Main traveller, does it need all that mechanical advantage ?

[thunderhoof]

Boats with end boom sheeting require less mainsheet force to shape the main but more force to haul the traveller to windward compared to mid boom sheeting. Furthermore mid boom sheeting necessitates multiple blocks on the boom to spread the load on the boom section otherwise there is a real danger of breaking the boom during an accidental jibe.
If you want to reduce the purchase at the boom I suggest you reinforce it with a doubler solidly attached for at least the length of the original block arrangement.
I believe you will regret reducing the traveller control purchase partly because the geometry of mid boom traveller track does not support a fixed distance from boom to traveller track when the boom is on center vs off center. To maintain this relationship the traveller track would need to be horizontally curved or, if straight, to be dipped significantly in the middle.
The result of the poor geometry is that the mainsheet is effectively tighter when the boom is off center, the opposite of the effect you should want - requiring more effort to move the traveller if the car is off center.

[PineyWoodsPete]

Originally Posted by thunderhoof

Boats with end boom sheeting require less mainsheet force to shape the main but more force to haul the traveller to windward compared to mid boom sheeting. Furthermore mid boom sheeting necessitates multiple blocks on the boom to spread the load on the boom section otherwise there is a real danger of breaking the boom during an accidental jibe.
If you want to reduce the purchase at the boom I suggest you reinforce it with a doubler solidly attached for at least the length of the original block arrangement.
I believe you will regret reducing the traveller control purchase partly because the geometry of mid boom traveller track does not support a fixed distance from boom to traveller track when the boom is on center vs off center. To maintain this relationship the traveller track would need to be horizontally curved or, if straight, to be dipped significantly in the middle.
The result of the poor geometry is that the mainsheet is effectively tighter when the boom is off center, the opposite of the effect you should want - requiring more effort to move the traveller if the car is off center.

A little correction needed here: To travel the same arc with the same sail forces, end-boom traveler car lateral forces are half that of a true mid-boom traveler, but with twice the line needed for, say, a 4:1 ratio. In a friction-less system, same amount of total energy expended for the same arc-degrees hauled, though.

[s/v Jedi]

Owners thinking they know better than the engineer and designer of their boat are almost always wrong. Every single change done by the first owner of our boat lead to trouble and I reverted it back to original to fix it.

[Kd9truck]

Is your system a aftermarket product or is it original to the vessel?
There are many different loads, lateral, vertical, shock, ischemic, dead, and inherent. There are many components that participate in sharing and dispersing the loads,the boom Vang, the screws that mount the traveler, the rope, the pulleys, and the shackles.
All play a part including the most unpredictable wind and skipper. If they designed something From the factory I would stick with it. An unplanned Jibe, a gust from hell and you’ll be looking for advice on replacing the standing rigging.
One of my occupations was load testing rope and rigging for the second largest fire department in the world, you would be surprised what happens when you expose things to sun and salt and static tension. Everything has a life expectancy the boat builders build to that spec.

Enjoy the season

[Dave_S]

Thanks all.

The loads according to Harken at 30kn on my main. The main sheet might make 1.5t and at that the traveller might see 0.3t.

So at 2:1 ratio it would be 150kgs on the end of the traveller line. Easy for the winch but not to good on hands and if you don't secure the line I'm sure the traveller will run.

[Dockhead]

Originally Posted by thinwater

Also consider one size smaller line. Fat line is a common cause of trouble. But it does need to work in the jammers.. . .

Amen to that!

My traveler is 2:1 with dedicated winches. The forces are pretty large; the winches work hard. I am using 8mm polyester double braid for the traveler control lines.

Mainsheet is 3:1 and forces are also pretty big, but this is a large sail, about 65m2. I downsized the very long mainsheet (long boom -- 6 meters -- end boom sheeting -- 3:1, so mainsheet is something like 45m long) from 14mm poly double braid to 12mm racing dyneema and handling is totally transformed -- the new main sheet weighs like 1/3 of what the old one did, and is much more flexible and runs much better through the blocks.

[Dockhead]

Originally Posted by PineyWoodsPete

A little correction needed here: To travel the same arc with the same sail forces, end-boom traveler car lateral forces are half that of a true mid-boom traveler, but with twice the line needed for, say, a 4:1 ratio. In a friction-less system, same amount of total energy expended for the same arc-degrees hauled, though.

Right. Mid-boom sheeting is a mechanical DISadvantage for both sheeting and traveler. I.e. a mechanical advantage for the sail, against you . Less rope needed but higher forces on both.

Getting back to the OP's question -- on my boat, I would not want 2:1 on the traveler if I had mid-boom sheeting. 2:1 is barely enough with end boom sheeting and dedicated winches. YMMV depending on the size of the sail.