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Old 02-02-2008, 07:22 PM   #1
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Hi, all,

I don't see this topic in the archives. But...offshore folks--what, besides the engine mounts do you have in place to keep your engine "in place" in the case of a knockdown or roll? We can put cables (not tight) from our engine lifting rings down round to the structural floors/engine stringers...but I haven't seen anything anywhere which actually talks about this.

We're putting in the gen-set and engine in the next few weeks which is why it comes up now. Also, have any of you experienced a serious knockdown and what (if any) damage did it do to systems? Did you have to check prop shaft alignment after? etc? I only know of one fellow who had a knockdown and he had some very minor prop shaft alignment issues but was in the midst of an ocean race at the time so didn't figure that out until about a week later once the race was over.

Thanks!
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Old 02-02-2008, 07:25 PM   #2
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Old 02-02-2008, 10:19 PM   #3
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We have laid Watermelon on her side quite a few times. When we were racing in the Heineken Regatta one year with a young pickup crew, I laid her on her beam twice within 10 minutes! The poor kids were ready to jump overboard and swim to shore rather than sail with this madwoman!

We have had a few other knockdowns for various reasons. With her fin keel, Watermelon would just lay over, and as she righted herself she'd round up into the wind. Shake herself off and keep going.

We had no fastenings other than the engine mounts, and the engine never moved. Good thing, with such a madwoman at the helm.
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Old 02-03-2008, 02:38 PM   #4
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I was just talking to a yachtie at a beach bar here who ran into a problem during an offshore passage last November. He was sailing in 35 kts or so with 20+ foot following seas when a big wave came up on his beam and slammed into him hard. The engine was OK, but it knocked his gen set off it's mounts. It was after dark, so he didn't see it coming.

I've had odd waves slam the boat from a totally different direction than the prevailing swells, too, but never sustained any damage from them.
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Old 02-05-2008, 01:30 AM   #5
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I was just talking to a yachtie at a beach bar here who ran into a problem during an offshore passage last November. He was sailing in 35 kts or so with 20+ foot following seas when a big wave came up on his beam and slammed into him hard. The engine was OK, but it knocked his gen set off it's mounts. It was after dark, so he didn't see it coming.

I've had odd waves slam the boat from a totally different direction than the prevailing swells, too, but never sustained any damage from them.
That's along the lines of my question. Our 8kW Onan genset has the mounts it came with and I wasn't even thinking about it coming off its bed, though it weighs 500 lbs and that wouldn't be too good either. Its the engine and tranny at 1300 lbs that I'm more worried about. I spoke with a machinist/sailor who makes custom engine mount systems and he states that one must have a cable system in place in addition to any engine mounts one might use. This, to minimize risk of the engine sustaining damage (or damaging other things, for that matter!). I just haven't heard a lot of folks talking about this at all.
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Old 02-05-2008, 12:39 PM   #6
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I've never heard of anyone having an engine thrown off it's mounts due to a knock-down or wave impact.

What I have heard of is boats having their engines pulled off their mounts when a line (e.g. jib sheet) became wrapped around the prop shaft. The rope exerts tremendous pressure as it bunches up between the prop and the shaft log area of the hull. I think that's your biggest risk for unseating your engine.
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Old 02-05-2008, 03:59 PM   #7
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I've never heard of anyone having an engine thrown off it's mounts due to a knock-down or wave impact.

What I have heard of is boats having their engines pulled off their mounts when a line (e.g. jib sheet) became wrapped around the prop shaft. The rope exerts tremendous pressure as it bunches up between the prop and the shaft log area of the hull. I think that's your biggest risk for unseating your engine.
Wow, just another way to screw things up, huh? I've heard of lines wrapping 'round the prop and would think that without CV or thrust bearing, yup, the engine/tranny would be at risk.

The risk you refer to sounds like it might be encountered with more frequency (as you state... "biggest" risk...) by more than just offshore sailors because one can make the error of having lines in the water at any time without even an external influence like stormy weather or waves. One can also run into fish nets, run aground, etc...all with disastrous consequences for the drive train.

In addition to the use of shaft based line-cutters on the outside and CV/thrust bearing/flex shaft coupling flange setups to minimize impact of improper shaft related loading on the engine...it seems that one's procedures and deck layout can help minimize the particular risk--i.e., on our sloop, the jib sheets aren't even long enough to end up near the prop shaft (though the main sheet is, and the halyards may just barely be long enough if they were free)--but if you're doing something like trailing warps, well, you've got lines in the water but without the load of a head sail on the other end.

I understand and "deal with" the lines-in-the-water risk. The reason I started this thread is that it would seem that no procedures are going to help out if one doesn't have a set-up that precludes the engine or other large engine room equipment from literally falling/pulling off their mounts due to heavy weather boat movement; The (admittedly few) offshore racers and experienced offshore cruisers I personally know have stated that this is an issue which must be dealt with. Yet, I don't find sufficient information available regarding ways of dealing with this risk w/o introducing new vibration paths from the engine to the hull. The only way I've heard of is adding a cable system.

A lot of times folks just ignore things that are too hard to think about dealing with them properly and I wonder if that's what happens with this particular risk for offshore sailing vessels?
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Old 02-06-2008, 12:06 PM   #8
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If the engine could be thrown off its mounts when the boat was thrown on its side, then, IMO, the engine would not be safe in any bad weather where the boat would be tossed around. I just don't think that a seaworthy boat will have engine mounts that cannot handle these momentary forces.

On the other hand, catching a line in the prop can certainly exert forces that can dislodge an engine, or do other serious damage. For example, many years ago I read a report that a charter boat in the Caribbean caught its jib sheet in the prop and it pulled the prop strut out of the hull, leaving a large hole that sank the boat.

Just about any line on a boat is long enough to reach the prop. The main or headsail sheets when the headsail is out. The halyards when the sails are raised (most mainmasts are longer than the boat's length, so there will be at least that length of halyard free when the sails are up).

I have a hard time believing that engine manufacturers and naval designers haven't considered these forces when designing the engine mounts.
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Old 02-06-2008, 03:55 PM   #9
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If the engine could be thrown off its mounts .......
Hi, JeanneP, hope you're well and good.

While I'm constantly complaining that our headsail sheets are way too short on our sloop (they are!)....I had a ditzy moment there ...yes, they are long enough to trail in the water near the prop shaft when the sail is out and close hauled

I'm also not questioning that fouling the prop can be disastrous--that just wasn't my question or issue. The use of thrust bearings, flexible flanges, CV joints mounted to the hull to take up the thrust loads are well known and established and there's always some discussion of hitting/fouling the prop when considering installation of such things. There are plethora of solutions to help with large thrust loads to keep them from reaching the engine.

What brings this up is that one of the folks I was talking to about engine mounts was a machinist/sailor fellow who works MAKING engine mounts for one of the reputable engine mount companies . So. I'll believe him when he says "add cables" to the system. I don't have personal experience on the loading up of engine mounts from EITHER knockdown OR prop fouling scenario. I can understand the dynamics of these two very different situation though. Thrust loading from fouling / hitting the prop is severe and different than the sort of loading on the mounts that one would be likely to get from a knock down. The folks who would be thinking about this mounting issue and doing something about it include engine mount manufacturers and boat builders (with the associated supporting engineering staff). I would imagine they HAVE thought about it and do their best. I also imagine that a shock load during a knockdown type event could be severe enough to cause pull-out, cracking, or dislodge individual mounts--thus the cautionary advice from the engine mount making machinist to have a cable system in place.

I really had hoped that a few people on the forum would have personal experience or could tell me that while they've never experienced a knockdown, yep, they have a cable system and it works like .... etc.
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Old 02-06-2008, 05:08 PM   #10
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I am no expert but I would think that engineers and naval architects have done their sums here and therefore worked out what is necessary to withstand the forces you mention.

What concerns me more is that after years of vibration (from the engine), shocks from pounding and rolling, corrosion and maybe crack building, the mounts will eventually suffer metal fatigue and throw their hand in. Then a problem arises! Maybe mountings should have "best before" dates?

Aye // Stephen
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Old 02-06-2008, 05:29 PM   #11
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Aye // Stephen
Yes, I believe fatigue life and damage tolerance certainly play a part here in reducing reliability over the life of the engine mount system. (both in the mounts and the engine stringers). And, perhaps that's why a "back up" cable system is proposed by this fellow I mention.

Typical fatigue based life isn't related to years but instead to cycles. However, today's more popular rubber/synthetic materials used in soft mount systems probably have very real "life expectancy" as well.

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Old 02-06-2008, 05:40 PM   #12
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The bit about the "best before" date was a little on the light hearted side but I should think a system, such as used in the aircraft industry would be in order whereby the "sensitive" parts are changed after XXX number of running hours or YY years, whichever comes first. That should take into account both metal and synthetic components.

It would be interesting to know why this is not done.

In the professional field, we have planned maintenance systems which are designed to assist with this kind of thing. Sure, after a certain number of running hours you will be reminded to have an oil analysis made (we don't change luboil just because the engine has run 1000 hours. t would be far too expensive to do that) but the system should also warn when the time is approaching for more major items. Also, commercial ships are subject to survey every 4 years with a major survey at 12 years, a more major survey at 24 years and so on. If the ship's engineers don't pick up a problem it is to be hoped that the surveyors will.

Navies and coast guard organisations have their own system of inspection too.

Aye // Stephen
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Old 02-06-2008, 07:39 PM   #13
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If indeed there is some problem with the integrity of soft engine mounts (A proposition I have neither heard of or considered in the past), perhaps there is a real and compelling case for hard mounts.

Cheers

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Old 02-06-2008, 11:27 PM   #14
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If indeed there is some problem with the integrity of soft engine mounts (A proposition I have neither heard of or considered in the past), perhaps there is a real and compelling case for hard mounts.

Cheers

David.
I'd stick with soft mounts but keep an eye on aging and get input from the engine mount manufacturer regarding life and cycles whether hard or soft. (I've emailed the manufacturer of our engine mounts to request this info so I can put it in the boat's maintenance file/schedule).

The hard mounts would be more likely to be susceptible to catastrophic failure upon impact, IMHO.

Regarding fatigue or aging--

Degradation of soft mounts on engines (both automotive and marine) is something that most folks just don't think about nor worry about. I have changed (soft) engine mounts on my automobiles with regularity based on age and in one case based upon failure of a soft, oil-filled, engine mount. Upon inspection and note of compressive wear, I've also replaced hard rubber/bronze bushings on suspensions that nobody even bothers to think about, much less replace. On an automobile, it makes an admittedly small difference in performance unless there's an actual failure of a mount which could, of course, lead to engine or systems damage.

On a boat, that small difference in performance could involve movement and wear on the prop shaft, cutlass bearing, CV's, any thing else in the drive train. Again, most folks don't look at these things, it seems. They look at their stuffing box and wonder why things are dripping more than expected, or, they may note noise at certain engine RPM that didn't used to be there...but somehow many folks don't follow through with checking alignment and engine mount condition or having their mechanic do so...

I digress.
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