How big a Sail can I put on this thing...?

Tim R. · Jan 13, 2012

Your main concern beyond actual fit of the sail is whether your genoa cars can handle the angle of the sheets to the clew.

Jackdaw · Jan 13, 2012

Squidd said:
Genoa Sail.. My I measurement is 34', my J measurement is 11'8"

That makes a 150% or 151% at about 18' foot (at least according to my calculatiions)

Bacon is selling some 150-151% (listed) with a 19' foot..generally with a 33' Luff and 31' Leach, no matter what the foot layout was...110s-130s etc...

I also found a sail locally that is 31'8" Luff, 30' Leach and 21' foot...

I scaled it out on a sail plan drawing of my boat and it "looks like" it will fit... foot is parrallel to deck (on the same plane as 151%) clears safety rail but about a 1'6" longer...

My aftmost sheet lead block is on the toe rail, so I can adjust leach and foot tension...

So is there any problem running a 170% genoa...? (I understand clearing the Mast on a tack, but so too the 151%)

Squidd,

The size of sail is a ratio to the sails LP (Luff Perpendicualr) to the boats J. Not the foot. The LP is the measure from the luff 90 degrees to the clew. Its easy to measure, its always the shortest distance from the clew to the luff. See lines below in RED

In any case its a big sail. You will want to make sure you can get good sheeting angles from the sail. As a good starting point, the sheet should follow an imaginary line from the clew to the midpoint of the luff. This can be the LP line but rarely is. See lines below in BLUE

Note that's why the clew is cut higher in the biggest sail in your picture. If it were lower, the ideal sheet line would behind the boat. Smart sailmaker.

RichH · Jan 13, 2012

Tim R. said:
Your main concern beyond actual fit of the sail is whether your genoa cars can handle the angle of the sheets to the clew.

Repeat - Your main concern beyond actual fit of the sail is whether your genoa cars can handle the angle of the sheets to the clew. ... etc.

If the tack to clew dimension of an 170LP is at less than 10° from the boats centerline/tack position ... that angle measured from the tack of the sail to its fairlead on the rail, etc. ... the aerodynamic efficiency for 'beating' will be a net loss. ... and thats the primary reason that 'large LP headsails' have virtually disappeared from 'competitive' sailing.

For 'very light wind' upwind sailing (in less than ~5kts), there generally isnt enough energy in the wind for the flow to stay 'attached' for the whole cord length of a large LP ... and the usual result is 'separation stalls' of the air flow ... another reason that large LP sails have lost their popularity.

The 'only' advantage with a large LP (greater than 140-150%) will be for between reaching and downwind sailing, when a spinnaker or 'gennaker', etc. isnt used.

Jackdaw · Jan 13, 2012

Rich brings up a GREAT point.

I can see you desire for more sail area, the PY260s SA and SA/D numbers are on the low side.

The good news is that the boat is stand up well in a Lake Superior blow.

The down side is that you'll seem stuck on light air days.

If you do get a big genny, make sure you find a whisker pole to go with it for off the wind fun. Or maybe look for a used asym??

Ted · Jan 13, 2012

How big a sail can I put on this thing

Rich, In your reply referenced below, shouldn't it state that an angle greater than 10 degrees while beating will be a net loss? Or is it that a genoa with a large LP can't maintain attached flow in light air conditions if the angle is less than 10 degrees.

"If the tack to clew dimension of an 170LP is at less than 10° from the boats centerline/tack position ... that angle measured from the tack of the sail to its fairlead on the rail, etc. ... the aerodynamic efficiency for 'beating' will be a net loss. ... and thats the primary reason that 'large LP headsails' have virtually disappeared from 'competitive' sailing."

Merlin Clark · Jan 13, 2012

Squidd said:
OK, so what's an SA and SA/D number and where would I find such info for comparison..?

Good source: http://sailboatdata.com/viewrecord.asp?class_id=788

Jackdaw · Jan 13, 2012

merlinuxo said:
Good source: http://sailboatdata.com/viewrecord.asp?class_id=788

Yup,

And here is a pretty good take on the meaning of the numbers.

http://www.tedbrewer.com/yachtdesign.html

Joe · Jan 14, 2012

Jackdaw said:
Note that's why the clew is cut higher in the biggest sail in your picture. If it were lower, the ideal sheet line would behind the boat. Smart sailmaker.

Ummm.... Am I misunderstanding this comment, reading it out of context, perhaps? Geometrically, the line from clew to luff midpoint.... which infers equal tension on leech and foot... would be more vertical the closer the clew is to the deck.

In fact, the picture you refer to shows the largest sail's clew cut lower than the smaller ones.... if it were cut higher the ideal sheet line would extend behind the boat

Imagine, if you drew a line from the luff's mid point to the farthest point aft that you could lead the sheet. Anyplace on that line would be the limitation of clew placement no matter what size sail. The midpoint on the luff is fixed. Clew placement is variable. You could very easily rig an oversize sail with a LOW cut clew. In the IOC days a decksweeping 170 on a masthead rig was very common. The difficulty would be in a very large sail with a HIGH cut clew. Altering the clew's height above deck changesthe LP's point on the luff, but it doesn't change the mid luff point.

Jackdaw · Jan 14, 2012

Joe said:
Ummm.... Am I misunderstanding this comment, reading it out of context, perhaps? Geometrically, the line from clew to luff midpoint.... which infers equal tension on leech and foot... would be more vertical the closer the clew is to the deck.

Imagine, if you drew a line from the luff's mid point to the farthest point aft that you could lead the sheet. Anyplace on that line would be the limitation of clew placement no matter what size sail. The midpoint on the luff is fixed. Clew placement is variable. You could very easily rig an oversize sail with a LOW cut clew. In the IOC days a decksweeping 170 on a masthead rig was very common. The difficulty would be in a very large sail with a HIGH cut clew.

Nope, I meant higher. Good catch!

One thing to add that I didn't point in my diagram and you don't note here is that the midpoint on the luff is fixed for any given sail. If your jib is not full pull (like the the one in the Py26 picture) your midpoint will be lower. I didn't mention it in my diagram, but its probably good to call that out now.

Relentless · Jan 14, 2012

Squidd said:
I have some sort of pole that came with the boat...a clip on one end and an open hook with small pulley on other.. There are also heavy rings on the mast just above boom height...

It's on my list of "things to ask questions about"...just haven't gotten that far yet...

That's a reaching strut, it's used to keep the spinaker guy off the stantions and keep the proper angle so the pole does not buckle.

Merlin Clark · Jan 14, 2012

Jackdaw said:
Yup,

And here is a pretty good take on the meaning of the numbers.

http://www.tedbrewer.com/yachtdesign.html

Thanks Jack!

Jackdaw · Jan 14, 2012

Squidd said:
I was questioning that too because on the drawing the bigger sail"s clew is lower..

For some reason the outline of the "new sail" (the one in question) did not show up on the drawing... However, I drew in the luff center-clew-block line and it came out about the same attachment point as the other two sais do....with the shorter luff (almost 3' shorter than "I" measurement) the sail can be set at less than "full pull" lowering the clew and giving even more adjustment options for leach and foot tension... (if I'm understanding all this correctly)

Not sure what you mean about the sail not being in the diagram... did you add it somehow?

Anyway if a head-sail is not full pull you will always want the extra 'open' stay on the top, normally with a wire pendant attached to the head and then to the halyard.

If you got a good sheeting angle its a good start, that will give you balanced tension on the foot and leech. You can expected that to move forward and aft a bit depending on wind strength.

RichH · Jan 14, 2012

Ted said:
Rich, In your reply referenced below, shouldn't it state that an angle greater than 10 degrees while beating will be a net loss? Or is it that a genoa with a large LP can't maintain attached flow in light air conditions if the angle is less than 10 degrees.

Several things must be considered.
1. That 10 degree sheeting angle will be the relative minimum for the boat to not be 'pinching' (or stalling / separating the air flow across the sail). As an extreme example imagine sheeting the sail to an even smaller angle .... no go! The only way that this will be effective is if the sail has a 'flat luff entry shape' - a racing cut sail; conversely, a sail cut for 'forgiving cruising' will be 'too rounded' at the luff and will VERY easily stall/separate in light to moderate windspeeds when held at such a close sheeting angle ... it will be like trying to beat by pulling the mainsheet traveller/boom to the windward side of the boats centerline ... and the 'interaction' between jib and mainsail will always be 'off' when beating.

For 'displacement hull boats' that have a finite maximum speed, A jib is usually calculated/designed for the normal airflow 'upwash conditions' just in front of the boat ... the 'upwash' is air that is 'moving out of the way' of the oncoming boat ... is usually at a 10-12° angle to the centerline of the boat when beating; if the jib is at less than this 'upwash' flow angle the sail simply doesnt 'work'. BTW, the 'faster the boat' the larger that upwash angle becomes.

2. As the fairlead is led further aft to attempt to maintain at least a 10° sheeting angle .... the important slot-distance (distance between the mainsail and jib) will close ... and the sail combo will only be useful for very low windspeeds. When the windspeed increases that slot distance must be 'opened' (by moving the fairlead forward, opening the sheeting angle) and hence you lose pointing ability .... another reason that large LP headsails have disappeared from competitive sailing.

Summary. For a large LP genoa to operate it must be able to adjust the 'slot distance' (and in this case will lose pointing ability because the sail will be operating 'too close' the mainsail in anything other than very light winds); and with the fairlead car set at less than 10° to the sails tack (sheeting angle at less than 10° off the centerline) due to the boats geometry (LP vs. beam) the aero efficiency will only occur when the boat is 'heading off' and with the jib sheet eased, not beating. .... and because the beam of the boat becomes less wide 'aft of middle'. This 170 arrangement when attempting to 'beat' is going to result in a VERY SLOW boat, and most times in 'light' winds when attempting to beat, will be carrying large separation stalls - air flow not attached to the leeside of the genoa simply because of the less than 10° sheeting angle, in higher winds the 'slot' will probably be 'choked'. Additionally when beating, the cap shroud is probably going to be in constant contact with the sail and will prevent the sail from being sheeted to its proper sheeting angle for beating.
Simply look to what the high end competitive racing fleets are using today, hardly ever does one see a 'large LP' headsail used anymore when 'beating'.

Scott T-Bird · Jan 14, 2012

Curious about the dimensions of PS26 ...

Your boat appears to be nearly identical in dimensions as mine with regard to LOA, LWL, beam, SA, displacement & ballast (except mine is shoal draft). Even the overall SA is nearly identical. Even I and P is nearly the same. The odd diffence is that J is about a 15" longer and E about 20" shorter. The way I read this is that with everything else nearly identical, your mast is aft about a 18 inches in relation to mine.

So I'm thinking that a 170 genny is a very large sail, especially with consideration to relative size of your sails, being that your genny is already larger by definition of your J dimension. Based on the boats dimension your foresail area is 20 sf larger than mine while your main is 30 sf smaller (we both have masthead rigs). Just my opinion, but I would look no larger than 150 or even 135.

I have 150 and will definitely cut it down when I re-fit it for a new furler. I find, like Rich says, that in light wind there is flow separation and the added size probably doesn't help any at all. I also find that when the wind is up to 15 knots, I get a lot of flutter at the leech which is not easily trimmed to avoid. Besides that, if you don't have a furler, hanking, and especially dousing and bagging a 150 gets to be a real ball-buster, especially in the hot sun. I'm not a wimp when it comes to those chores so believe me when I say it gets tiresome. I can imagine what a b!tch a 170 would be. Personally, I don't think you get any benefit from a much larger genny.

OTOH, with a whisker pole and downwind sailing, you might find it a joy to have. So it may depend on your normal orientation towards the wind.

Jackdaw, I was curious about your comment regarding a pendant. If the genny is not full pull, it would make sense to add a pendant at the tack if you want to raise the foot, but if you want the foot at the deck, why the need to add a pendant at the head? A pendant would merely be an extension of the halyard, so there is no need when you are simply pulling the halyard tight anyway.

How big a Sail can I put on this thing...?

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