Category Archives: Design Questions

Hull Core Materials

I always assume that everybody is fully up to speed on the different hull core materials. Then I come across some choices that I see being made. I ask “why would they do that?” Then I realize maybe a reminder is needed.
I saw where cedar was recently chosen for a 50′ catamaran. I assume western red or similar.

I don’t understand why someone would choose that over Core-Cell foam for example. True, cedar is a “live core” in that it does usually satisfy global loading of a hull, with the off axis glass fabric binding the strips together and protecting them.
I consider it to be far too heavy however. While it does have slightly more compression strength perpendicular to grain (240 psi in the Wood handbook) than Core-Cell (165 psi) it is far heavier at 22 lbs/cubic foot, compared to the 6# foam at, well 6 lbs. For a cat with two 1000 sqft hulls lets assume 3/4″ core. The cedar core will weigh 2750 lbs. compared to 750 lbs for the foam core. Actually the foam will be a bit less as 6# is only needed in high load areas.  But dude, that a ton.
And the cedar is not stronger than the core in everything. The NFPA gives the cedar a horizontal shear strength of 70 psi. The 6# foam has a shear strength of 191 psi.

Cedar does have a bit more compression strength perpendicular to grain compared to 6# Core-Cell.  240 psi compared to 165 psi.
But, for me the biggest advantage of the Core-Cell is the hystereisis; it bounces back when impacted.
In panel bending tests to destruction for the USCG, the laminates would practically explode (and I recall that Al had some great numbers, like 70,000 psi bending strength) and the Core-Cell was intact. It could and would stretch up to about 30% as I recall, and bounce back. On impact the cedar does not bounce back. And since the cedar has less laminate covering it; remember the 0 degree laminate is not needed as the cedar takes care of the global loads. The cedar is thus less protected from impact but it needs the most protection.

Finally throw in the foam’s resistance to water damage, and up in the high lattitudes, insulation values.  (Isn’t it snowing in south Australia this week?)

Why would someone build catamaran hulls out of cedar?

 

40′ Dive Cat

About a year and a half ago I did this simple, flat panel dive cat. I don’t think I had time to post it back then. Or if I did, I have tightened up the design since then. It was designed for inboards with the hull melding into a skeg. The design brief changed to outboards. They may be in production now. Foam/glass flat panel.  A variety of house cabins are possible.

Loa     42′-8″     13m

Boa     18′-5″     5.64m

Disp     15,070 lbs.     6835 kg.

Draft     1′-8″    0.5m

100 hp per side for 20 knots at above displacement.

Amilee Transom

Nice little shot of John Jacques expanded 37 trimaran transom. Says he modeled it on my 72′-75′-79′ trimaran design transom. (customer took me through complete revisions to each length before skipping out) So I can finally see what the 79 might have looked like if I squint.  Lots of nice detailing.

IBEX 2017

Is everybody going to IBEX this September 19-21?
Nothing has jumped out at me as something I need to know more about.  Though Steve D’Antonio or David Gerr or Scott Lewitt or Richard Downs-Honey are always worth the time. And it is on the balmy west coast of Florida now.
Still I get the feeling it is more about chopper-gunned bass boats than what I do.  Am not sure I would learn anything.
I must admit that I am a bit cranky that they were utterly uninterested in my paper on building an R-3 permitted tiny house using entirely composite boatbuilding technology and materials. I always thought interdisciplinary work was intriguing often very important. I guess not.

Let me know if you going and what you expect to see.  Certainly you will miss the eclipse, and maybe a druid ritual or two.

New Primary Phone Number

Seattle just changed how numbers get dialed here last Saturday. That means my land line forwarding no longer works. I set that up like 25 years ago and see no record of how to change forwarding.
So lets use the cell for everything. And it takes text also. 206 719 4893. For everything.

No More Epoxy Primer at Farwest Paint

For years, maybe even decades, Farwest Paint has sold a Matson 2 part epoxy marine primer that I always called 545 at half the price.  Many of my builders have used their great products at much less than the rock star paint’s prices.

At my last trip I was informed that they no longer carry it. They have replaced it with a one part. 20 years ago a change usually meant an upgrade. Now days it could just mean that sales only increased 8% per year and corporate quashed it.
I bought and tried. It does make life simpler; not having to mix and wait to induct.


The new product didn’t feel as tough in my unscientific opinion.
And the guys at the sales desk were new to me and unlike in the past, didn’t seem to know anything about the products. I wonder if Far West was bought out? I will find out.

http://www.farwestpaint.com/

Nice Power Tri

I just got this picture from Fisherman’s Bay, Lopez Island. No wake and fast. Of course. I don’t know what design. It looks about right to me though.
Maybe a bit bigger amas with reverse bows also. For that badly timed run out Cattle Pass.

Back

Finally starting to get better. Several people here have jobs I’m working on. Almost 2 weeks ago I got slammed with the worst cold I have had in decades maybe. I have the flu shots and usually I beat it in a couple of days. Not this time. Finally able to eat and drink.
I haven’t forgotten those jobs; I just vanished more than a week.
Starting back.

37 Trimaran Picture

I just got this picture of one of my 37′ trimaran designs from the old days. It must have been the third or fourth design I ever did. August 1986. Hand drawing days. I’m struck by how good it looks to me at the first telling glance. Cylinder molded plywood epoxy.  I hear that it also may be for sale soon.

Mystery Catamaran

I got these pictures of one of my cats from Australia’s gold coast. I was told it is about 45 feet and open bridgedeck. I would have guessed is Paul’s Quemarla or however is spelled. Anyone know more about it?  I see is named Gato.

I see that Owen has discovered a huge amount of great stuff and will dribble in in this week.  I have had some unexpected parent health issues so has been demands on my time last week or two.