All posts by Kurt

Fish Expo Time Again

And again, they have gone upscale and now call it Pacific Marine Expo. Fish expo it will always be to me.
Nov. 16 to 18th. Century Link Field Event Center. Seattle.
It is a PNW event, but mariners can always be heard speaking a dozen languages there.
It is the serious boat show.  I can’t find the link.  Google it.

Rapido 60

When the Rapido 60 trimaran first appeared, I figured it was some kind of a joke. The styling recalled an F27 from 20 years ago. I teased that they owed Ian royalties. It’s beam overall was just over 38’, which some of mine, and most modern 40’ + trimarans, equal.  My GS 60 beam overall, from 25 years ago, in E-glass, was 44.5’. Everybody knows that when you push a multi, wide is what keeps you right side up. So making it not wide had to be something to push onto the unsuspecting, right?


Almost all the pictures I saw of them had the crazy camouflage paint so it was never clear what was going on. I figured that they were not serious and didn’t think much more about them.
It was just pointed out to me that the R60s don’t have continuous mainstrength beams. Blew me away. Followers of this over the years have seen the importance of continuous fibers, fiber orientation, co-curing of mission-critical parts, not forcing composites into sharp turns…..
And here is one design that seems to ignore all that. What gives?
And that explains the narrow overall beam. That’s the only way to keep the loads down, besides throwing carbon at the problem.

Again, I have always declared that with enough carbon and enough money, one can have almost anything designed. This seems to be a prime example.
If we assume 24,000 lbs sailing weight, and a 12’ cantilever of the beam, then hit it with a shock load on one of the beams. The moment at the root will be something like a quarter million foot pounds. If the bury is 3’, then the load to resist will be some 80,000 lbs.
No wonder it is so heavy. Yes, heavy. 20,000 lbs. lightship. It is all carbon, right? That carbon has some 5 to 7 times the modulus of E-glass. Compare to my GS60 at 13,000 lbs., as designed, in mostly E-glass.
Main point. You can’t beat a continuous D section for the most beam strength and stiffness, the least weight, and least cost to build.
And again, all boats inhabit a place on a continuum between a habitat and a vehicle.
The R60 seems a bit confused.  All the carbon tells me vehicle, but chopping up the lightest, strongest possible connecting beams to get more cabin space is right back to a 1960s Horstman; habitat.
None the less, I’m sure they will sell a lot of them. The owners can “Hey baby, I got a carbon boat.”
I prefer direct, simple solutions to magical ones.

VHB Tape Fail

Part of what I am doing on the lunar lander dwelling project; building a tiny house using boat construction, is to test the limits of many techniques and products. I took the VHB tape past its limit.
I tried to use it to attach an acrylic shower door without any fasteners; a worthy goal.
While the VHB tape is amazingly strong, it has limits. Its weakness as I understand it, is long duration loading, while depending on peel strength. The shower door provided that.  It’s tepid resisting the energy of initiation, followed by energy of propagation, made it fail.

In the picture, the VHB tape attaches both the hinge and the angle brackets.  Both failed after a while.
On a window, peel strength would not even enter into it. I’m always curious about where the real world limits are.

40 Foot Performance Shorthanded Trimaran for Owen

Use program:
Shorthanded sailing for both racing and cruising.
Demountable and able to fit into a tallboy container.
This design is the latest update to a design that I did several years ago for Phil Steggall.


It also has several features that I developed while sailing my own F40 Geko. First of these is the addition of an actual cabin from main hull flare. Any time a few people come aboard for a sail, their gear has to go somewhere, The 7 foot wide cabin also allows a canopy to hide under in bad weather. On the much narrower Geko, that space was taken up by winches.
The outboard is mounted beside the cockpit instead of back on the transom. When shorthanding having the motor right there without leaving the cockpit is important. On the Geko an 8 hp outboard would push it to 7 knots in chop and once did 11 knots on flat water.
It has a single board in the main hull. Vertical and aft of the mast a bit. In Marchaj we find that a vertical board has the most even stall characteristics and also less deflection for the span. Fully down, the board is a couple of feet below the cabin top. Downwind the boom can be lifted a couple of feet to reduce board draft. I don’t understand the trimarans that suffer the inefficiency of swept boards.
Board down, the draft is something like 10 feet.
As usual it has 200% buoyancy amas.
Presently the design has ama rudders.

Foils were not chosen as they work best with larger crews.

Construction is strip foam and unidirectional e-glass for the main hull. The amas could be the same or even a combination of developed plywood and carbon fiber.
Beams are core with carbon fiber.
Geometry is virtually square with the width almost a much as the length overall.  Doesn’t that make it wider than a Rapido 60?

IBEX 2017

I did see that it did go on despite the exciting weather. Did anyone go and anything to report?

I was also pissy as I thought a house built almost entirely like a boat, and permitted, would be a great topic.   Epoxy, foam, vacuum bagging, BS 1088 plywood, biaxial roving,  glass gloth over everything, 12v electrics, stainless fittings, 2 part poly paint, Beckson ports.  Technology transfer.  IBEX powers were completely uninterested.

Back. What This Time?

I was a little scarce last week and the week before. The Seattle Times is doing a feature on the lunar lander dwelling. It had to get substantially finished for the photo shoot by last Thursday.   Built like a boat with epoxy and vacuum bagging.

The usually away-team problems compounded by metal fabrication that didn’t fit made me run scared.
And a parent passed away so all kinds of cleaning up and organizing.  Am back now and getting to everyone’s projects.

Glow In the Dark 12v Switches

On the lunar lander dwelling project one of my holy grails has been finding blow-your-mind glowing 12v switches. One company I saw at IBEX had some for what $30 each I think it was. An earlier one I bought online was only slightly cheaper and didn’t actually work.
These beauties look great. They glow in several colors. Sailors might want red to save the night vision. Buck 95 each. How cool is that. I have not used in marine environment yet. OK, I have not yet used at all, but they look right to me. I will soon.
www.adafruit.com
A woman owned company that quotes Bucky.

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?