10th Jan 2008, 05:42 PM #1
Jarcat vs the Kitten 18 trailerable catamarans
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11th Jan 2008, 01:02 AM #2
Know nothing about the Kitten 18 catamaran, but if you can't get hold of David Roy, the Jarcat 6 looks to be a similar size, & capability. Ross Turner is Brisbane based... local support & etc. http://www.members.optusnet.com.au/rhturner1/index.html
Better yet, something like 200 Jarcat 6's are on the water. http://www.themultihull.com/misc2/rn1.htm Not just an idea.
Last edited by Boatmik; 18th Jun 2008 at 04:46 PM.
14th Jun 2008, 06:41 PM #3
Actually I am quite shocked... the Kitten is so close to being a copy of the Jarcat, but without Ross Turner's understanding of boat structures.
The Kittent looks mostly like half inch plywood and they even mention 2x2" in the framing!!! This is really heavy construction for a multi. Pains taken to cut holes in ply to save weight but the sizes are so massive. There is no rocker in the hull which makes it a good shape for high speed motoring, but not so good for sailing and expecially bad for tacking.
The use of the partition down the middle of the cabin, I can see the merit of that. I don't get the way that the bow is framed up using ply with a big hole cut in it then another layer of ply is added on top. One layer would be enough (on looking closer at the Jarcat it uses the same method but with much lighter plywood. The Jarcat is a much better boat in almost every way.
It is amazing it is so similar to the Jarcat, but the Jarcat uses a lot of 1/4 and ply and much thinner framing so could only be half the weight of the boat above. The popularity of the Jarcat shows that the structure actually works with the thinner plywood.
The 1/2" ply and 2x2 timber on the Kitten indicate a real lack of knowledge about the loads that small boats are really likely to take and have probably been chosen because they are available at the local lumberyard. You start to see these sorts of thicknesses on multihulls around the 35 to 45ft mark.
Last edited by Boatmik; 8th Nov 2008 at 10:04 AM.
15th Jun 2008, 12:40 PM #4
Good points Michael - also, the smaller J5 used 4mm skins for bottom & sides (I *think* it was 6mm on the cabin roof and cockpit though).
Lots of them still going strong.
15th Jun 2008, 02:23 PM #5
At about 1/3 the weight of the boat above!
If using 4mm for this size of cabin boat I am sure Ross would be specifying some thin glass for the Jarcat. Three ply is a bit of a pain as far as splitting along the grain adjacent to framing and 4mm is always three ply (unless you are using aircraft ply). By a adding a thin layer of glass it solves this problem - and on a 5m cabin boat that lives on a trailer it is warranted.
I wouldn't consider glassing a canoe, kayak or dinghy being built of 4mm as it is not warranted for most uses - just adds weight, expense and labour. An expedition canoe, kayak or dinghy is a different matter!
The thinnest 5-ply you see is 6mm.
15th Jun 2008, 03:28 PM #6
Actually the more I look at the Kitten - the more upset I get.
This is all Ross Turner's work. Let me show you.
This is the Kitten
<picture and website has gone>
These are the Jarcat
The Kitten Catamaran completely crosses the line, copying much of Turner's Jarcat, but does it heavier but with a much lower performance potential.
Build a Jarcat please! You will be glad that you did, rather than the second rate copy.
Last edited by Boatmik; 19th Apr 2011 at 02:40 PM.
16th Jun 2008, 03:42 PM #7
We found it quite hard to source 6mm 5ply years ago - could only get 7mm. Hopefully that's changed since the 6mm we did get was very nice stuff (Brims' hoop pine).
16th Jun 2008, 11:26 PM #8
This confirms something I have had a hunch about - that some glass - even if very light might be just as effective at preventing abrasion damage and wear and tear as much heavier glass.
I'm talking over the top of plywood - not about timber strip planking where the glass is there partially to prevent the timber from denting.
Plywood won't usually dent much anyhow.
But Mcarthur, did you think the boat, which is still quite a big boat was quite resistant to bumps and bits of dragging over the bottom and all the the other sorts of wear and tear a boat gets?
If such a light glass worked on something as big as a Jarcat then it will work quite nicely on a canoe or kayak and will save quite a big proportion of weight.
I have even more respect for Ross Turner - he was thinking about all this about 20 odd years ago.
20th Jun 2008, 08:24 PM #9
We've run our J7 into a wharf at some considerable speed and dented the stem - the glass actually gave way a bit into the dent and only delaminated (?) along the side rather than the front of the stem for about 2cm. No, this wasn't done to test the theory, just that two big wingmasts outperform a 3.5hp tohatsu in full reverse under the conditions .
Another time we took off from Harvey Bay over to Coongul Ck. Now Harvey Bay has a series of sandbanks running north-south (see a little here) while we were going almost straight across them. On low tide, you've got, oh, say, 10cm of water over them - perfect for cats . We sailed across, getting out when we hit a sandbank (hard), pushing across, and so on. An absolutely perfect day. We had copper-poxied underwater and there wasn't a scrape in it at all. Ten years later, that copper poxy is still there and almost hasn't a (big) scratch.
We've run the J6 sideways into poles. No problem (except our nerves). I haven't done the most silly thing I've heard of and anchored at high tide over a star picket and waited for the tide to ebb .
So, in all, I think the glass-as-abrasion backed by good marine ply totally epoxied on the inside works.
I should note that there have been ideas over the years on the Jarcat mailing list to change the design either a little or a lot. Very few people have tinkered with more than the superstructure though.
24th Jun 2008, 10:18 AM #10
24th Jun 2008, 01:06 PM #11
So THAT one is your boat!!!
It is such a radical beast - in the simple way it is achieved too! Did you ever build the drop on cabin pod? Tell us about what it was like and the things you have done.
15th Oct 2008, 08:28 PM #12
When I was restoring a sailing dingy in Darwin I was told to epoxy the hull and Dynel sheathe (spelling?) the hull.
This was apparently purely for abrasive resistence and from memory (going back a few years now!) it was basically a cotton that was glassed on the same way. The advantage over just using a woven mat was it apparently is much lighter.
16th Oct 2008, 09:39 AM #13
It is a legitimate way to go with Dynel. It is lighter but can float a bit if too much resin is added ... so don't add too much resin or do follow up coats until the first one has gelled enough to stick the Dynel down.
I do prefer glass because it adds abrasion resistance as well as a lot of strength. Something that Ross was depending on in his Jarcat structure. Main reason is it will turn the 3-ply plywood into effective 4 ply with much greater strength and stiffness across the grain of the ply.
So as little glass as possible for lightweight structures balancing that with required strength. With a dinghy I would seldom worry about sheathing at all because they are generally light enough and slow enough not to do much damage.
But if you have beaches made of rocks ... I would be reconsidering too!!! Dynel or Glass please!
27th Dec 2010, 09:11 AM #14
For those who may not be aware Ross Turner has sadly passed away on the 23rd of December 2010 after a long battle with brain cancer.
His designs live on, may all those who sail, or dream to sail on his designs have fair winds
27th Dec 2010, 03:52 PM #15
Thanks for the sad news cookiesSA,
Ross's son (I think it is his son) has been running the plans side of the business for a year or so, so the plans will continue to be available from the existing outlets.
Ross was a great wood engineer (as you can see comparing the Kitten with the Jarcat above - the Jarcat it about a third of the weight or less. Ross was a nice bloke too - I've run into him at boatshows where we both were exhibiting several times..
By boatchippy in forum BOAT BUILDING / REPAIRINGReplies: 19Last Post: 23rd May 2007, 09:11 PM