Category Archives: Design Questions

23′ Trimaran Update

I finally got the first run of modeling the updated 23 daysail trimaran. Version B will have ama rudders and the even hotter version C will have foils. It is a developed plywood/epoxy unit with core vacuum bagged onto the flat surfaces needing that. And carbon fiber where it helps. At around 360 kg lightship weight, it can be built for around $5000 us in construction materials. The connecting beams should be carbon mast sections. The camper version comes next.





The New 35 Tri

I finally got a chance to model this on that I have been looking forward to doing since before thanksgiving.
No windows nor cockpit are cut into the model yet until I verify the interior and weight/trim study. It will probably be built with vertical bows, but I hope not. Main hull not more than 84″ wide.
Displacement is 4217 l bs. It takes 5 HP to go hull speed of 8 knots.





USCG Submittal

A basket of thoughts on submitting plans the USCG MSC in 2017.

A fellow who was quite informed about other catamaran designers told me that John Marples has given up on dealing with the USCG submittals.  He also thought that Gold Coast had not had a new submittal since Ganulin retired.  On the othe side, Schooner Creek thought the whole process went fine on a new submittal.

As I have noted, I am very wary of the new “kids” there and,  as I found out last spring,  anything that we had as settled regulations for the last two decades could be over.  Which leads me to my next thought.

Building departments charge a lot of money for plans submittals.  The USCG MSC charges nothing.  I imagine that as soon as Trump realizes that some part of the government is doing something for nothing, that will change. 

If any of you are thinking of having me do a new plans submittal to the USCG, I urge you to do it now.

Catamaran Bow Truss Fail

The KHSD 42′ daycharter catamaran operating out of Key West, Blu Q, suffered a total bow truss failure. I call it a bow truss instead of bow tube because it was built as a Gold Coast style unit out of timber.  I expect that the GC units had pin ends.

It did have more than 25 years of service in it.  And rot was involved.  The take away lesson is that it had  fixed ends instead of pin ends.  I’m sure the repeated stress started a crack and water got in.   It is being replaced by a standard aluminum mast section bowtube.



IMG_7781 (1)

Fake Trimaran

Has to be another Palmer Johnson. Not sure why they even bothered adding the amas. It is still a huge fuel guzzling megayacht.  It must be some kind of cultural change when vestigal amas are added to megayachts as style points.

As an aside,  Andre Cocquyt is presenting the 32′ KHSD power tri at the PBB Refit Show in Ft. Lauderdale later this January 26 and 27.



Better Wingmasts

Back in 1994 I had an idea that if you took the shear web out of a wing mast,  and added that material to the sides, you would have better section properties, and a stiffer wing mast,  with no increase in weight. And the panel aspect ratios would be closer to 1:1 so stronger actually.
In fact few alum masts have shear webs, but everybody forgets that.

First of all, I built two nearly identical wing masts; one with shear web and the other with the half of each shear web glued to each side .  Then I load tested them.  The improvement was remarkable.

Next I had Paul Steinert PE run a finite element study of the idea.  The results were so good that we wrote a technical paper together on it.  The paper was given and published at the 1994 MACM marine composites conference.

The paper had some difficulty later getting online however.  Word5 for DOS had a great equation writing feature.  The file would however completely  lock up any later  windows version of word.  Also, the images were slides of photos of the computer screen.  Those took some work to get digital.  Meanwhile I got busy and neglected that paper.  Recently I have realized that nobody has any idea what I am talking about without this paper being able to be online.  So, along with everthing else, I will get it into InDesign and make it available.

Meanwhile here are some of the graphics that will be in it.

Old style stainless hound for a big catamaran
Preferred composite hound base.
Athwartships displacement study under load.
von Mises stress study.