beach cat hulls built surfboard style

So, before getting into building boats, I built several surfboards. Most of the ones I built were hollow wood, but I also have some experience with foam cored ones.

So, for those who don't know, fiberglass surfboards are typically built over a foam "blank". The blank consists of a thin ply "stringer" running fore and aft, technically more of a keelson. On each side of this stringer is glued the foam (not the high density stuff fyi). The foam is then shaped, and the whole thing covered in at least one layer of 10 oz cloth. This results in an extremely lightweight surfboard.

I noticed that when I build hollow wooden surfboards, which are almost universally strip-built with 1/4in cedar planks and then covered in light glass, the boards can weigh easily twice that of similar 'glass ones. (although I think they look and ride better-I'm obviously a little partial)

Gary Dierking gives plans for fiberglass amas built the same way, and he says they are lighter and just as strong as strip built ones. I was thinking, can I expand on this theory and build 14ft beach cat hulls in much the same way? I don't know why not, and they would be really light I imagine. Maybe I would add some light ply ribs, or deck? What if Instead of solid foam, I built it in hollow 1in foam planks, with lots of 1in foam ribs for stiffness, maybe even covering the ribs in glass to stiffen them more? I wonder if two layers of 10 oz cloth would be strong enough, or even overkill?

Any thoughts welcome on this subject, I just think it would be cool to have a cat hull that weighs not much more than a longboard, throw it on top of the car and gooooooooo.

Apex, if you comment on this thread, please keep the comments positive and constructive, and try not to insult all of us who are not as wise and brilliant as you are. Thanks.

 

You're going to have to consider global loading, rigging loads and several other considerations before you can assume your "new" method will be successful. This method is in fact employed in hull construction, though I'm confident that your understanding of suitable scantlings for a cat boat are less then probable. This isn't an intention dig at you personally, it's just that considering your questions and observations, you'll need more engineering comprehension, before you can expect success. Laminated structures usually require a fair bit of material physical properties awareness and clever structural arrangements to take advantage of these physical properties.

 

Which is why I have posted this question.

I am not certain how I would attach the hulls, rigging, etc and certain structural reinforcement will be necessary. Since it is only a 14' beach cat, and I don't plan on using a high performance rig, the stresses shouldn't be out of the ordinary. My guess is to reinforce critical areas under the glass with hardwood attachment points. I am on this forum for ideas, or for advice from someone who has done something like this before.

This is just a small beach cat, a fun project, I would appreciate a response that doesn't just tell me that I don't know anything and shouldn't try.

If I had that attitude, I would have never built anything, and I am proud of the modest and serviceable builds I have under my belt. They bring me great enjoyment and contentment.

 

My point isn't that you shouldn't try, but that designing one yourself is an unreasonable expectation, particularly with all the various materials/systems/engineering questions you have presently.

You'd be best advised to use a set of plans, where scantlings, material choices, hull shapes, rigging, balance and sail plan decisions have been ironed out.

 

The method you describe would work, presuming you incorporate the necessary reinforcements for rigging and mounting points. It seems to me it would be rather fragile for typical trailering and beach launching. Most of the damage to small boat hulls comes from rough handling and accidents in the garage or at the dock, not in the water.

I think for example the typical 14 or 16 ft beach cats could be much lighter, but they would be easy to damage in handling. Your typical user would not considered a boat very durable if you gashed the hull when they dragged it over the beach to the water. Many beach cats are also used as rental boats, which also take a lot of abuse, and a very lightwight hull, while fine in the water, would not last very long in daily abuse by rental clerks and inexperience customers. Consider that even a small sailboat is much heavier than a surfboard, and just setting down on a hard surface could crack the fiberglass skin since all the weight would be concentrated on a rather small part of the hull.

I have built sea kayaks that weigh as little as 10 to 15 lbs, but there is no way these would be suitable for a typical kayak rental fleet.

I think what PAR was pointing out is that to optimize a new construction method takes specific engineering knowledge. You can develop a small design by trial and error, making it stronger where ever you find problems, but this is always more time consuming and more costly than starting with proven plans.

If you like experimenting and do not mind making numerous changes, by all means try it. But there are often practical reason they do not built hulls the way you propose.

Good luck.

 

Inspiration

Check this out and also the thread:

http://www.youtube.com/watch?v=JbOr46fV4n0&feature=related

the thread: http://www.boatdesign.net/forums/multihulls/planing-catamaran-30415.html

an old boat of mine:

(click on image)

 

I and others have preformed this sort of test on many occasions and a foam sandwich, beach cat will be heavier then a plywood taped seam cat of similar dimensions. This is because the plywood is self supporting in the taped seam build, but the foam core relies solely on the 'glass skins. Since this is the case, the skins have to be fairly thick to offer the same strength, which generally weighs more in the size range. In larger sizes the weight of the plywood becomes a detriment and foam core an advantage, but not in small craft.

This can be easily seen in class racers. many older racers were made in the new "wonder material" in the 1950's and 60's. The idea was to reduce maintenance coast and weight. Well, that's not what happened. When the 'glass boats where made strong enough to accept the loads of the wooden sisters they were to compete against, well, they were just too heavy. In fact, several of these classes still compete today and the wooden versions have to carry around an "equalizing weight" so the poor pitiful 'glass versions can keep up.

This isn't to say you can't build a foam cored cat, because you can. It will be light too, but not as light as other methods. This isn't what I really have issue with though. My main point is designing beach cat and developing scantlings that will not drown you when you're farther from shore then you can swim back to isn't as easy as it might appear and again judging by the general tone and Peter's questions, he's not skilled enough to do this with a reasonable expectation of success. There are many dozens of beach cat plans available, most for not much money that will insure a reasonable level of success.




These are two different Glen-L designs the top one 12', the bottom 16, both about 200 pounds and the cost of plans less then 100 bucks. They both are intended for plywood construction, but a foam core conversion could be made if you wanted to work in that medium and have heavier hulls.

 

Funny to see today's classes that have no weight restrictions like the C Class Cats and the Moths do not use ply instead of the "wonder materials". I think there is a reason for that.

Ditto the historic classes that have used both ply and 'glass construction over the years. In the I14s, 505s, Tornado Cats, A Class Cats, etc no one currently uses ply to build competitive boats. No one has for many years.

It doesn't seem prudent to make 2010 decisions based on 1950s and 1960s technology.

 

It does if you want to keep costs down. The examples you give are far more costly, and too difficult to make for almost all home builders. The object is to create fast sailboats at the lowest possible cost that can be built by the owner at home.

 

Paul B once again has done what he always does, look for specific members of this board, reads their posts in an attempt to find an argument. He's the forum pariah in this regard and has haunted many members over the years. There is hardly an active member on the board who hasn't had to battle this nondescript. Eventually the board will have to make a decision about his repeated and abusive behavior.

He nurses his activities well, controlling himself, just enough to remain, while he works his search a destroy missions. He, by his own admission has designed no boats, he has built no boats, but he is the self absorbed authority on the subjects he comments on. Of course he's never wrong or could admit such either. How many here feel this isn't true? How many others consider a thread dead, when Paul B enters the mix. How many good contributing board members have been battered unreasonably by Paul B? How many have left this forum, sighting Paul B as a major factor in their decision? He's the type of person everyone admits is intelligent and knowledgeable and also that they would never willingly invite to anywhere they'd want to be. The very definition of the board pariah.

 

That is interesting thanks. I had already chosen a design, a paper tiger. Have the plans, was gonna build in 4mm okoume s&g. I thought maybe solid foam core would be lighter but now im hearing that it wouldn't be, which sort of moots the point of building in glass. Still, it would be an interesting build, something new at least. On gary dierkings foam fiberglass ama, he uses just one layer of 10oz cloth. Remember, there is a ply stringer running down the ama. If i chose to continue this idea of a solid foam and glass vaka for a paper tiger cat, with the ply stringer, anyone recomend how many layers of cloth to use? Epoxy, not poly resin btw...

 

From experience I can tell you, the amas that Gary Dierkings designed are delicate and easily damaged. Obviously the longitudinal stiffness comes from the plywood stringer (shown here). this is nothing against Gary, who by all accounts is a skilled, intelligent, unassuming fellow.

Again, it would be possible to make the hulls of your Paper Tiger from foam. In fact the class rules permit any material. I'm not sure what the plans include, but it might be worth checking out. I suspect it would be difficult to have as tough a boat in foam core as in plywood for the same weight, but if you where willing to do routine repair and maintenance, you could have a "delicate" version made of foam core. Without a good look at the plans, it would be difficult to recommend a sheathing weight. The Paper Tiger, fully rigged weighs about 160 pounds, which is light (plywood version), so you'd be looking at 10 to 12 ounce skins on the foam with local reinforcement and stiffeners. Naturally this is easily damaged.

It's an interesting choice the Paper Tiger, I think you'll be pleased with her preformance. If you lived "down under" you'd have lots of these puppies to race against. I'm not sure about their numbers in the USA. To get an idea of how tough and/or fragile the 10 ounce over foam actually is, make a test cylinder. I'd make it about 24" long, 10" around with a piece of 1/2" plywood down the center. This uses very little by way of materials and will offer you a very good idea of how much work is involved (I hope you like sanding) to make them. Once it's cured for a few weeks, smack it, bounce it off the floor, hit it with stuff, etc. to get an idea of how much force it takes to breach the 10 ounce skin. You'll be surprised how tough and light it is, but also how easily a crisp edge or point can break through the sheathing. Now imagine loading it onto a trailer at the boat ramp and having a small wave lift it up and suddenly drop it onto the corner of the trailer frame (or something hard and/or edged). In any case, please do the test cylinder, you'll learn a lot from it. We all end up doing this sort of home brewed testing eventually. It can save you a bunch of headache or enlighten you as to a better way of doing things. I say go for it.

 

PAR sounds very angry.

It seems he believes I have no experience, yet somehow I seem to have more knowledge and expertise than he does. If his belief is correct, what does this say about his skill set?

I can see how this would be frustrating for him.

 

===========
Absolutely ludicrous!!!

In your own words:

 

Reading comprehension is becoming a lost art.