As an aknolleddged xprt on this subject,It is some sort of valve in the engine fiel line thingy that sort of strangles the flow of fuel stuff.
so less fuel less power less speed simple innit.
<hr width=100% size=1>If it aint broke fix it till it is.
was such a long load of posts on that thread I got bored and missed the bit about valve trolling.
So Brendan "I read and understand everything" Spillane is Oldgit right then?
<hr width=100% size=1><A target="_blank" HREF=http://www.suncoastmarine.co.uk>Sun Coast Sea School & Charter</A>
I do not believe trolling valves work as oldgit says by reducing fuel flow - they would just stall as they are only of any use if the in-gear idle speed is too fast.
They work on large hydaulic gearboxes (often in fishing boats) by bleeding off some of the hydraulic pressure which clamps the clutch plates together. This allows some slip and so the output shaft (and prop) turns slower than the input from the engine shaft. Fairly obviously it only works with a wet plate clutch to allow for heat dissipation - normal dry clutches as in cars don't like this treatment.
'The Newage trolling valve is also available as optional equipment on PRM260, 500, 750, 1000 and 1500 models, enabling propeller speeds to be varied from 1200 rev/min down to zero. This electronically-operated unit is fully inter-changeable with the standard control valve and can be retrofitted in service.
The Newage trolling valve enables low propeller speeds to be obtained by the use of an electrically controlled pressure reducing valve in the clutch pressure operating circuit. It also avoids the use of special oils for the gearbox when fitting the trolling valve.
The operating lever is a Morse type NB unit with locking handle. The housing contains the electrical circuits for operating the trolling valve which again are encapsulated to provide a waterproof seal.
Depressing the ON/OFF switch causes the hydraulic oil to flow through the pressure reducing valve and by varying the position of the control lever the clutch pressure is increased or decreased with an associated increase or decrease in clutch slip. An interlock facility is provided in the form of an electrical connection which can be wired to a microswitch on the fuel rack to switch off the trolling circuit if the engine speed rise above 1200 r.p.m.'