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J105 Tuning Guide

J105 Tuning Guide

Getting Started
. Boat Preparation
. Mast Prep
. Deck and Rigging Details
. Setup and Tuning
. Rig Tension Guide
. Installing Your New Sails
. Mainsail Trim
. Jib Trim
. Spinnaker Trim
. Upwind Sailing Tricks
. Downwind Sailing Tricks
. Line Guide

1 PB Intro.jpg


The J105 has become the success story of one-design racing in the new millennium. With over 680 boats built to date, the class is the largest cruiser-racer one-design. Easily sailed with a small crew, the responsive design allows the boat to be fun to sail with only a main, jib and asymmetric spinnaker. Here we will explore the process required for success with your J105 racing program.
Success in one-design can be summated into one sentence: He who makes the least mistakes wins.
Let us break this down into specific details and progressions towards advancement. The most important factor is boat speed. A racers IQ elevates exponentially as the relative boat speed increases. Boat speed is created through enhancing many small features. Every time you comment that does not matter write it down, because it does matter. Add up 10 insignificant items and you get something tangible. Add up 20 items and your sailing experience changes.
Be advised: there are many roads to victory and this tuning guide outlines certain proven techniques that are no way meant to be the only way. We expect the prudent racer not to consider this the bible but to add these concepts and techniques to your existing bag of tricks.
Doyle Sails is happy to have and will continue to support the growth of the J105 Class. I am a committed owner and want to help you get the most out of your boat. The better everyone in the class, the better the class.

~ Paul Beaudin "PB"

Boat Preparation / Bottom

The fairness of your bottom and the correct shaping of your foils, keel and rudder are of paramount importance. Perfect foil shape will allow the blades to work to maximum efficiency. Along with a fair bottom allowing minimum drag will result in a maximized boat speed potential.
As you will see in the following text everything we do while sailing is geared around maintaining foil and hull form efficiency. The keel is the reason the boat goes forward and not side ways.
Always make sure your bottom is perfectly clean. It is shame to cover a beautiful bottom job with slime. Not to mention, very slow. In my area the boats are wet sailed and cleaned weekly by divers. I paint my bottom with a hard finished paint and use a lighter color to make it easier for the diver to clean.

Boat Preparation / Minimum Weight

Drag is slow; keeping the boat at minimum weight will result in greater boat speed. Anything less in the boat will result in greater boatspeed except crew weight, which is movable ballast. Keep everything that is not required, off. Keep all required gear stored as low as possible. I store these items along with a few spare lines, hardware, repair kit and tools in the storage below the galley and nav table with the anchor, 2 required dock lines and bumpers under the starboard main cabin bunk. No bilge water, cooking stuff, unnecessary dock lines, redundant clothing, cruising sails, stamp collections, etc.  Absolutely keep everything out of the aft compartments and V-berth (except the spinnaker).

Boat Preparation / Weight Aloft

Sailing is physics; righting moment vs. wind pressure equals boatspeed. Weight up the rig decreases righting moment exponentially. Again anything not required is slow. Use minimum weight halyards (3 only), small size Windex (unlit) and minimal weight wind instruments. No masthead VHF, lightning rods or Tricolor lights. Remove any redundant wiring.
Note: I am using 10mm halyards for the main and jib to keep clutch slip to a minimum. I use an 8mm Spin halyard. My halyards are not stripped to make them last longer and I get them with a luggage eye in both ends easily end for end for extended life. I will suffer a bit of weight, here and there, but with my other due diligence I can afford a little latitude.  I have no masthead light or instruments, only a small windex. 

Mast Preparation / Forestay Length

I like my forestay at the old maximum 13.035 meters from the forestay attachment to the stem sheerline.  You will usually need to add a toggle to the top of the forestay to make the forestay long enough.
Make your furling drum as close to the deck as possible. On the older Harken III furlers, we will have the adjustment screw on the bottom of the furler all the way in. We will fine tune our stay length with the internal adjustment screw on the furler. Use a small shackle on the drum to attach the jib. This keeps the jib close to the deck and creates a better endplate effect. Increasing the efficiency of the jib

Mast Preparation / Measuring with the Mast Down

First measure the distance from the stem/sheer line intersection to the center of the forestay pin on the bow tang. Then measure the forestay, center of pin to center of pin for the difference. Secure the locknut on your furler turnbuckle and you should not need to touch this again.

Mast Preparation / Measuring with the Mast Up

Place a mark on your mast 1000mm down from the top of the black band at the gooseneck. Attach a metal tape measure to your jib halyard and pull tight to the top. We use a metal tape because it will have less stretch than the halyard. Measure to the mark on the mast, pendulum the tape to your forestay and make a mark at the same measurement. The distance from this mark to the stem sheer line intersection is 1270mm. Secure the locknut on your furler turnbuckle and you should not need to touch this again.

Mast Preparation / Set the Mast Rake

This is a critical element of tuning. The Hall Spar in most boats is a fairly soft section for the job at hand. As will be further discussed below, it is hard to get the mast stiff enough, as the breeze builds, to maintain the amount of forestay sag we need to make the jib point well upwind. We want a straight mast, with no prebend (bend in the mast, at rest, without backstay).

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Mast Preparation / Set Your Mast Butt

Loosen all the shrouds to slack. Take the spinnaker halyard around the upper shroud and secure aft to one of the spinnaker sheet block bails in the back of the boat. Tighten the spin halyard to remove the slack from the forestay. Mark the position of the mast at the deck fore and aft. Remove the deck chocking, if possible. My mast has Spartite that centers the mast in hole, but I can slide it up and down to do this measurement. Loosen the mast base bolts. I use a rubber mallet and a block of wood to bang the butt forward and aft. Move the butt so the mast is in a neutral position at the chock mark and reinstall the deck chocking.  The aft face of the mast should end up about 10 inches from the bulkhead aft (not the molding) on TPI built boats.

3 Center the rig.jpg

Mast Preparation / Center the Rig

Hoist a tape measure up the genoa halyard. Measuring from side to side to the base of the chainplates, center the rig using the Upper shrouds only. Dont tension to create a compression bend, just enough to keep the mast from flopping around. Keeping the intermediate shrouds loose hand tension the lowers keeping the mast perfectly straight.
Note: Hall masts have a design flaw which kinks the mast at the hounds (forestay attachment) aft usually around one inch. This has little effect on sailing but if your mast is kinked, to have no prebend, the mast should be straight up to that point.

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Mast Preparation / Mark Your Spreaders

Install three tape marks on your lower spreaders at 3, 6, 9, 12 inches from the tip for future reference. We usually sail with the leech of the jib between the 3 and 6 inch marks. The 9 and 12 inch marks are for viewing through the mainsail window and should be a different color. 

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Mast Preparation / Rig Tools

Combo Wrenches, Waterproof Notepad, Pencil, Calipers.

Combo wrenches 3/4 and 9/16 tied together will work on 90% of the boats with open turnbuckles

Mast Preparation / Setup & Tuning

These are general numbers to get you started. Each boat will tune a little differently and the Loos gauges are not entirely consistent either. Make sure you understand the underlying goals of tuning and you will be able to adjust your own numbers accordingly.
The goal is to keep the mast as straight as possible. With the minimal sweep of the spreaders and the size of the spar section the mast is soft for this size boat. We need to keep the mast as straight as possible to maintain its ability to support the forestay as the breeze builds and backstay is applied. This also allows mainsheet tension to also auto trim the headstay in light air. With a straight mast, as you tension the mainsheet or backstay more energy is applied directly to the forestay. The straight mast will also allow for the most projected mainsail area as roach is pushed out to back of the sail.
All this rig tuning is done to allow the mast to fit your sails and for your sails to be as flexible as possible to work through the entire wind range. We are asking a limited number of sails (only 2 jibs upwind) to do the work that as many as 10 sails might have done on similar boats under handicap rules.

7 headstay sag.jpg

Nice shot of the correct  headstay sag for the base setting.

How I set up my initial Base Tune. 5-10 knots

Using a Loos #10 Rod Tension Gauge. Tune the Upper Shrouds to 35, 45 on a pre-scrimp boat. Intermediates hand tight. Lowers hand tight -1 full turn. Now I go sailing, in 5-10 knots.  While sailing upwind I will dial in the intermediate and lower shrouds. With this dock tune you should have a fair bit of leeward sag in the mast. You can easily sight this from the front looking up. I will tune the lower and intermediates to bring the mast to showing just a hint of leeward sag on each tack. You should be able to tune the weather lowers and intermediates in this much wind and the process will not be too hard. With the backstay slack, the mast should be straight fore and aft. Next I will check the headstay sag, which should be right around 10 inches. The headstay sag is probably the most important part of this equation. 
Note: On pre-scrimp boats dial the uppers to the 10 inches of headstay sag first. I have seen a big variation on how much tension it takes to get there from boat to boat. Not all pre-scrimp boats tune the same.  Scrimp boats seem to be more consistent in this regard.
This is your base setting for 5-10 knots of breeze.
From here it gets pretty easy.

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Get out your waterproof note book, pencil, and calipers.
Measure the distance between the gap of all the shroud studs and record, as shown.
This will become your Tuning Bible.
Note: for Ronstan turnbuckles, use the calibrated numbers to records your gaps and double the amount of turns below for each tune. You are only turning one screw, as opposed to two on the open body style turnbuckles.

Hall Spar Rig Settings 2022.jpg
Sparcraft Mast Rig Settings 2022.jpg

Installing Your New Doyle Sails

Roller Furling Class Jib

Make sure you have a small shackle at the furling drum and not a snap shackle or connector. Keep the tack of the sail as low as possible. This sail has no UV cover so if you store it on the furler, use the optional jib cover sock to protect it from damaging UV rays. Hoist the sail up by hand until the cloth is snug. Mark your jib halyard as it enters the front of the stopper and add 2 marks in front of this mark at 2 inch intervals for quick reference.

Class Mainsail

Lay the sail out on the deck and install the battens, tapered end inboard. We like to roll the main for long term storage, but will usually flake it on the boom removing the slides from the mast when the sail comes down. Hoisting the main with the Allslip slides is pretty easy. Again mark your halyard for future reference.

Class Asymmetric Spinnaker

This is launched from the forepeak out of the forward hatch.

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Upwind Sailing

Over View: In light air we are keeping the boat as powered up as possible and trying to go fast rather than point. We try to keep our weight centered in the boat and low, with a minimum amount of movement. As the breeze builds the primary focus is on the amount of helm. We do everything we can to keep the helm light with just a hint of weather helm. To maintain the proper helm, through a given tune range, we will adjust the crew weight (hiking), backstay, traveler and jib leads to balance the helm.

Mainsail Trim / Halyard

Adjust halyard tension to keep the draft (deepest part) of the sail at 45-50%.
You will have wrinkles in luff in winds to about 12knots TW . Basically keep
tightening the luff as the breeze builds.

Mainsail Trim / Cunningham

Set your halyard tension to the lulls for the beat and adjust your luff tension
with the cunningham as the breeze changes on the beat. We use no
cunningham below 10knots and snug to remove the wrinkles in 10-20 knots.
Above 20knots apply firmly. If the wind build consistently remember that
your halyard will have to be tighter on the next upwind.

Mainsail Trim / Sheet Tension

We design the sail so you can trim hard with out it closing the top too quickly.
Keep the top batten parallel with the boom and the top telltale flying. When you are at full speed you can trim a bit harder to get the top telltale to stall.
In light air with lump conditions open this up a bit, maybe have the top batten
5 degrees open and always let the top telltale fly 50% off the time. In heavier air as we depower we will again allow the top to open and the top telltale will always be flying.

Mainsail Trim / Traveler

Keep the boom on centerline until you have to depower. In light air we pull the traveler all the way to weather and adjust the sheet to keep the boom on centerline. Progressively lowering the traveler as the breeze build to balance the helm and heal of the boat. We never drop the traveler below the leeward seat.

Mainsail Trim / Backstay

This is not the quickest tool on your boat so we will have to use it as a general trim adjuster. Make sure you have a batten taped to the cylinder to record your settings for the next beat. In light air keep it just loaded with the slack out. 
If your mast is set correctly you should not invert the main, which you will see by wrinkles forming from the clew up towards the middle luff. If this appears, your mast butt may be too far aft.  Make sure to tighten cunningham as you use heavy backstay to keep the draft forward in the sail.

Mainsail Trim / Outhaul

In light air we have the outhaul eased about one inch in flat water and 2 in lump. Once the crew is fully hiking we tighten just to close the shelf foot.  In heavy air crank it hard.

Mainsail Trim / VangWe never really use the vang upwind. In very light air you might have to have a little tension to not over twist the leech, but the rest of the time, while sailing upwind, we have the vang control just slack.

Mainsail Trim / Leech & Foot Lines

Only use these to remove flutter and remember as the breeze lightens ease them off.

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Jib Trim / Jib Halyard

The jib halyard is very important and frequently forgotten on these furling boats.
Unlike the main, the halyard will not have a s large effect on the draft of the sail.
It is pretty fixed on a laminate sail. In light air ease the halyard until you have
noticeable wrinkles in the luff. This will move the draft aft and increase fullness
for power. As the breeze builds, increase halyard tension, to, just, remove the
wrinkles, until very firm in the heaviest wind. Equally important is to release the
tension if the wind drops.

Jib Trim / Jib Lead

Set the jib lead to have 9 track holes showing in front of the car. This is your base position. Mark the track at this point. When I go to the medium tune I will go back 1 hole on the lead. As the breeze builds we move the lead aft through a range of about 6 holes from light to heavy air. The jib lead is an effective method to depower. If I am caught at the top of a tuning range and the boat has too much helm, I will move the lead car aft along with tightening backstay, lowering traveler and tighten the halyards.

Jib Trim / Jib Sheet

In light air I trim to the leeward cabin top winch and in heavy air I cross sheet to the large primary winch. Run the sheet through the top check block for a better lead to the primary winch.  Your new Doyle Jib will have leech telltales. Trim the sheet until the top leech telltale just has a hint of break (10%). This is my base upwind trim position. This will also put the leech of the jib between 2 and 4 inches in front the lower spreader tip. Out of a tack or in slow speed conditions ease the sail to the spreader tip. When up to full speed in flat water we will trim a bit tighter to have the telltale breaking 25% of the time.
To cross sheet you need to mark your jib sheets. I put a series of 4 marks,  on my jib sheets between 17 and 18 feet from the clew end of the sheet. I will use this as a trim guide while cross sheeting to the large primary winches, in breeze. These marks will be right at the weather winch and will allow repeatable settings from tack to tack without having to go down to the low side. For cross sheeting: the jib trimmer will tack the sail and grind it in to the conditions base setting, with the leech at the spreader tip. The main trimmer will then handle the fine tune trim.

Jib Trim / Jib Inhauling

I rarely use any inhaul. At best, in perfect conditions, we might just tighten the lazy sheet to pull the clew over the track, about 2 inches maximum. Any more just seems to stop.

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Downwind Sailing / Mainsheet

Make sure to ease the main out enough as you go downwind. In light air you will sail higher angles and have it in more and as the breeze build you will ease it out.  I usually have a knot in my mainsheet at the maximum out position (boom just off the shrouds) so the driver can uncleat the main around the weather mark and let it run. In very heavy air only ease the sheet to put the boom out 45 degrees and adjust the vang to control the leech twist.  This makes jibing the boom much easier. You might also try pumping the vang, rather than the sheet, to help the boat surf down waves.

Downwind Sailing / Backstay, Outhaul & Vang

Ease the tension off the backstay and lock. I don’t like the backstay eased to the point of the cylinder flopping around.  In light to moderate air ease the outhaul until the foot of the sail is about 3 inches from the boom. I do not ease it in windy conditions. Adjust the vang to keep the top batten parallel to the boom in the lulls.
Make sure to remember your halyard, backstay and outhaul settings for the next upwind.

Downwind Sailing / Spinnaker Sheet

Trim the sail to always have a slight curl in the luff (about 6-12 inches). Pay attention to the load on the sheet. When you get too far off the wind, pressure on sheet will immediately drop. A good trimmer will constantly communicate with the driver regarding the amount of load on the sheet.

Downwind Sailing / Tack Line

Adjust the tackline to keep the curl just above the middle of the luff.
If it breaks high lower the tack, if the break is at the bottom raise the tack.
Average tack heights:

under 8 knots / 0 inches
8-10 knots  / 6 inches
10-15 knots / 1 foot
15+ knots / 2 feet

13 Downwind tricksSpinnaker.jpg

Sailing Tips & Tricks

Upwind / Pointing

Go fast forward, never try to pinch a J105, it just stops. Better boatspeed through the water will help the keel and rudder provide lift and reduce leeway. Although your angle might not be as high the boat will be making less leeway and effectively sailing higher overall.

Upwind / Trim Fore and Aft

Keep the crew weight centered. In light air we have one crew in front of the shrouds. As soon as we are all hiking we have the crew aft of the shrouds and grouped together as much as possible.
Downwind / VMG

When the tack line is eased and we are in running mode, I will steer to keep the tack line vertical. If it tips to leeward, I will head down and if it tips to weather I will head up to keep the tack line straight up and down. This will keep you very close to the perfect VMG downwind.

Downwind / Running Deep

The trimmer should always be easing the sheet to get the sail to rotate out in front of the boat. It is a common mistake to have the sail over trimmed and not rotated properly. Look around at the spinnakers on the boats close to you, if you are having speed problems, and try to match the trim of the fast ones.


Line Guide

  • Jib Halyard 95 ft  10mm Spectra DB (double braid) with eye splice attached directly to furler swivel shackle

  • Main Halyard 105 ft 10mm Spectra DB with headboard shackle

  • Spinnaker Halyard 105 ft 8mm Spectra with medium flush style snap shackle.

  • Mainsheet 85 ft 10mm Soft Spectra Braid with low friction ring for 20 ft 8mm 2-1 fine tune

  • Jib Sheets 45 ft each 10mm Spectra DB with eyes and soft shackle.

  • Mark sheet between 17 and 18 ft every 4inches for cross sheeting reference.

  • Spin Sheets 70 ft each 8mm Spectra DB with eyes. Use 12inch 6mm pigtail on every spinnaker clew and bowline to sheets.

  • Tack Line 40 ft 8mm Spectra DB with optional eye and soft shackle. I bowline mine.

  • Misc:  Traveler 30 ft 8mm, Reef 20 ft 6mm, Pole 35 ft 8mm low stretch yacht braid.


Contact Paul Beaudin for onsite clinics and racing talks.


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