Slip­ping Lis­ter

Canal Boat - - Back Cabin: Experts -

QThe Lis­ter LH150 hy­draulic gear­box on the ST2 en­gine in my 53ft boat works per­fectly in re­verse and neu­tral, but in for­ward it slips on higher revs. I’ve ad­justed the bolt in­side the box to give a 2mm gap. It runs at about 4mph with no slip­ping (but it does labour a lit­tle pro­duc­ing some black smoke); how­ever, if you give it more revs the prop doesn’t turn any faster.

I have changed the pro­pel­ler from a 17x13 to a 16x12 and this helped, but I still think it is over-propped be­cause of the black smoke. I do not have a re­duc­tion box. Do I need to look at clutch mech­a­nism, or is it still slightly over-propped caus­ing slip?

GARY, via email

ATONY REPLIES… My prop on a 54ft boat with a 2.5:1 gear re­duc­tion and a 35hp en­gine is some­thing like a 14x12. As a Lis­ter LH150 with no re­duc­tion box fit­ted gives a di­rect drive (1:1) and the ST2 pro­duces about 20hp, I would say your boat is over-propped. That ex­plains the smoke but not the slip.

The LH150 uses oil pres­sure to give neu­tral and astern, while ahead is en­gaged by the re­moval of oil pres­sure from the ahead pis­ton, al­low­ing a set of strong springs in a hub be­hind the ahead cone clutch to en­gage it. There are two pos­si­bil­i­ties. The first one is that the cir­clip has fallen off the clutch ex­ten­sion that holds the clutch into the spring hub. But more likely it is old age and the clutch needs re­plac­ing. You should also check the free length of the springs in the hub when the box is stripped.

The free play on the ad­just­ment gets less as the cone wears and, just like on old cars, this can cause slip­ping. The 2mm gap should be okay but when you next have the top off the box, make it a bit wider.

I would sort out the slip­ping and worry about the prop later. A prop spe­cial­ist might re-pitch the prop for less than a new one.

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