35' cat concept for the inside passage.

Thanks a million alik

 

Nice looking p-cat...front reminds me of the Lagoon 43.

 

I've just converted an international 7.3 IDI diesel to run on motor oil. It puts out, with the modifications I"ve made, about 230hp, on a good day. I'll have to get it dino'd once I get it all dialed in, but I'm pretty sure I'm in the 220 ~ 230 hp range. It weighs about 1000 lbs. http://s29.photobucket.com/albums/c262/bostonpyramidbuilder/?action=view&current=DSCN0257.mp4

The Mercedes 300D IDI weighs in at about half that, and produces about 80hp before tricks and turbo chargers. Both these engines are considered the exceptions for measuring reliability in a passenger diesel. Both convert really easily to alternative fuels. The 7.3 has been around since about the 1940s and the 300D since about the 1930s . Both are still in production. I can get a factory new 7.3 for about $3500, pretty damn cheap, the 300D for about $4500, factory new. You could trip over the parts for either of these engines at the auto parts warehouse they are so common. If there is any way at all, I can manage to jamb one of these engines onto the build, I'd do it. Sprockets, chains, belts, any way I might have to I'd run as reliable an engine as possible even if it meant Micky and Minnie Mouse themselves were my engineers on getting that power to the shaft...... No reason at all to buy anything else. All I need to do is keep the thrust off the engine and I'd not need any major modifications.

 

groper

I agree with Alik. I thought your power estimates were a bit optimistic

FWIW my computer says my 35ft powercat will do just over 20 knots with twin 60hp outboards

VERY roughly, for this size boat every 1 knot extra speed over 10 knots needs an extra 10hp

And windage is a major (but often forgotten) drag, as everyone who has ever sailed under bare poles knows. And a powercat usually has a 20 knot headwind as a minimum

See here for solar panels

http://www.sunelec.com/

typically 1USD per watt or less and prices are coming down all the time

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

The figures i provided were not meant to be taken as a total analysis end product, but rather as a comparison for different hull shapes to be considered. As the general arrangement and styling remains constant for a given design, the aerodynamic drag will be essentially constant, so i figured we can ignore this for now and just play with some different underwater geometries and find the best fit for this boat in question. This will become interesting as things progress with regard to certain hull shapes and performance regimes and we shall see which way the spiral goes, and why...

And yes, solar is getting better all the time, prices have really come down in the last few years havnt they! $1 per watt is great value, and with all the other equipment were running off it becoming more energy efficient, the days of needing a genset are numbered i promise you... The only real breakthru we need is in energy storage, or better/lighter batteries at a reasonable cost... whomever cracks this nut is gonna take over the world... I was reading somewhere about someone experimenting with a special new capacitor that was very lightweight and sounded like it had interesting energy storage potential, ill have to dig it up... at any rate, its all great news for catamarans aint it

BTW Richard, i like the way youve moved the double beds aft under the sofa and kitchen in your skoota 36, its enabled you to move the bridgdeck further aft and reduce the chance of slamming at high speeds with the efficient fine entry bows... nice arrangement

 

Much later than that but whatever.

Look at the Havana 38 for packaging ideas..I think Malcolm Tennant designed it.
http://www.cruisercats.com/product-range/havana-38-express

 

Interesting.

Remarkably similar to the Patterson designed Twins 43 (vintage 1989) motor sailer cat I wrote about earlier

http://www.multihullcentre.co.uk/mhctwins43.htm

I have motored this boat at over 15 knots with twin 110hp. It has since sailed through the Roaring 40's and is possibly the only catamaran to cruise the Keguelen islands

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

I think in the end it comes down to personal style and how a boat is used. I have considered a cat power platform for the North West and have a friend with one. I have owned about 20 boats including a multi for 10 years and fully appeciate and undersand the type.The type will work given enough LAO and beam to handle the accomodation without geting lopsided. If the asthetics are not right you will take a big hit on resale and with a cat I believe its harder to get right than a mono. Also if you are the pack rat type stay away from the multi,extra weight will lose most of the performance advantage. If you like to go to docks in the North West the wide boat is going to be very limited even the modern wide body monos are getting squeezed up north. After considering the options I decided to go with a mono long and low with a shallow downeast hull.

 

Hey I like that thing. That probably the first power cat I've seen yet that appeals to my senses, thanks West

 

Then we like the same thing in cats.I don't like the high exposed bridgedecks..more along the lines of sailing cats.

I saw this 60' aluminum one in France,built for circumnavigation etc it looked like this one but a lot larger.
Give me a while for the memory banks to click....

 

Depends where you are using it.

An enclosed low helm is a PITA if being used in areas of high heat, blazing sun and reef strewn waters but there is nothing preventing one from having both.

I'll have engine controls and autopilot repeaters inside for passage when weather precludes use of flybridge.

 

I am concerned with something that keeps getting brought up tho , this time by Chulman. The weight issues. If these things really have such a narrow weight range in which they operate efficiently then carrying large amounts of fuel might be an issue. I was hoping to jam a whole lot of fuel onto this thing. Means I do less collecting and more motoring. Although I think I can figure out some form of design I'd like eventually I'm not so sure I could overcome the narrow weight range within which these things seem to working efficiently.

I estimated my range at 800 nm with tankage of 200 gl/us and it was suggested I might be pushing it to expect 8 knots out of 20 hp each hull . So I'd want to carry more fuel. say 400 gallons or about 2600lb of fuel. Maybe more.

 

Also looking thru my bookmarks I found Power Cat World site- you should find something on here as they feature most everything about commercial p-cats built and being built.

http://powercatamaran.typepad.com/

I also considered a cat but for 1/4 - 1/3 the price I have a very nice 6 year old 50' cruiser.
It doesn't get the fuel economy,but at 100-150 hours a year it would take centuries to make it back.And there's few cats that can do 30 knots.
Plus I can throw on all kinds of stuff (pwc) and not be worried about weight.

 

Easy fix.
Same size accom. on 50ft hulls
Simple.

 

Ahem! Cough Cough!

http://www.boatdesign.net/forums/boat-design/35-cat-concept-inside-passage-40844-3.html#post507209

(see last two paragraphs in red)

You will definitely not be making 8 knots with the current design @20HP per hull. Probably more like 6 knots and that's if you don't drop 2600lbs of fuel in. You'll need 30HP per side to approach 8 knots.

Carrying more fuel won't help you. You're getting stuck in the "bad" side of the design spiral again (more weight, more fuel, more power). You have to keep the weight off to get the range you are seeking, so... maybe... the cat is the wrong platform, unless you are willing to start counting pounds like a model counts calories.

Do you have a spreadsheet yet that adds up all the hull materials, epoxy, glass, rudder stocks, engine, engine gear, running gear (props), windows, interior wood work, tender/dingy, outboard and fuel for tender/dingy, water tankage, black water tankage, diesel tankage, wind generator, wiring, plumbing, sinks, faucets, anchor, windlass, generator (if any), batteries, etc...???

If you are building a catamaran, you need to track all of that stuff in order to get that range you are looking for - or - see if it is possible to get that range.