Drifter Foot Length Question

I have a Precision 16 sailing dinghy. I currently have only the original sails - a main (95 ft2) and 115% jib (65 ft2). The unballasted centerboard fractional rig sailboat has the following specs:

disp: 390 lbs.
beam: 6.7 feet
length: 16.25 feet
LWL: 14.0 feet
draft (max): 3.7 feet

I will be adding a drifter type sail to my inventory. The sail will have a wire luff, be made of 3/4 oz. nylon and cut as flat as drifters are cut to optimize pointing ability. I sail without a motor and have the need to sail in very light winds. The drifter will be flown free and a couple feet forward of the jib headstay (will be adding a small bowsprit for the drifter tack and running the head of the drifter about two feet above the hounds).

The luff of the drifter will be 20 feet. My question is how long to make the foot. My sailmaker says that they normally make their drifters 170% of the distance between the drifter tack and the mast. That would give me a foot of about 15 feet and a total drifter sail area of about 146 sq. ft.

I'm not an expert with this type of sail. I believe there are several factors to be considered here. If you are going to sail in light airs, you want a large headsail. However, for any given fabric weight, the larger the sail, the more the weight, and hence will tend to be more difficult to fill in very light air. Also, even though I want a large sail for the lightest air, I also don't want to overpower the unballasted little sailboat if a 5 knot breeze comes out of nowhere! Somewhere I should think there is an optimal range for foot length and hence size of this type of sail for my type of boat. Can anyone suggest where they think this range might be?

Thank you very much!

Terry Farrell
Tampa Bay, Florida

 

Correction, the jib is more like 57 square feet in size. Here is a PDF brochure of the boat:
http://www.precisionboatworks.com/boats/P13-14-16/p13-14-16.pdf

Thanks!

 

I made a drawing of my sail plan with my new drifter. I hope it appears!

 

LP...length perpendicular to the luff.

Its always a tough call to spec a versatile light weather sail. If you choose max size the sail becomes unstable in a seaway and collapses under its own weight . If they collapse and are unstable, you go slow.

I prefer a smaller sail, light cloth, high cut clew with its shape optimized for 50 to 100 apparent wind angle . Bigger is not always better in light wind.

 

I think you'll have two main issues with that arrangement, one will be an undesirable mast bend and the second will be sheeting angleswith the clew that far aft.

 

Mast Strength

Thanks for your input. Considering all the details related to deciding on the size and characteristics of my new light-air head sail have been quite an education so far. I think I am closing in on making some reasonable decisions.

I agree with your comment regarding sheeting angle and clew. My thinking is that how I have it drawn is at (but hopefully not past) the limit to a reasonable sheeting angle when on a close reach. I do have concern that I might have too much headsail area as drawn. I could increase the length of the leech to make sure a proper sheeting angle is not past the stern, but I know I don't want the sail any larger and I want to be able to see a little bit under the sail. So I can always make the foot a little shorter. What I am going to do is put the mast on the boat up and use lines tied in a triangle - one each for the luff, leech and foot - and experiment with length adjustments for overall size and sheeting angles, etc. I think that should help quite a bit.

My mast is your run-of-the-mill aluminum 2" x 3.5" x 3/32" x 23' stick. The hounds are about 6.5' below the top of the mast. As drawn the drifter halyard would be mounted about 2.3' above the hounds. Clearly such an arrangement will put stress on the mast. My intention is to only use this large drifter in light air - when sailing upwind, likely only 5 mph maximum. However, I do know that the wind sometimes comes in poofs - and I'm guaranteed to have it up for some period of time when I shouldn't. I'd prefer to not break my mast. So I have two questions related to mast bending: Do you think my rig as drawn poses a danger of actually breaking or permanently deforming my mast? And, if not, do you think that it would potentially bend the mast enough during intended use to present a detriment to sail efficency (i.e., will I notice that the boat doesn't sail well because the mast bends at the top in 5 mph of wind)? I realize you don't have all the data you'd like to answer those questions, but if you can answer in generalities, that would be very much appreciated. And lastly, regarding mast bend, if you do think that my drawn mounting position of the drifter halyard is to far above the hounds, is there a reasonable safe distance above the hounds you might recommend? I realize that AT the hounds is best from a safety standpoint, but I'd like to get it a little above the hounds - even six inches - so that I can tack (I will be using a small roller-furler for tacking and dousing).

Any comments on overall size would be appreciated.

Maybe I should add - I'm not a racer, I am a cruiser. However, one thing I have learned is that it's always much more fun to cruise fast than it is to cruise slow! So yeah, I do enjoy pushing the boat a little bit. I'm not crazy - I'm 57 years old and not very athletic - so I don't really relish the idea of a knockdown, but then again, I am realistic and know darn well that pushing a non-ballasted sailboat will eventually cause a knockdown. So I am not looking to get wet, but I am prepared for it.

 

Drifter Size

Correct. That's my understanding. I'm not sure what your point is - but I'd like to know.

"Its always a tough call to spec a versatile light weather sail."

I'm sure finding that out! Adding to the difficulty is not knowing a whole lot about the process! This has really been a good learning experience for me.

"If you choose max size the sail becomes unstable in a seaway and collapses under its own weight . If they collapse and are unstable, you go slow."

That's my understanding and experience - and hence my questions about some optimal range for drifter sail area for my boat.

"I prefer a smaller sail, light cloth, high cut clew with its shape optimized for 50 to 100 apparent wind angle. Bigger is not always better in light wind."

Well, that sounds very consistent with what I want. I'm certain there is some point of diminishing returns as a drifter design grows in size for a given application. Given my drawing and boat specs, do you have any recommendations for clew height, foot length and sail area?

Thanks!!!

 

Google CODE sails.

Ask your sailmaker about CODE sails. These sails really improve performance and are many times set off a roller furl.

If your mast was set up to handle spinnakers , then you should be OK with a light headsail or CODE sail

 

I use two headsails, given the possiblity (LTU 1592):

http://www.piranija.eu/2011/papa-19-dalyvaujanciu-bus

The page is in Lithuanian, but photo does not need translation.

A few more photos attached.
A gallery: http://www.piranija.eu/2011/papa-18-daug-eismo-ir-mazai-vejo


Speeds in drifting conditions, closehauled: 2- knots with single jib, 3+ knots, with outer jib added.
Sheeting angles should be correct, of course, each successive sail sheeted closer to CL by ~4 degrees.
The boat do not sail as close to the wind with outer jib, but dramatic increase in speed is worth it in this case.
It also feels like tree-sail combo is less prone to stall in drifting conditions, i.e. it is more forgiving to helmsman's errors and apparent wind fluctuations, so characteristic in extreme drifting conditions.

If you have a spare jib, this modification will be virtually free.

 

drifter details

Terry, I was a Precision dealer and know your boat and your sailing area well. ( I always liked the 16) Several of my customers rigged their 16's with spinnakers and the boat carried them well. The 16 has a lot of form stability and can carry more sail in light air.
If I were rigging one today, I would add one of the light weight roller furlers on the sprit and use the sail like a reaching a-chute. I think you will find that you use it a lot, and often in more than 5 kts when you know you can furl it quickly. I would probably spec .6 oz- as light as possible, and not go over a 170%- you will get plenty of power. The stock mast can take it. B