SOF Splinter catamaran contemplation

[csmead]

My building plans for Splinter, the Dave Gentry skin-on-frame outrigger canoe, have sat in my drawer for a few years. I always thought it would be a fun boat for 1 person to sail, but I wanted a different bow and stern, and even then, it just isn’t quite what I was looking for, so I didn’t build it. I built Dave’s "River Pram" a few years back and I loved using that that awesome boat! But, it really only sails with one person, and it’s slow. You can fit more people while rowing, but that’s slow too. For this reason, it doesn’t get used much, especially since I finished my Chebacco last year. We’ve had a ton of fun with her, but she needs a ramp to launch.
Splinter cover.jpg

[csmead]

Re: SOF Splinter catamaran contemplation

I thought about buying a Hobie cat if it would fit on top of my minivan, which would be a blast. But even funner would be making my own catamaran. Could I make one out of two Splinters? Two crossmembers with planks between? I'd have to step the mast in the middle, but the same fore-aft position as Splinter.

There I was, daydreaming at my work computer. I fired up my super-sophisticated CAD program and started making some lines (while I should’ve been doing more productive things).
footprint 1.jpg

[csmead]

Re: SOF Splinter catamaran contemplation

The sail for Splinter looks the same as the sail for the river pram. I have one! It’s an unstayed balanced lug, about 40 square feet. I looked for similarly-sized catamarans and saw a 14’ Wharram has a much bigger sail area, 110 total sf! Well, that boat is stitch-and-glue plywood and presumably much heavier (says 190 pounds on the site) and it has a jib. I want a jib. Can you even have a jib with a balanced lug? How big should it be? Should be proportional, I guess. I looked around. Todd Bradshaw, in his Canoe Rig book, has a (gorgeous) picture of a canoe with a 40 – 17 sf split between the two, albeit different types, of sails. Maybe I could do that. Do I need a bowsprit? Maybe I’ll try without one. Wharram doesn't use one, although those hulls would be way stiffer...
My River Pram Sail: pram sail.jpg
Wharram Hitia 14 from their site: Hitia 14 Brazil.jpg
Todd Bradshaw's canoe (with boomed jib and gaff main): Todd canoe rig.jpg

[csmead]

Re: SOF Splinter catamaran contemplation

I’d like to get by with only 2 crossmembers to save weight, if I can make it work. That means the mast step will have to be rigid enough on a single crossmember to hold the unstayed mast.- Dave has the pivoting leeboard on the side of the hull (of course). I thought about putting it out on the midline but it got complicated in my mind.
footprint 2.jpg
Do I need hatches? This isn’t exactly an expedition boat. More for light winds and free-spirited day sailing. But… I don’t think sealing up a skin-on-frame boat is a good idea just from a ventilation perspective. I should have at least one hatch on each hull. How about here? I thought about rudders but I have two 6’ oars from the pram. I could use one as a steering oar to keep it simple. That would also help me if she has trouble tacking, by just paddling her around.
By the way, none of this is in any way endorsed by the Dave Gentry, the designer of Splinter.

[robm]

Re: SOF Splinter catamaran contemplation

I cannot see how you will support even the tiny sail area you propose with an unstayed mast on a plank, or even two crossing planks. Use a forestay to a bridle, and two shrouds, and the mast will have a better chance of standing. You will need somewhere to sit, and that single plank in the middle does not look comfy. With 8 ft of beam and only 57 sq. ft of sail you may not need to put your weight to windward, but it makes it a lot easier to see where you are going. The hulls will need spray decks to keep them dry(ish).

[csmead]

Re: SOF Splinter catamaran contemplation

I cannot see how you will support even the tiny sail area you propose with an unstayed mast on a plank, or even two crossing planks. Use a forestay to a bridle, and two shrouds, and the mast will have a better chance of standing. You will need somewhere to sit, and that single plank in the middle does not look comfy.

This makes sense. Rather than just planks for the crossmembers, I was going to use some kind of I beam or box beam. Here is one from a Wharram 26 blog. Some scaled-down version of this.
crossbeamexterior1.jpg
If I add shrouds and a forestay, I imagine the force would be directed downwards into the crossbeam at the mast step. But, it reduces the size of the plywood "box" I was imagining would be needed as a mast step. I'll have to mess with this some more.

Oh yeah, I was going to plank all across the deck, like in Post 2, I just removed them in the other picture to think about other stuff.

[johngsandusky]

Re: SOF Splinter catamaran contemplation

Looks interesting. I would buy catamaran plans and convert the build to SOF.

[Woxbox]

Re: SOF Splinter catamaran contemplation

Looks like a great project. I would go with a biplane rig. Make up a second balanced lug sail to match the one you have, and stick one, unstayed, in each hull. It's been done and it works.

Here's a well-respected sample:

[csmead]

Re: SOF Splinter catamaran contemplation

Looks like a great project. I would go with a biplane rig. Make up a second balanced lug sail to match the one you have, and stick one, unstayed, in each hull. It's been done and it works.

It does?........ I'm stunned, Dave. I saw you post last night, but the jarring effect of seeing those two sails side by side reverberated through my entire body, rendering me unable to respond. It sure would solve a bunch of design issues. I'm going to sit with that idea today at work. Come to think of it, I DO love biplanes.

[Woxbox]

Re: SOF Splinter catamaran contemplation

That photo is of Miss Cindy. You can read about it in a series of blogs by builder Tony Bigras here: http://turtleislands.net/tmc/

It's a great read, and he talks from time to time about the strengths of the biplane rig he put on the boat. He created a slick roller furling system to make reducing sail easy.

This is a unique catamaran rig. I know of two attempts to create race-winning boats on a big scale using this approach, and neither one was especially successful. One just wasn't fast enough,

and the other broke. Which was Team Phillips, below.



But it has been done enough on cruising boats, where I think it makes a lot of sense. No headsails to tend so the rig is self-tacking. If the wind picks up, you can douse one sail completely or both sails half way, or some mix thereof. Experience with the boat will dictate what's best. In your case, you'd double your sail area by adding a second mast without adding any height to the sailplan. That would give you 80 square feet, which ought to work well.

One thing to think about -- you don't want the boom to catch on the mast opposite. Usually not an issue, but a consideration when the hull separation is figured.

Another fun option -- for downwind runs on light days, you can set the sails wing-and-wing, and then hang a big square bedsheet of a sail between the masts. Hang on!

Do a Google photo search of "biplane catamaran" and see what fun stuff pops up.

[csmead]

Re: SOF Splinter catamaran contemplation

Alright, well, I'm convinced. It'll fix the design problem of the central mast step. It'll give more overall sail area. It might give more forward visibility. I'll have to step the masts through the skin but I don't see why that's a real problem. I'm going to start cutting some plywood frames.
footprint 3.jpg

[csmead]

Re: SOF Splinter catamaran contemplation

A small step, cutting the frames, but it feels significant to take the first step! I remember doing the same for my 19' Chebacco back in 2018 and, a little over 3 years later, it was a real boat!
bulkheads.jpg

[Woxbox]

Re: SOF Splinter catamaran contemplation

And the beauty of SOF construction is it doesn't take 3 years. I'll be following with interest, of course. The other nice thing about a boat like this is that it will be easy to adjust things once the sea trials begin.