Does anyone out there have any experance converting two kayaks into a catamaran?

Hi,
I'm new to this page but I am trying to convert two scrambler xt kayaks into a catamaran. I so far have worked out basic plan and would like to get some feedback on the probility of this working.

I have two scrambler xt sit on top dive kayaks.
Thay are 12' long and 29" wide and can carry about 300 to 350 lbs each.
I bought 2 sections of aluminum tubing 6' long and 3" dia.
I have secured the kayaks together using cargo straps as one would do when securing them to a roofrack.
I have passed each tube through snug fitting holes an aluminum 6"X3"X6' box section.
To this box section, through both sides I have inserted a 10"long 1" dia S/S bolt backed with washers and fastened tightly to the box section. Onto the end of the bolt I placed my center board.
The center board is a 1'X4' alauminum plate with wood fastened to it and shaped into a clean foil shape. It is free to rotate if it strikes the bottom and then is pulled back down by strong rubber shock cords. I have placed it at a point I hope is just forward of my sails center of effort to get a bit of weather helm. It would be no trouble to move it if I need too.
My sail is a windsurfer North Sails 6.5. I know this is a very large sail for this type of craft, but I already had it just collecting dust in the shed, same wirh the two Kayaks. So I'm going to try to use it. I'm to old to windsurf any longer and a mild case of Parkinse has me needing to sit down when I sail.
I think I can install a sort of stub mast made of aluminum tube 1 1/2" dia, and about 5 1/2' long into the box section of my "Catamayak" as I've started calling it. I'll set it up so the stub mast inserts into the mast of the sail about 4' or so. And it can rotate a full 360, so if I start getting over powered, I can slaken the sheet and let the sail weather cock in the wind. I think that will spill out enough power to get to a lee shore safely.
In my time I used to ride an 8.5 race sail on my windsurfer at wind speeds around 18 to 20+, I hope by allowing the sail to spill all of it' wind on a cat with a 6' beam, I'll be alright.
I am going to install a large kick-up rudder, to complement the 4' long centerboard, and do a capsize recovery drill or two on a calm day just to see if I can do it alone.


Does anyone see any way to improve on my design? If you do see anything I did not think of please let me know.

Sorry I took so long to lay all this out but I wanted you to have enough info to not recover some fact I may not have told you about.

Thank you Amy

 

Where are you going to sail it? The amount of sail it can carry safely will be limited by its speed as well as the hull spacing, weight and structure. SOT yaks are not generally known for speed; trying to push inefficient hulls too fast might be risky.

 

If you keep the bows up you should be fine. My sailing canoe can have its sheets eased direct downwind and it does get you out of jams. I'm not sure if your sail has a wishbone to keep in the camber. Practice depowering in the light stuff to see if it pulls in unexpected directions if it does. What do they say about race cars ? If it breaks make it stronger, if it doesn't break you made it too heavy !

 

Hi guys,

Thanks for the quick response. I'll be sailing out of Berkeley ca. mostly.

 

could you post a few pics of what you got and what

you are planning to do?

Personally, I would have started with some less stubby SOTs for a kayak cat, such as maybe a pair of 16' Ocean Kayak "Cabo" tandem/triples.

If you need odd pieces of metal for odd projects in SF Bay Area in recommend Alan Steel and Supply in Redwood City.

 

I was considering it until one of the kayaks got stolen.

 

I'm going to try something similar, but with a small electric trolling motor. My kayakamaran will rule your catamayak!

 

Why don't you build a catakayakmaran or a kaycatamaranak?

 

Sorry I've been away so long, but my pc died and I just got a new one for my b-day. Thanks to all who responded to my posting. Home Depot sent me the wrong metal parts, and it cost more to ship that wrong stuff back, as well as a (30 percent restocking fee) then it was worth!

Im going to try to build this catamaran using stuff from around my house. I have a pile of redwood from a deck we removed, and the two kayaks and 6.5 sq. meter sail just sitting in the shed. sporting equipment I can't use anylonger. (I have a mild case of Parkinsens disease) It has messed up my ballance. So I do not care if I go fast. I just want to sail again, on a watercraft that is not so tippy.
Slow is fine as long as I come home alive.
I'll try to post a photo of a mock up I made out of some old scrap wood in my yard. It was never ment to sail, just to get a feel for the proportions of my components.

Thank again Amy

 

do not use redwood. It does not glue very good and it does not hold fasteners very well at all. They all seem to work loose and on a boat it would not take long. If you do use it BOLT IT WITH LOCKING WASHERS. test any adhesive you use on a couple of dry pieces. It will last forever and that is it's only good point. It must be dry or the tannic acid will cause havoc.

 

Happy birthday.

 

That looks like a great plan. Nice sail too! I would consider having the kayaks a bit further apart (longer beams required) to make it more stable.

Also, you need a proper rudder, a paddle will be inadequate to control it, you need something fixed to the frame. make it sturdy, do not underestimate the forces on the rudder, or a keel or dagger board if you are using one.

You might look at these for some ideas:

http://www.youtube.com/watch?v=K226V2vwQyI

http://www.youtube.com/watch?v=eN2mNBASYQ4&feature=related


Great project, have fun and get some pictures of it on the water for us.

 

I'm using the Redwood, because I have it laying in my yard. I'm using it because it's free not because it's the best choice. I think that if this boat works well, I will rebuild it with better materials. But for the checkout phase, I will use whatever is cheap and available.

The mock up I built in the photograph was made narrow because the wood I had available to me was too short to make it wide. But I want to get a look at how the sail would look on the kayak.

I'm going to through bolt with stainless threaded rod large flat washers and stainless steel locking nuts. Remember, this is only a prototype. If this works well I won't change it I would just rebuild it. But if it does not work well, I can modify it before I rebuilt it, thus tweaking it in before I invest any money of significance in this project.

However, I have already run into one snag. The 4x4 cross beams that I was planning to use, may not work. It seems that one them has a knot critical area. The flaw may weaken the beam to the point failure. It is my intention to cut out as much of that knot as is possible during the rounding phase the beam. But I am afraid it will take the beam down to about 2 inches in diameter. A bit thin for my tastes.

I may reconsider and only round the portion that this is the kayaks, maybe leaving the excess wood in place will stiffen the beam and make it stronger. But I don't know if I should orient the crack created by that knot, turned so it is facing up or down.

Anyone have any suggestions? How thick of beam do I need to support two 60 pound kayaks and possibly two passengers and a minor amount of gear?

I don't know if cutting a 4x4 down to a round section will lighten it sufficiently to make it practical to use, and now I may not even be able to do that. This thing could get fairly heavy. So should I look for a better piece of wood, or work with them knot and upright or down facing position?

As for the steering being done by the oars this was only a temporary condition, it was never meant to last more than one or two outings. I just needed to get the feel for how this thing will handle, with the sail placed where it will hopefully end up being, and the centerboard placement where it will be. I will move them around as necessary, until I get it right. And I will mark it, drill it seal against the water, and began testing it.

I will post more pictures as they come available of the actual work in progress as well as the finished product if it works!

Thanks in advance for any help you may be,

Amy

 

The beams look pretty solid. The one holding the mast has to be stronger than the mast and each must be able to withstand the crew standing on it while it’s on the ground. If you can’t break it like that you won’t be able to do so in the water before it flips. 2" dia is likely to be much weaker than 4 x 4 even with a knot. Please wear PFDs!

 

If the crack is near the center of the beam, orient it so it is horizontal, if it near an edge, put it on the tension side, down. If you are worried about it you can nail on a piece of plywood over the weak spot, going about a foot either side of the knot. Though as mentioned, I think the beams look plenty strong for your use, even with a knot.

Even as a temp rudder, a paddle is inadequate to control a sail boat. Install a proper rudder, even if made from a chunk of plywood with two door hinges on it. It will not give you a proper test if you can not control the boat trying to hold a paddle in your armpit as a rudder (I know, I have had a rudder failure on a small boat I built!).

Even lashing it in place would be better than holding it. Just put it as far back as reasonable, about one square foot below the water, attach it to the aft beam, or even to one of the kayak sterns, and it will work fine.