how to add sail area to an unstayed kat ketch

Herb2

New member
The whishbone booms are really heavy, the topping lift has a two to one purchase  to adjust it and take the weight off the leach.  Newer designs would use a carbon fiber whishbone.

 

ryley

Super Anarchist
5,501
656
Boston, MA
@fastyacht that's fair enough, and I had pretty much convinced myself of that too. the Freedom 40 also had wraparound sails so the conversion on mine was to a sail track and conventional booms. I think the sail controls end up feeling more conventional than, say, a Wyliecat 30, where tuning the sail through the choker is kind of an art. But you are probably right, especially these days, that the sail materials and designs can handle a lot more roach and area without removing the wishbones.

 

ryley

Super Anarchist
5,501
656
Boston, MA
The whishbone booms are really heavy, the topping lift has a two to one purchase  to adjust it and take the weight off the leach.  Newer designs would use a carbon fiber whishbone.
you could also do what Herreshoff did and use spruce - also light and strong. They only did a half wishbone too.

 

fastyacht

Super Anarchist
12,928
2,596
you could also do what Herreshoff did and use spruce - also light and strong. They only did a half wishbone too.
I designed a spruce half wishbone for a 15 footer back in 89. Never finished building it. Damn it.

 

ryley

Super Anarchist
5,501
656
Boston, MA
I designed a spruce half wishbone for a 15 footer back in 89. Never finished building it. Damn it.
here are the ones from my parents' boat after I refinished and re-rigged them.

20190428_165933.jpg

 
A

Amati

Guest
no the sloop build has chain plates and stays ect not a flip between option one or the other as built

lite air and off wind boat is HEAVY 5200 LBS 

may plane in a cat 5 but I do NOT expect it to in normal use
Sorry to take so long getting back-  if you’re only looking for light air performance, you might be able to get by with more sail area if the sails are really light and easy to take down quickly.  I’m wondering if you could do some sort of light added top mast, kind of like a folding or sliding Gunter, esp if you’re unstayed. Roachy.  Spinnaker nylon fabric? You might be able to get by using windsurfer masts to attach to the masts you’ve got with hoops, or parriels (spelling?) wrap around sails or sleeves on the topmasts. Taller and skinnier sails are better for light air, add a huge mizzen light downwind sail, sheeted to the stern. But you’ve got to be able to get them down or dump them fast.  Berndt Kohler has done some of this kind.
 

you might also be able work out a sprit rig- nice light long carbon poles might do the trick, nylon sails, extend the peak up another 5 or 10 feet?  You’d get a quadrilateral sail out of it, which could add some effective SA, and you might not need a lot of added downwind sail.  There are some newish nylon sail fabrics that are pretty tough for light winds. Imagine these with modern sailcloth
https://www.christinedemerchant.com/sail_sprit_sail.html

If you really want to go hardcore, you could go with dipping lugs, which are really powerful, but sporty to tack/ gybe. You’d have to figure if your masts and deck could handle the stresses. They would add SA too.  Quadrilateral planform.  You could even go standing lugs.  They aren’t as bad as you might think.  Look up Micheal Storer designs- he has a bunch of info on standing lugs that are pretty spunky, performance wise.

https://www.storerboatplans.com/tuning/lug-rig-setup/test-for-google-docs/

the goat island skiff planes, fwtw, powerful rig

Nigel Irens did this, unstayed masts- don’t even need booms.  Look up Roxanne for rig details.

6A99D0DA-BA28-4F13-A7BF-44BD1139BB25.jpeg

 
Last edited:

pschwenn

New member
You could increase the area, making little or no change in center of effort and reduce induced drag by about 1/2 (that's a lot) with sails as is (or newly "as is") by extending the foot of the each sail down to deck level through the wishbones.  The sail foot need not rest right on the deck but use a deep curve on the foot so that much of each sail is at least close to the deck going upwind.  Then you'll wish you could still see underneath the forward sail - so as on many smaller racing boats, make much of the foot from transparent plastic, which you clean as often as you'd like to see through it.  The airfoil of the extended foot need not be as beautifully realized as the rest of the sail's shape.

A sailboat that does not bring the foot close to the deck (when two sails are working together the outer one is enough - e.g. overlapping genoa outside a main) is like an airplane which has no wing skin outboard of the fuselage for a few feet - just the naked spars of the wing.  Even supposing that emply space has only beautifully streamlined spars in it, the induced drag is ~doubled and a considerable amount of wing area is lost.

Not only will the balance not change much, but the extra area is low so that less additional righting moment is required than if you are adding area at the top of the current sails.

You might ask why so many rigs don't do this, e.g. unstayed mast boats - even those with jibs.  You might well.  Partly its the "easy-going cruising aesthetic" which abhors a genoa obscuring vision to leeward.  Sometimes it's a class rule.  And a slow boat is not as dangerous as an airplane that lost some skin.  Perhaps the wishbone boom got "outmoded".  Mainly it's that to become a Yacht Designer or (except in a couple of States) Naval Architect, one need only engage a sign painter.

[simplest: is a someone already noted: big roach battens as need to support.]

regards

 
Last edited by a moderator:

fastyacht

Super Anarchist
12,928
2,596
That is because everything ketch is quintessentially salty and endlessly fascinating. Ketch--even better than a yawl. Haha

 




Top