Sobstad T-10 Tuning guide

Boat Prep
Strut & Prop
Trimming Ballast

Mast Prep
Mast Head
Jib Stay Hounds
Spinnaker Haylard Exit
Spinnaker Pole Track
Topping Lift
Mast Rake
Mast Setup
Shroud Tension

Deck Layout
Jib Tack
Jib Cunningham
Spinnaker Sheets & Twings
Jib Windward Sheeting
Boom Vang
Mainsail Outhaul
Mainsail Cunningham
Mainsail Traveler
Happy Crew

Crew Work

Sail Trim
Jib Trim
Mainsail Trim
Spinnaker Trim

Sobstad sailmakers sailed the prototype T-10 with Charlie Britton off Grand River in December of 1977 and have sailed and raced T-1O's ever since. Our sails have come through quite an evolution to today's molded shapes and load oriented strength members.

This guide contains concise information for getting top performance out of your T-10. In nearly two decades of T-10 racing we have developed these techniques to achieve maximum speed in all wind and sea conditions.

Proper boat setup and sail trim are vitally important in T-10 racing as we use our one suit of sails in all wind conditions. We shape the Class jib to sail in flat drifters through 25 knots of breeze. The mainsail must be deep enough to power through the short chop of the Great Lakes and still be able to flatten out in a big blow. The all-purpose spinnaker must reach in all wind conditions and then run downwind at planing speeds.

These guidelines are what we at Sobstad, as well as several other class champions, use as a rule of thumb for setting up the T-10 rig and trimming Sobstad T-10 sails. We cover boat and rig preparation, rig tuning, crew work, and sail trim, This information will help make your sailing safer, easier, faster and most of all, more fun!

Note: All suggested part numbers are by Harken Yacht Equipment unless otherwise noted.

Boat Preparation


First start by reworking the keel-to-hull joint with a grinder. Remove all putty or glass work that may be there. Grind 6" on either side of the seam down to bare lead on the keel and bare glass on the sump. Tighten the keel bolts. Using epoxy, wrap the joint with layers of fiber glass tape. Build the seam back up to the Class minimum section.

Fair the rest of the keel using epoxy with low density and microlight fillers to the Class minimum sections and square the trailing edge. Finish with epoxy barrier coat and a racing bottom paint.


Fair the rudder to remove factory imperfections and to make it symmetrical. Square the trailing edge. Finish with epoxy barrier coat and a racing bottom paint.

Harken rudder bearings are great, but they're not necessary. As are alternative, wrap the rudder post with Teflon tape and lubricate it with grease before inserting the rudder in the boat.

Replace the original rudder fairing with 1 1 oz. polyester fabric epoxied onto the skeg using small fasteners for back-up.


In general, the bottom should be smooth and fair. The Class rules allow factory imperfections to be filled. Use an epoxy barrier coat and a racing bottom paint and wet sand the finish with 600 grit paper.

Strut & Prop

To fair the hull at the strut area, remove the prop and shaft and then grind out the filled area around the strut. Remove the strut and rebed it in epoxy with a large backing plate and new bolts. Build the

hull back up with glass mat and epoxy and then fair it in with epoxy and microlight filler. Finish with epoxy barrier coat and bottom paint.

Martec will re-build your prop for approximately $250. We recommend replacing the cutlass bearing at the same time. Make sure the shaft is straight to minimize vibration and avoid cracking around the strut. Reassemble the prop and shaft with a Martec zinc ahead of the strut. Shorten the shaft if necessary to keep the prop as close to the strut as possible. Finally, re-align the engine to minimize vibration.

Trimming Ballast

Class rules permit us to remove the lead Tartan Marine placed in the bow of the boat as trimming ballast. Locate the rectangular fiberglass containers molded in the bow peak and remove them along with the bow lead.

Mast Preparation

Mast Head

Try and keep it as light and clean up top as possible. One pound aloft equals eight pounds of keel weight. Use a 1 0" Windex mast head fly. If you plan to sail at night, use just the Windex mast head light to minimize weight aloft and to reduce windage.

Not Needed:

  • Radio antenna and cable (mount on stern railing)
  • Mast head light and power cable
  • Wind instruments and cable
  • Second jib halyard. Remove it if present.

Jib stay intersection or hounds

Replace the jib and spinnaker halyard sheaves with Schaefer 34-35 exit boxes. For the spinnaker halyard bracket use a Schaefer 78-71 bow eye. This is a 1/4" SS rod eye that will not fail. Its round rod construction reduces friction and will not damage the spinnaker halyard. We highly recommend a rope to wire jib halyard using 5/16" Spectra/Technora line and five feet of 5/32" wire to the halyard shackle. This new setup is really hot!!!

Spinnaker Halyard Exit

Jumping the spinnaker halyard at the mast saves time and eliminates problems. Cut an exit hole for the spinnaker halyard on the starboard side of the mast eight feet above deck level. Finish it with an exit plate and twelve inches below this mount a cam cleat an la flat base in line with the halyard. Install a standing block on the deck, ahead of the mast step spinnaker sheave, to lead the halyard back to the cockpit.

Spinnaker Pole Track

This is optional, but if you want to adjust the pole under load it's great.

Parts Needed:

1. 780 spinnaker pole car

2. (2) 082 bullet blocks on the car

3. 10' of 154 track with 173 end stops

4. (2) 282 eye straps to dead end lines

5. (2) 150 cam cleats

6. (2) 092 cheek blocks for control line

Be sure to bring the track all the way down to the mast step so you can sail upwind with the pole attached to the mast.

Topping Lift

The spinnaker halyard exiting up on the mast frees a mast step sheave on the starboard side. We've used this to double end our topping lift. This allows us to adjust pole height quickly and more easily from either side of the boat. The 2:1 purchase eliminates the need to use a winch to raise the pole and the cam cleats work much faster than opening a sheet stopper.

Attach a swivel block to the topping lift inside the mast. Lead the topping lift control line into the port sheave, through the block and out the spare starboard sheave. Mount cam cleats with fairleads on both sides of the companionway next to your sheet stoppers to control pole height.


Opinions vary on what instrumentation is necessary, but most people agree that the place for the Sailcomp and speed displays is on the mast just below the boom. This requires a custom mast bracket but helps to keep your focus out of the boat and allows the entire crew to watch the numbers.

Mast Rake

The mast needs to be raked back as far as possible to help balance the helm. Make sure the headstay is maximum length. Check this by measuring the distance between the mast butt and the bottom edge of the forestay attachment.

If the distance from the butt of the mast to the attachment is less than: Then the forestay (maximum length) should be:
34' 3" 36' 3" + 1/2"
34' 4" 36' 3-7/8" + 1/2"
34' 5" 36' 4-5/8" + 1/2"
34' 6" 36' 5-1/16 + 1/2"
34' 7" 36' 5-1/2" + 1/2"

Come only to within 1/4" of the maximum as different measurers will get different lengths.

Mast Setup

First, make sure the mast step is on the center line of the boat. Measure back 14' from the jib tack to each toe rail and mark this point on each toe rail. Measure from each toe rail to the mast step. If the mast step is off center, use the aluminum spacers to help center the mast in the mast step.

Step the mast with the aluminum spacers pushing the mast all the way forward in the step. Lead the main halyard to port and the jib halyard to starboard.

Release any backstay tension and remove the boom from the boom topping lift. Attach a 100' tape measure to the main halyard and run it up the mast. Starting with all the shrouds loose, center the mast head by tightening just the upper shrouds while measuring to the marks on the toe rails. Tension the upper shrouds five full turns past hand tight while checking for center.

Adjust the lower shrouds until they are hand tight. Then add approximately five additional turns while continuously checking the mast for straightness. You may need a different number of turns on each side to make the mast straight. Pin all of the shroud turn buckles with trailer hitch pins. After sailing and returning to the dock, carefully re-measure and check the mast for straightness.

Shroud Tension

Use the Shroud Tension Guide and a Loos large "B" tension gauge to adjust shroud tension for various wind and sea conditions using numbers from the following table.



Loose lower shrouds help the boat accelerate in light air. The loose uppers allow headstay sag to power up the jib.

40 38
LIGHT 5-10

Upper shrouds should be tighter than the lowers. By tensioning the upper shrouds, you will get 1-1/2" of pre-bend which opens the lower leech of the mainsail.

44 38
MEDIUM 10-15

Uppers and lowers should be the same numbers (or as tight as you feel comfortable). This keeps the main powered up and also keeps the forestay tight. As a puff comes, use the combination of backstay and mainsheet to keep the boat on its feet. When the backstay is loose, the loads are on the leech of the mainsail, not on the backstay. This gives you headstay support.

45 45

Upper and lower shrouds should be tight. The key thing to remember is the backstay will now de-power the main and also de-power the jib. The upper shrouds will become loose because of compression bend, while the lower shrouds become tighter. Looking up the mast, the top will fall off at least 6 to 8 inches (in a symmetrical curve).

49 49+

Values are from Loos large, size "B", tension gauge scale,

Deck Layout

When setting up your T-10 deck layout, it is important that you have the proper equipment and that it is placed in the best area of the boat to ensure ease of use. Consider the strength of your crew and add enough purchase to your controls so they can be adjusted without using a winch. Consider the number of crew you usually sail with and lay out the controls for each crew position.

As you will see, we recommend moving many of the controls to the starboard side of the boat. This keeps weight on the high or windward side of boat to keep the boat flat when going around marks to port. We recommend Spinlock XT/R stoppers with special cams for the new high tech Spectra lines or the Antal V-Grip. They hold well, can be released under load, and help reduce line wear.

Jib Tack

Starting at the bow of the boat, remove the jib tack horns and replace them with a Wichard 1411 long "D" shackle. This will bring the jib tack on center line and will eliminate problems that happen with tack horns.

Jib Cunningham

Mount a II 3 pivoting cheek block on the stem head for a jib Cunningham. The jib Cunningham dead ends on the tack shackle, leads up through the Cunningham cringle and then down through the cheek block on the stem head. This runs back along the deck 6" ending on a 082 single block.

Attach a 362 block with cam cleat to the stantion bases at the shrouds on both sides of the boat. Lead 1/4" line through the control block forward through the floating block and back to the control on the other side to get 4:1 final purchase, This allows you to control the jib luff tension from either side without leaving the weather rail.


Down wind we adjust the pole constantly and find it quick and convenient when it's double ended and can be adjusted from either side of the cockpit.

Parts Needed:

1. 688 pad eye on fore deck replacing the original fairlead. On most boats, there is an aluminum plate glassed into the deck that you can drill and tap for the fasteners.

2. (7) 168 single swivel blocks.

3. (2) 240 swivel base and cam cleat.

Set the cam cleats on deck according to the preference of your crew. Our setup allows the foreguy trimmer or the pit person to easily reach it on either side of the boat.

Spinnaker Sheets and Twings

Use long "D" shackles to hook the spinnaker sheet turning blocks to the toe rail and lash the beckets to the life lines to keep them from binding. Use Spectra sheets for light weight and low stretch. Holt Allen 1375 snatch twing blocks are great for twings. They allow you to go between light and heavy spinnaker sheets transferring the twings quickly and easily.

Parts Needed:

1. (2) 150 cam cleats w/328 fairleads

2. (2) Holt-Allen 1375 snatch blocks for twings

3. (2) 169 blocks with beckets for light air spinnaker sheets

4. (2) 1550/1572 midrange hexaratchets with beckets for heavy air spinnaker sheets

The Sobstad companionway spinnaker launcher is very convenient in short course racing. The chute goes up and down quickly without going below and re-packing.


We recommend upgrading the primary winches to self-tailing models, either Harken B40.2STA or Lewmar 40AST. This allows you to trim and adjust the jib sheeting quickly and positively. Move the standard #40 winches back for secondary spinnaker winches.

Mount winch handle holders in convenient locations on both sides of the cockpit to minimize confusion during your tacks.

Jib Windward Sheeting

Cross sheeting the jib allows the crew to adjust the jib trim from the high side rail. This lets you work the jib in and out in puffs, shift gears for waves, or duck other boats, without sending weight down to the leeward winch. Also, it's easy to duplicate settings that were fast in previous conditions. Mount 1548 mid-range cheek blocks on the deck just ahead of the primary winches and lead the jib sheets across the cockpit in windy conditions.

Boom Vang

The 3:1 aspect ratio of the mainsail requires at least 12:1 purchase to adjust the boom vang. Multiply your present vang purchase using wire and wire blocks and your existing block and tackle to achieve 12:1 or better. You need the power and adjustabilty and must adjust it from either rail when going upwind or spinnaker reaching.

Mainsail Outhaul

Class rules allow the mainsail clew slug in the boom groove to be replaced with track and a ball bearing car. With this set-up you can adjust the foot of the mainsail anytime as conditions change. This also eliminates the clew slug pulling out of the boom.

Parts Needed:

1. 15" of 1800 track with 1801 mounting kit and 173 end stops.

2. 1776 high load car

3. Wichard 1402 "D" shackle to connect the sail to the car.

4. 300 wire block and a 137 eye strap

We suggest adding additional purchase and leading the outhaul back to the cockpit for continuous adjusting by your mainsail trimmer. If you use a 300 wire block on the car or on the sail, and dead end the outhaul wire on the end of the boom, you will double your purchase. Use a number scale on the boom to duplicate fast settings.

Mainsail Cunningham

Use at least 6:1 purchase and lead the mainsail Cunningham back to the cockpit so your mainsail trimmer can adjust this as needed.


Use your existing hardware, and add the necessary blocks to convert to a 4:1 / 16:1 gross tune/fine tune main sheet system. This is a must for vang sheeting going up wind in breezy or puffy conditions. We can easily re-lead the mainsheet in light air eliminating two parts to get a 2:1 / 4:1 combination. See Harken system 4 on page 206 of their catalog.

Mainsheet Traveler

It is essential that you upgrade your traveler as the original is not sufficient. The T-10 is a perfect application for the Harken windward sheeting traveler car. It is convenient and works well which helps to keep your mainsail trimmer's head outside the boat. Use the 1576 long mid-range car with 1511 tall track and 1516 single sheave end controls. The 3:1 traveler control is sufficient and minimizes drag.


Lead the backstay controls down and forward on each side of the cockpit for 4:1 purchase. Mount 150 cam cleats with 328 fairleads on the sides-of the cockpit so your mainsail trimmer can adjust it from either side.

Happy crew

Split 1" PVC tubing or foam pipe insulation placed over the toe rail from the shrouds to the cockpit saves your crew's legs.

Happy Skipper

Mount teak strips on the edge of the seat behind the traveler for the driver's feet. They are a must in heeling conditions.

Crew Work

Most of us sail with seven people but the boat can easily be handled by five in moderate conditions, The T-10 sails to weather best when it's kept flat. In heavy air we race with as many as nine people to help hold it down.


In light air, hike to leeward to induce heel and to help pre-shape the sails. Keep your weight between the shrouds and the 3rd stantion. Roll tack the boat to minimize steering while helping to throw the sails through the tack. Watch ahead for puffs and observe what other boats on the race course are doing.

In puffs or building breeze, move some people up to the weather rail to flatten the boat and to keep the helm neutral. Roll tacking is fast in medium breeze.

In moderate to heavy breeze hike hard on the weather rail and move forward lining the rail from the shrouds back. Watch for puffs and call out approaching waves and chop that may slow the boat down. When tacking, get everyone across to the new high side rail as quickly as possible to keep the boat flat and pointing high.


In light to medium air, keep the boat flat side to side and move weight forward between the shrouds and the 3rd stantion. This lifts the butt out of the water reducing the wetted surface area. Have

one person stand against the boom, holding it out, while looking back for puffs and for other boats that may try to get on your wind.

As the wind builds, move people back to keep the bow up. In medium air, hike the boat to weather slightly to project the mainsail area higher and to help the spinnaker drop out from behind the main. In heavy air, call out approaching surfable waves and puffs.

Sail Trim

The final and most important factor in boat speed is sail trim. Upwind, three adjustments affect speed more than ail others: mainsheet trim, backstay tension, and jibsheet trim. In general, if you're pointing high and going fast, leave things alone. If you're going slow ease them out. Remember: When in doubt ease it out!

Jib Trim

The molded in shape of the Sobstad GENESIS Platinum jib is very versatile. The full entry and flat exit of our jibs allows them to be trimmed very hard without any noticeable back-winding of the mainsail. The laminated in tapered battens keep the leech open and the exit clean.

It is important that the lower shrouds are tight enough to support your headstay. If they are not, you will get a great deal of forestay sag, and the jib will appear very full with the draft forward (you will notice that the inside tell-tales will tend to stall). In addition to the proper rig tune, the jib is affected by luff tension, lead position, and sheet tension.

Luff tension affects the draft position in the jib. In light air we slide the draft back by sailing with 1/2" scallops between each luff hank. As the breeze builds, use the jib Cunningham to tighten luff tension until the wrinkles disappear in 1 0 knots true and up.

Stock jib tracks should have additional holes drilled between the second and fourth original holes allowing you to adjust the jib lead in finer increments. In light to medium air the car adjustment pins are set in the 2-1/3 hole. As wind increases move the cars back one hole to open the leech. In heavy air, slide the cars back to the 3 hole and in 25+ knots into the 4 hole.

For an easy jib trimming reference, put tape stripes around the spreaders 30" out from the side of the mast. Sight up from the winch and line up the jib leech with the stripe on the spreader to judge the jib trim. When tacking upwind in light to medium air, initially bring the jib in only to the spreader tip until the boat accelerates. As the boat speed builds, trim in using the guidelines in the following table..

Mainsail Trim

Sobstad's T-10 mainsails have all the power you need due to their large elliptical roach. Early T-10 mainsails relied on luff curve and mast pre-bend to control draft in the sail. Today's designs keep the, mast straight when sailing in moderate conditions. This enables us to build the largest roach possible while staying within the Class girths. Sobstad mainsails are built using large 2-ply reinforcements, so you can control them through the entire wind range without distortion.

Normally, sailing upwind, the main halyard should always be kept at maximum hoist. Draft placement is easily adjusted with the Cunningham, outhaul, and backstay tension.

Position the boom as close to centerline as possible. Adjust the traveler and mainsheet to set the top batten parallel to the boom. You will notice the second batten is slightly to weather or parallel due to the open head design. Exceptions to this would be:

While accelerating after tacking. Drop the traveler 1 0" to leeward.

When the boat is overpowered. Flatten the foot with the outhaul and drop the traveler to keep the boat upright.

When more twist is needed in wind shear. At this time only, the boom may be above center line.

In very light winds of 5 knots apparent or less. Drop the boom to the leeward quarter.

In flat seas with winds between 5 and 20 knots apparent. Trim the mainsheet until the top telltale flies free 50% to 70% of the time (slightly stalled).

When sailing in choppy seas, disturbed air, or in winds of more than 20 knots apparent, a stalled upper batten will cause the boat to heel (which is slow). In these conditions it is essential to vang sheet the main and work the jib trim together to keep the boat flat. This allows the boat to accelerate in the puffs and prevents rounding up to windward. The helmsman must aggressively feather the boat to keep it flat. Have the crew on the high side calling wind and waves to work the boat through difficult conditions.

It is important not to over-trim the main. Twist will reduce heel and enhance speed. The mainsail is the accelerator pedal of your T-10.

The vang should be set up early so you can use it to control twist. In over-powering situations, play the mainsheet in and out with the fine tune adjuster. This is faster than letting the traveler down.

Downwind, ease the outhaul and Cunningham or halyard tension and have the forward crew adjust the vang while sighting up from under the boom to set the upper batten parallel. In surfing conditions, pump the mainsheet as you start down the back of waves to help induce planing.

Spinnaker Trim

The Sobstad chute is an all purpose cut that has gone through extensive testing and design. The current shape and construction is very fast on a run and also reaches up to 80 degrees.

Generally, keep the clews even height and the pole square to the wind. When tight reaching, lower the pole extra and over-square it slightly.

In light air, sail higher with wider gibe angles to maintain boat speed. In average conditions, drive down deeper in puffs while you bring the pole back and up. In surfing conditions, pump the spinnaker sheet as you start down the back of waves to help induce planing.

Good Luck and Have Fun!!!


WIND SPEED(True) 0-4 5-9 10-14 15-19 20-24 25+
SHROUD TENSION(Loos gauge number)            
Uppers 40 44 45 49 49+ 49+
Lowers 38 38 45 49+ 49+ 49+
JIB TRIM            
Jib Car (hole) 2-1/3 2-1/3 3 3 4 4
Jib Luff wrinkles slight wrinkles no wrinkles no wrinkles smooth smooth
Jib Leech(inches in from spreader tip)            
Flat water 3 3 3 3 3 working
With chop 0 1-1/2 3 3 3 working
MAINSAIL TRIM            
Top Batten Trim slightly open slightly closed slightly closed slightly closed working open working open
Outhaul 4" shelf 3" shelf 2" shelf no shelf maximum maximum
Cunningham off luff wrinkles off luff wrinkles slight wrinkles no wrinkles maximum smooth luff maximum smooth luff
Backstay full off full off working in puffs working maximum maximum
Boom Position down 12" center line center line slightly below center down working on the quarter
Top Batten soft soft standard standard standard standard
Traveler/Vang Sheeting traveler traveler traveler both vang vang


Sobstad T-10 Running Rigging

Jib Halyard 5/16" 95' T-900 Technora/Spectra Core w/ Polyester Cover Nicro 12000S
Main Halyard 5/16" 105' T-900 Technora/Spectra Core w/ Polyester Cover Wichard 81433
Spinnaker Halyard 3/8" 100' STA-SET X Parallel Polyester Core w/ Polyester Cover Nicro 12000S
Topping Lift 5/16" 25'



STA-SET X Parallel Polyester Core w/ Polyester Cover Wichard 2313 Snap Hook
Jib Sheets 7/16" 45' STA-SET X Parallel Polyester Core w/ Polyester Cover -
Mainsheet Fine 1/4" 25' STA-SET Polyester Double Braid -
Mainsheet Gross 7/16" 65' STA-SET Polyester Double Braid -
Spinnaker Sheets Light 1/4" 70' STA-SET X LITE Spectra/Polypropylene Core w/Polypropylene Cover NAB 3000 Plastic
Spinnaker Sheets Heavy 3/8" 70' SPECT-SET II Spectra w/Polyester Cover Wichard 2673 and Donuts
Twing Lines 1/4" 13' BRITE LITE Spectra Core w/ Nylon Cover Holt Allen 1375
Foreguy 1/4" 55' STA-SET Polyester Double Braid Wichard 2313
Vang Line 5/16" 35' STA-SET Polyester Double Braid -
Traveler Line 5/16" 18' REGATTA BRAID Polyester Braid -
Backstay Line 5/16" 50' STA-SET Polyester Double Braid -
Main Cunningham 1/4" 25' STA-SET Polyester Double Braid -
Jib Cunningham 1/4" 40' STA-SET Polyester Double Braid -

This information is provided courtesy of New England Ropes, Fall River, MA.