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Old 19-04-2009, 21:14   #1
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Replacing mast head rig to fractional swept back

Hi readers/viewers
I am interested in any experiences people have converting a masthead rig to a fractional swept rig for cruising. I like the idea of getting good drive from the main - especially off the breeze and the simpler handling of smaller headsails - particulatly in the inconsistent breezes as we often have in "the roaring forties". Any thoughts would be welcome.
Ian
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Old 19-04-2009, 22:27   #2
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It is not somthing I have done, but it is something that you would want to think about very carefully because it is not a small exercise, nor cheap. Bear in mind that you have to either move your mast forward, with all the heartache that entails, or move your chainplates back, with all the trouble associated with that.

This does not strike me as a cheap or easy project. Put it another way; If you want a fractional rigged boat witha swept back rig you would in my (unqualified opinion) be better off to sell your masthead boat and buy a frac rigged / swept back rigged boat.

Others may well have different opinions
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Old 19-04-2009, 22:37   #3
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Probably my thinking too - there is a Doven here in Hobart that has gone fractional - certainly improved the speed of the boat but I think they went with runners also.
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Old 20-04-2009, 06:19   #4
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I converted a C&C24 from a masthead rig to a fractional rig last year,i had aquired the boat without a rig and there was a used J24 rig available in town with a small dent at deck level which i was able to buy reasonable which is the only way it was worthwhile from a cost standpoint. I had to move the mast foreward 20" to achieve the correct lead of the center of effort over the center of lateral plane.I cut the mast off just above the dent as it is now cabin top stepped. From a sailing point i could not be happier,this is a sweet sailing boat that is perfectly balanced under every sail combination so far and i am very pleased with how it sails under main alone.I should point out that i have never sailed a C&C24 with the stock rig so i cant compare but im sure it is better under main only as its much bigger but with the spinnaker which i have not set up yet it is a lot smaller.The boat now looks right too.
Steve.
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Old 20-04-2009, 08:54   #5
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Clockwork is right. Converting to a frac rig usualy requires moving the mast forward in order to preserve helm balance. If you have lee helm now, highly unlikely, maybe you can do it. But if you have weather helm now, likely, you can't just convert without moving the mast.
What kind of boat are we talking about?
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Old 20-04-2009, 12:19   #6
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My boat comes in both a masthead rig and a fractional. The compression post for the fractional is "in" the aft bulkhead of the head / forward bulkhead of the salon. When they do it as a masthead the compression post is "thru the table" about 30" aft (a guess). In both cases the post sits above the keel.

I like the fractional. (hate big genny's)
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Old 20-04-2009, 12:41   #7
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Send a message via Yahoo to gonesail
you may also need to move the shrouds down from their masthead connection point to where the new fractional head stay is located.
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Old 20-04-2009, 15:47   #8
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Originally Posted by bob perry View Post
What kind of boat are we talking about?
Doven 30 (a.k.a. Knoop 30) designed by Walter Knoop (Tasmanian builder / designer) in the 70's... think IOR 1/2 tonner but cruising orientated more than racing....

Doven 30: Sailing Boats for Sale - Grp - Tasmania (Tas) - Barnes Bay, Tas

Boat Sales Tasmania - Doven 30

Knoop 30 Half Ton: Sailing Boats for Sale - Double Diagonal King Billy - Tasmania (Tas) - Hobart Tas

The above are a couple of examples
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Old 20-04-2009, 16:49   #9
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The boat is an IOR 1/2 tonner. It is beautifully balanced at the moment but does lack drive out of the main. The Knoop 30 is a later version (See above Knoop 30 Half Ton) was purpose built as a fractional rig with a significant improvement in all round performance. Mine - the Doven 30 is great to windward when nicely powered. The extended cab top allows for the mast to be moved forward and there is a bulkhead which might support the mast about 800mm forward of the present mast position.
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Old 21-04-2009, 09:24   #10
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Well, given that the boat is an old IOR boat you probabl have a huge fore triangle and a ribbon mainsail. That was the style that worked with the IOR for years. You can move the mast and probably improve the boat but it will require a lot of work. You can probably leave your chainplates where they are and go with about 28 degrees of sweep to the spreaders.
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Old 21-04-2009, 16:12   #11
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You can move the mast and probably improve the boat but it will require a lot of work.
And this is my point: You take a $50k masthead boat. You spend $20-25k and lots of time/effort on moving the mast position, buying a new mast, new rigging, new sails, etc and you have a $50k fractional boat... Wouldn't you just sell your $50k masthead boat and buy a $50k fractional boat, thus saving yourself $20-25k and a bucketload of time and effort?
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Old 21-04-2009, 21:37   #12
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Thanks Bob - that was my thinking - the work doesn't worry me but I suppose the overcapitalisation suggested by Weyalan would worry me. A friend of mine managed to buy a fractional rig very cheap a few years ago - (an insurance fire sale from a wrecked yacht) - so I suppose if something like that came along it might be worth thinking about. I could extend the boom length by about a metre now (the existing main is a ribbon!) and that would probably give considerably more drive without the hassle of mast moving and without compromising balance too much. I will have to buy a new main in the not too distant future so all of this is assisting my decision making - so thanks folks.
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Old 22-04-2009, 08:50   #13
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I think Wey is correct. It's abit like taking an old MG and trying to bring it up to date. So much of the design is based on the thinking of 30 years ago that moving the mast is only a small step in trying to "modernize" this boat.

Leave it alone. Enjoy the old MG for what it is and be happy for it.
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Old 22-04-2009, 09:35   #14
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Fractional rigs have much higher shroud tensions, so that has to be taken into account. Ours is tensioned to between 15-20% of wire breaking strength.

Chris
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Old 22-04-2009, 09:47   #15
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One thing I haven't seen mentioned in this thread yet is that a fractional rig has a different mast. See link below. The masts are smaller at the top and different in design for more flexability if you want a real fractional rig.

Z Spars Mast section Z601 - part numbers from 1999
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