Jump to content


  • Content Count

  • Joined

  • Last visited

Everything posted by DDW

  1. You may want to view Rod Collins recently posted page on drop in replacement LFP. There can be a lot of differences between quality and budget. Also some discussion on Will Prowse reviews and what might be missing from them in a marine context.
  2. I had a B&S Micromaster about that size, full hydraulic automatic feeds. Bought it for $450 on Craigslist. Took too much floor space for the little I used it, sold it for $2000 :-). Ti would be good. Only needs to be Grade 2. Was the 45K for one or two? Were they sand cast or investment cast? They look like investment castings. I think they are too tall for 3D printing or that might be the way to go. Wish I had the prints for my ZF drive leg, I'd get it quoted.
  3. Actually I misread the graph in the link that I posted. It is more like 1500W at 8.5 knots, as in your chart. So, twice as bad as my analysis: what you get in an hour at hull speed lets you expend 1500 watts (= 2 hp) for the next hour. The price though is correct. 20,800€ is for the saildrive, but the whole system inluding controller, batteries, etc. is more than double that. A question about saildrives: why does every manufacturer make them of disposable materials, as in dissolves in seawater? It wouldn't be that hard to do in bronze or stainless.
  4. Yes but even looking at the Oceanvolt SD15. This is a 15 kW input motor, or about 20 hp at full chat. About what you would expect in a 28' boat, Oceanvolt says "equivalent horsepower 30 - 45 hp" and they think suitable for up to 45' (my 45' boat has a 75 hp diesel, equivalent and real). The regen claimed at 6 knots is 500W, at 8.5 knots (hull speed for the 45') it is 3000 W, both with the fancy prop. That is 5 hours at hull speed for an hour motoring. They claim 25 mile range at 5 knots with their 19 kWH battery. That means motoring for 5 hours at 3.8 kW input. Marketing license being what it
  5. If people used common sense, it wouldn't be a problem. But common sense isn't very common anymore. Rules are the replacement for common sense.
  6. It's just another one of those things like a refrigerator - if you don't have one at home, you won't miss it on the boat.
  7. I believe he pulled a ballasted 1000 lb rowboat from the city front to Alcatraz, handcuffed, and was something like 60 at the time. Well apparently not: And two 23 kW generators made it motor at 8.5 knots. At least with that system, way more than 3 hours/hour.
  8. This is true, but we are already talking a minimum of 3 hours sailing for every hour motoring. And realistically, let's just guess 50% efficiency going uphill for prop, electronics, battery resistance (the efficiency going downhill already sunk cost) now you have 6 hours sailing (at 7 knots) for every hour motoring. In areas with consistent wind, not a problem - but then you don't need the motor much anyway. In areas with inconsistent, or nonexistent wind, regen is not going to make much difference as a charge source. I've sailed in places where motoring was 1-2% of time underwa
  9. You don't need 3 kW for anything - except recharging your electric boat batteries. It takes about a 30 kWH battery to get 3 hours motoring duration in a medium sized cruising boat (10 kW/h is about 13 hp). At 3 kW charge, it will take 10 hours to replace that 30 kWH, all the while providing >1/3 of the thrust in reverse.
  10. That's an excessive amount of toilet paper, we are led to believe. Let's say two events a day or 558 attempts. Single ply is 1000 squares a roll. You should only need a little over 2 rolls for that trip. A bidet would improve the chances, but a bidet on a composting toilet seems problematic. I wonder if the users of 4 squares on the boat also do that at home. If not, that is either depravation on the boat or wasteful excess at home.
  11. Do you ration/issue 4 squares to guests? I'd suggest you are an outlier in this regard.
  12. Also the problem with the ubiquitous Splendide. Wash and dry in the same drum, without attention - which is convenient - but can dry only 1/2 the load it can wash. I'm still wondering if 3200 rpm is usefully different than 1000.
  13. Our heads (Lavac) are mounted on low steps, perhaps 5 inches high. By happy accident, it is very easy to kneel on the shelf, and pee directly into the bowl from about 4" above the rim. This almost entirely eliminates the splash. If I was building a boat or redoing a head I'd try to arrange that again. As Alex says, in full gear it can take a long time to prepare to sit.
  14. The foredeck awning is hung from the center and stretched by battens. It can be tilted into the afternoon sun, almost right down to the deck. That is what I would attempt to do on a main boom awning too: fiberglass battens athwartships to support it, balanced on, or suspended above the boom, overhanging the rail a little each side so that it can be tilted down to the lifelines into the sun.
  15. All the little Chinese plastic washers spin at around 800 - 1200 rpm. The dedicated spinners go 3000+ rpm. Since centripetal force has an rpm^2 term, faster is more than a lot better. That's why I'm wondering if anyone has tried one. Home horizontals spin at 1000 rpm, cloths come out damp but not wet. Some pools/gyms have the spinners for your suit, of course it is synthetic which helps, but the thing is practically dry after a minute in there.
  16. Usually in ad copy they will say "Up to 300% increase". If they really say "300% increase" then they can be held to their word. Not enough attorneys working there? I'd be surprised at those numbers too. There was a well done test (by an owner but still well done) on a trawler comparing properly pitched conventional props to Autoprops. The Autoprops were better, particularly at cruising speeds well below max rpm, but the peak difference was more like 8% peak and falling off at both ends for speed/rpm, and a max of 20% in mpg at given speed in the sweet spot. No regen figures obviously, but
  17. There are no LFP manufactures that allow charging below freezing, drop in or otherwise. A few of the "drop ins" have heaters now, and a few more have a temp sensor that will disconnect the BMS for charging when too cold. It takes a very cold day on the water for batteries to get below freezing being generally installed low in the boat and below the waterline. Much more likely in an RV.
  18. The biggest problem with washing on board is actually drying on board. There are cloths spinners that spin at about 3000 rpm that are claimed to get things nearly dry. Has anyone tried one of those? About the size of a 5 gallon bucket, requires 110V but not very much and for not very long. Early in my boat design, there was much contemplation for how to get a washer/dryer on board. I even bought a Splendide, the kind you see in RVs and motorboats with the idea of de-cabineting it and building it in somewhere. We experimented with it at home for awhile, the wash worked brilliantly but the
  19. Yeah, Piaggio bought Vespa years ago. But unlike Garmin's typical behavior, they improved the product. I've got one, and ride it sometimes. I don't even care that it looks like "an old woman sitting on a commode".
  20. So lets talk hot coating for a minute. The directions on the can (I'm talking Epifanes) says not to. But in a warm and not too humid climate it seems like you can get a second one on in say 5-6 hours. This gives two coats a day and literally cuts the time require in half. How many of you'all are hot coating?
  21. There are three things the Autoprop does: keeps the leading edge the leading edge always, keeps the blade section correct for the flow, and varies the pitch to maintain constant angle of attack. The first happens anyway in regen (though not in reverse). Having the camber the right direction is quite important to efficiency, especially when combined with having the pitch wrong. The last one is perhaps the most important. Purpose built aerobatic planes have symmetric airfoils, planes that don't fly at very noticeably higher angles of attack (when upside down) to make up for the camber being turn
  22. You can specify the torque, or the rpm from the motor - just not both. No different that a diesel. On a diesel (boat) motor the lever selects the rpm, the prop decides how much torque is required, and the governor supplies enough fuel for that torque. A fixed pitch prop has a single line function between rpm and absorbed torque (though boat speed complicated that a little). You can find efficiency graphs all over the internet, a lot of them theoretical rather than practical. It is best to go to a manufacturers product page and look at the actual plot for a specific motor as tested.
  23. Keeping in mind that Defender itself has now been sold to some corporate entity thingy.
  24. Just an example grabbed at random from the interweb: The problem with a normal prop is, you don't get to specify the torque, it is a fixed function of speed pretty much. On diesels this is also problematic because the available torque is always greater than the prop can absorb except at one point. A gear shift - or a variable pitch prop - gives you some control over this, decoupling the fixed torque-rpm relationship. The Autoprop is a brilliant design in that it does mostly the right things automatically.
  25. As I said before, cooling the motor on a boat isn't a problem if that is what is required. I noticed that the efficiency of BLDC motors drops off fairly steeply once out of the sweet spot. I wonder if the solution for a boat is a variable pitch prop? The motor could be run at it max efficiency rpm all the time, and the power needed adjusted with pitch. It might also greatly improve the efficiency of regen when sailing, too.
  • Create New...