rig fore aft position limits for catamaran

[patrik111]

Hello,

I am designing catamaran. First some outline details before the key question just to set the scene.

I will need to fit it inside 9*3,5m, I would like it not to be folding.
It needs to sleep 4, with sitting headroom on half the berth. The mental picture I have is "Ferrari with a Caravan"
First rig iteration will be based on the Tornado Sport but with a slightly larger self tacking jib. This may be upgraded to something more tuned to available RM when it is known, but using the same mast step.
The boat need to be build in parts which can be extracted through garage doors 2,1 cm wide
The boat would be used for costal cruising within sheltered waters (archipelago).

I have centered in on having a design that has a central nacelle with sitting height and sleeping 2 with 1 more berth in each hull.

I am struggling in deciding if the mast will go before the nacelle/pod, like some of Richard Woods designs, (the berths in the hull aft ) or placing the mast on the nacelle rear bulkhead, like the G32 (with the berths forward ).

I am somehow a bit attracted to the latter, but would like to not have the pod to far forward, ideally ~3m from the back.

How far aft can I reasonably the mast and therefore daggerboard case?
Looking through the interwebs the furthest aft Daggerboard position I have found is on the new F18 Cirrus 901 which I estimate at roughly 35% of LOA from the aft perpendicular. Where most others are around the 40%-45% mark.

Any input welcome!

Patrik

 

[oldmulti]

Patrik. Its not where the mast is it is where the sail area and lateral resistance is. There have been mast aft all headsail rigs to mast forward with no jibs. This is about the totality of the design. If you want a fast 9 x 3.5 meter EG cat then maybe a two masted rig with a lower centre of effort may achieve a result. There are 2 racing cats in Australia that had in 2 mainsails small headsails that embarrassed many other cats upwind. To get fast you need light, long with an effective rig. Stability helps but if you are constrained in beam then a low centre of effort helps. The first jpegs are of Shotover 2 a 12 meter racing cat, the second set of jpegs are of a Jarcat 7 which was a 23 foot plywood design that ended up with a removable cabin. Both these cats could sail very well in all conditions. Both had wing mast rigs. Just some thoughts.

 

[patrik111]

Thanks OldMulti,
that is indeed food for thought! And also a large thank you for the long thread on multihull structure! It has kept me company many nights .

While 2 mast is quite an interesting proposition that I'll have to have serious think on, I have a donor rig and sails in my back yard which I yet so far have based my thinking around, that is the rig blocked in to the pictures.

Please find below (if I succeed) pictures of the current state of design.

The mast forward position to me looks more aerodynamically sound with boom closer to the deck, but from an sailing perspective, I am more used sitting, hiking, trapeezing facing the mainsail, and not being "behind" the sail so to speak. That also gives more flexibility in terms of changing the rig with longer boom. A updated larger rig would be accompanied with sit out racks that can be folded in for increased RM.


Kind regards
Patrik

 

[fallguy]

Dodging the boom does not emote Ferrari. I am no sailor, but the mast forward seems far more elegant.

 

[Erwan]

I would vote for the second design with the sailfoot sweeping the roof of the cabin, you are bringing down your Sail 's CoE
Good for performance especially upwind.
To remove a little part of the frontsay's load on the front crossbeam, have a look at the frontstay arrangement elaborated on the SL16 , designed by Yves Loday.

 

[patrik111]

Fallguy,
There are constraints also with sports cars... Not unlike limboing under a boom

 

[patrik111]

I would vote for the second design with the sailfoot sweeping the roof of the cabin, you are bringing down your Sail 's CoE
Good for performance especially upwind.
To remove a little part of the frontsay's load on the front crossbeam, have a look at the frontstay arrangement elaborated on the SL16 , designed by Yves Loday.

Hi Erwan,
I have scoured the internet but cannot find any good pictures of the forestay setup you are referring to on the sl16. Would you have a picture or a sketch to illustrate?

Kind regards
Patrik

 

[fallguy]

I love the humor my friend. @Richard Woods would have some wisdom to share versus me saying what looks pretty.

And perhaps he'll enjoy that fella crawling out of the Ferrari as much as I did.

 

[Erwan]

There is a 2/3 feet long aluminium tube, to move higher the connection between the forestay in order to alleviate the lateral loads on the hull's bows.
The aluminium tube allows you to put the jib lower than the wires/forestay connection point as usual.

 

[Erwan]

Please read:

the connection between the bottom point of the forestay and the 2 short wires (going to the hull's bow)

 

[patrik111]

Hi Erwan,
If I understand correctly, this is the same as the tornado sport rig in the picture below?

I would likely have a furling and selftacking headsail, possibly on beam with a seagull striker, a beam also helps netting between hulls

There is also a need to be able to get to the bows with some ease when going ashore, as most places are simply rock a kind crewmember jumps on to. A picture to illustrate of where we are staying tonight, celebrating midsummers eve. But that is subject for a whole other thread.

Best
Patrik

 

[Erwan]

Yes, It looks exactly like that.

 

[oldmulti]

Patrik this power cat may be of interest for its build and layout. The concept could be have a rig on it with finer sterns and without the large outboards. Its on page 123 of multihull structure thoughts. Multihull Structure Thoughts https://www.boatdesign.net/threads/multihull-structure-thoughts.62361/page-123#post-910840