DIY Simple Catamaran Sailboat Design

Skyak, I am in fact using stitch and glue method! No chine logs, just zip ties, fiberglass, and epoxy.

 

wheat flower will work as filler - just throwing it out as I have skipped parts of the thread. we want more photos!

 

I second that!

 

Marsh Duck

Petros suggested I stop by & comment on this thread. I created and have enjoyed using the Marsh Duck. The thread's gone on from when she was mentioned, but perhaps a few would be interested in some update.

The sail shown in the picture in this thread is 56 square feet - used summer of 2012 during her first cruise. From May 10 to early August 2013 I sailed her all over the Salish Sea (Port Townsend Washington to the north end of Vancouver Island - San Juan Islands, Gulf Islands, Strait of Georgia, and all the islands, passages and rapids north of the Strait of Georgia), with a 107 square foot big headed, fully battened sail (racing dinghy style) with 3 reefs down to under 25 square feet - sailing in everything from light breezes to 35 knot winds with whitecaps 2 to 4 feet high.

There is lots more about the boat, design, and cruising on her, including some video, on my blog: www.scotdomergueblog.wordpress.com

The hull shape is based on the IC 10 racing canoes. The cabin is 6 ft 4 inches long. Hull beam is 42 inches (cabin almost that at shoulders) with side decks (for hiking out) extending to 54 inches. She's designed as a planing mono-hull, with sliding-seat rowing when there's no wind. I row her at 4 knots. Even when cruising heavily loaded and reefing early I've found myself sailing up to 7 1/2 knots and probably quite a bit more a few times when I wasn't trying to look at the GPS.

 

Thanks Scot!

Wayne

 

Scott I have actually spent a lot of time on your website, it is very helpful and well written, didn't expect to have you here in person though! Thanks for coming in

I have almost finished cutting the wood for the canoe, although sanding it to shape by hand is going to be a doozy, at least a few hours of hard work. Well that's okay... Anyways, I rented a jigsaw for a day, so it went much quicker. While building, a few concerns popped into my head.

Firstly, how is the flat bottom going to effect my performance? Was that a bad choice for the ocean? Well, I am stuck with it, unless I modify the already-cut pieces of wood, which I guess might not be out of the question...

Tomorrow I will epoxy the plywood pieces... Or should I put them all together first then coat the large pieces in epoxy? That way I would encase the butt block in the epoxy as well. Should the butt blocks be facing outward? Or will that get in the way of the fiberglass? Is 2 gallons of epoxy really gunna do this for me? Or may I need more? I have about 1 quart of a different type of epoxy... Small blue cans, I forget the name. Part A and part B, equal sizes.

Anyways, here is a picture of the progress so far.

 

Flat bottom will give you more 'slap.' Not as good as a rounded or 'v' type bottom - especially the front half or third of your boat.

But, you are just a canoe, so you might just live with the slap .... you won't be going fast, so unless you are paddling into the wind, I am not sure it would be a significant difference for your project ....

Are you still wrapping with glass? If you are, you could wrap the bottom in Polystyrene (fancy styrofoam). Then fair the bottom to a less flat bottom, and then wrap with the fiberglass .... On Polystyrene, the points were you glue pieces together are stronger than the Polystyrene. So, the joints would need special attention in your fairing process.

Wayne

 

Well am I crazy for thinking that modifying the bottom wouldnt be impossible? In fact, as a strange coincidence, the bott ends are the only pieces I haven't cut yet. All the higher pieces and all the frame is done, and the bottom middlw piece, but no others. Would a shaped cut down the middle of the flat bottom make it possible for me to stitch together for a chined bottom? Or is that too much effort for not much difference..? I have a feeling that I want a chined bottom! (V bottom, idk what to call it exactly)

 

I am not sure I understand what you are describing.

'vee' bow area: http://en.wikipedia.org/wiki/File:Outrigger_Camiguin_Philippines.jpg

rounded bottoms: http://en.wikipedia.org/wiki/File:Racing_outriggers.jpg

remember round and flat goes through surf better - keeps enough buoyancy when in the 'foam.'

'vee' shape tracks better ....

 

Some thoughts on bottom shape and "slap":

Canoes tend to be narrow and pointed. Even with a flat bottom, if it's narrow enough, slap shouldn't be much of a problem.

In the ocean the horizontal distance between waves tends to be longer and a canoe at 15 to 18 feet is going to go up one side and down the other rather than slap. It's short, steep, choppy waves that will give you bad slap. On lakes or inland water ways when a strong wind comes up, it's more of an issue.

Chine simply refers to a shape that has flat surfaces (panels) with angles between - as opposed to round bottom or round bilge which has a continuous smooth curve from the more vertical sides to the more horizontal bottom.

From what I understand, your canoe is chine, and from the panels in the picture I'd guess "double" chine which means two "corners" between the bottom and the top of the sides. This is the same as my Marsh Duck.

With a canoe or kayak (without outriggers) you're always balancing stability and drag. The wider and flatter the shape, the more stability, but also the more wetted surface and the more drag (as long as you're not on plane). With a flat bottom and single chine (for example sharpies) you get more wetted surface and therefore more drag for a given amount of stability. A shallow V and double chine, like the Marsh Duck, is noticeably better. As you add chines (for example Hugh Horton's Bufflehead) you get closer and closer to a round bilge shape - which will give you the best stability relative to drag, though I understand that in the change from single chine to double chine you already get most of the benefit as long as the hull shape is otherwise good.

Most commercial canoes are round bilge AND flat bottomed, at least for most of the boat, AND they are narrow enough forward that slap really isn't much of a problem.

Personally, I wouldn't worry about the flat bottom of the design you're using. I'll bet it will perform close to as well as if you added a bit of V forward. And modifying the design may have negative side effects (possibly including less stability).

Some thoughts related to using outriggers: these give lots of stability regardless of hull shape! Most tri's have very narrow, sharp V-bottomed hulls. Since stability isn't an issue, this gives the best performance in most ways, and slap simply isn't an issue since the sharp V cuts through the waves. This difference is one of the reasons that I generally don't favor ADDING outriggers/amas to a boat that's designed as a mono. If performance is much of a concern, you want a quite different hull shape for a tri or catamaran.

Best wishes!

 

And don't start customizing existing plans as you go. It is not wise for many reasons and will likely just result in big waste of time. Any boat is a compromise but picking an existing proven design is likely a well thought out compromise - I don't think you have any of the experience/knowledge to start making alteration.
The kind of boat you are making is not going to be perfect but that is not a problem.

You can live with it - you are challenged by time and budget so stay with the plan despite temptations.

 

Okay, I think you are right that it would be foolish try to modify the plans myself, so I won't try. I have finished all the plywood, picture related, and I have also purchased 50 yards of 6inch fiberglass, but now I have a few questions, and a few concerns...

Firstly, what the heck do I do now? Well I'm going to sand all my pieces to the correct shape, if I can figure out the correct shape for each of them (might be harder than it sounds I am thinking...) Then, I need to join all these long panels together.

Should I really do butt blocks for all of those?? Even the wide bottom piece? Is 50 meters enough fiberglass for me? If I do 6 meter strips, inside and outside, down the 6 joints, that will be 72 meters... ****. Well, maybe I can skip fiberglassing the outside of the joints if I put the wide fiberglass on the outside of the hull?

If I am going to do butt blocks, how doea that go exactly? Do I make them from plywood? I can't find a great guide anywhere online, except for fiberglass splicing them... Is that out of the question?

After that, I need to coat the wood with epoxy. I'm guessing I should coat inside and outside with epoxy... Im also guessing I should do that after I put the butt blocks/splices on, for extra strength.

From there on out, stitching them together, I understand somewhat, at least enough to not have questions at this point. There are also enough online tutorials to get me through that process for the most part.

Thanks for all the help Guero and everybody, all is greatly appreciated.

 

construction process

Hello again,

I highly recommend that you watch the Pygmy Boats construction videos (google Pygmy Boats, click on Kit Construction Process, and follow from there. I had never done stitch and glue before I started the Marsh Duck, and found these videos invaluable! There are lots! So plan to spend some time on-line with it. I'm sure you'll find it worthwhile!

Yes, the first step is to splice the panels together to make them full length. I did this using simple, fiberglass butt joints as shown in the videos. I used 2 inch wide 2 oz fiberglass for that. IF you are covering the outside of your boat with fiberglass cloth (rather than just taping the seams), that is enough. I would never use butt blocks for a stitch and glue project, and certainly not on the outside of the hull!

I haven't thoroughly read the thread, so perhaps you've mention and I missed: what is your plywood? (thickness, quality, etc.)

I recommend that you use fiberglass cloth over the entire outside of the boat (and preferably the inside as well) rather than just taping the seams. With relatively narrow panels, you probably won't add significant weight, the process will be easier, and the boat will be much stronger and tougher!

Since you've already bought the 6 inch tape, you may not want to do this, but I'd suggest you seriously consider.

I used cloth on the outside and only taped the seams on the inside (and also saturated/coated the bare wood on the inside). I suspect it wouldn't be any heavier if I'd used cloth on both sides. The outside of the boat is VERY tough. I can drag it up on gravel beaches and even bang it on rocks without more than superficial scratches on the outside. But the several times it's been banged on rocks, the inside has buckled and split the ply because it doesn't have a fiberglass skin to hold it together and reinforce it. So then it has to be repaired, which is a pain! In one case the damage was under the cockpit floor where I couldn't see it. I didn't realize it had been damaged (didn't even realize it had been banged on a rock; there was no noticeable damage on the outside). Water got into the damaged area from the inside of the boat during capsize testing, and the ply de-laminated and even rotted a little before I discovered the problem. That was a real hassle to fix!

I would definitely use cloth on both sides! I recommend this in my Marsh Duck construction manual.

I used West System Epoxy and followed their instructions. I did not do a separate saturation coat of epoxy before the fiberglass, but followed the West System dry laid approach. It is essentially the same as in the Pygmy Videos EXCEPT that you don't do a saturation coat of epoxy before laying the fiberglass cloth. After you've prepared the surfaces (seams and wood), you lay out the fiberglass as shown in the videos and then apply and squeegee the fiberglass - all one step, making sure you use enough epoxy to saturate the wood and the fiberglass, but also making sure that you squeegee it well enough that the cloth doesn't "float" and that you don't have excess epoxy. I'd suggest that you request the West System User Manual. I did that and studied it before I ever ordered epoxy.

Between the Pygmy videos and the West System User Manual and whatever manual comes with the epoxy you use, you should have all the info you need. If you have any specific questions as you proceed, I'll be happy to explain whatever I can from my experience. My direct e-mail is scotdomergue@yahoo.com[/email].

Scot

 

PS: given the shape I see in your picture I think performance will be fine and "slap" won't be a problem

 

Hello again, and apologies to all. I just went back an read most of the thread and realize that there is a LOT that I'd missed, and some of my questions and comments aren't relevant. A couple of further thoughts:

Given a better understanding of your planned use, limitation of budget, and not much caring about it lasting a long time, using full width cloth rather than only taping the seams might not be so important, though with the thinner ply you are using (4mm? 3mm?) it would be better for strength as well as durability. With 6mm ply I doubt that strength would be an issue. Though with a flat rather than V bottom, the unsupported width of ply is larger and strength of the bottom panel more important.

Paddle vs row - I decided on sliding-seat rowing for the Marsh Duck for 2 reasons:
- a double bladed kayak paddle is excellent for a narrow, light, low sided boat like a kayak. As the boat gets wider, it becomes more difficult and awkward. I tried Hugh Horton's Bufflehead and decided that @ 33 inches beam it was too wide for me to enjoy paddling, though part of the problem was low seating position and high sides at maximum beam.
- I wanted a boat that was big enough for extended voyaging, potentially carrying supplies for months at a time, and water for up to a month. A wider boat with more stability also appealed for sailing but requires greater power to push it through the water. Sliding seat rowing is far more powerful than paddling.

As noted by others, a double bladed paddle is far smaller, lighter and easier to deal with than oars. Sliding-seat rowing uses BIG oars, requires the sliding seat arrangement (more stuff and expense), and needs a way to mount the oarlocks almost 5 and 1/2 feet apart.

For your smaller boat with budget and time limits, I think the paddle makes more sense. AND I suspect that the boat you're building will be wide enough that paddling will be slower and more tiring than I would like . . . PARTICULARLY if you have an outrigger.

Finally, I would suggest that you include a small fiberglass repair kit in your packing list. I use West System G-Flex and a small amount of fiberglass cloth (or tape) and a bit of sandpapper. I've been known to mix the epoxy on a piece of driftwood or cardboard with a small stick and then spread it with the stick. A small, light plastic spreader helps with the cloth.