Nissan Outboard below deck

[TOHATSU GURU]

Re: Nissan Outboard below deck

Do to the potential liability involved here the best thing to tell you is to stop. The risk of carbon monoxide posioning is simply not worth it.

 

[Plandeck]

Re: Nissan Outboard below deck

Do to the potential liability involved here the best thing to tell you is to stop. The risk of carbon monoxide posioning is simply not worth it.

I appreciate your cautious approach. When the ship goes down, a certified technician does not wan't to be on the hook. That said, the carbon monoxide poison risk seems minute to me...I mean it's a 26' sailboat, not a sleep aboard yacht. All sailing is done from the open air cockpit and the only time the 8 hp motor runs is getting into and out of the harbor...I suppose I could put an alarm below deck.

But, I will admit I am a little concerned about the seal giving way..maybe after a couple of years use, and water entering the boat through the exhaust/ 2 lower unit drain holes. This wouldn't be a problem, but according to SELOC (forgive me for not having the shop manual) there is some secondary cooling water drainage down the gear shaft housing (would you confirm this?) and thus since it is going to be sealed, it will need a small drain hole to the boat bilge. How much seepage would you expect from the water pump connection? Again the exhaust and drain holes in the lower unit are sealed, so any seepage will accumulate up to the power head without a drain hole being introduced.
Thanks.

 

[pvanv]

Re: Nissan Outboard below deck

There's no "secondary" cooling system. All the exhaust and the vast majority of the cooling water (aside from the telltale) exits the bottom of the powerhead. In a normal installation, the through-hub exhaust system scavenges the exhaust and cooling water at speed. At idle, the idle relief ports allow that mix to spill out up high, reducing back pressure.

If you still want to pursue this installation, in the simplest design, you would not seal the exhaust port at the LU, but would instead close off the idle port and the drains, as well as the telltale and fabricate a seal for the shift rod. Then everything would always go out of the prop hub. Otherwise, you will have exhaust and cooling water spilling out through those areas, and accumulating in the boat... or, plumbing the drains, idle port, telltale, etc., out the transom would involve some creative plumbing that could tolerate high temperatures.

Once sealed-in, all motor service would have to be done in the field. You would have essentially built a sail-drive.

 

[Plandeck]

Re: Nissan Outboard below deck

There's no "secondary" cooling system. All the exhaust and the vast majority of the cooling water (aside from the telltale) exits the bottom of the powerhead. In a normal installation, the through-hub exhaust system scavenges the exhaust and cooling water at speed. At idle, the idle relief ports allow that mix to spill out up high, reducing back pressure.

If you still want to pursue this installation, in the simplest design, you would not seal the exhaust port at the LU, but would instead close off the idle port and the drains, as well as the telltale and fabricate a seal for the shift rod. Then everything would always go out of the prop hub. Otherwise, you will have exhaust and cooling water spilling out through those areas, and accumulating in the boat... or, plumbing the drains, idle port, telltale, etc., out the transom would involve some creative plumbing that could tolerate high temperatures.

Once sealed-in, all motor service would have to be done in the field. You would have essentially built a sail-drive.

Thank you for the thoughtful reply. I am concerned that closing the idle port will create too much back pressure at startup and idle because, (as is the main challenge of this installation) the motor will be installed way below it's proper height relative to the water line of the boat, thus when not running water will enter up the exhaust to find its level at the water line of the boat. This almost reaches the height of the power head and sloshing in rough water might even foul a valve right?

Reliability is of paramount importance with the motor of course, and a sloshed valve or too much back pressure to start at sea could be a disaster, not to mention a major repair problem etc.

For this reason, I am considering sealing the lower unit and modifying the idle port too accept a tailpipe that takes all exhaust out the transom. Problem here is the idle port is below the water line and the tail pipe must angle upward to exit the transom above the power head which will make draining it of "scavenged" cooling water a problem right? Any thoughts? Other inboard motor installations have the exhaust port on the motor below the water line with the tail pipe exiting at a level above the power head. How do they solve the scavenged water issue?

Sealing the lower unit with a rubber gasket at the junction with the intermediate unit and caulking the drains should solve the gear shift rod leak problem....maybe a little seepage where the rod enters above the lower unit can be taken up by the bilge. Any scavenged cooling water exiting through the L.U. drains down the gear shaft housing from above? Of course the telltail will have to be plumbed out the transom, should be no problemo.

Of course I realize such an installation will void any warranty and require special servicing. However, (after the boat is raised out of the water) the motor should still be removable.