Proper gap size between shaft and tube?

I have a 1.5" shaft. I'm trying to find the allowable gap between it and the stern tube that allows adequate space for shaft alignment while limiting the amount of water that could enter the boat if the hose on my stuffing box failed.

I'm sure I saw a reference to an ABYC standard somewhere but I can't seem to locate it.

 

The available stuffing boxes determine the size of the tube. A 1.5" will typically use a 2.5" hose to attach to the tube. That means the tube will be about 2" ID.

 

That would result in a potential ~1.4 square inch opening, or a 1-3/8 ID pipe equivalent. Maybe 1,700 gph. I'll have to double check the rating on my bilge pump. Might want to increase that, or add a second.

With no bilge pump I'd have about 15 minutes before my engine and battery were imperiled.

I guess I can live with that.

 

Actually it is not as bad as you've calculated.
There certainly is a bearing or bushing at the propeller end limiting the inflow of water. And your stuffing box may develop a leak, but it will not disappear completely.

 

I would have 2 bilge pumps anyway.