two trailer sailers to make a cat

[markcampbell]

I have the opportunity of purchasing two 26 ft noeleda trailer sailors and am thinking of converting these hulls to a single catamaran - Im thinking of positioning the pontoons exterior at 65-70% the length of the hulls
IE 20 ft width

the pontoon beam waterline width is 5 foot 6 inches leaving a waterline width between pontoons of 9 feet

Has anyone tried this
Does anyone know of anyone who has tried this
Any ideas would be a great help

How does the width of the pontoons affect steering capabilities and

What is the wave disturbance between pontoons called IE the radiating bow wave leaving the bow and meeting the other bow wave called and where can we research this and what are the formulas

what are the formulas for bow wave disturbance other other hull ie port pontoon bow wave on inside of starboard rear pontoon

we are thinking of attaching the hulls with aluminum 75ml * 75ml box section in 3 places any comments


we are thinking of leaving the mast and boom in place and have two masts and booms any comments we know annie hill recently built a junk rigged cat
with masts on each pontoon




thanks

[frosh]

Hi Mark, I have only one bit of advice DON'T DO IT. It could be the biggest mistake of your life. The fact that no yacht designer has ever configured a catamaran with hulls of this length/beam ratio should send an ominous message. Also your overall weight will be ridiculously high! This is only for starters. Best to stick to conventional ideas unless you are willing to create a disaster that will eventually have to be thrown away! :(

[Figgy]

"Frankenstein's Catamaran"!?! HAHA! Seriously tho', Frosh is right. Really wouldnt be a good move unless you have WAY too much money. Try to something else with the hulls.

[SeaSpark]

Have a look at this thread:

http://www.boatdesign.net/forums/showthread.php?t=7206&highlight=J24+Hobie

[markcampbell]

1 opinions are cheap
2 we need formulas
3 what is the width to length ratio and why
4 where can we research this
5 Rounded and wider pontoons should make the turning arcs easier
6 the distance between the two internal hulls and possible drag from bow waves is the hydro dynamic question that we are asking

[Figgy]

1. So are ideas
2. Be more specific. Formulas for what?
3. Usually the beam is half of the l.o.a. You can make it as wide as you want though. If your going to break the mold, shatter it!
4. There is a couple of programs. Search this thread. http://boatdesign.net/forums/forumdisplay.php?f=4
5. Aero-hydrodynamics of sailing by C.A.Marchaj. Part 1 chapter G
6. See #4

[frosh]

Mark, To say to people more experienced than you, and in all seriousness that their opinion is cheap is a bloody insult. Why bother asking for advice if you already know all the answers. If that is your attitude then state what you intend to do, and also state that you dont want any responses to your posting!:mad:

[CT 249]

Probably not a good idea to post "Any ideas would be a great help" and then say you don't want opinions.

I have sailed two small cats with wide-beam hulls. Both were very slow and handled poorly.

Because of the popularity of catamaran ferries, I think there have been many studies on wave interaction. I've never really looked at them (it's not my interest) but I seem to recall that there is still no universal method for calculation. I may be wrong, but a trip to the library of any university with a NA course should tell you.



Has anyone tried this
Does anyone know of anyone who has tried this

[marshmat]

I agree with frosh and figgy. These hulls (length/beam 4.7) are too stubby and fat for a catamaran. Cats generally don't work with length/beam under about 8; 10-14 is not uncommon.
Three 75mm square aluminum tubes cannot possibly hold up to the loads this thing would be under while out in waves. Cats of this size and weight generally have an elaborate 3-dimensional truss-like structure in the centre to take these loads.
I would strongly suggest you keep these monohulls as monohulls. Joining them into a cat would give you an overweight, tricky to handle boat that would have a hard time staying intact in any sort of seas.
There has been a great deal of work done on wave interaction within the hulls of a cat. Mostly it involves a lot of tank testing as well as CFD and the results are unique to a particular hull family.

[markcampbell]

1 the tendency for cruising cat hulls is going wider to accommodate double beds lower in the pontoons.
2 we anticipate this cat with a bridge deck and fiberglass bracing as a small coastal cruising cat. Thanks for the information about the alloy beams not being strong enough of course they wont be.
3 the pontoons with a wider and shallower hulls will have a shallower draft, compared with an exact same weighted vessel.
4 speed is not critical and a loss of speed around 20% on a similar weighted cat would be acceptable

[hansp77]

mark man,
what do you want to hear?
do you want to hear that it's a great idea?

Well, to someone like me, who really doesn't know jack about catamarans, about wave interaction within the hulls, about stress loading, or about boat design in general, let me tell you this-

mark, that's a great idea!
well maybe not great, nor actually original, but sort of interesting at least,

that is of course, untill I hear from those that actually do know about catamarans and advanced boat design, telling you that this is actually A VERY BAD IDEA.

Now of course every one is free to do whatever they want, including suicide, and or wanton destruction of two perfectly good sailing boats.

If you have actually read through the link that SeaSpark provided
http://www.boatdesign.net/forums/sho...ight=J24+Hobie
then you will have witnessed another individual (Delane) who is stubbornly set upon following through with one of these plans, against all the provided expert advice. Now who knows, improvisation and going against the flow is not fundamentally an incorrect practice, and actually lies at the base of some of humanities most revolutionary breakthroughs. As apposed to you however, Delane has managed (its not too hard) to humblely acknowledge, if not accept, the effort, advice and dissuasions that the experts have offered him (considering he and you have asked for such). He has managed to not directly offend or insult anyone. This is something that if you plan to continue battling out this idea of yours upon this forum, you might want to take notice of.

p.s. Cocky point form replies, and stating that "of course" the alloy beams that you had asked for advice upon won't be strong enough, don't exactly warm ones opinion of you.

p.s.s. In my short time on this forum (be that only slightly longer than you), I have found that the people who offer me advice upon my novice questions and queeries generally know what the hell they are talking about, and do so in a polite and generous manner. If you do choose to contradict or criticise as "cheap" their opinions, then you had better know what the hell you are talking about.

Good luck with your two boats,
and better luck if they ever do turn into one.
You may just need it.

[Figgy]

Man, this guy has a stiff one for a cat!
Well said Hansp77, but I'm giong to humor him.
3 the pontoons with a wider and shallower weight will have a shallower draft.
A shallower draft than what? It might sit higher on the water lines, but thats it. And after you make your bridge deck, with a HUGE rig to push her through the water, I'm not so sure. Have you found out how much the hull displaces?


4 speed is not critical and a loss of speed around 20% on a similar weighted cat would be acceptable
Now I havent crunched numbers, nor am I about to for this project, but thats a good start. Atleast you won't be shocked on your first outing.
Check it out Mark, you're going to sink a huge amount of cash into something like this. To retro-fit two hulls like this is going to take some engineering. You can't just slap on a few cross beams, fiberglass them up and go.
I have the opportunity of purchasing two 26 ft noeleda trailer sailors
Just buy a new cat, don't do this.

[marshmat]

Quote: Originally Posted by markcampbell I have the opportunity of purchasing two 26 ft noeleda trailer sailors

Just buy a new cat, don't do this.

I second that.

[frosh]

Mark, ask yourself honestly, why do want to create a cat in the unusual way that you proposed at the beginning.
These are some of the possibilities, trying to get inside your head (figuratively speaking only)
(1) You see it as cheaper option than buying a good condition existing cat.
(2) You want to try something out that will be uniquely yours and will work pretty well.
(3) You want to be some sort of design pioneer establishing a new design trend, and you will get the kudos for the brilliant idea.
(4) You see it as way to get a reasonable performing cat with heaps more living space than any existing cat of the same overall length.
(5) I can't imagine any other reason you might have!

MY ANSWERS
(1) Maybe if you are getting the trailer sailers almost for free.
(2) It will be uniquely yours, but almost positively will not work well.
(3) Wishfull thinking! More likely embarrasment!
(4) It will give you heaps more living space at the dock, I wouldnt want to take it anywhere.
(5) The idea of posting on this forum is to get feedback and learn from it, even so called experts who have designed boats all their life are still learning and occasionally make mistakes. Mistakes are OK per se, but really dumb when you have been well warned in advance.

I agree with the others, if you want a cat, buy one, there are a huge number on the market for heaps less money than replacement cost.

[markcampbell]

1 New purchase price for cat at 26ft @ $200 000
2 2 glass hulls only 10% wider on water line with all partitioning, keels, steering, rigging, etc all to within 10% average fit out of new cats means a saving of hundreds of hours skilled labour and materials
3 retrofit is limited to opening cutting open both insides of pontoons @ 500ml above waterline, using the internal fibreglass cut outs and windows as external forms for marrying up the bridgedeck sides and glassing up a bridge deck
4 extra weight of bridge deck say 500kgs will provide adequate areas for diagonal bracing
5 the wider pontoons will handle the extra weight better than any other arrangment
6 26ft is our porposed length price is very important
7 we know you guys already think this will frankeinstien but we are not asking about your opinion of appearances merely the forward speed and hoe it will be affected and why
8 the other main question is manuoverability and turning
9 we look forward to exact replies and to those who have given them so far thankyou

[markcampbell]

and why??

[marshmat]

Last question to all - what do you think would be faster and more maneuverable plus all-round performance a catamaran with its thin hulls or two monohulls braced together with the same length
Definitely the dedicated catamaran hull. A dedicated cat hull will be far faster, more manoeuverable, easier to sail, safer and a lot more fun than a cat made of similar monohulls.
Explanation: Monohulls must be fat and wide, relatively speaking, or else they'd tip over. Long narrow hulls are much faster and more efficient than wide fat hulls. Hence the advantage of a cat, and the main reason for their existence- you get long narrow hulls AND stability. For further explanation, see previous posts in this thread.

[CT249]

Well, I'm no designer or mathematician, but .......

I think you'll find that one rule of thumb (pretty well accepted as far as I know) is that form drag rises by the square of the waterline beam. Therefore the form drag of two Noeleda hulls (total waterline beam say 12') would be about nine time the form drag of a 2' waterline beam cat. That will rather restrict your pace.

I would also have thoought that wetted surface of the broad mono hull will also be considerably higher than that of a cat hull, which can come much closer to the elliptical/round form that reduces surface area for volume.

So you may find you go a lot slower than a "real" cat which will make tacking hard (less momentum, less flow over the foils, plus having the slew one hull around the other).

Secondly, there was nothing in your first post that made it "obvious" that you were not relying on the narrow alloy beams.

[frosh]

Mark, believe me we are trying to be a helpful as possible, and even though it might appear that some of us are trying to ridicule you, it is definitely not the case.
You mentioned that the Noeleda hulls have a waterline beam about 10% wider than that of a dedicated cat hull. If that was so then your concept could have some merit, but please check your math first. I would be extremely surprised if you were right. L/B ratios of 26 ft.trailer sailers are in the order of 3.25 overall and maybe 4 at the waterline.
A cat hull of the same length (cruiser) would have a waterline L/B ratio of around 8 to 10.
Your costing also of $200,000 sounds at the very high end. I have seen a demo cat Radical Bay, design also 26ft. approx advertised at $100,000 ONO.
Just for interest I have given you the link to the web site for the Radical Bay design. http://www.schionningdesigns.com.au/www/page.cfm?pageID=271

[marshmat]

7 we know you guys already think this will frankeinstien but we are not asking about your opinion of appearances merely the forward speed and hoe it will be affected and why
8 the other main question is manuoverability and turning
9 we look forward to exact replies and to those who have given them so far thankyou
Mark, none of us care how it will look. Everyone who has replied so far has commented on how it will perform and sail. The consensus so far is that it will be as manoeuverable as a sewage barge and not much faster than the average chunk of driftwood. We have given you exact replies with regards to L/B ratios of real cats, price of real cats, etc. And it has been pointed out several times that the thing would be a hydrodynamic oddity at best and a dangerous failure at worst. Please, take the advice of everyone who is trying to help you out.

[Figgy]

2 2 glass hulls only 10% wider on water line with all partitioning, keels, steering, rigging, etc all to within 10% average fit out of new cats means a saving of hundreds of hours skilled labour and materials
3 retrofit is limited to opening cutting open both insides of pontoons @ 500ml above waterline, using the internal fibreglass cut outs and windows as external forms for marrying up the bridgedeck sides and glassing up a bridge deck
4 extra weight of bridge deck say 500kgs will provide adequate areas for diagonal bracing
It sounds like you have it all figured out. What do you need from us?
merely the forward speed and hoe it will be affected and why
8 the other main question is manuoverability and turning
We told you and you don't like the answers. I'll say it again, slow. Your pushing two hulls through the water.
5 Rounded and wider pontoons should make the turning arcs easier
Your talking about two monohulls tho'.
Mark, believe me we are trying to be a helpful as possible, and even though it might appear that some of us are trying to ridicule you, it is definitely not the case.
Frosh is correct, we're not ridiculing you, but you're not listening to us. We answered your questions. Its frustrating. Just go to a design office and talk to a NA there.