35' cat concept for the inside passage.

Discussion in 'Boat Design' started by Boston, Dec 6, 2011.

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  1. Boston

    Boston Previous Member

    Just kinda day dreaming my way through the holidays and found myself sketching out a cat. Its intended as a live aboard, part time charter boat for eco tours, whale watching, things like that.

    LOA 35'
    LWL 34' 6"
    Beam 17' 6"
    Hull beam, to be determined
    Building material Plywood with aluminum cross hull beams.
    Tunnel height 2' 9 1/2" (31.5") min.
    Standing room 7' max 6' 1 1/2 min ( I might change the camber of the roof so the minimum standing room is about 6' 6" )
    disp 12,160 lbs
    power 2x 35hp diesel or one Mercedes 300D running WMO
    cruise ~8 knots
    top 12 knots
    fuel 200 us gallons
    estimated range 800 NM at 8 knots (12 hp each engine at each prop, call it 20 with all losses included, 20 hp/hr pr US gallon of diesel = 8 NM pr/gl each engine or 800 NM Range,
    water 75 us gallons

    trawler style pilot station window
    raised pilot and navigator accommodations in the helm area
    great room with wet bar
    2 dbl cabins
    2 3/4 baths

    I drew it up with two possible cabin widths. One 2' wider than the other. Neither make for a great deck walkway,




    ( edit ) I've been updating this first picture to show the latest concept being considered, so some of the commentary might not match the picture above )

    working on the plan view.

    looks like it needs bigger side lite's and maybe a little more min head room. From the inside the wider cabin would be a nice addition, from the outside the thinner cabin looks better and allows better access forward.

    The drawing can be detrended to show a 7% increase in head room, I dosn't seem to look much different but it might have an effect on initial stability. So I want to consider the option separately.
    Last edited: Dec 13, 2011
  2. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    Looks good...put a little stubby mast on her for lifting the tender to the cabintop , some chunky wrap around rub rails for coming against piling and a chunky smoke stack that is really a propane BBQ.

    Make her single screw with top class diesel, then hang your tender outboard on the lazy side.

    Perhaps make her deck layout asymmetric, slide your cabin house over to the lazy side to make her working side deck wider for when coming alongside.
  3. Squidly-Diddly
    Joined: Sep 2007
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    Squidly-Diddly Senior Member

    click my handle and go to my Gallery for my concept of cat about that size.

    It might be a good starting point, plus, it is fully modular and container-able and scalable.

    I envisioned rolling on trailer RVs or erecting Army style structural tents.

    Maybe an 'open air' Thai long boat style engine hanging from the beams, or outboards, or inboard/outboard(stern-drive).

    In calm water with normal load it would have enough clearance to store canoes and kayaks underneath.
  4. liki
    Joined: Nov 2008
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    liki Senior Member

    How did you plan to fit 2 en-suite double cabins?
  5. thudpucker
    Joined: Jul 2007
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    thudpucker Senior Member

    I don't see anything wrong with your design. That might not mean much though.

    I lived in SE AK for some years and saw a lot of Liveaboards in all the harbors down there.
    "Warm Salt water" is what the waters down there are referred to and they corrode (badly)!
    Anything left in the water or up on deck suffers, as it rains salt water and Salty Fog's sit on us for sometimes days.
    So find a way to keep your "power" up outta the water. Fiber glass and Wood last a long time up there, but the Fasteners don't.

    You'll need Heat in the Cabins and plenty of Air flow to keep the Mold from developing.

    There are untold numbers of places to anchor. You can go all the way up to Haines or Skagway easily.
    ROCKS! Way out from shore. I never saw a 'sandy' beach. All big round rocks with Barnacles!
    Got an emergency "Toon" patch kit?
    You need a "Tender" too. A couple Anchors as well.
    Other than that your roving living room is handsome and looks like a lot of Liveaboards up there.
  6. Boston

    Boston Previous Member

    well thats a lot of positive responses, thanks, I shoulda mentioned construction is plywood with plastic fasteners over epoxy. Silly Bronze were necessary.

    Nice catch on the modular plan. Its designed to be built ( some assembly required ) in four pieces, shipped and assembled on site. With a minimal of additional work to complete. Thats why the aluminum cross beams and the long flat line just oboe the deck/cabin interface. Each segment could fit on a typical over the road trailer without the need for a drop trailer or any special permits. Once assembled it would not be able to be dissembled, at least not without a chainsaw. The main work to be completed once assembled is the cabin roof and floor, which would have to be completed once the hulls were joined and the cross beams installed.

    the original drawing was at 40' with 5' wide hulls. I took it down to 35 with basically 4' hulls and tight head room. The double cabins are still in the hulls but they're pretty skinny. Composting heads and shower on one side of the entrance and bed and shelving on the other. Galley is on the main deck, and its still got a slightly raised bridge deck. The cabins would basically take up a lot of the hulls but fuel, engines, stores, all the heavy stuff's gotta be jammed in there first. I like the idea of belt drives to keep the thrust away from the engines so I could use lighter engines and I had a kinda crazy idea of putting to inflatable tubes down the length of the roof, one each side. in case of a capsize, both so huge that when inflated they'd rite the boat. The windows are all smallish and could be storm shuttered pretty easily. The two inflatable self writing tubes would run down the length of the cabin roof and pop open on demand. Not sure if its viable in the long run but just a thought for now.

    I should draw in the stacks, two 4" running up through the main area with heat exchangers and threw the roof. And some soundproofing. The back deck area is where I was thinking of storing the dingy. I'd extend the two main headers over each ext wall back under the rear deck roof and have a telescoping deal that would extend out as davits, lift and bring in the tender. I've got 5' x 17' back there on the rear deck and I thought that being back there would do two things for me. One is protect those back doors when doing any serious cruising. The other is to protect the boat better from being washed overboard. Another might be to keep the wind resistance low. I debated a rear deck at all, but thought that without one the aft would look blocky and not be a sea worthy as I wanted it. With a dory or whatever stashed on the back deck it should be able to take a pretty big following wave and not see any damage to the main cabins aft wall. I'd also design some serious lashings to hold that dory down.

    I was thinking of putting a rail around the top and an access to the roof. It would make a nice observation area. And I still need to work on access forward so I can dock the thing. I've got a 2' walkway but there's a 1' roof overhang to help keep the rain off my nice wood windows, and a lot of camber to the deck which doesn't provide very good footing, I need to work on that. The boats white above the lower rub rail and maroon below. which gives it a long line to help with the illusion of length. Trim is all cherry, the roof is white.

    here's the first very rough draft of the floor plans outer shape


    the pilot area might need to be a bit bigger but it works for one chair at the 35' length, I just wanted two so I might push it forward a foot or two. The radius 7' works fine for width with two chairs but its only out about <4' deep, which means your view directly to the side is obscured. Might push if forward about a foot and fix that. My thinking on the wrap around window forward was that the curve lends a lot of strength to the plexi so it could hopefully take some water and still come up ok.

    Another idea I had for the thing was to take the main cabin all the way back and use the large inside space as a floating shop. Give up the chartering idea. Maybe if I have trouble finding enough whale watchers I'll take up wood work ;-)
  7. Richard Woods
    Joined: Jun 2006
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    Richard Woods Woods Designs

    I assume you have already looked here


    Tony Bigras' version of the same thing

    He's probably better know for his travels in Miss Cindy, the 16ft catamaran he car topped to Baja Mexico and then sailed to Cuba and beyond

    Richard Woods of Woods Designs


    My inside passage 36ft power cat is on my New Designs page
  8. Boston

    Boston Previous Member

    Hadn't seen Tony's design but your right its very much along the same lines as mine. I'll have to dig into it some and see what kinda ideas I can draw from it. Looks like he's got a ton of standing room. And it looks like he's got a single fuel tank per hull dead center over a small keel. The hulls are really out of my league, I've got no idea whatsoever how to design an efficient hull form for a cat. I was thinking Bolger style cause it looks so damn easy to build and repair. Although I' wouldn't mind some flair forward, maybe in strip planking.

    I've been pretty much exclusively thinking of a commuter style but the cat offered some interesting advantages. My last commuter design, which by the way is way beyond my present budget.


    I've got woodwork pretty much down so anything I build tends to have a lot of tricks in it. I'll post some pictures of other projects but I'm really dying to get cracking on something that floats. I'd like to do a raised panel deck house with a lot of antique styling, in cherry laminated over cedar. Some white oak in the structural areas.

    If you look carefully you can see the box joints at the corners, ( hand cut, no filler ) the raised panel is also done by hand ( IE hand held tools ) Rather than on a big shaper. The girl just happened to be hanging out.


    This ones a slightly larger project I did a few years ago. Still its all hand cut raised panel, there's an outside corner panel that you don't see to often and the whole thing puzzles together with the only metal fasteners being the deck planking screws and two bolts in the railings. Take the two bolts out and the whole thing except for the deck come apart.




    My summer project ( rebuilding my old truck is just about done and I'm just itching to start something new.

    Oh and thanks for the tip that your new design is up, I've been kinda waiting to see that ever since you first mentioned it


    Hey Richard
    your links not coming up for some reason.
  9. sabahcat
    Joined: Dec 2008
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    sabahcat Senior Member

  10. WestVanHan
    Joined: Aug 2009
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    WestVanHan Not a Senior Member

    That's a darn nice staircase and deck,I'd feel bad walking on it and scratching it all up....

    Anyways nice ideas with the cat-I guess you've looked at commercial cats to see how they fit the cabins in.
  11. Boston

    Boston Previous Member

    I got the HP off a prop calculator, basically I input 1/2 the weight and the waterline length to get the power and prop needed to hit displacement speed. Came up to 12 hp or something like that. So I tripled it and thought that would work out OK. Oh and nice cat you posted, looks well proportioned and economical. No wood work but still it looks good. All in all I'd most likely use a Mercedes 300D diesel engine which runs at about 80hp. Maybe run one central prop but more likely two v drives.

    And no West I've been pretty lazy about looking up other cats. Just kinda seeing what I come up with. I was really just trying to come up with a cruising cat that was blue water capable and yet efficient for the inside passage.
  12. Boston

    Boston Previous Member

    My rough calc for displacement was based on using x number of sheets of ply. I averaged out all the ply in the boat to 5/8 which is supposed to weight in at 44lbs a sheet http://www.boulterplywood.com/MarinePlywood_4.htm. I estimated high on the number of sheets and went with 100 or 4400 lbs. then I doubled that to estimate the weight of the rough hull. Then doubled it again to estimate the weight of finish and mechanical, fuel and stores. Came up with about 17,000 lbs. Then I wanted wide hulls so I could effectively use the space. Which resulted in a shallow draft. Something that tends to be easily driven. Then I gave it lots of reserve buoyancy for open water work and thats pretty much what determined the shape of the hulls. Oh that and Bolger like simplicity with maybe a flair forward at the sheer line. I though 17,000 was a realistic estimate so I went with it based on what weights I've seen for other similar length boats. If its heavy, it might actually give it a more comfortable motion. Which is one reason I kept the overall beam down. So it rides a smaller swell without that crazy catamaran double roll thing that can get some folks feeling pretty ill.

    I'll do a few more sketch's tonight and see if I can't work out the sections and how they might best fit together.
  13. sabahcat
    Joined: Dec 2008
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    sabahcat Senior Member

    You dont think you're getting a bit carried away at 5/8th?

    Even a cat this large only uses predominately 3/8th and 1/2in
    with lots of 3/16th and 1/4 as well
  14. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Big flat panels either have to be thick or have a lot of reinforcement. Some extra curvature and a vee forward would allow lighter scantlings.

  15. Boston

    Boston Previous Member

    I was aiming for heaviest case scenario. And I'm still working on the structural details. Another nice cat there tho. A bit shy on head room but looks solid. Damn thats a big boat. 50+' is a lot more boat than I could afford, but at 50 its probably got plenty of head room. And you say its built out of primarily thin sheets eh. Crazy. I was kinda thinking of really beefing up the bottom on my 35 design so it could be beached if needed without holing it. I'm pretty hip to the strength characteristics of ply and it doesn't always point load real well. So ya Gonzo I was thinking of a long arched shape on the bottom. but no rocker side to side or v form. Kinda like a sharpie hull. Scaling it down from 40 to 35 left me with 4' 4 1/2' hulls, I'd probably take that to 4' and just go with two layers of 3/4 ply and a 1/4 veneer of white oak. Kinda heavy but might take a liking and keep on ticking. Was thinking the sides of the hulls at 3/4 and the undercarriage at 3/4. And ya I'd put an arch on the sides of the hulls just as you suggest. Should be able to take a beating with those scantlings come up fine. Topsides at 1/2 and roof at 3/8 if I don't go with the upper deck, 5/8 if I do. Interior bulkheads 1/2 with white oak stringers, chines and backing for the bulkheads. seemed like 5/8 was a nice average for the lot.

    Clamps and deck house can all be cedar core whatever, mostly cherry. with raised panel over a sandwiched ply wanes coat, Not sure what to do with the ceiling and the floor yet but some light material with a nice light finish to offset the darker cherry of the wall structures. Rail and trim also of something with a light tone.

    I'm still way early in the game but its a fun exorcise
    appreciate all the suggestions by the way, I wasn't sure what kinda reception the boat would get.
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