I prefer the pod.
So do I đ
Yes, Pro the Pod, too ,
I like the ama also a lot , look a lot like one of our favourites ...........good water shedding properties ,... andâŚ. quick plywood construction
Hi Chris
I donât know if I am being over cautious due to my recent experiences but I am nervous about the effects ama and by extension pod drag on steering. Imagine being hit by a sudden gust and the pod digs into the water. This may cause him to bearaway worsening the situation. Additionally to counter this you will want to go forward and outboard, is there not a danger of running out of seating platform.
I think I would prefer one of your supper CNCed hydrodynamic safety amas and parallel seating platform.
Have you done any calculations of crew position effect on trim? a 24â vaka sounds like a lot of hull to trim
Tink
There are certainly concerns about the effect of the pod on steering. But its not going to come into play until the ama is 28â above the waterâa point where Iâm getting worried about stability.
Of course that assumes flat water. Weâll see how it works charging into chop.
I have not run any calculations on steering, but SRIR is only 3â longer on the waterline than Proud Maryâbut should have more lateral area because the Vâed bottom will sit deeper than a flat bottom.
Weâll see if that makes any differenceâŚ
Hi Chris,
I have not run any calculations on steering, but SRIR is only 3â longer on the waterline than Proud Maryâbut should have more lateral area because the Vâed bottom will sit deeper than a flat bottom.
Well, I now have some GPS data on PM, not that great, at best it does 65* to windward. :-(
I think you might need more lateral resistance as well, but not sure how much, maybe Vâed bottom and extra length do itâŚ
Steering is the one thing I think youâll be fine with! (famous last wordsâŚ)
Please see PM thread for more info.
I must say Iâm loving SRIR, and hopefully with a few more tests on PM youâll be able to get it right first time!
Okay, the mast is back in the hull. The rig stays up when caught aback, because thereâs a line tied around a puck a the extreme leeward edge of the pod, wrapped around the mast. Now I can cant the rig to windward (or leeward, if the mast is stepped further to windward). Its going to induce some bending, but no more than the slot does. Its not shown yet.
I have been adding lateral area by making the pointy bottom of the boat deeper. It now draws 19â at 1200lb and the floor is 7â above the waterline. The pod, fully immersed displaces about 1000lb. It has hatchless lockers inside the pod, that drain into the cockpit. Heavy stores go under the cockpit floor.
The deck is a plywood skinned foam sandwich with a raised hand hold/ tie down rail around the perimeter. Its 4â wide and 10â long
Having no mast or anything on the deck provides plenty of room for scooching or walking around to steer.
Iâm designing a rudder/steering paddle based on the one on Equilibre, for security on downwind courses.
This boat could be rigged in a variety of ways! But I like the boomless gibbons/dierking rig that furls around the yard (lowered, on deck). Adding a sprit boom might be cool. I also like the idea of long battens that are parallel to the yard to give it some roach. But it could easily be set up with a crab claw, Pizzey-ish Isoceles sail, jibs, and a bunch of other stuff Iâm not thinking of.
Iâm really liking where this is going as a simple little, butt and rig steered camp cruiser.
a few more shotsâŚ
Here it is with some roach. Battens (rod, like the hobie adventure islandâs) parallel to the yard give it 30 extra square feetâfor a whopping 150 square feetâŚenough to get this 16:1 canoe moving.
The lateral area in the water is over 26 square feetâmore than 4x Proud Maryâs.
Iâve been thinking about rudders for SRIR.
Iâve sketched a bunch of interesting steering paddles based on the cool one on Equilibreâhalf rudder (pivots on a shaft) and half paddle (you unhook it and stow it when you are done).
Then I started thinking about Pizzeyâs kick up rudders on a bent shaft. The shaft is the pivot point for the rudder, it bends 90 degrees, through a generous radius, and then becomes the pivot for the rudder to swing up. A small line attached to the rudder keeps it from kicking backâlike the torque line on Gary Dierkingâs motor bracket.
So hereâs the new part. Instead of kicking up and being generally vulnerable with the blade horizontal near the water or sticking up in the air vertically, the rudder flips back 270 degrees and stows in the canoe. Now the blade near the bow is safely stowed away. My trick is not to put the kick up pivot axis perpendicular to the mid line. Its shifted about 5 degrees, so that as it swings around it finds its way into the canoe.
On most courses, both rudders would be stowed. But on downwind courses, you could, flip one over (lifting up and back, then tighten the torque line to pull the blade forward. The torque line can be used to tune the position of the rudder fore and aft, to a certain extent.
Its still a system that pierces the waterâs surface, but its well protected. The rudder doesnât extend lower than the keel, which at 1200lb is 19â below the waterline.
The blade is a naca section 12â front to back and 18â tallâat least in this model. There is stilk a litttle bit of the top or the blade showing at full displacementâbut maybe not once everybody is aft, on a downwind sleigh ride.
Part of me is disappointed that the foil less boat just got two foils, but you have to go down wind some time.
Iâve been thinking along very similar lines, except on shunting letting the bow rudder float up by itself, and then fastening it under the beam once underway. Trying to think of how to elegantly handle the tiller etc.
It might make more sense in your case to design it so it is easy to (un)attach completely while on the water?
-Thomas
Garyâs comment on Johannesâ circular rocker thread got me thinking a lot about rocker.
http://proafile.com/forums/viewthread/298/P30/#2776
So I thought Iâd play around with SRIRâs keel profile. I lifted up the bottoms of the stems a few inches, to reduce forefoot. I added 2 feet of overhang to the boatâso each bow overhangs 18â. So she grew from 24â-26â because I didnât want to change the waterline length of 23â for comparisonâs sake.
Then I drew a horizontal, straight keel and connected that to the stem with another straight line, and rounded the corner.
I loved the overall effect, but straight lines on boats can make me a little queasy. It also makes the plywood bend too much in one place which seems wrong both from a structural and hydro POV.
So I left the straight keel and built a very soft spline between the stem and the keel. Okay, now weâre getting somewhere.
The new shape has almost identical displacement but 28 sq feet of lateral area instead of 24. And the cutaway forefoot should make it more sensitive to weight shiftâsince more of the buoyancy is concentrated in the center.
Anyway, here is a comparison of the old shape and the new, much more marshallese looking shape.
And as long as I was in there messing around, I did a round of refinement on my rudder.
This rudder should only be for courses off the wind where butt steering canât be as effective.
The thing I like about this design, shamelessly stolen from Pizzey, is as simple as any I have seen.
One of the things I donât like about outboard rudders is having something hanging off of the boat near the bow. These stow in the canoe by flipping them back 270 degrees. Thereâs a line going from the front of the blade, just above the waterline to the foreward aka that limits rotation when its down. That line will have some âfuseâ in it to allow the rudder to kick up.
I made the blades bigger, which meant some rejiggering of the whole geometry. Its very interdependent!
Anyway, the result is a rudder system with two moving parts per side; the bent tube that acts as the kick up pivot AND the rudder shaft, and the blade/tiller assembly.
Above the blade the front edge is sharp to (somewhat) reduce the spray of a surface piercing foilâshamelessly stolen from Gary Dierkingâs leeboard mod.
Maybe it would be possible to adjust self steering downwind by trimming the rudder forward or aft, using the tiller just for small corrections.
I think the last iteration of your SRIR looks gorgeous with those overhanging stems.
They will add a lot of resistance to pitchpooling and give a softer motion when going through waves.
I really love your beautifull renderings of proas.
Cheers,
Johannes
I think the last iteration of your SRIR looks gorgeous with those overhanging stems.
They will add a lot of resistance to pitchpooling and give a softer motion when going through waves.
I really love your beautifull renderings of proas.Cheers,
Johannes
Thatâs something that I have never been able to understand. I have seen many times that a very curvy/springy keel line with long overhang is considered a good thing for pitch polling or pitch controlâŚ
For me, for the same overall length, a boat with a flat keel line and âsquareâ bows will be much more resistant to pitch polling.
The pitch angle you have to get to for those overhangs to start to get into the water and generate lift, the straight keel hull will already have a lot of buoyancy forward by much more hull volume in the water.
If you want to avoid pitch polling, you have to attempt to move the center of buoyancy forward as much as possible for the minimum pitch angle.
How are long overhangs better for this end result?
Cheers,
Laurent