Engine Mountings - are they knockdown proof ?

[Pblais]

I think that their concern is 500 lbs of engine flying around the cabin while you're upside down.

The mass of the engine upside down exerts the force of gravity (32/ft/sec/sec). In a knockdown what is the accelleration of the boat at the point where the most stress would occur? Force = mass X accelleration The problem is you can't know the force of the dynamics of a knockdown. More force might be placed in one point than the others causing that point to fail. A boat falling a distance off a large wave and hitting the water could generate a large decelleration force that would easily rip the mount from the boat leaving it still attached to the engine.

Cables around mountings won't make them stronger given the cables are attached to the mounts. Cables add nothing.

Any force that can break a mount is going to do massive destruction to the boat even if the engine somehow manages to stay attached. Just going upside down won't break a mount nor create a large decelleration force that might rip the mount out.

[MidLandOne]

If one isn't inclined to rely on bonded mounts (but I suspect any reputable make ones would be fine in an inversion for typical small sail boat engines) then the mounts made by Isoflex in Australia provide mechanical restraint of the engine in an inversion.

There may be others that do the same too but Isoflex are ones I know of off hand.

EDIT: Out of interest just had a look on the internet at bonded shear mounts and there are some of those available too that are fail safe in case of the bonding failing so no need for wires unless you have some great monster of an engine to restrain.

[Chief Engineer]

Sounds like an "nanny state" bureaucrat at work.

Sounds like a "surveyor" that is making it up as he goes along.

If there is such a requirement...ask for the chapter and verse of the law.

[Stillraining]

Very interesting question indeed...

However in all the books I have read nor all the tales I have listened to have I heard this being a problum...has it happened? I am sure it has some where...not a bad idea as backup now that I think about it though if your a blue water boat.

FWIW..
Grass root street rodders put a chain on the tourque side motor mount to keep from ripping it out.

[r.furborough]

Certain countries have a requirement the boats be approved for offshore passages, in the UK it's called a Cat4 inspection.

ENGINE MOUNTS

[Chief Engineer]

I would think thet the proprietery engine mounts by Yanmar should be ok.

The weakest link might be the engine bed(s)

[Chief Engineer]

we don't need the gobmint protecting us from ourselves any mo'

Originally Posted by r.furborough

Certain countries have a requirement the boats be approved for offshore passages, in the UK it's called a Cat4 inspection.

ENGINE MOUNTS

[Cheechako]

The cables are attached to the engine bed. Often this can be done drilling athwartships through the bed and a long bolt or eyebolt. A 3/8 or 1/2 bolt will be incredibly strong even in shear. Then you need a place to attach it on the engine block, there always seems to be a few spare threaded holes there, but you need the biggest you can find and a tab of some sort to attach the cable eye to. I cant believe a good engine mount set would break in a heavy broach. A pitch pole possibly, but then you have other worries to consider really. Does anyone remember any boats in the Fastnet or NZ storm stories losing their engine mounts?

[AdamY]

Originally Posted by Chief Engineer

Sounds like an "nanny state" bureaucrat at work.

Sounds like a "surveyor" that is making it up as he goes along.

If there is such a requirement...ask for the chapter and verse of the law.

Agreed. Go around your marina and finid out how many people have had their 500lb engine "kicking around" their boat when completely inverted at sea.

While we're at it, go ahead and post it to this forum. We can do a little survey. I'll start it off... 0 times here. :-)

Ignore your pedantic surveyor. While you're at it let them know that if they put it on the survey as a "must fix" you will lambaste them through the community. Some surveyors try to look better by calling out anything their imagination can conjure as a failure.

Cheers,

[r.furborough]

Originally Posted by Chief Engineer

we don't need the gobmint protecting us from ourselves any mo'

Agreed!!

Also I think this issue has to be looked at not only from a 'roll-over' situation but also in heavy weather motoring or sailing. an engine puts an awesome amount of stress on the flexible mounts and engine bed, both of which tend to be ignored or forgotten until a boat is surveyed.

Yanmar mounts are terrible, they are not 'fail-safe' or durable and they extremely expensive compared to generic mounts. I know this as I am in the process of replacing mine....

Robert

[cal40john]

Originally Posted by AdamY

Agreed. Go around your marina and finid out how many people have had their 500lb engine "kicking around" their boat when completely inverted at sea.

While we're at it, go ahead and post it to this forum. We can do a little survey. I'll start it off... 0 times here. :-)

Ignore your pedantic surveyor. While you're at it let them know that if they put it on the survey as a "must fix" you will lambaste them through the community. Some surveyors try to look better by calling out anything their imagination can conjure as a failure.

Cheers,

Yup, probably nobody here in Puget Sound has this, but look at the OP's location. Maybe he has different criteria than some of us.

John

[Alan N Crichton]

[quote=Stillraining;230596]Very interesting question indeed...

However in all the books I have read nor all the tales I have listened to have I heard this being a problum...has it happened? I am sure it has some where...not a bad idea as backup now that I think about it though if your a blue water boat.

Not only agood idea but a legal requirement for blue water crusing

Offshore safety tie

The mount on the left is the type used under 2GM to 4LH series engines, if you need to pass a Cat 4 inspection for off-shore, put a wire or small chain through the centre 'nose' and over the top of the top metal piece and 'Talurite', crimp or u-bolt the ends together. I have never seen this mount fail because the bonding failed from reasonable use. The failures were always incorrect installation, age, or they became covered in diesel.

Mnay thanks to all for the information it is appreciated ! Regards Alan

[Topfin]

The Isoflex MDC30 is specifically designed for the small Yanmars. It is failsafe and has a duel core for optimal dampen while stable underload. It's a Really nice mount.

[newhaul]

Originally Posted by Cheechako

The cables are attached to the engine bed. Often this can be done drilling athwartships through the bed and a long bolt or eyebolt. A 3/8 or 1/2 bolt will be incredibly strong even in shear. Then you need a place to attach it on the engine block, there always seems to be a few spare threaded holes there, but you need the biggest you can find and a tab of some sort to attach the cable eye to. I cant believe a good engine mount set would break in a heavy broach. A pitch pole possibly, but then you have other worries to consider really. Does anyone remember any boats in the Fastnet or NZ storm stories losing their engine mounts?

No way to tell how many failed , how many that sank have been surveyed to asertain all dammages that were incured. ( loose engine would put a real big water leak into a vessel)

[Captsteve53]

Try these mounts and tested for up side down condition and are known as fail safe (ISOFLEX) great mounts !

Search marine engine feet and vibration isolators | IsoFlex