Cat 22

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Johnston
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Cat 22

Post by Johnston »

I have been looking through some more bateau plans and the Cat 22 has caught my eye also. I am curious how these planing cats perform at intermediate speeds (where the Pangas/ GS28s seem to shine)?

Are they efficient or very inefficient at speeds around 7-12 kts?

I know there are displacement cats on the website as well but they don’t have a very high top speed.

Also I am curious about the ride of a planing cat vs something like a GS 28?

fallguy1000
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Re: Cat 22

Post by fallguy1000 »

I won't answer your question, but I might offer some advice.

What type of seas do you plan to use? And why the targeted speeds likely below hump?

A planing catamaran will have a clear 'hump'. That is where the boat accelerates and is finally 'up' on plane. Some boats can back off speed a bit after reaching the hump. How much is largely based on the boat's weight and area of hull in the water.
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TomW1
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Re: Cat 22

Post by TomW1 »

The Cat22 design is a planing cat and will be less efficient at your 7-12 mph displacement speeds. Once you get over the hump then you are at the most efficient fuel rates. For example, a Yamaha 70 single on a monohull is most efficient at 3500rpms at 20.1mph with 8.7 mpg. At 7.5mph it was getting only 5.7 mpg. Now this is only an example but all planing boats behave the same way. They are just not designed to be displacement boats.

Please read the study plans all the way through Jacques explains the handling of the Cat22 pretty well in them. I also note that Jacques noted that you have experience in building one of his boats before taking on the Cat22, I highly support this even if it is the free canoe that he suggests.

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Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

Johnston
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Re: Cat 22

Post by Johnston »

fallguy1000 wrote: Sun Mar 06, 2022 9:11 am
What type of seas do you plan to use? And why the targeted speeds likely below hump?

A planing catamaran will have a clear 'hump’
Much of our fishing is done at these speeds - trolling lures for Pelagics. 12 kts is on the high end - more like 7-9 kts usually - but 12 kts is a comfortable speed on some of the choppy water where inlets meet the ocean in our pangas and we can’t go faster - so I included that range of speeds.

I had always believed that a catamaran had a better displacement speed (the length of the 2 x 22 foot long hulls added together) than a similar length mono hull - but I am not sure where or why I have been led to believe this - but I was under impression that a cat on displacement mode was more efficient than an equal length monohull general speaking.

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Re: Cat 22

Post by Johnston »

Johnston wrote: Mon Mar 07, 2022 2:25 pm
fallguy1000 wrote: Sun Mar 06, 2022 9:11 am
What type of seas do you plan to use? And why the targeted speeds likely below hump?

A planing catamaran will have a clear 'hump’
Much of our fishing is done at these speeds - trolling lures for game fishes. 12 kts is on the high end - more like 7-9 kts usually - but 12 kts is a comfortable speed on some of choppy water where inlets meet ocean in our pangas and we can’t go faster - so I included in range of speed.

I had always believed that a catamaran had a better displacement speed (the length of the 2 x 22 foot long hulls added together) than a similar length mono hull - but I am not sure where or why I have been led to believe this - but I was under impression that a cat on displacement mode was more efficient than an equal length monohull general speaking.

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Re: Cat 22

Post by fallguy1000 »

This is a better question for the designer, but I will try.

For the same general hull shape, a monohull of same beam as a cat of same beam will have a greater waterplane at rest.

At speeds less than at plane, this means a catamaran will be more efficient below the hump than its monohull counterpart. Simple physics, the monohull has more drag. The tradeoff is the catamaran has lower immersion rating. So, a catamaran sinks lower in the water for the same mass above.

Will the cat be efficient at high trolling speeds below the hump? It will be more efficient than the equivalent monohull, but a planing cat will be less efficient than a semi displacement hull. The tradeoff between the semi displacement cat and the planing cat is the planing cat can go faster. There is probably an argument to be made about waterplane and immersion between the two, but it is in the noise for me. The tradeoff is mainly fuel economy.

If you want to speed troll; this means you are probably in the ocean. And the PC22 is not really meant for open ocean offshore work. I hate to push customers away from JM, but he has said before the PC22 is not really an offshore boat if I recall.

Tell us more about where u fish.
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Johnston
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Re: Cat 22

Post by Johnston »

Off shore fishing yes - and also through some rough inlets - in Gabon.

If as the study plans suggest the design was based on the Noosa cat, it looks plenty “offshore” capable for my uses.

https://youtu.be/0CtedRYVF9U

I suppose the question then is at what speed does the boat transition to planing (if built to correct weight)…

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Re: Cat 22

Post by pee wee »

Johnston wrote: Mon Mar 07, 2022 3:11 pm Off shore fishing yes - and also through some rough inlets - in Gabon.

If as the study plans suggest the design was based on the Noosa cat, it looks plenty “offshore” capable for my uses.

https://youtu.be/0CtedRYVF9U

I suppose the question then is at what speed does the boat transition to planing (if built to correct weight)…
I'd looked at the study plans a long time ago, but a refresher was in order. I found this:
"The cat hull form had some natural advantages in handling rough water: stability and softer ride. The Cat22 is an
attractive alternative for blue-water anglers looking for a stable offshore craft with plenty of room to move. The
shape of cat hulls means that the bow section of the boat is almost as beamy (wide) as that across the aft end.
Fishermen or families will appreciate that."

and this:
"The hulls have relatively wide sponsons aft which contributes greatly to the stability and the lift of the hull. In rough
conditions these allow you to plane along at reasonably slow revs."

Looks like a good choice from what I read. Here's another tidbit: " . . and whatever the engine size, the CT22 will be more efficient than monohull planing boats at any speed."

I know that doesn't answer your question, but maybe it will help focus the discussion.
Hank

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Re: Cat 22

Post by fallguy1000 »

I think perhaps I confused the ponton cat and this one. My apologies. Thanks Hank.
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TomW1
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Re: Cat 22

Post by TomW1 »

Thanks Hank that is why I suggested he read the Study Plans all the way through for those exact things you posted and others. Tom
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