For an overall discussion of this design go to: SHEWAC Aberration
Since my blog on Aberration in October last year, the concept has come to life and is now operating to a level where I can ponder my brilliance (right) and mistakes.
As a designer it is particularly interesting and cathartic to find yourself on the receiving end of the design. I often write blogs to think through a problem, and in this blog in particular I expect to have learned something once I have it all written down in a stream of consciousness.
The earlier blog focused on the complexity of hybrid stinkpotting, and I made some performance predictions.
Since we now have some performance numbers, I will address those issues first. In the earlier blog I predicted full speed at 7 knots at half load. Soon after that estimate, John Scarano sent me some info that indicated that the top speed would be higher, and while I have simply not been interested in getting top speed numbers (I will explain that later) we have no problem hitting 8.5 knots at half load.
My greatest delight in the performance has been the ability to hit 4.0 knots at half load at 3 kW. Imagine, this boat at 14,000 pounds can run at 4 knots with the power of two hair driers! It boggles my mind. The sweet spot is around 5 kW where the boat will do about 5.5 knots. 4 knots is a little slow, but 5.5 knots is basically sailboat speed and that is how I grew up and how I like to boat.
5 kW gives me 5 hours run time at 27.5 nm range. The solar panels are all hooked up and running and on Memorial day it was semi sunny and after 4 hours running at 5.5 knots we came home with 45% of battery capacity. I left the boat at the dock that evening and did not hook up to shore power and the next evening the batteries were pretty much fully charged (and kept the home sized fridge running).
While we used the generator to run the boat from Albany to the Jersey Shore, I would not be surprised that there will be many days on the boat that neither shore power nor the generator will be used.
Since 5.5 knots is such a sweet spot I have simply not been interested in exploring top speeds. It is no fun to run full throttle because the batteries drain so fast, and when I am running the boat I don’t want to think about starting the generator. Proper high speed runs also would require weight analysis and trim variations. Just too much work. I am training Seascouts to run the boat and maybe some day I will make them put together a proper program. Todd Simms, former Torqeedo rep and electric drive guru, also pointed out to me that the boat may be underpropped for top end. I have not spent a lot of time thinking about that for reasons noted above, but also suspect that my excellent 5.5 knot performance may be related to fortuitous prop optimization at that speed.
Note that in all what I have written so far it turned out I was wrong; it turned out I was very much too conservative in my expectations.
With regard to the generator, I purposely selected the lightest generator I could find. Weight control is absolutely vital in a slender and wide catamaran and in selecting the super light Fisher Panda 15 kW mini (Yeah right, that is what they call it, but it is only 12.5 kW) I knew I was taking a chance. I bought it with the factory sound enclosure, which is supposed to rate the unit at 54 dB at 7 meters. Yesterday I verified that sound level (with my smartphone dB meter) and it came in at exactly that level with the engine room door open and then also with the door closed. But there is sound and then there is sound, and this is not a pleasant sound, mostly because it is high frequency from the high rpm diesel engine. Regardless, when running with the generator during the Hudson river transit, the overall noise was still much less than IC propulsion and can be totally tolerated. Now, knowing that the generator will be much less of a operational presence than expected, I consider myself lucky (can’t claim smart) with the generator selection.
In the October blog I noted that I purposely had selected a generator that was smaller than the propulsive power. Interestingly, knowing what I know now, I think I still sized it too large. If this generator needs to be replaced I almost certainly will go down to 10 kW and maybe even 8 kW. Hopefully at that time I can run on hydrogen too and make it a 10 kW fuel cell.
Note what I am saying here. This boat is a quite a stunt in weight control, but with emerging technologies we are not done yet. We can still do better.
Having mentioned weight, I congratulate myself, and, moreover, everybody at Scarano, with our weight control. We were dead on. The only time I did better, percentage wise, is when I was tasked with weight control on Eagle, the 1987 12M, and, in many ways, that was an easier problem. A major contributor to our success was our mutual paranoia. We kept forcing each other to revisit the issue and thereby avoided “good enough”, which is never good enough in weight control.
It needs to be mentioned that this design could not have succeeded without the magic of Plascore. This super light and stiff prefab material consisting of a one inch plastic honeycomb core and super thin epoxy fiberglass skins, allowed us to build this huge superstructure without overloading the boat. If there were no Plascore, we would have had to build in carbon fiber and that would have required a fortune in tooling.
John Scarano’s suggestion to use Garolite (Tufnol) for some of the structure resulted in wide ranging use of this “ancient”, but super useful material. In composite construction it is the missing link that is the perfect substitute where you would be tempted to use wood. Unfinished it even looks pretty woody and visitors generally do not realize that the boat’s caprails are not wood.
Other things are just game changers. We spent a large amount of mental effort on the wheelchair lift. In the end it is quite elegant, but I also think if there were just the perfect human rated winch (which may well be a version of the reel type anchor winch that is installed on the boat) we can further simplify it and make it much less expensive. That would be great for the boating industry. I designed it for Anne and her wheelchair, but two weeks ago we celebrated my Mom’s 90th birthday and after Anne was loaded aboard my Mom said: “Yeah, I’ll take that too, no climbing the boarding ladder for me”. And she was far from the only visitor who preferred the lift over the ladder.
There are also ladders to the lower hulls, and the guest head is in the starboard forward hull. But there is also a head in the master cabin on the main deck. This head is under a lid next to the bed and allows Anne to easily use the head at night. But with older passengers aboard in the daytime, I directed them to that head. It is nice and spacious with a nice view aft and to port without visual intrusion from the rest of the boat. Soon enough everybody was using it and when somebody walked in on another user, we even discovered that the (over priced) Perko door handle to the master cabin had a locking switch. So now the rule is: “Feel free to enjoy the main deck head in the daytime. Don’t forget to lock the door.”
At the design stage I thought about ventilation, but thought about it wrong. The boat has two very powerful extraction fans that can suck the stale air out of the boat in minutes. But at the dock the boat just heats up too much in the sun. It is difficult to install roof top vents because of all the solar panels. Yesterday I installed one of those solar powered roof vents in the Master cabin where there is roof access, but I will have to think of further ventilation options. (Weird, just writing about it I am starting to think of a great solution. See; that writing/solution thing happens all the time)
The boat is designed as a starboard to boat and I got a great ADA slip at Molly Pitcher Marina, but to be starboard to, I need to back the boat into the slip. I was aware of that at the design stage and had done some thinking about how I could pull that off with a high windage relatively low powered boat and poor aft visibility. Well, first of all, low power is not the problem. These Torqeedos put out the torque and thrust. Almost too much because the throttles are superlight and you cannot hear the motor response, so I often over power. Windage is a problem and we kept a long keel and added substantial tracking skegs. The boat tracks just about right and maneuvers very well, but very much unlike other boats I have operated. As a sailor I always focused on having enough momentum to reach the dock (and as a glider pilot on enough potential energy to reach the landing field), but here you stop short of the dock and use the combination of differential power and steering input to bring the boat to the dock. There are almost too many control options and keeping track of them, together with rather restricted stern visibility (enhanced with a rear view camera), the limited throttle feedback, and a desire to single hand the boat, I have a lot to learn. What is really cool though is that I am convinced that with ample practice I will be able to read and write in cursive with this thing. Early on I toyed with installing an integrated steering system, but then felt the boat was complex enough without it. With independent steering on the outboards that would be possible, but I am actually looking forward to becoming good at operating the present set-up, hopefully without too many scrapes, underwear changes, etc.. In totally wind still conditions where I can go super slow, and think my way through every move, I already noticed that this boat will go where you want it to go once you know how to do it.
At cruising speeds the boat is almost insensitive to wind and loses much less speed than expected with headwinds (and gains less with tailwinds).
In waves she is a little pitchy which can be expected from a catamaran, and, so far, we have not really run in large ocean waves. As far as full throttle tugboat wakes is concerned, the trick is to chop the throttle and the boat becomes a raft that mostly goes up and down. In pitch she is equivalent to our 50 foot trawler, but a little twitchier. In roll she is just so much better and one would not expect anything else.
I will devote a separate blog to the Torqeedo system and the overall power control system. So far the Torqeedos are impressive, but with a few design detail duds that make me want to find the designers and dope slap them with a “what were you thinking” admonition. In fairness, I do think that (like this boat) I am still dealing with Mod. 1 stuff and would not be surprised that improvements are in the pipeline.
Keith Duffy, Scarano’s chief designer, designed the entire boat in CAD and all the panels were cut on an NC cutter. So in theory it would have been a lego snap job, but we blew a significant amount of money getting the NC machined superstructure to match the hand built, not quite even, hulls and lower pontoon deck. In the end it worked out, but I think the super structure sits a bit lower on the starboard aft quarter.
We really sweated boat trim and we came in dead on with the transoms right at the submersion point in all load points. The boat lists 2 inches to starboard, which I intended because I expected people would be loaded more to port than starboard and that would give the boat even keel in running mode. So far that has not yet happened. People tend to sit all over the boat and there is little port side passenger bias. However, this may change once the port side settee is fully tricked out. In the meantime I am training my 95 pound dog to stay on portside.
Since I have the sense that the starboard aft quarter sits a bit lower on the hulls, the static starboard list at the dock irritates a little more than it should every time I walk up to the boat. If you did not understand what I tried to describe here, do not reread it because then you can be blissfully ignorant when walking up to the boat.
And ignorance is bliss. I see the little details that did not turn out exactly correct, but visitors to the boat do not, and they are blown away. It was not until this weekend, when a few dozen knowledgeable boaters had been aboard and expressed their amazement, that I fully realized how wild this thing is.
It will be a great escape for my wife, but it is also an amazing device for other less capable passengers and, with its huge deck space, it is an excellent sea scout training vessel and race committee boat. I can see that she is a great moderate weather coastal boat and an amazing canal and river boat all at near zero carbon load. Quite the Leatherman tool, and I mean the Skeletool; the best of the lot.
Most of all, it shows us all that we haven’t even begun to really consider all the possibilities with all the new technologies that are coming out. What have I really learned?
Don’t look back; there is much better stuff ahead.
