New to site, design and looking for perspective!?

Discussion in 'Boat Design' started by bjdbowman, Apr 23, 2017.

  1. bjdbowman
    Joined: Apr 2017
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    bjdbowman Junior Member

    I enjoy reading this site so I decided to join in. I do like all the professional insights and I could use some guidance.

    I am not really a designer but a dreamer. I have architectural design experience and I work as a civil engineer therefore boat design is something that I have only played with and dreamt about. But it is time as I am building my shop and gathering my tools.

    I am planning on a retirement build of a “one off” 32 feet long cruising cat. Construction will be using simple building insulation foam (1-1/2" Owens Corning FOAMULAR 150) as the stay in place male mold.

    I've worked with this material before and I can cut it quickly and accurately with a 3 axis CNC table. All parts of the boat will be milled and glued in place and then faired with a hot cutter/epoxy fill. I refuse to spend any time with sanding and fairing… what we get out of the foam is what is going to be covered with glass and painted… done without any after thought of “does this look straight/fair enough?” Who are we to say what is ugly? Ugly is just in the eye of the beholder… most times not found within the mirror.

    I’m not even going to fair different layers or thicknesses of glass but will try to make natural breaks between areas of different thickness like between the area below the waterline and the sides of the hull.

    I want to build the whole build using nothing but this construction foam (glued and hot glued together) and then covering the exterior and interior with glass and epoxy (connecting the interior hull to the exterior here and there for strength). I am thinking to keep the boat light and well insulated from sound and cold/heat. There will be some marine ply milled on the cnc and then added to some areas for connecting equipment etc. Rub rails and the keel runner will be aluminum and laminated plywood and then glassed.
    The concept for this build is nothing pretty or award winning but utilitarian in nature where function over form rules. This will not be your father’s shipwright’s classic boat nor your great grandson’s futuristic flying cat but a realistic quick build. This is to be a live aboard with beaching capacity, good carrying capacity and to me comfort and safety rather than style. With that said no polished wood, chrome or beautifully polished hulls, but a simple battleship flat gray with little concern to cosmetics.

    Think of the MingMing 2 (

    Now apply this idea to a 24 foot class level of service stretched into a 32 foot cat for a family of 4… a cross between camping and RV life… a MacGregor type level of comfort without all of the prettiness of a production model.

    I would compare to a class C type RV. Not looking for resale value but most importantly rugged comfort without the total loss of speed. I want to be able to go places without fearing that we are over our heads… maybe an Atlantic crossing and definitely poking around in the Caribbean.

    I would like to understand why so many cats have their weight centered so far stern? I see so many power boats with forward cabins and yet most cruising cats are designed with the salon in the center with the cockpit in the rear. I have seen a few cats with center cockpits (at the mast) but never any front loaded cabins in front of the mast. Why can we not build with weight over the bow and stern equally?

    I’ve attached a conceptual sketch… with a center cockpit. This idea would have the mast at the rear of the front cabin and most importantly the owner’s queen bunk under the center cockpit at the center of the boat to limit the movement… same with the cockpit. Placing the cockpit and the mast at the center of the boat makes sense to me for easy sail adjustments with the added visibility 360.

    Am I just nuts?

    Dodger on that front cabin would keep spray down. And I want settees on the very front of the front cabin for reef and dolphin watching.

    With that said, here are my questions:

    First: Any comments on the arrangements and configuration of a dual cabin and center cockpit?

    Second: Any comments on the construction method? Anyone use this foam or something like it before? I am thinking cost, insulation, speed and strength of the build. The plan is to build the hull upside down from the water level up until the bottom side is 90% and then jacking up the boat higher to build the remaining boat upside down. I will use the cabin roof and the hard Bimini as a floor for working on the interior. I have a simple idea how to do this. I will use the inverted hull as the boat house to work out of the weather and heat. The idea is to have the boat to a solid point (75% complete) prior to flipping it so this would force me to complete a very strong structure as I will be working on top of my structure as I build… maybe a bit too heavy up high, but I will address this later on in the actual design.

    I plan on using a single center mounted outboard.

    Third: This may seem even weirder er… but why can we not design planing hulls on a cat. I want to design this 32’ long and 14’-15’ wide cat as a tunnel hull with 2 planing cats forward and a center hull aft which the engine will hang from. The cat hulls will continue aft but above the waterline as the wetted surfaced of the last 1/3 of the boat will be centered on a planing v hull with the areas between the outer and inner hull being the tunnel injecting air to create a lifting force.

    The bottom line is I want the cat to easily hit 30 knots under power on a smooth river or sheltered waterway.

    For the rig, I am thinking two modern freestanding carbon fiber cat sail as found on windsurfers… easiest as possible to sail for me as I don’t want my girls to think that sailing is too much work.

    This sounds like a dream but that’s what I am… a dreamer.

    Anyone have an opinion? Should I break out this into specific threads?

    Let me know what you think.

    Thanks in advance,


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    Last edited: Apr 24, 2017
  2. Wayne Grabow
    Joined: Aug 2003
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    Wayne Grabow Senior Member

    You seem to be confident that you have all the answers you need, so no reason for me to try to change your mind.
  3. bjdbowman
    Joined: Apr 2017
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    Location: Florida

    bjdbowman Junior Member

    Thanks for the warm welcome.

    I have no clue... just observations and desire. And yes you have no reason to reply... so next time please don't.

    To me I asked logical questions about my direction. I am not a novice yet, but want to move forward.

    Thanks to anyone who cares to reply for the good of the project.
    Thanks again...
  4. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    The most obvious question would be what leads you to want to throw away all your actual materials experience and build a boat using materials you have no clue about? Excellent boats can be built using the materials, engineering, and methods you already know.

    Foam-cored composite builds are the last thing you want to consider for the sort of boat you have described. They are fragile, fussy, hard to engineer, tedious to build, and expensive. And you are basically screwed if you forgot anything in the design. You can't go back and bolt or weld anything to a foam sandwich hull unless you have already put in the reinforcing when you built the hull. So zero versatility over time.

    32' cats scream for plywood. If it were a bit bigger, you might consider steel or aluminum. Ferrocement is an option for you, but there are probably fewer than ten people who would accept such a boat if you offered to give it to them.

    Building a rough-looking hull is not any cheaper or easier or faster than building a reasonably good looking one. It is the fit out that sucks up money. Some 32' cats will have $150,000 worth of electronics and appliances. Some will have $150 worth. Some will have $30,000 worth of sails, spars and sailing do-dads, some with have $5000. But the hulls are basically commodities. Anyone can get a decent hull out the door.

    If you want a battleship of a simple 32' catamaran, look no further than the Iroquois MK1 and MK2.
  5. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    The simple answeris Nope, your material choices aren't appropate, but give the few details about stucture and general scantlings, you have quite a bit of rearch to perform. Foam/sandwich composites are not very forgiving materials to play with. Given the load paths are nearly all in the laminate schedule, you can see how gettig this right is impotrant. Once you've plowed through the weights, centers and scantlings work ups, you may wish your understanding of the hydrodynamic asspects of the design are also suitable, which given your questions suggests you have work there too. In short a fair bit of study and research or buying plans.
  6. bjdbowman
    Joined: Apr 2017
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    bjdbowman Junior Member

    quick example of function over form

    Thanks for the replies... this is just a quick example:

    Jacques Cousteau must have loved this design enough to build it... but none of our wives would ever let us purchase this (see below) ... most would call it ugly, but Jacques Cousteau called it necessary. So FUNCTION OVER FORM... not pretty.

    The reason that I was thinking of using the foam sandwich design:
    1) I can carry large panels like a 32' long hull side
    2) I like the idea of the insulation to beat back the sounds while at anchor
    3) heat/cold insulation of the entire hull/topside
    4) It can be hot glued and epoxy glued at the same time = instant set = no waiting or clamping for the foam components

    Other than that I once owned a 24' Bayliner fiberglass cuddy cabin which was just a thin hull/topside with minimal reinforcement in a production boat. It worked well but was hot/cold and an echo chamber inside. And yes if you needed to add anything you had to add backing plates for strength.

    What is the downside to building with foam sandwhich? Granted no-one is using house insulation. If done correctly can it not be a viable alternative?

    The main reason i want to use foam is speed ease of handling during the build and I believe that if done correctly it can be stronger than a female molded fiberglass hull.

    But what do I know... I was hoping someone had built with this method before.



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  7. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    In principle, without further explanation, I see no reason for this to be so. And, on the other hand, a hull does not have to be "too strong" or "stronger than", it just needs to be strong enough.
  8. Rurudyne
    Joined: Mar 2014
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    Rurudyne Senior Member

    Yeah, it's the bridge deck where the problem starts. Some months ago there was a plywood beast that broke up out California way, IIRC, where the bridge deck was noticeably flexing just sitting there floating in the calm. No way it was going to end well for that boat.

    Thing is getting scantlings for the beams. Gerr flat out punts. A set of rules that I've downloaded a few years ago (and can't exactly remember from where) as Rules for Construction of Wooden Ships (Marina 2011) seems to give scantlings for most bits BUT the beams of said bridge deck, where they make a few nice statements about said beams like making sure they're full width and positioned to prevent racking as much as possible. Which is kind of a punt but not wanting to seem to be punting to my way of thinking.
  9. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    You can do the beam calculation using common civil engineering formulas. The forces acting on them has to be known first. That depends on the design of the hulls and the expected sea conditions.
  10. JosephT
    Joined: Jun 2009
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    JosephT Senior Member

    Agree with philSweet & PAR on the material selection. In my opinion, I would not try to reinvent the wheel for a retirement boat. You'll find out like many others you'll need extra money for filling your fuel tank and stocking up on groceries & rum!

    Suggestion: Find a good ~30ft CAT for sale that's in good shape and within your budget. If you're a good craftsman you could also build one from an existing kit. Choose a proven hull that's seaworthy. Here's a nice 30ft cat that's got impressive performance and they offer kits.

    There's many others out there.

    At the end of the day hopefully you'll be happy and your family will be safe too.
  11. bjdbowman
    Joined: Apr 2017
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    bjdbowman Junior Member

    Most of the desire is to build something different

    I want to build a boat... so I will, what and how is yet to be discovered.

    Someone mentioned a punt and I ran across this canoe built with floor insulation...


    Also below is a picture of my hero... thinking outside the lines. I like it.

    Some have tried... and I'm willing to try. I'm not just going to go out and purchase a boat, been there done that. I would like the pleasure of building the boat myself, then launching it and sailing it. That is the purpose of retirement to finally do something for yourself that you have not had the time to do.

    I'll keep looking... and reading.


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  12. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    You could write a book about all the people that come along here with plans to build boats centred around polystyrene foam. It is certainly useful stuff, but as a basis for a boat hull, not so much. It probably does have some uses as a former, but not as part of the final structure, other than as a buoyancy material. It is also bedevilled by being incompatible with many chemicals, including glassing resins except epoxy. Petrol destroys it.
    rwatson likes this.
  13. kerosene
    Joined: Jul 2006
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    kerosene Senior Member

    I assume you mean xps not eps foam. Eps is out of question, too weak. Xps is better but even that has weak shear strength. If you search there are a couple of xps threads.
    I have been playing with the idea of using xps core for a lightweight lake boat.
    I would never consider it for sonething that is an investment of thousands of hours and tens of thousands of dollars/euros.

    I am a dreamer myself so let me share a few points as soneone who has been here for a while. Your post is not all that unique, it shares elements with dozens of similar posts that i have seen. So here toes:
    -hull is the exciting visible part of the boat. It's were the shape of boat is created from flat building materials. From a boat building perspective its 1/3 of the cost. Beginners wanto invent totally new ways to build to save 50% here without understanding that even if they were right it would make the boat only 16% cheaper - with difficulties to insure and fraction of the resale value. All this while working with methods that you cannot get support from helpful and experienced communities (that are available for plywood, glass, strip etc.)
    -Idea that styling is central part of design. What boat looks like is a result of what its designed to do. Starting from visuals will be unlikely to end up as a good boat.
    -Idea that negative feedback is there to discourage you just for sake of putting you down. Your idea is not good. You are asking professionals who share their time, they tell you that but you insist that they just don't get it. What if they do 'get it' but still think its a bad bad idea?
    -unrealistic expectations of the budget and effort that a big boat takes. We see people who want t build 40-50ft boats and say cost is not a problem because they can slowly put money to it totalling 30k$. Well 30k$ is not going to get you a 40 foot yacht.
    -start by building a massive boat. The effort taken by a 14 foot skiff is tiny fraction compared to a big cat. Do that 1st. Then you can talk about fairing or not fairing. Not fairing is not smart and idea that you don't have to sand is just absurd. Your epoxy dries too much because of scheduling or just random reason x and you have to sand it to get things to adhere to it. not fairing to pristine is one thing but but not fairing at all is bad idea.

    Read the thread below. Note the dates. Read it all. Ignore the biblical arguments and concentrate on the boat design.
  14. rfleet1066
    Joined: Feb 2012
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    rfleet1066 rfleet1066

    Former dreamer

    I came to this forum about five years ago with a dream boat. It's finished now, and I'm building fixtures to launch her. Let me tell you a few things I have learned...........

    1) One does not build a boat to save money.
    2) Just because you can do a thing does not make it a good idea.
    3) The elders here will not heckle you unnecessarily.....but if they do, listen.
    4) Take any reasonable time and money estimates and multiply by four.
    5) The Sistine Chapel was not 'paint-by-number' Michaelangelo painted in strokes. Keep the design fluid and let the materials you choose have a loud voice.
    6)Boat ideas and dreams are cheap. Until you have done something with them, they are no more than nautical engineering m_asturbation.
    7) Do not commit to a project and approach it leisurely. Prolonged cumulative effort is required. Watch ants build an ant hill before you start.

    bjdbowman likes this.

  15. messabout
    Joined: Jan 2006
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    messabout Senior Member

    Very well said Rfleet1066.

    BJDBowmans link to Jeremies blog might be misleading. Jeremy is a shrewd and experienced builder and experimenter. He builds boats to be powered by a Makita cordless drill, the boat to operate on a pond. . A mighty lot different from a power boat or sailboat. The target weight of the CCC boat was 12 kilograms. That is the reason for foam and scant glass and resin.
    Last edited: Apr 25, 2017
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