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Thread: Mainsail efficiency

  1. #1
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    Default Mainsail efficiency

    Since 6 years now I sail a Catalac 9m and am generally very pleased with both comfort and performance. But I am also looking for improvements, not least in my own competence to get the best out of the boat.

    One thing I wonder about is the efficiency of my mainsail. What is normal to expect when trying to sail a Catalac to windward?

    My experience so far is that it almost does not work at all sailing close hauled with only mainsail. In 14 knots of wind, I get no more than 1-2 knots of boat speed. With only headsail,* genoa, I will do maybe 4-5 knots in the same conditions and with both sails around 5-6 knots.

    Is this normal, and if so, why is the mainsail so inefficient?

  2. #2
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    Default Re: Mainsail efficiency

    I think it fair to say that our boats ability to point is directly related to the Jib and how you are using it .... as all sloops are more efficient hard on the wind with the jib than on the mainsail alone. In this case, the jib serves the purpose of increasing the windspeed over the main by forcing it through the slot between the two sails. The increased speed (Bernoulli Effect) creates more lift in the main and is why it is important to trim both sails to work together. And then there is boat balance .... my rigging is tuned to sail with a slight bias to windward when going to windward, without the jib I imagine my helm would be hard over.

    Mary Lack addresses windward issues here:
    Windward Performance

  3. #3
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    Default Re: Mainsail efficiency

    You are probably right in everything you write. So is your conclusion then the same as mine: The Catalac is not at all able to sail to windward under main alone?

  4. #4
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    Default Re: Mainsail efficiency

    Quote Originally Posted by Baste View Post
    You are probably right in everything you write. So is your conclusion then the same as mine: The Catalac is not at all able to sail to windward under main alone?
    The point I made is that I wouldn't sail hard on the wind with any sloop rigged boat, of which a Catalac is certainly one. It just wouldn't occur to me to even try it.

  5. #5

    Default Re: Mainsail efficiency

    Quote Originally Posted by Tropic Cat View Post
    The point I made is that I wouldn't sail hard on the wind with any sloop rigged boat, of which a Catalac is certainly one. It just wouldn't occur to me to even try it.
    I don't understand. Probably 90%+ of all sailboats are sloop rigged, does that mean none can sail to windward?

  6. #6

    Default Re: Mainsail efficiency

    Quote Originally Posted by smj View Post
    I don't understand. Probably 90%+ of all sailboats are sloop rigged, does that mean none can sail to windward?
    A key element of being able to sail to windward is the sheeting angle. Most monohulls because of their inherently small beam have quite narrow sheeting angles and therefore will go to windward using a relatively large headsail. Their pointing ability is more to do with their low windage and deep keel. It is also true that many monos do sail better to windward under staysail and main.

    On a cat and I suspect this is the case on a Catalac the sheeting angles for the genoa are large (on the side decks?). Very fast cats usually sport fractional rigs with small headsails so that the headsail can be sheeted very close, on the coach roof or even centrally in the case of self tacking headsails. This is necessary especially in light winds where the apparent wind angle is drawn very far forward the faster you go relatie to the wind speed. Does the Catalac have a staysail that can be sheeted tighter?

    I suggest that the inability of the Catalac to be able to sail under main alone is to do with the CE of the main sail relative to the CLR of the hull.

    One last point, no one has mentioned the outhaul this is a primary and often forgoten mainsail control (or just ignored completely inside a stackpac) as it will change the camber and power of the mainsail. The latest wingsails (Americas cup boats) have 2 ridgid sections and their power is derived by adjusting the camber (equivalent to a conventional outhaul).

    Peter

  7. #7
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    Default Re: Mainsail efficiency

    I would like to bring this discussion back to the original question: Can the catalac sail to windward with only mainsail?

    Unlike Tropic Cat I can see value in doing that. Eg. a fast way of reducing sail is to furl the genoa and continue with main alone. On monohulls I have been used to do that and it does work fine. On the Catalac it does not and I still wonder why.

    Peter, could you elaborate on your suggestion about CE related to CLR,* what it means and what effect it should have?

  8. #8

    Default Re: Mainsail efficiency

    Quote Originally Posted by Baste View Post
    Peter, could you elaborate on your suggestion about CE related to CLR,* what it means and what effect it should have?
    The CE is the centre of effort of the sails and the CLR is the centre of lateral resistance of the underwater profile. Neither of these are static.

    On a monohull these change position when the boat heals. On a cat it is much more complicated because the underwater profile is very wide and changes shape according to the angle of travel, a 3D problem.

    The aim is to get the CE and CLR to line up, the boat will be balanced and will sail well (efficiently). With the CE "slightly" behind the CLR the boat will tend to head up "slightly" and sail well to windward, the other way round and the boat will try to fall off and not sail so well. If they are very far apart the boat will perform very poorly and experience weather helm and lee helm respectively. There will also be excessive drag imposed by the rudders trying to counteract either of these conditions.

    I suggest that the shallow hulls and relatively small rudders on a Catalac mean the CLR is very far forward and with the mainsail only the CE will be very far back. So, it needs a smallish headsail in order to bring them closer together. Too big a headsail and the CE will be too far forward.

    Even when balanced the boat will only point as well as the foils and sails will allow, that will depend on sheeting angles, keels, centre boards etc.

  9. #9

    Default Re: Mainsail efficiency

    Quote Originally Posted by Peter View Post
    A key element of being able to sail to windward is the sheeting angle. Most monohulls because of their inherently small beam have quite narrow sheeting angles and therefore will go to windward using a relatively large headsail. Their pointing ability is more to do with their low windage and deep keel. It is also true that many monos do sail better to windward under staysail and main.

    On a cat and I suspect this is the case on a Catalac the sheeting angles for the genoa are large (on the side decks?). Very fast cats usually sport fractional rigs with small headsails so that the headsail can be sheeted very close, on the coach roof or even centrally in the case of self tacking headsails. This is necessary especially in light winds where the apparent wind angle is drawn very far forward the faster you go relatie to the wind speed. Does the Catalac have a staysail that can be sheeted tighter?

    I suggest that the inability of the Catalac to be able to sail under main alone is to do with the CE of the main sail relative to the CLR of the hull.

    One last point, no one has mentioned the outhaul this is a primary and often forgoten mainsail control (or just ignored completely inside a stackpac) as it will change the camber and power of the mainsail. The latest wingsails (Americas cup boats) have 2 ridgid sections and their power is derived by adjusting the camber (equivalent to a conventional outhaul).

    Peter
    I believe Rick posted a link that shows the Catalac does have sheeting points on the coach roof. My question was why does a sloop rigged boat not point well compared to other type rigs? The Catalac is a very well built boat but by design doesn't point well.....and I don't believe it has anything to do with being sloop rigged.

  10. #10
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    Default Re: Mainsail efficiency

    Quote Originally Posted by Peter
    I suggest that the shallow hulls and relatively small rudders on a Catalac mean the CLR is very far forward and with the mainsail only the CE will be very far back. So, it needs a smallish headsail in order to bring them closer together. Too big a headsail and the CE will be too far forward.
    Peter, I guess the conclusion of your suggestion would be that with CLR and CE far apart you need more rudder angle to compensate, creating drag that could explain less speed to windward with only mainsail.

    But why would shallow hulls move CLR forward? I would have guessed that the lack of keels on the Catalac would move CLR backwards.

  11. #11

    Default Re: Mainsail efficiency

    Quote Originally Posted by Baste View Post

    My experience so far is that it almost does not work at all sailing close hauled with only mainsail. In 14 knots of wind, I get no more than 1-2 knots of boat speed.
    Is this normal, and if so, why is the mainsail so inefficient?
    I don't get much better with the mainsail only either and have tried many times just for the experience. I have a behind the mast roller furled main and always thought that was the reason ,but it seems it might not be since you also have this problem. I do get a bit better than 1-2 knots but not significantly (2-3 knots). With the jib and main the best I ever did was 8 knots in about 15-20 knot wind.

    One of these days I might just have to play around to see what I can do again.

  12. #12
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    Default Re: Mainsail efficiency

    I don't have a behind mast furler, so pobably that is not the cause.

    I have wondered if my sail may be worn and has lost shape, even if I don't think it looks that bad.* But if others, maybe with newer sails, still have the same problem that could be a waste of money.

    Maybe the cause lies in Catalac design as Peter suggests. I have not paid attention to how much more weather helm I use when sailing with only mainsail. Maybe that is the brake?

  13. #13

    Default Re: Mainsail efficiency

    I wondered if my main sail was baggy too but I get great performance when I use it and the jib. About as good as most other reports on the 8m so am leaning that's not the problem.

    Sorry I can't be of more help. I hope someone else here can try theirs on mainsail only and report back too.

  14. #14
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    Default Re: Mainsail efficiency

    Thank you for sharing your experience. It is interesting that we both see the same thing happen. It could be an indication that it is how the Catalac works. But I would still like to know why.
    It would be very enlightening if someone with more knowledge of Catalac original design and history could comment. We cannot be the only ones that ever tried to sail with only mainsail.

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