Got my old Mk9b on the water last week and was pleasantly surprised how nice it is to sail. I have lost of small snags to sort out but I was wondering about mast rake. The rake is not adjustable but what is the opinion on a good starting point. Also, I understand about raking to de-power but I've never seen a scientific explanation on rake. Should we look to using very little rake on the river in light airs for example (and if so why)?

I'm pondering similar questions.There are quite a few neewbies to the Vintage fleet due to recent interest (e.g. Thames) Obviously the tuning sheets on sail makers websites are geared to the latest boats. Could on of the experienced Vintage fleet hot shots (Tammy guys?)
knock up a Sailmaker type tuning sheet for Classic/Vintage boats?

My IXb 2143 had initial rake of 9 inch from gooseneck to main halyard when halyard weighted like a plumbline. I think in Ian proctor wrote in his book Racing Dinghy Sailing that with boat level, and mainsail hoisted, adjust rake until boom is horizontal. It's 30+ years since I read the book, so memory might be off.

I am looking at this thread with interest.  My old MkVIII suffers from a lot of weather helm when the wind blows up - which makes here a struggle.  So far I have been recomended a rake (measured using a level boat and the main halyard acting as a plum line) of between 5 and 8 inches with the jib under tension.  But I have also been recomended that I try and move my mast foot forward as well.  Appreciate all these old boats are different.

Weather helm is all about the difference between the centre of effort of the sails and the centre of resistance of the boat. If the centre of effort of the sails is aft of the centre of resistance of the boat then the boat will turn into wind. You can certainly move the mastfoot forward to reduce weather helm but this alters the rig balance in all winds. If your problem only really manifests itself in stronger winds then you need to alter the trim as the wind increases. In older boats it is not so easy to rake the rig on the water and hog-stepped and case-stepped masts don't respond quite so well to additional rake as deck-stepped masts (all down to the relationship of the spreaders to the shroud set-up). Strong winds tend to blow the sail out of shape and the centre of effort moves aft as a result and causes your weather helm. Your best bet is to haul the cunningham on and rake the centre board back as the wind increases. This moves the centre of effort of the sail forward (this is a simplified version of the effect of the cunningham)and the centre of resistance of the boat aft. This compensates for the wind blowing the sail out of shape. If you play with these controls (and the kicker!) it should be possible to tune the boat to sail very sweetly in stronger winds. It won't necessarily help you keep the boat upright but it should stop it turning into wind which then causes you to pull on the rudder which then puts the brakes on, (and probably stalls), which then slows the boat which then increases the pressure in the sails which then makes them blow out of shape even more which then causes the centre of effort to move further aft which increases the weather helm and...and...and ad infinitum. Play with the centre board, kicker and cunningham and see if that helps.

I forgot to add that another common cause of weather helm is over-sheeting the mainsail. This also has the effect of moving the centre of effort aft. If you ever try over-sheeting a Laser it will turn quickly into wind and the rudder can't stop it!!! Ease the mainsheet and the weather helm disappears (and the boat accelerates!).

& of course keep the boat flat.  I rake the board back as well when it blows admittedly on a raking rig boat but even if you don't rake as you flatten & ease the main the centre of effort moves.  If it is howling the simple thing to do is sail all the way round on half board, gives you one less thing to do so you can focus on keeping dead upright.

The right aamount of rake can vary from boat to boat. My Mark 12 sailed best with 7 and a half inches of rake but others from similar builders had different settings.
In respect of Desparation, am I right in think that it had a swept back rudder? If so, that might be an issue in a breeze and you could get a deep rudder that might alleviate this issue.

Chris

It is Desperation and it does have a swept back rudder.  I have another spare straight one, but it is not a simple fit as both the pintal and gudgeon on the aluminium stock are in the wrong place.  I will have to hack this one about to get it to even half fit and then it will look odd.  It is not clear if I can swap blades either.

 So I was thinking of trying to fiddle with the rig a bit before I abandon the swept rudder.  Also there is not telling whether the rig is set up properly anyway as the previous owner was even more clueless that me :)

I've one of the older IYE stocks - 

the pintle position is actually quite easy to adjust (needs a drill and steay hand) - once the blade is out...

HTH

Colin (3387)

David - sailing on the river, you need your mast just off upright and you may want to induce a little mast bend depending on the era of your sails.