Is my main sail sheet rigging OK?

[ferrailleur]

I'm not sure about my rigging of this main sail sheet (Catalina 27). I have been experimenting in my basement!
Maybe tooo much force on the middle section of the boom?


1) first pic is the general view. The short red tape marks the entry and direction of the sheet. The long vertical red tape marks the end attachment point.

2) 2nd pic is the central vertical section of the rigging (sorry for the inversion)

3) 3rd pic is the bottom assembly attached to the traveler.

4) 4th pic is the top assembly middle of boom.

Thanks for your comments and help

[odonnellryan]

I'm not an expert, but I don't notice any glaring problems.

That's 7:1, going to be a 8:1 ratio when you buy line? That seems like a lot. My C25 had only a 3:1 and it was fine.

Only problem I can think of there is you're going to have to buy a lot more line than you'd need with a 4:1 or 5:1.

I've been thinking if 6:1 for my 37' boat was too much! And I'll probably end up with a 4:1 or 3:1 and run one end to a winch at the end of the day.

[Benz]

I agree that it's overkill. I could easily control my 27' boat mainsail with a 4:1. Also, I understand trying to minimize bending load on the boom by spreading the block locations, but unless the boom is a joke, it should be able to handle the upper blocks landing in one spot. Your tackle will be more efficient that way too.

[psk125]

Was going to say it looked like overkill, but scoping out pictures and videos of Cat27's shows their mainsheets set up the way you have it. You may need a longer sheet to let it out going downwind, but it should work. We have 8:1 on the mainsheet of our J/36, and it works for us.

[Jim Cate]

The inherent friction in an 8:1 tackle will be very noticeable, especially when easing in light airs. 4:1 will be more appropriate for a Cat 27.

Jim

[Adelie]

Is the traveler on the cabin top or in the cockpit? On the cabin 8 to 1 is reasonable but the block shouldn’t be spread out so much. In the cockpit it should be more like 4 to 1.

[roverhi]

Because it's probably mid boom sheeting, extra purchases may be needed but they will really slow down the uptake, take a lot of line and probably the boom will have to be pushed out in light air. I'd try 4-1 and add the additional purchases if you need them. The blocks are a bit pricey but a two speed set up would probably a good solution to speed and power but will take just as much line. https://www.garhauermarine.com/trave...er-25-2sp.html

[FabioC]

8:1 is certainly an overkill, and it is going to be extremely slow and even frustrating in light air. 4:1 should be plenty, I would start from there as well.

[TrentePieds]

What are you hoping to achieve with such complexity on a "low end" boat with a piddling 150 sqft of main like a Cat27?

I assume you know how to calculate the mechanical advantage of a multi-part tackle? You are not likely to be sailing a Cat27 in much more than 20 knots of wind, so how much "pull" will you need on the fall of the sheet to trim such a small sail? A "purchase" of 1:3 will be sufficient. Whether the sheet is rigged to the end of the boom to match a sheet track near the transom (which was the original set-up on the Cat27), or whether it is rigged to the middle of the boom to match a sheet track on the house top (which is a modification sometimes seen) matters a little, though not much. For a mid-boom attachment use a purchase of 1:4.

Remember that every time you take a line through a block - let alone a fairlead - you increase the friction of the tackle, and make life harder on yourself. On a sheet by using a purchase greater than necessary you also diminish/destroy the sheets ability to "run out" without help from you, particularly in light airs. So keep it as simple as you can.

Remember also that the VERTICAL motion of the boom is controlled with the vang. It is only the HORIZONTAL motion of the boom that is controlled with the sheet. Rigging as you show in your pictures was sometimes seen on racing dinghies in days of yore as a means of combining the two functions. I don't, myself, think that doing that works anywhere near as well as keeping the functions separate.

If it turns out that you don't have the muscular strength to trim the sheet in a high wind (because you haven't enuff purchase), just head up a tad till the sail empties, then trim as desired, then fall off to your course again.

TP

[jmorrison146]

Rig it as per the Catalina 27 manual.

[Captain Anthony]

TRENTEPIEDS, I enjoyed your knowledge above. So, I have just purchased ( no pun intended) a 1980 Tartan 37. Please give me your opinion regarding the " purchase" which is best for my vessel. Thank you

[Pete7]

Somewhere on the Harken website is a calculator to work out sheet loads. I think our main on a 31ft yacht was 350kg in 30 knots of wind and 500kgs in 42 knots of wind.

From memory I think ours is 4:1.

Pete

[TrentePieds]

Hello Anthony and thank you for your kind words. I suspect you are just testing me, but even so ;-):

The Tartan37 is a different breed o' cat from the Cat27. She was not precisely a "low end" boat, though she was indeed designed and built to be "affordable" for the many new entrants to the seafaring life that we saw in the 1970s. She has twice the displacement of the Cat 27, and therefore far, far better "drive" in any kind of water that we Sunday sailors normally encounter.

She has basic design ratios that don't differ significantly from those of the Cat27. It is her additional size, expressed in her additional displacement and in her additional sail area that makes her feel so much more "like a ship".

Back in the '70s it was racing that kept the new entrants amused, and the T37 recognized that fully. S&S had long experience in designing "fast" sailers and you see that expressed in the T37's high aspect ratio rig. A consequence of that is that the boom is relatively short and therefore the sheet needs to be taken to the house top which implies some loss of leverage. Another consequence of "designing for racing" is that the boat sails essentially on her headsail. That's fine as long as you recognize and respect the downside of that, viz that boats so rigged can become intractable and dangerous far more quickly and with less warning than do boats with a more old-fashioned distribution of the canvas.

As for the purchase on the main sheet, bearing in mind what I said about vang and sheet functions, I would think that in your boat, in 20 knots of wind, 1:4 is still appropriate. 1:4 is sort of a "default" value from which you can work up to 1:5 or more if necessary. Pete7 gave us some values that I'd not thought about for a while. Let's use Pete's "350Kg in 30 knots" as a datum. 350Kg = 800 lbs (remember we are talking "working approximations" here!) so with a 1:4 purchase, you need to haul on the fall with a force of 200 lbs. Not likely you can do that standing on yer plates o' meat in a rolling cockpit. So what's wrong with the argument?

Two things: Firstly, 30 knots is a LOT of wind for Sunday sailors. It is 1.5 times 20 knots of wind. As I'm sure you know, the force you can "harvest" from wind is proportional to the SQUARE of the increase in windspeed. So a 30 knot wind has 1.5 x 1.5 = 2.25 the force of a 20 knot wind. Apply that to my argument and you will see that a 4 part tackle in 20 knots of wind requires only 200/2.25 = 90 lbs of pull-ye-haul-ye applied to the fall. If you go for a 1:5 purchase, the required pull is now 70 lbs. A well-grown woman can supply that. Pete sails a Moody 31, I believe. Her main is just about 200 sqft. Yours is 250 sqft. The principle I just demonstrated is always true so now you can play with the numbers and determine the purchase YOU would be comfortable with. There is no specific number laid down in law. Based on the physics you work out what is BEST FOR YOU given WHERE you sail and HOW you sail. Pete sails in the Solent an the English Channel, I believe. I sail in the Salish Sea, so we have different operational requirements, PARTICULARLY in terms of typical wind velocities. Therefore, for any given boat, we might choose different purchases on the main sheet.

Secondly, the forces Pete mentioned are for sails disposed SQUARE to the direction of wind. Those numbers are relevant to dimensioning the anchoring points for the sheet and the shackles and blocks to use. When you are running broad or before, you don't need to pay a lot of attention to the mainsheet fall. Your heads'l sheets will demand your attention. As you come up to a beam reach the PROJECTED area of the main increases as you trim it in, and the force required to shorten up INCREASES. As a (very) rough guide, the force required to come from fully wung to beam reach might be a quarter of the maximum, i.e. 20 lbs in our example above. As you point higher and the sail begins to act as an airfoil rather than a plain bag, the required force to haul the sheet will increase further.

And, of course, as I said in my previous post, if the pull-ye-haul-ye is getting a bit strenuous, just bear up, spill some wind, trim the sheet and fall off again.

So all in all, 1:4 is a good starting point. Upping that to 1:5 if you feel it necessary is a piecacake :-)

TP

[Jim Cate]

TP, in the above treatise you seem to have ignored the likely fact that a Tartan 37 will have a winch to trim the mainsheet. This, of course, alters the dynamics completely.

Case in point: our previous boat, an IOR one-tonner (as, I believe the Tartan was as well) had a slightly larger mainsail than you quote. We had a 4:1 purchase on the main sheet (boom end attachment) and the fall could be lead to a Barient 22 winch. The winch was only needed when hard on the wind in the upper reaches of un-reefed conditions, ie 20-25 knots apparent. On other points of sail, it was easy to trim without use of the winch.


Also, in your example of calculating loads in 30 knots hard on the wind, you didn't consider that the boat would likely be on the first, or possibly second reef by that point, and thus the loads would be lessened.

Jim

[KimSails]

I agree with the general consensus that 4:1 would be fine.

I used to own a C27 with end-boom sheeting. It used 4:1, no winch, and a *really* long mainsheet. I never had any issues trimming the main in w/o a winch. But easing the main out in light air was often a manual effort due to friction in the 4:1. That end-boom is different than your mid-boom, but I still think 4:1 would be fine.

My present boat is a Sabre 34, with mid-boom sheeting. It also uses 4:1, but there is a small winch that is helpful, and only needed, in a strong breeze while trimming in hard close-hulled. IIRC, I had three Beckets on my boom and had to figure out how to rig it on my own as the prior owner had passed away.

If your photo 1 is reasonably accurate with respect to the relative placement of the boom beckets over the traveler, then I would suggest eliminating all of the line going up to the middle becket and back. Just use the fore and aft beckets (and the single blocks you have there) to spread load on the boom. Terminate the main sheet at the fiddle block becket on the traveler. Effectively, your mainsheet will look like a "V" line going to/from the fore and aft beckets on the boom.

At the traveler, you will only need one of the two fiddle blocks you show in photo 3. Presumably the one with the cam-cleat, unless you have another method to cleat off the mainsheet. Generally, there will be a spring where the fiddle block attaches to the traveler to keep the fiddle block upright and not banging on the traveler and deck when the main luffs -- and this presumes that the fiddle block has a post and pin at the end opposite the becket for attaching it to the traveler.