWL^.5)-602*(DR^2/SA) 

where SA= .5*(I*J)+.5*(P*E)


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## Faster (Sep 13, 2005)

Adding 2 feet to the boom may make more sense, but you'll probably have increased interference with the backstay (in particular difficulty gybing through in light air) esp if you get a significant roach... so keep an eye on the dimensions for that. It may end up being a bit of an odd looking sail.

Look on local CLs etc, cruise boatyards for a boom the length you want that you might use to replace rather than try to modify the one you've got.. it may be a better overall plan.

I too suspect you'll get a harder hit than 1 sec.. but time may prove it worthwhile.... or not....


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## cousineddy (Nov 27, 2011)

The stock boom barely reaches the cockpit. +2 feet should put it in proper proportion. Thats my solution then. Thanks!


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## Sanduskysailor (Aug 1, 2008)

Here is one PHRF areas calculations: Mainsail penalties shall be calculated per the following: Where one or more of the following mainsail girth
dimensions are exceeded (ref 2007 IMS rule):
HB > the greater of .5’ (15.2 cm) or .04 * E
MGT > .22 * E
MGU > .38* E
MGM > .65 * E
MGL > .9 * E
mainsails shall be penalized by 3 seconds per mile, plus an additional 3 seconds per mile for each 5%
increase of sail area calculation per the following:
MSA (Main Sail Area = (P/4*(E+MGL)/2) + (P/4*(MGL+MGM)/2) + (P/4*(MGM+MGU)/2)
+ (P/8*(MGU+MGT)/2) + (P/8*(MGT+HB)/2)

Bottom line is that there is no free lunch.


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