tuning tips for multihulls

[schoonerdog]

I might be doing a thread hijack, but I'd be very interested in what people do for tuning their main sail. I find that one of the more difficult sails to get properly tuned. Also, if I'm replacing the main, should I look for a square topped main as a cruising sail or is it a useless advantage?

[fastcat435]

the reason that you tiller arm is feeling busy when the rudders are parralel is that they are not pushing towards he center of your arm but rather freewheeling and this tells the story having them facing slightly inward increases resistance and at the same time pushes toward your tiller arm.
try a handheld gps on a calm lake and try out both , you will see at least 2 % speed change and more with less wind

[fastcat435]

On the FastCat we have made the outhaul adjustable from the cockpit to make it easier and faster to adjust.
Having your top of the main made squire only has real advatages if you use your main mostly with the wind from behind , But knowing a bit about you you will not do that but set a spinnaker or a gennaker or even 2 straight downwind.
Just order a slightly build out mainsail with 5 carbon fiber thin batten made by CT battens in New zealand , saves you 40 lbs in weight and they curve the sail better.

[2Hulls]

Originally Posted by schoonerdog

I might be doing a thread hijack, but I'd be very interested in what people do for tuning their main sail. I find that one of the more difficult sails to get properly tuned. Also, if I'm replacing the main, should I look for a square topped main as a cruising sail or is it a useless advantage?

Hi schooner - as for tuning the main, I think all the conventional wisdom for tuning battened cruising sails applies, although those of us who grew up on beach cats may get frustrated at the difficulty or practical impossibility of adjusting batten compression. Tough to capsize these boats on the beach to do it.

When ever (if ever) I need to replace the main I plan on discussing a square top with the candidate sailmakers. I don't see this as a useless advantage on an otherwise performance oriented cruising cat. It can't be THAT much more expensive. For a non-performance oriented cat, it would probably look like a spoiler on a Winnebago. JMHO

Dave

[Tropic Cat]

As my Main sail ages it's getting baggy (sigh). I tending to compensate by tightening both halyard and outhaul and pay more attention to the traveler position on all points of sail. I also added a few more telltales to assist in trimming.

Originally Posted by schoonerdog

I might be doing a thread hijack, but I'd be very interested in what people do for tuning their main sail. I find that one of the more difficult sails to get properly tuned. Also, if I'm replacing the main, should I look for a square topped main as a cruising sail or is it a useless advantage?

[2Hulls]

Originally Posted by fastcat435

On the FastCat we have made the outhaul adjustable from the cockpit to make it easier and faster to adjust.

Gideon - glad to see you didn't ignore the good ideas that came before you. You weren't trying to suggest you're the only builder who does this, right? That would be dishonest.

Originally Posted by fastcat435

Having your top of the main made squire only has real advatages if you use your main mostly with the wind from behind

I suggest you have a conversation about this with someone who really knows sails. Squaring the top of the main is specifically for on the wind work - to increase sail area not shadowed by the mast upwind and to permit better twist control. Square tops de-power themselves easier because they'll twist more on their own with that bigger moment arm way up there. Sure, downwind area is increased, but that's not the primary reason.

Dave

[Therapy]

I have a question about the testing of the wind gen.

It would seem to me that the mast top mounting would expose the whole apparatus to some rather severe forces knowing that some cat rigging forces are accentuated because of the "short" and "stiff" motion inherent in a cat. This, it seems to me, would unduly stress the gen.

I am no math man but I am thinking 20ft mast is "normal" (high?) going to 60ft........that is 3X and forces would be at least squared (cubed)???

I ain't no math whiz like I said.

It just seems the top of the mast would be a hard place to have a hinge to hang on.

[Eleven]

Many many thanks to fastcat for giving away his design secrets in the interest of sailors. Much appreciated.
I'm limited to an old Prout but the option of 'plastic' shrouds and rigging makes sense even on these. The latest sail fabrics have got much better and will improve performance with performance maintained better over a similar life span.
Diesel tanks should be kept to a sensible working minimum. On a cat extra 'long range' diesel can be carried on board in convenient containers and stay clean even if the main tanks go slimy.
Solar panels have to a good way to go and do save battery capacity and still work when the engine packs up.
Fit the panels to the tender and if you do have to bail out you can plug in GPS, VHF etc and get rescued quicker. Water maker should also live in the dinghy so it goes with you in a hurry. Add a few more items, fish hooks, LED lighting and you have a cruising lifeboat that will keep you out of more trouble for a couple of weeks.

[schoonerdog]

Dave, precisely what I don't understand, twist control on the main. Can you explain? What are the disadvantages of a square topped main? Also, regarding the carbon battens, some really recommend against them as they can shatter more easily against the shrouds.

Originally Posted by 2Hulls

Gideon - glad to see you didn't ignore the good ideas that came before you. You weren't trying to suggest you're the only builder who does this, right? That would be dishonest.



I suggest you have a conversation about this with someone who really knows sails. Squaring the top of the main is specifically for on the wind work - to increase sail area not shadowed by the mast upwind and to permit better twist control. Square tops de-power themselves easier because they'll twist more on their own with that bigger moment arm way up there. Sure, downwind area is increased, but that's not the primary reason.

Dave

[2Hulls]

Originally Posted by schoonerdog

Dave, precisely what I don't understand, twist control on the main.

Hi schooner. I'll try, but I don't claim to be an expert - just enough to know square tops aren't just for down wind. Perhaps a sailmaker can chime in.

Square top sails provide extra area aloft where supposedly there's more pressure. It's the best place to add area as it'll be more useful and it adds area further away from the mast so the air flow over the extra area isn't shadowed by the mast. On a normal pointy top main, the top several feet are essentially useless upwind. On a square top, the extra area straight back from the head becomes a lever as the wind increases or gusts and there's less resistance to the top twisting off vs a non-square top. The induced twist travels dowe the leech, taking the upper portions of the sail with it to leeward - more so than without the square top. When the wind gusts, it's sorta like a monohull heeling - the induced twist depowers the sail. The depowering is proportional to the leech tension which is controlled by the main sheet tension. So, contrary to what you might think, the additional sail area actually makes the main more "automatic" in strong or gusty wind. In effect, the extra sail area causes the sail to twist more and cause the top of the sail to flatten out. Twist is especially important on taller rigs typical of cats because the apparent wind angle shifts aft as you go up because of the increase in wind velocity.

Dave

[ireaney]

2Hulls Dave, Sorry to sound stupid, but what you are basically saying then, that with a square top it can actually be a bit of a safety feature, ie. in a strong gust it can effectively help spill the wind thus depowering the main and possibly save any serious mishaps or give the helmsman more time to act to save a possible disatrous situation - am I right??

[2Hulls]

Originally Posted by ireaney

2Hulls Dave, Sorry to sound stupid, but what you are basically saying then, that with a square top it can actually be a bit of a safety feature, ie. in a strong gust it can effectively help spill the wind thus depowering the main and possibly save any serious mishaps or give the helmsman more time to act to save a possible disatrous situation - am I right??

Hi ireaney - yes, that's what I understand - assuming you're not too tightly sheeted. I imagine this is more apparent on smaller boats that are more prone to capsize. There's some interesting reading if you google "square top sail" or sail + "square head".

Dave

[Keegan]

I "tuned" my cat more recently by adding an LG washer/dryer combo unit. The clothes smell clean all the time and on the high spin cycle we can get an extra knot out of the boat while sailing

Keegan

[2Hulls]

Originally Posted by Keegan

I "tuned" my cat more recently by adding an LG washer/dryer combo unit. The clothes smell clean all the time and on the high spin cycle we can get an extra knot out of the boat while sailing

Keegan

But in the southern hemisphere you'll lose a knot.........

[Keegan]

Originally Posted by 2Hulls

But in the southern hemisphere you'll lose a knot.........

Yeah, I did not think of that...