Will moving the mainsheet affect performance?

[steve]

I am planning on moving the mainsheet car from the bridge deck to the cabin top and I've just been told that this will affect the behaviour of the boat, that is, that it will reduce weather helm because with the point of attachment further forward there will be less leverage exerted on the boat. Is this true? And if so, could it be serious?

 

[vyv_cox]

I don't see how this can be the case. Weather/lee helm is dictated by relative positions of Centre of Effort and Centre of Lateral Resistance. Moving the location of the mainsheet attachment has no effect on either, assuming the boom to be adequately rigid.

The amount of effort required to tension the sail to a specific level is exactly the same regardless of mainsheet position. Moving it forward reduces the length of lever but increases the force. Result - no change. The same must apply in the reverse direction, so the moment applied to the boat is the same.

What you will find is that sheet loads will go up, so you may have to increase the purchase by adding blocks, or using a winch. If loads are not increased the leech of the sail will be slacker and the CE could then move forward, possibly increasing lee helm.

 

[davel]

I agree with Vyv.
The info you've been given is probably based on the practical outcome of moving the mainsheet position rather than the theory. As Vyv points out, moving it forward along the boom means that you're reducing the leverage you can exert. Thus for any given force you apply to the main, you'll be sheeting in/tightening the leech less than under the previous arrangement. This can be countered by applying more force but you're ultimately limited by your own strength

More a case of effect than cause.


Dave L.

 

[halcyon]

There may be a number of problems.
Moving the traveller up, ie from bridge deck to cabin top, and further forward to nearer the gooseneck will increase load on main sheet. The centre of effort remains in the same place on the sail, the pull instead of being below is now forward and up, this means the a larger proportion of your effort is taken up in trying to pull the boom forward into the mast.
Second point is that there will be/could be more boom movement when sheeted in, nearer the traveller is to the gooseneck the less control you have. Similar situation as the kicker, the near the mast the more the main sheet can swing.
Look at control with boom out, ie anchorage on coachroof / boom attachment and angle of mainsheet.
You can move attachment to boom towards mast, but the closer you get to the mast, the greater the loads, but the more control when sheeted in.


Brian

 

[johna]

I assume that the point of connection to the boom will also move forward and therefore the additional loading on the mast may not be significant. However, it does change the loading on the boom from a simple beam to a cantilever.

I made such a modification to a Sabre 27 but used twin main sheets, one to port and one to starboard (in effect two mainsheets). Excellent control over the boom at all times except when fully downwind and even then it provided a partial preventer. When sheeted hard in with the boom in the centre of the boat or to windward the bend in the boom had to be seen to be believed. I really needed a stiffer boom but what I did was to provide a single fixing in the cockpit such that I could always re-fit the original mainsheet to the end of the boom if I considered the loads too great.

Trust this is helpful.

 

[halcyon]

How did you do having the two main sheets ? how was having to let two out or bring in two ?
Looking at moving the traveller from bridge deck to over the tiller, we have a short cockpit with a lazerrette on our Halcyon 27. Noticed a yacht the other day with twin mainsheets, would save fabricating bridge to carry a new traveller over tiller.
A bit worried about the operation of twin sheets though.

 

[johna]

I understood from your first post that you wanted to move the mainsheet from the bridgedeck forward to the cabin top not over the tiller.

The aim of my solution was to remove the mainsheet from the companion way and the consequent dangers to fingers and bodies when crew were seated in the cockpit. At any one time only one of the sheets is the main control sheet the other is a lazy sheet albeit under some load. The sheets are routed from fixings just forward of the spray hood back into the cockpit via eyes and sprung clam cleats. A quick upward movement releases the sheet and a pull through the cleat tightens it. My Sabre had wheel steering and I could operate the sheets while at the wheel and the Sabre cockpit is relatively long.

E-mail me direct if you want more info.

 

[Avocet]

Moving the mainsheet forwards by the same amount top and bottom will increase the bending load in the boom. if the boom bends, it will flatten the middle of the sail a bit so it could move the centre of effort and alter the way the boat feels. That said, if the boom is stiff enough to resist the force, there shouldn't be any difference.

If the bottom of the mainsheet has moved further forwards than the top (say, because you needed to miss the companionway hatch), then some of the force in the mainsheet will be pulling the boom forward and the rest will be pulling it downwards. The forwards component of the load will try to bend the mast (which you may well not want!) as someone suggested in an earlier post.

 

[steve]

Thanks. I knew it sound fishy.

+

 

[Guest]

I have a Colvic Horizon 28 (No 1) which later became Colvic Countess.
The Horizon which was designed by Ian Anderson was designed with a coachroof mounted horse with the mainsheet led from two pulley blocks on the boom to a travelling block attached to the horse. I have seen no problems with this arrangement and it does give a clear cockpit and hatchway. You do have to be aware that there are some very strong loads applied to the horse so the horse or the mainsheet block have to be firmly and properly attached to the coachroof.