How to minimise the roll

[stevd]

Over the weekends sailing, we went out in some good winds which was great, but through the night the wind was blowing hard all night. This created a 7 - 8 m swell, which I enjoyed.

When it came to return, the most direct course meant that the waves were coming in on the beam, as well as the wind. We werent over canvased and the helm was very managable. However this did cause quite a lot of rolling motion. I was always ready with the mainsheet to let it out if any big gusts came, which wanst required.

I am sure I have read somewhere that the sails can be trimmed to reduce the roll caused by the waves in this situation, if so, any advice in simple terms on how to do it

Many thanks

 

[neilf39]

Not confusing this with having the main up and sheeted in when motoring are you, as that is used to dampen rolling when you would normally be motoring. If you are sailing then that should keep rolling to a minimum. Assuming its not wind against tide then when sailing with waves on the beam, as you ride up the front of the wave this tends to push you further over relieving wind pressure on the sails which then offsets the roll. As you go down the back of the wave this tends to bring you more upright so the increased wind pressure pushes you back. How well damped this is will depend on various factors such as wave size in relation to wind strength, stiffness of the boat etc etc. You probably want to be sailing so when you ride up the front of the larger waves you roll no further than just shy of your angle of maximum stability. That way you will be sailing close to the boats stiffest point so the effects will be more damped. Perhaps not if waves are breaking, in which case you probably wouldn't be sailing beam on to the waves anyway. I am assuming the waves were not so large they threw a wind shadow over you when you were in the troughs...

 

[neilf39]

Not confusing this with having the main up and sheeted in when motoring are you, as that is used to dampen rolling when you would normally be motoring. If you are sailing then that should keep rolling to a minimum. Assuming its not wind against tide then when sailing with waves on the beam, as you ride up the front of the wave this tends to push you further over relieving wind pressure on the sails which then offsets the roll. As you go down the back of the wave this tends to bring you more upright so the increased wind pressure pushes you back. How well damped this is will depend on various factors such as wave size in relation to wind strength, stiffness of the boat etc etc. You probably want to be sailing so when you ride up the front of the larger waves you roll no further than just shy of your angle of maximum stability. That way you will be sailing close to the boats stiffest point so the effects will be more damped. Perhaps not if waves are breaking, in which case you probably wouldn't be sailing beam on to the waves anyway. I am assuming the waves were not so large they threw a wind shadow over you when you were in the troughs...

 

[dom]

...we went out in some good winds which was great, but through the night the wind was blowing hard all night. This created a 7 - 8 m swell, which I enjoyed.

That's a pretty huge swell for this part of the world!!! No way you'll stop rolling in that.

 

[[10753]]

Thats not far short of the height of my mast so I guess you had no wind then loads !

 

[TQA]

This is a fairly common situation where I sail in the Eastern Caribbean when sailing between the islands.

I think you will find if you reef down and go one reef further than the wind suggests then things will smooth out.

Mind you my swells are usually pretty long period having a 3000 mile fetch.

 

[William_H]

Much depends on the style of boat. A lighter boat that relies on form stability will be much worse than an older style heavy pendulous keel. The problem is that the form stability is based on the sea being level. ie the hull sits square to the water level. (mast perpendicular to water level) The catmaran is extreme example of form stability. When on the face of a wave coming sideways the boat tries to stay perpendicular to the water level which is at quite an angle followed by the trailing face of the wave which sloped in the opposite direction.
The sails have to follow this change of angle of the boat and in the case of a mobo with sail up it can cause the boat to resist the rolling. Your sails should do this however in lighter winds it will mean the angle of attack of the wind will change on every roll. ie in no wind the sail would tend to tack as the mast moves from port to starboard then back to moving starboard to port. So on a mobo with sail up the sail is sheeted in tight. In a stronger wind on the beam this mast motion will change to more wind less wind but also therefor apparent wind closer to the bow or closer to the beam. In a sail boat relying on the wind for motion you need to ease the sheets to give forward drive from the sails which then frees them to flop about. In the end all you can do is adjust the sheets to give the most stable sails along with speed and put up with the rolling. olewill

 

[SHUG]

A good wheeze with a ketch is to sheet the mizzen in tightly and run under main and genoa.
One of the few merits of the ketch rig!