smaller jib with square top main , catamaran

[grafozz]

I have recently fitted a new square top main and it is very good , it gives me around 1 knot of boatspeed over the old , tired main .
As the main has more area it has got me wondering if a smaller jib of 100% would give better pointing ability than my current 130 % jib ?
The theory is that it is a main driven boat and now that it is bigger needs less jib area which should help pointing ?
any thoughts please ?

 

[garvellachs]

I don't sail a cat, but you asked for thoughts:

We have a blade and a big over-lapper; I notice that the big genny points better overall - because I think the genoa track allows the sheet car to be at a better angle to the forestay. So maybe you'll need to think about sheeting angles if you go for a blade jib?

Also, with a bigger main and a smaller jib you may alter the balance of the boat and helm, although it hasn't been a problem with us.

Cats are reputed not to point well - due to lack of a keel - and altering the sail balance isn't going to affect that much I'd have thought? Do you have dagger boards or similar?

 

[oldbilbo]

I have recently fitted a new square top main and it is very good , it gives me around 1 knot of boatspeed over the old , tired main .

What sorts of 'sizes' are your main- and head-sails? How much more area do you now have in your main? What about interference from your backstays - if you have 'em?

 

[garvellachs]

Solaris Sunstar?

 

[Fantasie 19]

I don't sail a cat, but you asked for thoughts:

We have a blade and a big over-lapper; I notice that the big genny points better overall - because I think the genoa track allows the sheet car to be at a better angle to the forestay. So maybe you'll need to think about sheeting angles if you go for a blade jib?

Also, with a bigger main and a smaller jib you may alter the balance of the boat and helm, although it hasn't been a problem with us.

Cats are reputed not to point well - due to lack of a keel - and altering the sail balance isn't going to affect that much I'd have thought? Do you have dagger boards or similar?

So not wanting to steal the OP's thread, I have the same'ish issue.. big genoa that I find points better when I roll it in a little.. what are the best positions (relatively) for the sheet/car on the track with a big genoa.. and yes I know it's fairly relative and dependant on position and size of track but some advice would be welcome...

 

[bbg]

As a general guide, the sheet should bisect the angle of the clew.

More specifically, you need to look up the leech and try to get about the same amount of twist in both the main and the genoa / jib.

 

[lw395]

As a general guide, the sheet should bisect the angle of the clew.

More specifically, you need to look up the leech and try to get about the same amount of twist in both the main and the genoa / jib.

Another guidline is to project the line of the sheet up to the luff of the jib, it should be close to half way.

Really these are only starting points, it's worth getting some tell-tales near the jib luff and on the main leach, plus one or two on the jib leach perhaps.
Then you can get the twist about right in the main. Without that, the jib is just working in a mess of confused air.
Then try to get the jib tell-tales behaving more or less together.
Also keep an eye on the fullness of the main and jib, you don't normally want one flat and the other full.
You sort of end up going around a loop, once the sails are flowing well, try sheeting both in a little and see if the speed drops as you head up.

 

[grafozz]

howdid you guess that ?

no backstays -
aft swept spreaders
main size app 40 sqm old main 36 sq m
jib app 24 sq m

mini LAR keels

if I bring the jib car forward too much far it opens the leech of the jib so losing power then ,
and pointing ability .

very little pressure on the helm , indeed , with the jib and main sheeted / adjusted well ,she will sail a straight line without the a/pilot .
its just a quest for better pointing I am wondering about ?

 

[markhomer]

If you want a cat to point like most boats its all about leech tension , in racing beach cats which ive raced over 30 years this is the case ,

Cats can point suprisingly well , ive done regattas insingle handed cats and over stood windward mark and had to bear of, whilst monohulls tacking up to it below lay line .

Lot of sweeping statement up post from non cat sailors .

If you are down south speak to a cat sailing sailmaker , such as grant piggot of gp sails , he has vast experience of all cats

 

[Triassic]

Don't forget to also consider the relative speed between multihulls and monos when looking at pointing ability. Clearly the faster you go through the water the more you move the apparent wind forward so it always appears you are not pointing as high, however your VMG will still be better. I've just got home from the Burnham week regatta during which we found ourselves sharing marks with some relatively high performance monohulls on more than one occasion. It was quite interesting trying to work through a pack of them going to windward due to our different speeds and angles.

 

[lw395]

howdid you guess that ?
...
if I bring the jib car forward too much far it opens the leech of the jib so losing power then ,
and pointing ability .

very little pressure on the helm , indeed , with the jib and main sheeted / adjusted well ,she will sail a straight line without the a/pilot .
its just a quest for better pointing I am wondering about ?

Moving the car forwards increases leach tension, decreasing twist in the jib.
Unless they are already so far forwards that there is very little foot tension, making the jib very full?
it may be that your jib tracks are too far outboard for best pointing, a barber hauler to pull the sheeting angle towards the centreline of the boat might be beneficial?

 

[grafozz]

as the jib is larger than the original size the track is probably not in the optimum position ,I have a yankee cut jib spare and will try that next .
I have gbarber haulers rigged up , mainly to hold the genoa out when broad reaching , but they could be used to close the slot too .
will try these and post the results .