Timber or steel for engine mounts

[GILow]

Hi all,

I’m repowering. What fun.

The old engine was a 420 kg monster, about 1.3 meters between the engine mounts fore and aft, 500 mm athwartships. The new engine is a featherweight 260 kg Beta, only 500 mm between the mounts fore and aft, but still around 500 mm across.

I have the option of bridging the span between the exisiting beds using either some lengths of angle iron, or timber beams. Both would be pretty easy to fabricate and both would be plenty strong enough. Labour feels about the same for each.

So, I wondered if there were some unobvious reasons for choosing one or the other that I should consider.

Basically, I’m trying to break a stalemate in my mind.

Matt

Edit, the title should read engine beds, not engine mounts.

[sailormed]

I am in no way a specialist in this area, but my personal preference would be wood because of better vibration absorbtion qualities.

[RaymondR]

Nay mate, neither wood or steel, alloy is the only way to go, doesn't rot or rust.

I used 75 x 10 x 30 alloy angle which I bolted the engine mounts to with countersunk bolts tapped through the angle from the bottom. The two alloy rails then sat inside the old rails and were located by pins welded into the old rails. I could remove two large retaining bolts and lift the engine out without disturbing the alignment. Drop her back in wiggle over the pins, two bolts and the drive flange and she was ready to go.

[GILow]

Originally Posted by sailormed

I am in no way a specialist in this area, but my personal preference would be wood because of better vibration absorbtion qualities.

That’s a thought... I reckon you’d be right.

[GILow]

Originally Posted by RaymondR

Nay mate, neither wood or steel, alloy is the only way to go, doesn't rot or rust.

I used 75 x 10 x 30 alloy angle which I bolted the engine mounts to with countersunk bolts tapped through the angle from the bottom. The two alloy rails then sat inside the old rails and were located by pins welded into the old rails. I could remove two large retaining bolts and lift the engine out without disturbing the alignment. Drop her back in wiggle over the pins, two bolts and the drive flange and she was ready to go.

Hadn’t considered aluminium. Feels like it would be kinda springy for this job? It’s spanning a meter. It sounds like you were lining an existing bed?

[El Pinguino]

I am no expert..... however

I would consider laminated hardwood beams ...glassed...

Only experience in this area is using the above concept to glass in a pair of longitudinals in the focsle to stop her 'oilcanning' when going to windward... wind to port... swell to stbd .. issues..

[GILow]

Originally Posted by El Pinguino

I am no expert..... however

I would consider laminated hardwood beams ...glassed...

Only experience in this area is using the above concept to glass in a pair of longitudinals in the focsle to stop her 'oilcanning' when going to windward... wind to port... swell to stbd .. issues..

Well, you will sail these flimsy UK-built boats mate. What did you expect?

But, yes, I should have mentioned, I would glass in the timber if I went that path.

[jimbunyard]

Another vote for aluminum. I used 4" x 2" C channel laid on, its side, spanning longitudinally for 48", as stringers to attach the motor mounts on a 500 Kg Volvo 200 hp.

No problems with flex, nor much vibration, though I can't say that wood might not reduce what is there a bit. Good, properly rated motor mounts are mostly the key for reducing vibration and related noise and its transmission into other parts of the boat...

[Wotname]

Another non-expert chiming in...

Why don't you go for the best of both worlds and use something like Wandoo (or similar).

While it is timber, it is almost as strong (and hard) as steel, very unlikely to rot over several engine lifetimes, won't rust and is certainly suitable for the task. Used for railway sleepers, bridges and wharves etc. Don't drop it over the side though, it will sink, not float.

Cutting and drilling isn't easy but if you work it like a piece of aluminium rather than as a wood, it isn't so bad.

https://fremantletimber.com.au/wandoo-timber/

[Ken Z]

I used aluminum and it works great, no rust, no rot.

[billknny]

My vote would be for galvanized steel. Strong, easy to work. Cheap. Should last about forever.

The concern for rusting of a steel part is misplaced. Even plain steel--properly painted--should have a really long life. We have painted and galvanized steel parts in our engine room that are 25 years old and have two circumnavigations on them that have not a trace of rust. You are bolting a really big block of cast iron to these frames (the engine!)

If your engine room is wet and/or salty enough that painted or galvanized steel rusts quickly you have bigger problems that need to be fixed before you put an expensive new engine in there.

[gabilo]

An other non expert.... that’s why I would talk to Beta... suppose they are the experts

[Stewie12]

Wandoo is wood from the Eucalyptus tree. When it dries it goes as hard as steel. In Spain they used to use the thin branches as scaffold poles

[AndyEss]

Can you provide a photo of the existing beds/mount and/or a sketch of what you are trying to achieve?
I like that you are losing weight (on your boat). As we load more equipment, spares, etc our boats submerge further and further.
When I replaced my LA house bank with LFP batteries, I could see my waterline change.

[boatman1]

Well, steel would be my choice. If this were my project, I’d fabricate a thrust bearing which, as the title defines, would end any and all engine alignment issues. Imagine the reduction of vibration and the increased life span of the bearing(s) on the aft end of the transmission. Gives the designer/installer flexibility to mount the engine where ease of maintenance can be enhanced, rather than at the same angle as the prop shaft. You’d only need to do it once.