Could you give me more info about my boat

@Joakim,

Tab is flat with bottom of the boat (that would be 0 degree angle if I have understood your question well), like making the bottom of the hull longer without any "step". According to earlier "measurement", that means that anti-ventilation plate is about 2cm above the bottom of the hull. And now I have remembered, that is why I have chosen the longest available extension for the drive (2.5 inches) that will lower the plate as much as possible to be in line with bottom of the hull, but there was not longer extender so this was the closest possible (2cm above bottom of hull - again, be reserved of this 2cm as explained earlier, can't find the drawing now). And it was not possible to make the drive housing bell lower in the hull because of the hull, engine and gearbox geometry. Beside geometry, oil and other connections/fittings had to be reachable, too. Typical room/space constraints with boats.

According to our discussion, removing the central tab is on high priority list for the spring to see the difference, before any attempts of customizing the prop. I do expect big difference, but experience with boats so as with engineering tells mi that "slow is a pro" and that you should never rush to conclusions.

Thank you for the explanation about the anti-ventilation plate, very useful and straight-forward since I do understand the difference between ventilation and cavitation processes.

Does anybody have any comment on making that adapter for the shaft so that standard rubber hub props can be used? Do you see any problem with that? Main goal is the broader range of prop selection (D, P, BAR, number of blades, shape of blades), but the hit protection would be somewhat better, too.

@Mr. Efficiency,

Truth, it does look like something is missing there, but it works. I needed time to get used to it in the beginning, too and always seemed like there should be something more, but like you said, it is what it is.

Anyway, I will report the result when I test the boat without the tab so that this thread can be useful in the future for someone else if encountered with similar problem.

How much did the original engines weigh?

But I'm quite sure that 504 weighs in over a ton....and we're surprised that with an extra 1000 pounds (?) of engine weight it won't get up on plane?

It would be heavier than 2 x petrol sterndrives, in all likelihood, but not as much as 1000 lbs, I'd say. Maybe 500 lbs tops. Combine that with a power deficit, and it might explain at least some of it. Obviously the tabs went on since the conversion from twin engines, so there seems to be a squat issue ever since.

I was meaning just the engine. Looked it up dry weight is right at 2000 lbs.
Add the exhaust and gearbox, oil,coolant, and that has to be another 400-500 lbs...so about 2450 lbs?

I looked more closely at the specs in Italian and it seems with google translate "peso del gruppo" of 2x322kg is 1400 pounds.

So about 1000 pounds more sitting back there..

OK, you don't normally think in terms of 1 x 190hp diesel weighing 1000lbs more than 2 x 150hp gasoline, but if so, the wrong engine has been selected. Other brands are way, way lighter than the figure of 2000 lbs, if that is correct, there is no hope of it working.

It looks like WestVanHan has nailed it, an avoirdupois nightmare....maybe the engine was secured at a bargain price, but it belongs in a trawler, not a weight-sensitive boat, so apologies to the OP for not checking the weight of the engine, but whoever installed it should have been the one to do that !

Are you sure you have found the correct weight? I found earlier 700 kg (1500 lbs), which didn't seem that bad, although not optimal. E.g. https://gce.cummins.com/gce_hist/curves/4200_429.9/DS4214.PDF
http://www.barringtondieselclub.co.za/cummins/v504.html

Weight was discussed already in the beginning and Nidza gave weight estimations in the first post.

Possible excess weight doesn't explain the high rpm. That is a propeller related problem.

Funnily enough, I googled the engine description, and immediately saw text to the effect it was 2000 lbs, and didn't bother looking further. But I'd guess at a dry weight of 1500, there wouldn't be much change out of 2000 when you add drive, gearbox, exhaust fittings, oil and what-not.

If my memory serves me well, marine version of engine V-504-M with mounted Borg Warner gearbox (net dry) is about 800kg (1764lbs), but I do not have the brochure with me at the moment and I could not find one on the internet.

To that weight add 70kg for the outdrive and weight for all the fluids (18 liters of engine oil, 32 liters of engine coolant, 11 liters of outdrive oil, about 2 liters of gearbox oil), both exhausts maybe 20-30kg max (by the way, designing water cooled exhausts was the biggest challenge and concern for me, because of fear knowing the consequences if done bad).

The center of weight of engine is now somewhat closer to the bow than the original since the engine is longer, so as the engine room (still heavier stern than original). In the attachment is the approximate drawing of new setup. In original setup, that middle tank was 200 liters fresh water, and from each side of it was the 300 liters tank of fuel (600 liters total), so I have removed those two fuel tanks, and have left only the middle one, which is made bigger (250 liters now and compatible with fuel). To compensate a bit for that weight aft, for fresh water tank I have chosen flexible 260 liters tank in the bow, in which I can pour about 200 liters of water.

I said that it is heavy at the beginning, but I do not feel that engine is currently working heavy at higher/maximum RPMs and prop is probably slipping as Joakim has explained (according to previous discussion possible due to ventilation). I do not expect it to be an excellent planning performer and I am using it in displacement region anyway which is not problem for this hull shape. But, something is not wright and I would expect to have problems reaching maximum RPM or at least some longer time needed to reach it if weight would be the only problem.

I would not go deeper into explaining my reasons for this engine, it was this or some new/newer diesel engine with maybe maximum 50 BHP. Since I could have this (504) engine "new" with zero hours on the clock (long story) and that it could fit the engine room "nicely" (everything is easy to reach), that was my choice. Long long term would be to change it with smaller engine, since I am very satisfied with the boat itself (even at displacement speeds). By the way, engine is 195 BHP, and I think 185 SHP.

Just for the purpose of better illustration, here are also three photos, one from the almost finished engine room before returning the engine room lids/hatches and the second from earlier phase viewed from the opposite side, and the one showing the gearbox and illustrates the distance between the engine and the stern.

Also my boat is a bit different inside, there were two versions. The one that I have does not have the bow cabin and bow bed is shorter, instead it has the separate kitchen of same size as head, just on the opposite side of hull. The convertible table and seats are therefore moved to the bow, and on the opposite side of table and seats is also bed/bench, but the "back" can be lifted so that upper and lower bed can be formed. Under lower bed, and behind the back are the "storage" "rooms".

You can't make it lighter, and as you say, the performance is consistent with a propellor issue, but exactly what you do about that propellor is the $64 question.

When I was looking up the weight I checked a few places..hoping I was going to be wrong,for Nidza's sake.

Few years back at the marina some guys were pulling one out of a rotten old fish boat,transmission and all.
They put it in the back of a Ford 1 ton dually: the springs went right down on to the stops,and the tires were bulgy. Well over a ton.
They wisely pulled it off and sought a bigger truck.
One for sale on youtube,bare engine with accessories,he says shipping weight is 2200 pounds...

Suggest to enjoy it as it is,you have a great engine,it'll be trouble free and give you many
hours of use.

@WestVanHan,
The last sentence that you have said is what I was counting and hoping for long term. Talking to a friend of mine, who is Cummins engineer I was told that using it as recreational boat, I probably will not live until the time for the engine overhauling, just to keep up with the maintenance. Time will show what is going to happen.

For the sake of correct data, I am just looking at two different brochures of the marine engine V-504-M. One brochure is engine with Twin Disc MG-502 gearbox and it says net weight, dry with accessories and gearbox 800kg, the other brochure is engine with Borg Warner gearbox and it says net weight, dry, with accessories and gearbox 771kg (gearbox with included reduction box on the photo). Well, anyway, I am aware of that since the beginning of the project, but I am still hoping for better results with a little bit of experimenting. Of course, exhaust risers, waterlocks and other external equipment all add up to the total weight of the boat/engine.

@Mr Efficiency,
exactly $64 you say, where is that?

Speaking of same boat from the earlier video, I have just managed to contact the owner and I do hope for more info soon about some peculiar details like prop specifications, speed, etc. It is duoprop, but the stern of the boat has really strange extension, as you can see from the reconstruction photos ( http://www.mojalbum.com/mando/bora ). I hope that, soon, the owner will clarify that. One thing that comes to mind is that skeg was too close to outdrive removing waterflow, but I will wait for the response. It is astonishing how that modern engine looks small inside the boat and compared to my engine.

It looks like they wanted to have more set back. Maybe to put the drive deep enough below the water surface or then further away from the keel. The latter seems unlikely reason, since keel is not that close and the difference is rather small.

Other reasons may be making moor room for the engine inside the boat and optimising weight distribution.

Here is a picture clearly showing the extension. Doesn't look that long.
http://www.mojalbum.com/mando/bora/foto/22466293#!22492011
Here is a picture inside the boat:
http://www.mojalbum.com/mando/bora/foto/22466293#!22455911

There was an extension already before the engine and drive replacement:
http://www.mojalbum.com/mando/bora/foto/22466293#!22279147
But here it is cut away:
http://www.mojalbum.com/mando/bora/foto/22466293#!22311874
Here is the new one:
http://www.mojalbum.com/mando/bora/foto/22466293#!22412561

I have finally found the photo, just before going into the water for the first time, that very good represents the tab and outdrive situation and geometry. It seems to me that even the higher part of the prop is above the tab when in trimming/driving position (-5 to 10 degree). And since the tab is below the anti ventilation plate, seeing that plate with my eyes during the ride seems to be really bad ventilation situation.

Do you have different conclusions/opinions watching this photo?

Can't wait for the spring now, but I am pretty optimistic now about removing that central tab!