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

Jackdaw · Jan 14, 2012

Scott T-Bird said:
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.

T-Bird,
You COULD put the pendant on the tack. But for any given sail area, you want the Center of Effort (CE) as low as possible. It lowers the heeling action. You are right some people are bothered by the low foot of a big gennie blocking the view, so they raise the tack. But its a so-so solution to the problem. On a jib, no need.

You could run the head of the sail sans pendant. But a lot of sailors like the luff of their headsails to be the same length, because they mark their halyards at the clutch when the sail is all the way up. Makes it easy to know when you are at full pull.

RichH · Jan 14, 2012

Jackdaw said:
T-Bird,
You COULD put the pendant on the tack. But for any given sail area, you want the Center of Effort (CE) as low as possible. <SNIP>

Locating the foot of a sail as close to or ON/touoching the deck (deck sweeper) will close off the short circuiting of air flow from the high pressure side to the low pressure side along the foot of the sail ... and such will vastly increase the aerodynamic efficiency of the sail. With the sail raised of the deck such short circuiting will lead to less performance and aero efficiency from the sail ... and you will need a much larger sail to do the exact same job, in comparison to a sail that is 'sweeping' the deck ... called 'end plate' effect ... the reason you sometimes see 'winglets' on keels and airplane wing tips, etc.

This isnt to be confused with sails that are used on furlers and where a pendent (at the head or at the tack) ensures that the top swivel on the foil is at the very top of the foil and is at the correct 'lead angle' to prevent 'halyard wrap' on the top-swivel or foil.

;-)

Jackdaw · Jan 14, 2012

RichH said:
Locating the foot of a sail as close to or ON/touoching the deck (deck sweeper) will close off the short circuiting of air flow from the high pressure side to the low pressure side along the foot of the sail ... and such will vastly increase the aerodynamic efficiency of the sail. With the sail raised of the deck such short circuiting will lead to less performance and aero efficiency from the sail ... and you will need a much larger sail to do the exact same job, in comparison to a sail that is 'sweeping' the deck ... called 'end plate' effect ... the reason you sometimes see 'winglets' on keels and airplane wing tips, etc.

;-)

Rich - Interesting... I've heard about that as well. But I've never heard a sailmaker and MA give it any real credence. The ones that I've talked to say the airflow at the deck is too messy anyway. Do you have a authoritative reference? I've love to read it. Put it my winter pile! ;^)

RichH · Jan 14, 2012

C. A. Marchaj's "Sailing Theory and Practice" would be a good start.

Most certainly Arvel Gentry and his 'modern' explanations of the applicable treatise on the aerodynamics of sails ... numerous discussions on 'end plate' affect: www.arvelgentry.com Since the Arvel Gentry data, etc. is all now web based, just do a websearch for "Arvel Gentry" + "end plate" and that will give you about 50 'hits'. Or go to the webpage and start with 'magazine articles' ... and "how sails really work", " "what goes around comes around" etc.

This is 'heavy reading' for the non-technical minded but Gentry and Marchaj are perhaps the only authors who are aerodynamicists (Marchaj is also a hydrodynamicist) as well as sailors, all other authors of such subjects use these two as their 'root source'.

Another good source if you live near a 'good' engineering school is to search their library for the NACA compendium "Ancient Interface" .... A fluid dynamics compendium that focused on sails and hull shapes, keel shapes, etc. and their application and which has a lot of test data that supported such 'experiments' and trials.

Although these works are now 'dated', they do represent the 'core' or basis of 'modern' sail aerodynamics, etc.

Ray Bowles · Jan 14, 2012

Squidd, I sail a San Juan 23 with hank on sails. I use a 4.5 oz. 153% genny for my light wind sail. On low wind days the wind doesn't have the strength to make the sail work. The weight of all that canvas simply overcomes the wind strength and the sail tends to colapse. Therefore, for the those days, I use a 170 drifter that is made out of 1.5 oz. nylon. That sail is very impressive and the boat speed it pulls is incredible. It points about 55 degrees upwind.
The 153 is still a much used sail and is great downwind for those times I'm alone and don't fly my standard spinakker. When I want to point as high as possible with fair winds I use my 115 sheeted inside my shrouds.
Hope this helps.
Ray

Cayennita · Jan 15, 2012

Get a 150. Yes it wraps around the shrouds but it is still more efficient than a smaller headsail for your type of boat in winds up to about 13-15 knots. You will never see a racing boat not using a deck sweeper for their upwind sails. Some have furling drums and the sail maker will build a generous skirt to get it down to the deck if possible.
Many boats have the drum below the deck just for that reason.
If you are going to get a short sail and have a drum, then you might as well add a pennant to the bottom since the winds aloft are stronger and usually are at a different angle than at the surface.
The latest racing machines have very tall rigs just for that reason. Think of it as a sail plane. Very long wings and short cord. More lift. Same reason for the square top sails.

shemandr · Jan 31, 2012

Not to mention you won't have to deal with the PHRF patrol

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

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