20 foot 1997 Maxum 2050 bowrider propeller question

[Bondo]

I took care of that, it was adjusted too close and was killing the throttle so I twisted it out and now it's ok. The rpm varies but it's at 650. The timing in the video varies with the rpm need to find out at what rpm it needs to be to have timing at 10btdc.

Ayuh,..... At idle,....

 

[achris]

Ok, plenty to unpack here. I've skim read most replies, and I think you're missing a few bits of information....

I am using this boat offshore in SOCal to occasionally go to the Channel islands, yes I know it's a bowrider but it works great. I recently rebuilt the Alpha 1 gen 2 drive myself successfully.

Excellent, you used all the right shimming and rolling torque tools I assume.

So the propeller on the boat is a 14.5x18 aluminum, not the original size which broke, one that I bought awhile back. I am not too happy with it especially in semi choppy waters.

Need more information on this prop. 3 blade, 4 blade? Manufacturer?

The gas mileage sucks but these are gas guzzlers compared to let's say my friend's Trophy II 115 outboard that can do 247 miles per tank.

You're engine should be making around 260hp. More than double that outboard. I'd be shocked if you didn't use more fuel. Also, he's getting 247 miles (statue miles or nautical miles?) but you didn't say how big the tank was (or the boat). If it's 250 litres, that's lousy, if it's 50 litres, that's brilliant. It's like my wife's car only gets 850km on a tank, but my car gets 1200km. Which one uses more fuel do you think? It looks like my wife's, but her car has a 70L tank, and mine has a 145L... Looks a bit different now, yes?

So I will never be able to reach such a performance since I have a 5.7l sterndrive.

Rubbish! Don't measure your performance by how many miles you can go 'on a tank'. To do it properly (and compare apples with apples) you need to be working in litres/nautical mile, and account for different boat sizes! As a comparison, at cruising I get around 1.3litres/NM. Given your boat is very similar to mine, with a slightly larger engine, I would expect you to be in the 1.5 to 1.7L/NM range.

Carb is rebuilt to specs and adjusted properly. Going to the Channel Islands from Oxnard is roughly a 12 miles trip with another 6 there and coming back I spend roughly 14 gallons of gas.

US gallons or imperial gallons (not everybody lives in usa). I'll assume US gallons (which are only 3.78L to the 'gallon'.) 53 litres for 16 NM (I have assumed you're using statute miles as you are using imperial for everything else ). That's roughly 3.3L/NM, and that's not good. Something's up.

And in semi rough water with winds of over 12 knots even more. You guys probably know about it.

Haha, I'm on the lower west coast of Australia. We call wind under 15 knots a 'breeze'. Our 'afternoon seabreeze' is almost always over 20 knots, and I've been caught out with it belting in at over 30 knots (this is what happens when you're underwater for an hour ).

My question is can I get a different propeller that can get the boat on plane below 20mph that it does right now.

Yes. Have you tried a stainless steel 4 blade?

At WOT I get 4100rpm and 40 miles per hour speed.

Ok, we have a problem. That WOT engine speed is WAY too low! You need to be getting it up around 4500rpm as a minimum. And that low a WOT RPM will also be contributing to a few driveability issues you may not even notice you have. Boat's sluggish and unresponsive to throttle. Struggles up swells then races down the other side.

30 rpm is 30 miles an hour. This motor specs say 4200-4600 RPM. I don't care about speed since yesterday was the first time I could take it and actually reach 40mph the ocean was the calmest I have experienced in a long time. It's August after all.
So what size propeller and pitch and why? Thanks in advance.

So, I have run the current figures through my prop calculator, and it all looks ok for what you have (with respect to the prop)...



But I think you have other issues. A 260hp engine should be pushing that boat at WAY quicker than 35 knots! I have a similar boat with 40hp less and I'm pulling up at the 40 knot mark (with a 3 blade prop. 38 with a 4 blade). I'd expect you to be up around 42 knots with that engine. I suggest you do some more engine checks and make sure you're getting all the horses it should be making. I know speed isn't what you're looking for, but a low top speed indicates a engine performance problem somewhere, and that is likely the reason for the unexpected high fuel consumption.

Start with a compression test.

I'd also like to know exactly which '5.7L' engine you have. Please post engine serial number, or at the very least, engine model and year.

Chris..........

 

[achris]

I want to show the timing check again. The mark drifts left and right when idle goes from 630 to 1000 and back. But it doesn't seem to be at 10BTDC, more like 15 to 16 BTDC.

With that much advance, you're going to blow holes in the pistons!

 

[gica]

With that much advance, you're going to blow holes in the pistons!

Thanks a bunch for being involved, other end of the world but great nonetheless.
My pro is a 4 blade aluminum. The thing about this boat is I rarely took it out in the past 10 years. I recentul rebuild the drive, all the rubbers, some bearings, used the proper dual torque yes. I usually do my own repairs no matter how difficult. I am now fixing my son's 2012 328i engine after a complete teardown and replacing everything from the bottom up. His main water hose broke(typical bmw issue) and all the synthetic oil inside the engine bunched up in big huge ball of carbonated **** down in the oil pan. Never ever seen anything like it. The head and intake cam are history but oddly enough the bottom of the engine was fine. So as you can see I go from one end of the spectrum to another.
Back to the boat. Since the timing mark is jumping all over the place it's hard to say how far off it is if at all.
If you can watch the video you might get an idea. The boat is running pretty good does have power but as you said probably not full power.
When I did the drive I tested the compression and it was pretty close on all 8, don't remember the number though, maybe 165-170.
That's good compression.
I don know why I get the idle going 640 to 1000, might be a leak somewhere. The engine is not overheating at all. Stays solid at 160⁰.
Salt water is a destroyer of engines I know but lakes are too boring.
So let me know what you think I should do next. I was looking at 14.5x17 4 blade prop. Don't want to spend 500 for a SS so am staying with aluminum unless I find a used one. But first have to find the right combo.
I will look in the service manual on the timing and idle issue. Plugs and wires, cap and rotor are all new.

 

[achris]

...So let me know what you think I should do next. ...

Please post engine serial number, or at the very least, engine model and year.

Chris..........

Watched the video. The engine sound doesn't match the rpm variation showing up on the timing light. I see a serpentine belt, which means it's likely a TB-V ignition system, and I wouldn't mind betting you didn't have it in base mode (hence the timing jumping around). That would also explain the indicated speed jumping around. The timing light calculates the rpm from the time between sparks, and if the ignition system is invoking 'idle speed spark control', then the time between sparks isn't going to be consistent, which throws a spanner in the works of the timing light's RPM calculator..

Get the ignition into base mode, then check the timing.

Chris......

 

[bman440440]

Had a chuckle at this. Hope you don’t mind. Pushing the boundaries of known physics a little there. 210hp 20ft performance lacking hull, 54 mph. Close to a prop slip figure that mti would kill for…and all with a 4 blade cheapo prop. Legendary! Fair play !

I dont mind at all... ;-)
54 is the highest top speed I have ever hit and it all actuality I prob had much less than 35 gallons of fuel and coming in the big bay with the wind at my back and only the last 2-3' of boat in the water with the drive trimmed up to a point where I had the fastest speed without blowing out the prop (just done for testing purposes) and with a cruise load of my girl, dog and lunch for the day without crazy trimming up it is normally 48-49 MPH... I do know that my prop has a dual blade design that really works well... I had another 4 blade aluminum with single profile blades and only got 45 MPH with the same pitch and load of people and fuel.

 

[gica]

Watched the video. The engine sound doesn't match the rpm variation showing up on the timing light. I see a serpentine belt, which means it's likely a TB-V ignition system, and I wouldn't mind betting you didn't have it in base mode (hence the timing jumping around). That would also explain the indicated speed jumping around. The timing light calculates the rpm from the time between sparks, and if the ignition system is invoking 'idle speed spark control', then the time between sparks isn't going to be consistent, which throws a spanner in the works of the timing light's RPM calculator..

Get the ignition into base mode, then check the timing.

I am looking for the info on how to get the engine in base mode.

 

[gica]

Watched the video. The engine sound doesn't match the rpm variation showing up on the timing light. I see a serpentine belt, which means it's likely a TB-V ignition system, and I wouldn't mind betting you didn't have it in base mode (hence the timing jumping around). That would also explain the indicated speed jumping around. The timing light calculates the rpm from the time between sparks, and if the ignition system is invoking 'idle speed spark control', then the time between sparks isn't going to be consistent, which throws a spanner in the works of the timing light's RPM calculator..

Get the ignition into base mode, then check the timing.

Chris......

Ok got the info on the base mode and will do it soon. I have to redo the idle mixture and idle speed in base mode

 

[gica]

I did the Base timing check and in my opinion it's right on 10, manual says 8 though but close enough see for yourself. Also there is a picture included with the purple white wire. I will redo the mixture at 1 1/4 and set idle at 650. The speed has to be done in the water I think.

Dropbox

www.dropbox.com

 

[gica]

Was just reading on the vacuum advanced on my thunderbolt V since it's 10 at base idle 650 rom what is the total timing advance at, 32? And at what rpm, 3500? Wanted to check that too as the guy at the boat place said I should. This doesn't have to be done in Base mode right? And in the water or can it be done in the parking lot?

 

[Rick Stephens]

All electronic advance, no vacuum. I believe the Thunderbolt V is 24 total degrees. You should be at max advance somewhere over 2500 RPM. You can check advance in base mode, that is disabled. The correct way to check total advance is with a electronic advance timing light. They aren't expensive and worth their weight with electronic ignition.

 

[gica]

I have one already it's in the videos I posted. But I thought that 32 is max. That's what people have been saying on different threads.

 

[gica]

I see what you're trying to say it's 24 for the advance only plus base in my case 10 for a total of 34. At least that's what I read.

 

[AShipShow]

Seems to me that to maximize fuel efficiency would be to minimize the wetted hull area (maximize planing height) while minimizing engine speed.. obviously the hull design is going to have a lot to do with planing speed and contact with the water, but for a pretty standard v hull bowrider, I'd say your pretty close to the point of diminishing returns on wetted surface area around 25mph or so...
So I would think you would want a very high pitch prop to allow you to run close to that speed at the minimum rpms... not sure if my logic makes sense but thats how I would think it would work...
Do you have any marinas near you that will let you try out props?

 

[Rick Stephens]

Seems to me that to maximize fuel efficiency would be to minimize the wetted hull area (maximize planing height) while minimizing engine speed.. obviously the hull design is going to have a lot to do with planing speed and contact with the water, but for a pretty standard v hull bowrider, I'd say your pretty close to the point of diminishing returns on wetted surface area around 25mph or so...
So I would think you would want a very high pitch prop to allow you to run close to that speed at the minimum rpms... not sure if my logic makes sense but thats how I would think it would work...
Do you have any marinas near you that will let you try out props?

Not to pick on you, but you should figure out how to rephrase that, it makes no sense at all to me. Slower RPMs and higher pitch is far less efficient - your motor will be lugging.

First priority with ANY propping is to hit the target RPMs at WOT. Your target may not be to spec RPMs, but you better have an idea of why you are going outside of recognized torque range. (for instance propping down for better hole shot when dragging bait, I mean wakeboarders)

Best efficiency, sanest, and best longevity is never to pull a higher prop pitch than the hull, motor and drive gearing can handle. Hence there is a spec.

 

[gica]

Not to pick on you, but you should figure out how to rephrase that, it makes no sense at all to me. Slower RPMs and higher pitch is far less efficient - your motor will be lugging.

First priority with ANY propping is to hit the target RPMs at WOT. Your target may not be to spec RPMs, but you better have an idea of why you are going outside of recognized torque range. (for instance propping down for better hole shot when dragging bait, I mean wakeboarders)

Best efficiency, sanest, and best longevity is never to pull a higher prop pitch than the hull, motor and drive gearing can handle. Hence there is a spec.

I read you I ordered a 14.5x17 to at least get me in the ball park rpm at WOT. I don't remember what the original prop was but I have a feeling I went up an inch when I replaced following the same theory that bigger is better. I am not 100% certain of this but I get that feeling.

 

[AShipShow]

Not to pick on you, but you should figure out how to rephrase that, it makes no sense at all to me. Slower RPMs and higher pitch is far less efficient - your motor will be lugging.

First priority with ANY propping is to hit the target RPMs at WOT. Your target may not be to spec RPMs, but you better have an idea of why you are going outside of recognized torque range. (for instance propping down for better hole shot when dragging bait, I mean wakeboarders)

Best efficiency, sanest, and best longevity is never to pull a higher prop pitch than the hull, motor and drive gearing can handle. Hence there is a spec.

No worries... I was more just thinking out loud..

My thinking was that these engines produce their max torque at lower rpms (around 1500) and the fuel consumption is going to be highest at the top end of the rpm range, so my thought was if you could maximize hull speed (high pitch prop) at the max torque engine speed you'd be at your best efficiency, but I guess I understand that if the engine is struggling to get to and maintain that speed than maybe it doesn't make sense... I dunno, I could be way off lol

 

[gica]

No worries... I was more just thinking out loud..

My thinking was that these engines produce their max torque at lower rpms (around 1500) and the fuel consumption is going to be highest at the top end of the rpm range, so my thought was if you could maximize hull speed (high pitch prop) at the max torque engine speed you'd be at your best efficiency, but I guess I understand that if the engine is struggling to get to and maintain that speed than maybe it doesn't make sense... I dunno, I could be way off lol

Your understanding of this issue is basically like mine was at first. But in boats it seems you first make sure all is adjusted with the engine, RPM, timing, carbs if you have them, compression and then you make sure the prop gets you at proper RPM at WOT. And let me tell you if you're not you feel it when it's choppy as the boat doesn't respond properly to commands as I already experienced in 4 foot waves and 18 knots winds coming back from the Channel Islands. It was my first experience of its kind and basically 1 hr and 1/2 later I was back at the marina going WTF just happened. Now reading some of the comments of what happens with a over sized prop I can remember the experience when you struggle to go up bigger waves only to fall down the other side, or going in and out of plane at the wrong time etc. On lakes I was perfect king of the water did not even realize I had issues. Again the lakes in SOCal are not Lake Michigan or Superior. It's crystal glass water only disturbed by boaters and jet-skiers. The ocean is the real test. And it will kick your ass for sure. But it's freaking great if you're a little nuts.

 

[nola mike]

No worries... I was more just thinking out loud..

My thinking was that these engines produce their max torque at lower rpms (around 1500) and the fuel consumption is going to be highest at the top end of the rpm range, so my thought was if you could maximize hull speed (high pitch prop) at the max torque engine speed you'd be at your best efficiency, but I guess I understand that if the engine is struggling to get to and maintain that speed than maybe it doesn't make sense... I dunno, I could be way off lol

I think you're thinking is in auto applications. You have different gearing to stay in the best rpm range at any given speed, and importantly under different loads. Boat is always under load (no real part throttle or downhill/throttle off conditions). So at a given speed in a boat, a lower rpm might not be most efficient because the load on the engine might actually be higher. (Not sure if that makes sense, having a tough time explaining it).

 

[AShipShow]

I know what you're trying to say lol... but I don't necessarily agree... if I was driving my boat to achieve good efficiency, I don't think I would cruise around at full throttle.. I would try to just get on plane but keep rpms low.. same reason cars have transmissions...
If your car had the equivalent of only 1st gear, then you'd accelerate fast but your long road trip would be pretty inefficient and take forever... but if you're car only had 5th gear, your mileage would be much better (if someone gave you a good push start) lol...
Again, not sure this theory works cuz boats and cars are definitely not the same...
Just still makes sense in my head that you would want a prop with higher pitch that would maximize your speed at minimum rpm