Sabb Engine Bearers

[Liam]

I've got a single cylinder Sabb G, which is a slow revving 10hp engine. The problem is that, when running, the boat vibrates quite badly, and I'm pretty sure this is purely to do with the way the engine is sat on it's bearers.

 

At the moment its sat on 4 bearers all in all. Two either side of the gearbox and as you can see in the pic below, there are two holes either side. Only one either side is being used at the moment and it's the one nearest the flywheel. The one next to it isn't being supported so I'm going to get one added in.

 

 

The problem is the room down the engine hole. It's very tight down there as on one side I have the steps down into the cabin which is on the outside of the boat, and on the other side I have my gas locker, as it's a cruiser sterned boat.

 

I will obviously have to take the engine out to weld the second steel "foot", but once I've done that I'm wondering what I should use. At the moment, the bolt is welded to the bottom of the bearers and then the engine sits on these with wood imbetween. The wood is old and has gone a bit flat so I'm going to replace this but people are saying different things. Some are saying use wood only, some are saying use hard rubber only and others are saying use both.

 

What do you lot suggest?

 

Thanks

[Tony Brooks]

I've got a single cylinder Sabb G, which is a slow revving 10hp engine. The problem is that, when running, the boat vibrates quite badly, and I'm pretty sure this is purely to do with the way the engine is sat on it's bearers.

 

At the moment its sat on 4 bearers all in all. Two either side of the gearbox and as you can see in the pic below, there are two holes either side. Only one either side is being used at the moment and it's the one nearest the flywheel. The one next to it isn't being supported so I'm going to get one added in.

 

The problem is the room down the engine hole. It's very tight down there as on one side I have the steps down into the cabin which is on the outside of the boat, and on the other side I have my gas locker, as it's a cruiser sterned boat.

 

I will obviously have to take the engine out to weld the second steel "foot", but once I've done that I'm wondering what I should use. At the moment, the bolt is welded to the bottom of the bearers and then the engine sits on these with wood imbetween. The wood is old and has gone a bit flat so I'm going to replace this but people are saying different things. Some are saying use wood only, some are saying use hard rubber only and others are saying use both.

 

What do you lot suggest?

 

Thanks

 

 

I would get the beds welded as firmly as possible to the bottom plate (they may only be tack welded) andn perhaps fit transverse "braces" to join the two beds.

 

I would the sit the engien on soem form of hard wood and really tighten it down.

 

With a bit of luck this will stop any sympathetic vibration, but it is stilla singe cylinder engine and it will thump.

 

I understand kitchen towel between the plates helps!

 

;-)

 

 

Tony brooks

[Liam]

Thanks for the reply Tony.

 

I'm pretty sure the beds are welded firmly but a good idea about tranverse braces. I had thought of this but wasn't sure if there was enough clearance between the two beds. I'll get the hard wood sorted!

 

It's a thumper alright, sounds lovely in tick over, but there's a spot imbetween tick over and normal cruising speed where it's particularly worse. The back handrail shakes, as does the roof. It looks a bit like Rofl Harris's board!

 

Plates aren't a problem at the moment, neither are cups, saucers and all the other gear.. I don't have any!

[John Orentas]

Hi Liam.

 

At the risk of preaching to the converted, the important thing is that the fixings holding the timbers down to the hull and the fixings holding the engine to the timber bearers must be entirely separate items. That metallic path no matter how minor between engine and hull is what transmits all the vibration and noise.

Edited January 3, 2007 by John Orentas

[magnetman]

I recently fitted a SABB 2G in a boat and mounted it on 3 inch thick hardwood.

I buried the bolt heads with square plate washers about 3/4 inch in from the bottom of the wood when bolting the engine to the wood then I bolted the wood to the engine beds separately so as to remove any direct metallic link between the engine and the beds/hull. This does reduce knocking sounds a lot.

 

The major problem with this approach if modifying an existing installation is the increase in the height of the gearbox output shaft which will call for a short hardy spicer driveshaft which isn't favourite unless it is completely necessary.

A relative of mine has a SABB G single in her boat and it is directly driving the propshaft, no UJ, that one's mounted on 1.1/4 inch thick hardwood (from memory) which isn't thick enough to bury the bolts' heads in the way described.

I reckon just make sure its bolted down really tight and firm on new, seasoned oak.

Superb engines.........................

[Sir Nibble]

Adjustable rubber feet are available. Is the gearbox supporting the unmounted end? Beware also that you don't fix it totally inflexibly. If the vibration is not allowed to go its own sweet way on mounts with a bit of give in them it is likely to start causing fractures in the metalwork.

[magnetman]

SABB user manuals, gearbox manuals and parts lists can be downloaded from this link

 

http://www.sabb.no/CDA/ZonePg.aspx?parentzone=4&zone=19

 

this link threw an exception at me but it will work if you persevere.

 

And a company called Sleaman and Hawken still do parts, and probably advice too.

[Liam]

At the risk of preaching to the converted, the important thing is that the fixings holding the timbers down to the hull and the fixings holding the engine to the timber bearers must be entirely separate items. That metallic path no matter how minor between engine and hull is what transmits all the vibration and noise.

 

Hi John, I had read about that somewhere, but wasn't told about it but makes perfect sense and something I will definately look into doing.

 

 

I recently fitted a SABB 2G in a boat and mounted it on 3 inch thick hardwood. I buried the bolt heads with square plate washers about 3/4 inch in from the bottom of the wood when bolting the engine to the wood then I bolted the wood to the engine beds separately so as to remove any direct metallic link between the engine and the beds/hull. This does reduce knocking sounds a lot.

 

The major problem with this approach if modifying an existing installation is the increase in the height of the gearbox output shaft which will call for a short hardy spicer driveshaft which isn't favourite unless it is completely necessary.

A relative of mine has a SABB G single in her boat and it is directly driving the propshaft, no UJ, that one's mounted on 1.1/4 inch thick hardwood (from memory) which isn't thick enough to bury the bolts' heads in the way described.

I reckon just make sure its bolted down really tight and firm on new, seasoned oak.

Superb engines.........................

 

Yeah it's an existing installation that I'm trying to get sorted. There also won't be the room to bury the bolt heads into the wood as it'd put the engine too high for the gearbox and prop shaft. Would I have to move the engine forwards to put a UJ in there? There's next to no room as the flywheel is only a few cm's from the engine bay bulkhead.

 

Adjustable rubber feet are available. Is the gearbox supporting the unmounted end? Beware also that you don't fix it totally inflexibly. If the vibration is not allowed to go its own sweet way on mounts with a bit of give in them it is likely to start causing fractures in the metalwork.

 

There's 2 feet on the engine. One either side but each foot is quite long and has 2 holes in. Only one is being used, and that's the one closest to the flywheel. The other end closest to the gearbox isn't being used. I've already had 2 of the bearers split down the weld on me as they were only tack welded. I've had them fully welded but want to secure this little thumper as much as possible to reduce the risks of similiar problems in the future. I only found out there's another couple of holes available to support the engine further this weekend when I was checking the oil and water.

 

SABB user manuals, gearbox manuals and parts lists can be downloaded from this link.

 

http://www.sabb.no/CDA/ZonePg.aspx?parentzone=4&zone=19

 

this link threw an exception at me but it will work if you persevere.

 

And a company called Sleaman and Hawken still do parts, and probably advice too.

 

I've seen Sleaman and Hawken linked on another forum thingy when I googled for Sabb, but I forgot the link, thanks for that.

 

I'll be going to the boat this weekend so will look at it properly and think how I'm going to tackle it and bring the welder, the wood etc together.

 

Will let you know how I get on... thanks again for the advice

[John Orentas]

Soft rubber mounts don't work well with low frequencies, if fact they can in some circumstances amplify the problem. The principle behind timber mounting is that the characteristics is of a low hysteresis system or in other words vibration is absorbed as opposed to being modified and re-transmitted.