Need help with laminate schedule and drawings for 52 ft catamaran home build

[CatBuilder]

Originally Posted by PAR

There's no such thing as a preformance cat with an extra heavy laminate schedule. Assumptions are for circumnavigators in 7' boats, but the rest of us don't attempt to draw these types of comparisons, as there are so many possible variables, that "averages" just can't be accepted as a "norm" for a particular length or configuration of vessel.

Very true. Also, the closer you start getting to performance, the more important a proper structural analysis is.

[Ismotorsport]

Cat builder,
Is it fair to say that the NA is responsible for the structural design and the engineer is responsible for providing the laminate details and drawings?
It seems that most firms have an in house engineer.. Ormshould the NA be able to do put all the information together?

[CatBuilder]

Originally Posted by Ismotorsport

Cat builder,
Is it fair to say that the NA is responsible for the structural design and the engineer is responsible for providing the laminate details and drawings?
It seems that most firms have an in house engineer.. Ormshould the NA be able to do put all the information together?

I am not a designer, just building a boat with complete plans. Others who have posted in your threads are actually designers. I will give an opinion, though.

In general, it's best not to divide that work up at all. One person, if a single designer, or one team should work on the entire craft since the two factors are not independent.

The skins you have on a foam hull panel affect the stiffness of that panel as well as the ability of the panel to carry a load and the panel's weight. The hull panel's weight affects the loads a crossbeam needs to deal with. The weight of the crossbeam will affect the weight of the entire vessel again, because maybe you need stiffer hulls... it can be a cyclical nightmare because you don't have one person deciding.

That's why people keep saying you have to recalculate the whole boat. Each boat is different. Each has different loads and strategies for handling them.

One guy picking up a half finished design has to pretty much start from scratch to make sure everything is right.

I hate to sound like a broken record here, but the original NA needs to provide you with the laminate scantlings for the hull panels. He is the one who figured out all the loads. Should take him no time at all, since he already did everything else. This assumes he is a solo small business. If he's on a large team and wants to rely on the engineer in his team, that's his option, but he should be the one bringing it all together and giving you complete plans.

[DavidJ]

First, a naval architect is an engineer.

Second, the person that does the structural design is almost always the same person that provides the scantlings. It can be very counterproductive to separate the tasks. As groper explained the scantlings can very wildly depending on the structural arrangement. So if the arrangement changes the calcs need to change to match. If the calcs show a potential for failure then the arrangement needs to change. For example say your initial arrangement results in a calculated panel with a requirement for a 3 inch thick core to have the desired stiffness. Obviously that is ridiculous on a small boat so more stiffening will be required. If it was two people doing these two tasks the guy doing the calcs would then have to go over and say hey buddy your arrangement on this panel doesn't work. Do it a different way and then send it back to me. If just wouldn't make sense. The calculation of scantlings and the arrangement of the structure is a back and forth process of optimization and fine tuning.

In a small company that same guy who designs the structure will also produce the drawings. In a bigger company there may be a draftsman or junior engineer who does the drawings (or a team of them). They would of course be working under the guidance of the senior person who did the calcs and structural arrangement.

Structural details are usually handled in one of two ways. Either the designer chooses or the builder does. There should be a discussion early in the design process between the designer and the builder to determine how things should be done. There is no point in a boat being designed for vacuum infusion and foam core when the builder plans to hand laminate with balsa core. Likewise if the builder has a preferred method for building stiffeners it would be a waste of time for the designer to draw up sheets of details for their preferred method of tophat construction.

[Ismotorsport]

Structural grid rendering. The longeron is not mounted under the mast and there is a grid under the mast area that is not shown. There may be a need for additional ring frame forward between the first two bulkheads either side as well as in the galley/ salon areas of each hull. (I believe that depends mainly on core thickness and laminate, correct?)

[gonzo]

I think your multiple posting of the same question is creating confusion. They should be consolidated.
Core thickness and laminate are only two of the parameters of the structure. Stiffeners, shape of surface (flat, curved), position in the boat and local stresses, etc. all determine the final structure. You keep on insisting that someone give you an answer to a wrong question.

[Ismotorsport]

[IMG][/IMG]





Some rendering to give an idea of project.

[rawleyjerel@yah]

if you like contact me at rawleyjerel@yahoo.com