Doesn't the generator pull off the port side.

 

I think that fact that more fuel was used out of the starboard side made me think that genny is using strbd tank, but I just checked the manual and according to diagram on page 74 genny is actually using port side tank. Thanks for pointing this out. Now I'm convinced that genny uses very little fuel compare to the difference in the way counter rotating props/trans performing on the strbd side.

 

Both engines run in forward direction. One transmission runs in reverse, so, they have different gear ratios. This gives you counter-rotating props, but at slightly different RPMs when the engine RPMs are matched. Your props come from the factory mis-matched by .5" pitch, same diameter, in an attempt to match the engines' performances. The port prop has more pitch. I had mine tuned to even more pitch than the factory provided. Mine are now mis-matched by about 1.25" pitch, port higher. Now, they both run at identical engine RPM and fuel flows.

 

Both engines run in forward direction. One transmission runs in reverse, so, they have different gear ratios. This gives you counter-rotating props, but at slightly different RPMs when the engine RPMs are matched. Your props come from the factory mis-matched by .5" pitch, same diameter, in an attempt to match the engines' performances. The port prop has more pitch. I had mine tuned to even more pitch than the factory provided. Mine are now mis-matched by about 1.25" pitch, port higher. Now, they both run at identical engine RPM and fuel flows.

So....if I understand correctly......if you run both engines at the same rpm, and the sync gauge shows them to be as perfectly matched as possible....the port prop is turning slightly slower because of the different gear reduction. Sea Ray compensates for this by spec'ing the port prop with slightly more pitch, to provide more thrust, to make the boat run true. If this is true, the port engine should be under more load, and consume more fuel. did I get it right, Hampton?

 

so what you are saying is that we should run the port engine at a slightly higher RPM than the starboard if our prop pitch is not quite right????

 

I didn't say that, but, that would match the sides more equally. Problem is, SC records how long each engine spends in each RPM zone. I would rather put more gas in one tank than try to explain why the RPMs are mis-matched during survey at re-sale. If that is no concern, yes, I would match the fuel flows, if all else is equal. Your boat will, overall, run truer and therefore more efficiently.

 

Thanks for the explanation John.

I had my props tuned this spring to Class 1. One was up to specs and the other slightly off, so it was tuned. I have:

LH - 18.997 x 19 x 3
RH - 18.499 x 18.5 x 3

I thought that size difference was to compensate the counter rotating props/transm, but I guess the builder left a design gap for fuel usage.

Is this the case for most V-Drives boats or just selective models?

 

Thanks for the explanation John.

I thought that size difference was to compensate the counter rotating props/transm, but I guess the builder left a design gap for fuel usage.

Is this the case for most V-Drives boats or just selective models?

That is what I said. The last post I made above was to answer a specific question about engines that were not matched by proper prop tuning.

In the past, one engine ran backwards, so, the transmissions were both in forward with the same gear ratio and matched props which spun opposite directions. I don't know about other transmission designs. I believe it is at least a Hurth issue, if not with many similar transmissions. The way they are engineered, they cannot get the same gear ratio in forward as reverse (at least not without additional parts, weight, and re-engineering...).

 

Is this why I see the engine sync gauge get buried to the starboard when I go on plane by pushing the throttles forward together?

 

Guys, the engine load is the same.

There is about a 2% difference in transmission ratios, port to stbd, which is handled by the odd pitch combination on the wheels. Therefore, the engines run the same speed, put out the same hp/torque, the transmission makes fewer turns on one side, but that prop has more pitch which moves the boat further thru the water, so the net effect is 0.

A one gph differential is normal.......it is a different engine, has different wear, different clearances, different ECM, different injectors, etc. This may be a case of information overload......SmartCrap gives us actual fuel burn, its different, so we worry.

If we didn't know actual burn rate, would we even question a 1 gph differential?

 

Thanks, Frank. My brain was beginning to hurt from all that nonsense.

 

How is this nonsense? People come to this forum to discuss the intricacies of boating. That is what we are doing. We enjoy it. If you don't enjoy it, skip it. If people start trying convince others to yank their boats and props, then send them to their own personal shop to add 1/8 pitch to every other blade under threat of the boat exploding, that would be nonsense. This is boating.

 

When I saw this thread and the responses I was glad to see others have noticed the problem with the different gear ratios in the ZF Hurth v-drives. Most boaters that I've asked are totally surprised about this. The ratios are different? I must say until a recent failure of my starboard transmission I never even new the ratio of mine or that the ratios would be different. When I was collecting the model number and ratio I realized the ratios were different. As soon as I discovered this it started explaining a lot on how the boat performs.

I know a few of you here have figured this out and how to compensate. I've been trying to calculate the right changes to make to the port prop and have been working in an excel spreedsheet for a few days now calculating theoretical movement, engine rpm, shaft rpm and prop slip etc.

Hampton, what ratio is your ZF Hurth 63 and what diameter/props did you start out with and what are they now? How did the RPMs change on each engine from before to after. I'm surprised you made such a large change in pitch.

My 370 (sorry not a Sea Ray, Cruisers Yachts) with the 420hp 8.1 Volvos has ZF 63 IV transmissions wtih a ratio of 2.5:1 (S2.48, P2.53) and I have 22 x 23 4 blades with no cupping (michigan wheel). At WOT this amounts to the engine RPM to be out about 100rpm to achive the same prop shaft rotation. At cruise when engines were synced starboard always used more fuel, throttle advanced is more and has a slight pull to port. Started running the gennie off the port tank to compensate a bit. During the repair of the transmission while the boat is out of the water I'm going to have the props checked and then make a change to the port one as it is exceeding WOT limit by about 100rpm. Currently WOT on port is 5100 and starboard 4900. Once I have the thrust equal on both sides I'll have to figure out where the other 100rpm is being lost. Based on the info I've calculated I should increase the pitch on the port prop by 1/2" to equal the thrust out. If I do more than that I'm afraid and be transferring the problem to the port side. I also don't want to compenstate too much as I need to see why the starboard engine rpm should be a bit higher at WOT currently.

Any other examples rpm, pitch etc from anyone else that has been able to even things out would be great as I don't want to pull the boat out mid season just to tweak a prop.

 

Alex,
My 320 factory 3 blade props had 1/2" more pitch on the port side. I replaced them with 18x18 4 blades and now my starboard side runs 130 rpm slower at WOT than port. Both the prop shop and I suspected this might happen but they did not have an 18x17.5 RH prop in stock so they said they would reduce the pitch on the RH prop to compensate if necessary. Before grounding, my port side was running more than 100 rpm less at WOT with the factory props so with that data we decided to go with equal pitched 4 blades initially to see how they preformed. I suspect that something was either binding on the port side or the factory port prop may have been slightly bent by the PO causing it to run slower. So FrankW's point about the slight transmission ratio difference is correct or I would not see the difference with my new shafts, couplers, cutlass bearings and props.

 

Don't get hung up on fuel burn rates unless there is a huge difference. I was at a Crusader Engine Clinic a few years ago and the instructor made the observation that there is variation among engines of the same model. I think he said HP for example could vary by 5-7% for a given engine model due to manufacturing methods and the engine is still considered to be in spec. Couple this with running conditions being so variable, and gennys running off one tank, cross over valves for some configurations or not and you soon realize the issue is not worth fretting over. I run my boats sometimes 7-8 hours at a time over many miles. I used to be somewhat surprised when the fuel requirements for each tank were within 4 or 5 gallons at the end of a run. Many times there were differences of 20 gallons if sea conditions were rough. With the current boat, fuel usage differences are invisible as both engines and the genny draw from one large fiberglass tank. I've come to realize that it is change that you need to pay attention to. If you are suddenly using much more fuel, or suddenly hearing something different with your equipment, you need to pay particular attention. Otherwise, just do your maintenance as scheduled and enjoy the ride.

 

For those who care about the minute details:

Bought boat with props out of tune and had them tuned prior to 700 mile journey home. After that, Stbd burned more than port.
WOT right after tuning props when I first bought the boat (4600 recommend by Sea Ray):
Stbd: 4650
Port: 4800

The place that tuned my props matched them. They were not supposed to be matched.

I got the data from SR and had them tuned by a local expert. He first measured the props:
LH spin:
Stamped: 18 X 21.5
Marked Dia: 18 Measured Dia: 18
Marked Pitch: 21 Measured Pitch: 21.01
Cupping: 5 - .073 (Don't know what this means)

RH spin:
Stamped: 18 X 21.0 (Less than other one)
Marked Dia: 18 Measured Dia: 18.00
Marked Pitch: 21 Measured Pitch: 21.373 (too much)
Cupping: 5 - .073

After the first tuning by the experts:
LH
Stamped: 18 X 21.8
Marked Pitch: 21.8 Measured Pitch: 21.786

RH
Stamped: 18 X 21.4
Marked Pitch: 21.4 Measured Pitch: 21.369

While these were getting tuned, I had new manifolds put on the boat. I replaced the Aluminum ones with the Cast Iron ones. I immediately notcied a more "Throaty" sound to the engines, and the WOT numbers went up. Also, they still weren't matched perfectly, so, all these things combined, I had the LH prop re-tuned by the same experts.

LH:
Stamped: 18 X 22.5
Marked Pitch: 22.5 Measured Pitch: 22.497

My Props are Teignbridge Z3033/Z4140 with 1 1/2 Bore, .8 DAR (?), 5 - .073 Cupping, NiBrAl. The LH is 18 X 22.5 and the RH is 18 X 21.4.

My engines achieve WOT between 4600 and 4700 (Can't remember exactly), and during cruise, they burn within 1 Gal of eachother after even 200 total gallons. I don't match them by fuel flow but by RPM. The fuel consumption is for all and intents and purposes identical at matching RPMs.

 

While these were getting tuned, I had new manifolds put on the boat. I replaced the Aluminum ones with the Cast Iron ones. I immediately notcied a more "Throaty" sound to the engines, and the WOT numbers went up..

John, don't want to get off topic, but I also experienced an increase in WOT RPM after my manifold change this spring.
About 100 more each side. Brought it up to 250 over...enough to make me pull the props at haul out a few weeks ago and take a peek.

 

This is what I call a great topic, with even greater answers. You All are way to much info stored in your noggins. I like it

 

John,
This is great information. Just what I was looking for. I put your numbers into the spreadsheet I've been working on and it was interesting that the perfect match should have been P21.8 and S21.4 to get equal thrust. This was the same as the Prop tuner had calculated initially but was off a bit. Do you remember where your rpm was when they were like this? Maybe when I do mine I'll bump up the amount on Port just a bit more than I've calculated. I'm assuming your props are 4 blade. With your current setup I'm guessing Starboard would have slightly higher rpm now at WOT? I know mine are not cupped and that also will have an impact on the thrust/rpm. I'm also wondering after the starboard trans gets replaced what difference this might make. I may have had an alignment issue that was robbing me of some rpm. I do know that both props would spin with the same effort when it was out of the water. The more info I get the better. I won't have a chance to test any of this in the water until April. When I get the props checked it may explain the current situation. Great post.

 

I can't explain the numbers, but they work really well. I haven't run top end in a while, but I documented it in my log book last time I did. I'll have to look it up tomorrow and get back to you, which I will. Seems to me it's the opposite, even though that doesn't make sense.

What makes me happy is that at all normal operating RPMs, they both run very smoothly and use the same amount of gas. This set up has survived 3 1/2 years. I aligned the engines since the last time I tried WOT. Maybe it's time to try again.

The alignments, though out of limits, did not affect the gas mileage or relative fuel consumptions.

 

If I run my boat with the sync gauge centered my engines will burn the same amount of fuel. But doing this there is the drone of the engines not being in sync. Now sync them to the sound of both motors running the same and my port engine will burn about 5 to 6 gallons more on a about a 180 gallon fill up. 93 gallons port to 88 gallons starboard. The sound of the engines being in sync versus the gauge is just the pilot in me and drives me nuts. Was going to get the props done over the winter and just have to find the right shop to get them to.

 

Was going to get the props done over the winter and just have to find the right shop to get them to.

Wish I would have known, you and Cheryl could have joined us, now that we're out of the water, we're not sure what we are supposed to do on Saturdays and Sundays, so we dropped ours off last Saturday morning at the prop scan franchise in Huron Ohio...then took the ferry over to PIB and spent the night. Here's the link if you want to give it a try

http://www.propscanusa.com/propeller_repair_network.asp?state=oh

I'm thinking of picking them up when/if we go to the cleveland boat show...call me if you decide to do it.

 

Chuck,

You may be in the category that the guys above were aluding to. This may not be worth your time. I'm like you - I needed to try to make them exact, and I feel like I achieved that even though the numbers don't make sense (transmission ratios versus pitch differences).

If you think of it as a project more than a necessity, then, go for it, but I wouldn't lose any sleep over your current differences.

It is interesting that the sync gauge matches the motors and the fuel comes out even, but when you match them, they differ. How do you explain that?

 

That is strange to me as well. If my synch is straight up I usually have a good sound with minimal "drone" but the RPM's are a touch off. I usually end up with more throttle on the starboard side.

 

With the sync gauge centered both tachs are pretty close (considering a non digital tach) and I have the drone sound. Now even them up by the engine sound and the starboard will usually appear to be 50 to 75 rpm less than the port. I don't worry about this much as when taking friends with us they don't notice the difference. I in particular drove the boat while I sat in the back(doesn't happen often) and ran them together with the sync and she droned away. It isn't much but I know it. Also this appears to be around 3500 to 3600 rpm. Max rpm is around 4750 and they both at that setting are pretty close. 3000 to 3200 are close as well. So if this is just at that given rpm I like Hampton feel that it isn't really that big of a deal but I just wanted to join in and see if anyone else had this same issue. And yes Mark let me know when you head back down and will probably go with you if I'm not working.

 

Don't try to assume the job of the prop professionals. Getting you the right rpm's for your set up is what they do, every day, all day long so they understand the technical aspects of ratios, rpm's pitch, diameter, etc. Take them the information and let them determine what to do..........which also gets you some protection in case they miss it the first time, since most reputable prop guys will repitch props if they miss the desired mark.

Why not ask Carver what they are doing to handle the different ratios?

Sea Ray tweaks wheels at the factory to handle the slight ratio difference and the difference for the 2.5:1 630ZF is usually .5", but the local prop shop handles it differently depending upon how a boat performs, size of prop, etc......sometimes they use the .5" pitch differential; other times they handle it with a cupping differential.

 

Ran WOT yesterday, and as we suspected, the port ran lower than the starboard. The bottom hasn't been cleaned recently, but I don't know of any significant fouling. When I exactly matched the RPMs at 3500 off of the digital SmartCraft, the port indicated about .5 gph higher burn rate. I probably put too much differential in them.

The main thing for me is that when they are matched at cruise, the actual fuel burn is identical through a whole tank of gas. If I had them re-done today, I would take out 1/2 of the additional pitch which was added to the port side during the last tuning.

 

John,
That makes your additional port pitch .6". I've come to the conclusion that I will try .5" on the port so what you've already discovered has helped a lot. Even if I want to revisit it at at the end of next season I can. Thanks for all the detailed info.
Ray

 

I'm glad. Please take down data from before and after and share it here.

 

Don't forget the Power Steering Pump. Mine runs off the Starboard side.

 

Does anyone know if the straight-shaft setups like my 1990 310EC has the same reduction issue with the tranny running backwards. Both my engines are left-hand and I have Hurth ZF630a gears.

I just did a major overhaul which included new props. The props I put on came from the previous owner and had been reconditioned. Prior to my port engine having a drink of water -- which is what prompted the overhaul -- both engines ran at the same RPM when in synch. Now with a brand-new port motor and these new props (the PO said they were identical to the ones on the boat), I notice the port engine running a couple hundred RPMs faster. Its new and not yet quite broken-in, so IDK whether I have an issue or not. I also have not gone up to WOT yet since its not recommended until after 20 hrs. Overall the boat runs better than before at an easy 3100-or so RPM cruise.

Before reading this thread, I had never heard of this issue and having to have 2 different props to compensate. I was wondering if its particular to V-drives (which I know nothing about) or to ANY tranny running in reverse.

Thanks!