MV catapult

Build logs from members building catamarans, trimarans and other multi-hull variants.
groper
Posts: 239
Joined: Sun Nov 18, 2012 11:23 am
Location: cairns

Re: MV catapult

Post by groper » Sun Dec 30, 2012 8:52 am

Yes mate, most of the boat is built from infused flat panels off a table - i even changed the design from my initial one to get rid of nearly all the compound curves from the boat so it could be built this way. Why? i quickly learned that infusing flat panels is so much quicker and easier, not to mention a more enjoyable type of work thats clean and at a comfortable working height... i just wish i had a table that was full length so i could make bigger/longer panels which would speed things up even more and eliminate some of the joining ive had to do, but i just dont have the space for an 11m table in my carport :mrgreen:

For compound curves, you need molds... i made a temporary female mold (used for 2 pulls) from frames, battens and celluka board (pvc foam sign board) shown in my first post. The mold wasnt fair, so i still had to fair the parts after they were pulled.

mikeb
Posts: 136
Joined: Wed May 26, 2010 3:01 am

Re: MV catapult

Post by mikeb » Tue Jan 08, 2013 10:36 am

Hi Groper
Great looking build. Do you have a background working with infusion or can you recommend a book/article that gives the low down? Everything I've read says trial & error is the way to go so I guess that's where I'm heading... I've been doing some research on various cores and thought making my own panels would be much more cost effective. Do you mind if I ask what brand/density of foam you're using. PM me if you prefer.
Keep up the good work!
Mike

groper
Posts: 239
Joined: Sun Nov 18, 2012 11:23 am
Location: cairns

Re: MV catapult

Post by groper » Tue Jan 08, 2013 7:15 pm

No probs mate... i have actually used 5 different foams in this boat so far, i think ive been through all of them... i started with airex and corecell both 80kg/m3, and more recently have been using diab divinycell in both 80kg/m3 and also a 68kg/m3... for high density core replacement such as under deck hardware in in the transoms etc, im using coosaboard - i forget the density but its probably up around 300kg/m3.

No, i have no boat building experience before starting this build, i had laminated and vacuum bagged a few small things over the years and had basic understanding of fibreglass composites but thats about it.

For infusion, you definately simply need to play with it for a while and get a feel for it, no doubt about this whatsoever. Also helps to talk to people who are doing it (on the phone) and plug them for as many tips and tricks as you can - im happy to help in this regard as others have helped me... Once you understand how it all works and get the theory behind you (reading), by doing some small infusions you will quickly learn what NOT to do and what stuffs things up! - these are the things you cant really read about, you need to physically see it for it to make sense and understand how you need to prevent the problems that can occur.

I started with doing some small infusions of little bulkheads, stuff that wouldnt cost an arm and a leg if things went bad... the more infusions i did, the more i understood what works and what doesnt, and my confidence built up quickly - i never lost a panel completely, some needed minor repairs tho. I soon realized, that infusing the largest panels possible is the most efficient and least amount of work per panel area and once your doing big panels, its actually quicker and less work than just about any other method, including building in plywood IMHO... an entire topside hull panel only takes about 5 hours from applying the mold realease to opening up the resin lines. When its done, you have a panel that you simply peel off the peel ply and can take directly to paint with no pinholes showing -provided you dont stuff it up that is! Nearly all of my exterior panels do not need any fairing so this will save me heaps of time later, i can tell by the reflections i can see in the panels... you need to let the panels fair themselves tho, so dont try to pull them tight into a bulkhead or any misalignment of the bulkheads will bend the panel out of fairness. I usually only end up with a couple of mm gaps under the panels anyway, fill these up with bog when coving and taping, too easy...

Send me a PM and ill give you my number if you wanna chat about it,
Nick

rexd666
Site Admin
Posts: 157
Joined: Tue Dec 15, 2009 7:15 am
Location: Melbourne, Vic

Re: MV catapult

Post by rexd666 » Thu Jan 17, 2013 10:21 am

Note split posts on Windows across to http://diy-yachts.com/forum/viewtopic.php?f=27&t=982

groper
Posts: 239
Joined: Sun Nov 18, 2012 11:23 am
Location: cairns

Re: MV catapult

Post by groper » Sat Jan 26, 2013 11:31 pm

Aftermath after the storm.... allowed me to take a photo from a different angle tho... the prro old plastic shed copped a bit of damage... ive wrapped her up and will wait until after the cyclone season before assembling anymore stuff on her. The building process will continue however, ill make a few things in the shed over the next few months and then once the weather is good, alot of progress will materialize on the boat. Need to work on the furniture and cabin for the most part.

Image

dennisail
Posts: 61
Joined: Tue Feb 19, 2013 1:42 pm

Re: MV catapult

Post by dennisail » Sat Feb 23, 2013 2:12 pm

Love this build. I am sold on bagging my own foam panels. If I build this is how I will do it. Was it a steep learning curve and long process to design your own boat? How did you come up with the scantlings? What sort of percentage price saving do you think you would have when making your own panels compared to say paying $80K for a duflex kit?

groper
Posts: 239
Joined: Sun Nov 18, 2012 11:23 am
Location: cairns

Re: MV catapult

Post by groper » Sun Feb 24, 2013 6:52 pm

Well the design i literally pondered over for a good 6 months prior to commencing the build... i almost bought a design from a well known designer, but decided against it as i didnt think the price was worth it at the time and figured i could work it out. Still dont know if i made the right decision or not, i will have to wait until the boat hits the water to find out for sure. But yeah, its a complicated process to design something that will work well, good software made it a bit easier but you have to have a good handle on what elements are required in a successful design. I already was familar with AutoCAD and other software and have done a bit of technical drawing for a civil engineer etc. Freeship software (free) is half decent and simplifies some of the basic calculations including the hydrostatics and you can use for panel areas and weight distribution, CoG etc. I also played around with michlet for resitance predictions etc. Im keeping a running excel spreadsheet for real panel weights and moments so i know where im at every time i add another panel to the boat. This allows me to position my tanks and other heavy items ideally to achieve a well balanced boat that floats on her lines. If you familiar with all this type of thing and basic engineering, and be prepared to learn what you dont know, then id say you can design your own boat no problem, tho it will take many many hours to do it.

The scantlings are something else... the thing is noone really knows what the loads are, so without knowing the loads, you cant design anything. The only thing a naval engineer has to go by, are the class rules set by the classification societies. In these rules, they tell you how to calculate the scantlings to satisfy their classification for the type of boat and its area of usage. Its reasonably basic engineering, not too difficult if you have a good understanding of maths. If not, forget it.

The problem with duflex is that the surface quality is poor (pinholes etc) and i dont like the idea of a balsa cored boat. Balsa has brilliant mechanical properties, but boats being boats means inevitably water will get in somewhere somehow someday... for this reason i prefer foam. The total materials cost for my boat shell is looking like going a touch over $40k as i have just about everything i need to finish the boat on hand. This is only glass reinforcements, infusion consumables, resin and foam. A duflex kit for this size boat probably would have been around $70k including furniture, so there is a considerable money saving. Theres more time in making the panels, but i beleive this will be somewhat offset by time savings when it comes to fairing and painting her. Most of my panels are ready to put the paint straight on, no fairing or bogging beforehand. Duflex must have every bit covered and sealed, sanded and faired before painting - not so much fairing, but when you apply the sealing coats you introduce some uneveness which must be sanded out. If you build a good table mold, infused flat panels come out perfect. You could even apply an "in mold coating" before infusing which means use a special paint like a gelcoat. You can do this now with epoxy.

If i were to do it again, i would do a few things differently but i do have limitations in terms of building space which contrains my efficiency somewhat. I wish i had room for a full length infusion table instead of a half length table in a double carport... i would have made it perfect from day 1 with a duratec mold surface finish instead of this melamine crap which scratches too easy and develops vacuum leaks. I would have then infused all my panels with the high build paint already on them as an In mold coating. Also, i would have used infusion grid cut and perforated foam and infused that way, instead of the SCRIMP flow media method which wastes more resin and generates more waste plastic to throw in the bin.

All in all, i dont regret infusing my own panels instead of a duflex kit - i plan on building a larger sailing cat next time, and will do it a similar way but a few changes like i mentioned earlier.

dennisail
Posts: 61
Joined: Tue Feb 19, 2013 1:42 pm

Re: MV catapult

Post by dennisail » Tue Mar 05, 2013 2:15 pm

Thanks for the lengthy reply. I think you made the right decision designing it yourself. Not that this would be a good idea for most people. But for someone with your capabilities I think it would be a rewarding experience. It will give you the confidence to do your larger more expensive sailing cat, not that this is a small project.

Can you explain what is happening in pic 2 on your first post? You have a blue board of some type. Is this a mold you are using to hold the table infused bottom and side panels together with prior to infusing them together at the bottom with a curve that contains no foam? What causes the dark colour? Do you add a die to the resin when infusing so you can see where it is flowing or is this carbon :shock: ?

Image

44c
Posts: 1148
Joined: Tue Aug 08, 2006 5:08 am
Location: Hervey Bay, Qld

Re: MV catapult

Post by 44c » Tue Mar 05, 2013 2:59 pm

groper wrote:The problem with duflex is that the surface quality is poor (pinholes etc) and i dont like the idea of a balsa cored boat. Balsa has brilliant mechanical properties, but boats being boats means inevitably water will get in somewhere somehow someday... for this reason i prefer foam. The total materials cost for my boat shell is looking like going a touch over $40k as i have just about everything i need to finish the boat on hand. This is only glass reinforcements, infusion consumables, resin and foam. A duflex kit for this size boat probably would have been around $70k including furniture, so there is a considerable money saving.
The kit for our Oram 44C was about $65k. Not including furniture. I doubt your boat would have run to $70k even with the furniture.

The reason Duflex has pinholes is because it has extremely good glass/resin ratios. Every drop of excess resin is squeezed out. Because hydraulic presses are used, pressures available are far higher than can be achieved with infusion, where pressures are limited to around 0.8 of an atmosphere, or around 10 psi. Pulling deeper vacuum than this risks "boiling" the resin.

The weave on Duflex is easily filled - just a squeegee of a runny glue mix.

I disagree that water ingress is inevitable. There are balsa cored boats 30 and 40 years old still in perfect condition. And many of the early boats used polyester resins, which are nowhere near as good as modern epoxies.

Not knocking your methods or the job you're doing, which is excellent. Just that some of your comments about other materials needed correction IMO.

dennisail
Posts: 61
Joined: Tue Feb 19, 2013 1:42 pm

Re: MV catapult

Post by dennisail » Tue Mar 05, 2013 4:15 pm

The reason Duflex has pinholes is because it has extremely good glass/resin ratios. Every drop of excess resin is squeezed out. Because hydraulic presses are used, pressures available are far higher than can be achieved with infusion
Where is the resin squeezed out to? Wont it just end up inside porous the balsa? I honestly don't think that having pinholes through to the balsa core due to awesome resin to glass ratios is a very good selling point. Its kind of like saying rust makes your car better due to weight reduction.

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