Is There A General Rule of Thumb For ...

[rardiH36]

... angle of jib sheet block location from the boat's centerline and ability to point?

Specifically, my 1980 Cherubini Hunter 36 was not fitted with inside jib sheet tracks up against the cabin top. Instead snap blocks are attached to the toe rail openings and moved forward/aft depending on sail size, amount of sail furled, and wind velocity.

Installing a jib sheet track would move the blocks about 20-24 inches further to the centerline than my current toe-rail method. My beam is 11'1".

In-hauling with a barberhauler hasn't worked too well because of conflicts with the lifelines and the frequent strong wind tacking I do on San Francisco Bay.

I know that hull and keel also play a major role in the pointing ability of a boat. But are there any rules of thumb that might help me predict the likely pointing improvement by installing an inside jib sheet track? If it's just couple of degrees, then I'll keep my deck neat and tidy and uncluttered. If I could expect say five degrees, then doing the installation will be my next project.

Thanks
rardi

 

[sandpiper10471]

Your angle of attack will improve dramatically but your speed will drop hugely with a consequent loss of lift from the underwater foils, increasing your leeway. This will be exacerbated with wave action. You may feel you are pointing higher but the VMG will likely in fact be reduced.

 

[rardiH36]

Hi Sandpiper:

Thanks for the info. Yes, I can appreciate that the loss of VMG. But I'm also thinking that better angle of attack might have offset benefit when head-on currents are also involved. In my case for instance, when trying to beat out under the Golden Gate Bridge during a flood current and the prevailing winds also coming in, I observe that another boat that might be pointing better, but is slower than me as a consequence, is nonetheless able to "punch" through. Where me with my beam more sideways to the current is pushed back at a greater rate by the current. Your thoughts on this?

Question: Did the 37C also come ex-factory without inside jib-sheet tracks installed? If so, have you converted?

rardi

 

[RichH]

Most sailboat designers use a tack to clew angle of ~10-12°. 10° for lightweight boats, 12° for heavy cruising boats. This is the 'initial setting' geometry for 'cruising cut' sails when used in approx. 12 knots of wind strength; racing cut sails may have a narrower tack - clew angle.

The 'slot open distance' in actual practice helps to govern the amount of air 'upwash' in front of the sail plan (the more upwash, the higher the attack angle at speed is obtained) - and is set to a less angle for light winds; and, more open slot distance for above moderate wind speed conditions.

The easiest way to set correctly the slot open distance (by use of a barberhauler or 'athwartship' fairlead track, etc.) is to:
1. first obtain the absolute highest VMG when beating (via 'perfect trim' using tell tales and the 'speedometer') and THEN
2. adjusting the 'slot open' distance while watching (or calculating) the 'velocity made good' - VMG to a mark while at optimum sailing closehauled (and usually ignoring any slight luffing that occurs in the mainsail).

Note/FWIW: when correctly setting the 'slot open distance' after setting up with 'perfect' trim and optimized sail shape according to the tell tales and VMG ...... especially in lightwinds and low boatspeed, you will often see that the windward side telltales at midcord and luff on the mainsail will 'point FORWARD' - physically indicating the CIRCULATION airflow 'AROUND' sails. So, once the boat is optimized via tell tales and boat speed, once you begin to further optimize by adjusting the 'slot open distance' .... use the VMG reading on your GPS and almost ignore the luff and midcord telltales on the windward side of your mainsail. The 'goal' then is 'best VMG'.

 

[RichH]

Hi Sandpiper:

Thanks for the info. Yes, I can appreciate that the loss of VMG. But I'm also thinking that better angle of attack might have offset benefit when head-on currents are also involved. In my case for instance, when trying to beat out under the Golden Gate Bridge during a flood current and the prevailing winds also coming in, I observe that another boat that might be pointing better, but is slower than me as a consequence, is nonetheless able to "punch" through. Where me with my beam more sideways to the current is pushed back at a greater rate by the current. Your thoughts on this?

Question: Did the 37C also come ex-factory without inside jib-sheet tracks installed? If so, have you converted?

rardi

If waves are now present in such a scenario, dont forget to re-adjust your outhaul for a bit more sail camber/draft; especially if you initially set up the outhaul to obtain maximum speed out of the boat in flatter/flat water.
The larger the waves, the larger the amount of draft; the flatter the water, the flatter the sails ... outhaul: adjusted in accordance to maximum reading on the 'speedo'.

 

[thinwater]

... Installing a jib sheet track would move the blocks about 20-24 inches further to the centerline than my current toe-rail method. My beam is 11'1"....

It would help if you told us the distance from the tack to the middle of the track. Also, bear in mind that when you move the lead inboard you may also need to move it back a similar distance to get the correct twist. This you should experiment with barbarhauling.

 

[rardiH36]

Thinwater and RichH:

Thanks for your interest. Learn something reading the posts every time.

My "average" sheeting position on the toe rail is 19' from the tack. (Surprised that I know this? .. I was on my boat today when I saw Thinwater's response on my Blackberry. So I measured!)

With this info, and that I still remember really basic high school trig, I calculated the sine value for both the toe rail and inside jib track locations. Entering these into the ASIN trig function in Excel yields angles from centerline:

- At the toe rail = 17 degrees
- At the potential inside jib track = 11.6 degrees.

So the inside track location is in the range of RichH's approximately 12 degrees for heavier cruising boats. (However angle at the "clew" would be greater since the sail pulled further off center depending on wind velocity and sheet tension.)

Notwithstanding the benefits of trimming for best slot performance, will the difference between 11.6 degrees and 17 degrees (≈ five degrees) be really noticeable in pointing performance?

rardi

 

[thinwater]

Yup, your trig is correct.

Interesting you should put your final question that way. I'm currently relocating the tracks on my boat as well, asking similar questions of myself. This is not my first boat and I've moved tracks around before. However, my boat is a cat with more windage and less keel, so I'm more interested in footing than pointing.

http://sail-delmarva.blogspot.com/2013/09/sheeting-angle-and-keels.html

I have some additional challenges: the shroud is in the way and keels are the wrong place and a little too small. The plus is that the boat is generally fast I and can make a lot of that up, but there is room for improvement. The boat was set up at the factory for a much smaller jib and fitting a large genoa has changed things.

Will a change in lead angle result in better VMG? There are many discussion points, but as a simple engineer I always run a test if I can. Beats theory hands down. Take your boat out on the water, barber haul to the locations you think best, and use the GPS to develop data. The nice thing about GPS for this is that it will show course over ground. The challenge may be to find a place or time well out of any current. I posted a simple data table for my boat.

In my case, I settled on a broader angle, but my situation is VERY different from yours. Based on what you have written, you seem on-track. I certainly would not go smaller than 11.6 degrees, and you will have the option of adjusting between the tracks. There will be days (lighter winds and slop or heavy winds and reefed down) when 11.6 is too tight.

 

[FastOlson]

Pointed thoughts

One factor not usually considered, esp. by internet info exchanges, is the actual design of the "foils" of the boat in question.
If the boat has a less-efficient keel profile, it may not have been designed to point any closer than the original factory sheeting angle... Don't forget the rudder shape, also.

Beyond that, when the boat was built, the factory may have been working extra hard to keep the base price low and opted Not to put the T-tracks or other jib sheeting hardware inboard. Often they would (and still do...) assess their target audience and if they see that a large percentage of them are buying the particular model as a day sailor and second home, the whole deck design will be restricted in devices and placement, and... cost.

While there are sail boats would benefit from 6' inboard tracks and higher-$ genoa cars, if only a handful of owners really want them and understand how to use them from the git-go, it's not worth the bump in base list price and loss of market share to install the gear on all model versions.

And then, back to the underwater part ("foils") of the equation, many many older designs from the 60's/70's had either internal ballast, iron ballast, or lower-efficiency keels and rudders and their optimal pointing angle, even in smooth water, is a few degrees less than boats from the 80's onwards.

So, just be aware that you may gain a bit of pointing smooth water, but perhaps not any more than you'd gain by having good sail shape, a clean and fair bottom, and a feathering/folding prop.


And, speaking of degrees of pointing, if you are dragging around a fixed prop, that alone will like cost you a couple of degrees.

Cheers,
Loren

 

[RichH]

Good points by Thinwater and Fast Olson.

Dont 'commit' to inboard or athwartship tracks without doing some extensive 'trials' ( with temporary 'barberhaulers', etc. etc.) to develop the possibility that any such (expensive) changes are worth the effort and the cost.

For such an attempt at increasing VMG and pointing ability, the first attempt probably should be a suit of 'racing cut' sails (even dacron sail that are 'racing cut'). Such will allow higher pointing angles right out of the box; but, will require keen helmsmanship to keep them at their inbuilt quite narrow angle of attack. Race cut sails (for these type of displacement hull boats) are usually made with a very 'flat' entry shape at the luff so steering/trimming will have to be quite precise; 'cruising cut' are usually well rounded at the luff entry section, thus 'forgiving' to the inattentive helmsman.
If total racing is not your goal, you can have sails made partly for racing and partly for cruising ... a 50:50 blend of the two configurations. Be sure you discuss your helmsmanship ability when discussing such 'blends' with your sailmaker/loft - be totally honest of how good you are with the rudder and where you 'want to be'. Ditto - in describing to the loft the 'exact' sea-state and wind/wave conditions that you intend to 'race'.

Also too, if wanting to increase pointing and efficiency potential, dont forget to Fair the Hull and apply smooth bottom paint - do most of your accurate 'fairing work' on the first 30% of the underwater length/shape (leading edge and 30% back on the hull/keel/rudder) - the areas that produce the bulk of the 'drag'. All those small nicks and teeny gouges and rough paint are 'speed killers', especially on all the 'leading edges'.
Bottom paint that was applied with a 'roller' is like applying gritty sandpaper and 'speed brakes'.

Summary: dont simply 'blow money' onto a boat expecting it to be better in performance; rather, do some trials using temporary 'bread board' equipment and trial apparatus to see which 'improvement' gives you the 'best bang for the $buck'.

 

[rufus1138]

+1 on fairing the bottom, money spent there and any money spent on learning to be a better helmsman/crew/all around, these things will help infinitely more than any sail you will buy, my neighbor could probably whip any of us on here in most conditions single handed on a barnacle ridden cruiser with diaper sails, i say that because ive been aboard said cruiser when we flew past a pearson 34 that had just spent 20k on new racing sails and thought that was tantamount to buying himself the finish line.

 

[dziedzicmj]

I know that thisi has nothing to do with the jib sheeting angles, but it is about the boat performance. I have recently read an older study on the propeller drag (compared to the boat). Apparently, a standard 2-blade non-folding prop generates a drag that is comparable to half of the entire hull's drag. The test was done, if I remember correctly, with a Beneteau (somewhere around 30-32'), but the results should be applicable to most modern sailboats. So, it sounds, that the best investment, if you want to improve the performance is the folding prop. Maybe right after the new sails.

 

[thinwater]

dziedzicmj, you are not so off topic as you think. RichH used some of the same logic, though did not put it in these words; ANYTHING that reduces drag and increases speed, increases water flow over the foils, and thus reduces leeway. Conversely, unless you are going to make some effort to reduce drag, tighter sheeting angles mean more leeway. In my case, moving the sheet leads was always just one part of a multi-step process.

Yup, it's the whole package.

 

[sandpiper10471]

Interesting discussion! And to anwer an earlier question, the H37C did not come with tracks other than toerail. I have no desire or intention of adding tracks to mine. If I wanted better upwind performance, I would do the whole fairing thing and convert to a sloop with a big blade headsail and tracks. I would not be using the staysail track. It is not wide enough for a big blade IMHO.

 

[Davidasailor26]

So, it sounds, that the best investment, if you want to improve the performance is the folding prop. Maybe right after the new sails.

The priorities there may depend on your motives. We race in a PHRF handicapped fleet, and get 6 seconds per mile for having a fixed prop. From that standpoint I'd sooner spend my money on improvements that won't hurt my handicap advantage (new sails,etc.) before changes that in theory will be offset in the handicap. Having said that, if you're going for pure performance, the fact that PHRF thinks a fixed prop is worth so much time is all the more reason to switch to folding.

 

[rardiH36]

Hi Everybody:

Just to let you know that as the instigator of this thread I am still following.

Observations about the very useful insights given as applied to my considerations:

- Certainly what's happening underwater (hull/rudder shape, smoothness of hull, type of propeller, etc) has effect. But from a practical standpoint, he's/she's got down there what he's/she's got. Difficult to change much. So I'm more interested in the above the waist aspect.
- I keep my hull and rudder and keel reasonably clean of growth. My prop, while not folding, is a Campbell Sailor Prop which per Mainsail's test and review exhibits much much less drag than a standard two-blade or dumbo ears three-blade.
- I use several head sails. Firstly, the older but good fabric condition 135 Genoa and the 90% Yankee cut sail each showed much better upwind performance after I removed the #6 foil luff tape, cut the luff straight and re-sewed the luff tape back on. Interestingly, both sails' 43' luff sail also gained about 8" in luff length which indicates how much the dacron had stretched through the years. Anyway, the previously stretched luff portions of the sails are now much flatter than before. This alone improved close-reach performance. Before: the mast head fly was just outside of the marker to keep the windward luff tell tale streaming straight. After: Right on or just a bit inside the marker. I also have a kevlar racing sail. Not stretched out. Exhibits the same performance as my re-cut Dacron sails.
- I do have a split backstay tensioner. So the headstay has enough tension to avoid too much sag.
- I sail most often in 15-25 kt winds.
- Between wind shifting in direction and velocity almost constantly, and SF Bay currents changing within a hundred yards, trying to measure changes in VMG on the GPS or knot meter that might be attributable to subtle modifications of sail trim is not possible.
- Irrespective of boat hull/prop/keel/rudder design, why is it that the luff jib tell tales on many boats are flying just perfect many more degrees into the wind than mine? Yeah, my boat's underwater stuff might hinder actual speed verses angle, but still it would seem that on the deck and higher, sail performance should be the same? Yes, speed of the boat does change the apparent wind angle. But say between 5kts (in a 15kt wind) for my boat vs. 5.5 kts (in the same wind for another boat) is that change really germane to what angle into the wind the tell-tales are true?

All this why is I am asking if inside track sheeting (11.6 degrees off centerline for my boat) vs. toe rail sheeting (17 degrees off centerline) is a more critical factor than anything else. ??? It's the only thing I can really change on my boat.

I'm enjoying the learning. Thanks everybody.

rardi