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Old 02-06-2010, 08:44 PM   #1
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Admittedly it is not the best choice for blue water cruising, but anyway.

Have fun!

smalcat_brochure.pdf
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Old 02-06-2010, 09:01 PM   #2
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Wonderful. Thank you, magwas.
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In 1986 we went cruising for a few years. After 20 years and 50+ countries and several oceans, we are STILL "cruising for a few years".

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MV WATERMELON (New) | Cruiser's Dictionary, free ebook

= Cruiser's Dictionary, North America,
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Old 03-05-2010, 11:23 AM   #3
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Question, may be the first :- How did you arrive at an hull speed of 4.7knots?
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Old 03-05-2010, 05:18 PM   #4
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Question, may be the first :- How did you arrive at an hull speed of 4.7knots?
Looked up the equation in the web, and inserted LWL.

http://en.wikipedia.org/wiki/Hull_speed

I am happy you are interested in this little adventure of mine.

Yesterday I have redesigned it again. Today I have spent some 6 hours building a model of just one of the kayak hulls.

It had been a notable failure. Both of design and implementation.

Now gathering energy to make the needed modifications.
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Old 03-06-2010, 12:23 AM   #5
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Quote:
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Looked up the equation in the web, and inserted LWL.

http://en.wikipedia.org/wiki/Hull_speed
Just a couple of pointers; the formula used is the one that is generally used for 'displacement hulls' is not used for the type of catamaran your design depicts. The other minor point is the term 'small cat', present terminology favours the classification "Beach Cat"

Probably the best example and nearest to your design would be the Hobie 16 :-

The Hobie 16 is a 16 foot / 4.9 m catamaran with two sailors and has been a popular racing catamaran for 40 years. Hobie Cats were born in a surfboard shop in Southern California in 1969 and are named after the designer, Hobie Alter. Numerous Hobie catamarans have been designed over the years with the most popular racing boats ranging from 14 feet to 20 feet in length. The boats are easy to launch from sandy beaches, physically rewarding to sail and popular all over the world.

If you go to this link : http://www.hca-na.org/

then on the top right hand side click on 'resources' then on 'Technical information' where you will get :-

Technical Information

Line Guide (all boats)

Wire Guide (all boats)

Hobie 16 assembly manual

Hobie 14 tuning guide

Hobie 16 tuning guide

Hobie Tiger tuning guide

Hobie FX one tuning guide

The above information may be useful in determining the placement of control hardware and provide a guide to correct line and wire sizes on your beach cat.

By the way, the H16 beach cat has recorded over 22 kts on several occasions (there may be some official record with a much higher speed)

Here is a U tube of a Hobie sailing at speed
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Old 03-06-2010, 08:07 PM   #6
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Just a couple of pointers; the formula used is the one that is generally used for 'displacement hulls' is not used for the type of catamaran your design depicts. The other minor point is the term 'small cat', present terminology favours the classification "Beach Cat"

Probably the best example and nearest to your design would be the Hobie 16 :-
Thank you for your interest and useful info.

I am quite hoping that my design would easily plan, and would be capable of much more than its displacement speed (yas, maybe it is better term here than hull speed), but as I am not very well versed in planing hull design, I cannot tell. As I recall one hull's modeled resistance is below 100N near displacement speed, so I am hopeful. Putting in a speed of 5 knots seemed to be in line with the tone of the brochure.

Yes, I admire Hobies. I am regularly looking up them when I want to see how others do things. (Trifoiler absolutely amazes me. It is a shame they no longer do them.)

For example the solution to my deck hardware problem had been shifting the bow aka back to the middle of the boat, where Hobie (and other similar cats) keep them.

But today I have made another esign decision: just forget the complicated structure, keep it simple. Now it seems I would just use some alu beams and a net to create the middle platform, and put the mast either on the bow beam, or use a biplane rig. I am now exploring options for mast.
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Old 03-06-2010, 11:14 PM   #7
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Quote:
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For example the solution to my deck hardware problem had been shifting the bow aka back to the middle of the boat, where Hobie (and other similar cats) keep them.

But today I have made another design decision: just forget the complicated structure, keep it simple. Now it seems I would just use some alu beams and a net to create the middle platform, and put the mast either on the bow beam, or use a biplane rig. I am now exploring options for mast.
Remember, the reason for keeping the mast as aft as is possible is to prevent 'pitchpoleing'

(when the cat is going very fast and where the leeward hull digs in to the wave ahead and the boat turns 'head over heels')
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Old 03-07-2010, 06:51 PM   #8
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Remember, the reason for keeping the mast as aft as is possible is to prevent 'pitchpoleing'

(when the cat is going very fast and where the leeward hull digs in to the wave ahead and the boat turns 'head over heels')
Thanks.

This is the first useful info on mast positioning I got frome someone else (not had to figure out for myself).

(((I am gravely dissapointed by people at boatdesign.net.)))
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