Building a cat using pontoon floats - SailNet Community
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post #1 of 15 Old 04-05-2011 Thread Starter
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Building a cat using pontoon floats

I have a 26' C& C Yacht and also an old 22' Macgregor (that has little value and I have put too much into it!!). I would like to have a cat, but I sail on a large lake (Lake Kerr, which strattles the NC and Virginia border . . . 50,000 acres), and am not interested in living quarters on the boat. I just want something that has a flat deck for people to sit on (no furniture) and has sails. Maybe a small 10hp motor.

I have read a few articles about this, and most of what I have heard is the pontoon boat will not handle the downward stress of the mast and they are not wide enough to keep from getting knocked down.

I plan on basically only using the floats and designing a craft that has a width of 60% the length (probably 24' by 15') Using a solid beam for the mast with aft to stern (about 4 feet each direction) suport to assist in spreading the load. I also would build a "dolphin striker" under the mast to help distribute the load.

I probably would start with an adjustable dagger board and a twin rudder system to allow the small motor to stay on center line.

I plan on making the craft so it will fold in a gull wing formation to trailer.

Is there any reason that this would not work? At lest in up to moderate winds, say pu to 20 knots on a lake.

Thanks,

Jerry
Zebulon, NC
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post #2 of 15 Old 04-05-2011
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Theoretically you can sail just about anything I guess. And I have to say, your plan sounds ambitious - and just a bit crazy.

Take pics as you go dude! This is going to be one unique boat!

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post #3 of 15 Old 04-05-2011
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Having dabbled in small boat building a bit, there are three things I have learned that may help you out...

1. It's easy to design a boat that will float and function, lots of simple / crazy designs work, if not work well. Heck, I rowed a log down a shallow river before. Poor design, but memorable If your main goal is to have fun building it, putter around a bit and have people go "hey, look at that!" It's not to hard, just consider the worst case scenarios and make sure you are not putting yourself or others in danger.

2. It's very hard to design a boat that works well. Even slight differences in angles can drastically change the performance characteristics of a boat. This is why good designers make good boats. If you want to spend a lot of time and money and have a boat that sails well, look into building from plans. (I don't think this is your goal, just say'in.)

3. Some times the "better" boat (the one you enjoy more) is the odd, cheap, poor performing but interesting idea boat that you nail together and play with for a year before it completely falls apart.

Just be sure to think through the bad "what ifs" first. What if it turtles, can anyone get stuck underneath? Is the water warm enough to be in it for a while if there is a problem? can you swim to shore if needed? Can someone else be along with another boat the first few times out for safety, until you figure out what the boat will do?

Sounds like a fun project, if you go through with it, post some pics!

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post #4 of 15 Old 04-05-2011
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The pontoon idea is great. The small motor idea is great. The sail idea sounds like nothing but trouble.

Hey, maybe instead of a single mast, how about a sunfish rig at each corner of the vessel. That'll work.
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post #5 of 15 Old 04-05-2011
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Sounds like you need to build a Wharram --
James Wharram Designs -Home of the self-build Catamaran.
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post #6 of 15 Old 04-05-2011
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Thinking about this more, I think a nice big loose footed, square rigged sail on the front would work well for a starter. It would obviously only be a down wind rig, but it would be a nice, safe-ish way to start, and keep your deck nice and free. Add a few cannons, and you got yourself a themed party boat!

Small sail on each corner?! I actually like that idea, interesting! Could work down wind (wing and wing style) or broad reaching. Hmm...

I think we are straying into Bolger design territory here. There was a brilliant designer doing odd and crazy things that actually worked. If you want some inspiration for alternative boat designs, take a look at his work. Here are a few links with some pics, you can google him to find more, plans, and books.

DE7
https://picasaweb.google.com/Pemaqui...fIndianSummer#
Phil Bolger - Wikipedia, the free encyclopedia

I've seen a boat like the Indian Summer linked to above, now there's a boat that makes you go "huh?" when you see it in person. But the owners absolutely loved it.

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post #7 of 15 Old 04-05-2011 Thread Starter
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Thanks for all the comments! And some of you may be right, I just like being outside the box a bit. And Islanderguy, you are correct, I have thought of the things you mention. First, a float on the mast to keep in from becoming a turtle, and even some thought to a controlled knockdown close to shore to see what it would take to right the boat if it did go over. No cavities in the boat to get stuck in. I do have a chase boat to try it out with. No motor or fuel on board and only essential sailing personnel on board in proper safety gear to find out how it will sail.

There are no plans out there for a boat of this kind. My plan is to use the parts off my Mac 22 and design the forestay and shrouds, etc to match the angles and heights of the Mac 22. The Mac, of course, has a 650 centerboard which I would not want on this craft. I plan to mimic the rudder of the Mac, only have two of them. The dagger board is the real problem, and I think I will design it so I can easily move it fore and aft and also up and down, and even try several sizes to see what works. I do know that many cats that do not have a centerboard are designed that way for safety. They get a lot of leeway, but will not knock down easily because the leeway takes to pressure off.

Tacking or running close hauled is the only problem I see, and I might find out that is what the motor is for!! Be like drift fishing . . . run up wind, pull the sails and go back!!

I would, however, like to know if anyone out there would have any input as to why the pontoon floats would not work as well as the hulls of a small cat. Other than the fact of there is no storage space and the cat hulls may have more weight. And weight is no problem, it is easy to add weight. Of course performance could then be an issue. It would be quite easy to add water ballast when running up wind to keep the boat from heeling. How fast you could add the water would be the issue.

Again thanks for the thoughts.

Jerry
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post #8 of 15 Old 04-05-2011
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Why not get another Mac 22 ,they are cheep and strap them together with a platform, then you would have your Cat with side by side sails and two rudders, then the motor would be in the middle. Me I would spend my time and money on the C&C and then go real sailing.

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post #9 of 15 Old 04-05-2011 Thread Starter
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Overbored . . . sad to say I did think of that!!

And the C&C is in great shape! Except it is old and ugly and beat up . . . but we love her!! That is why she is called "Audacity"
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post #10 of 15 Old 04-05-2011
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I'd say make a sailable float, if you can get 24 foot pontoons, deck it over with 80 16 foot 2X4s would be better if you could get 3 pontoons one down the middle to help suport the mast, at least a beam in the middle to tie all the 2X4s together, I've thought of simalar using 55 gallon drums, insteat of a centerboard think about lee boards,

Then later if it all work well you could build up some arc beams and put a tramp in it and sail it fast. then build up a pair of foil hulls and and

bottom line go for it, sound fun
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