I posted a few weeks ago a photo of my new homebuilt cat in the general forum. Later I discovered there was an special forum for home built cats.
So here it is :

http://www.catsailor.com/gallery/displayimage.php?album=lastup&cat=&pos=4



Design is based on Prindle-15, but with adaptions: more volume in front (anti-dive), higher hulls, standing surface on the side and last but not least wider (2.50 m).
It is constructed with a shaped foam core and a ca. 1 mm glass/carbon/kevlar epoxy lay-up skin. Beams are fixed and selfmade of foam,wood and a mixture of glass/carbon epoxy. Surprisingly I had no need for a dolphin striker, it was strong and stiff enough.

Hull weight is 29kg each, and the total weight is around 110 kg.
It sails like a beast on my home beach; which is the North Sea shore on a spot with a very rough sea.
Strenght was the main issue and improved sea behaviour. I'm not a speed man. Often I go too fast at sea, I let rope out to slow down!

I'm curious if anyone else has done something like this also and what his specifications were.
Also I plan to home-built the mast of carbon (in this month I spoiled two old masts!)
Has anyone experience with mast building?

Nice cat! I have the feeling that you has used the idea of “too strong has never failed” at least for the hulls.
We have been doing similar things on the F12 including the mast, check the F12 thread.
You also find some stuff on http://www.gust.ax/gallery
If you are not an engineer get somebody with good experience of composite and spars to make the carbon setup for the mast, guesswork is a costly and time consuming thing when carbon is involved.

Gato, thanks for your comment. Yes you are sort of right: "(too !) strong never fails".
But this the oldest and still never solved dilemma for sea sailors. Look at the material problems of the last Vendee Globe or the still going Volvo Ocean race.
I have build already 30 years my windsurf boards and there every ounce of weight counts, so I'm used to compare my boards with that of my friends who for instance used one layer fiberglass less.

For me, after spending so much time at windy seas the last 30 years, sailing still means first the material and then the sailing itself.
I have encountered in the past some serious problems at sea, alone, and afterwards when you are playing the movie back sitting safe in your chair, you always think what can I do that this will never happen again. Moreover I'm 63 year and my strength is decreasing rapidly, so I cannot survive the conditions that I was used to in the past.

Hence my strive for strength in my boat, while of course never forgetting the weight.
I couldn't do it less, even if I wanted it.

I think 110Kgs is very good for a "bulletproof" surfboat! You are not that far off from F16 min weight.

Not on topic but just to satisfy my own curiosity. If you find your strength decreasing as you get older, what do you do to improve your strength? It is never too late to work out, if you dont already do. I have seen 80 year old chaps do handstands..

ref: http://www.youtube.com/watch?v=lDlMyJooTok&feature=player_embedded
http://www.youtube.com/watch?v=kK2XU4wPQws&feature=related

If I can do stuff like that at age 70, I'll be happy. This guy still seems strong enough to do some serious sailing. As long as he keeps at it, I bet he can do the same at 80. Age is a mental thing I think..

It would be very interesting to learn some more on just how you did the composite beams. Someday in the future I might want to do a wood/carbon beam in strip plank. How about the mast step?

Okay Rolf, with regard to your comments. Yes, you are quite right, normally If you are lucky to have a non-problem body you can train yourself until you are maybe hunderd and/or die.

But as you understand already my sailing career has unfortunately damaged my body by constant "sur-charge" (overload) which showes up now with aging. My biggest problem is my shoulders with on each side a thorn labrum, which infact is medically only known after serious motoraccidents.
In my case it is indeed caused by constant hanging in overload sailing conditions in wintertime on ropes, wishbones and so on. I have let myself been operated ten years ago by a orthopody professor, but his repair didn't hold.

So far about the unlucky sport-career. With regard to the beams:

As you might see on the picture, they have the sectional profile form of a diamond which gives less water resistance and helps against torsional stress.
This diamond profile is internal built up with wood from 18 mm thickness. The wood is red cedar (light) and plain sawn! out of the tree. In the middle of the diamond there is also an red cedar stringer which connects up and down. The two internal "holes" left and right are foamed up with PU foam. By the way the wooden parts are glued together with thickened epoxy and are (as far as it was possible) finished with epoxy "fillets". The holes to work in were very small.
The result was already a very stiff and strong wooden beam which weight about 7 kg.
This was covered with one layer of square glass (280gr.), a layer of square carbon (200gr), two layers of unidirectional carbon (2 x 340gr.), one layer of carbon /kevlar (165 gr.) and finally a finishing layer of glass (160gr. ). Total beam weight 11 kg.!

Yes, I know heavy-duty and weighty. But the beams were my greatest fear.


The mast step finally is the normal half-ball from prindle which I screwed on the sawned rod from a prindle dolphin striker.

A lot of different fibres with very different characteristics put together. I’m maybe not the right one to analyse this, but using so many different materials and get them to work together is not the easiest thing to do. At least to my understanding there is not much use to put wood, glass and carbon fibres in the same direction on a spar as they will just brake at different points of bending of the spar.
I have a bad experience of thick wood combined with glass and epoxy. The wood is “alive” and you can not avoid humidity getting into it. The epoxy is gluing the glass so well to the wood that it will brake the fibres when the wood is expanding due to humidity variations.
It would be great if Scarecrow or somebody with more knowledge than me would comment on this.

Gato, I assume that you are talking about my beam construction. Okay,here is my comment:

The use of different fibres for a layup-skin has proven for me its strength in my windsurfboards. I use that mixture already for years with content. The foam by the way in the inner part of a surfboard contains a lot of air which can even flow (alive), because the foam is not completely closed-cell. So the internal humidity with regard to water condensation-point is also fluctuated. Besides that, I open the boardhulls after sailing because of depressurizing for heating by the sun.

My beams now ,in contradition with above, are completely sealed off the external world, they are airthight and ofcourse waterthight. The PU-foam is closed-cell; so in my opinion the humidity status of the wood is frozen and I don't see the problem.

Yes, I was thinking about your beams and also the mast you said you would make.
I’m not doubting that your beams, but as I am not a rich or strong I try to avoid adding more weight and cost than necessary.

Gato, the mast design I am still thinking of. Don't worry I will be using no wood at all (besides for strengthening the places for screwes and so on). I'm still searching for a method for increasing the fiberpercentage with regard to resin without vacuum. My handlayup gives me now 50-50 % fiber-resin, which is to less for a mast.

With regard to the multi-layered skin again, I would like to add that in my opinion it is a serious alternative to the modern sandwhich-like skins which industry tends to use moreover. The danger of sandwhiches is always delamination and a weak outside for point-oriented loads.
The weak point in my skin construction is micro-cracking of the resin between the fibers. Which ofcourse can lead eventually to total breaking off (My shoulder-problems are a good example of that by the way).
In fact that's what I see when a surfboards breaks at the beach.
The stress loads on catamaran hulls are maybe a little less compared to that with regard to actual bending?

Very quickly about your shoulders as I could go on at length about training and injuries. Even if you have torn labrums there are exercises you can do for the rest of your body. Core strength, legs, cardiovascular system, stretching/agility etc. All will help if the goal is to continue sailing.
I am no expert on your condition, but strengthening all the different muscles around the shoulder joint would be something I wanted to look real hard on. I would want my supporting muscles to offload the labrum so I could function as close to 100% as possible. Your fysio therapist should know how to do it. Sounds like you have been hanging on/doing stuff directly off the joint/skeleton and not the supporting muscles.
I have had several injuries of various severity. I find that if I dont work out my injuries actually become worse. When I work out, I dont notice them much after the first weeks. I have 60 more years of working out to do..
Please stay active, dont give in to age!

Your beams are quite heavy compared to your all up weight. Did you do the engineering yourself, or was the design a case of experience and some guesswork? I am sure they will work well for your application. If I was to do wooden beams, I would use strip planking with carbon inside and out. I would also vary the dimensional section but it is not likely to happen now so it is just fantasy.

I would like to see more pictures on how you fitted the trampoline if you have some. How did you do the foils and daggerboard wells btw? I am asking as there is always something to learn.

Rolf, you are quite right about working out my shoulders. Actually it is nice to meet someone who knows what shoulder labrums (or is it labra) are. It toke me fifteen years of shopping around fysicians before the right diagnosis was done. And that only after the time that MRI was available for non-cancer patients.
The problem with strengthening the rotatorcuff muscles is the disloading of the labrum itself. Strong painkillers (NSAID's) after effort helps me. I keep trying because I'm still a sea junkie!

Yes I know the beams seems a bit heavy and yes I know it seems guesswork. In fact it was that partly. I wanted to start with a solid wooden core, because of the natural resisting force of wood against bending and its own stiffness.
Standing on it in the middle in my living room, I could easily test this and add the necessary layers of fiber-epoxy composite.

Ofcourse I ended up with a construction with a lot of "spare". But that's okay, the stress loads at sea are dynamical so you have to multiply your calculations anyway.
To vary the dimensional section in the length is ofcourse a sensitive option; a bridge is the strongest in the middle.
Frankly, I forgot it and didn't consider it.

The trampoline is not a mesh, but an open net construction with very large mazes.I'm always at the trapeze and only have to pass during gibing. I never go through the wind the normal way.
This polyester net I have ordered in the States and it was worked off with rope-sides. The hulls were prepared for this with the standard Prindle holes in the sides for a thin lacing-cord which connects the net and the hull every 10 cm.
In fact I glued a polyester staff on the side , covered it with some layers fiber and drilled small holes every 10 cm. right through the staff.
I did the same on the aft beam and the front beam was laced around as you can see on the picture.

There are ofcourse no daggerboards, the hulls are assymetric. Round on the inside and flat on the outside. And the hulls are quite outbend to the outside in the lenghth direction.
Rudders and even the castings itself are also home-made from, you guessed it already, wood and epoxy composite layup. The main reason for adopting the oldfashioned Prindle ruddersystem as design, was the fact that I sail always single-handed.
At the beach I always have to start with my rudders high because of the undepth. So jib on, mainsail open, fighting against weather on the steeringtube. In the break or just after I have to click the rudders down and no way I come near the leeward side of the cat (it would capsize). So I have this rope system with which I can pull actually the rudders down.

Thanks for sharing the information. Some more pictures of your minds creative expression (your boat) would be appreciated very much. Especially the details, as that is where the time devil is eating the time in building projects. Wood rudderheads sounds really nice! I bet you have other very interesting details on the boat as well.

I have done a lot of rock climbing and my preferred workout today is gymnastics (the challenges there are endless). Your injury is not unknown in climbing, while gymnasts know about it and build muscles + uses the muscles to avoid these injuries. I hope you can find some exercises that will work for you, as I really believe in using your body. If you dont use it, you loose it.. Sail on! 62 years and you are still a young man, if you want to be one. Guy who taught me to climb was 75 when we started..

Rolf. A quick picture to satisfy your interest.

http://www.catsailor.com/gallery/displayimage.php?album=163&pos=0

You see the net connection, the special ropes leaving the tillerarm which operate the rudder internal the casting, the standing surface for my feets (very,very comfortable) and the rudder+casting. Mind the external spring which in fact holds the rudder down when clicked on.

Rolf and Gato, I have the feeling that we are approaching, for the time being, the end of this little thread and maybe not commonly done, but I would like to thank you both for the interest shown.

I would still like to add two small technical details. First the question about how to catch the severe stress loads froms the stays on my puttings mounted on a skin from 1mm (on a soft foam interior). This point gave a lot pain in the stomach in the design state.
The solution was quite obvious: a wooden underlayment built in the foam, sort of half bulkhead, to have "meat" for the screws and to spread the load. Further on the skin was enforced ofcourse at that places with extra layers to divide the stress.

Second question was how to make the rather complicated hullshape (assymetrical and not straight) mirrorlike identical to the second hull. Well I didn't succeed 100% in that; there was also a time period of several months between making the hulls. And my working space, a cold and very narrow shed with a leaking roof, didn't help much.
In sailing I can notice the difference between the hulls quite well, but I tried to compensate that with different rudderangles, which helps a bit.

Finally I would like to add an anecdote which actually happened to me a few weeks ago and clarifies a lot of my ideas of homebuilding:

I live in village on the dutch seacoast in a very old cottage about 1000 meters from the sea. I don't let my cat on the beach because of vandalism. So I drive it with a little drawer on small road through the village. I was used to do that with my mast mounted standing-up, but because of overhanging trees and lighting poles, I had to divert a lot which was annoying for my fellow roadusers (summertime, tourists).
So this year I used myself to mount and dismount the mast on the beach each time I went sailing. But because of my shoulderproblems I cannot walkup the mast in the old fashioned way. So, I put the cat on its side and walk the mast, already in its side stays, in a horizontal way up on its ball on the frontbeam.
A few weeks ago, my worst nightmare came through. Just after loosening my mast with dismounting, the cat started to fall towards me and the mast. Ofcourse careless, but in a hurry for the diner and still high from a afternoon nice sailing.
(on one hull showing off for a fully loaded beach with tourists)
The devil or god, I don't know which, punished this immediately and with a bang that let every body on the beach rise, my cat fell upside down on the mast. People started running at me. Mast was gone, dented and bent.

But the miracle was that the cat who hit the mast upside down with its forebeam, was not damaged at all. No dents, blushes, not even a scratch!

My intuition for choosing a wooden based over-solid beam construction payed off exactly that moment.

So I thank hereby "the spirit of sea" (or whatever supranatural phenomenon it is), who I spent so many time with at sea, for helping me with my design.

It is an interesting design and build, so thank you for sharing! For your use, it sounds like the perfect boat (until you build another one).

I still would like more pictures and details on how you built items, but my thirst for information will never end (at least I hope so).

Happy sailing! And if you decide to do other projects, please share!

I agree completely, it’s interesting to see what others are doing.
I would still like to make a comment on the fixations for the stays rudders etc.
It’s not too difficult to make everything in carbon and laminate it directly to the hull with all the material needed to shear the loads.
On the Tabby I have excluded all metal parts, bolts, pins and screws included, and so far nothing has broken.
Thanks again for shoving your cat it looks great!