GNAV...

When i sailed 29ers we had about 4 or 5 of us who got new boats at a similar time, they all came with dodgy bottom sections which werent strong enough. We got them to do massive S bends downwind ina bit of breeze and most of them buckled when we did, which was nasty when 3 went on one run at training. dunno if this had anything to do with gnav forces tho. 

Edited by Yann

Originally posted by redback Here's another consideration.  Enterprises and Scorpions have deck stepped masts and the anchor for the kicker is in the bottom of the boat - this tends to increase the forestay tension - quite useful!

which is why you need to look after the front bolt in the mast step...if you don't the kicker loads make this shear and send your mast through your foredeck...

Where are Contender's kickers anchored?

Did you go straight out and photograph it!. Interesting anyway since again this kicker will increase the forestay tension when used, whereas if it were actually onto the mast it would not.

Right, getting back to rigs.  Just think in engineering terms.  Many of these skiff type boats have a mast unsupported by a gate at deck level - no wonder they need lowers.  The 29er doesn't, but it has to take all those bending forces fed in by the kicker or equivalent.   The 29er has a big roach on its mainsail requiring quite a lot of force down the leech - usually provided by the kicker in a breeze.  Unfortunately as leach tension increases so does the bending force from the kicker.  One solution is make the lower section thick and heavy like a Laser bottom section, the other solution is ease the kicker when the boom goes out over the side of the boat - which would you prefer? 

I suspect its quite easy to overbend a 29er mast and get creases from the end of the boom to the middle of the sail.  On the Laser 4000 the solution is use lowers to restrain the mast bend, just as well because the 4000 has quite a thin section for its length and power.

Just as an illustration of the affect of the lowers is an incident I had last summer - I broke a lower on a close reach when hitting a wave badly.  The crew got dunked and I eased the main thinking I'd lost the rig.  I was amazed just how much power the boat lost with no restraint on lower mast bend.  In fact I now alter the lowers to suit conditions.  If I have them tight the boat is more powerfull and I can get the crew trapezing in only a few knots of wind however the boat does not accelerate in the gusts and I have to play the mainsheet and I can't do it fast enough on inland waters, so this setting is only used at sea.  Inland its much faster to ease the lowers by half a hole and let the mast breath.  The crew doesn't get out on the wire so much but I don't have to play the mainsheet so much and the boat accelerates in the gusts.  When the wind is stronger still, I let out another half a hole and the sail becomes much less powerfull, and with the mast raked back a bit (equivalent of letting the lowers off more) the boat becomes completely tame at 25 plus knots of wind.  So control of mast bend is really singnificant, however the section is thin and if I didn't let the kicker off just before the windward mark it would be over the side if I let the boom right out.  Futunately if you don't get time to ease it you can always temporarily not ease the mainsheet and that keeps the mast supported until you do get time.

I understand the Star is many times more complicated in keeping the stick in the boat.  I once raced a "Quarter Tonner" on the east coast - that had a rig which would fall over the side at the slightest inattention - but it didn't even though we broached and broached more times than I could count in one race.

If you want a fast boat you have to accept the rig is vulnerable.