Aft Mast help please

Hello Deepsix,

The guy who cut the sail is a mono huller, so it wasn't made flat. I didn't know back then when I had it made. Never the less, on a close haul the sail looks a lot like your top picture - when I can pull the sail in enough in lighter winds.

That is however not where I get max speed. Letting the sail out a little so it makes a bigger ball a little more aft suddenly accelerates to almost double the speed. Weird, I tried to sail it on the same shape as the windrider's sail.

Too much to wind and the sail behaves the same as your's would on the leading edge, the part just behind the forestay goes limp and begins to fold in like in AM1. A slight shift in rudder and the sail would fill out properly and the boat accellerates a little as can be expected.

I tied a lint on the foot of the sail just behind the furler, and if the leading edge is pointing at the same angle as the lint I get max speed, from a broad reach to a close haul. The sail would, since there is no boom, ball out where it wants to depending on where the wind forms it. AM5 is almost a beam reach while AM6 is about a close haul.

The clew I made fast right where I sat, I couldn't pull it in enough when I tacked so I left it there. The sail kept it's form except for the clew part which folded in towards the centre of the boat and would of course result in a loss of speed since the wind cannot slide off there - see AM8 and AM9.

One question I have, would a flatter sail work better for this setup ?


The foot of the sail has a rope in it, with it I can shorten the foot of the sail some so I also get a form above the foot of the sail if it is shortened. If this rope is shortened, it should result in more spill to aft instead of off the foot of the sail right ?

This may be the reason the sail is difficult to pull in. If the spill is aft on the schroud ? or above the clew, it may explain the force on the clew.

Assume I shorten the foot of the sail some, what would be lost or gained ?


If one implement a ball along the foot of the sail, shouldn't this result in more air spilling aft ? instead of down also ? The leading edge creates an upward and foreward pull due to it's angle, if the foot of the sail creates a slight downward pull it may stiffen the sail to become slightly more flat around the centre ?

I will look in on the Saildesign guys a bit later. Thanks for the reference. It would be interesting.

I will have to add blocks, arms too thin

 

hows the aft mast working.

I have a small tri i am going with an aft mast on. for my own ridgid reasons. i have sailed about 200 hrs with a geona. jib. main sail on stay. blue poly tarp. my sails are not new. my up wind pointing has been about 40' degrees to port and 35 to starboard. I think it is a blown out sail problem.
my first boat a double ender. two canoe catamaran. the mast could piviot 360' and sail forwads and backwards. its up wind ability was very poor. It was a swing keel with a flat rudder with no foil. the wind drag on two open hulls was a problem.
i seen your posts from years past.

 

Looks to me that you are sheeting the sail from the centerline of the boat.
If you had a "traveler" to move the sheet out from the centerline for a reach or down wind the sail would set much better and be more powerful with less drag.

 

Fanie,

I finally looked closely at the pictures and your building blog.
This is an extremely good boat for a few weeks. I'm really impressed.

I believe you could really control the sail much better with a boom. That way you could set an outhaul to shape the foot better, and adjust the angle of the mainsheet control by having different bails along the boom.
You could also set up a Barber hauler to allow better downward force on the main sheet attachment for when you were broad reaching and running.
I know that would put your head in danger in the position you were sitting but as you said you really need to get lots more weight forward to level out the boat (bow down). you have nice generous sized bows (height) so driving the nose under the water should not be much of a concern. If you were to set in the middle of the boat length wise that would trim out the boat much better and if you were down in the boat your head would be a comfortable distance from the boom.

How much does the mast weight? Having your body, the mast and the motor on the rear beam is really making you stearn heavy.