UK-Cherub Forum
Cherub Chat => Tech Chat => Topic started by: ghislain_devouthon on May 14, 2008, 07:33:59 AM
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Gilles, owner of Aquamarina has the idea of building a Cherub over an RS700 hull.
The assumption is that an RS700 is a fast and stable hull. It respects the Cherub rules considering the width, chine ... and the mast is about the right place. Some modification needs to be done especially cutting down approx a meter and modifying the bow.
What do you think of this fullish project ? :o
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A bodge. But what the hell. If he wants to do it and it works. Good! Wont it have a lot of rise in floor if your cutting a meter off the stern and wont the centre board in the wrong place?
The bow is going to need modification for a snout and to take the stresses of a 21m kite. I would think that a 700 hull needs some sort of reinforcement as they don't use loads of rig tension compared to the amounts that modern Cherubs use.
There isn't a lot of free board there either. And will this have any effect on it?
4.1.3 Depth of Hull - Depth at mid - length, measured vertically from sheer to the lowest
point of the hull, shall be at least 450mm.
AND I think it will be heavy.
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The idea is to use the RS700 as a plug. The rest of it will be appropriate to cherubs (reinforcments, centreboard position, weight, stresses ...).
As racks are part of the 45 cm it will be fine.
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I would of though the rocker would be quite high ( or in the wrong place ). As you are likely to be cutting off the area of the 700 where this flattens out. But I've not studied the 700 so can't really remember what it's line look like.
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Just tell him what ever he does, don't cut up a 700 hull. It would make me cry.
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There is a rumor going round that the 700 hull is asymmetric...
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you'll probably find that most boats are asymetric though ross unless they've been made using CNC moulds. The people building them are only human!
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There is a rumor going round that the 700 hull is asymmetric...
You can notice that B18 are either. The center case is not on the keel line :o :o :o :o :o
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There is a rumor going round that the 700 hull is asymmetric...
I've yet to find a boat that wasn't. The early Bistros were hilariously asymmettric at the stern at deck level (where it doesn't count for much).
On the orginal concept, I would say that the boats are just too different in length to be worth considering. I'd be very suprised if there was a good result. Consider that the RS700 is designed for an appreciably lower all up weight than a Cherub (being a singlehander) then think that you're chopping the ends off, reducing the weight carrying still further. Even if you allow for the lower weight of a Cherub you're still ending up with a boat designed for a total crew weight of around 14 stone (~90kg?).
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Everyone better start dieting then otherwise a couple of topper sailors will be beating everyone before long.
It's a novel idea but i wonder if it would be more succesful using a 49er hull as a mould and not using the back of that.
I have also wondered if it is possible to make a cherub using single curvature pannels, single chine hull form and hence replicating the early home building revolution that saw the succes of the Mirror and Enterprise. if the hull pannels could be cut out of foam (perhaps with one layer of reinforcement on the inside) and stuck together in some simple jigs you could avoid using complex jigs or a female mould. The P7 appears to be a refined single chine hull form so the concept could produce a quick boat.
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I have also wondered if it is possible to make a cherub using single curvature pannels
I too have wondered that (well it is easily possible to make a developable surfaced cherub as nearly all the pre foam sandwich boats were). I could be the way to go if you intend on just making the one hull.
Doug Culnane has just finished a moth that is built just as you describe,Phil. Read back through his blog http://dougculnane.blogspot.com/ (http://dougculnane.blogspot.com/) to find out more about Lord Flasheart.
You could argue that hull shape is less critical on a foiling moth.........
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Gilles, owner of Aquamarina, has the idea of building a Cherub over an RS700 hull
At the risk of stating the obvious, why doesn't he just take a mould off one of your purpose-designed and built Cherub hulls instead? Or am I missing something (as usual)?
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I have also wondered if it is possible to make a cherub using single curvature pannels
I too have wondered that (well it is easily possible to make a developable surfaced cherub as nearly all the pre foam sandwich boats were). I could be the way to go if you intend on just making the one hull.
The ply boats were mostly semi tortured into a degree of double curvature. Single is just a bit too floppy. One of Spence's radical ideas in the early days was to ake saw cuts in the ply near the bow and keel which meant you could get a *lot* of 3d shape in!
The trouble is its so much more difficult to make a decent ply boat than a foam one, and time is so precious these days that its very hard to justify what you'd save in materials. Read up Andy's (well mainlyAndy's) article on ply sandwich on the website though.
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I have also wondered if it is possible to make a cherub using single curvature pannels, single chine hull form and hence replicating the early home building revolution that saw the succes of the Mirror and Enterprise. if the hull pannels could be cut out of foam (perhaps with one layer of reinforcement on the inside) and stuck together in some simple jigs you could avoid using complex jigs or a female mould. The P7 appears to be a refined single chine hull form so the concept could produce a quick boat.
Provided you have a mould or jig building the hull part of the boat is quite quick, a few of weekends should do it. The rest of the structure deck, hard points wings etc all take much much more time.
For a 'jigless' design to be worth while it needs to be quicker than the existing designs. If the compromises needed are going to make it slower then you would be better off just to use an existing jig or splash an existing hull.
A flat pack "cherub in a box" idea might work possibly with a shaped bottom section and flat panels for the sides but it would still be 3.7m long.
a very minimul complete hull could be 3.7mx90cmX45cm which could be filled with flat panels for the bulkheads and the deck and the tubes. shipping might not be too bad on that.
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Does anybody else know what happed about Dudley Dix designing a ply 'stich and glue' kit?
Check out the Paperjet 14. He builds them to 45 kilos!
http://www.dixdesign.com/paperjet.htm (http://www.dixdesign.com/paperjet.htm)
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Did anyone ever build a ply P7? How do you go about building a ply hull? I guess you just have panals cut to shape and you bend it round a jig, glue and clamp.
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All the P7's were foam sandwich, however King Tubby (http://www.sailingsource.com/cherub/test/doku.php/boats/2650) a P6 was I think the last ply boat built
Have a look at:
Building in Ply (http://www.sailingsource.com/cherub/test/doku.php/tech/wood)
Basically there is a lot of mesureing and templating and carefull cutting of wood to be done. Then some gluing then loads of frames to stiffen the panels. Foam is much eisier
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would it be possible to build a wooden hulled boat that would take the strains from an 05 rules cherub? i know that time wise this could take longer and be a lot more complicated, think i would be more inclined to throw a £100 or so at a wooden design hull as a bit of a laugh rather than spending many pennies on a carbon foam boat.
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EDIT:Started a new topic instead http://www.sailingsource.com/cherub/forum/index.php/topic,172.0.html (http://www.sailingsource.com/cherub/forum/index.php/topic,172.0.html)