The purpose of this string is to provide information to individuals who are considering replacing ZF SD10 sail drives either with identical drives or swapping them for something else. If others have done this or something similar, I hope they will also share their experiences. One of the things that made deciding to do this difficult was that there seemed to be very little information posted by people who had done it.
Background: I had two Nanni 3.100HE engines with SD10 sail drives. The engines and drives had approximately 2400 hours on them and I was detecting saltwater intrusion in the sail drive
oil.
When the prop
seals were last changed, I noticed the shafts had grooves in them where the
seals rubbed on them. Repairing shafts seemed to be limited to coating the grooved areas with chrome or ceramic material. In some cases double lipped seals have been used as a temporary solution. However, getting the shafts repaired in a foreign country (Italy) where transportation and language were a barrier did not seem practical nor did anyone know how to do it.
Through a dealer I contacted ZF which only wanted to sell me a complete leg at about 4,000 each. I eventually got them to agree to sell the shafts and some related
parts for about 2,000 per
engine. In the process of questioning why I needed a 10mm nut and plastic cone for 100, ZF said via
email they no longer were going to answer my questions. I was able to find a better
price for the
parts in
Malta but the cost of hauling there was out of sight.
I then went to a
boat show in Cannes solely to talk directly to a ZF representative. By luck I met with the after sales
service manager for the entire company. I asked him what I should expect in
maintenance cycles. He shared the following:
Replace prop shaft seals every 700 hours
Replace prop shafts every 1400 hours
Replace clutches every 1200 or more hours depending how they are used (i.e. if it was a charter boat you would be lucky to get 1200 hours)
He later confirmed this information via
email. I concluded my drives were toast.
Alternatives: I considered doing a complete
rebuild of the drives but I have never had any luck with this approach when dealing with transmissions and quickly abandoned it.
I then explored replacing the drives and found SD10 drives would cost approximately 3700 each plus
shipping and VAT (19-22%) etc. During this process, I discovered that Nanni was no longer using ZF drives and had switched to Twin Disc SP60s. I also learned Beta engines were using the SP60s as well as a Spanish
engine company and that Nanni made a kit for facilitating the conversion. The SP60 drives cost about 2,400 each plus
shipping and VAT.
However an
engineer from a Nanni dealer told me that it was a straight forward job and only required a few new holes to be drilled and tapped in the embedded metal ring that holds the drives down on the engine base fiberglassed to the
boat. This created a major dilemma.
Purchase new SD10 drives and do a
plug and play replacement or get involved with modifying the boat to accept SP60 drives and expect a much larger labor bill.
After seeing a disassembled SP60 it appeared to be bettered engineered with superior
water seals and I later came to realize a much heftier dampening plate. Twin Disc also makes the complete parts list and
service manual for the drive available on line; information not made public for the SD10.
Decision: I ultimately decided to replace the existing SD10 drives with SP60s. It turned out the holes lined up perfectly and no drilling or tapping was necessary. The information I had been given was wrong. It took only 11 hours of time to do the job versus the 40 hours I had budgeted.
The two brands of drives do sit differently on the engine base. With the SP60s the engine moves forward about 0.5 (12mm) and down about 0.75 (18mm). This is part of what the kit was designed to help achieve.
The
installation had one complication. The Nanni kit did not anticipate a factory installed
Balmar alternator option on both engines. This was accommodated by modifying an engine mount and a weight (from the kit) which is attached to the side of the engine.
One other point is to be sure the shift linkages are correctly adjusted for the SP60s. They shift differently than the SD10s and the linkages need to be set correctly to be sure forward and reverse are fully engaged.
The ratios on the two drives are also different. The SD10s are 2.52 and the SP60s are 2.38 meaning the SP60s spin the prop at a slightly higher speed for the same engine
rpm. In some cases this may mean re-propping. In my case, it did not.
When the SD10s were pulled I discovered they were also leaking
transmission oil into the bell housing. However only time will tell if the SP60s have a longer life than the SD10s.
If anyone wants to see my spreadsheets comparing costs and the sources I contacted. please pm me.
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