I dont know anything about working with fiberglass

enough speed to waterski?
how many HP?
what plywood for it?

thanks

 

You need a design. I can see that. Look around. See what's out there.
Specific questions can come later, when you have settled on a design.
I wouldn't suggest you design your own boat, as you seem to be ready to build, but not ready to design.
Anything that could pull skiers would have to go at least 25 mph and have at least 30-40 hp. I wouldn't suggest a catamaran for such use. Ski boats are very maneuverable and cats are not suited to anything more than "also pulled a skier once", and at 14 ft, that skier was just a 60 lb kid who started on the dock.
If you want to ski, you want a shallow V monohull with plenty of power.

Alan

 

trust me i will be designing for the next 3 months (funds,parts lists)
i thought about using a two speed tranny, one gear without skier(10HP),with(30
40 HP)
what if i uped it to 18'? then make it with 1/2" plywood and FG with 50 HP?

 

It's not that simple. If you are certain you will be the designer, then design the boat. Only when the drawings can be analyzed can anyone make suggestions as to scantlings and materials.
If you cannot design the boat (and most people can't!), there are lots of folks here who can help you to choose a design.
There is nothing wrong with using an existing design. Why would you want to design your boat? It's not very enjoyable to go through the design process unless you are fairly certain that your efforts will pay off and give you something very close to your expectations.
Guesswork can and will get expensive. Trust me, I have done my share of guessing.

 

A good way to get things clearer in your mind is to build a model of the boat you want to end up with. Something about 3ft long is nice to handle. It will give you an opportunity to understand the building techniques.

This is an age old method of boat building before there was readily available CAD software. The thing about software is that it does not get your hands dirty and if you are starting from scratch then this is essential before you get into more expensive building projects.

Use the techniques you plan to use on the full scale boat. Use 3-ply or balsa instead of 1/2" ply. One or two layers of low weight glass rather than heavier cloth.

You can then post some pictures for others to critique.

I can see an issue with a single inboard engine and a catamaran hull.

The cost and weight of a boat goes up roughly in proportion to the volume. So if you build a 3ft model of a 15ft boat then it should cost about 1/125 of the full scale.

The time to build it can be reduced by good planning and a good workshop. The model will help you plan the steps to build the full scale boat.

Rick W.

 

i was planning on building a model but is it plosible to use a scale R/C Cat hull?
take a look at this! http://www.plumkrazyrcboats.com/site/1565872/product/MTI CAT
its just a tad shorter than i am!
would it work for a model? (big model)
ive had my eye on it for a vary long time and now i have a exsuse!

 

Building the model is the whole point of the excercise. Going with one already made or a kit is defeating the purpose.

 

The idea is to use the model to gain experience in the aspects you need to develop. If you want to buy a boat, then buy a built model. Will teach you how to bargain on price or just accept the sticker price. It will teach you something about getting a boat to water and using it. You will not learn much about hull design, getting materials and putting them together.

Getting the model may whet your appetite for fast boats but close to useless as a learning exercise for actually designing and building a full scale boat.

If you were going to use an outboard motor then getting the engine kit and mounting in a hull you have built would be relevent experience. Mounting a car engine in a hull has greater complexity.

The models you are looking at have racing hulls and not particularly practical for the power level and use you have talked about earlier. The boats on this link are in the size range you have discussed earlier and possibly more practical:
http://www.markhammarine.com.au/cats_pleasure.html

Before you start building a boat it would pay to spend some time looking around to see what sort of boat might fit your needs. I would expect that you could buy a second hand boat cheaper than you could build it unless you have access to cheap materials. Most pleasure boats get little use and they depreciate quite fast so they are normally good value on the secondhand market. So if you are going to spend something like $3000 on a model you might go to say $5000 and look around the secondhand market for a boat that will do some of the things you mention like skiing. This will give you more valid experience for your end objective than buying an RC model. If you buy carefully you could end up with a trailer and an outboard that can be used on the boat you eventually build.


Rick W.