What is it?

[Anonymous]

Hello Mike, <BR> <BR>I will try to attach a little drawing which will illustrate for everybody the original way that the system in our boats was set up. This will be a drawing of the tee fitting or vented loop that was originally installed on many a Hans Christian. If this original tee fitting is still under your sink top you will see what it was all about. The original bronze tee is still on my boat but the system has been changed around somewhat. The bottom of the tee was plugged off as I think you are saying is yours. I would imagine this is because the engine flooded at some point and because this original vented loop system from Hans Christian is so unconventional that a lot of people didn't understand it. The only failing in the design is that the tee located up under the galley counter top is not high enough after these boats get loaded down with cruising gear as is evident by the problem that we all have with our galley sinks not draining well. <BR>The two things that are unconventional are; 1) they divided the water at the tee (or vented loop if you will) so that approximately 40% of it would be separated out so that it could be injected into the exhaust to cool the exhaust hoses. The approximately 60% remaining would go to the lazarette (through a separate hose) to be injected into the standpipe and discharged with the exhaust. The reason for this is to keep the exhaust back pressure to a minimum. On these boats there is a particularly large rise in the exhaust system because the engine is so low in the boat. Typically you want to limit the rise between the wet box and the highest point in the exhaust hose to 40" (more critical on a turbocharged engine than a naturally aspirated one). By separating out more than half of the water you make it easier for the engine to push the water and exhaust up through the exhaust hose thus keeping the exhaust back pressure lower. The 40% of the water is adequate to keep the exhaust hoses cool. 2) The other unconventional thing is that instead of using an anti siphon valve at the top of the loop they ran a vent line to the wet box to vent the loop as we discussed above. All of this would have been fine if only the tees tucked up high under the counter top had been high enough above the water line. I doubt that these systems would have been modified over the years to the point to where most of these systems have been changed enough to where the original intent is now just about unrecognizable. <BR> <BR>I have rebuilt my entire exhaust system starting at the engine. I rebuilt the exhaust injection elbow out of 316 SS and Inconnel 600 rather than use the cast iron ones that rot out so easily. At the same time I eliminated the riser part of it all because the riser never made it above the water line anyway and if properly set up it isn

[Anonymous]

It sounds to me as though they tied the hose that goes from the cooling water circuit to the shaft seal into the cooling water circuit down stream of the vented loop rather than on the upstraeam side of the loop. I have seen this mistake made before with the same result. One of the nice things about our old Hans Christian wet box mufflers was the plug in the aft side of it which allowed you to drain the wet box into the bilge if you had this problem and then all you had to deal with was the engine. <BR> <BR>I have also filled quite a few engines with diesel as Mike describes and have always met with good results. I think this is a great solution to the problem. <BR> <BR>It is pretty amazing how that sea water is always right there trying to get into a sailboat engine and it is only the slightest little thing that makes the difference as to whether or not it does. <BR>Chuck

[admin]

Hello Doug, <BR> <BR>Your question about engine size is one that is fairly complex and one that I have not had much time to respond to until today. (Slow day at work today). As I recall the 4B Cummins are a fairly stout engines weighing in at about 800 pounds or so. While conventional wisdom these days is that 2 HP per ton of displacement is a good figure for sizing an engine there are a lot of other factors that you normally have to consider. The main one aside from physical size and weight being the propeller aperture and the size of the propeller that you can swing. If you can

[admin]

I agree with Chuck on this. <BR> <BR>Interestingly our Yanmar 67 turbo at 2500rpm gives us 6kts comfortable cruising on an amazing 2.55lts/hr we can make aroound 8.5-9kts at 3500 but the fuel burn goes crazy & the vibrations isn't good so why do it unless its an emergency! <BR> <BR>The yanmar dealer tells me that the same block, pistons, crank etc is used in an uprated version giving 135hp, my way of thinking is that when you overstress componets that were originally designed to produce 67hp comfortable why push you luck to give a higher hp which usually ends in something going bang at an earlier age!! But thats just my opinion. I suppose Yanmar look at it that they can sell a bigger HP for more bucks as the same manufacturing cost = more profit. <BR> <BR>Mike