The following great idea was made by Geoff "Sailingpages" on the Jeanneau Owners Forum.
On some recent Jeanneau models the variable water pressure can cause the shower rose to switch out of 'spray' mode as the pressure drops before the pressure pump kicks in again.
The shower rose can be simply modified by dismantling and removing a small coil spring.
With the spring removed the shower no longer reverts to 'single' flow automatically, but you are still able to be manually switch between 'single' and 'spray' function by toggling the rocker at the rear of the shower handset.
There are "flats" on the centre rose that can be unscrewed with an adjustable spanner.
The spring simply pulls out. Then reassemble the rose fitting.