35' cat concept for the inside passage.

Fuel, water and black-water-waste from here http://www.turtlepac.com/en/products/super-deck-tanks.html and is what I am considering fitting. easier on the structure and lighter when empty...

 

Controversial statement... Why do you think ply would be better? I happened to like ply, but wouldn't it be heavier?

 

Could use thinner ply than Duflex, Yes a weight penalty, but with grp on either side and longitudinal re-inforcing in the form of "shelving" which will be needed anyway and facia with holes for access, similar to present boat structure will be box girders everywhere... The designs by http://easycatamarans.com/index.htm Peter Snell use "grp covered/sealed ply" other links to catamaran designs etc can be found here http://www.puremajek.com/catamaran-designers.html

 

How much fuel does a small power cat need for 500 mile range at 8 or 10 knots ?

 

Oh, nothing then that a little helium in the hulls can't fix...

 

I always get confused by US glass weights. Metric is so much simpler

Sheathing a hull I'd use 8oz glass. Sheathing decks 6oz is OK. I'd use 9mm ply for the hulls and decks. 12mm for the underside of bridgedeck.

I suggested moving everything forward because, like all the posters here, I think you will be too stern heavy. I suggested 6T, not 6000lbs, as a total cruising displacement

You should use between 5 - 10mpg at 8-10 knots

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

So 8oz biax cloth is a sufficient outside skin...and what inside ?

 

I was talking about sheathing the ply, not using it as a core material

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Three quickies

If you want to use the boat as a charter boat you'd better start checking the USCG rules. It's unlikely they will accept a home designed boat

Turbocad offer a completely free 2D CAD program. version 4 LE

Forget about sailing in the PNW. And even if you use a kite instead of real sails you'll still need big rudders and some way to stop leeway

As someone else posted, no boat is perfect. So don't try to turn a Inside Passage whale watching charter boat into an ocean cruiser or a kite board

Before you get too far in your design I suggest you take a ferry north to Juneau from Prince Rupert or Bellingham, and try some kiteboarding.

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

thats what I was thinking to Richard, just a layer on the outside, and yes I understood 6 tons as well. Reason I mention the

( thats with the previous cloth thickness though. )

is because I'm estimating my finish weight to be roughly twice what my shell weight might be. So if I aim for 3 tons on the shell I can be relatively sure I'm going to come in under 6 tons all up. Between mechanical, safety, and all the other stuff I might want to carry as well as at least 1 ton of fuel if not more.

OH well lots of new posts and I've gotta run. Imagine me doing a structural inspection on a church. Ok then I guess this contractors license is coming in handy for something. I'll have to go over all when I get back.

If I have to do the COG analysis by hand then so be it but all in all I'll just eliminate sheets that are equidistant from the COB and see whats left over rather than figure out the moment of every offsetting piece. Seems like it would be easier that way. If the engine weighs in at ~1000 lbs or two engined at ~500 each and the shell is even 15% heavy aft then 0.15 x 4681lbs = ~700 lbs at the extreme, which means that 1400lbs of something would be needed at 50% forward of the center of buoyancy. Hmmmmm, I better not be more than 15% heavy aft. Even at that I could still balance the thing out tho. I can see where its far better not to be out of balance to much on any one thing, might give it an odd motion or something.

Anyway gotta run,
cheers
B

 

Robert Perry once described summer winds up here as 3 knots gusting to 0.

 

On my boat 2 engines at 3 litres / hour each at cruise, range is significant and on a passage at 6 knots on one engine some 3000 N miles... theoretically, but boredom will surely seek both engines and 10 knots at times...

 

Bos. consider what I did. I felt I could not afford 2 engines +++ if I build the Bearcat. Solution was to design a center sponson the same width as the outer ones but only running forward about 12" before dying upward to the top of the tunnel. Whether you use outboards or inboards this will work for directing the nesessary water to the props.
Great fuel savings, no loss of speed-just use more HP. Just have a good kicker engine,
high thrust, for emergencies. My 2 bits. P.S. this will add floatation if you are rear heavy.

 

The centre sponson is sitting how far below the waterline ?

 

Well that's the basic solution I have used on my Skoota 20 and 24 powercats. certainly you don't want to use a central engine unless you have a mini hull or fairing in front of it.

But on a larger boat I don't think it is a good idea because twin engines are so much more maneuverable, and also of course make the boat safer. (Although many powerboaters seem to be happy with only one engine)

People often run their engine at anchor to charge batteries. And it is then better to run a small engine rather than a large one.

I also don't think a kicker outboard will be a good emergency solution on a 35ft 6T powercat. In fact I wonder how many people have tried motoring with their kicker engine in bad weather.

Richard Woods of Woods Designs

www.sailingcatamarans.com