Why so many unnecessary cabins and heads?

[BigCat]

"I wonder if it would be feasible to completely separate the engines electrics from the rest of the vessel (i.e. separate earth plate, extra alternator, batt etc)?"

Separate grounds is considered dangerous, due to both shock potential and electrolysis. The rest is feasible. This is how I am setting up 'BigCat.' I am leaving the stock 12 volt electrical systems on the engines to run the starting systems (one per engine,) and attaching extra high capacity alternators ( Amptech L135/24 Alternators, 135A, 24V ) for the 'house' system.

In fact, the voltages of the three systems are different. The starting batteries are 'starting' types, and the house batteries may be AGM--I have recently heard that Lifeline claims that AGM batteries must be fully charged every time you charge them, or they lose capacity! I spoke with their rep at the Seattle Boat Show about 6 months ago, and got a 'weasel' answer about this. Maybe I'll go with industrial batteries (forklift / golfcart type) and water-saver caps for that reason.

All advice I have received, and I have gotten lots, is that these three electrical systems must be connected at the ground / electrolysis / lightning bonding system - it doesn't matter if the voltages of the systems are different.

I'm not sure why all the concern about lacking engines is all about on this thread. Aren't we discussing sailboats? So sail, if you have no engines, or anchor, if you are in shallow water with no wind. The wind may go away, occasionally, but the wind always comes back, you know- I've been there and done that with no problems.

[BigCat]

gosstyla- I, too, believe in 'little' big cats. You should check out my 'BigCat' on my website. It has many similarities with your concept, except it isn't narrow. The beam you want will result in an unusually narrow cat, so you better make sure it has less sail area than other cats of its length. Personally, I'd use the usual 1.9 to 1 beam length ratio.

I have been thinking lately that Derek Kelsall's idea of putting all the accomodations on the bridgedeck is a good idea, if you don't need much in the way of accomodations. Then narrow hulls would be no problem. You could make such a cat rather like a tri, with lower hulls and connector beams that go on top of the hulls. I'd keep the bows high, though, to help prevent pitchpoling. If you wanted inboard engines, you could use Steyr diesels, if you don't want to do a lot of motoring.

[gosstyla]

Originally Posted by BigCat

gosstyla- I, too, believe in 'little' big cats. You should check out my 'BigCat' on my website. It has many similarities with your concept, except it isn't narrow. The beam you want will result in an unusually narrow cat, so you better make sure it has less sail area than other cats of its length. Personally, I'd use the usual 1.9 to 1 beam length ratio.....

As the length increases the beam length ratio can safely decrease. Also, I'm splitting my sail area between two masts keeping the CE lower.

[BigCat]

Originally Posted by gosstyla

As the length increases the beam length ratio can safely decrease. Also, I'm splitting my sail area between two masts keeping the CE lower.

Hi, Gosstyla, I understand all that, as I have done the calculations. I posted how to do the calculations on the 'righting a cat' thread a couple of weeks ago. Even so, you will find that you will have to have less sail area that other cats the same length. There is a footnote at the bottom of my web page about this calculation, as well. There is also a link to a Dave Gerr article about cat stability at the bottom of my website.

[BigCat]

[quote=BigCat;175334]"I wonder if it would be feasible to completely separate the engines electrics from the rest of the vessel (i.e. separate earth plate, extra alternator, batt etc)?"

"Separate grounds is considered dangerous, due to both shock potential and electrolysis." I forgot to mention the danger of lightning side strikes between the two systems--a very compelling reason.

[44'cruisingcat]

Originally Posted by BigCat

I have been thinking lately that Derek Kelsall's idea of putting all the accomodations on the bridgedeck is a good idea, if you don't need much in the way of accomodations. Then narrow hulls would be no problem. You could make such a cat rather like a tri, with lower hulls and connector beams that go on top of the hulls. I'd keep the bows high, though, to help prevent pitchpoling. If you wanted inboard engines, you could use Steyr diesels, if you don't want to do a lot of motoring.

What you're talking about is a podcat. There are quite a few of them here in Australia. Possibly the best known of them would be Raw Nerve, which has won several Brisbane-Gladstone races. Raw Nerve is a racing boat, but there are also cruising boats, Bob Burgess' designed and built AMA 2 and B52 are a couple of examples.

Bob Oram has a design for a 50 footer and a 46 footer, which he is going to build for himself.

You get less space per length than a full bridgedeck design, the accomodation "pod" is much shorter than the hulls, and the layout inside is more akin to a mono, but as Bob puts it, you get "the biggest footprint for the least money"

They can be very fast boats.

[BigCat]

I'm thinking of something midway between a podcat and a standard model-with a bigger deck house than an 'el strippo' racing boat, for 'fast cruising,' but not much in the hulls, except for engine rooms, some storage, and tanks.

[BigCat]

Originally Posted by gosstyla

As the length increases the beam length ratio can safely decrease. Also, I'm splitting my sail area between two masts keeping the CE lower.

Hi, Gosstyla- You got me thinking with your interest in very narrow hulls. Here is a fast, skinny hull version of the BigCat 65. Just for the heck of it, I gave it a tandem (bi-plane, twin) rig using marconi sails. Also, I made it shoal draft, since a performance boat should have daggerboards. The hulls are only 6' wide, and only 4' wide at the waterline. Zoom, Zoom, Zoom! As Bill Lee used to say, light is fast, fast is fun! It's still a cruising boat, though. See:

http://www.dunnanddunnrealtors.com/catamaran88.jpg

[exfishnz]

Originally Posted by BigCat

Separate grounds is considered dangerous, due to both shock potential and electrolysis. The rest is feasible. This is how I am setting up 'BigCat.' I am leaving the stock 12 volt electrical systems on the engines to run the starting systems (one per engine,) and attaching extra high capacity alternators ( Amptech L135/24 Alternators, 135A, 24V ) for the 'house' system.

If you're refering to "stray currents" etc then that does make sense.

The extra spares sound like a better option. EFI doesn't seem to come into use on some diesels until you hit 100+ hp continuous (re: lightning damage through complete electrical systems).

Re: alternators. Electrodyne has brushless 24v models that go as high as 300amps.

http://www.electrodyne.com

[BigCat]

Originally Posted by exfishnz

If you're refering to "stray currents" etc then that does make sense.

The extra spares sound like a better option. EFI doesn't seem to come into use on some diesels until you hit 100+ hp continuous (re: lightning damage through complete electrical systems).

Re: alternators. Electrodyne has brushless 24v models that go as high as 300amps.

http://www.electrodyne.com

Hi, Exfishnz -

I sent them an e-mail asking if you could use them with a Balmar controller which varies the fields so as to balance the charging of two alternators working simultaneously and never got an answer. I do know that they are very expensive. I once replaced the brushes on an old car's alternator. It wasn't that bad a job. It takes a lot of hours to wear out the brushes on an alternator. I have had failure of the rectifiers on a Hitachi alternator on a Yanmar. I don't think we blew them by turning of the battery switch, but I am installing Zap Stops on the boat I am building now.

Another issue with alternator size is charging rate-you need to make sure that your batteries will accept the output of your alternators. Conventional batteries are limited that way, and there seems to be an issue with AGMs about loss of capacity if you don't fully charge them when you charge.

[gosstyla]

Big Cat

That's a little more in line with what I intend but still way too heavy. I prefer the John Shuttleworth/Kurt Hughes flared hulls. Designs that have specs and many aspects I like are:
Concept 63 by Chris White
Gunboat 66
Waterline 1750 by Schionning
However they all have may more "house" than I want.
Probably a Conser 47 scaled up to 65ft gets close.

Sorry for the thread drift.

[BigCat]

Originally Posted by gosstyla

Big Cat

That's a little more in line with what I intend but still way too heavy. I prefer the John Shuttleworth/Kurt Hughes flared hulls. Designs that have specs and many aspects I like are:
Concept 63 by Chris White
Gunboat 66
Waterline 1750 by Schionning
However they all have may more "house" than I want.
Probably a Conser 47 scaled up to 65ft gets close.

Sorry for the thread drift.

Hi, Gosstyla - Those boats would have more speed potential, but have, from my point of view, several drawbacks. A Conser 47 capsized while carrying passengers for hire in Hawaii, just off Lanai- on a gusty day in which 30 odd knots gusted to, it is said, 60 knots. Be very careful with such light boats!

My design is more of a cruising design-but the 41,000 # is what I call voyaging trim-that is with food, water, and fuel for an ocean crossing for 10 people. In more ordinary use, it would probably usually weigh about 32,000# - still not in the ultra light class you mention, of course. My design is meant to have more payload, and be more 'bulletproof.' My years as a voyaging yachtie have left their mark.

My 'Sport' design is also meant to be dead easy for home building, as I don't have the patience for a year of long-boarding, nor the budget for epoxy / carbon / Kevlar / foam. It is my usual vinylester, quad e-glass, solid bottom, balsa elsewhere layup. The house as shown on my bridge deck can be modified to suit - the interior changed or made smaller. I think, as built, the boat could be home built for under $300,000. Theoretical hull speed = 35 knots - That's a lot of accommodations and boat speed for the price! So, in short, my design goals are: A cheaper price, a quicker build, more payload, and less probability of capsize that I think the lightest class of cruising catamarans offer.

For use in the tropics, I visualize the house as having only half bulkheads on the sides, with cloth / flexible clear plastic removable upper halves, like a dodger, and perhaps a cloth top, aft of the fwd cuddy and fwd. of the bridge deck heads. That would be fun.

(You're right about the thread drift, but I think the thread originator has been well answered by the explanation that there isn't all that much else that you can do with a catamaran's interior spaces. I started a more appropriate thread, but nobody has commented on it-)