Tuning Guide

Introduction

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 105 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.

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).

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 Prep

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

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.

Measuring 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.

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).

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.

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.

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. 


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.

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