Going to be below freezing and boat is still in the water

[viper1216]

Hey all,

My boat is still in the water (saltwater). Was trying to leave in as long as possible to get a few more dives in. This weekend, it is supposed to drop down into the 20's overnight (Rhode Island). I have a 2010 Mercuiser 3.0. Draining the block is easy enough, it's just 2 hoses. So I was planning to run down to my slip and do this, just to be safe. But my question is, if it's still sitting in the water, will that just fill right back up again, or does it need to run with the impeller to fill that area up?

 

[Scott Danforth]

draining the block and manifold is pulling the manifold plug and the block plug, then the two hoses

however if you're still in the water , the water is not frozen, you should be good to go for a night

or put a 40 watt bulb in the bilge

 

[viper1216]

Nah, water is definitely not frozen. It's still like 56 degree's.

 

[tpenfield]

Salt water freeze point is about 26˚ F, So, as Scott said, you are probably OK for an overnight . . . but draining should be enough for peace of mind . . . the engine/manifold will not fill back up on their own.

 

[Lou C]

I would do as suggested, drain the engine and manifold, the water temp around the boat is not going to drop nearly as fast as the air temp will.

 

[stonyloam]

It is all a matter of heat loss. If the water is 56°, I would not worry about it. As the block looses heat by convection to the air it will be quickly be replaced by heat flowing from the water through the outdrive to the block which is a much more efficient process. it is doubtful that the block would cool much below the water temperature and the air in the engine compartment would be warmed by the hull which will be the same temperature as the water. If the water temp was near freezing and the air temp were in the low teens, then I would worry.

 

[Lou C]

It would be interesting to go out to the boat with an IR Temp gun and take readings of the block and manifolds, see if they are actually warmer than the air temp....due to the water being much warmer than the air....

 

[racerone]

The water would be a heat source through the hull.-----Motor box should be well insulated on all sides.

 

[viper1216]

Thanks for the info everyone. They upgraded the forecast and it looks like it's only going to get down below 27 degrees for about 3 hours. Should be good I think.