35' cat concept for the inside passage.

Shy on headroom?
You using pogosticks?

Plenty of 35ft cats getting around built from 9mm ply that take to the beach.
If you are that concerned, why not just double up on the bottom panel saving weight and dollars over the rest of the structure.

 

This one's layout may be along your lines....but make it more of a displacement vessel.
I kinda like it as it is not the usual "too wide and too high" but I have a nice enough boat already

http://www.multihulldesigns.com/designs_stock/46pwrcat.html

 

Cat there are no beaches in Alaska, its a euphemism for rocks anywhere in the PNW. On a very calm day, as in glass, you might be able to beach a boat if it had a seriously tough bottom. I wouldn't think 3/8 would survive. In the Caribbean or maybe Hawaii but never the PNW.

Oh and you are right, I misjudged the size of that one also. Damn thats another nice cat.

West, nice boat.

 

Well I dunno anything about Alaska but there's many a sandy (or pebble stone) beach in BC.
Was looking at a Brazilian cat a few years ago that had a sacrificial wooden runner along the bottom of each hull.

How about kevlar on the bottom?

 

to expensive and I'm already sitting on about 1000 bd/ft of 4/4 white oak, but its only in 8 foots, got a pile of cherry as well, maybe 300 ft in 8/4 stock. So I'm well on the way when it comes to hardwood. Might need another 1,500 of 4/4 cherry 12~16 foots and some of the same in black walnut. The oak will work fine as a sacrificial bottom veneer and maybe flooring. Veneer plank over ply of course. White oak is really pretty tough so it makes good flooring. Working on a good source for the BS 1088. I suppose I could cheap out and buy some dougy ABX and use it above the water line but that stuff checks like a ***** so what it saves in cost it spends in weight to veneer it with something that will finish. Might just be worth the up front expense to go 1088 and save the extra labor, do up the bulkheads like flat panel work. The decks and hull I'd likely put a thin layer of glass over, just to help keep the water off it and hide any pesky joint lines.

I'm getting ahead of myself here, I need to finish the basics and price up everything to see how doable this is. Gotta remind myself its just a day dream for now.

so far my interior layout looks more like a smiley face

 

that suggest of yours Sabacat is very interesting. Its mostly foam composite with ply bulkheads. One thing is its got its cabin a lot more forward than I do, I was kinda thinking I might draw up an alternative plan with mine that way and see what it looks like. I'm still very much just in the conceptual phase with this so no big deal to make major changes at this point.

Very interesting tho now that I have a chance to read through there site. It basically weighs about half of what mine might and is only 30'. In sea trials they ran it well over its hull speed and paid for it getting only 1nm per gallon. Which they bought a round for. At 8 knots using something between 12 and 20 hp each engine and given that 1 gallon diesel contains about 20 hp hours of energy ( engine variations will skew that number ) I and running two engines I should get about the same mileage. If I went with the Mercedes 300D single engine plan with a single centrally located prop, I'm sure I could better that. But I'd have some losses in the gearing I might not have with a smaller engine set up.

cheers
B

PS, working kinda late on the floor plan of the hulls, I've managed to cram a 3/4 bath and a double bed plus fuel tanks and an engine/mechanical room. As well as find access for the companionway. And sorta maintain one of my main goals, That if a hull was punctured there would be no discernible list. IE the total submerged area of the hull would be filled with flotation material. One big thick foam core floor so to speak. I'll be sitting to take a shower but thats about the biggest sacrifice, that and sleeping on top of a couple hundred gallons of fuel.

 

I used to own a 34' Wharram. It was built of 3/8" ply with 3/4" stringers. The hull was only coated with epoxy paint.

 

crazy, what was it over frames every 9" or bulkheads every few feet ? As I said I'm in over my head on the hulls having never even seen a big ocean cat before, even when I was a kid. Lobster boats is about my only real experience, that and my little sailboat from when I was a kid. Does sound like I could get this thing down a bit on weight tho. I'll recalculate it based off of 3/4 bottom with 1/4 white Oak veneer on it and half inch sides/tunnel. But that seems awfully light. There must be some online cheap *** prints to help me see what the typical scantlings are on a sharpie style hull. I want that curvature someone was mentioning, I just don't have a french curve to draw them in.

My thinking is that going to the PNW were there is pretty much nothing but rock and gravel I want a flat bottom like a sharpie with some extra thickness to it. That and the waters about 36°F up there which gives me about two minutes before ole pops a Popsicle, so positive flotation and a little extra fat on the hull. I wouldn't be comfortable with 3/8 ply, pulling it up on a beach. Going to have to go look up Wharrams and see what I can see. That and try R Woods page again.

Cheers and thanks for the tip

 

There are always two design spirals you can use. Make it lighter so the loads are less, so you need smaller engines, so the boats is lighter, so you can reduce the scantlings, so making it lighter etc

Or you can make it heavy, which needs bigger engines, thus increased load and so scantlings have to go up thus increasing weight

Successful multihulls tend to follow the first spiral. Go a bit further north than Alaska and you'll find the local boats are all made from seal skin.

I have done the Juneau/BC trip a couple of times. There are places where you can dry out. Although one time in Tracey Arm we were touching a cliff and our echo sounder read 900ft!

But I'm not sure why you would want to beach your boat. Indeed I haven't seen any cruising motor boat doing that.

I would suggest aiming at 6T, say 12000lbs, and try to reduce your enthusiasm for big bits of oak! (the photos you posted of your wood work look fantastic BTW)

I'd also tend to go deep rather than wide. For efficiency aim for a 10:1 hull length/beam ratio at worst

Don't even consider the one central prop idea on this size boat. One central engine with twin hydraulics is an option though

You won't ever capsize a powercat. Don't worry about it

I looked through my saved data of other powercats. This one looks a bit like what you are after

http://www.chernomor.su/shop_chernomor/motornyi-katamaran-fr-01.html

(Note: google translate does help!)

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

I may be the guy who mentioned Beaching. There is no good reason to Beach in the Inland passage.
I was thinking about needing to Beach for Repairs.
To repeat the wisdom of the Experienced boaters here. Don't build it with Beaching in mind.

I like your Henry Kaiser assembly boat idea.
Build it, n' make sure it's all gonna fit, then truck it to the Puget Sound country,assemble it and slide it into the water.
Hood Canal has some places where that might be possible.

 

I carried an aluminum ladder lashed to my bow beam to get down on the beach. A stern anchor helped get the boat off.

 

Boston, at 17,000lbs the L/D of a 10m catamaran is way over the top...it wont be efficient and it wont be fast... Why not a monohull designed for its hull speed if you need so much displacement? Much cheaper to build, less complicated and more efficient... the only downside is it wont have quite the same speed potential, provided you dont mind spending the money on fuel for that cat...

 

Have you checked out Tennant power cats..I believe they are all designed to be plywood.

Can at least get some ideas for layouts

http://www.tennantdesign.co.nz/index.php?page=powercat

 

Gonzo's ladder Idea is a good one. Two Anchor's is a good idea too.
The Ferry Wakes wash up on those Beaches. They'll lift your boat up and Drop in on those Rocks they call Beaches.

 

as squidly said, its a starting point. I've typically "only" considered mono hulls. so its a bit odd to deviate from the typical mass associated with the displacement type vessels. I'm not interested in planing my way across the PNW. I want something in the ten knot range and something basically unsinkable.

If I recalculate for 1/2 I still come up with 15,000lbs. But my logic of quadrupling the mass of plywood might be somewhat off. I'll play with it some more tonight after dinner.

Cheers
B

ps
something I really like about that boat in post #16 is the big wave deflector on the back 40. Looks like a great idea.