Platu 25 Tuning Guide
Introduction
The purpose of this Platu 25 tuning guide is to give our clients in the Platu 25 class some guidelines on how to get the most out of their North Sails.
Follow the guidelines, but always experiment and try finding your own trim. The weight of the crew, the balance of the boat, the stiffness of the mast together with specific local wind and sea conditions all have influence on the fastest and final trim.
Rig set-up
The North Sails TB-2 Main and LM-4 Jib are “state of the art” sails which did very well throughout the 1999 season. The main is quite powerful and needs some “prebend” (i.e. mastbend in non sailing conditions) in rig set-up. The pre-bend should be something like 50 mm. The best way to check this is tie the main halyard at the gooseneck, pull the halyard very tight and check the distance between the halyard and the back of the mast. This should be 50mm or close to that.
The uppershrouds must be very tight and as tight as possible in hvy. air conditions in order to tension the headstay. In lighter air you should slacken the upper shrouds at least 3 360 degree turns in order to get some headstay sag to make the front of the LM-4 jib as full as possible. In heavy air you should use the GH-2 jib (which is a bit smaller and Flatter as the LM-4 and better in a breeze).
The lowershrouds should be adjusted according to the pre-bend as described before. The mast should not bend more as 130-150 mm’s. Check the intermediates (shroud from the lower spreader to the upper spreader) in all settings (tight and less tight) so the mast is straight up untill the hounds (this is where the forestay comes into the mast). Some sideways mastbend must be accepted, because this cannot be influenced by any adjustment.
Mainsail Trim
Never pull the backstay. Sheeting the mainsheet does all you need to flatten the mainsail sufficiently. Adjust the foot of the sail (along the boom) enough the reduce the helm (pressure). Never pull the mainsail very flat on the boom, specially not when the waves are choppy and short. The boat needs enough “drive” to power through the waves, since it is very short and starts “hobby-horsing” i.e. bow up&down quite easy. Traveller should be played all the time in every gust, so the boat is feathered and not heeling, because that is really slow. If the traveller is not enough, ease the mainsheet a bit to keep the boat on its feet.
The cunningham should be used with care, never pull too much, it moves the draft (deepest point of the main) too far forward. Pull enough to remove some wrinkles, BUT NOT ALL WRINKLES !!
Try to accelerate, and NOT to heel!! The boats are very sensitive, and must be sailed with a lot of concentration and dedication, specially from the mainsail trimmer.
Keep the crew on the rail ALL the time. Use 400 Kgs of crew weight which is allowed since 1999.
Jib Trim
First thing you have to do is make marks at the upper spreader. Make a mark every 5 cmtrs. from the outboard end going towards the mast.
The last mark should be at 25 cmtrs. NEVER sheet the sail harder as to this last (most inboard) mark, so this mark should be a bit fatter or another colour, so it’s easy to see through the window in the main. The lead (trackposition of the jib) should be very close to the most forward end of this track. This makes the jib look a bit crazy, but believe me, that’s fast. The barberhauler MUST be pulled INBOARD all the time. In smooth water (no waves) up to 10 cmtrs. In waves no more as 5 cmtrs. Look at your boatspeed, and work the jib barberhauler, just as you must do with the mainsail traveller. More wind -> outboard, less wind ->inboard.
The best way to do this is lead the barberhauler across the boat. This means the barberhauler from starboard is led to the port cleat, and vice versa. That way you can adjust the barberhauler without leaving the rail, remember, the crew must hike HARD!
Length of Headstay
In light air you should use the longest headstay possible in order to create more weather helm.
Remember to adjust the shrouds as described above. In heavy air go 1 hole shorter on the adjuster, and again, adjust the shrouds.
Tips & Tricks
Put a device on the bow of the boat which prevents the spinnaker sheet from falling in the water. You will drive over the spinnaker sheet, and that’s slow, and difficult to get back on the boat as long as the boat moves forward.
Put a sailbatten on the top of the mast to prevent the mainsail leech from hooking behind the backstay. This is nasty, especially gybing in light air, which must be done frequently.
Crew weight & position
Move forward with 3 crew in light air, at least around the mast. This must be done with less boatspeed as 3 knots. Above 3 knots move backwards, but not a lot. Above 6 knots the crew can be in “normal” position.
Wind angles downwind (Spinnaker)
The Platu 25 is very sensitive to apparent wind speed. Smaller wind angles make the boat go a lot faster. My experience is to keep the wind angles as small as 95 to 100 degrees in light air.
Look at the boat speed, and check the win dspeed at all times. More wind, steer deeper (more downwind), less wind, steer higher (closer to the wind). Keep concentrated downwind, you can gain a lot of distance, but you can also loose a lot of distance.
Check the truewind angle. If neccesary gybe as soon as the wind shifts in your favour i.e. the app. windangle is getting greater. Talk with the crew trimming the spinnaker, let him decide if there is “pressure” or “less pressure”. He feels most, having the sheet in his hands.
Running in more breeze “work” the boat. Point the bow of the boat down the waves at all possible times and “rock” the boat, i.e. pull hard on the mainsheet and pull hard on both spinnakersheets. Your crew must be very tired after this leg. If not, they did not “work” enough!