Yanmar Gearbox Clutch
Nov 19, 2012 22:43:58 GMT
Post by MalcolmP on Nov 19, 2012 22:43:58 GMT
This issue has been raised before, but not that recently on this forum until today in a posting in our Down Under section which I copied below, but also look at the attached pdf advice from Yanmar
In my case I have a feathering autoprop which needs to have the shaft stopped as it really powers up if left in neutral. Touch wood I have not had a clutch problem and keep the prop locked in reverse.
There has been some confusion on this issue - iF you have a fixed prop you must let it rotate when sailing, but if you have a feathering or folding prop you can lock the gearbox by selecting reverse (well that's the way at least that I am reading the Yanmar guidance.....)
There is a lot on the web on this issue if you do a search, but there is a very helpful download from a multihull sailor on how to do a low cost repair if your cone clutch glazes:
www.dropbox.com/s/t2l224s4c0qavia/SD50%20cone%20replacement.pdf
This is specifically on a saildrive, but presume the repairs on the cone clutch will be similar on shaft drive models.
Sure the engineers out there may have some addition comments...
Hello everyone
Russ Middleton sent out an email on the Yanmar SD50 gearbox clutch problem.
I have done some research on it and how to avoid it. Here is a version of an article I was writing.
We were walking through the slipyard the other day and met a bloke pulling out two nearly new Yanmar 54 HP diesels with SD50 saildrives from his catamaran. He was replacing them with Yanmar shaft drives. It turns out that SD50 saildrives can need a lot of maintenance, depending on how they are used. Our Jeanneau uses the same saildrive so more research was needed.
The SD20 saildrive used on smaller Yanmar engines uses a dog clutch and is rugged and reliable. The SD50 uses a cone clutch and is also reliable provided you follow the manufacturer’s instructions. However, that is not always the way you want to use the engine. First, here is my theory.
The cone clutch gives beautifully smooth gear changes, because it relies on the friction between an inside and an outside cone. The torque from the engine tends to drive the cones together, so the harder you drive it, the better it works. The rub is that if you have a lightweight catamaran and two 54HP engines, everything is very lightly loaded, so the engine torque doesn’t engage the clutch hard enough.
Now it gets worse if you motorsail. There is even less torque coming from the engine and the propeller can even be driving the gearbox rather than taking the engine power. Add a following sea to that and the load on the clutch can be varying wildly, even going negative. The clutch slips, wears, and starts making horrible noises, needing premature maintenance. Lapping the clutch to solve the problem is fairly straightforward and doesn’t require slipping the boat, but why spend the time and money if you don’t have to.
That cat is an extreme case, but any boat could suffer the problem. Follow the manufacturer’s instructions and go a bit further is my advice.
Never engage the gearbox when you are sailing. Just put up with the propeller rumble and whine. After all, the louder it is, the faster you are going.
Avoid motorsailing when there is nearly as much power from the sails as from the engine. My rule is that we don’t motorsail at less than seven knots and the engine goes off if we can make three knots under sail. If the wind is coming in puffs, the three knots is on the peaks of the wind, not the lulls.
Don’t motor slowly with a big following sea. The seven knot rule applies.
Don’t travel slowly under engine any more than necessary. By slowly I mean less than 1500 rpm. Of course this only applies to passage making, not berthing or other maneuvers.
In my case I have a feathering autoprop which needs to have the shaft stopped as it really powers up if left in neutral. Touch wood I have not had a clutch problem and keep the prop locked in reverse.
There has been some confusion on this issue - iF you have a fixed prop you must let it rotate when sailing, but if you have a feathering or folding prop you can lock the gearbox by selecting reverse (well that's the way at least that I am reading the Yanmar guidance.....)
There is a lot on the web on this issue if you do a search, but there is a very helpful download from a multihull sailor on how to do a low cost repair if your cone clutch glazes:
www.dropbox.com/s/t2l224s4c0qavia/SD50%20cone%20replacement.pdf
This is specifically on a saildrive, but presume the repairs on the cone clutch will be similar on shaft drive models.
Sure the engineers out there may have some addition comments...
Russ Middleton sent out an email on the Yanmar SD50 gearbox clutch problem.
I have done some research on it and how to avoid it. Here is a version of an article I was writing.
We were walking through the slipyard the other day and met a bloke pulling out two nearly new Yanmar 54 HP diesels with SD50 saildrives from his catamaran. He was replacing them with Yanmar shaft drives. It turns out that SD50 saildrives can need a lot of maintenance, depending on how they are used. Our Jeanneau uses the same saildrive so more research was needed.
The SD20 saildrive used on smaller Yanmar engines uses a dog clutch and is rugged and reliable. The SD50 uses a cone clutch and is also reliable provided you follow the manufacturer’s instructions. However, that is not always the way you want to use the engine. First, here is my theory.
The cone clutch gives beautifully smooth gear changes, because it relies on the friction between an inside and an outside cone. The torque from the engine tends to drive the cones together, so the harder you drive it, the better it works. The rub is that if you have a lightweight catamaran and two 54HP engines, everything is very lightly loaded, so the engine torque doesn’t engage the clutch hard enough.
Now it gets worse if you motorsail. There is even less torque coming from the engine and the propeller can even be driving the gearbox rather than taking the engine power. Add a following sea to that and the load on the clutch can be varying wildly, even going negative. The clutch slips, wears, and starts making horrible noises, needing premature maintenance. Lapping the clutch to solve the problem is fairly straightforward and doesn’t require slipping the boat, but why spend the time and money if you don’t have to.
That cat is an extreme case, but any boat could suffer the problem. Follow the manufacturer’s instructions and go a bit further is my advice.
Never engage the gearbox when you are sailing. Just put up with the propeller rumble and whine. After all, the louder it is, the faster you are going.
Avoid motorsailing when there is nearly as much power from the sails as from the engine. My rule is that we don’t motorsail at less than seven knots and the engine goes off if we can make three knots under sail. If the wind is coming in puffs, the three knots is on the peaks of the wind, not the lulls.
Don’t motor slowly with a big following sea. The seven knot rule applies.
Don’t travel slowly under engine any more than necessary. By slowly I mean less than 1500 rpm. Of course this only applies to passage making, not berthing or other maneuvers.