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Old 26 November 2023, 23:22   #1
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Prop has too much grip?

I'm having a bit of trouble trying to get the best performance from what I've got here. Running a ford 2.5 TD in place of a 1.7dt mercruiser. I'm not entirely sure how much hp I have but somewhere between 120 and 140hp. I'm getting 15 psi boost but that only kicks in at 2900rpm. And it revs out to 3900rpm under load. I have played with fuel settings and i can't seem to improve low rpm boost. The boat is slow to get out of the hole as it's already on the plane before making any boost at all. 0-18knts is pretty slow. Then boost kicks in at about 20 and it's off, accelerating very quickly from 20 to 30knts by which point it's at max rpms.

It will sit at 30 flat out, making 5psi boost. This would indicate the engine is only lightly loaded. It could push more prop for a higher top speed but I know this will only make the above problem worse.

Would running less diameter improve the situation? The idea being to create more prop slip as the boat accelerates, allowing the engine to build rpms and create boost at a lower speed? Possibly going less diameter more pitch for higher top speed
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Old 27 November 2023, 11:59   #2
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I'm having a bit of trouble trying to get the best performance from what I've got here. Running a ford 2.5 TD in place of a 1.7dt mercruiser. I'm not entirely sure how much hp I have but somewhere between 120 and 140hp. I'm getting 15 psi boost but that only kicks in at 2900rpm. And it revs out to 3900rpm under load. I have played with fuel settings and i can't seem to improve low rpm boost. The boat is slow to get out of the hole as it's already on the plane before making any boost at all. 0-18knts is pretty slow. Then boost kicks in at about 20 and it's off, accelerating very quickly from 20 to 30knts by which point it's at max rpms.

It will sit at 30 flat out, making 5psi boost. This would indicate the engine is only lightly loaded. It could push more prop for a higher top speed but I know this will only make the above problem worse.

Would running less diameter improve the situation? The idea being to create more prop slip as the boat accelerates, allowing the engine to build rpms and create boost at a lower speed? Possibly going less diameter more pitch for higher top speed
Can you try a few different pitch / size props? there's obviously a few factors that affect a boat getting-on the plane, so I'd experiment
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Old 27 November 2023, 12:23   #3
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Can you try a few different pitch / size props? there's obviously a few factors that affect a boat getting-on the plane, so I'd experiment
I have a 19 and a 21 spare. With a 23 on it now. The 19 and 21 were used with the 1.7dt engine, it revved another 1000rpm hence the change to 23 for the ford engine. It's a 23 ballistic as that's the only thing I could get in 23 pitch. Not sure if it being a ballistic style prop would make a difference?
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Old 27 November 2023, 12:48   #4
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2900rpm sounds high for the turbo to kick in. Is the Ford engine out of a road vehicle? If it’s a road vehicle engine, then it’s expected to be connected to the load via a gearbox that will enable the revs to be kept in the power band. Ideally the torque needs to be peaking waay down the rev range (1500-2000rpm??). My instinct says that tinkering with props will have little impact unless you can lower the boost revs.
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Old 27 November 2023, 14:55   #5
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2900rpm sounds high for the turbo to kick in. Is the Ford engine out of a road vehicle? If itís a road vehicle engine, then itís expected to be connected to the load via a gearbox that will enable the revs to be kept in the power band. Ideally the torque needs to be peaking waay down the rev range (1500-2000rpm??). My instinct says that tinkering with props will have little impact unless you can lower the boost revs.
It would have started its life as a transit engine. Fitted to transits around 1995-2000. It had already been marinised before I bought it. I don't believe it is a Lancing marine one but the setup is the same. Bowman exhaust manifold/ heat exchanger, bowman charge air cooler, water cooled marine turbo, fuel pump fiddled with. Not long after fitting it she dropped a valve. I rebuild the whole thing, reconditioned cylinder head, and new pistons. I had a good look at everything else while in there. The bores showed little wear as did the big end bearings. I also fitted a new oil pump, fuel injectors and had the fuel pump away to a specialist have the fueling set up for 140hp. It should be a very healthy engine now.

I would agree, it should be making boost long before 2900rpm. Most high revving diesels tend to start spooling from 1500 and will be making near full boost by 2000. Do you think I could have an issue with the turbo? I was worried the hot side of it would have been damaged with shrapnel after the top end blow up but I checked it over and it looked good, bearings felt good, just a little play like a turbo should have, no end float and i'm not getting any oil ino the intercooler. I'm not sure what model of turbo lancing marine fitted to these nor am I sure which turbo I have got! It's a great big water cooled beast of a thing. I'm wondering if it's possibly too big for the engine and that's why it doesn't spool until well up the rpm. But then you'd expect more than 15psi too?
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Old 27 November 2023, 16:02   #6
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Exactly what prop are you running? There are possibilities to increase slip at low rpm, depending on the prop you are currently running. And what drive - I guess probably a Mercruiser Alpha?

Oh - and what turbo? Is it an automotive style wastegated one with an air cooled turbine housing, but water cooled cartridge? Or water cooled exhaust housing too? Amongst other things, make sure the wastegate isn't cracking open too early. For diagnostic purposes, you could just tighten it up a little a see what happens with it coming on boost - albeit carefully since you don't want to overboost it.

The other possibility is it could be running a little lean. Yeah, it's a diesel. But you need the injector pump to lead the turbo slightly as it comes on boost - which isn't really the done thing these days as it can make a little smoke in the exhaust - but on marine engines, is sometimes necessary to get it on boost.

Anyway - more details please.
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Old 27 November 2023, 17:25   #7
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It would have started its life as a transit engine. Fitted to transits around 1995-2000. It had already been marinised before I bought it. I don't believe it is a Lancing marine one but the setup is the same. Bowman exhaust manifold/ heat exchanger, bowman charge air cooler, water cooled marine turbo, fuel pump fiddled with. Not long after fitting it she dropped a valve. I rebuild the whole thing, reconditioned cylinder head, and new pistons. I had a good look at everything else while in there. The bores showed little wear as did the big end bearings. I also fitted a new oil pump, fuel injectors and had the fuel pump away to a specialist have the fueling set up for 140hp. It should be a very healthy engine now.

I would agree, it should be making boost long before 2900rpm. Most high revving diesels tend to start spooling from 1500 and will be making near full boost by 2000. Do you think I could have an issue with the turbo? I was worried the hot side of it would have been damaged with shrapnel after the top end blow up but I checked it over and it looked good, bearings felt good, just a little play like a turbo should have, no end float and i'm not getting any oil ino the intercooler. I'm not sure what model of turbo lancing marine fitted to these nor am I sure which turbo I have got! It's a great big water cooled beast of a thing. I'm wondering if it's possibly too big for the engine and that's why it doesn't spool until well up the rpm. But then you'd expect more than 15psi too?
CAVEAT! I'm guessing here as I know f'all about marine diesels, but maybe the exhaust flow from the engine isn't sufficient to spool the turbo. Is the blower too big for the job?
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Old 27 November 2023, 18:56   #8
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There's a really good book on turbocharging by corky bell.

Anyway, it's possible the turbo is a bit big - 5psi of boost is nothing, so it might have been sized to produce much more power.

It's also possible it's a non wastegated turbo - some marine diesels do this, esp jet boat engines. The wastegate is actually a weak spot - with it open at full power, things get a bit hot and the wastegate valve can burn away, so sometimes you go with a non wastegated setup.

Anyway, if the OP is happy with the 30 knot performance, which indicates everything is basically adequate, then prop choice comes in - you don't want to drop pitch, maybe even want to increase a bit - but need to dial in some slip to get the motor on boost at slow speeds. And perhaps add a little to the injection curve so the fuel injection just leads the boost coming on slightly. But that depends on whether the exhaust is perfectly clean at WOT trying to get on the plane and off boost or not...
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Old 27 November 2023, 20:03   #9
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Exactly what prop are you running? There are possibilities to increase slip at low rpm, depending on the prop you are currently running. And what drive - I guess probably a Mercruiser Alpha?

Oh - and what turbo? Is it an automotive style wastegated one with an air cooled turbine housing, but water cooled cartridge? Or water cooled exhaust housing too? Amongst other things, make sure the wastegate isn't cracking open too early. For diagnostic purposes, you could just tighten it up a little a see what happens with it coming on boost - albeit carefully since you don't want to overboost it.

The other possibility is it could be running a little lean. Yeah, it's a diesel. But you need the injector pump to lead the turbo slightly as it comes on boost - which isn't really the done thing these days as it can make a little smoke in the exhaust - but on marine engines, is sometimes necessary to get it on boost.

Anyway - more details please.
Alpha one 2:1 ratio. Prop is 14 1/4 X 23 Michigan wheel ballistic. I have played with the main fuel screw to the point it smokes a little before boost kicks in. On boost it is clean. I'm getting 15psi on boost which is safe for this engine, I don't think I need more, I just need it lower in the rev range. It's a proper marine turbo with the water jacket around the hot side. I'm unsure of make and model. The compressor looks quite big. About double the size of the one on the 1.7dti. More like what I'd see on a 6cyl tractor engine. Although horsepower figures would be the same. I have a tractor here with a 5.9 cummins that is 130hp at 2500rpm, it has a very similar sized compressor to this turbo on my boat.
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Old 27 November 2023, 20:17   #10
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There's a really good book on turbocharging by corky bell.

Anyway, it's possible the turbo is a bit big - 5psi of boost is nothing, so it might have been sized to produce much more power.

It's also possible it's a non wastegated turbo - some marine diesels do this, esp jet boat engines. The wastegate is actually a weak spot - with it open at full power, things get a bit hot and the wastegate valve can burn away, so sometimes you go with a non wastegated setup.

Anyway, if the OP is happy with the 30 knot performance, which indicates everything is basically adequate, then prop choice comes in - you don't want to drop pitch, maybe even want to increase a bit - but need to dial in some slip to get the motor on boost at slow speeds. And perhaps add a little to the injection curve so the fuel injection just leads the boost coming on slightly. But that depends on whether the exhaust is perfectly clean at WOT trying to get on the plane and off boost or not...
Yes it's a non wastegate turbo. I'm happy with 30 knots but I'd like her to get on the plane easier. It struggles a bit in a heavy sea when you might be on and off the plane a lot. Sometimes getting stuck on the back of a big wave unable to climb out of the hole. Boost comes in at 2900rpm right around 18 knots just as it's starting to plane. If it would come in lower it would be ideal or if the prop would slip so I could achieve that rpm at a lower speed then as the boat planes the slip would decrease and speed increase. Or would that be defying the laws of physics there?

I'm getting 15psi as she accelerates from 20 to 30knts. Then she will maintain 30knts with boost running only around 5psi. This would indicate that she is lightly loaded (boost being proportional to engine load) and game for more prop for a higher top speed but that would make the acceleration problem worse.
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Old 27 November 2023, 22:04   #11
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Assuming you're not up for getting a smaller turbo, I reckon a prop change is called for.

Something like this could be a good start - but you'd need to check the hub it comes with :
https://www.ebay.co.uk/itm/364565153311

Or you could be brave a drill holes in your prop - you'd have to experiment.

Basically what many of the quicksilver props have is exhaust vents holes, like you can see in the above one I've posted that vents exhaust into the prop until the thing is up and on the plane.

Now on my boat that runs a 21" laser 2 with mid-size holes in, it's too much - the motor spins up and I'm not going anywhere - but this is actually what you want! Many Laser 2, Mirages & Bravo props will have this. I suspect you don't need a bravo (too much blade area), a laser 2 is a general good allrounder that if you buy, someone will want and you'll be able to shift on to someone if it doesn't suit.

This article explains it all : https://boattest.com/article/mercury...ent-system-pvs
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Old 27 November 2023, 22:47   #12
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Yea I don't fancy changing turbos, that could get pretty expensive. I've not heard of the prop venting thing before, very interesting. I might just buy that prop off eBay there, I reckon it be worth having a play around with this. Thanks for that. I could drill the prop I've got but if it's not a success I'll be out with the stainless steel welding rods filling it back up! Anyway I want to try a normal prop in 23 pitch. Not sure on this ballistic style one I have, it was the only 23 I could find for sale at the time so that's why I ended up with it.

If I can get the acceleration sorted I might try going for more speed. Possibly changing to a 1.6 ratio gear set in the drive. I have seen a few 1.6 alphas for sale for not much money.
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Old 27 November 2023, 22:53   #13
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Laser 2 is a good allrounder prop. Doesn't have much bow lift, but at 30 knots I don't think that'll be too much of an issue - the mirage is an "upgrade" from the laser 2 with slightly more blade area and a bit more cup to lift the bow.

That one I've linked is an early one with the square holes - I believe the newer ones have standardised on a circular one you can put a rubber bung in. But this particular one is cheap enough to give it a go I reckon. Just check the hub it has in it - should be fine, but you won't want to have to go and buy small shaft hub or something to fit your drive - it'll add to the cost for the test, although you can switch hubs between props at least, as long as they are all "flowtorque" hubbed props.

Oh, and if you were patient you might be able to find a cheaper one. The cheaper ones currently listed don't have the vent hole or the pitch was wrong - depends on how keen you are.
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Old 28 November 2023, 14:29   #14
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Old 28 November 2023, 20:36   #15
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I've bought that one on eBay there. I'll give it a try next time I have her in the water. Currently rigging up an oil cooler and mounting a boost gauge on the helm console
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Old 28 November 2023, 20:42   #16
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Cool. I hope it helps improve things - let us know you you get on.
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Old 28 November 2023, 22:05   #17
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Yes, will do. Hopefully get out some time in the next couple of weeks! Cheers
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Old 29 November 2023, 08:09   #18
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Your non-wastegated turbo is typically what you'd use on a jet drive boat since they have no low down grip.

BUT...it's all good. Wastegates take a real beating when you run an engine flat out for a long period of time - like boats. The wastegate stays open and doesn't get the cooling it would when it closes in an automotive application (even racing) and so can sometimes burn out the wastegate valve. Which is why non-wastegated turbos can be useful sometimes - and obviously they need to be sized appropriately to give you the right boost you want. The downside is as you're seeing - it's not coming on boost until later. But the upside is once setup nicely, it should be a pretty rock solid setup.

The Round Britan race boat "Swipe Wipes", owned by a friend, has Steyr motors - it started life with wastegated motors, but these days runs the non-wastegated version offered by Steyr. It too takes a while to get up and running - but runs ever so well once up and going.

It will always take a bit more effort to get a non wastegated setup to spool up - I think a vented laser 2 will be a step in the right direction for you - but going even further, over hub props are available too and they really slip until hooked up.

I forgot to check, although I hope it's obvious - I assume your exhaust is going through the prop? This is pretty much a must.
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Old 29 November 2023, 23:14   #19
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The guy I bought this engine off had it on a jet that he was going to put in a dory. I think it was one of them projects that never got finished and he was flogging it on eBay. Not sure if it was marinised by him or what the story is. Lancing marine sold these as a complete engine I think but it's more common to see these in NA configuration around 80hp in displacement hulls.

As for wastegate vs non wastegate... It seems more common to find non wastegate turbos on fairly low boost applications. You'll see a lot of older tractor engines run non wastegate turbo and no intercooler but by modern standards produce quite low hp per litre of displacement. I have one tractor here that is 6cyl 5.9l and 130hp, no waste gate, no intercooler. NA the same engine would be 100hp. I have another tractor that is much more modern 6cyl 6.7l wastegate turbo, intercooled and 240hp probably producing around double the boost pressure of that older one.

Yep exhaust through the prop. Although when running the leg in a barrel of water some of the exhaust along with the raw water exits out of the drive from in around the transom shield somewhere. It has always done this which I assumed was normal?
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Old 30 November 2023, 07:39   #20
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Cool. And exhaust - yes, bit of leakage around the transom assembly is normal - there's a kind of rubber sleeve there that slides over the ali casting on the bellhousing as you trim in & out - so it never seals perfectly.

Fingers crossed the Laser 2 is a step forward.
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