new sail moves centre of effort - important ?

[sarabande]

I have a new (to me ) main sail, and drawing out the profiles earlier today, I estimate that the CofE of the main will shift forward towards the mast by about 4 to 6 inches, to a new distance of about 4' 9" from the mast. The height above deck is the same. Area of mainsail is approx 105 sq ft, so it doesn't generate a huge thrust.

Do you think that there will be significant changes to the slight windward helm I used to have please ?

The boat is 18ft waterline, 24ft OA, and displaces about 2.5 tonnes. Long keel, with an iron centre plate pivotting at the for'd end.

BTW, the new sail has full length horizontal battens, and luxuries such as leech line and reef points, so should be more tuneable.


TIA

 

[Lakesailor]

Bet you can't tell the difference.
Whilst in theory it'll reduce weather helm, the long keel will probably negate that.
If it's giving more power it may be noticeable, but on the other hand if you heel a bit more you may still need to pull on the tiller to maintain your course.

 

[PuffTheMagicDragon]

Are you sure about the "distance of about 4' 9" from the mast". Even if your boom is 10 feet long, it sounds like it is a bit on the high side - unless it has a huge roach, multihull style, or is gaff-rigged. Just a thought.

 

[William_H]

Weather helm

I agree with Phil you won't notice any difference. This concept of centre of effort versus centre of lateral resistance is much over rated to my mind. Sure in gentle conditions you may be able to affect the helm by adjustment of sail sheet tensions but as soon as the wind comes up the weather helm induced by heeling has a far greater effect. Enjoy the new sail. olewill

 

[penfold]

Agree with the others; you aren't going to detect any difference, or any difference will be easily adjusted for via the sheet/car position/cunningham/luff tension/foot tension/kicker.

 

[lw395]

It's not necessarily that easy to predict where the centre of effort of the sail will be in practice. You will probably just have to try it.
If you feel there is not enough weather helm, you could rake the mast back a little more or make the main fuller/jib flatter.

 

[stevebrassett]

You may also find that the new sail is not as stretched as the old, and therefore produces less of a heeling moment.

Basically, there are too many variables - try it and see.

 

[Sequoiah1]

I have a new (to me ) main sail, and drawing out the profiles earlier today, I estimate that the CofE of the main will shift forward towards the mast by about 4 to 6 inches, to a new distance of about 4' 9" from the mast. The height above deck is the same. Area of mainsail is approx 105 sq ft, so it doesn't generate a huge thrust.

Do you think that there will be significant changes to the slight windward helm I used to have please ?

The boat is 18ft waterline, 24ft OA, and displaces about 2.5 tonnes. Long keel, with an iron centre plate pivotting at the for'd end.

BTW, the new sail has full length horizontal battens, and luxuries such as leech line and reef points, so should be more tuneable.


TIA

Problem with the old adage that CofE leads CLR and that the ideal is by a certain percentage only assumes a static condition. Once the boat starts healing the whole underwater proile changes. Is the mainsail fuller or flatter? Better shape in the cross section and the fore and aft fullness of the sail is going to impact as well.
If you assume this traditional way of looking at this and having already made your apples for apples comaprison on the sails and all other things remain the same then potentially you are looking at a shift in the CofE of 2 - 3% aginst the lwl. That would be enough to see a change in the helm characteristics of the boat. If you dont see a change then you will know that the main is a different shape in its cross section. It may be that you will only notice a change on certain points of sail and wind conditions, reefing positions may have change from the old sail and this may also impact on the effect on the helm.