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Old 28-10-2012, 09:01   #16
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Re: this may sound silly.... mono cat?

You would not drop the Hp requirements by using 2 monohulls to make a cat, instead you would be doubling them since each monohull would require the same Hp as before, but now you have 2. + the extra weight of the bridging between the hulls.



Maybe you should cut the monos in half, add a 20 foot plug with specifily engineered bridging bracing and make a 72' cat. Then you would have a cat with similar length/beam ratios as a cat is made with! Same Hp as the two monohulls still, but a much faster displacement speed for that Hp.
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Old 28-10-2012, 09:29   #17
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Re: this may sound silly.... mono cat?

I think there are only to choices for 52' alu hulls, pontoon or power boat. Which are you planning on?
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Old 28-10-2012, 09:46   #18
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Re: this may sound silly.... mono cat?

A catamaran requires quite a bit of knowledge of naval architecture in order to join the two hulls. There is a significant amount of twisting and sheer forces between the two hulls that requires proper engineering. You can't just attach two cross beams and hope for the best. You are attaching two very long beams with the resulting forces caused by a lever arm. If the hulls are not engineered with adequate attachment points for the beams then it is not going to work.

The way I see it, why worry about all that when you can get a used catamaran where all of the engineering has already been worked out by a professional naval architect and where the hulls have been designed to be catamaran hulls from the begining. Doing it his way would be less expensive, provide for a safer and more seaworthy boat and take less of your time.
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Old 28-10-2012, 09:53   #19
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Re: this may sound silly.... mono cat?

I saw a boat being built years ago.. made of two fuel tanks left over from military use.. watched it for years take shape, and then scrapped.. never made it to the water..
On another note,
We bought our boat about 10 years ago, moved aboard in two weeks, and took off..
Have loged many miles and had loads of fun along the way,..
people we know bought a trashed out boat cheep and gutted it, and started the remodel.. they are still working on it after 9 years and have kinda lost momentium and have sorta misplaced their dreams...
So, my question is, being you only have so many years to live out your dreams, will you spend those years building something you dont know will work or buy a boat and go cruising...................?????????/
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Old 28-10-2012, 10:45   #20
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Re: This May Sound Silly.... Mono Cat?

Sometimes even a free boat is too expensive.
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Old 28-10-2012, 12:54   #21
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Re: This May Sound Silly.... Mono Cat?

yep. There's no such thing as a free launch.
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Old 28-10-2012, 13:51   #22
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Re: This May Sound Silly.... Mono Cat?

It sounds silly ...

;-)
b.
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Old 28-10-2012, 13:59   #23
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Quote:
Originally Posted by barnakiel
It sounds silly ...

;-)
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Old 28-10-2012, 14:57   #24
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Re: This May Sound Silly.... Mono Cat?

I dunno. How about welding them stern to? Dat's a lotta yot.
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Old 28-10-2012, 15:15   #25
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Re: This May Sound Silly.... Mono Cat?

60/40 tin solder is better for the welds,,it will not rust
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Old 28-10-2012, 16:54   #26
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Re: this may sound silly.... mono cat?

Quote:
Originally Posted by David M View Post
A catamaran requires quite a bit of knowledge of naval architecture in order to join the two hulls. There is a significant amount of twisting and sheer forces between the two hulls that requires proper engineering. You can't just attach two cross beams and hope for the best. You are attaching two very long beams with the resulting forces caused by a lever arm. If the hulls are not engineered with adequate attachment points for the beams then it is not going to work.

The way I see it, why worry about all that when you can get a used catamaran where all of the engineering has already been worked out by a professional naval architect and where the hulls have been designed to be catamaran hulls from the beginning. Doing it his way would be less expensive, provide for a safer and more seaworthy boat and take less of your time.
i own a set of plans for the MS65 cat from Bruce Roberts.

the entire kit is 115,000 or so, and thats not welded, only cut.
i would pay him to engineer a set of custom plans to weld the hulls.
i like the idea of cutting one in half thou and making it that way. sounds really good, and would save me quite a lot on buying two boats, and transporting them.
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Old 28-10-2012, 16:59   #27
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Re: this may sound silly.... mono cat?

Quote:
Originally Posted by Randyonr3 View Post
I saw a boat being built years ago.. made of two fuel tanks left over from military use.. watched it for years take shape, and then scrapped.. never made it to the water..
On another note,
We bought our boat about 10 years ago, moved aboard in two weeks, and took off..
Have loged many miles and had loads of fun along the way,..
people we know bought a trashed out boat cheep and gutted it, and started the remodel.. they are still working on it after 9 years and have kinda lost momentium and have sorta misplaced their dreams...
So, my question is, being you only have so many years to live out your dreams, will you spend those years building something you dont know will work or buy a boat and go cruising...................?????????/

the problem with using old tanks is the same reason you dont make a frame-less boat. Bruce Roberts has a great writeup on it somewhere.

i am really young, just hit 30 this year. but i married a co-pilot this year
so i have a second person to work on small things.
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Old 28-10-2012, 17:07   #28
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Re: this may sound silly.... mono cat?

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Originally Posted by scoobert View Post
i am really young, just hit 30 this year.
Yepper, that says it all.
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Old 28-10-2012, 17:33   #29
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Re: this may sound silly.... mono cat?

Cutting a boat in half and grassing on flat panels may be an even dumber idea than taking two hulls and frankenwelding them together with cross beams.

Scoobert you keep trying to reinvent the wheel, and it just doesn't work. There are a lot of good reasons why boats are designed and built the way they are, and trying to 'customize' them without knowing the first thing about boat design is a waste of both your time and the forums.

As with many things it could technically be done, but the trade offs for it are massive, and you will have a resulting structure that can't really be called a boat, or even a barge. Just a floating junk yard, however nice you make the interior.

If you can't find what you are looking for at a price you are willing to pay you have two real options. 1) pay more, or 2) have an engineer design a custom boat for you. That's it. Boats are not like houses, where you can just add a new room wherever you want, and in fact the engineering of a boat is actually more complicated than that of an aircraft.

The stresses, and loads of a boat can be harder to calculate than those of an airplane, and the number of trade offs for a boat is actually more difficult to do well than to design a good plane. Trying to weld two boats together makes about as much sence as welding two 747's together wing tip to wing tip. Sure you might get it off the ground, but I wouldn't want to fly in it.
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Old 28-10-2012, 18:13   #30
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Re: This May Sound Silly.... Mono Cat?

Quote:
Originally Posted by scoobert View Post
so i can buy two monohull 52' aluminum hulls.
and i can get them cheaper then i can build a cat.
now 52' is shorter then we had planned, but here is my idea.
i can cut half of the top of the boat's off. make a good bridge between the two. and i have my cat....
the boats are from the 50's. very cheap, and all the wood is shot. very perfect. this would get us on the water two years sooner.
whatcha think? and i am being serious.
Ok, rather than ridicule you, I'm just going to ask a couple of questions for clarification.

1) What is your desired end state?
2) What do you believe you need to make that happen? (It seems like you are saying you need/want a 52+ catamaran for two people)
3) What is you budget?
4) What is your tolerance for unmitigated risk? (IOW, if you did buy them, try to get it work, utterly screw it up and THEN had to pay to have it removed -- how bad would that hurt?)
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