Running engine in gear on swinging mooring

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eddystone

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This is beyond my maths. 4.4 ton displacement boat on swinging mooring with 30hp motor. I will need to run the engine in gear (reverse) to purge air from the cooling system when refilling.
The sinker is 3.8 tons and the riser chain was strong enough to lift said sinker plus mud from the river bed in November 2019 - mooring strops are 2 x 24mm nylon with oversize s/s shackles
Any opinions?
 
Wouldn't be much of a mooring if it didn't cope with the motor in astern.
I assume you want to ensure it's up to temp and the thermostat open etc. Not sure that's necessary to fill it but maybe prudent to check it out before leaving the mooring.
 
Astern at cruising revs is likely to be equal to F7 - F7

Lots of us like to go hard astern to check our anchor is dug in.

Are you worried? If so replace your mooring now!

- W
 
Not sure why it needs to be in gear but if your mooring isn't strong enough for that then you need to look for a better mooring
 
webcraft said:
Lots of us like to go hard astern to check our anchor is dug in.
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+1

Assuming I anchored under power, I give it five or ten seconds at max cruising revs in astern, watching a transit. Most of us would expect a mooring to be more secure than an anchor (though I have my doubts in Braye!).

Pete
 
jbweston said:
Many of us don't like to run engines for any length of time without a load. If not under way, running in gear provides a load.
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Reason is to get it to full working temperature which is not likely in neutral; the Beta manual has a procedure for refilling cooling system which involves gradually increasing load to purge air out of system.

Thanks for advice - it seems definitely OK then.
 
Its a very crude rule of thumb and depends on the prop but you can work on 10hp offers 100kg of thrust in reverse at cruising revs

I measured our 2 x MD2020s, obviously 2 x props (Volvo 3 bladed folding) and read 400kg on my 2t load cell. So the figure seems acceptable (to me). I suspect your prop is smaller than ours so tension might be less.

This is approximately equivalent to the tension in our rode in a steady 30 knot breeze (no veering, no chop) - I've measured that as well.

Your mooring strops are well overstrength. It is very unlikely you can move a 3.8t sinker (our 38' cat has the windage of a 45' Bav and our sinker is 1.5t) - especially if the sinker has sunk into the sand/mud. If your mooning has not been serviced within the last 12 months and you are in a high abrasive area, for mooring shackles, I might be hesitant - but if the mooring is regularly serviced.....

I do wonder why you have such a heavy sinker.......

I can fully understand why you want to run the engine under load AND remain tied to 'security' - seems very sensible to me.

Jonathan
 
bedouin said:
Not sure why it needs to be in gear but if your mooring isn't strong enough for that then you need to look for a better mooring
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Running under load is supposed to stop the cylinders becoming polished but I have never really understood why, nor why they don’t become polished when running at constant RPM in gear?
 
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Ian_Rob said:
Running under load is supposed to stop the cylinders becoming polished but I have never really understood why, nor why they don’t become polished when running at constant RPM in gear?
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It's glazing rather than polishing that's the problem. See for example Bore glazing and polishing in diesel engines

PS - I should have read to the end of that article - polishing can be a problem too, apparently
 
The question I want to ask is , “Why full revs in reverse?” The engine will be under load at half revs and you shouldn’t be using the mooring if it won’t take that.

if the tidal stream or current is so weak that the boat moves in a circle round the buoy, so what?

I’m always bemused by those who swear by full revs astern. They evidently have auxiliary motors on sailing yachts. On many power boats and some motor sailers you would almost always drag the anchor if you put full power astern on... This is with a modern anchor well set and appropriately sized.

PS. Full revs shouldn't be a problem for the OP on his mooring either as others have pointed out.
 
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Well, I have what you might call a motor sailer, actually a decksaloon ketch. For many years I have been in the habit of leaving the boat at anchor for periods of four weeks, in sea lochs in the Outer Hebrides. I use a Bahamian Moor, and you can bet your bottom dollar that each anchor is subjected to prolonged full revs, to give me the confidence that the anchors will be capable of withstanding whatever the weather throws our way. If your anchor cannot withstand full revs, please don't come sailing in Scotland, until you upgrade your ground tackle
 
NormanS said:
Well, I have what you might call a motor sailer, actually a decksaloon ketch. For many years I have been in the habit of leaving the boat at anchor for periods of four weeks, in sea lochs in the Outer Hebrides. I use a Bahamian Moor, and you can bet your bottom dollar that each anchor is subjected to prolonged full revs, to give me the confidence that the anchors will be capable of withstanding whatever the weather throws our way. If your anchor cannot withstand full revs, please don't come sailing in Scotland, until you upgrade your ground tackle
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Hmm. I lived and worked in Scotland for a couple of years or more and kept our boat in the Clyde. We had some fantastic times (mostly at anchor) in the Western Isles.
I’ve enjoyed sailing in Scotland and my boat and it’s (Spade) anchor hasn’t ever let me down. But we’ve only got 40 hp and a max prop on 12 tonnes of big heavy sailing boat. I think you missed the bit where I tried to explain that full power on many motor boats and some motor sailers is too much.
The fact that your motor and prop isn’t big enough to drag your anchor is interesting but irrelevant.
I’m pointing out that it’s not a perfect rule for all boats.
 
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