The purpose of this tuning-guide is to give our clients in the Platu
25 class some guidelines on how to get the most out of their North
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.
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
powerfull 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.
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
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.
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
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 spinnakersheet
from falling in the water. You will drive over the spinnakersheet, and
that's slow, and difficult to get back on the boat as long as the boat
Put a sailbatten on the top of the mast to prevent the mainsail leech
from hooking behing 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"
Wind angles downwind (Spinnaker)
The B'25 is very sensitive to apparent windspeed. Smaller wind angles
make the boat go a lot faster. My experience is to keep the windangles
as small as 95 to 100 degrees in light air.
Look at the boatspeed, and check the windspeed 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
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!
Good luck on the water!