General comments

[bob the builder]

any thoughts?

improvements?
http://www.boatdesign.net/gallery/showgallery.php/ppuser/31994/cat/500

http://www.boatdesign.net/gallery/data/500/cat_plans.zip


i can change anything at this point in time.


cheers,
mal

[MikeJohns]

If you want qualified comment then you need to say what is you intended use of this vessel and it's vital statistics and some lines.

I think the bridge deck is too low for anything other than sheltered waters.

[Ad Hoc]

I'd like to know if anyone has calculated the shear paths and deflections!

"...i can change anything at this point in time..."

Try keeping your posting just technical...drivel leaves just that and nothing sensible.

[bob the builder]

hi MikeJohns.
clearance? - i wouldn't have a clue


i'm a nerd (i live in a cave, have a pallor vampires envy, and my online name is Sword of Justice!)

so i've lurked here for years, slowly digesting what i can.
60cm seems not as low as 30cm, (quite a few cats have) n not as "!round the cape against weather, ARRR, " as 90cm

i really dislike sailing against the weather, having had some (real) bad experiences.

will be cruising, with all the time in the world to wait for good weather.


cheers big ears,
mal.




(
instead of the plans.zip then, i'll post all the pics here.

see? now you don't even have to click on a single link!


i now expect a comment frenzy. frenzy.
)

[bob the builder]

South pacific island hopper.

440cm wide
31 feet long
hulls 90cm wide at the aft waterline, flat, no rocker, 15cm deep
60cm bridge deck clearance

minimum sail plan;
boom 3 feet from deck, 390cm feet long
mast 10m high
sail area 15m2 main, 15 jib (center of effort 4m above the water,

minimum displacement 1100Kg
average cruising 1300


Live on. Lots of flat open usable space.

Lots of aluminium beams - (120 Kg of ) Stop rig unloading, minimum flex around deck/hull joins means the glass will still be unbroken and not sloppy after a year on the water, to keep the deck stiff and unbuckling and in plane under load.

Flat hulls (considering over standard minimum drag jobbies)

Tiniest bit heavier than normal scantlings - want it still stiff in 30 years (i have a THING! about sloppy fiberglass EEW! etc)

100 Kg/m2 weight/ water planing area

fiona sinclairs for a single (700Kg) hull
around
30 kg drag at 10 knots
70 kg drag at 15 knots


i like the design so i'm about to have it engineered and softwared.


http://www.boatdesign.net/gallery/data/500/plan.jpg


http://www.boatdesign.net/gallery/data/500/medium/profile21.jpg


http://www.boatdesign.net/gallery/data/500/model2.jpg


http://www.boatdesign.net/gallery/data/500/medium/Image2a.jpg


http://www.boatdesign.net/gallery/data/500/p2w.jpg

[bob the builder]

and to help start all you guys speaking!
here's some ideas i'm thinking sticking on.




the hull shape . . .

fiona sinclairs applet generated fat cat hull shape
optimised for surfing, planing.


i can either build plain vanilla hulls (low drag optimised displacement) or flat ones.


this question seems to have been asked over and over on these forums (was asked again just the other day)

elsewhere on the forums . . .
"
.... Would the planing hull boat be faster ?

At 20kts a 12m planing hull displacing 6 tonne would require twice the power of the best 12m cat of the same displacement.

Rick W.
"
and he knows his maths.

but then the question, why bother having a planing sailing boat at all? if displacement hulls do have lower drag than flat? something is not right here.



so
will i end up building it? i really can't say, waiting for this thread really.
http://www.boatdesign.net/forums/sailboats/new-flat-hull-shapes-28676.html

those aren't old designs, but expensive ultra new jobbies which gives me hope



i might blend it with a michlet

how much will a bit of rocker hurt planing?
or
how much will flat aft sections hurt normal hulls drag?

my michlet progresses slowly, and rick has already done an example cat with full transom somewhere round here.


why so much effort?
why not go plain vanilla minimum drag?
the weight to planing area is so good! 100 Kg/m2 (same as a LARGE surfboard. imagine the fun! in the open ocean . . .
and the Sail Area /Weight ratio, as you can see from the pic above,


makes me ponder . . .

and ponder some more.





A bridle on the nose
to attach the front stay to.
want the boat to have as long a life as possible.

attaching to one point gives all the shock and load in the middle of the beam. sticking a bridle on reduces the length of beam to 1/3 of what it was, (which increases strength due to shorter beam) while halving the shock load, since there's now two points.

might do it, might not





More sail
the conservatism of the minimum sail plan is high because i'm very lazy. n im not sure if i wanna get off my arse (or worry) for squals and drivel. (35 knots to lift a hull with full sail)

but if the hulls will plane early, around 10 knots i reckon, then i'll maybe go with 45m2

(
i'm pondering
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa! etc
)



comments?

[apex1]

hi MikeJohns.
clearance? - i wouldn't have a clue
i'm a nerd (i live in a cave, have a pallor vampires envy, and my online name is Sword of Justice!)
so i've lurked here for years, slowly digesting what i can.
60cm seems not as low as 30cm, (quite a few cats have) n not as "!round the cape against weather, ARRR, " as 90cm
i really dislike sailing against the weather, having had some (real) bad experiences.
will be cruising, with all the time in the world to wait for good weather.
i now expect a comment frenzy. frenzy.
)

You might be surprised Bob, but sometimes Mother Nature does´nt play to YOUR rules, so avoiding adverse weather means sitting at anchor or cruising round the approach buoy.

Richard

[MikeJohns]

I'd like to know if anyone has calculated the shear paths and deflections!

"...i can change anything at this point in time..."

Try keeping your posting just technical......

Ah I see this has been discussed on another thread, I missed that.

Although if this is the concept then the design spiral will unfold in due course.

But right at the start.... the design is not suitable for offshore Pacific IMO.
Poor bridge deck clearance and an exessive fore-n-aft extent. In offshore cat design and there are many poor designs that are way slower than a monohull and pound intolerably and dangerously at sea.

Planing hulls ?
Planing hulls are useless in this sized vessel in a seaway. A cruising vessel also carries a lot of weight. The Pacific trade wind belt is boisterous there's often a big underlying swell and 25 knots constant unless the southern convergence kicks in then it blows 50 knots for a few hours. It's not the smooth sailing people imagine. This vessel as you have designed it is not suitable for anything other than limited coastal, sorry to be blunt.

[whoosh]

yes well mike I may well be a romatic at heart

I have also done a lot of SE trades sailing and yes it is not calm weather at all
It is wonderful, BUT you need a strong boat with strong gear and strong people
Paricularly light cats do not sit well at anchor, and often up in the Islands it is impossible to find an achorage where the swell does not roll in the motion is very very uncomfortable in a light cat .
the boat that sits best is a chine mono
BOB you must be bonkers, there are so many GOOD second hands cats out in the Carib, for 30% of what you will build for
Buy me a ticket I,ll sail it back for you Real Rum there too

[bob the builder]

thanks Mike.

don't be sorry, i'd PAY to hear these sort of comments.

how else am i gunna learn?



good call.
limited coastal is exactly what it started as.

and i've thought for years making it a plain vanilla job, ie large tramps that go halfway etc,
i've done several larger designs before this one, but decided to stick to day sailing/island hoping and the smallest boat i can reasonably get away with.

basically i wanted a great barrier express with better long term accommodation.

i didn't want something too large and heavy. and went the very light way instead.



"Poor bridge deck clearance and an excessive fore-n-aft extent."
yes, spotted perfectly. it would have pounding if you were on the wrong heading, and it was in weather.

performance is not primary with this design, obviously accommodation is.
it is not the best design for open ocean, but on the other hand, it is better than a LOT of production cats that only have 30cm clearance, and they call them open ocean. and it has much better accommodation than all the boats it compares to, ie Great Barrier Express etc.

years ago all my designs were plain vanilla ie no full bridge deck. but i've been reading stories from owners of full bridge decks and they prefer the extra area over all weather ability. and thats exactly where i am.



purely as a matter of interest,
which of these would you call unsuitable for South Pacific Island hopping?
http://www.sailingcatamarans.com/25_30.htm



"a few degrees course correction can end it" (pounding) ??
can anybody confirm this statement?
anybody ever done it?



(
i've recently been on big cats, 35 to 40 and decided i wouldn't do it at all if i had to stick with these. just too big for me to feel comfortable handling all on me lonesome.
so i'm not all that keen on building bigger though.
i just don't want a big heavy cat. so i can either loose some front accommodation or change course, or not sail that day. i can build the hulls a few feet longer, but they are already 10 (10) feet longer than they started.
)



cheers,
mal

[bob the builder]

whoosh . . .hmmmmmmm.

"the boat that sits best"

a yacht eh?

hours spent trying to reach safety, and safety so near, and yet so f!ing far away, vomit everywhere, bashing into a southerly, engine on, all sail, and making no way. F that. been there. rather die trying to stick a yacht up my arse than actually sail one again.

Strong people? an old lady once felt my hands and said i had the softest hands she had ever felt on a man, and had i ever done a days work in my life?

Bonkers?! after they released me they even gave me a piece of paper which PROVES i'm not.

i'll buy you a ticket, but only if it's one way.


(see you monday)


mal

[bob the builder]

Beams

i don't have a clue what's really needed or a good size. i have zero experience in the real world. truly, you the reader has a much better idea than me. i just chose because you gotta start somewhere.

REALLY wanna shed some weight from these specs (120 Kg on the beams), but then, i don't really know. maybe this is really really good? (certainly is brilliant the amount of work they help avoid! no wooden beams or beam boxes to build, just some aluminium welding, then bolt them onto bulkheads)


comment positive or negative if you have any real world experience with aluminium specs please.

http://www.boatdesign.net/gallery/data/500/beams.jpg


beam boy shows i've got twice the modulus needed on the mast beam (Ix 3 700 000 )
(using 15000 Newtons moment in the middle gives 4mm deflection for two of 76mmx76mmx3mm, one on top of the other (one under the deck, one on top - trying to minimise the impact on living space.)


here's that catalog link again, just in case you feel the urge (bored on a Sunday afternoon? ) to try and save me some weight.
http://www.gjames.com.au/cgi-bin/priv?url=/marine/gjmarine-metric.pdf



http://www.boatdesign.net/gallery/data/500/thumbs/boxbeam3.jpghttp://www.boatdesign.net/gallery/data/500/thumbs/mainbh.jpg


http://www.boatdesign.net/gallery/showgallery.php/cat/500/page/2/ppuser/31994

pics of all the beams here

[bob the builder]

Weight
(i'll change this photo as people think of stuff to add)

do i really need such thick timber?
bulkheads, hull frames etc. whats the minimum i should go?


http://www.boatdesign.net/gallery/data/500/weight.jpg




18mm ply @27Kg/2440/1200 0.3472 x 27 Kg = 9.3 Kg/M2

kiri
25mm 7.5 Kg/M2
20mm 6
15mm 4.5
12mm 3.6
10mm 3.0

[bob the builder]

Deck

i was just about to make my first purchase on ebay, (excited!, first boat purchase!) some carbon fiber for the decks. cheap.
but this stuff is cheaper,

http://composites.jp/english_site/carbon_fiber.html

minimum order 20m
which is exactly how much i'm after
(to do all the top deck, (7.5 x 2.6m wide)
so i'll have that walking on steel feel for 30 years)

600gsm stuff, 12k (cheapest, strangely. all the 3k 200gsm is twice the price. weird)
$23 US/m2



Centerboard. aluminium/kiri
(flat aluminium strip 25mm wide x 2mm T6, kiri 25mm square) x 20
= 54cm long x 2.5cm wide

n say 90cm deep under the water

??





already shed all the water, down to 25 L plastic fuel tank, 10mm strip plank on the cabin

the quest . . .

"
building lighter than what is now considered normal, you will just have a better, cheaper boat, paid for by the saving in materials
rob denny
"



Strip plank sizes
anybody here done it before?

[whoosh]

whoosh . . .hmmmmmmm.

"the boat that sits best"

a yacht eh?

hours spent trying to reach safety, and safety so near, and yet so f!ing far away, vomit everywhere, bashing into a southerly, engine on, all sail, and making no way. F that. been there. rather die trying to stick a yacht up my arse than actually sail one again.

Strong people? an old lady once felt my hands and said i had the softest hands she had ever felt on a man, and had i ever done a days work in my life?

Bonkers?! after they released me they even gave me a piece of paper which PROVES i'm not.

i'll buy you a ticket, but only if it's one way.


(see you monday)


mal

yes well the biggest majority of these PACKAGE monos, do not sail to weather
, sailing to weather is not fun, but inna boat that can sail to weather it is very satifying
the very same boats make so much leeway even cracked off, that they never go places
I,ll be there are many cruisers who dont know where the block should be on the traveller in various condition upwind
Reckon you would learn more on a crack racer in one weekend, that a decade fiddling:)) So Mr Oates, is looking for ballast , ciao

[Rick Willoughby]

....
http://composites.jp/english_site/carbon_fiber.html

......?

That is a good price. Let us know how you go with the purchase.

I thought you had an aversion to plastic?

Exchange rate AUD1 = USD0.84 is looking better as well.

Rick W

[bob the builder]

whoosh. - "dont know where the block should be"

what's a block?

[bob the builder]

i've decided on my hulls.
i'll go planing.


i realise full well every person who reads this would advise against this course of action.


i realise everyone of you here would say good displacement jobbies are the sensible thing to do.





but,

true planing SA/D 37 or above

45m2 sail and 1400kg
500ft^2/2800 pounds heavily loaded 1400kg
= 39.5


light load, 2 people, no water, little fuel 1250kg
500ft^2/2500
= 42.6


so fiona sinclairs generated hull shape optimised for min drag at 11 knots.


and you're all invited
(mooloolaba 12 months from now)

[bob the builder]

http://www.boatdesign.net/gallery/data/500/strongback.jpg


http://www.boatdesign.net/gallery/data/500/hullresistance2.jpg

[peterAustralia]

To Bob,

Building a catamaran is an expensive thing to do. May I ask most politely why you do not buy an existing design from a professional designer. I think the time saved in materials and build time would much more pay for the cost of the plans, not to mention resale price. Additionally as skilled as any individual may be, a professional that has designed many many catamarans will probably design a better craft.

[bob the builder]

hi Mr Australia.
nice to have anybody who contributes/helps drop in.



to quote from the Wikipedia entry for catamaran

"
There are a lot of folks doing long-distance offshore cruising in monohull yachts of 9m (30 ft) and less. No responsible designer or multihull sailor would recommend this for a multihull. 12m (40 ft) is the minum recommended LOA and 15m (50 ft) is preferred. This size allows adequate storage for necessary cruising equipment and still give you a good turn of speed in comfort and safety.
"



15m (50 ft) is preferred.






Camping.

if you want to visit a national park in australia, to go camping, then a camping vehicle is necessary. a camper van.


there are mosquitoes that carry dengue fever, which can KILL you.
so mosquito netting all around is vital

also,
without water you will DIE!
so water is needed.

a shower is nice, hot water to, tele of course

more people DIE! from food poisoning in australia than car crashes, so a freezer is a necessity.

a microwave makes sense if you have a freezer.

are you old? did you know heat stress kills many old people, so air con is essential (you can truly DIE! without it.

solar panels are vital because we are killing the planet by over consumption

a generator is also needed because you can't realistically run the fridge, microwave, or aircon on solar.



to take all this gear when you go camping to visit nature that hasn't died from climate change (ie the 30% of coral thats left), you'll need some power to SAFELY go uphills, say a 200KW engine? ultra high tech for fuel efficiency, to be extra friendly to the environment, so twin turbo.



So the list of SAFE camper vans is growing shorter

Winnebago!

http://www.smh.com.au/ffximage/2006/05/08/winnebago_wideweb__430x301,0.jpg




so i think we've fairly well proved by scientific reasoning that my camper ($800, and built by yours truly) is nothing but a death trap (aaaaaaaaaaaaaaaaaaaargh! etc)




great resale!
Winnebago Wilderness 1998 - Caravans Onsite Australia - Buy sell ...
Price: $135000





Same story in pictorial form
(for the hard of hearing)(so deaf people can enjoy this thread as well)
(the more gifted of you can skip on ahead)


a man wants to go camping,

http://www.janesoceania.com/australia_aboriginal_traditional_society/aboriginal6.jpg

and quite rightly,
arrives at the same conclusions i did. the (current) apex of human brain power.


TA DA!

the Winnebago.


http://www.roamingtimes.com/a/consumer/images/2008-winnebago-destination.jpg



http://img23.imageshack.us/img23/8687/ch002.jpg



The End.








"
Additionally as skilled as any individual may be, a professional that has designed many many catamarans will probably design a better craft.
"

i have no doubt they could design a better Winnebago than me. (see that bit on the side!

http://www.chooseyouritem.com/rvs/photos/107500/107829.2000.Winnebago.Ultimate.Advantage.jpg







James Wharram, began designing Polynesian-type catamarans and built Tangaroa, a 23-footer for $420. He then proceeded to cross the Atlantic with it in 1957.

james! the load carrying capacity! leave the girls behind you fool! don't you know about load capacity?
you fool James! come back!!!! it's not 50ft long! aaaaaarrrgghhh!!!! (etc




i know richard hangs out here, and will definitely read this (hi richard!) and i have NO wish to rain on his parade, (thanks again richard for all your help!) but i've seen the astounding effort and hours that go into building one of his designs. have a look at this effort. read the entire thing, look at every photograph. i did.

http://www.navigare.com.ar/construccion_catamaran_27pies_english.html

astounding time and effort just to build a single wooden beam.




i've read other strip plank professional guys who say they can strip plank a hull in one day. n i'm going to do this. one day.

and i've planned the build process so it's almost finished when you turn it over.

2 days so far. :o)
truly, my planned build process should be astoundingly faster than average. people stick to what they know.





"
Building a catamaran is an expensive thing to do
"
no. building a winnebago is an expensive thing to do.

my cat is $2000 of wood.

?



was James Wharram a fool? his boat wasn't 50ft long, and he overloaded this cramped craft with german backpacker chicks as well. thats two major mistakes he made. he should have read Wikipedia first.
then
worked for another 20 years to get the Winnebago.






i presume from the gist of your mail you love your job (and would rather work than build a boat, and then pay to have somebody build it for you)

me?
i've retired (young) and LOVE having time, rather than responsibilities.
love having fun, rather than carrying weights every day.


to sum it all up,
sex - sure Duece Bigalow (Professional Gigolo) could do it better than me, but i think it's more fun if i do it myself, and i know i'll be much happier, much longer than if he did it for me.

(
Deuce Bigalow: Male Gigolo with Ruth the tourette syndrome girl
http://1.gvt0.com/vi/XBhlyXQeAL0/0.jpg
http://www.youtube.com/watch?v=XBhlyXQeAL0
)


"think the time saved in materials and build time would much more pay for the cost of the plans,"

well, politely - this place your at, it's called the Boat Design net, not "gimme money dot com"
and it's where guys hangout who are designing their own boats.


if i charged me for my time at my rates, my plans would cost how much?

have a guess.





also,
most politely,
haven't you ever wanted to build your own meal, rather than eat MacDonalds?
why design your own home?
why cook your own meal?


you get exactly what you want.




annnnnd,
Cheers big ears!
mal :o)

[Rick Willoughby]

Mal
The drag prediction seems way out. Not that it matters a lot. The hulls power quite easily.

Michlet gives a total drag of 904N at 12kts. The lowest drag hulls for this speed requires 834N. Both estimates for calm water of course which only relates to belting along in a sheltered harbour or close to a windward shore.

As far as the transom goes. With a boat this light it will not matter much. You simply move a bit of weight forward to lift the transom in light conditions. I did this in a 3 tonne boat with just crew weight.



Rick

[peterAustralia]

Well each to their own I guess

I asked a polite question and got a kinda rambling answer that I tried to follow but found it hard.

From what I could work out, you want to build your cat on an extremely small budget which to me seems difficult to achieve. Well I guess good luck then. I will leave you to it.

call me Peter, you to do not have to call me Mr anything
N Peter Evans
tacking-outrigger.com

[bob the builder]

hi pete.

look at the time you got though!

and all that effort
(to come to the wrong conclusion)


the answer was FUN




it's time.

i've got buckets of time
some people garden with their time because they like doing it.

some people design boats and hang out here. for fun.



we, you and i, have such vastly differing perspectives from which we view the world, that it is astoundingly difficult for us to communicate. no doubt there.


you have to be extra careful what you type. people often take offense at attempts at humour.

yet if we were speaking together, you would not mistake me, because emotional tones, facial expression carry the real base of the conversation, and were we speaking face to face i would have said straight out,

"
don't you realise what a weird thing you've just asked?
like asking on cooking recipes dot com why don't you all go to a restaurant.
"

if this was cooking dot com, how would you reply to the person that asked that question?

lemme know


mal.

[PAR]

From what I can gather Bob here has turned this into a ranting of ridiculous concepts, contradictions and imposable to fully comprehend desires. Possibly his personal blog.

Frankly, if he was my client I'd have tossed him out of the office by now and kept the retainer as "frustration factor".

Is there something you need Bob? Will you still need it tomorrow? Just following your posts suggests you're either very foolish and/or very young or possibly needing medication.

You've shown sparks of comprehension, intermixed with gibberish and garbled efforts at humor, weirdness and just plain lack of communicative skill.

If you desire something from a discussion arena of mostly industry professionals, you'll find most success based in responding accordingly. Leave the melodrama at home and attempt your best diction, syntax and analytic philosophy, which can form a base from which to expand your understanding. Currently, I don't think anyone here has a clue what you want or even if you know what you want, which frankly is keeping most away. Clear, concise questions, get the same in reply generally. If not, this thread will die a useless death at least in regard to meaningful answers.

[bob the builder]

rick,

i knew fionas was out,

michlet kept giving me higher answers for a better hull shape (lower drag job)


but the overall gist of her hull shape does match generating lowest amplitude bow wave smeared over the longest wavelength, plus the lowering of drag at 10 knots.


the FreeShip hull file is not finished yet. the nose needs a lot of work, way too thin, then too fat suddenly. Cp.7333 at present. when get hull to .9 drag should drop some more


http://www.boatdesign.net/forums/attachments/design-software/33934d1249726345-anybody-good-delftship-image1.jpg







aversion to plastic?

only professional stuff

(ie cheap shit
polyester, vinylester, cheap, cheaper, cheapest. whatever the market will stand)

my plastic is not polyester fiberglass on foam




i can't think of anything better than epoxy/glass kiri sandwich.

and heavy carbon for the decks? brilliant.


chalk and cheese.
a world of difference.
specially after the first year. foam/polyester boats loose so much stiffness.
epoxy glass wood composite sandwich will have a hundredth? of the stiffness loss? (and i know you were egging me on, just to set me off. ) so there it is.









(
general interest to everybody;

my freeship generated michlet input file flashes up on the screen then disappears, the infamous invalid input file problem. can be quite painful to fix.

but just discovered Delftship 3.2 works perfectly.

generates a working in.mlt
)







can anybody recommend what to do next?

what would you change?

[TeddyDiver]

what would you change?
Designer? :rolleyes:
Seriously.. cheap and light don't fit in the same concept..

[Rick Willoughby]

......
can anybody recommend what to do next?

what would you change?

You have Michlet running. It is not much more effort to run GODZILLA. You can use it to determine the lowest drag hulls for set constraints.

You can use GODZILLA to see what shapes are best under given conditions.

With most cruising cats the minimum beam of the hulls is constrained by the need for accommodation space. If your hulls are only for storage than you can tolerate narrower hulls.

The actual lift you will achieve from your "planing" hulls will be quite small. It will not be useful until you get up over 15kts. Even at 20kts the lift from planing will be less than half the displacement.

The outright speed of a cat on a reach is achieved when it is on the verge of lifting a hull so it is really working as a monohull. The driving force is limited by the beam and the height of the centre of pressure on the sails. The boat is really a monohull with windward ballast. Doing drag analysis for an equally loaded pair of cat hulls for this condition is meaningless.

Going downwind the cat will power over the short seas you get inside the reef off Queensland. You need to consider what happens coming of a wave if you intend to drive hard downwind to make use of your "planing" hulls. Narrow bows with large flare tend to stop when they bury in a wave and the buoyant stern wants to keep riding the wave. The boat becomes a catapult.

Have a look at the amas on the big tris. These are the hulls that count on these big flyers when going hard.

You have eliminated one of the significant constraints cruising cats work within but I do not think you have made the best of this. Narrower hulls will power a little easier for most speeds of interest and points of sailing. It would be worthwhile determining what the lowest drag hulls look like and go from there.

I would be interested to know what foam sandwich boats you have found "soggy". Who built them? I have found that it is easy to get variability in the adhesion so am interested in construction methods and quality assurance procedures used.

Rick W

[jamez]

I have no comment on bobs concept other than to say I think its as built (ie. the model) as it ever will be. I recommend a course of Thomas Firth Jones re. minimum cruising requirements. Or a bit of Gilbert for a min Pacific cruiser concept;
http://www.duckworksmagazine.com/04/s/columns/gilbert/010/index.htm

The Wiki catamaran entry is full of misinformation and the quoted source for the 40'minimum 50' better multihull comment is laughable in terms of its commentary on multihulls. The lack of understanding demonstrated is mind boggling.

[bob the builder]

thanks rick

love to hear from you.


done Godzilla (just for the name alone of course!)
done michlets x lots


fall back hulls are/were fat tornado's, they do power easier of course, but as you know, it ain't by much, and i'm willing to wear the difference.


but,
understand plain vanilla and have agonised for a long time being the only person in the world to take this brave course of action. to boldly go etc

"
i realise full well every person who reads this would advise against this course of action.
i realise everyone of you here would say good displacement jobbies are the sensible thing to do.
"

but there are some positives;


fastest acceleration furthest out from a big wave,

best load carrying capacity of any hull shape (load X makes the least difference to the performance of these hulls)

best reserve buoyancy (lifts faster from a big wave than any other shape (except plain flat

some round for a bit of strength

great entry angle (you've seen the wave drag)

no rocker equals longer hulls in terms of passage making

no rocker gives best surfing

and wave drag goes flat real early as you know, and i'm more than happy to have the 3Kg/hull extra viscous drag at such high speeds





of course, normal rockered lowest drag jobbies also have their benefits.






these plans are going to be finished real soon

when they are, i'm going to release them here for the general public.

gunna call them Open Source Cat Plans Version 1.0

the average builder would like plain vanilla hulls a lot more though

you can do this faster than me. if you generate a michlet you're happy with, i'll do full build plans for them.

truly no idea why this web site doesn't already have a hundred plans in a repository from all the guys here.








"
The actual lift you will achieve from your "planing" hulls will be quite small.
"

true. but the hulls aren't finished, and there is no angle of attack on them yet.

i'll probably keep them straight/flat, and have water and fuel all the way aft, people too. this should do the trick. 3 to 400 Kg on the bum for average cruising, so i shouldn't need to put an angle from stem to stern like fionas hull has.




will digest your comments further,
and return after pondering.








"I would be interested to know what foam sandwich boats you have found "soggy". "

haven't you ever walked on any?

specially those that have been around the block a few times.

just go shopping for boats. there are plenty of old soggy polyester/foam jobs out there. at any marina there's always a brokerage with hundreds of boats to walk over in a day.

just walk on some foam and tell me what you think.


(my bias comes from 20 year old polyester fiberglass thats gone sloppy underfoot, so i am extremely biased i admit, and once this happens to you, there's no turning back either.

i've also had polyester/glass surfboards and i could cry when i think of what a true rip off they are. you get a brand new sexy shiny looking board with all the strength of a wet tissue. a leg rope will cause polyester to delaminate.





remember,
i haven't finished digesting yet.

am going away for a few days, will ponder more on narrowness etc (did work out planing lift for surfskis, water skis, wakeboards etc but the basic Pa/m2 story is 90cm wide at 10 knots or above)










jamez
thanks for dropping by.

all are welcome here who help. nice to have your contribution.




thank you all,
mal

[yipster]

$2000 wood and a day build is hard to belive on that hull
but see your gettin there putting a winnibago on top

[bob the builder]

Yipster,

http://www.paulownia-timber-sales.com.au/Price%20List%20as%20at%20January%202009.xls

and the weight sheet specs it. cheaper than $2000.

they must charge way more in the netherlands. lots of paulownia plantations here in oz.






got the drag down some more Cp is past .8


next goal is to remove some of the fat (white arrow)


here's the new in.mlt for those as interested, and the delftship .fbm

how do you smooth curves and auto fair in delftship? i can't get the option to go black (enable)


suggestions please. . .

[yipster]

bob, had a look, bow seems a bit unfair, heck, dont know how to autofair now, manual?

starting with less points 3 for example and putting res high gets you a easy to work with fair hull you can always refine

material can be low priced i know and pricelist is there but there is more involved rite

what i ment early'r above was: why strip plank if you want to keep it cheap and simple like wharam

a flatbottom long dory is stronger and faster build and above hullspeed the chines dont increase resistance

personally i would go nice slooped devellopable plating all the way for deckhouse too

or something like this http://64.251.22.171/articles/design/ngdesign/plaquette_Ekolokat_ENG.pdf dont thrust the daggerboards tho

[bob the builder]

rick,


narrower hulls are sensible. everybody has them.




the clearance is 60cm with a full bridge deck. so hull slamming is going to happen at some angle/speed combination





i don't want to build a larger boat.

i want the huge accommodation a full bridge deck gives.


sailing close to the wind into waves, the faster i go, the more i head in the direction of the waves, the worse hull slam is going to be.


if i had narrow hulls, the slamming would be much worse. i'll slice into waves (which lowers the deck height to the water) and the hulls will go deeper, for longer time, and the faster i go the worse it will be.

the leeward hull will already be pressed down, the windward hull lifted somewhat. (so the deck is lower to the water surface)

so narrow hulls in the worst case of sailing into it, will slice further into a wave (downward loading, so the deck is closer to the water surface), will have least acceleration upwards (so be there for a longer time period), make the deck closer to the main wave peak (forward momentum, exposing the deck for longer to wave superposition), and the deck will already be closer to the water because the leeward hull will already be pushed down when the wave peak hits. the narrow leeward hull will stay down a lot longer traveling into the wave face because it's already depressed 10 cm?



extra fat planing hulls will rise the furthest distance from the wave peak, will rise with the fastest upwards acceleration, will not slice into the wave face due to forward momentum. the leeward hull only depresses a maximum of 7 cm when flying a hull, and so has negligible leeward hull depression normally. the deck then has been exposed to slam for much less time and at a much greater height.



i suggest these hulls have so much more lift than normal, i'll be able to sail faster and closer to head on, with the minimum deck slam for this 60cm deck clearance height.




still might change everything though





"
GODZILLA
and,
Even at 20kts the lift from planing will be less than half the displacement.
"

still crunching numbers/ hull angles / Pa/m2.

still digesting, will reply soonish.

[bob the builder]

yipster

rtfm, there'll be a simple trick to get the option to enable. it'll just take weeks to find is all.


i'll try taking some points out. let you know what happened.


http://64.251.22.171/articles/design...olokat_ENG.pdf

is nice for sure.



"flat. keep it cheap and simple"
nah.
got me little heart set on strip plank. n want lots of round organic shapes just because they please my eye.



cheers,
mal

[yipster]

and want wood, wood sucks, even encapsulated in epoxy vinylester etc it gains moist and weight, use foam, ooch what did i say, i'm outta here :P

[yipster]

was reading wharrams yard site http://www.andy-smith-boatworks.com/asite-renewed/index.html
and again very clearly noticed a boat is what you make it outside and in
you also have fixer uppers for a grand, 3k for free labor half builds etc
wharram is also using crab claws that seem to perform well
looked into my alu space frame idea and boards and foams

a boat should be small enough to take home or big enough to live on
phil bolger?

a well, i (we?) miss ya :p

[bob the builder]

further hull ponderings

"at 20kts the lift from planing will be less than half the displacement. "






my reason for having aspect/angle on the entire hull was formed years ago.

basically,
after looking at pictures of many cats sailing, i came to the conclusion that under normal full sail, the nose gets pushed too far down.

a normal sail load pushing the nose down does not appeal to me at all.

this is the reason why i allways intended to have lots of weight near the transom.
so a good full sail load of 300kg makes the hulls sail flat.

(water tanks, fuel tanks, engine and people all in the space between the transom and the chainplate/cabin start will keep the nose out until reefing (ie 400Kg on the sails).









the hulls sail with 0cm at the stem and 15cm deep at the stern

14m2 SA, 1400Kg, so 100Kg/m.


perpendicular 1m2 @ 1ms, Pa = 10000 N

(15cm deep over 14m2 planing surface area

(sin-1 .15/930) x 2hulls SA (15cm over 9.3 meters gives 1 degree angle)

= .02 * 14m2 = .3 * 10000 N
=3000 N



@1ms need 14000N from (angle/area/velocity) to plane

@2ms need 7000N sail force to plane

@4ms need 3500N sail force to plane

@5ms need 3000N sail force to plane





so
"at 20kts the lift from planing will be less than half the displacement." if the hulls travel flat.

if they have 1 degree angle either built in or balanced in, then fully supported at 5ms, 10 knots.

which matches fionas wave drag graph perfectly. ie starts full planing at ten knots

[Rick Willoughby]

Mal
If you take your calculations a step further you would predict a narrower deeper hull of the same displacement would plane easier. That is not the case.

Planing hulls are similar to foils or wings but with only one lifting working surface rather than two. The lift resulting from movement is related to the dynamic pressure not static pressure. The dynamic pressure is a function of the velocity change relative to the far flow up to the point of the flow becoming turbulent rather than streamline. THe highest lift pressure is where the oncoming flow first meets the hull and is slowed down. The aft end actually has negative dynamic pressure because the flow velocity increases as it moves up behind the hull.

Here is another useful little bit of software that you can use:
http://illustrations.marin.ntnu.no/hydrodynamics/resistance/planing/index.html
If you put your hull values in it you will see that the trim up continues till about 25kts and then levels out - see attached. This is in close agreement with the NACA data I used to work out the lift at 20kts.

You will get more lift at a given speed if you angle the hull upwards but it is nowhere near fully planing at 10kts.

Actually did you see the hull shape of X-IT that Brian Ballard posted:
http://www.boatdesign.net/forums/attachments/boat-building/34053d1250153720-my-little-piece-peace-dscn2348.jpg
These hulls are more suited to being easily driven throughout the speed range than your current design.

With the weight you are targetting you can trim it how you like by shifting weight around.

You would find a simple hard chine with narrow flat bottom and some rocker would work well. Have a look at some of the east-to-build beach cat hulls. Most big cat hulls are designed for volume and accommodation. You have gone past this thinking so why not make the most of it?

Rick W

[bob the builder]

foam ponderings for you


"
I would be interested to know what foam sandwich boats you have found "soggy". Who built them? I have found that it is easy to get variability in the adhesion so am interested in construction methods and quality assurance procedures used.




all these things are engineered. so there's no sense in considering this aspect at all.

can i suggest looking from two perspectives at the same time? start with the engineering perspective, but also consider MacDonalds killing people.

ie it's capitalism, not engineering.




an organism seeks to survive. there are competitors. they have to make a profit or they won't exist. ergo, the people building right now have made profit. but how do they stay alive?

by cutting costs.
and
increasing marketing


(just like current MacDonalds advertisments on the tele, they market their food as the healthiest food, and back it by science. the reality?, they kill more americans than car crashes. have you seen american bums lately? HUGE!)







so;
survival of the companies that reduce their costs the most, while increasing brain share.

reducing quality while increasing perceptions of quality (increasing rich 3d visual information, shine, lustre, sex appeal triggers)



how do they cut costs?

build time, materials.
and now, you know we're talking foam, and something-esters here.





if you only ever consider from an engineering perspective, you will only ever see MacDonalds as a supplier of scientifically proven good food.

rather than the largest killers of other peoples children on the planet.

(heart attacks
- people are genetically evolutionarily hardwired to POUNCE! on FAT and protein, as in the wild fats and proteins are very hard to come by. food scientists understand these knee jerk circuits and of course tap your knee to trigger the reflex. it's their job)

have a look at american arses next time you can. their butts are HUGE!, and similarly, there is as much fat on the inside, in their arteries.





if you were a surfer and had ever bought a polyester surfboard

(SHINY! NEW! SEXY! LUSTER!

and had the FKING! thing break the VERY first time you used it (leg rope force delaminated the tail) you would be suspicious of survival of the fitest suppliers of goods, engineered or otherwise.





professionals? all yours mate.

[bob the builder]

hi rick.
"
If you take your calculations a step further you would predict a narrower deeper hull of the same displacement would plane easier. That is not the case.
"

no i wouldn't.

do i understand the maths you are talking about?

yes.
i understand exactly what you are saying. and you are correct.

this was just the quickest way of arriving at the required answer

if you ignore the progression, and focus on the relationships, i know you will see.




did pure maths at uni.
used to localised pools of consistency (limited pools of completeness)

engineers are used to universal maths, like the ocean.

but realise that swimming pools DO exist,
and they don't touch the ocean.



(further reading on the philosophy of mathematics;
bertrand russel,
showed how logic breaks down at the first step)




it's a difficult thing to explain to somebody
look at how much drivel i've been forced to write, to defend an OBVIOUSLY wrong mathematics. how can a sane person even consider defending wrong maths?


1 + 1 = 2 is not true, and has never been true

you have two oranges, one is small, green and rotten, the other is fully suculent, ripe and delicious.
you have two small children.

you hand the good one to one child and the crap one to another child.
engineering maths has occurred.
1 + 1 = 2, and everybody is happy.

no.

one child cries and the other is happy.
reality has occurred.
1 + 1 =2 is a con job.





the maths is good, the pool was good, but yes the maths used was not universal, so the relationships are true, the result true, but yes, the steps are of use in this one tiny pool only.

hope you understand.

do you understand the maths that i used now?







i realise the plastics speech uses extreme examples.

but it would just take so much longer to get the point across using normal examples, and then there's counter examples that have to be countered etc etc etc ad nausum.

far easier to ignore an entire invalid methodology than try and reason WITHIN it, on their terms. (and of course, this is your job. to reason within this forest)




can foam/glass/cheap plastic be engineered? to stringent specifications? obviously
is the ISO valid? extra valid
can you defend yourself in a court of law? absatively

well then, engineering wise, i guess foam/glass/cheap plastic is the way forward.


and for normal people it is.
a winnebago is a good product

just not for me. the stiffness loss after ONE year is just too much for me, let alone 30 years.



some of these (i'm drunk by the way) new cats have foam mast bulkhead/beams. see, the engineering says OK, the foam numbers say sure, use it for under the mast because it's 1 meter high, (foam panel) i say get f*cked you moron. it's a trick. twice the depth gives you squared stiffness ? so the numbers say yes! use a foam esky to support 20 tonnes shock load, an i say, i've felt sloppy foam n glass with my feet (as have others on this forum, called the "walking on jellyfish feel". and so, if you argue with engineering, of course its valid to have a mast beam made of 1" thick foam, as long as it's 1 meter deep. see?



i just don't care. it's the entire pool of logic they operate in that is wrong.

and they are bound inside their universe, never to see out.






same as rocker sucking you down.

V's planing pushing you up.


ever held a spoon under a tap? i have. sactly the same as rocker. you can feel the suction.

lowest drag sucks you down. see these photographs?

http://upload.wikimedia.org/wikipedia/commons/c/c7/Yacht_Ellide.JPG


http://www.boatdesign.net/forums/attachments/boat-design/9305d1159120043-hull-shape-hull-speed-wave-system-2.jpg

the bulge in the middle creates a suction, that sucks you down.

for every knot faster, you get sucked further and further down. using more energy, to create more actual displacement.

V's the planing hull, which pushes you up. every knot faster you go, the boat gets lighter (displaces less at the waterline)

[Rick Willoughby]

hi rick.
"
If you take your calculations a step further you would predict a narrower deeper hull of the same displacement would plane easier. That is not the case.
"

no i wouldn't.

......)

OK - you wouldn't.

The fastest way to learn is to have a go. Just build it in the way you think will work the best.

Rick W

[bob the builder]

yeh yeh,
but what do you think! about all my advanced theories?

did i convince you that one and one doesn't equal two?????

did i?

:o)

[DaveJ]

Hey Bob, just to stir the pot, are you sure the hull is being sucked down, or is it falling down because as the bow wave increases due to the energy being applied to it due to the increase in friction because of the increase of hull speed so the water required to create this bow wave is coming from under the hull and thus it looks like the hull is being sucked down but in reality it is falling down.

As far as displacement / planning hulls, i hate to tell you this, but they are the same. We have a saying in the Avitation industry 'With enough horse power even a brick will fly', this also applies to boats aswell (the equation for an aerofoil is the same for a hydrofoil, the only part of the equation that is change is the density of the medium from air to water). I will bet my lefty that a sheet of marine ply on it edge will plane, mind you you will have to be going very fast, and it will not be the most stable thing on the water, but it will plane.

Imagine if they make a propulstion system that is an equivelant to the jet engine in air but for water, the speeds that would capable, the speed of sound in water is much faster than air. Imagine the day they overcome the sound barrier in water and your boat is supersonic in water. The shochwave coming of the hull.

[Rick Willoughby]

...
did i?

:o)

No.

The photos of the slender vessel are interesting. I have seen them before but I have not seen the underwater shape. I expect it is deep forward. I have attached a photo of a somewhat better design of slender ship for high speed. It has lifting sections to well aft of the mid section but then the lines lift toward the stern.

It is interesting with planning hulls that the stern is actually pushed down as well as the bow being pushed up. There is a low pressure region where the water accelerates to get from the high pressure under the hull to the atmosphere. It forms a rooster tail as it rises. The attached coloured photo of WHIO might challenge your theories on planing hulls.

The lift to drag from a long slender planning surface is not very good. That is why wide planning hulls take less power for a given weight. As stated before you will not get much lift in your hulls under 20kts because they are slender.

Also the best lift for area will come from flat bottom. Makes for a simple build with a hard chine. Keep the hulls slender so they are easily driven in your normal speed of interest. If you are worried about slamming the bridge floor then flare the sides outwards so buoyancy increases as they bury or load up when heeled.

Rick W

[bob the builder]

rick,


there is a real fork in the road between us.

both our cases are strong



(mine stronger




all of your reasoning is sound, and plain vanilla
yet predicated, built by a brick upon brick logic, that is unassailable



it is obvious that your suggestion of rocker, least drag (at slow speeds only), narrow hulls is the apex of your life;

and is pyramidal (based on many, many steps of logic, each one depending 100% on the one beneath it.



and yet, i feel one photograph invalidates everything

(the photo shown above of the boat being sucked down. and it did every single thing you suggested.

to me this one photograph invalidates your apex conclusion, the highly suspect engineering fruit you are offering

all so then, your entire chain of reasoning, and therefor, every single perfectly logical step.





what is going on here?





i feel the only way we can understand each other is to talk philosophy.

(the philosophical underbelly of mathematics is logic, how well maths does at mapping the real world


we know all maths is incomplete and inconsistant.



Socrates once argued successfully that black was indeed white

the proces he used was dilution.

you dilute or pervert the first logic step slightly, and so on until you reach 180 degrees.


because i mentioned it, i know you've now read bertrand russel and understand how any logic system is perverted in a single step.


incompleteness
any system that is inconsistant leads untimately to incompleteness

ie it folds back upon itself to be self referential, 180 degrees wrong, and so incomplete (it has boundaries, and REAL THINGS STILL exist outside these boundaries, which usually have to wait for the next generations dominant paradigm to arrive. (until the old scientists die according to linus pauling)





so;
mapping problems do exist.

ie maths trying to describe reality. zillions of forms of maths are used that are totally nonsensical outside of their own tiny little pools

with your unassailable engineering maths, what you have done is to add one orange and another orange to suggest a boat that sucks itself down to hell


the more effort i put in, the bigger it sucks.




this is why

one single photograph



got me to go the exact opposite way to what you are suggesting.