Catamaran Idea...

[*brotha]

Ok...basically here is the idea. To make a 5 person katamaran that would be mainly based on rowing but may eventually have a sale. As drawn in the picture there would be 2 rowers on each side and one who would steer/rest in the middle.

so the basic question here is before anything else is... Do you guys think it would float? The hulls would be made of 1/4 inch plywood and joined inside by a frame somewhat shown in the pencil drawring.

they would be aprox 12-13 ft long
1ft-1ft12nch wide
and about 2 ft tall.

so if we had these 2 hulls made and joined together...they would foat correct?

the boat would not just sink right?

[*brotha]

anyone cmon?

what do you think of this idea? i did not elaborate on it fully yet because i just want to find out if it will float or if the hulls themselves are designed well.

[messabout]

Each hull would support about 600 pounds of weight if they were immersed 12" The boat would float with 5 normal sized people.

Sorry Brotha, you could not design a worse boat, for rowing. The boat could possibly be used as a power boat if only one person were aboard. Even as a power boat it will not be efficient. If you want to row the boat then abandon the catamaran idea. Draw a long boat that is narrow, make it a double ender (pointed on both ends). for starters, draw it about 45 to 48 inches wide and 20 feet or more in length. It will support about 1200 pounds at 6 inches draft. If it is as boxy as the one you have shown it will still be a marginal row boat but far better than the catamaran.

[*brotha]

why will the catamaran be so poor?

if there are 4 people rowing...the ends are very sharp so it would cut through water pretty well.

this is also really just a lake, wide river boat.

THe design is based on these points.


1- Be able to dissasemble easily
2- Be able to hang out on the boat without having to worry about the tipping factor
3- still be able to go pretty quickly.

[*brotha]

bump.

cmon, there are 60 people viewing this thread can someone help me out here?

i would build a one hull boat but would have no way to transport it.

[marshmat]

For rowing, you want the most efficient possible hull shape- period- for a fairly low speed/length ratio in the case of a recreational boat. Box-like hulls, even with the pointy bow, just don't have the right hydrodynamic shape for efficient low-speed operation (in technical terms, your longitudinal and vertical prismatic coefficients are both far too high; rowboats have both prismatics around 0.5ish, on yours the longitudinal prismatic coeff. is around 0.8 and the vertical roughly 1). And for rowing, long and thin is almost always better. Your boat is wide and fairly short. It's just not a rowing shape.
But let's look at your design points:
1- Be able to dissasemble easily
Your proposed structure appears to meet this one.
2- Be able to hang out on the boat without having to worry about the tipping factor
This thing's meant to laze around on quiet lakes with friends and a cold drink? I think it meets this requirement too.
3- still be able to go pretty quickly.
If you put a couple of lead-acid batteries in each hull and add a trolling motor, you should be able to do around four or five knots without too much trouble. But it'll be a dog to row.

[*brotha]

the thing is each part is only about a foot and 1 inch wide, so its almost like a pencil.

i can understand that it will be pretty heavy but once it picks up speed wouldnt it be pretty easy to keep going?

cuz the boat is almost like two canoes, its does not have that much area in the water, mainly just hanging over it.

hmmm

what about with a small sail? would this work better?


also the 4th point would be the ease of making factor.

[marshmat]

cuz the boat is almost like two canoes,

Not really. It shares the pointy bow but that's about all. A canoe's hull is smooth and rounded, no sudden changes in curvature, nothing that would force the water flow to quickly change direction. This cat is boxy; there will be vortices along the chines (sharp edges at the bottom) and the water flow will be redirected not smoothly, but in several sharp jolts at the kinks and transom. Unless it's excessively bow heavy, it will try to climb to plane if you push it too hard. It could be rowed, yes, but it will not have the directional stability of a canoe or rowboat (ie, it will tend to yaw from side to side if the rowers are not perfectly co-ordinated). If good rowing performance is absolutely essential, I'm afraid you'll have a hard time with any sort of cat form. You could certainly try a sail, I won't offer any predictions as to how it might react there.

also the 4th point would be the ease of making factor.

And it wins on that. Take the kink out of the sides and just bend the plywood around the frames, this will be more efficient and easier to do. But you could probably whip it up in less than a week for a few hundred bucks, if you aren't too picky.

[*brotha]

well the thing is the person in the middle will steer the boat, so the two rowers on each side will not have to be so perfectly coordinated.

there will be a rudder at the end of each hull, both controlled together.

how do you exactly go about bending the plywood so much? Is there something that needs to be done to it before hand?

[messabout]

Brotha;
The guys on this forum do not mean to be discouraging. They really do try to be helpful. There are a lot of boat smart dudes fooling around in these threads,and it would be well to believe them.

Marshmatt mentioned prismatic coefficients. That is an important technical a term that numerically describes the volume of the ends of the boat. Despite its' importance, we can just try not to agonize over it. Let's approach your project in a more simplistic way.

Your sketch shows a shape that has a hard corner where the pointy end tapers to meet the main body of the boat. The hard corner has to go. The transition should be a smooth curve. Plywood will do that if you bend it around a frame. Next; the drawing shows a square end (transom) at the stern. That'll create way too much drag so you must get it up out of the water so it will not drag. Looking at the side view, you will need to curve the bottom up as it approaches and eventually joins the transom. That is called rocker. Now you need to give the forward section some rocker as well. If you don't do that the boat will be hell to try to turn. When some rocker goes into the bottom it affects the total bouyancy of the boat. You really don't want the boat to draw too much water so each hull must be wider. With all those guys frolicking around on the boat it will need plenty of bouyancy. Heres what to consider......Make the hulls about 24 inches wide, put in about 6 or 7 inches of rocker at the stern and probably 4 to 6 at the bow. This will not make a great boat but it will get the job done. It will draw about 6 inches of water with an all up weight of 800 pounds or so. Add more weight in the form of more crew members and it will merely draw more water. If you make it this wide then you can safely cut the height down to about 18 inches. The term "safely" is to be used cautiously. This will not be a boat that is safe in rough water or stormy conditions.

If the boat is to be a rowing machine then I presume that the top will NOT be decked over. In such a case the rowers will sit in the boat rather than on it. The higher the sides the longer the oars will need to be. In addition the two boats (catamaran) will need to be widely spaced to clear the oars on opposite sides. Excessive width, between the hulls, will also make it difficult to turn.

I think it would serve your purposes better if you make a long single hulled, double ended, boat and saw it in half at the middle. When you get to the lake simply bolt the two boats together in the middle and go have fun. That will amount to having the same two boats to transport as in the catamaran, but the single hulled boat will work far better and there will be no cross beams to fool with.. There are numerous designs out there that do this stunt and do it quite satisfactorily. There are even three piece designs that are 50 feet long. It will be possible to unbolt the two parts and paddle or row them individually. That will make some competitive juices flow.

Your original drawing is suggestive of those ill begotten monuments of design ignorance from the halls of Hades. They are called pontoon boats. You might take note that they all seem to have 50, 100, 150 horsepower motors. They have a pointed end with a hard corner and a squared off back end just like your drawing. Most of 'em are made of aluminum pipe welded into a hydrodynamic travesty. Yes, they float, and they are spacious. Beyond that they are criminal affronts to efficient operation and on top of that they throw enormous wakes when they use all that horsepower. I'll get off my soap box now !

[*brotha]

i dont really get what the rocker is...do you have any pictures?

And the people are supposed to sit on the middle part of the boat, or on top of each hull not inside.

It would probably have longer larger oars that would be clipped in.

[*brotha]

i guess but all the single hull boats will be rocky and not as good for hanging out on.

I wish the Catamaran thing some way worked; it would be the best possible hanging out boat.


can anyone comment more on its possibilties with a sail?

[Trevlyns]

My advice, since you are obviously ignoring sound advice from knowledgeable people, is just go ahead and build it anyway then see what happens.

[waikikin]

I am keen to be the dood resting in the middle- kicked back with the eski full of coldies, the shaded "day bed" arrangment looks like a cool spot to enjoy some peacefull boating from, may be a quicker "build option" would be to buy a cheapy Hobie/Nacra/Windrush sail cat(very easily driven hulls with low HP) on Ebay & convert for paddle/sail/elect-petrol outboard- get out on the bay soona & get the hulls at terrific secondhand value, looks like a really cool concept boat- dont be discouraged just do it & enjoy the results of your endeavours for fun- for 4-5 people you might need a bigger sail cat or just get 2 smaller ones & double the fun!Regards from Jeff.