Sundancer 320 Four blade propeller

Esakkal

New Member
Jun 8, 2010
1
mamaroneck , NY
Boat Info
320 sundancer 2006
Engines
Inboard Engines
Hi,
Can somebody tell me if its worth to chang my propellers for a four blade prop. I had the boat for 3 yrs and stillhaving problems with the starboard prop at full speed I had 150 RPM diference with the port one.
Thank you
 
Why do you think 4-blade props will fix your RPMs?

Having difference in RPMs is normal due to the fact that transmmission on one side is spinning in different direction. I always have 80-100RPM difference and I'm sure others with similar configuration have similar affects. 150RPMs sounds a bit more than I would like to see. You can always contact Merc or SR to find out what's the acceptible RPM difference range.
 
I had the exact same problem with my 01 340 dancer. No matter what I tried i had a 250 rpm difference between port and starboard engines. I finally took off both props and took them to the prop shop here in Nashville. They had very little pitch difference. It would have been $350.00 to re balance both props. He happened to have had a pair of four blade props that he was selling. I bought them for $650.00 plus my old props. This was without a doubt the best money I ever spent on my boat. What a difference, better getting on plane, better steering at cruise speed, better docking steering and most of all perfectly balanced on the RPM's of both engines. The only drawback that I found was I top out at 3600 RPM. However my speed increased by a few knots. I highly recommend that you swap them for four blades.

Thanks
Steve Bone
 
4-bladed props tend to give you better low speed performance and handling and a little faster time to plaining speeds. They also tend to be smoother running. There may be a slight increase in top end speeds, but don't count on it.

The physics going on are that 4 blades with less pitch per blade moves the same amount of water as more pitch with only 3 blades. With less pitch, the individual blades on the 4-bladed prop tend to be more efficient because they have less slippage per revolution.

The reason one side needs slightly more or less pitch is not just because one side turns in reverse. One some ZF transmissions, the gear set yields a slightly different ratio in reverse then in forward. The reason has to do with fitting gears inside the cast gear case. For example, with the ZF 63IV gear, you have a nominal transmission ratio of 2.5:1, but you really have 2.477:1 in position A and 2.528:1 in position B. With other ZF v-drives, both gear positions A & B have the same drive ratios. That means the anomaly of needing slightly different props on one side than the other is pretty much limited to gas engines using ZF-63IV transmissions.
 
I had the exact same problem with my 01 340 dancer. No matter what I tried i had a 250 rpm difference between port and starboard engines. I finally took off both props and took them to the prop shop here in Nashville. They had very little pitch difference. It would have been $350.00 to re balance both props. He happened to have had a pair of four blade props that he was selling. I bought them for $650.00 plus my old props. This was without a doubt the best money I ever spent on my boat. What a difference, better getting on plane, better steering at cruise speed, better docking steering and most of all perfectly balanced on the RPM's of both engines. The only drawback that I found was I top out at 3600 RPM. However my speed increased by a few knots. I highly recommend that you swap them for four blades.

Thanks
Steve Bone

It sounds like you had pretty good deal on the 4 blade props. But, fixing the greater RPM difference should be accomplished just by tuning the original 3 blade props (providing they're in good condition and all other engine/trany components have been checked off. So, switching to 4 blade is not the answer or I guess is not the only answer. Prop shops can tune original props for the boat to perform according to the specs. I'm sure that if you hadn't bought those 4 blade props you would have gotten tuned original props and chances are the boat woul have ran fine.
 
It is certainly possible that they could have tuned the props back to factory specs and that would have helped the rpm's. I had done everything possible to remedy the problem before I changed out the props. We tuned both motors, adgusted throttle cables, checked the transmission and on and on. The owner of the prop shop said he could tune them in. I would have had to install them and if they weren't dead on, I would have had to pull them again untill he adjusted the pitch on the port side to compinsate for the RPM difference. I was real happy as soon as I put the four blade props on.

Thanks
Steve
 
My boat doesn't have V-Drives, but my WOT difference was not due to a difference in props! It ended up being a miss in the one engine under load. Fine now that the miss was addressed.
 
I thought that mine was an engine problem too. I had a sea ray tech on my boat while we ran it down the lake with his diagnostic computor hooked up. Intersting that the computor can tell you exactly how many hours are on an engine. Anyway, everything was balls on acurate on both motors. He said it had to be the props and he was dead on the money. He had also said that the dealer that he worked for changed out several 3 blade props to 4 blade props and the owners were thrilled with them and it fixed several problems like the one I was having with the RPM's

Steve
 
Dumb question: if the 4 blade props are a significant improvement on the 320DA, why didn't the factory choose them instead of the 3 blade wheels?
 
I was told by the service tech that they should have used them on the 340s and that they would offer an upgrade to buyers at the dealer before the buyer took delivery. Same as why didn't GM use a better motor then the 305 when the 350 was available and a better choice then the 305. Cost and fuel consuption.
 
I don't have a 320 but on my 330 the four blade I put on this season was like night and day. 3 blade i was bow high at any speed 4 blade the faster i go the straighter she gets, also plane quicker, at lower rpm
 
the 4 blade prop that is required has to be determined by a prop shop. However the diameter will remain the same but the pitch and cup size will usually be 1 to 2 inches less, example a 18 x 19 3 blade will go to an 18 x17 4 blade.if you want to pick up rpm then the 4 blade choice will be an 18x 16 with a #5 cup.These props are not cheap a good nibral prop can cost 1200 each. For the 320 the Michigan wheel DQX version is a great choice.
 
I just tried my new Michigan Wheel 4 blade DQX 18x18 Nibral props out today and can give them a resounding thumbs up compared with my factory 3 blade props for the following reasons:

1. Smoother operation which others have cited.
2. Improved docking maneuvering. Specifically when putting shifters in opposite directions the boat spins faster on a shorter radius. Also the boat at idle moves slightly faster in both reverse and forward.
3. Gets up on plane easier with no trim tabs at lower rpm. Now I can be on plane between 3400-3500 instead of 3600-3700 rpm.
4. Better instantaneous fuel economy on plane by 1+ gph.
5. Higher rpm at WOT which is now well within the 6.2L spec of 4600-5000. However the top speed was identical to what I had with my 3 blade props of 34.4 mph.

Inspite of these improvements I will still need some adjustment to my starboard prop over the winter since it is running about 130 rpm less. In 2006 and 2007, Sea Ray changed their prop spec for the 320 with V Drives to 18x19 LH and 18x18.5 RH. Only 18x18's were in stock for the DQX so Airmarine said to try these and make pitch adjustments if needed later to equalize both sides.

Finally the cost of these props was covered by insurance since the old ones were toast after I ran aground a month ago. I just got back in the water this past week. Otherwise they would have cost around $2,250 for the pair.
 
Bob,

That's great. Thanks for posting your test run results.
 
Bob, I want the same prop set up you did, how much cupping dod you add to each prop?




I just tried my new Michigan Wheel 4 blade DQX 18x18 Nibral props out today and can give them a resounding thumbs up compared with my factory 3 blade props for the following reasons:

1. Smoother operation which others have cited.
2. Improved docking maneuvering. Specifically when putting shifters in opposite directions the boat spins faster on a shorter radius. Also the boat at idle moves slightly faster in both reverse and forward.
3. Gets up on plane easier with no trim tabs at lower rpm. Now I can be on plane between 3400-3500 instead of 3600-3700 rpm.
4. Better instantaneous fuel economy on plane by 1+ gph.
5. Higher rpm at WOT which is now well within the 6.2L spec of 4600-5000. However the top speed was identical to what I had with my 3 blade props of 34.4 mph.

Inspite of these improvements I will still need some adjustment to my starboard prop over the winter since it is running about 130 rpm less. In 2006 and 2007, Sea Ray changed their prop spec for the 320 with V Drives to 18x19 LH and 18x18.5 RH. Only 18x18's were in stock for the DQX so Airmarine said to try these and make pitch adjustments if needed later to equalize both sides.

Finally the cost of these props was covered by insurance since the old ones were toast after I ran aground a month ago. I just got back in the water this past week. Otherwise they would have cost around $2,250 for the pair.
 

Forum statistics

Threads
112,948
Messages
1,422,806
Members
60,930
Latest member
Ebrown69
Back
Top