Saildrive vs Shaft Drive

[smj]

Originally Posted by Captain Bill

This saildrive versus shaft drive seems to be a religious issue and no one will convince those with an opposite opinion. I had some issues with my saildrives last summer and was doing a bunch of research. What I found is that no sailboat transmission, either saildrive of shaft is designed for cruisers. Cruisers are simply not a big enough part of their market. Sailboat transmissions are designed to get you in and out of the slip and down the channel to open water where they expect you to sail. Their target market is weekend sailors. They are not designed to motor hundreds of miles in calm winds. From what I could gather most have a target design life of 1500 hours. They expect this to take 15-30 years to accumulate. This applies to saildrives and shaft drive transmissions.



I would note that I have personally sheared a shaft coupling and pulled the shaft out after hitting a crab pot, which resulted in a lot of water in the boat. I have hit several crab and lobster lines with my saildrives and never had a problem with water in the boat.

Nothing about your 2 year old saildrives needing the transmissions replaced? Or the designed life of your saildrive prop shafts are 1400 hours and cost to replace them is $5700 each as they no longer sell replacement shafts so you have to but the entire lower unit?
We have owned 6 diesels with transmissions and never had any problems. 1500 hour life span for the transmissions? Never heard of that, makes me love my outboards even more. And on outboards your able to get that chunk of aluminum out of the water when not in use.[emoji848][emoji1303]

[DotDun]

Originally Posted by smj

Nothing about your 2 year old saildrives needing the transmissions replaced? Or the designed life of your saildrive prop shafts are 1400 hours and cost to replace them is $5700 each as they no longer sell replacement shafts so you have to but the entire lower unit?
We have owned 6 diesels with transmissions and never had any problems. 1500 hour life span for the transmissions? Never heard of that, makes me love my outboards even more. And on outboards your able to get that chunk of aluminum out of the water when not in use.[emoji848][emoji1303]

Which saildrive? The lower unit for my SD20 is $2100 (parts only). Hard to believe it would be more than a couple hours to change the lower unit.

FWIW, I replaced the prop shafts @ 2500 hours. IIRC I paid ~$500 for each shaft new (from old stock).

Changed the rubber diaphragm @ 15 years, old one appeared as good as the new one. The mechanic asked me why I was changing them, his suggestion is not do it unless there is a problem, which he has never seen.

[smj]

Originally Posted by DotDun

Which saildrive? The lower unit for my SD20 is $2100 (parts only). Hard to believe it would be more than a couple hours to change the lower unit.



FWIW, I replaced the prop shafts @ 2500 hours. IIRC I paid ~$500 for each shaft new (from old stock).



Changed the rubber diaphragm @ 15 years, old one appeared as good as the new one. The mechanic asked me why I was changing them, his suggestion is not do it unless there is a problem, which he has never seen.

It was what Captain Bill posted in the cost of catamaran sailing thread.

[rom]

Originally Posted by Captain Bill

This saildrive versus shaft drive seems to be a religious issue and no one will convince those with an opposite opinion

Typical result of uneducated forumers talking loud unfortunately. There are pros & cons to each, one shall understand them and choose accordingly.

[smj]

Originally Posted by rom

Typical result of uneducated forumers talking loud unfortunately. There are pros & cons to each, one shall understand them and choose accordingly.

So please inform us of your education and understandings

[Captain Bill]

Originally Posted by smj

Nothing about your 2 year old saildrives needing the transmissions replaced? Or the designed life of your saildrive prop shafts are 1400 hours and cost to replace them is $5700 each as they no longer sell replacement shafts so you have to but the entire lower unit?
We have owned 6 diesels with transmissions and never had any problems. 1500 hour life span for the transmissions? Never heard of that, makes me love my outboards even more. And on outboards your able to get that chunk of aluminum out of the water when not in use.[emoji848][emoji1303]

Ok, I'm back and will explain these items. The problem I had with my saildrives was due to a known defect in the particular set of serial numbers that I happened to buy. This replacement was not due to a problem with the concept of a saildrive but only the execution of a particular set of serial numbers, therefore not pertinent to the saildrive versus shaft drive conversation, so I didn't raise that issue here. Since I had the drives apart i decided to replace the prop shaft seals and discovered that there was a groove worn in the prop shaft that was near tolerance levels. I had 1200 hours on the saildrives at that time. That is when I discovered that drives made by ZF had prop shafts that had a design life of 1400 hours. I also discovered that ZF only sold lower units and did not sell replacement prop shafts. Note that though the drives were built by ZF, they are Yanmar branded SD60's. The only option for replacing the prop shafts from Yanmar is to buy the whole lower unit. I found that this is also the only option for ZF brand drives. I had the shafts sleeved instead for about $150. Only time will tell how well this works. I mentioned in another thread that the design service life for most sailboat transmissions is about 1500 hours. This is time between overhauls, based on the design service life of bearings. If you get the shop manuals, not the owners manuals, they often list the service life of many components, without which the unit will not operate properly. This is not to say that they won't sometimes last longer, but beyond that limit they are not considered a premature failure. On my original saildrives I got about 3000 hours, but the bearings had a service life of 1500 hours according to the shop manual and would have been replaced by someone doing an overhaul to Yanmar specs. Interestingly, I saw the same service life listed for bearings in a service manual for shaft transmissions sold for the same engine. So Yanmar saildrives and Yanmar shaft transmission parts have similar or the same design service life. This also makes service life irrelevant to the discussion of saildrive versus shaftdrive.

The cost of prop shaft/lower unit replacement is outrageous in ZF based drives. I will never buy another ZF based saildrive. This again is a characteristic of a particular manufacturer and really has nothing to do with the saildrive versus shaft drive conversation. Even if everyone agreed that shaft drives were better this forum would argue to the death about whether to buy Volvo, Perkins, Westrebeke, Yanmar, or Beta. My apologies to any manufacturer that I have left off the list.

If I ever have replace my propshafts/lower unit I will buy Seaprop 60 saildrives by Twin Disk. They are the only saildrives I have found that advertise that they are designed for commercial use, the rest are for recreational use. I don't know they are any better than anyone else's, but how much worse can they be? I would point out that Beta Marine dropped the ZF line of saildrives and moved to the Twin Disk line. I know a guy who used to work there and he said they reduced their parts inventory significantly because the Twin Disk drives just didn't fail. I also know cruisers that have gone through a couple of transmissions on shaft drives.

On a personal note , I would observe that I have never had a problem with a saildrive caused by having that chunk of aluminum in the water. I am aware of two instances where stray current had destroyed the aluminum sail drive housings. Then again I am also aware of two instances where neglecting zinc maintenance has caused heat exchanger failures in shaft transmissions resulting in destruction of those transmissions. Saildrives get rid of excess heat directly through that aluminum case and require no heat exchanger. It seems like the lesson here is maintain your zincs, no matter what kind of transmission you have.

While the current boat I own has saildrives I have no particular position in favor of them or against them. My observation is that both systems have their own issues requiring appropriate maintenance. I do observe that shaft drive proponents seem to have a particularly bad opinion of saildrives but I have yet to see that based on actual personal experience. As noted before, I nearly lost a boat because of a simple crab pot line on a shaft drive. I not only had a lot of water coming in but the shaft jammed my rudder as well. I had to go in the water in the dark to un-jam the rudder. I have never had a drop of water in the boat from a saildrive failure and even If a pot line pulled my prop shaft completely out of my saildrive, no water would come in the boat and there is no possible way it could jam my rudder.

Both systems have their inherent strengths and weaknesses and one simply needs to be aware of those just like any other systems they have on their boats. Scaremongering by people who don't seem to have actually experienced the failure modes they have fantasized about does not add anything useful to the conversation.

[smj]

Originally Posted by Captain Bill

Ok, I'm back and will explain these items. The problem I had with my saildrives was due to a known defect in the particular set of serial numbers that I happened to buy. This replacement was not due to a problem with the concept of a saildrive but only the execution of a particular set of serial numbers, therefore not pertinent to the saildrive versus shaft drive conversation, so I didn't raise that issue here. Since I had the drives apart i decided to replace the prop shaft seals and discovered that there was a groove worn in the prop shaft that was near tolerance levels. I had 1200 hours on the saildrives at that time. That is when I discovered that drives made by ZF had prop shafts that had a design life of 1400 hours. I also discovered that ZF only sold lower units and did not sell replacement prop shafts. Note that though the drives were built by ZF, they are Yanmar branded SD60's. The only option for replacing the prop shafts from Yanmar is to buy the whole lower unit. I found that this is also the only option for ZF brand drives. I had the shafts sleeved instead for about $150. Only time will tell how well this works. I mentioned in another thread that the design service life for most sailboat transmissions is about 1500 hours. This is time between overhauls, based on the design service life of bearings. If you get the shop manuals, not the owners manuals, they often list the service life of many components, without which the unit will not operate properly. This is not to say that they won't sometimes last longer, but beyond that limit they are not considered a premature failure. On my original saildrives I got about 3000 hours, but the bearings had a service life of 1500 hours according to the shop manual and would have been replaced by someone doing an overhaul to Yanmar specs. Interestingly, I saw the same service life listed for bearings in a service manual for shaft transmissions sold for the same engine. So Yanmar saildrives and Yanmar shaft transmission parts have similar or the same design service life. This also makes service life irrelevant to the discussion of saildrive versus shaftdrive.



The cost of prop shaft/lower unit replacement is outrageous in ZF based drives. I will never buy another ZF based saildrive. This again is a characteristic of a particular manufacturer and really has nothing to do with the saildrive versus shaft drive conversation. Even if everyone agreed that shaft drives were better this forum would argue to the death about whether to buy Volvo, Perkins, Westrebeke, Yanmar, or Beta. My apologies to any manufacturer that I have left off the list.



If I ever have replace my propshafts/lower unit I will buy Seaprop 60 saildrives by Twin Disk. They are the only saildrives I have found that advertise that they are designed for commercial use, the rest are for recreational use. I don't know they are any better than anyone else's, but how much worse can they be? I would point out that Beta Marine dropped the ZF line of saildrives and moved to the Twin Disk line. I know a guy who used to work there and he said they reduced their parts inventory significantly because the Twin Disk drives just didn't fail. I also know cruisers that have gone through a couple of transmissions on shaft drives.



On a personal note , I would observe that I have never had a problem with a saildrive caused by having that chunk of aluminum in the water. I am aware of two instances where stray current had destroyed the aluminum sail drive housings. Then again I am also aware of two instances where neglecting zinc maintenance has caused heat exchanger failures in shaft transmissions resulting in destruction of those transmissions. Saildrives get rid of excess heat directly through that aluminum case and require no heat exchanger. It seems like the lesson here is maintain your zincs, no matter what kind of transmission you have.



While the current boat I own has saildrives I have no particular position in favor of them or against them. My observation is that both systems have their own issues requiring appropriate maintenance. I do observe that shaft drive proponents seem to have a particularly bad opinion of saildrives but I have yet to see that based on actual personal experience. As noted before, I nearly lost a boat because of a simple crab pot line on a shaft drive. I not only had a lot of water coming in but the shaft jammed my rudder as well. I had to go in the water in the dark to un-jam the rudder. I have never had a drop of water in the boat from a saildrive failure and even If a pot line pulled my prop shaft completely out of my saildrive, no water would come in the boat and there is no possible way it could jam my rudder.



Both systems have their inherent strengths and weaknesses and one simply needs to be aware of those just like any other systems they have on their boats. Scaremongering by people who don't seem to have actually experienced the failure modes they have fantasized about does not add anything useful to the conversation.

Lagoon 50 which almost sank from catching its dinghy painter in the saildrive. Ruptured the sealing gasket which opens up a huge hole for water to enter. No scaremongering, facts.
http://xa.yimg.com/kq/groups/1384184...rveyors%29.pdf
Would you feel comfortable if your boat had aluminum thru hulls?

[Captain Bill]

Originally Posted by smj

Lagoon 50 which almost sank from catching its dinghy painter in the saildrive. Ruptured the sealing gasket which opens up a huge hole for water to enter. No scaremongering, facts.
http://xa.yimg.com/kq/groups/1384184...rveyors%29.pdf

You can cite one instance in 40 years of existence of saildrives and you declare them dangerous. Even then the boat only flooded because someone had put holes through the watertight bulkheads below the waterline. I guess you forgot to mention the instance in the Atlantic a couple of years ago when a whale surfaced under an FP and drove both the saildrives and rudders up through the hull. Or was this incident only forgotten because no one had drilled holes in the waterproof bulkheads and the hull did not flood therefore rise to the scary level. I know a guy that had a dripless shaft seal fail offshore and it scared him so bad he put the boat in a marina, rented a car and drove home. I know another guy that lost a shaft seal and only discovered it when he stepped into the water above his cabin sole when he went below. Towboat brought pumps and managed to stop the boat from sinking but the saltwater got to the engine and the insurance company totaled the boat. The only reason we know it was a prop shaft seal is that the auxiliary pumps got ahead of the flooding and they were able to see it. If the pumps had not arrived and the boat sank we would not have known. I actually know these guys, and had my own issue with flooding because of a failed shaft drive, I didn't read it online somewhere. Saildrive failures like the one you cited make the "news" because they are rare and dramatic just like commercial airplane crashes. Car crashes rarely make the news because they are so common. Yet travel by air is much safer than travel by automobile. I personally can't tell you if statistically a saildrive is more likely to cause flooding of a vessel than a shaft drive because I don't have access to the data. My guess is that only the insurance companies have access to those statistics. If they did and saildrives were more likely to cause a problem then saildrive boats would be charged a premium for insurance.

I once hit a submerged lobster pot line attached to a string of pots doing 8.5 knots under full sail in nearly 20 knots of wind. It dragged us to a near stop in only a couple of boat lengths. It bent one blade a stainless steel prop and wrapped the line tightly around the prop, yet there was no sign of any damage to the drive, the seals, or the mounts. Two days before I helped rescue a shaft drive boat that had a jammed rudder, and a displaced shaft
from snagging a pot line with only one pot attached. My wife went into the water to try to help them, but could not un-jam the rudder. Their shaft seal was only dripping and did not threaten the loss of the boat, but they did have to get towed and hauled. My saildrive clearly survived a lot more stress than the shaft drive.

I stand by my statement that you are scaremongering based on internet/news stories rather than personal experience. I know a lot of people with saildrives and a lot of people with shaft drives The only instances I know of where water got in the boat due to a failure of a saildrive or a saildrive seal are ones I have read on the internet. I cannot make that statement for water getting in the boat from shaft drives. If you can cite personal knowledge of a saildrive seal failure I would like to hear about it.

[smj]

Bill, obviously from this statement you made you don’t have much faith in saildrives.
“If I ever have replace my propshafts/lower unit I will buy Seaprop 60 saildrives by Twin Disk. They are the only saildrives I have found that advertise that they are designed for commercial use, the rest are for recreational use. I don't know they are any better than anyone else's, but how much worse can they be?”
I looked at a Noseman 40 last week that had the saildrive pushed up through the hull, actually ripping the engine beds from the hull. You could imagine the damage done both to the fiberglass and the interior from flooding. Would a shaft drive have faired better? I don’t know but my guess is yes.
I’m sorry Bill, but in my 25 years of owning various cruising catamarans the money I’ve put into propulsion systems is a fraction of what you’ve probably spent on just your saildrives in 7 years.
As I stated earlier, if the boat of my dreams only came with saildrives I would probably still purchase it but it wouldn’t by far be my first choice.
And yes Bill, I don’t think the leaking watertight bulkheads had anything to do with the saildrive seals breaking loose, in fact the opposite. The saildrive seals breaking loose brought forth the problem of the leaking watertight bulkheads.

[Captain Bill]

Originally Posted by smj

Bill, obviously from this statement you made you don’t have much faith in saildrives.
“If I ever have replace my propshafts/lower unit I will buy Seaprop 60 saildrives by Twin Disk. They are the only saildrives I have found that advertise that they are designed for commercial use, the rest are for recreational use. I don't know they are any better than anyone else's, but how much worse can they be?”
I looked at a Noseman 40 last week that had the saildrive pushed up through the hull, actually ripping the engine beds from the hull. You could imagine the damage done both to the fiberglass and the interior from flooding. Would a shaft drive have faired better? I don’t know but my guess is yes.
I’m sorry Bill, but in my 25 years of owning various cruising catamarans the money I’ve put into propulsion systems is a fraction of what you’ve probably spent on just your saildrives in 7 years.
As I stated earlier, if the boat of my dreams only came with saildrives I would probably still purchase it but it wouldn’t by far be my first choice.
And yes Bill, I don’t think the leaking watertight bulkheads had anything to do with the saildrive seals breaking loose, in fact the opposite. The saildrive seals breaking loose brought forth the problem of the leaking watertight bulkheads.

Actually my problem is with a specific manufacturer of saildrives. If I had more experience with shaft drive transmissions I might have the same issue with certain brands of transmission. There's a guy in Oriental NC that used to work for a well known marine transmission manufacturer. None of the transmissions they made for sailboats were built to the same spec as those made for power boats. They sold lots of power boat transmissions to commercial customers that would not put up with having a 1500 hour service life. He once referred to one of the transmissions as a $2/hour transmission $3000/1500 hours. The dependability of the mechanical components of any one saildrive maker is not at issue here any more than one shaft transmission maker who makes crappy transmissions is pertinent to shaft versus saildrive comparisons. I will restate my position that no sailboat transmission that I am aware of(that is designed from scratch to go into a small recreational sailboat and by small I mean less than 50 feet) is designed to stand up to the use profile of cruisers and that includes saildrives. The only company that I can find that might come close to this is twin disc as they advertise they are commercial duty units, not recreational duty. I have no experience to confirm this claim and am only repeating their claim.

Thank you for sharing the information about the Norseman. Do you know what happened to cause the problem.

You have noted that you had six diesel transmissions in 25 years. I am guessing from the way you stated that that this was on multiple boats. Maybe three or more? If so perhaps you were just smart enough to sell them off before you wore them out.

[rabbi]

Originally Posted by Captain Bill

I once hit a submerged lobster pot line attached to a string of pots doing 8.5 knots under full sail in nearly 20 knots of wind. It dragged us to a near stop in only a couple of boat lengths. It bent one blade a stainless steel prop and wrapped the line tightly around the prop, yet there was no sign of any damage to the drive, the seals, or the mounts. Two days before I helped rescue a shaft drive boat that had a jammed rudder, and a displaced shaft
from snagging a pot line with only one pot attached. My wife went into the water to try to help them, but could not un-jam the rudder. Their shaft seal was only dripping and did not threaten the loss of the boat, but they did have to get towed and hauled. My saildrive clearly survived a lot more stress than the shaft drive.

These problems happen with both saildrive and shaft drive.

Personal experience with my own boat, back in 2011:
A 12 year old Lagoon 410 with original Yanmar saildrives, the large diaphragms had just been replaced a month before the incident. Both upper and lower rubber seal and the water sensor between had been replaced.

We were doing 8-9kn under full sail, and ran into a huge pile of disposed fishing net. I mean huge, the size of a house but still invisible as we were sailing into the sun and it was floating just below the surface.
We had fixed props and engines were in reverse so the props were not spinning. The net hooked into the port prop and the boat stopped in just a boat length.
We dropped sail and once fully depowered the net sank a little more and the boat freed itself.


We took on water, but very very little. maybe a glass per hour. Yet the alarms was not active, but it had been tested a month before when the diaphragm was replaced.

We hauled out and removed the saildrive for inspection. Saildrive itself was OK, but the fibreglass engine / saildrive bed was cracked. The holes of the SS bolts were enlarged and water was leaking through the cracks.
With a little more speed this could have been desastrous as the 410 has no watertight bulkheads (older design with engines under the bed).

This shiit happens regardless of drive type and it doesn't keep me awake at night. We still have boats with saildrives. Watertight bulkheads are more important IMO.


EDIT: This board doesn't replaces some shitti words with **** so I have to add typos to confuse it. Parental advisory: Explicit content!

[DougM]

Originally Posted by GordMay

Has anyone used the Hübner-Braun “cycloidal” (fixed or retractable) propeller (similar to the larger Voith-Schneider system)?

Gord - interesting question. Have often thought that it would be an awesome drive system for a cat, although the steerable thrust feature would be of little use if you had a drive in each hull. I saw a website years ago (German, I believe) that offered hubner braun drives for sailboats. Looked like a startup company, and then it disappeared.