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  #46  
Old 12-06-2016, 08:07 PM
Mr Efficiency Mr Efficiency is offline
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It is a no-brainer to be having an adjustable tab that is in front of, and below the cav plate. Asking for trouble. Whether getting rid of it solves your problem is not certain, but is has to go, next to useless anyway, even if it didn't interfere with in-flow to the prop. Something like a Permatrim would have been a better idea, but also offers minimal lift till you get moving faster than your current top speed. Incidentally, the other trim tabs visible look like a home made job, hard to imagine they hold their shape properly under load.
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  #47  
Old 12-07-2016, 01:01 AM
Joakim Joakim is offline
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The trim tab in front of the drive looks really bad for this boat and propeller. It seems to be permanent, not adjustable. Hard to see how the drive is installed relative to the hull.
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  #48  
Old 12-07-2016, 04:58 AM
Nidza Nidza is offline
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Central tab is permanent, not adjustable. I have already told earlier, anti ventilation plate is about 2 centimeters above the bottom of the hull in the middle of the boat (not keel bottom, hull bottom, that permanent tab is in line with the bottom of the hull and anti ventilation plate is 2 centimeters above that). Obviously, we all do agree now that central tab must be removed.

At current top speed and even slower than that, the boat angle does react to the angle of two stainless steel adjustable trim tabs. Those tabs are about 3mm thick steel plates, so they will not loose their shape easy. Although at my top speed, using them to change angle is probably making more resistance than gaining speed due to changed angle.

I got very useful answers from the owner of the boat in the video. Engine before reconstruction was diesel Mercedes 80HP/2500RPM, but it was not matched to the outdrive and prop, outdrive was just taken as it is from older original gasoline engine. That owner has been using it as a house on the water. Top speed was 5.5 knots at 2300RPM. He does not know why is that stern extension there, and as it was there he used it as it is, just made it stronger.

Current engine is 265HP, about 600kg with outdrive and gear. He says that his new prop is 19 inches in diameter, but did not give me more data about it. He has left two original fuel tanks (he says 350 liters each) and 200 liters water tank in the middle. On the first trial day, he says the boat itself was 4000kg with 350 liters of fuel and no water. Speed tests were done with 250 liters of fuel, some water, 4 grown-ups and 5 children on board, therefore total around 4500kg. Do not know how did he measure weights though (except for the people). These are the results that he gave me:

RPM Knots liters/hour
1600 7,4 7,3
1900 8,5 12
2100 9,5 15
2500 10,5 22
2800 12 26
3200 16,5 35
3500 21 45

I am a bit confused since I was expecting much less of total weight than he has described to me. If it would be less weight than he described, I would be very pessimistic of my results, since he has lighter engine and more HP, but I do not know what to think now. If we take fuel consumption as power reference, than it seems like he is achieving 16.5 knots at 206HP (35/45 * 265), that would be my very rough approximation for my boat, but not sure since described weights.

One very important thing, he says that by comparing our boats, his keel is much deeper and that mine has a gradual diagonal finish/end and he does not have it that way and he is considering cutting it differently, to be smaller and has better fuel consumption he says. I was trying, but I really could not see that difference on the photos. I do not know now if his keel has original shape, but only my opinion is that I personally would never change original shape/design of hull, rather change the boat in that case. Hopefully, designers/engineers knew what they were doing (although with today short deadlines, one cannot be sure of that anymore).

I am still optimistic about removing that tab, but not so optimistic about gaining the calculated speed (18-20 knots). Let's say if I take into consideration that he has maybe calculated/measured the weights wrong, I would expect that my maximum speed reach 15 knots if that tab removed and prop changed if needed. We shall see, one by one. At least I do have some comparable data now, in some way.
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  #49  
Old 12-07-2016, 05:34 AM
Joakim Joakim is offline
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The data doesn't quite add up. A 265 hp diesel should consume 55-60 l/h at full power, not only 45 l/h. Is this VW TDI 265-6, which is also used by Cummins Mercruiser? Just checked one measurement with that. 58.9 l/h at full power (4250 rpm in this case). 3500 rpm is also very low maximum rpm for this engine.

45 l/h would suggest about 200 hp and 35 l/h maybe 160 hp. Maybe the maximum rpm is missing or the propeller is too big for the engine?
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  #50  
Old 12-07-2016, 05:50 AM
Nidza Nidza is offline
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You could be wright, those are the data that he gave me and I was too excited, therefore not checking full power consumption for the given power and engine specs. Truth, if we take rough approximation that diesel engine uses around 0.2 liters of fuel per HP, then 265HP would really be closer to 53 liters/h of fuel consumption or 58.9 l/h according to specs as you have said. Anyway, I do believe that the owner was easily able to measure speed and RPM, so that is probably what he has. I will try to find out more details from him.

I believe that it is VW TDI with displacement of 3.0 liters. Truth, all those VWs are spinning at more than 4000 RPM.

If that is truth, better for my case, but I will wait for his response about that issue.
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  #51  
Old 12-07-2016, 08:54 AM
Nidza Nidza is offline
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The crane has measured that weight.

At maximum throttle engine reaches 4000RPM, no data of speed yet, fuel consumption is 53 liters/hour at that RPM. He is considering greater prop diameter (20'') for gaining higher speed at lower RPMs.
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  #52  
Old 12-08-2016, 09:25 AM
Nidza Nidza is offline
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One more info, just to see the angle of the boat at different speeds. At the beginning of earlier video, boat is at full throttle taking over the boat with camera. At the end of the video, boat is riding at 10 knots near the boat with the camera.
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