A friend has a 31' Allmond with a diesel engine.
He was told that he had to use the glow plug every time he wanted to start the engine even if it was just turned off a couple seconds before the restart attempt. Don't remember the engine model probably Universal.
Have you every heard of something like this?
The way I figure it once the engine is hot the glow plug is not going to make it any hotter.
It might be helpful to temper all the replies with a re-read of the OP for this thread.
the person with the actual question. It's his friend, who reports some 'advice' from another
person who 'told' him to do something.
First, have that friend log in and start a conversation with first-hand information. And, then also confirm the actual engine make and model.
And further, tell how the starter circuit is wired...
For example, our '88 Universal M25XP has a separate momentary-contact switch for the glow plugs. Start motor switch is separate. Ericson wired it that way, AFAIK
FWIW, I have seem boats with the series circuit, as others have described.
I like having the option to pre-heat the cylinders a little or a lot, depending on ambient temp or how much heat remains from the previous running. We have a bit over 2K hours on ours.
As for either engine head design being inferior/superior, nothing to argue about. The cylinder head design is quite different. It's not like the two 'types' of diesel engine are identical and one just happens to have an extra hole bored in each combustion chamber for a glow plug.
I've met boaters that spend a lot of time in colder latitudes and really prefer the pre-heat type of engine, and others spending most of their time in hot or at least temperate climates who have no problem with either design.
I have, very occasionally, started our engine up when the ambient temp was in the low 20's (f) and it took a good 20 seconds of glow plugging to start 'er up. At the time I was told a guy in the yard that a similar middle-aged Yanmar would have been a Lot
harder to light off.