Trouble reversing

[Lyndon]

I own a Kelt 850 with a Yanmar 1gm10 with a fixed 2 blade prop, it pushes along at 5.5 knots in flat water but wont go backwards!!
To qualify that, it goes backwards when the weather is calm but trying to stop with any wind behind us is a joke.
Would a 3 blade prop give us any more grip in the water, I know I would sacrifice some sailing performance but being able to stop when approaching a downwind marina berth would be quite nice.

 

[Juggler7823]

The kelt has a wide backend with a narrow cut away bow. It like many modern yachts want to turn its bow downwind, particularly when in reverse. The stern is pushed upwind by the engine and the bow is free to move downwind.

Roy

 

[Guest]

If as many Kelts she is a lift-keeler .... then she has no grip in the water and skids ... in the wind !

Question : Does the engine un-load easily when throttle is opened full quickly ? If so then the boat is likely underpropped. An engine should build up to unload - indicating that prop is about right. If the engine is struggling then it is over-propped and can then lose drive as if its too small !!

Of course another aspect is cavitation that can often happen when a boat is moving one way- you throttle the other to stop it / slow it down and prop literally whizzes away in a hole. The trick here is to use smaller throttle amounts and less speed to correct ......

 

[AndrewB]

Gearbox?

It could be the prop is inadequate, it could be to do with hull shape, then again it could be the gearbox. Since the yacht goes perfectly well forwards under power, the gearbox would be my principal suspect. Smaller engines often rely on a gearbox that uses a friction collar to engage reverse. These wear out in time, leaving the yacht with little power in reverse.

That having been said, stopping a yacht with a following wind does require a surprising amount of power. Yachts naturally like going forwards. Possibly your expectation of a small engine is a bit high.

 

[tonykerry]

I have a Moody 36 which would not reverse with a 2 blade prop fitted. I changed to a 3 bladed prop and it is much better, more drive in forward at lower engine revs. Reversing in a confined marina with a crosswind is still not easy, but is better than it was. Suggest you contact other owners with your boat (or the Owners Association) to find the best prop size.

 

[airbubble]

Get a two blade autoprop. Because of the much better thrust in reverse the propwalk is much less. It'll give you better performance fwd as well.
Depending on your gearbox reduction, you'll probably need a H20-360mm. They retail for about 850 ex vat in the UK but get a budget quote from David Sheppard at SIBS or autoprop@compuserve.com

 

[Miker]

Agreed. I fitted a Brunton 2 blade and the boat now stops on a sixpence, apart from when a sheet of plastic was wrapped around one of the blades.