Hey James,

what you said about the cabin and cockpit is quite close to what I had in mind. My thinking was to give a cabin a 0.6m high pod-like feature to windward, which is long and wide enough to sleep two, much like Jzerro’s lee pod. Then to leeward of the double bunk would be the narrow main part of the cabin, providing 1.2m of height, so sitting headroom. It would feature a mini-galley in the ‘front’ and the head at the ‘back’. There would be a hatch/companionway to leave the whole cabin to leeward. The cabin roof could be extended to leeward, providing an say a 0.5m overhang (like they have on the new Volvo Ocean 65 boats), so that you could be outside, and be quite well sheltered from the wind and rain, but would be able to sail the boat, espcially if that overhang had windows toward the bows so you could see properly. You’d actually have a dodger on a proa then! This entire assembly would make up the pod-car. I’m going to have to sit down and do a proper CAD-Model of a potential pod at some point; that’s going to be a lot of work to find something good though.

Where reserve buoyancy is concerned, I was thinking of something around about the 200% displacement mark. Maybe extra freeboard at the bows would do the whole thing some good though, but with this entire Tepukei-based layout I’m quite worried about the potential of burying the hull… Has anyone here on the forum actually ever sailed on a Tepukei?

At the moment I’m considering to option of building a simple on with a 5.4m hull, to test the concept, and to see if it buries itself… If it does have submarine tendencies and I abandon the concept, then I could still use that hull as a somewhat too short and suboptimal ama for ‘Firstborne’. Since I’d build the ama for Firstborne before the vaka anyway (for space reasons), making a boat out of it would also get me to the water faster, and wouldn’t be as large a detour as would otherwise be the case, particularly since the ama needs a support-structure of significant height anyway, to connect it to the horizontal iakos on Firstborne (= the height of the raised platform on the Tepukei prototype?).

Cheers,
Marco

This video shows some Tepukeis sailing. Right at the start you can see the front portions of the vaka turn into a submarine in that wave there. The boat slows down rather violently the moment the wave slams into the flat vertical faces of the beams supporting the superstructure. That may be a problem one would want to fix by not having a flat panel there (easy to do, just support the whole superstructure on struts), but on the other hand it is kind of an emergency brake which will prevent the hull from burying itself any further…

I’m inclined to say that supporting the superstructure with struts is better though. Violent deceleration like that can be really dangerous.

Thanks for your reply Marco. I hope you have time to draw the pod as I’m very intrigued by your description and, indeed, by this style of proa.

Putting the superstructure on struts does have that advantage of lessening the sudden ‘brake’ and is in keeping with the whole ‘spidery’ nature of Tepukeis. The trad ones used the structure between the hull and deck for stowage. If you wanted to have that capacity too without the ‘braking effect’ in breaking seas (unconscious word play there!) you could fair the ‘turret-like’ structure in so that it formed a mini pointed hull on top of the vaka.

I’m aware that the Santa Cruz Islanders didn’t make Tepukeis less than 40’ long. So I’m wondering if the form would perform (sorry!) at smaller lengths. i.e. would a scale model give any meaningful results?

To increase bouyancy at the bows, maybe some ‘pahi’ styling could be employed.

James - 01 June 2014 08:17 PM

Thanks for your reply Marco. I hope you have time to draw the pod as I’m very intrigued by your description and, indeed, by this style of proa.

James, I decided to make your wish come true… See the pics below! 😊

I also redesigned the vaka to make it look better; the inverse flare (there’s probably a separate term for that in naval architecture?) is essentially just there for looks. Vertical sides and a rounded deck to shed the water would be fine, but this way should shed water fine as well and I think this looks much cooler. 😉

Putting the superstructure on struts does have that advantage of lessening the sudden ‘brake’ and is in keeping with the whole ‘spidery’ nature of Tepukeis. The trad ones used the structure between the hull and deck for stowage. If you wanted to have that capacity too without the ‘braking effect’ in breaking seas (unconscious word play there!) you could fair the ‘turret-like’ structure in so that it formed a mini pointed hull on top of the vaka.

That ran through my head too, sort of like the fin/sail of a submarine. You could have two pods (about 2.4 x 0.6 x 0.6m each) on either side (windward and leeward) of the fin, so the whole superstructure would look like a ‘T’ when viewed from the front, to provide two bunks for sleeping. The vertical part of that T would provide the required vertical headroom to fit a head and a sitting galley, down in the middle of the cabin (fore and aft). You could enter and exit the cabin through a hatch in the deck (middle of the cabin). That would be a significantly smaller way to build a 2 person cruising Tepukei, but without the RM- and other benefits of a pod car then.

I’m aware that the Santa Cruz Islanders didn’t make Tepukeis less than 40’ long. So I’m wondering if the form would perform (sorry!) at smaller lengths. i.e. would a scale model give any meaningful results?

I dunno… If you’re just sailing on a lake and there’s no waves anyway, then it’s as fine a vessel as any other, but it could be that this type of boat suffers from shortening / scaling down more than others when it comes to burying itself in waves. I guess there is only one real way to find out though! If the scaled down version proves itself capable of handling waves, then I think it’d be safe to say a larger boat would handle them much better still.

To increase bouyancy at the bows, maybe some ‘pahi’ styling could be employed.

Yeah, that would indeed be an option, and I could imagine that from an aesthetic point of view it might work quite well too.

Cheers,
Marco

I forgot the windows (fore and aft) in the dodger! The flat panels on the side of the pod are probably quite bad from an aerodynamic standpoint as well; I need some way to make that rounded, while ensuring it remains easy to build…

Thanks very much, Marco. Much appreciated 😊

Making a Tepukei aerodynamic or at least aerodynamic looking and also aesethically pleasing is a real challenge. The one aerodynamic advantage it has is that there is not much of it for the size boat. Aesthetically, i think the only way is to make use of its quirkiness somehow rather than trying to make it look like a ‘normal boat’ because it just aint normal!
Another way of using the T form you suggest would be to have seating either side of the hull and mast with an open footwell over the vaka with a false sole to provide a self draining ability. Below the cockpit floor could be water and fuel tanks. With the cabin close by to provide shelter and some righting moment.

Here’s some more food for thought. Again, this is from Othmar. The whole cockpit/cabin could be shuffled leeward a couple of feet so the (freestanding) mast is stepped in the vaka and your inflatable safety ama added.

James - 02 June 2014 04:46 AM

Another way of using the T form you suggest would be to have seating either side of the hull and mast with an open footwell over the vaka with a false sole to provide a self draining ability. Below the cockpit floor could be water and fuel tanks. With the cabin close by to provide shelter and some righting moment.

That’s a really nice idea, especially the fact you’d be sheltered by the cabin, and have a hatch which opens to leeward, would be massive bonuses when the weather is really bad. Having a central cockpit with the mast right there is also good from the perspective of seaworthiness, since you have just about everything right in the cockpit.

The downside for a small boat though is if you want sitting headroom, say 1.0 - 1.2m, then you are creating a structure which is quite high overall (remember you still have the freeboard of the fin below you). I think what we need is some way to fuse the two—offsetting the mast to leeward seems problematic though, at least if you intend to use a bermuda rig…

In general having the mass of the accomodations set slightly to windward, would be nice for the windward courses (compared to a Jzerro-like configuration), for the extra RM it provides, particularily if you’re using Dave’s auto-flight mechanism to keep the ama out of the water regardless. Off the wind, where the auto-flight mechanism can’t operate anymore though, that’s not so nice, since the ama is carrying more weight than a Jzerro-like boat would be, meaning lower performance. That applies to both the travelling and fixed versions of the cabin, since even the pod-car is windward of the vaka when hauled all the way in.

Marco

So let’s say we did offset the cockpit to leeward, so that it’s the leeward side of the T, with head and galley in the vertical part, and sleeping room for one in the windward side of the T. The other person could sleep in a net spanned over the vertical section of the T; that makes the windward pod only ~60cm wide instead of 120cm, which saves weight since the structure is smaller overall, and it brings the center of mass pretty much over the vaka just like the Jzerro-like boats.

What sort of a rig would be use though? Using a bermuda rig seems a bit problematic to me if the cockpit is set to leeward. If you attach the tack of the jib to the front of the vaka somewhere, there you wouldn’t see squat from the cockpit because the jib would always be blocking the view. The slot between the jib and main may also become too small then when sailing to windward…

And there’s the curious question of what to do with the jib anyway; it can’t really go all the way to the deck of the vaka, since it’d be exposed to the waves then… If we do move the tack of the jib upwards along the forestay, can we get it up high enough to be able to see something from the cockpit again?

Or maybe we should be considering an entirely different rig here?

All of the Tepukei configurations discussed so far have a higher CG then a boat built in the Jzerro-Configuration would have, since a pod to windward requires significantly more clearance below it than if it was on the more sheltered leeward side (as rules of thumb I use 35cm to clearance to leeward, and 60cm or more to windward). Sven posted at some point that Pacific Bee does actually slam under the cockpit in rough weather sometimes, and if I recall correctly it actually has around 60cm clearance.

An alternative would be to mirror everything here and just do it like it’s done on Jzerro. Cockpit and mast to windward, a cabin pod to leeward without anything inflatable, and if we want to build it small, we do it like I intended for Firstborne and span a net in the vaka to sleep the 2nd person, allowing a narrower pod. What we’ve done then, is decided to trade the weight of the freeboard in the forward sections of the hull, for extra length instead, and we’ve increased the height of our superstructure a bit.

Alternatively we could also say that 30cm of extra height in our superstructure doesn’t bother us, the aerodynamic footprint of the rest of the hull is so small that overall we’re probably not losing anything anyway. If the rig has to be positionted slightly higher up though, then we are losing some of our sail-carrying ability.

Been catching up on this thread—lot of deja vu here… Marco, are you familiar with harryproas?  www.harryproa.com  These seem to be more controversial than they deserve, and they do not feature moveable pods, but the basic sailing geometry is surprisingly similar to your proposal and a great deal of thought and experimentation has gone into things like rigs, sailing geometry and interior layouts. They have a very active forum on their site—there have been something like a dozen of them built—and another half-dozen currently in build. From 60-80’. In this sense they are more prolific (a pun for James 😉  than Brown/Bieker type or even Cheers-type proas. Check them out!

I can´t say i understand the rational for Harryproas. Every time i add weight to the ama or try 50 + 50 % weigh distribution between the hulls the whole proa-concept crashes. It is a shunting catamaran, with all the loads on the crossbeams and supporting structure but only one hull to live in. It is (in my experience - and yes! i have tried the concept with scale-models with horrible results) the worst properties from the proa (lack of accomendation and a huge overall foot-print) combined with the worst properties from the catamaran (twitchy motion, huge stresses in the crossbeams and structure) without the speed-potential of a pacific proa.

If someone has documented (video) other results, i would love to see that. The videos on youtube are only flat water and low speeds. Nothing like making tea at 17 knots in Jzerro going through some real waves.

Cheers,
Johannes

Dave! Thank you for dipping your oar in the water here. I don’t suppose you happen to work part time as an angel at Lourdes do you? 😊
Reading your comment made me both happy and sad. It was also a relief but, still, there was some consternation for me as you will see.

I was happy because I knew I would have won a handsome wager on who would mention that word “harryproa!” first 😊
And sad because I had no-one to accept my wager :( as I would have had to mention the word myself first. You can see it was quite a pickle for me. Foretelling the future is not all plain sailing, as some might think, and does have its tensions and drawbacks!

Marco,
I think I would go for a freestanding mast or masts (schooner). Possible rigs could be balanced lugs(s) or Wharram wingsails or Chinese Junk(s) though they are not considered high performance rigs if that is what you are after.

Another option might be a reefable Gibbons rig that I keep promising myself to draw out. Hopefully it would be a ‘lifting’ rig and presumably help with the relative lack of bouyancy at the bows.

If Dave’s ingenious foil could be used, it would lessen the need to offset the rig to windward which would simplify that part of the design, I think.

Impressive fortune-telling there James!—The original wording of the first post here mentioned that for this design there’s no real distinction to be made on whether it’s a weight to windward or a conventional pacific proa but I took it out for the sake of brevity. 😊

Personally I’m not convinced of the weight to windward concept, because you’ll have little to no chance to scim (or fly) the ama in normal sailing conditions—even Dave’s auto-flight can’t help you there. If I had to guess, I’d wager that on a boat like Delirium, the pod would usually be pretty close to the vaka (reaching and running), to allow the system to fly the ama when going to windward. You’d need either a strong and steady breeze, or some really large light-air sails, to make it worth it to move the pod way out and make it a weight to windward. That condition does exist, the sliding pod is there to allow you to carry a loftier rig after all, but the ama belongs in the air, or scimming, and not lugging loads of weight around, simply because one hull is faster than two, and to avoid sudden ‘tensions and drawbacks’ in that there structure. 😉