Trying to design my own cat.

Actually a transom is a nice thing to have if you hang a little outboard on it. Most sailboats have a stern suitable for an outboard, the shape of it doesn't have to cause any drag and you don't have to sacrifice hull shape either. You just add the outboard since it is the secondary propulsion for emergencies. So what if the outboard isn't going to be as fast as it can.

One thing you may take into consideration regarding the amount of displacement your hulls have. Let's say you have 1000kg of total displacement. You load your stuff and the crew gets aboard, so let us say you have 400kg of added weight.

When you travel at speed (doesn't have to be fast) and you approach a wave, then the weight of you vessel as well as the added weight has a tendency to resist any sudden movement in any other direction than what it is going into already. The result is that the hull may dig into the aproaching wave, and what gets it out and over the wave is the force of the residual bouyancy the hulls may have.

If you travel down a wave and you now have to go up the next, if it is steep, the change in direction may double the weight of the whole boat, and cause the boat to sit in the water much deeper untill bouyancy has overcome the change in gravity. Don't know if this makes any sense. It is easier to catch a brick falling from two feet up than cathing one from ten feet up.

I have seen you mentioned the width it has to be to be towed legally, that is limited (I have the same problem). This leaves only two options, you could make the hulls higher... or you could make them longer... or a bit of both. Longer hulls are faster than short hulls - nothing to do with racing.

The length of a towed object is not as much limited. If it's very long it may require a longer car port or garage. I recently saw a small truck that was very long. Closer inspection I saw it was one they used to transport gliders in.. you know, those aeroplanes without engines Nobody thought it was funny, even longer vehicles exist. So towing a longer boat is not a problem.

Making the hulls high could cause a worsoning effect on pitchpolling. I always consider the worst case in both directions, this gives one a feel for where you are with what you have... from too high to too low, and then what am I prepared to live with.

A boat will always try to go right through a short choppy wave.

BTW, my hulls have flat bottoms for waling on also. It is terrible to walk on a round surface.

 

Hi Fanie.

I have already thought about that stuff and came to a compromise. The BWL is less than half the length. If the hulls were much longer I would be starting to get into weird proportions and I would be a bit concerned about handling problems. Also, I'm not sure how a long narrow tunnel would effect waves in there. Could be a nightmare.

I accept that 6 people on a boat my size is probably asking too much in choppy conditions. If I can have a boat that can take a big load on a lake, and take a smaller load in the chop, I can live with that. It doesn't have to be the perfect boat for all occasions, as long as I get some good adventures from it. As I said, I might have two boats.

After reading Gary Baigent's comment again about the stern turbulence, I think he was referring to the flow being faster on one side of the hull than the other. It would not be hard to make the underwater hull symmetrical and maybe it would be good to give it a knuckle...maybe not. Maybe I will have rocker and transom. Maybe not.

I think people are probably getting tired of this boat!!

Well...I've learnt a huge amount from all the generous people in this forum (including you)....and especially Rick Willoughby. I've also learnt a lot about California real estate, marine conditions, marina rules, beach rules, road rules etc etc etc. When I am there I will talk it through thoroughly with a naval architect and I will be able to understand what he is talking about.

 

The photos below show the cave, and the view from inside the cave that I lived in for 9 months when I was 'camping' in Sydney, about 8 years ago. I had run out of money, so technically I was homeless (without the whiskey bottle). However I could have gone back to NZ any time I liked, so I was not desperate. I just really enjoyed living there!
It's a tiny cave on a small cliff face at Tamarama beach. The nights were usually very hot, but I got used to it. I slept under a net to keep out the mosquitos that lived in rock pools around the cave. It was actually very comfortable.
I wasn't concerned about being stabbed because the area is quite safe.
Only my shampoo was stolen. Might have been another homeless dude!
I used public toilets and showers (cold) nearby.
After a while I started to make friends in Sydney, and could have moved out, but the cave gave me privacy and tranquility when I wanted it....so I kept sleeping there. Weird huh?
Every morning I would be woken up by the sun and I would roll out of my bed and jump straight into the ocean. The water was always warm. I felt like a cave man.
I ate food from christian charities. The food was the surplus food from restaurants - stuff that was made for the previous night. Absolutely delicious...and there was always too much!! Sydney-siders are extremely generous to the homeless. I never considered myself homeless, and at first I felt a bit guilty about eating the food....but after a couple of first class meals, my guilt disappeared. My stomach became judge and jury.

It was an interesting time. Australia has beautiful long summers. If I couldn't live in Los Angeles, Queensland was my second choice. I spent some time there too (in a house).

 

Not weird at all

Hello all,

Richard, for a day cat going narrow is not a problem. You have to be mindful of the considerable weight the crew will have and the large effect this will have on stability. This means you can go for a narrow cat and use crew weight.

In fact the second cat to sail around the world - World cat - was a CSK design and they were very thin in todays language but excellent boats. The early off the beach cats by CSK like Manu Kai were about 3:1 length to beam and fab boats.

In fact if an assymetric hull, thin, double ended cat is what you want you must read about Rudy Choy, Woody Brown and the CSK mob. They designed and sailed great cats starting over 50 years ago. So Richard - get onto Amazon and buy a copy of "Catamarans Offshore" by Rudy Choy. It will serve you very well. A slightly smaller Manu Kai may be a great boat for you and you will be doing your bit for keeping multihull history alive. In fact Rudy Choy and Woody Brown built a half size -19ft - version of Manu Kai - the first modern cat. You may be able to get lines for it on the Yahoo groups CSK forum.

Remember to stand on the shoulders of the giants

Phil

 

I can see why you had to roll out of bed

 

Phil, that's very interesting. Just when I thought I've gone as far as I can, something new (old) comes along. I'll check it out. Thanks.

 

Fanie, yeah there wasn't much headroom....always dry though, even during a couple of big storms. If I wanted headroom, I would sit on the boards you can see beside the bed. I would put a mirror and my shaving stuff on the ledge that hangs over (top of pic). A very well designed cave I had a few caves to choose from. That one was the best.

 

Something like the bridal suite He he... not much headroom. Sounds a bit like Richards cat

 

Richard, with my little beachcruising cat Slider, I designed a little more rocker into it than would be appropriate for a speed-oriented boat, but I needed to do it in order to get sufficient displacement from my fine hulls.

This means Slider is probably slower than she could be, but on the positive side, she tacks as easily as a monohull, and I attribute that at least partially to the rocker.

Ray

http://slidercat.com/blog/wordpress/

 

I have decided to buy a monohull. It will be better for dealing with California's choppy and light air conditions, with large payload, and easy to rig and slide onto a trailer. It will be big enough to take 8 adults and gear.
OK its going to heel, and it won't feel like a cat, and I won't beach it, but it will still be great fun to sail to Catalina island and survive the trip. Definitely don't want a big cat.

If I have the storage space, I will still get my 'canoe-cat' drawn up and built, but it will be for sheltered waters only. It will probably be about 25 ft long, 10 ft wide, double-ended, no rocker, symmetrical below the waterline, and a whole lot of fun.

This post is not exactly fascinating, but as the thread is about to die again, I thought I should just disclose my final final FINAL decision. Thanks to everyone for helping me get to it.

 

Richard what kind of trailerable monohull is going to be big enough to take 8 adults and their gear to Catalina?

Ray

http://slidercat.com/blog/wordpress/

 

something like a "Court 750" I raced in in WA....?

 

um....all the trailer sailors I've looked at so far have 5 or 6 berths. Is there one that can take 8 adults?? Or are there towing restrictions? Do I have to rip out all the furniture and throw the engine and anchor overboard?

PLEASE tell me there is a trailable monohull that has a decent payload.

 

On the 750, all the bunk cushions were removed and swags rolled out to sleep around the camp-fire, after it served its purpose as cooking place....

 

Hi Richard,
I've been catching up with your past posts and a thought occured to me. Correct me if I'm wrong whether these fit your requirments:
1. You want to be able to sleep at least two adults and a couple of munchkins.
2. Not too concerned about performance for six individuals mucking around in.

Howza bout a trailerable cat/tri switch hitter to suit one or the other?
Two hulls for point #1. A slip-on third hull for the gang on point #2.

With aluminum tubes already designed for in the plans for this cat, I'm sure you can attach a removable central pontoon...er hull for a party barge to leasurely cavort around in with a crew of six or seven. Here's a before and after shot of what a 'Duo900 Frankenpontoon' might look like that I've butchered up in a paint program for you. And here's a link to the designers website.
http://www.ikarus342000.com/DUO900page.htm

Regards,
Bob