35' cat concept for the inside passage.

Geezus, you really haven't looked at many cats have you?
They mostly all have something similar, its called a back beam, designed to hold the boat together and balance the beers on, not deflect waves.

 

If you build in plywood covered in glass/epoxy, theres no reason you cant build a 10m displacement cat with a design displacement under 10,000lbs...

Heres another version of similar concept to the chamerlin cat from post #16...


2X60hp outboards for top speed of 18.7kts, cruise @ 15kts, 1 engine only = 15kts...

Design displacement is 4135kgs, empty weight = 3000kgs. This boat could be built even lighter for more payload btw...

 

Actually, I prefer Bostons original sketch. Its more Houseboat and looks to be a very pleasant chug ,chug, lets enjoy life platform.

Everyone has a speedy, stylized, high tec composite cat these days... The French mass produce them. I say be unique and build an elegant, form compliments function, cat houseboat

 

im not suggesting a change in style, merely offering an example - more so from a performance perspective. You could still drop a boxy, large volume cabin "as ugly as you care to make it roomaran", on a similar hull form, made from plywood, to get similar performance...

The key is length to displacement ratio, and waterline length to beam ratio... if you dont get these right, then you might aswell build a monohull...

So in that, i mean build the thing LIGHT... then put LIGHT furniture in it, and think carefully about what really NEEDS to go in it - so that you can MINIMIZE WEIGHT even further... Then you can make the hull waterline thinner for better efficiency if displacement is less, so then you can reduce the size of the engines and the scantlings furthermore because its LIGHTER... all this makes it cheaper if its lighter... THEN the boat would actually cruise reasonably fast and do it on the smell of an oily rag, so running costs are cheaper... all because its lighter... you get the drift?

A cat this size would comfortably be built from 8-9mm okume ply, thats 3/8" i think in imperial, with 600GSM biax glass/epoxy laminate for the hull and decks... The engines would only need to be 50hp each side for a 15kt cruise provided you keep the weight under 10000lbs... the beam to length ratio of the hulls waterline i would aim for around 13:1, so around 800mm wide at the waterline, You probably wanted more volume than this provides, but you can flare them above this to get more volume if you need it.
The price of fuel these days, efficiency is important IMHO...
Ill leave you with this --> http://www.patentgenius.com/patent/4079688.html
One of the best peices of info ive found on the net... ive modelled various hull shapes in michlet and the minimum resistance hull described in the patent was in full agreeance with the results from michlet... its also remarkably similar to the most efficient catamarans on the planet today ie the americas cup cats and tri`s...

 

yah I'm not into the wanna be spaceship looking boats at all. Gotta be a way to justify function with form and come up with something that doesn't look like ET is about to jump out of it.

And No Saba I never really did give cats much consideration, there just butt ugly and so damn expensive to park. I'd end up living on a hook if I went the cat direction. I like the advantages cats offer, but seldom do I see one that has much appeal, for me at least, obviously lots of people like them and for some water they are the perfect choice. The Caribbean for instance, where shallow draft is so important.

at 13:1 or even 10:1 The usable space in the hulls reduces to zilch, Means I'd have to bring the cabins up on deck or jam them under the pilot station. Not very appealing from a comfort point of view. I could scale it back up to 40", keep the 4' beam hulls and at least be at 10:1. But considering the laps in the ply it would take another full 8' sheet all the way around. That and I'd want to be a few inches under 40 cause every ten seems to be a price hike at the marina.

Anyway lots of new information to incorporate,

Cheers
B

oh and one thing I've not mentioned yet is the fuel, I run my truck on used motor oil, worked so well that I decided to restore the POS. Its what delayed my starting a boat earlier in the year. And one reason I've got all this extra wood laying around cause I'd started collecting stuff. I get the used oil (WMO) not waste vegetable oil (WVO) free so its better for me to run with huge tanks, suffer the weight issues and be running on free fuel. I was thinking of increasing the fuel tankage to 600 gallons/two tons, tripling the range and just fueling off my big 200 g tank in the truck

speaking of which this is the engine as I was tuning it to run on nothing but waste motor oil, its an International 7.3 IDI. This engine is to heavy for the boat tho, weighs in at about a half ton.

http://s29.photobucket.com/albums/c262/bostonpyramidbuilder/?action=view&current=DSCN0257.mp4

The reason I consider the Mercedes 300D engine as a candidate to power the boat is that its easily convertible to run on alternative fuels and as long as the engine I start with has good rings and seals in ti to begin with I can always get it to pass emissions, I hope And it weighs about half what the 7.3 does.



OK so I skinny'd the hulls down to 3'6"
The new displacement target is 13,440
Means I have to start over on the floor plan and raise the double beds and loose some head room over them, but I'm pretty sure I can still make it look like something
I realize that lite is better but I would want to do a nice finish on this thing. Specially the interior. Even if it means I end up using wicker furniture from Pier One or something.

I've decided to leave off the roof top deck, saves weight, and lighten up the ply roof. Include a nice wood skylight instead.

 

Hmmm, i think a "no compromise" approach is required for decent performance... If you reduce the displacement a little and skinny the hulls a little, all you will achieve is a boat with less volume and still poor performance, so you might aswell keep the fat hulls and fat displacement and at least keep it more comfortable...

There are ways of keeping the waterline beam skinny, still with good volume in the hulls tho. Here is an example of it done very well, --> http://www.lebreton-yachts.com/gallery-and-video.php
Dont pay attention to the fact its a sailing boat etc, just look at the hull form... You really have to look carefully through all the photos to see how its done, but the waterline length/beam ratio is quite high and this cat has excellent performance capable of sailing equal with the wind speed which means the hull has very low resistance,... yet the hulls have enough living volume inside them to not require a bridgedeck for living spaces. The method in which its done is increasing the flare in the stern and on the inside of the midship hull where it forms a fillet with the bridgedeck.

So there are ways of solving problems, sometimes it requires a shuffling of the arrangment to make it work however... Are you considering introducing some curvature in the hulls for that "egg shell" effect for increasing rigidity and strength? If you keep them flat you will need more in the way of stiffeners and stringers etc which will eat up some of your accomodation space...

 

People tend to be wider at shoulder level than lower down. So a flared hull makes sense as it fit the body well. Not only that but it results in a more seakindly motion

I suggested 6T disp because I understood that Boston wanted a displacement cruiser, would use a heavy engine and wanted to fit it out in wood

So I think what he is sketching does meet his own SOR. Incidentally I have seen a very similar boat to his sketch cruising the Bahamas last winter (photos are on a different computer to this one or I'd post them)

I think a view of Boston's interior layout would stimulate some discussion (hint)

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Are heres more to prove its being done lightweight and effectively in plywood/epoxy by Kurt Hughes in this 50fter example...





I dare say the hulls are built by cylinder molding the ply sheets... he claims 10kts from 17hp per side...

 

Just getting to this thread and it looks to be an interesting one (must go back and read from page 1)...

However, just wanted to pipe in quick and say that I wouldn't consider any of those production French cats "speedy"

 

That KH 50 above is a fantastic looking design. If I was going power cat, I would be very drawn to it. His power cats are getting very good speeds (and fuel efficiency).

Boston:

I have a real world data point for you. I had a 34' catamaran, 15' beam, 11,000lbs displacement with a pair of brand new Yanmar 3YM30's.

Top speed was 8 knots, really pushing it at 3400RPM BOTH ENGINES (1.5 gallons per hour EACH ENGINE, or 3 gallons an hour total).

This boat would do 6 knots with a single 3YM30 engine at 3200RPM (1.5 gallons per hour)

The advice has already been given, but definitely keep weight in mind if building a cat. Any efficiency or benefit you would hope to get from a cat comes from lower total weight/displacement. If you load it up, it'll be very disappointing.

I should point out that the cat I mention above in this post was one of the slowest dogs out there at those figures. You want to do better than that.

Also, as was mentioned, just make the bilge/bottom of the boat beefy for drying out. The topsides don't matter in that case. If you need to stay warm, use *insulation* on the topsides - lightweight, warm, foam insulation. It'll do a better job than thick plywood will anyway.

If you want stiffness and want to go with thinner plywood to get a good (lighter) boat, definitely put a skin of light glass outside to keep the wood in good shape. Also, you can use wooden stringers (stiffness). They're not so hard to put in. Notch out the bulkheads and slide them in from the stern while it's still open. Slide in full length ones the size of the entire boat and epoxy them right in place. It would take a couple days to do those.


And... a bit of a moon machine for you, so ignore the styling, but here is a 35' power cat I saw on Kurt's site:

http://multihulldesigns.com/designs_stock/32cat.html

Check out the stats...

Length overall: 35'-0" (10.67 m)
Beam: 12'-2" (3.69 m)
Draft: 1'-3" (0.381 m)
Displacement: 4,872 lb (2,210 kg)

And he has some reading about his power cats - worth a look.

http://multihulldesigns.com/pdf/powercatslt.pdf

 

first try at a floor plan for this thing.



There is a area open through the floor to the hulls right were the double beds are surrounded by a wood rail. Should make for some good ventilation. All three of the big chairs swivel, the one on the left is could be the pilots station or one of the two smaller chairs could be the pilot station. Still working on it, but if its going to make any money as a eco tour boat its got to provide a couple with some nice seating forward. So I was thinking of maybe a remote pilot station, that could do either location. Put in a wheel somewhere it looks good. Its a little tight getting in and out of the chairs but they swivel 360° so its not so bad if you pull you legs up a little and spin back around.

the rectangle behind the two forward seats is a gas fire place an entertainment center, put that in for Tad who I know just hates that kinda thing . There will be a foot rest and flip up table off the entertainment center as well. The couch can extend all the way over to the rail, I just didn't fix that before I posted. I'm slow and Richard seemed like he was getting anxious .

I've got about half the area in the hulls accounted for and I'm kinda struggling to figure out how to access the other areas. I only drew in one engine, in a space large enough to at least be able to work on it. Also there is a big access hatch from the outside aft deck area that would accommodate removing and/or replacing the engine without tearing the whole boat apart. I was thinking that the beds could swivel up and off to the side on a gimble like thing so I'd have access to the spaces opposite there intended access points. Might work, might not but I'll draw up something and show you what I mean.

Its only got one bath in this configuration. There's a vanity desk where you could have a computer terminal just forward of the galley. Or it could just be a storage area. The galley is centered around a 3x3 standing area. I'd wrap the upper cabinetry around that corner and balance it with the sink but I would really hate to crack my head on the corner that would leave just at the sink. Besides its always nice to have a window over the sink. I'm not so thrilled with there only being one window in the entire aft outside wall, and that in the door. Might have to change that.

I could push the aft wall back two feet but then its kinda tough to barbecue anything in the 3' that's left over. So still thinking about that.

Anyway thats what I've got so far. Its miles from being an acceptable product but its again, a start.

Hey just out of curiosity if your on a mooring do they charge by the foot still or just something for the mooring. I'd never be able to afford to park it at the dock for long anyway and if the mooring fee is standard instead of by the foot then it might be posible to afford something a little longer. I notice most of the examples folks show me ( that last was really nice by the way ) are in the 50' range.

 

Man you guys come up with some bomb suggestions, that KH 50 is really slick. So is that KH 44 someone pictured earlier. Kinda makes me want to start pricing just to remind me its probably out of the question.

So whats the deal with mooring fees. Are they by the foot or by the buoy

I might be able to build the hull, at 100 sheets for 5700, including resin and cloth. Which means by my previous criteria I could get it down to 11,400. But that was a very rough measuring system so I bet I could skinny it up a lot. Thing is I don't want plain epoxy paint walls inside or out. The hulls I'd insulate with reflectix in most areas, With minimal raised panel in the stairway, hall, bed, bath, It would save weight to fake flat paneling with just ply styles and rails in those areas. On the main deck I'd want raised panel veneer over ply, so the ply could be pretty thin since its getting a lot of support from the styles ( virtical pieces in a raised panel group. ) Fuel is killer, I want some serious tanks in this thing. 600 gallons seems about right. But from what I'm hearing that might not work out so well.

how about a new target weight of say 9,000 lbs dry. or is that still to much.

 

Ok i can see a couple problems already... what kind of final drive are you expecting to use, a stern drive? And where are the fuel tanks located and how much fuel do they hold? Im guessing right in front of the engines? Reason i ask is that with the engines mounted near the transom, your going to struggle with getting the bouyancy right, its going to sit bum down with all that weight so close to the stern... Every efficient diesel driven displacement cat i can think of, have the engines and fuel tanks mounted closer to midships to deal with this bouyancy problem, keep the boat in trim whilst underway and improve the shaft angle to the prop...

Finding the space in cats isnt easy is it theres very few arrangements that work well and all of them have already been done in one way or another...

You seem like a pretty handy guy, old school but able none the less, im sure you could learn how to draw in freeship instead of on paper, id highly recommend giving it a go as 3 dimensional drawing will allow you the freedom of more complex shapes and allows you easily measure the spaces etc....

 

fuel tanks are located center of buoyancy, There is only one engine and its not all the way aft but its close. Twin screws tho. There's a twisted logic to it, just read back a bit and you'll figure it out. I could put the engine on the other side, basically under the kitchen sink but then access to its an issue and removing its a real issue. But that would move it about 2 feet forward. Right now its not directly under the access hatch, but forward right behind the door. I figured I'd balance it out somehow.

oh and that KH 50 looks spectacular on the outside, not so much on the inside. And $6500 choke gasp, yikes.

 

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