Control of Weather Helm

[Jack Hattingh]

I sail a Morgan 31 keelboat in False Bay (South Africa) where the wind can change for the worst in an instant. She has a single fixture for the main sheet in the center of the aft coaming i.e no main traveler and car.
When reaching in strong wind she heads up substantially in which case I would release the mainsheet (scandalize the main) in an attempt to de-power but in turn completely loose downward force and seems to power the main up even more. Fair enough I can put in another reef or two but this slows her down substantially and I need to go up to the mast to reef.
My sailing experience is limited so I'm not 100% sure about my interpretation of the problem and I don't want to blindly fit a traveler and car if I'm not sure it will have the desired effect.
My intention is to, in addition to the the main sheet, rig a temporary twin sheave block system with snap shackles from a strop on any one of the aft mooring cleats to a strop tied around the boom. With this system I can hopefully apply downward tension to the boom whenever it exceeds the "effective" lee range of the main sheet and thereby attempt to reduce lift.
When tacking, I will release the snap shackle from the one cleat, swing the boom over and clip it to the other. Yes, there will be a safety issue but there will I will tension on the main sheet. If this has the desired effect, I would think a traveler and car system should have the desired outcome and I can make the necessary changes. This all comes at high cost here down south when taking into consideration our exchange rate, so any proposals or criticism on this approach will be greatly appreciated. Thank you.

[StuM]

You need a vang. On a 31 footer, there is no need for a fancy "rigid vang", just a multi-purchase line running from mid-boom to the foot of the mast.

[Dockhead]

What he said. But besides a vang, you actually also need a traveler, if you want to have decent control over the mainsail. It's a fundamental control -- controlling the angle of attack of the sail.

The vang controls the leech tension when the boom is beyond the range of the traveler.

[Jack Hattingh]

Darn good idea thanks, however the drawback is the height of the boom above deck which is 1.87ft (570mm), measured at the mast, and the vang currently reaches 2.7ft (823mm) along the boom, which is 13.2ft long. The angle is just too small to get any assistance with the vang no matter how taut I pull the sheet. Raising the boom at the gooseneck is not an option either. Jack

[Dockhead]

Originally Posted by Jack Hattingh

Darn good idea thanks, however the drawback is the height of the boom above deck which is 1.87ft (570mm), measured at the mast, and the vang currently reaches 2.7ft (823mm) along the boom, which is 13.2ft long. The angle is just too small to get any assistance with the vang no matter how taut I pull the sheet. Raising the boom at the gooseneck is not an option either. Jack

Well, you need an effective vang. If it doesn't do what it's supposed to do, then it needs to be reconfigured. You can't sail worth a dang without a working vang, and not only with regard to the particular problem you named.

[Jack Hattingh]

You've got me thinking! The boom is 13.1 ft long. I could mount a traveler and car beneath the boom, 5.56 ft from the mast (almost midway along it's length). That is the only spot available - just ahead of the dodger. I can lead the lines for the control block aft to cam-cleats and the sheet to a rope clutch in the cockpit.
What to do with existing (useless) main sheet? - do I retain it or remove it to the "new" traveler? Will there be any use for it in it's current position?

[StuM]

Centre boom sheeting puts big loads on booms. Sheeting the boom only 1/3 of its length from the mast would not be a good idea at all. Definitely not recommended unless the whole thing was originally designed for it.

570/823 is not too bad an angle for a vang (about 35°). What's the vang purchase ratio? Sounds like yours may be a bit light. 8:1 is not uncommon.

Take a look at the 8:1 Cascaded Fiddle on the Harken website:
Harken



or this one at
http://l-36.com/cascade_vang.php


One option if your purchase is too low is to set it initially with the boom sheeted hard on and centered.

And if the boom end is still inboard when you want to tighten while underway, just pulling down on the end can help get a bit more load on the vang.

[Steadman Uhlich]

Jack,

I think photos to show a particular boat's current setup are good to help others see the possibilities and possible limitations.

My Suggestion: Post a few photos showing your boat's current boom/cockpit arrangement, and indicate where you see problems. I would post photos from the mast facing aft, and from the stern or helm facing forward. Show the cabin top in a photo and the cockpit too.

A quick google search found this image of a Morgan 31 in SA and shows the use of a traveler in the cockpit. Your boat's setup may be different.

Hope that helps.

[Sailmonkey]

How about a twin sheet setup? A whole lot cheaper than a traveler.

[Jack Hattingh]

Thanks, if all else fails I will resort to a traveler in the cockpit companionway space. Had it the on a previous boat but the sheet is always in the way!

[Jack Hattingh]

Insofar the twin sheet arrangement, it was the first option I considered but the pushpit and safety line arrangement would have to be modified substantially to that the mainsheet could extend effectively beyond the toerails and it would crowd the rather limited space in the cockpit.

[Cheechako]

Seems to me if he wants to depower he wants that twist.... am I missing something? If over powered he needs to reef, sail flat and should be as fast as before. Maybe he needs reef points in different places... I suppose the traveler and the twist would help.

[dick sargent]

You might want to check out "boom kicker" instead of standard vangs.

[UNCIVILIZED]

To save yourself some money on a vang, in lieu of a few of the blocks in a cascade setup you can use low friction rings, or even large stainless thimbles as rings. Just orient them properly, & splice/seize them in place, along with using slippery lines like Dyneema for most of your vang.

[jrbogie]

Originally Posted by Jack Hattingh

I sail a Morgan 31 keelboat in False Bay (South Africa) where the wind can change for the worst in an instant. She has a single fixture for the main sheet in the center of the aft coaming i.e no main traveler and car.
When reaching in strong wind she heads up substantially in which case I would release the mainsheet (scandalize the main) in an attempt to de-power but in turn completely loose downward force and seems to power the main up even more. Fair enough I can put in another reef or two but this slows her down substantially and I need to go up to the mast to reef.
My sailing experience is limited so I'm not 100% sure about my interpretation of the problem and I don't want to blindly fit a traveler and car if I'm not sure it will have the desired effect.
My intention is to, in addition to the the main sheet, rig a temporary twin sheave block system with snap shackles from a strop on any one of the aft mooring cleats to a strop tied around the boom. With this system I can hopefully apply downward tension to the boom whenever it exceeds the "effective" lee range of the main sheet and thereby attempt to reduce lift.
When tacking, I will release the snap shackle from the one cleat, swing the boom over and clip it to the other. Yes, there will be a safety issue but there will I will tension on the main sheet. If this has the desired effect, I would think a traveler and car system should have the desired outcome and I can make the necessary changes. This all comes at high cost here down south when taking into consideration our exchange rate, so any proposals or criticism on this approach will be greatly appreciated. Thank you.

you make the same mistake in thinking that i've seen many make. you don't depower a sail by easing the sheet. you depower by INCREASING sheet tension. when you ease the sheet you induce more curvature in the sail, especially up front. you're powering up the sail. by increasing tension you flatten the sail and move the deepest draft aft thereby DEPOWERING the sail. a traveler is what you need. with it you can induce twist into the sail keeping the lower portion full and powerful and reducing power at the top of the sail where forces are acting to increase heel and therefore the weather helm you want to reduce. you would do this by hauling the traveler to windward, i know, counterintuitive but stay with me, and easing the main sheet. in a blow this moves the boom to the centerline of the boat for maximum pointing, powers up the lower portion of the main and spilling air out of the upper portion. much the same effect as tucking in a reef only easier.