zoidberg
Well-Known Member
Technomatic vs PRM.... mechanical.... Beta offerings.
What's to choose between them?
What's to choose between them?
Gearbox comparisons
- Thread starter zoidberg
- Start date
sailorman
Well-Known Member
PRM are bullet proof but you may / will req a feathering / folding prop as they need to park stationary when sailing
BabaYaga
Well-Known Member
Possibly for a hydraulic gearbox, but not for a mechanical. Page 11:
http://www.prm-newage.com/media/File/PRM80.pdf
earlybird
Well-Known Member
I suspect that if used correctly there's very little to choose. AFAIK they work on the same basic principal and either make is offered as standard.
When I bought my B25 I seem to remember that the TMC was the most readily available.
Beta used to supply Hurth 'boxes, but they seem to have gone out of favour.
Jcorstorphine
Well-Known Member
I fitted a Technodrive TM18 mechanical gearbox to a BMC 1.5 back in 1980 and it is still going strong as I saw the boat recently. The gearbox was in fact under-rated for the engine but as far as I know, there has never been any problem.
On the other hand, I fitted a Hurth (now ZF) HB 100 box to Ford 1.6 diesel and had problems with clattering at tickover speeds. Also had very loud clunk when putting in gear even with the engine almost stalling. In the end, I fitted a 20 mm thick flywheel mass which allowed the engine to run at a much lower tickover speed of about 600 rpm. This cured both the clunk and the clattering. The clattering of the gearbox was caused by torsional vibration of the engine.
Are you buying a complete engine and deciding which box to specify or are you fitting a new gearbox to an existing engine.
On the other hand, I fitted a Hurth (now ZF) HB 100 box to Ford 1.6 diesel and had problems with clattering at tickover speeds. Also had very loud clunk when putting in gear even with the engine almost stalling. In the end, I fitted a 20 mm thick flywheel mass which allowed the engine to run at a much lower tickover speed of about 600 rpm. This cured both the clunk and the clattering. The clattering of the gearbox was caused by torsional vibration of the engine.
Are you buying a complete engine and deciding which box to specify or are you fitting a new gearbox to an existing engine.
zoidberg
Well-Known Member
There's about £100 difference. I'm curious as to the balance of 'cost/benefits'...
earlybird
Well-Known Member
Is that comparing like with like?
On the Beta website, for say my B25, either the TMC40 or the PRM80, being similar ratings, are listed as "standard". Only for higher rated 'boxes, eg TMC60 or PRM120 are they noted as extra. When I ordered my engine I seem to remember being steered towards the TMC, can't remember a price difference.
michael_w
Well-Known Member
PRM 150 has the advantage that can power either RH or a LH prop, so for a new installation replacing the existing prop may be not be required.
zoidberg
Well-Known Member
Here's the Price List. Compare rows a. and c. for the Beta Marine 14 unit, shown in purple. What 'reduction ratio' is advised, and does 'Incl' mean it's a choice free of further cost? I need to ask....
Unless I'm missing something, there's an ambiguity there....
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macd
Well-Known Member
"Incl" means there's no additional cost. Any number, such as the "187" is the addition in £ to the standard engine/box combination. The apparent discrepancy in the 'b' row is explained by the down-angle 60A box/engine unit having a higher standard cost.
The reduction ratio would in part depend on the boat the engine is fitted to. If the engine being replaced is of similar power but different rpm characteristics, this would also inform your decision, the aim being to retain similar shaft revs. That way could allow you to retain the old prop if it's also right-handed. You'd need to run your installation through a prop-calc program for guidance. Companies such as Darglow are also very helpful.
It's an important decision so worth some research to get it right. If you give your specifics, you might find that other forumites have similar boat/engine installations.
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Minchsailor
Well-Known Member
The previous owner fitted a Beta 35Hp with a PRM80 box. Load of trouble as that gearbox does not have the bearings beefed up enough to take the torque/power. I fitted a PRM120 and no trouble since. (I am not sure that Beta should have sold that engine with the PRM80; it is no longer an option).
I fitted a Beta 14Hp to my last boat with the TMC40, no problems in 5 years (c1000hrs) running.
Probably six of one or half a dozen of the others.
I would have liked the slightly beefier PRM150, but that is hydraulically operated and not possible to lock it when sailing, so the prop would have been free-wheeling. There is not enough room to fit a shaft brake.
I fitted a Beta 14Hp to my last boat with the TMC40, no problems in 5 years (c1000hrs) running.
Probably six of one or half a dozen of the others.
I would have liked the slightly beefier PRM150, but that is hydraulically operated and not possible to lock it when sailing, so the prop would have been free-wheeling. There is not enough room to fit a shaft brake.
Tranona
Well-Known Member
The TMC 40 is the normal gearbox for the 14. I have one on the similar Nanni. The only reason for going for the 60 is to get the different choice of gearbox ratio. as macd says you need to do the sums (or get Beta to do them) to determine the correct ratio. 2:1 is by far the most common as it gives a shaft speed of 1800 which will swing a 13 or 14" prop that suits many boats in the size range for this engine. On my boat I have a 15" propeller so had the 2.65 to bring the shaft speed down.
As already suggested the PRM 180 is useful if you want to keep the prop and have a left handed one, but most people change props anyway so unless you already have an expensive fancy prop, not worth the extra and losing the ability to lock the shaft.
As already suggested the PRM 180 is useful if you want to keep the prop and have a left handed one, but most people change props anyway so unless you already have an expensive fancy prop, not worth the extra and losing the ability to lock the shaft.
