|Topic Review (Newest First)|
|10-05-2006 12:53 PM|
I'm never one to stop investigations or take just one opinion, but I think this answers the question. Just thought I would share it with you.
|10-05-2006 11:14 AM|
Originally Posted by dave.verry
I think the question as to whether a foresail should be full hoist (raise all the way to the mast head) depends on what jib it is, and what type of sail. A max luff length sail has some performance advantage, if you look at racing sails sized from 150 % to even 100% you will see them cut with max luff lengths. But I believe the performance plus is not that material that non-racings sails need max luff lengths. In general a 150% genoa is intended to provide performanace and should be full hoist, if it were cut for your boat. But as you go down the jib sizes of non-racing sails, the luff lengths will generally also shorten. For example, on my boat the 150% is full hoist, the 125% is about a foot shorter on the luff, the 85% has a four foot extension on the head, and the storm jib is even shorter.
I believe it is not a plus to full hoist a sail with a shorter luff length, although I cannot speak to the scientific dynamics as to why. I do know that when the sailmaker recut all our sails for the furler system, he added pendants to the heads, not the tacks, and of course in the extreme, storm jibs fly mid-hoist. I think there's probably a sweet spot for the center of effort of the jib that contributes to the boat balance, which your concern may mis-treat.
I'd raise your sails the way they fitted for use, unless you get knowledgeable advice that they arn't cut correctly.
|10-05-2006 08:45 AM|
Different pennants for different head sails, I guess I was having a Homer Simpson moment, “Doh!”. This seams to be the obvious solution, As long as get the head sail height correct, which, at the moment, seems to be almost all the way up.
My point about the foot of the head sail being lower then the boom is that it also makes it lower then the foot of the main. I’m not sure how much overlap the foot (foots, feet??) of both sails should have. It seems to me that there is little advantage in having the genny overlap the main, more turbulence in the air flow on the genny which should cause less lift (pull, fource). My expertise does not extend to fluid dynamics but I do know some basics, hence the question.
|10-05-2006 06:48 AM|
That's correct re the headsail on a furler but even so methinks that even with hanks the headsail is never tight up against the masthead. My previous boat did not have a furler and I remember the headsail still stopped short of the masthead. Maybe all that proves is that my headsail position was not correct. You would still need some gap between the masthead and the headboard simply because under certain conditions you would have the luff tension looser or tighter. Personally I woudln't be worrying unless the gap is significant. As , I think it was Sailingdog, has been suggested maybe you just need to lengthen the pennant a tad.
|10-04-2006 10:55 PM|
Most boats these days -- except for small daysailers -- have roller-furling genoas. Necessarily, because of the upper roller fitting and hoist, this means that the top of the genoa will be somewhat lower than it would otherwise be if the genoa were of the hank-on type. I remember when I converted from hank-on to roller furling (with a ProFurl LC-42) it was necessary to shorten the luff of the genoa somewhat.
Re: the comment on "lower than the mainsail", that's just my belief...not necessarily fact. The belief is that the portion of a genoa between its foot and the vertical distance from the foot to the height of the mainsail foot is largely "lost" in terms of increasing the "slot effect" on the mainsail. This "loss" may even be increased due to healing, as the genoa foot rolls down lower than the mainsail foot. However, the lower portion of the genoa clearly contributes to powering the boat on its own, witness the huge deck-sweeping genoas on racing boats.
Just a notion. I've not seen any "proof" of this.
|10-04-2006 10:20 PM|
While 24 inches seems a bit excessive most mast head genoas stop at least 12-18 inches from the masthead, or so I thought. Have a look through some of the image files in the Sailnet Gallery. The headboard is not hard up against the stay fixing point. I don't understand the point you were making regarding the foot being below the boom.
|10-04-2006 08:49 PM|
|sailingdog||Generally, if I have a sail on a pennant, I leave the pennant attached to the sail, that way I'm sure that it will be right. This means making up more pennants, but reduces long-term problems IMHO.|
|10-04-2006 08:29 PM|
Thanks, guys! It made sense from a physics viewpoint, but I couldn't remember from the other boats I had/sailed. I tried to find photos of masthead rigs under sail but couldn't find any that where definitive.
Does it make sense that the boat will point higher with the head sail higher? It seemed obvious to me that the slot was working better, but that judgment was subjective.
I will increase the pennant length after I check the other headsails (working Jib and Blooper).
|10-04-2006 08:04 PM|
|sailingdog||Sounds like your headsail was originally cut for a different boat. One thing you could do is get a longer tack pennant. That would put the sail higher up, where the wind is generally a bit stronger, and leave you more clearance below the sail to see and to clear things like the bow pulpit.|
|10-04-2006 07:54 PM|
Yes, it's usual for a genoa head to be "all the way up", i.e., within inches of the top of the headstay. The longer the luff, the more sailpower you have, other things being equal. It's like a longer wing on an aircraft giving you added lift. This is true irrespective of the "slot effect", i.e., the dual-purpose role of a headsail in creating a slot to speed wind through to increase the pull of the mainsail, while itself providing a considerable amount of pull.
This is why a headsail, alone, is often an efficient sail to windward. Also why, when you drop the headsail, the boat slows WAY down when going to windward. It's always fun watching newbies trying to sail to windward with just the mainsail :-))
The pennant at the tack of a headsail is often used to lift the foot of the sail up enough to clear the pulpit and lifelines. Since these are typically below the foot of the mainsail, only the "lift" effect of the genoa is compromised, not the "slot effect".
My guess is that the sail wasn't designed for your boat. But, if it's in good shape it might be just fine unless you're racing :-))
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