Wow!!! It is amazing how many separate questions Russ can ask in a single email. I'll make a stab at answering some of them, but perhaps I should preface my remarks as follows: I work with hydraulics every day, as applied to mobile heavy equipment and some stationary applications. I probably know the business better than most on this list. I don't say this to brag, but only so that you can understand where I'm coming from when I say that I feel like I'm pretty ignorant on the whole topic of fluid power. That is the reason that I would not undertake to design the system myself, but rather I plan to hire a fluid power specialist to design it for me. Certainly, anyone with less understanding of the business than I should consider doing the same. Even in my regular job, I frequently rely upon the opinions of certain fluid power specialists who I trust. The important thing is not to understand the business well enough to do your own design, but rather to only understand it well enough to be able to talk intelligently with those you might hire to do the design for you. Being your own fluid power designer is like being your own attorney or tax accountant. You can do it, but it will cost you a great deal of time and effort; and the result may have been more cost effective if you had hired the specialists to do it for you in the first place. It is not uncommon at all for me to pretty well know what I want, and then the specialist gives me another idea that saves hundreds or even thousands of dollars, but which I would never have thought of on my own. We have not done any more than the initial layout of Doulos II's hydraulic system, and that for the purpose of estimating costs. (We will work out the details later, when we actually do the installation.) I had pretty well laid it out myself before I showed it to the specialist. In a single day of working with it, he cut the cost by 30,000 dollars. I really mean it when I say that these guys pay for themselves. On the subject of having three engines on the boat: I have always thought that to be rather silly for a recreational boat. There is no need to have more than two engines on any recreational trawler; and they can back each other up nicely. I'd use one engine as the main, and then the other as the generator engine. The smaller engine would also serve as the wing engine. There is no reason at all why that cannot be done any number of ways. On the subject of using the same pump to drive several functions: That is done all the time, but sometimes it is more profitable to have separate pumps. Peter has already posted how cheap his 10 hp pumps were. You should know that pump cost is not linear. Many times, it is much less expensive to buy several small pumps instead of one big one. It is very common to have several hydraulic pumps all bolted together and turning on the same shaft. With that explanation, I should be able to snip most of Russ' note and answer what remains: At 08:02 PM 11/23/99 -0800, Russ Sherwin <russ@trawlerdogs.com> wrote: >So the first question is, can you share a hydraulic bow >thruster and naiad system off one pump on the PTO of the main engine? >They would never be operated at the same time. Sure you can, but by the time you analyze your system you may not want to. If you decide to do it that way, then you will need a larger pump, since it will have to give full power to your thrusters at a reduced main engine speed. For example, if you are going to get 10 hp at 900 rpm, then you will need a pump twice as big as if you were going to get the same power at 1800 rpm. >Now, I only need a 12kw genset, but the additional cost, weight and size >of a 24kw unit is not much. it seems to me that if you have a 24kw >genset, that's about a 20-25hp engine. 30 hp, actually. >If you put a PTO on it as well, >and drove the separate auxilary prop by means of a hydraulic motor, that >could eliminate the sailboat engine for the get home. For that matter, you could have a single diesel/hydraulic power unit; and use it to drive hydraulic motors for both the generator and also for the get home prop, or whatever else you wanted to turn. You could take a more or less standard wing engine set up, and put a PTO on it to mechanically drive the generator. You've got lots of options here. >It only needs to be forward-off-reverse, no speed >control. That is easy to do many different ways. >Now, we have two PTO, each driving a pump, and the third question is, >can you valve these things so that either the main engine or the genset >could drive any of the hydraulically operated devices? Very easily. I've got several pieces of equipment in which the entire hydraulic system is normally driven off a single main engine, but can be driven off of a smaller auxiliary engine. You can even drive your system off of both engines simultaneously, for the times when you want to run all your hydraulic accessories at the same time. (SCUBA compressor at the same time as cabin A/C and the bow thruster, for example.) >Someone has advised me that the main engine running at 1000 rpm during >docking is not sufficient to drive the bow thruster. Can you pull 10-15 >hp from a main engine turning at 1000 rpm, intermittently, in addition >to the main prop? No problem, as long as you design the system for it. >Paul Kruse (thank you, Paul) >suggested a "water box", the concept of which is vague to me, It is sort of a crude home made heat exchanger, which I guess is more common on commercial boats than on recreational ones. All you need is a box type tank, which you pump sea water through. Then you lay into the box as many rolls of copper tubing as you need to cool however many things you are trying to cool. The nice thing here is that it could be used for supplemental cooling for the gen set keel cooler, when the boat is not moving; but could be pumped dry when under way to save the weight. Alternatively, you could have separate keel coolers for the main and the generator engines; but use both of them for the generator when you are not moving. In cold climate, you could also plumb the generator cooling system through the water jacket on the main engine, thereby keeping the main engine warm. I know that dry stacks for generator engines are common on commercial boats, but recreational boats tend to avoid them. I guess they don't like the mess or something. +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ :: Paul and Cindy Kruse :: KJV Joh 14:27 Peace I leave with you, 165 South Kenneth Court :: my peace I give unto you: Merritt Island, FL 32952 :: not as the world giveth, give I unto you. E-mail: plkruse@iu.net :: Let not your heart be troubled, 407-453-6206 :: neither let it be afraid. :: +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++