Arvel Gentry

[dale17781]

Has anyone read anything by a man by the name of Arvel Gentry? I came across his site and he has some interesting things to say about sail trim. He uses alot of telltails on both the main and jib. Has anyone tryed this? Thought this would make for an interesting thread.

Dale

 

[h2ot]

gentry tell tales

I tried his theory and it works very well. Best results were had with perfect flat water conditions and winds under 15 knots apparent. You will need to spend lots of time experimenting with placement of the many tell tales for optimum results.

 

[RichH]

Re: gentry tell tales

Gentry (in mid 1970s) was the one who debunked most of the myths and mysticisms found in 'sailing books' (slot effect, etc. etc. etc.), was the first to properly give correct aerodynamic explanation of "How Sails really work", etc. Even the famous sailing aerodynamicist/hyrdodynamicist C. J. Marchaj cites Gentry as one of the current leaders in modern sail theory.
Most of what is taught in USA high schools, etc. about how wings work is simply BUNK and nonsense, ....... even the Wright Brothers knew differently.

Gentry was quite instrumental for the USA keeping the America's Cup for so long, especially when the cup was an 'amateur' venue. Most of the top-end world's sail racers continue use these methods (or the electronic facsimile) for perfect trim and shape.

His 'aerodynanmic' explanations of sails may be somewhat difficult for the 'layman' to understand .... but if you read and re-read several times, it will all begin to become clear. One should actually replicate his 'pepper flakes on the water' experiment to see the aerodynamic (hydrodynamic, actually) effect of flow stream action on a thin foil/wing - simple and profoundly amazing, ..... air VISCOSITY is what makes a sail 'work' !!!!!!!!!. Gentry is become over the years the key root source for much of todays understanding of sails.

www.arvelgentry.com

 

[ITMaster]

Just to Add to what you have said Rich

If I'm correct, I think he was actually "On the Clock" for Boeing Corporation when he wrote his papers about the Origin of Lift, and others such as the Application of Computational Fluid Dynamics to Sails, et. al.


This stuff is about as good and technical as it gets when it comes to easy afternoon armchair reading on a wintry day; a must read for every sailor that thinks they have it mastered .

 

[Jim Seamans]

reading Gentry is a trip

into another realm. I printed out his papers and keep them in the library (you know where). I find his explanations amazing - do the math. It was also amazing Boeing let him use the computers for most of his simulation work.

 

[sailingdog]

IIRC, he also advocated using a sail with far more tell tails than commonly found on sails.

 

[RichH]

Friends of mine who were on Ted Turner's 'Courageous' in the 1977 AC will state that their wins were partly due to the usage of the Gentry Tufts. Also used in the 87 AC, etc.

 

[paphman]

tells on main

Has anyone used the "extra" tells on your main? If so how many and where did you place them?

Dale

 

[RichH]

Re: tells on main

The extra (Gentry tufts) are rarely used on a mainsail, unless you are doing some serious rebuilding and need the precise shaping corrections OR are validating a total sail plan (for racing, etc) and are checking some very serious aerodynamic effects. Gentry tufts are usually found mostly on the headsails and are used for 'very precise' steering.

The real benefit of Gentry Tufts is when your headsail(s) are 'race cut' with a relative fine/flat entry shape at the luff, where one or two degrees of steering/rudder error can instantly get you into the 'slows'; cruising sails are usually cut with a 'rounded' entry so they are 'more forgiving' but still can benefit from the usage of Gentry Tufts ... set off the deck at about or slightly above eye level. Again, gentry tufts are used for 'steering' the boat and to 'keep it locked into the groove", to keep a very precise angle of attack, not for sail shape and trim.

Hint: if you are racing you want these tell tales as-small-as-possible so your competitors cant see them easily and take advantage of any shape/trim errors on **your** boat.

 

[paphman]

Rich

Do you mean that the tells run in a line from the luff back to the leach? How high up from the foot would you place these, and how many would you use? Thanks Rich

Dale

 

[RichH]

Yup, just a row of small 'tufts', about head high or a bit higher, running from the luff to about 1/3 back. If you have roller reefing/furling then the advantage will be to run the row to about halfway across the sail.

The greatest advantage in using the row of tufts to steer will be in the super light winds; the tales will accurately indicate when you have a separation stall at the leading edge of the sail. A separation stall is usually invisible to the human eye because there is no sail-shaking / luffing going on.