Possible loose prop, best solution?

[Satchmo]

Full disclaimer: to my great embarresment I know nothing about engines/mechanics, so I apologise if I sound at all ignorant in this post, I am trying to learn.
I took Baba Yaga for a quick cruise on Sunday and she was worryingly slow going forwards but seemed to be acting normally in reverse. After a quick chat with a fellow boat owner he suggested that the prop was either wrapped up with weeds or had come loose. He reckons it's come loose, explaining to me that the prop tightens anti-clockwise and therefore having it in reverse tightens it which is why it behaved better than when it was going forwards. Does that sound right?
I'm still hoping it's just weeds. I'll be grabbing my wetsuit and going for a dip to try and confirm either way sometime this week but I want to be prepared for the worst and so, if the prop has somehow come loose, is it possible to tighten it while it's still in the water? I have access to a plethera of tools but, naively, I never thought to look closely at the prop while the boat was on dry land and therefore am not sure what to expect, is it held on by a nut that I could tighten? I can't afford to have her taken out of the water right now but if necessary I can think of a couple of places I may be able to beach her... (I'm on the broads which are tidal so low tide in some places should be enough to get her high and dry)

Edited March 1, 2021 by Satchmo
Just more detail

[mrsmelly]

If you are talking about a narrowboat does it not have a weed hatch. Prop is usualy held in place by a key and a nut stops it coming off. The bit about it tightening up in reverse is rowlocks. First check is crap round it with engine off and keys in pocket.

[Tracy D'arth]

Unthreading prop is rubbish, I know of none that are threaded and even if it was it would have fallen off by now.

 

You have a prop full of garbage.

[Satchmo]

Kent class yacht I'm afraid, I did wonder about the reverse thing.

[David Mack]

I imagine your prop is attached to the shaft in the same way as on a narrow boat. The end of the shaft will be machined to a taper, with the hole through the prop boss also bored to a matching taper. There will be a slot cut in both tapers with a steel key in the slots. A

 Nut is screwed onto the end of the shaft to force the tapers together,  and the nut and shaft will be drilled for a split pin which prevents the nut unscrewing. This is almost certainly fine, but if the split pin has been lost, then the nut will unscrew fairly quickly, and you will lose the nut, propeller and key. As you still have some propulsion this clearly hasn't happened.

My guess is you have some weed or rubbish caught somewhere in front of the prop, and when going forwards it is interfering with the flow to the prop. In reverse it is all washed forward and so has little effect on performance.

[bizzard]

Stern end image of a Kent class motor sailer. Plenty of room for rubbish to accumulate on the long tube extention behind the prop.