View Full Version : An experimental catboat under construction

Norm Bernstein
11-26-2003, 10:53 AM
Hello, all...

I'm building a 15' x 6'6" catboat, and am maintaining a website log of construction, with high resolution photos, descriptions, and some occasional philosophical musings. All are invited to take a look:

The Ellipticat Project Website (http://www.marisystems.com/ellipticat)

Any comments, suggestions, criticisms, brickbats? Feel free to place them here, or email me directly (the website has an email ink).

Norm Bernstein

11-26-2003, 01:15 PM
Have you a set of lines produced or a picture of your model?. I was interested in how full your bow might be using ellipitical sections, rather than perhaps a line segment of an ellipse, to "mimic" the sections of the panel boat plans you worked from. It's important in a catboat to have those hollow waterlines forward or you end up tubby and pushing too much water. Nice to have ample flair above though to lift a heavy bow (from the mast weight forward) up over a wave rather than submerging, but still have a faster, finer flat water shape for speed potential..

11-26-2003, 09:53 PM
Good luck.

11-27-2003, 09:19 AM
That person would be Tom Kamila and his boat is a work of sculptural art truly. Lots of quality thought, materials, and craftsmanship. I think it would benefit the Elipticat, if before planking starts over those bow station molds, to review Tom's many pictures and see how his bow sections differ from what I'm seeing in the garage photo and how those hollow waterlines of Tom's work out forward. Very easily executed with limber, narrow strip planks. Not quite as easy to build the hollow shape in cold molded veneers on my MarshCat, but done nonetheless. A design compromise is made with twisting broad plywood panels, but review the Wittholtz 15,17,and 20 plyboats and you will still see hollow waterlines forward in all, just less gracefully styled. I'm truly concerned about you U sections forward, not on a narrow performance boat which needs flotation to keep a wide transom from pushing down the bow on a spinaker reach, but on a wide beamed, sailed flat catboat that needs a transition from a plumb bow out to a wide waterline beam along a good(fast) waterpath. If you look at the diagonals produced by the traditional hollow catboat entry, you can see why they are there. Have you drawn diagonals for your design?. Try tacking a batten over your set up molds in the direction the water will stream,aft and down and then back up, not the direction the strip planks will fasten (for a while at least starting at the sheer, but you will soon need to taper some strips, add stealers etc on such a beamy catboat hull.) Tom Kamila's contruction pictures will show you very well how it's inevitably accomplished.

11-27-2003, 09:30 AM
One other caveat. If that's Home Depot cabinet oak venenered plywood you're referring to- boil a piece before you use it. I have been disappointed in some interior cabinetry parts for my "big" fiberglass sailboat. Everytime I've found it was not waterproof after a few years' service. They do sell a laun ply ( as an underlayment) that is very good and waterproof. Better yet, look around for a Superply dealer and you'll be very pleased with the wood's looks and it's performance. Way cheapier than marine ply, beautiful laun faces,void free and waterproof glued. Redecked a 62 foot steel paddlewheeler and redid the paddle wheel blades, all in 1/2 inch at I think $17 a sheet earlier this year, and was made a believer.Might have gone up in the recent rise in plywood prices.

Norm Bernstein
11-28-2003, 12:07 PM
Thanks, JimD and Buddy, for your comments and observations.

With regard to that piece of plywood, it came from Lowes, not Home Depot, and might indeed have been Superply, although there was no label on it. I thought it was unusual in that it was 9 ply, with equal thickness plies and no voids, and face veneers of the same thickness as the inner plies. The usual 'cabinet plywood' that Home Depot sells has paper thin face feneers and some voids. Regardless, this piece became the centerboard, and has been heavily filled and glassed, so it ought to be OK.

With respect to the issue of the lines of the boat, first I'd like to state that I have almost reverential respect for the naval architecture art and science, and understand the intent, if not the specific details, of your comments about to the 'hollow entry' of a catboat. As an engineer myself (electronic, not nautical) I understand that there's a great deal of science behind the art.

However, you might be misinterpreting my intent. For the amatuer boatbuilder / woodbutcher like myself, it's enough of a challenge to undertake and complete a project like this, and highly detailed issues of shape, etc., go a few levels beyond what I'm trying to achieve. It may be true that the lines of the resulting boat may be less than optimum for a catboat... but, then again, they won't be much different that the double chined 'tack and tape' design from whence it came. I'll be supremely happy if it a) floats, and b) sails.... which I'm confident it will do.

It might be worth pointing out that designers like Phil Bolger (the designer of the boat from which my adaptation comes from) have designed elegant round-bilged boats of all sizes... along with ugly but functional plywood 'boxes' intended to satisfy the needs of the amatuer boatbuilder. While Mr. Bolger undoubtedly used sophisticated design analyses in the design of the latter, there's no doubt that simplicity and functionality won out over hydrodynamics, in those designs... but that doesn't mean they weren't useful or practical designs.

Perhaps, after a few more boatbuilding projects, I'll get a LOT more picky about design issues... right now, I'm just hoping that I can get through THIS project, to the end result!

Once again, thanks much for your comments!

12-01-2003, 06:08 PM
Cutting to the chase ( or rather ending it) sure the boat will float and will sail as you have her. I am truly concerned you'll push up a "slow" bow wave unnecessarily for the construction materials and methods you are using. Altering your first two bow stations now would fix the problem I suspect with a few hours (days?) of time and precious few dollars in plywood NOW, make a better sailing boat, better to resale boat IMO. Have you drawn lines or built a model that can reveal to you what I suspect? A little more time now could head off a lot (a little?) disappointment later is my point.
But she's your project and you decide what kind of point you want to build on her.

Norm Bernstein
12-02-2003, 01:40 PM
Buddy, I PROMISE that, should the resulting boat exhibit the bow wave phenomenon that you warn me of, and assuming that I can even recognize it, I'll be the first to log onto this forum, say a few 'mea culpas', and admit that you 'told me so'!

Actually, I have been looking at the bow since you brought the issue up. When compared to the original design, which was a double chined 'tack and tape' thing, the round-bilged conversion might actually be better. The original version might have benefitted from the lower chine cutaway, but the 'revised' design has less wetted area and volume between the stem and the first frame. Admittedly, it doesn't have a hollow entry... but neither did the 'tack and tape' design.

FYI, the planking arrives from Canada tomorrow... and I've updated the construction website, so feel free to follow along at:

The Ellipticat website (http://www.marisystems.com/ellipticat)

12-02-2003, 06:21 PM
Good luck with her and I'll look forward to following along.

10-25-2013, 11:32 AM
Bump. 10 year update?

Rich Jones
10-25-2013, 02:06 PM
Bump. 10 year update?

I think it's still sitting in his garage, waiting for completion.

10-25-2013, 03:18 PM
Did you private message him about it?