help with boat construction technicals

please be kind as i am new to this but am in love with the idea of boat building, i havee built a couple of small stich and glue dinghies and i have read a lot of the posts in this forum, i have just been reading the thread in powerboats entitled 6m cat, and have a few similar questions, im looking at making a 22ft longboat/panga similar to a ub580 southwind out of 6mm ply with 9mm ply bulkheads, i have taken a lot of measurements off it but am wondering
1) what is a good distance for the bulkheads to be apart is a metre fine or to much,
2) i have read that 6mm ply needs to be supported every 200mm( this comment was made in regard to standing on it so may not count) does this meaan that i would need a stringer or a chine every 200mm or does the ply have enough stiffness on its own?
3) what thickness should my rear bulkhead that supports my outboard be? is 18 mm with a build up around the outboard area enough or should i go thicker, im planning on using a yamaha 60 enduro for propulsion
john

 

Theone007,

Can you find plans for the boat you wish to build? There are so many large & small details involved you are really taking on a big task.

Of course it would be much more challenging going it alone.

Welcome to the forum & good fortune with your project.

TGoz

 

John,

Your requirements sound very similar to a set of plans I drew up recently for a client. 22ft, 6.7m stitch and glue. Clean and modern looking.

Please pm me (yours was disabled) and I'll get you some more details.

raw

 

i just tried but yours seemed to be disabled as well, i have just fixed mine so you should be able to pm me now, all help muchly appreciated
john

 

would love to help but looking for these answers myself, i reckon you should split you hull down the middle and build an assymetric cat
i probably would have settled for the buying of plans approach however no one seems to have what i want so i agree that as previously said there is the challenge reward factor of going it alone
sean

 

John,

I just sent you a quick email so you should be able to contact me.


Sean,
If you decide you do want somebody to prepare a set of plans, give me a yell with a brief so we can talk.

Raw

 

Explore http://www.boatplans-online.com/proddetail.php?prod=PG22

Pericles

 

i have the ub580 which is a japanese yamaha wasen, also called longboat panga etc.
i havent seen any stich and glue plans of this bottom line
it is being called, a delta pad lifting plane

the closest boats bottom line to it, would be the jet boats
http://www.outlaweagle.com/faq.htm

the yamaha ub580

 

i had a look at the pangas on the site previously mentioned but im not that keen on stitch and glue, i want if possible to avoid using all the glue and glass that they use as it is very expensive and was looking more at using frames with stringers and the ply screwed down onto the stringers with a light glass on the outside for waterproofing, could i use the fao offsets and build it this way?
john

 

The right answer for all your questions is that you must define maximum deflection limits (first) then design the boat such that those deflections are not exceeded. You really should understand some basic beam equations (which apply to plates and surfaces as well) and how to calculate deflection. Otherwise, you are limited to rule of thumb answers. For rule of thumb answers that will likely answer your questions, buy Dave Gerr's book 'The Nature of Boats'. He's got a series of methods that result in thickness determinations of the type that you are looking for. I'd buy his book and study it before trusting other answers, noting also that Dave tends to run a little conservative on things, e.g. his thickness calculations come out a bit thicker than typical... you won't get in trouble. Also, study boats similar to those you intend to design and copy them ...if it's a successful design, and uses plywood "X" inches thick and bulkheads "Y" inches thick and separated by "Z" inches, then you could use those same basics and it should work fine. Always weigh your work against known successful boats and you should be fine ...the apple won't fall too far from the tree.

Brian D