Progress is slow underway

This is one in a series of A Guide to Narrow Boat Problems.

Problem
Progress is slow underway and increasing engine speed doesn't help. Tiller may judder or vibrate.
Cause
 Probably weed or other obstruction on the prop.
Solution
A quick reverse thrust might help. If not moor up and switch off engine. Remove weed hatch cover and feel for obstruction. Weed should be cleared by hand or with the help of a serrated knife,  and disposed off on the bank. Wash hands and arms before proceeding.

This is the biggest thing we ever had jammed in our prop

Avoidance
Minimise risk from large areas of weed by setting prop to neutral before approaching the weed. Note that even when weed has been cleared (see picture below) for some time afterwards loose weed is very likely to entangle your prop.

Weed clearing on The River Nene. Thank you weed clearer!