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Reading sailing characteristis from drawings

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Seems I get a second chance for my topic - this time even with pictures. 

Sometimes I dream about building and sailing a Core Sound 20#3. I love the looks of her, I love the idea of water ballast, I love having a mizzen and this size of cabin and more.

But then : I love my existing boat too - and I wonder how the CS would sail in comparison to her. And I wonder how some people can read performance from the lines or pictures or data.

So here are the basic informations about my boat:

Her name is Muckla and she is a Diabolo, designed by Jüs Segger. 

A word about Jüs: he was trained as a boat-builder and became later an engeneer and yacht-designer, drawing and selling plans, mainly for plywood hard-chine-boats, aimed for the amateur-builder...... (anyone heared of a similar career??).

The Diabolo is 20 ft long, has about 190 sqft of working sail area + lapper and/or spinnaker and/or code 0. She has a ballasted centerboard. The lead in the cb is 60 kgs +  about 30 kgs of internal ballast + the heavy equipment in the bilge. This gives her a decent end-stability though I doubt if she would be self-righting if necessary. I rather not try. Initial stability is rather low so you can fine-trim her by moving your body. According to the previous owner she weighs about 600 kgs fully equpped.

In about 4 bft on a beam-reach she starts semi-planing with speeds of around 7 kts (hull-speed is just under 6), in a f 5-6 she gets to full-planing. I have read up to 10 kts on the gps so far. So for her size she is quite fast and also well-mannered. Only when reaching in very gusty conditions, she gets a bit catty.

So, all you knowledgable folks: if there was a race between a CS20#3 and a Diabolo - which one would be in front under which conditions - and: how do you know??

I hope, the data + pics give enough information.

Looking forward very much to your  thoughts & feelings,


2019-01-07 22.04.13.jpg

2018-12-22 15.56.08.jpg

2018-12-22 15.58.10.jpg



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Hi Tobias,


Your Muckla is a handsome boat.  I guess I just like dark-colored hulls.


The Diablo and CS20 hulls seem similar to me.  Anything beyond the effect of length of water line on hull speed is too subtle for me, but the CS hulls are known to be fast.


The biggest differences I see are in the sail plans.  Going upwind or on a reach, the sail is acting as an airfoil, and long, thin airfoils are more efficient (lift / drag).  Gliders and airliners need high efficiency, and they tend to have long, narrow wings.  Going downwind, the sail acts as a parachute, providing drag.  Parachutes (like spinnakers) tend to be fatter.   Since the Diablo has this tall bermuda rig, I'd guess it might beat the CS20 going upwind, and the CS20, with its sail area split between two  shorter masts might have an advantage downwind. 


Is speed your only criterion?   The CS20's cat ketch rig offers advantages in ease of use.  Tacking involves just moving the tiller.  There's no jib sheet to winch in, and there's no boom to duck under.  Speed is good, but I think stopping is often overlooked.  The ability to stop and rest, think, and adjust is important for safety in my opinion.  With a mizzen rather than a jib, you can haul in the mizzen, loose the main and the boat will weathercock right into the wind while you take a break.


If you are interested in getting into the technical details, I can recommend a couple of books.  In my book pile, "The Nature of Boats" by Dave Gerr describes a lot of the tradeoffs that go into boat design.  "High Performance Sailing" by Frank Bethwaite is a technical treasure covering everything from weather to foil shapes. 


Having said all that, the best boat is certainly the one you can sail.



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Thanks for taking the time to revisit your boat, in particular. But a few additional comments as it relates to your shots, the boat ramp looks like a nice facility for launching. Is there a link your general region with additional information of boating  in that area?  Do you have  any regional power boats in wood??

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Thanks gyus for your replies!

@ Meester: Speed of course is not my only criterion - but its important to me - and it is one of those which I can't judge by myself.

@ Oyster: the ramp acually is'nt so good. It is in Friedrichshafen, Lake Constance. This is by far the largest body of water around here. It is very beautiful with scenic landscapes around, pretty towns and villages everywhere and lots of historic sites, litteraly starting from stone age. All this of course makes it a magnet for tourists, so at times it's quite crowded.

If you really want a link:here it is: https://www.bodenseekreis.de/.😉

As for wooden power-boats: there are a few boatyards around .Here is a link to one of them:  https://www.martin-yachten.de/yachtbau/motoryachten.html

You asked for it....

Who said, he was a photo-addict?




2018-09-27 19.08.10.jpg

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On 1/21/2019 at 6:00 PM, Wommasehn said:


Who said, he was a photo-addict?



That could have been almost anyone on the forum.  We will let you know if you ever  post too many.

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Thanks for the info. I looked up the area and it does look pretty, probably more so in the summer time for me anyway not being a snow and cold weather person.B) 

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