efficient 10m displacement powercat

Just had a quick skim through this thread, so if I've missed something, I apologise, but from what I've read, you seem to have put a whole lot of horses before the cart...
1st off, I don't think it is feasible to build a durable 35ft cruising cat that weighs in at around 2500kg. Obviously, you need to do a thorough, detailed weight estimate before you can even begin to think about things like powerplants etc. As a starting point, you ought to at least look at some published displacement figures from other similar boats. Ideally, you want to know the as built weight, though this tends to be hard to come by... Perhaps Mas can tell us the weight of that Chamberlain, for instance...

 

Well, ive got a reasonably accurate shell weight including the 2 outboards which i added to the transom weight (highlighted in the pic below, weights are in tonnes so remove the decimal and you have Kilograms)

To this i need to add;
a few more small composite panels and stringers, internal furniture etc here and there which i havnt bothered drawing, done in 40kg/m3 foam with thin laminate;
then probably 20kg of paint;
then fitout inc all electrical, honda 2kva inverter, 60l fridge and 150l freezer, 2x batteries, hydraulic steering, cleats, ground tackle, mattresses and upolstery; toilet, head, pumps and water;
the fuel tanks are built into the composite structure already;
Id like to put down some 10mm teak strip plank decking in the saloon and on the back deck - which is gonna cost me about 100kgs, but i like the look so...
A bunch more other bits and peices, but thats the main bulk of it taken care of...

i reckon i can bring in all this under 500kgs comfortably, which means i have a lightship displacement of just over 2 tonnes...just add people, fuel and im fishin...

Most boats are built stronger and heavier than they really need to be, and until recently most boats used inferior composite sandwich materials or no sandwich structure at all - so needs to be much heavier for the same strength and stiffness. So one needs to be careful when making comparisons or assumptions of weight based on what looks to be a similar type of boat, you cant tell by exterior appearance whats really inside of it... it could be a lead sled (over engineered, chopper gun sprayed polyester solid skin boat) or a rocket ship (well engineered, PVC foam cored, glass/carbon/epoxy sandwich boat)

 

Why 10mm and why teak?
Have used 5 before with no issue and there are other products http://www.yachtdeck.com/

 

Hmm, didnt know this stuff existed... thanks for the heads up on flexiteek... i definately look into it...

 

The weight estimate for a boat like that - if it's prepared properly - will run to several pages in length. And whilst I agree that many boats are over-built, there are also a number that are marginal at best. The Chamberlain that Mas posted is designed by a very highly respected designer whose boats are probably at the lighter end of the properly engineered spectrum.
And for every home-built boat that floats on its marks when launched there are probably a hundred that are far heavier than they were expected to be.
Yes... a proper weight estimate is a lot of work. But a whole lot less drama than a boat that is too heavy.
Just my bit of advice... you can take it or leave it....

As far as synthetic teak goes, there are (IMHE) only two worth considering.... Esthec ("plastic") and Marinedeck 2000 (cork). I put the latter throughout my own boat and am very pleased with it....

 

Why are boat getting more and more ugly as time goes by
They used to be things of great beauty but seems we have lost all respect for beautiful thngs , the more ugly the more people rave over them ! sorry !!i i was looking to make a new boat and a designer presented me with drawings for one of these hidious looking things i would toss him out on his ear and tell him to go back to kindy !

 

There is another reason - poor weight control. Builder/Customer keep adding without looking at table of weights... Well, on MY boat difference in design weight and actual weight was 4kg

Meanwhile, may times when we see attractive specs for some Australian-designed cats we need to realize there are no option such as genset, air-conditioning, teak etc. included. At leas I try to design fair boat and put fair weight in specs, also structure in compliance with ISO12215-5.

 

Same for buildings, imho. There are plenty of beautiful ancient and old buildings in (for example) European cities which inspire a sense of deep admiration and respect for architects and artisans who have designed and built it. A care for details can be felt by looking at every single stone, brick or a piece of metal they are built of. The 18th century was particularly generous in that sense.

Today we have these giant cubicles made of glass, steel and concrete which inspire nothing to those who are observing them. Buildings with no soul, designed just for quick construction at minimum cost. Guess they're a perfect reflection of the times we are living in, ruled almost exclusively by God of money.

 

sorry tunnels, i use several different softwares to model the boat and at this time, its easier for me to use the freeship software with respect to the panel areas and weights shown above... the proper rendering (shown in white) was done a page back in the thread... if you still dont like it, then thats your perogative, i have designed what i like - for my eyes...

One thing needs to be remembered about this boat - its not a cruiser or liveaboard... its a lightweight sports fishing boat with minimal "creature comforts". Typical use will be day fishing trips and the occational "weekender" type trips, all within the partially smooth waters of the barrier reef...hence the need for speed due to limited time on the water. The interior will be very minimalistic and simplistic... no air cons or TV`s, no diesel gensets, nothing that doesnt need to be there etc... this is not a luxury boat...

 

Groper, I would be interested to learn how did you create frames and bulkheads with the freeship? To avoid the side-drifts in this thread, you could reply here (if you wish): http://www.boatdesign.net/forums/de...ated-masses-etc-freeship-delftship-38103.html
Cheers

 

Years ago I was involved with one boat built from light weight panels and the joints weighed more than the panels

Boats are usually heavier than you hope (and more expensive, and more time consuming). In any event never lighter/cheaper/quicker

Having said all that, a simple 35ft boat ex fuel and with light engines can weigh 2.5T built in foam sandwich

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Motoring into swells at 45deg is usually the best (ie least motion) option. Head on, or beam to, seas is usually a worse case

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Yes, thats the one I was looking for.
Not cheap, but neither is a laid deck.

 

I agree, which is why the designed displacement @ DWL, loaded and ready to sail is 3.5 tonnes... 2.5tonnes is the lightship displacement...

For those that havnt read the entire thread, the design has evolved and changed over the course of the thread...

 

As I said... I hope you will take my input in the manner iin which it is intended... I'm not having a shot at you.... just trying to be of assistance - that is afterall why you posted, isn't it?

I haven't had time to look over your short weight table in any real detail, but let's just look at two points:

1. You show the glazing as being 10mm thick all around. The required thickness is determined by material type, minimum spans and area of operations. The sides can usually be somewhat thinner than the fronts. But that aside... The density of Lexan is 1200 kg/m^3 - so 10mm thick will weigh 12 kg/m^2. The density of glass is approx 2500 kg/m^3, so will weigh 25 kg/m^2. Your weight table shows it at 6kg /m^2.....

2. It is unusual to see 40 kg/m^3 foam used as a structural core... 80 is the most commonly used. This varies of course, depending on the application and the engineering involved. Such low density foam will be more prone to damage from impact, so will compromise your desire for thin FRP skins. 13mm looks at 1st glance to be optomistically thin too... particularly for the hull shell and definitley for the decks. Such thin panels will require quite a bit of support (internal framing). I don't know how much experience you have in engineering a structure like this (you may have plenty...) - and there certainly isn't anywhere near enough detail in the images you've posted to make an educated guess, but if you are approaching this as an amateur, can I suggest that you at least go to the small expense of getting it checked by someone with the relevant knowledge and experience... it'll definitely save you money, time and heartache in the long run....

As to the looks... beauty is in the eye of the beholder as they say.... I reckon it looks a whole lot better than any number of boats I see out there - both proffessionally and amateur designed.... but then again I like steel and glass cubes...