Submersible hulls

I think part of the confusion comparing submarines to sailboats is that in the former all the living and storage space must be submerged, meaning a huge ballast and wetted surface, and corresponding inefficiency. If we only submerge the displacement volume of the sailboat then indeed there would be no wave resistance. But there might be increased wetted surface since the entire displacement volume must be enclosed by water.

But this has already been done better with hydrofoils, a more efficient solution because the lift provided by the foils comes at a lower cost in resistance than the equivalent submerged buoyancy. Hydrofoils don't work at very low speeds but there you don't have a problem with wave resistance anyway.

 

Yes, hydrofoils are better theoretically, but nobody has figured out how to cross oceans with them in varying conditions. Going from wave piercing to wave submerging (I think I came up with that term ) isn't a huge leap compared to flying on foils.

 

I build a little 10 feet long wave-piercing sailing out-rigger with modest and primitive sail surface, just a tarp cut in diagonal mounted on bamboo sticks. The hull was build in polyester FG with a round section half submersed the thing performed well in turbulent waters giving a speed of 8 knots and no sprays, min. pitching and min. windage. I build the amas flexible and that proved to be a success, no strong stresses and no need for heavy and strong bolting at the point of attachment. Than I altered the cross section by cutting the hull in half at the water line and joining a flat strip to achieve a higher then wider section and the results where horrific: pitching wild, splashes and less speed. I agree with Collin his idea can be a winner.
The only complain I can report on my project is the manoeuvrability: under sail had an excellent directional stability so to say it would go as straight as a rocket, but without sail, pedalling it at low speed was bad, it wouldn't respond to my will, perhaps is because the hull was a parallel pipe bluntly pointed at the 2 ends and had no rocker.
Next I'll' try to build it with a longer and sharper hull giving a bit of rocker and belly and as the first experiment, half under water section. Had a magic performance. I loved it.

 

That thing's really cool! 8 knots out a little 10 foot outrigger is pretty damn good.

How deep is the main hull?

 

Hi Collin nice meeting you. Considering the sail being such a poor quality, the result was more then satisfactory. I dare saying it touched 12 knots in strong gusts and once again no spraying, but hair raising experience, with all the bow cutting under water like a submarine and not knowing what to expect next. I believe, waive piercing is the design of the future for multi-hulls. No splashes, no hobby horsing and fast pleasant going. My fear is: how a cruising sailing cat will behave on following seas? Will it dig the bow in and pitch-pole?
Getting to your question, the centre part of the hull was made by glassing around a 10'' DIA PVC pipe. For the 2 ends I made a pattern in plywood and foam then glassed it in 2 halves each end. The monster, when half in the water, gave about 100 kg of buoyancy. Just enough for me (70 kg) and the craft. The cylinder (main hull) was partitioned each 1.1/5 feet as a bamboo cane, this insured compression resistance without the need of a lot of laminations, plus extra safety in case of a punch. The “box” over the hull, where the ama are attached to, proved to be next to useless. The water never reached the level of the scuppers. Too small to fit the feet in, extra weight and a lot of work to make. Hit and miss, this is the cost of experimenting
I just finished the sketches for the next one, far easier to make, lighter and more dive capable. Can't wait to make it.
cheers

 

So the hull gives lateral resistance and you didn't put any sort of leeboard?

I built a 15 foot hawaiian style canoe in SOF. Skinny little hulls can be very exciting. I don't think I ever reached anywhere near the maximum speed of it. I ended up breaking the mast step and cracking the mast, but couldn't find wind big enough to really see how fast it could go. The only downside is low wind performance. I'd prefer a mono hull in light winds.

I think if you were careful with your cuts, you could make a main hull like that boat out of 2 sheets of plywood and an outrigger float out of 1 sheet, or use a PVC pipe.

Also, you could use two straight sticks as crossbeams and save the time and effort of laminating them.

I'd be interested in helping you out if you needed any help.

 

What's SOF?
As for lateral resistance and consequent up wind performance I'm afraid I can't talk highly of it. But who can talk highly of up wind performance in cats? As for low wind performance sorely it was good and definitely better than any of the monos of its length.
I've tried to add a lee board but encountered more troubles than I wanted. I abandoned the project any way, after the F-up, that of catting the hull along the water line and increase the hight, to achieve more buoyancy. How stupid of me doing that, sob, I should have extend the length instead. Live and learn.
That of building in plywood is not in the agenda. I want it round and smooth some thing very light with folding ama to pack and carry with me on my old yacht. The idea is to use it in emergency as a life raft and for exploration around the anchorage. I can do things with it that I could not do with any other dingies.

Thanks for the offer I'll keep that in mind.

 

well done, might have to eat my words.

 

Might?

-Tom

 

Actually last night....I worked out you could squeeze a 12 foot proa out of 3 sheets of plywood. That 3 sheets includes the material to build the outrigger.

And being plywood, making it collapseable would be easy, but would add probably another half sheet of plywood. If you made the outrigger out of PVC, you could easily make the main hull out of 3 sheets and have it unbolt in the middle.

I'd say give up the rounded for ease of building. You can make a plywod hull quite nice looking with the right accents.

 

I am a patter maker, and have a fully equipped workshop, complex shapes are no limit to me.
And yes I have the right accent for the job.

 

All too right. I wouldn't go for totally immersed hulls. I would go for waive piercing, keeping in mind that the goal here is to envisage the best and practical solution for the construction of a cruising sailing catamaran. Hydrofoil is surly the fastest but not suitable for the purpose.
Horses for courses.

 

The more things progress the more they go backwards. Waive piercing might be a modern concept for as, but the savages did work it out a long time ago and mind you, without computers. Take a look at this.
http://outriggersailingcanoes.blogspot.com.au/
I want it.

 

This clay model is the first attempt to visualise the ends of the Wave Piercing Out Rigger I want to make.
WPOR sounds like a good name for this project.
What's your prediction on the WPOR performance?
I think its performance will be excellent in all respects BUT I'm very concern about its behaviour in following seas. The proa in the pic. previously posted, would nose dive in short rollers when running before the wind, without giving signs of pitch-polling. The WPOR is far sharper. What will it do?
Keep in mind the VPOR is totally symmetrical, so this clay model is representing bow and stern.

 

As a precaution, I added a “snapper forehead” or extended buoyancy. That should help preventing pitch-polling when running in following seas.