Catamaran Calculations

What am i going to use the boat for

Great question and the first one I asked, except it was too easy. We are going to live on it. We will sail of course, but the main function is a live a board. The size is to accommodate four cabins so my 3 boys can come home when they want and have a real home. That’s my wife’s number one requirement. A house boat could do the same thing except we do want to sail. I have seen exactly 2 multihulls that fit the bill. The Isara 50 gets me 95% of the way there. The other is the Privilege 745, and that’s the concept of this boat. As per launch and build, we think we found a place on the Hackensack River in Newark NJ. The boat will be slid not lifted and the mast will be set at dock on the Hudson.

 

Off topic, but just to clarify my experience.

I quote from the "Autobiography" page of my website

"I studied Yacht Design at the Southampton College of Technology. This course was (maybe still is) the only full time yacht design course in the world. Many famous designers have studied there, Bill Dixon was in my year, Dave Alan Williams the year above, Ed Dubois had also been a student there. I left in 1978 with distinctions in design, structures and stability.

I believe there is a big difference in being taught (anything) full time at a college, as I was, and by a correspondence school as many others are. Face to face discussions with fellow students, never mind with lecturers, must help ideas flow and understanding increase. And of course a college has assets that aren't available by mail. The use of a big test tank in my case.

I don't call myself a naval architect, even though many who took the same course as me do. Even some who have no formal qualifications at all still call themselves naval architects. I don't do so because I design yachts, whereas a naval architect is often someone who doesn't design anything, but knows a great deal about, for example, stability or ship structures."

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Thank you. I hope you have understood that it was not my intention to discuss your experience and professionalism, nor to compare it to anyone else's. It is well proven, and that's what imo counts more than the name of the school you come from. And I am the last guy who could be entitled to question your competences. I was just replying to a pretty acid post by another person.
Cheers

 

First and foremost my humblest apologies as intention was not to become or drag this post into any further negatives than the original poster had observed, it just amazes me how people straight off the bat assume this chap knows absolutely nothing of his desired direction and again I point out Richard with true professionalism asked the question in a manner all professionals ask qualifying questions before going further.

And yes I have dealt with Richard personally having purchased study information, his cruising Eclipse log and asked enough questions years ago to drive him mad, before undertaking my own course of study and even then after becoming qualified by paper (yes by paper as true qualification comes after one qualifies and has put said qualification into hands on years in the field) I purchased plans from Richard, the only example I was expressing was professionalism seldom is negative the chap asked a simple question yes simple answers were given but were the majority really answering what he was asking....

All the best to you all and again apologies.

 

Woaahh, hold your horses Richard. You’re painting with a very broad brush there on NAs. I could just as easily say the same about yacht designers, just doing fancy curves and nowt else!

Again, with respect, I think you’re missing the point on this one. Advice is what it is. Only the recipient will place the advice into the positive helpful side or the negative unhelpful side, depending upon their personal bias.

This is more so when the recipient only wishes to hear what they want to hear…thus anything that is outside this scope of replies, shall always be deemed negative.

 

Thanks for that Ad Hoc again I have apologised and stand corrected if I am wrong I shoot from the hip but am also fast to say when I am wrong and put my hand up as so... all the best have to go out to workshop and leave the computer and design work it is doing my eyes in

 

Catamaran of this size will be subject to significant global loads: transverse bending, twisting, etc. This has to be checked, and more importantly structural layout should be designed to cater for those loads. And definitely, structural layout is related to general arrangement... Even hull shape is affected because, say, chamfers at wet deck/hull joint will effect concentration of stress and span of wet deck stiffeners. Then, just think about table of weights in terms of structural weight - is there enough weight budget?

Thus one needs to involve NA at early stages, otherwise his calculations might not help if done too late.

On other side, I would never touch something 'designed' without involvement of NA from early stages.

The design started solely by 'designer' often ends up as disaster.

 

Agreed! Having a fancy graphics producing program does not a yacht designer make!

To the OP, in our defense:

There are similar posts to yours several times a year from people with no boating experience yet want to design and build a huge boat (or any boat for that matter). As you didn't indicate your experience in your first post we all assumed the worst. Now we know better.

However I still think a 75ft catamaran is too large for a home build project for a live aboard.

My neighbour is home building a 5000sqft house. Not sure of the exact size but I know it has 5 ensuite bedrooms. "Just in case the children come to stay". He's been building for at least 7 years and has several more to go. His children have said they'll never come to visit as they have now all left home and moved elsewhere.

Recently he told us of his regret in building something so large. In fact he said "I should have bought your house (1200sqft) when it was offered to me."

You know all that, but others reading (as opposed to replying to) this thread may not

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

This may help just for what it is worth another very reputable designer we can personally recommend http://www.lidgarddesign.com/oL73_studyplan.html#Lidgard Yacht Design
there is also a detailed website of it being built somewhere, Jeff Schionning also has the nBemuda 77 being built at http://www.thebermuda77.com/

 

1200 ft, 5000 ft .... what a difference.

 

Scubapro,

You mentioned a couple things I would like to clarify.

First, you could just get a house boat, but you want to sail. So, you looked at a couple of the multi-million dollar cats and decided to build a less expensive multi million dollar cat?

Why not use a house boat. And build a FUN cat .... that you can take out for shorter runs if all the kids show up?

You worked for a man who is AN NA, had a GREAT relationship, but he won't advice you on your retirement dream?

But, Richard did, and he doesn't know you .... ('not an NA,' but he has the skill set anyway.)

Am I missing something here?

Regards,

Wayne

 

Polypropolyn Hulls

Im adding this to my previous post of last Dec for continuity. I ran my 74 ft cat past my NA and he said it was fine. But I did look at lipgard yachts and ordered study plans for his 65 ' cat. In the course of discussion he offered me stock plans of a 65 footer that seems to fit the bill. I'm old school and so is he so we are both thinking cold molded. It seems that polypropolyn honeycomb is so light and can be purchased so cheaply, that it bears investigation. Anyone have experience with it. In the mean time we have begun construction using 3/8 ply for mock up so hat I can get the joinery and furniture fitted out.

 

Richard,

Hi, could you please comment on what it would take to handle a 74 ft. sailing CAT. How many crew members, and so on.

Thanks,

Mark Cat

 

We use PP honeycomb in our designs. Outcome: shear strength of 80kg/m3 PP (with surface tissues and resin about 100kg/m3) is equivalent to shear strength of 60kg/m3 foam. So a bit heavier but much cheaper.

Do not use PP in highly loaded areas. On small boats (L<10m) is works excellent everywhere except bottom. On bigger boats, we design smaller panel size (i.e. stiffeners located more often) thus PP will comply with required shear strength. We even used PP-H for topsides of 90' motoryacht, spacing between stiffeners was about 400mm but it works.

There are approved brands of PP on the market, with classification society certificates. There are also ones without formal certificate, but having same properties.

 

To Mark Cat

Am I the Richard you are talking to?

Well, Ellen Macarthur sailed a 75ft trimaran round the world by herself. So I guess the answer is one small woman as a minimum

Richard Woods