Mainsheet track redundant?

[Avocet]

I had the same dilemma on Avocet. The mainsheet track split the cockpit in two and made it very uncomfortable to lie down in the cockpit. Now all this talk of windward performance is all very well, but if a chap can't lie-full-length in his cockpit when at anchor, one really has to ask if there is any point in having a boat in the first place?!

My solution was to fit two ring bolts, one each side of the cockpit on the vertical faces just below the edge of the seat. (i.e. just behind one's knee when sat on the cockpit seat). To each of these is attached a short stainless strop, maybe 18" long, with a snap shackle. The tops of the two strops meet on the centreline of the boat at a shackle. The bottom of the mainsheet is attached to that shackle.

So looking from the back of the boat, there is the cockpit sole, then either side of it, two vertical faces, which at their tops, meet the inboard edge of the cockpit seats. From each of these intersections is a wire strop going upwards and inwards until meeting in the middle of the boat a couple of feet above the cockpit sole and the mainsheet attached to them both.

That gets me two, full-length, flat cockpit seats. If I want to keep the boom to windward, I can undo the leeward shackle. If I want to ease the boom out but close the leach, I can undo the windward shackle. Otherwise, I can leave them both attached. It doesn't, of course, give me fine adjustment, but it is like having a traveller with three possible positions. That's a reasonable compromise for me.

 

[JumbleDuck]

Yes. Having trouble with yours?

You might be surprised, Just because a sail is full does not mean that it's providing forward thrust: if it's sheeted right up to or even over the centreline the lift vector will be very close to athwartships and the drag vector will be doing its devilish work ...

 

[Daydream believer]

Perhaps another option is an adjustable dynema bridle with separate adjustment on both ends & have the fixing points as far outboard as possible ie in the corner of the seat & combing where the angular shape of the structure might give greater strength for a U bolt. One would have to have a block & tackle on both ends so careful consideration of layout is necessary. It would mean the mainsheet bottom block would be waving about high up with no fixed position to help adjustment but the tail could be transferred to the cockpit floor, or somewhere else, with the rest of the falls to the bridle

 

[William_H]

You might be surprised, Just because a sail is full does not mean that it's providing forward thrust: if it's sheeted right up to or even over the centreline the lift vector will be very close to athwartships and the drag vector will be doing its devilish work ...

This is of course the situation known as an airflow "stall" If a main sail or jib is sheeted in too tight the flow becomes confused. You might picture the air hitting the sail and some flowing aft and some flowing forward. This situation is indicated by tell tales on the lee ward side dancing about. it is a condition which in mild conditions and especially reaching can happen without obvious indications and means performance is lost with too much heel and not best forward drive.
One would not have the boom over the centre line if you were reaching.
However when beating to wind ward this condition seldom occurs if at all. The (apparent) wind will be coming from around 40 degrees from the bow. Even closer as you go further up the sail. The flow across the main sail is encouraged by the exhaust from the jib (the slot effect) and you are more likely to luff the sail than stall it. Luffing is averted by bringing the sail in to maintain airfoil shape and so correct flow over both sides of the main.
Granted to bring the sail in tighter means the lift angle is closer to athwartships but there is hopefully enough vector of lift angle in the forward direction to drive the boat forward. The angle of the sail to the wind of course is dictated by the heading of the boat. We want boat heading as close to wind direction as possible (ie reduced tack angle) So it seems to me that your best bet for beating is boom at or above boat centre line and sheeted as tight as possible commensurate with having twist so the upper area of the sail is correctly angled for the higher wind speeds there, and the jib sheeted at a suitable sheeting angle and tight as possible again commensurate with required twist.
In the end IMHO hull speed as compromised to best heading (into the wind) will get you to windward the fastest. ie to sail off the wind such that the boat sails as fast as near hull speed then you are not sailing close enough to the wind. If you sail so close that hull speed drops to less than 2/3 of hull speed then you are losing to much speed and are pinching too much.
I spend much of my sailing time racing so about half of that is to windward almost always with other similar speed boat in close quarters such that you can compare your windward performance easily and see what works and what doesn't. good luck olewill

 

[JumbleDuck]

This is of course the situation known as an airflow "stall" If a main sail or jib is sheeted in too tight the flow becomes confused.

No, quite the opposite, I'm afraid. Aerofoils stall when the angle of attack becomes to large and the flow over the top/downwind side detaches. It generally happens at an angle of attack of around 18^o and the flow looks like this:

Unlike aircraft wings sails do not work at very low angles of attack, because the fabric loses shape, so there is a minimum effective AoA as well as a maximum.

One would not have the boom over the centre line if you were reaching.

Indeed not. However, it's possible to kid yourself that the sail is doing something useful by sheeting it very close to the centreline, or even over it. Sure, the sail is filled, but the lift vector is by definition at right angles to the apparent wind and will have little, no or even negative forward component while the drag vector is getting more and more effective as it moves towards the stern.

It's very easy to think that a tightly sheeted mainsail is doing something when the engine is running, when actually it is not. Well, nothing to help the boat along, that is, though it may help increase directional stability and/or reduce rolling.

 

[PetiteFleur]

I am about to fit a traveller to my track - originally fitted with moveable stops(early Lewmar) but they were very difficult to lift up and move as the track is fitted aft of the rear cabin hatch, meaning you were almost at arms length trying to move them with the result I just kept them in the centre. However, I bought a set of travellers etc cheap on a well known auction site and am having them machined to fit my track. I'll fit them over winter and see how I get on with them. The boat is a Moody33, centre cockpit.

 

[Colvic Watson]

You might be surprised, Just because a sail is full does not mean that it's providing forward thrust: if it's sheeted right up to or even over the centreline the lift vector will be very close to athwartships and the drag vector will be doing its devilish work ...

I think your tone is rather arrogant and certainly self opinionated, you assume I don't know those things or that I am not aware of what my sail is doing - whilst declaring that you do. On some aspects of popular science you are a renowned expert. I however have the experience of owning a large, fat and very heavy family motor sailer. So on matters relating to large, fat and heavy motor sailers a less peevish tone will annoy me less.

 

[Ardenfour]

View attachment 55146View attachment 55146Some informative replies here. Anyway here's a pic of the offending article. Also to be seen is the timber footrest where I planned to fit the U-bolt

 

[grumpy_o_g]

View attachment 55146View attachment 55146Some informative replies here. Anyway here's a pic of the offending article. Also to be seen is the timber footrest where I planned to fit the U-bolt

Can you compromise and relocate the track on the cabin floor? It would be shorter but still better than nothing.

 

[Daydream believer]

I think your tone is rather arrogant and certainly self opinionated, .

Reading the posts suggests that it might be the other way round

 

[Kelpie]

View attachment 55146View attachment 55146Some informative replies here. Anyway here's a pic of the offending article. Also to be seen is the timber footrest where I planned to fit the U-bolt

What about relocating the traveller towards the aft end of the cockpit? My Vega had it running along the front of the lazarette hatch, with a bit of an angle up to the boom.

 

[JumbleDuck]

I think your tone is rather arrogant and certainly self opinionated, you assume I don't know those things or that I am not aware of what my sail is doing - whilst declaring that you do. On some aspects of popular science you are a renowned expert. I however have the experience of owning a large, fat and very heavy family motor sailer. So on matters relating to large, fat and heavy motor sailers a less peevish tone will annoy me less.

My apologies. I think many people delude themselves when motor sailing and it was rude of me to put you among their number.

 

[Javelin]

In light winds upwind you'll be applying way too much leech tension on the main to get the boom even a couple of feet off center line.
With a large overlapping genoa you really need the boom on or above center in light stuff otherwise you'll be choking the slot and not pointing as well as you might.

Check your leech tell tails off your batten pockets, they should stream 50% of the time.
If they stream all the time you need more leech tension, if they hardy stream the leech tension is too much.

As the wind builds you need to keep leech tension (mainsheet) but ease the boom down on the traveler to reduce heeling.
Without a traveler this puts a big reliance on a very powerful kicker.
Also don't under estimate the effect that mainsheet tension has on the forestay.
Without a traveler you will probably have more forestay sag unless you counter it with an adj backstay.

In the racing dinghy world many of us did away with travelers to reduce weight and complexity and replaced it with a split tail mainsheet where we could centerline the main without adding any downward pressure on the boom, needed in light winds.
Not sure if I've ever seen a yacht with this system but it worked a treat on the four trapeze dinghy classes I used to race.

 

[Colvic Watson]

My apologies. I think many people delude themselves when motor sailing and it was rude of me to put you among their number.

Apology accepted.

 

[dom]

I think I can see where some of these misunderstandings comes from. We need some sort of orthogonal framework (i.e. a grid pattern) to describe the forces produced by an aerofoil. The aerofoil depicted below is meeting the air at a defined angle of attack to the incoming airflow, or in this case the apparent wind. As you say the "lift" force is defined as being perpendicular to the velocity vector (app wind) whilst drag is defined as being parallel to it. No matter what the angle of attack is, lift and drag will always maintain this same orientation to the incoming airflow.

Now an aircraft wing typically operates at a low angle of attack and the pilot doesn't keep looking at the wing. In level in level flight the wing produces two components: directly upwards (lift) and a drag component he must counteract with his engines. The airflow remains roughly parallel to the front of his fuselage at all times and this combination (pointing into the airflow whilst being lifted upwards and dragged backwards) is intuitively easy for a human mind to grasp.

Now picture a sailor on say a beat. Here the airflow (app wind) is coming in at about 30 deg to his direction of travel. As with the pilot the easiest orthogonal framework for the sailor to imagine is where one of the axes is his direction of travel (i.e. the direction his bow is pointing) and when closehauled this is close to the chord of the sail nearest the boom (let's forget about twist here). The other axis is directly athwartship This is why sailors find approaching a port or buoy in a strong tidal crossflow a bit of a mind-twister so we invent new terms like ferry-gliding to explain it.

In this framework the closehauled sailor imagines his sails as producing a forward force (parallel to his boat and the chord of his sail) and a lateral healing force which his weight and keel must counteract. In fact one sees just such a decomposition in many textbooks.

Now all it requires is a piece of elementary trigonometry to reconcile the two. The trouble is that (and I think JD is correct here), the easier to imagine framework (boat direction & heeling force) creates all sorts of problems in properly understanding the effects of twist, of tightening the outhaul and cunningham (which slim the airfoil by decreasing the radius of curvature at the luff (leading edge) and simultaneously creating a long flat section behind that, the different effects on the sail of a boat slowed by hitting a wave and one slowed by a drop in the wind speed and so on.

Aerofoils stall when the angle of attack becomes to large and the flow over the top/downwind side detaches. It generally happens at an angle of attack of around 18^o and the flow looks like this:

Unlike aircraft wings sails do not work at very low angles of attack, because the fabric loses shape, so there is a minimum effective AoA as well as a maximum.

Indeed not. However, it's possible to kid yourself that the sail is doing something useful by sheeting it very close to the centreline, or even over it. Sure, the sail is filled, but the lift vector is by definition at right angles to the apparent wind and will have little, no or even negative forward component while the drag vector is getting more and more effective as it moves towards the stern.

 

[JumbleDuck]

The trouble is that (and I think JD is correct here), the easier to imagine framework (boat direction & heeling force) creates all sorts of problems in properly understanding the effects of twist, of tightening the outhaul and cunningham (which slim the airfoil by decreasing the radius of curvature at the luff (leading edge) and simultaneously creating a long flat section behind that, the different effects on the sail of a boat slowed by hitting a wave and one slowed by a drop in the wind speed and so on.

Thanks. Yes, it's all about angle of attack of the aerofoil which, unlike a wing, is not directly related to the angle of attack of the hull/fuselage. It's hard enough trying to think in two coordinate system (free-stream air flow and aerofoil) and adding a third (hull) makes it harder still.

 

[Avocet]

View attachment 55146View attachment 55146Some informative replies here. Anyway here's a pic of the offending article. Also to be seen is the timber footrest where I planned to fit the U-bolt

Ah! I see you already have two ring bolts in pretty much exactly the right places to do what I did on Avocet! They look like they're already in a nice stiff bit of boat. I just stiffened mine locally by laying up extra fibgreglass on the inside of the laminate and then put a backing pad on. One problem you might have with a U-Bolt on the floor is that from a broad reach to anything downwind of that, the main sheet might foul the edge of the cockpit lockers and / or the guard rails.

 

[Ardenfour]

Good point! I assume these u bolts are safety line attachments. How are you attaching your mainsheet to yours Avocet? If I use both for the sheet it still divides the cockpit, leaving me with the same issue. Or would I change over with each tack? But then I can't have the boom centred...

 

[Avocet]

I haven't got any decent photos I'm afraid, but you can see it in this one. The ring bolts are just out of sight on either side. I asked a local rigger to make up a couple of short strops with a crimped male toggle fitting on each end. There's a shackle from each lower end on to each ring bolt and then the pin of a single shackle goes through the top two eyes and the bottom of the mainsheet becket fits through the bow of the shackle. Yes, it still divides the cockpit, but what I wanted to do was clear the sitting area so that there wasn't a big "plank" across the middle of it running from side to side. Most of the time, I leave both strops connected. If I wanted to sail with the boom slightly to windward, I'd disconnect the leeward strop. If I wanted to leave the main to leeward, I'd disconnect the windward strop. Not the same degre of adjustment as having a traveller, but good enough for what I want to do.

 

[Avocet]

Here's another photo which shows the shackles a bit more clearly.