Nissan Outboard below deck

[Plandeck]

I am planning to move the 8hp nissan outboard on my 26' sailboat from the rear transom to below the cockpit floor just behind the cabin stair. There is a place here for an inboard style motor that came as an option on the original boat but was never installed. Installing the outboard below deck instead of an inboard will avoid a horizontal drive shaft and stuffing box among other things. However, the outboard unit will be much lower relative to the water line of the boat. When not running the water will enter through the prop exhaust up through to near the top of the drive shaft housing. Is there any concern that water might enter an open valve while the boat is healing and the engin turned off? Any other problems with this approach? Anyone ever try this before? I've seen it from the outside on another larger sailboat in the yard.

 

[Sea Rider]

Re: Nissan Outboard below deck

Is that a 2 or 4 stroke engine ? Is it possible to raise the engine inside cockpit to have the least tail inside water as to have less tail drag once engine is pushing ? Is it possible to install a folding prop as the prop will spin at neutral with more drag when engine is not on.

Happy Boating

 

[TOHATSU GURU]

Re: Nissan Outboard below deck

No, is the answer.

 

[pvanv]

Re: Nissan Outboard below deck

Your boat could maybe use a saildrive. Yuck. But to install an OB will require building up a well to get the motor at the correct height. There are some Olsons with that setup, as well as old Cal's that have a well in the cockpit sole. Keep in mind that a below-decks installation will require USCG safety considerations, such as for fuel lines, filters, and venting.

My HR-28 has the OB in a lazarette compartment well, and while technically exposed to the "outside" air, I do all the below-decks setups, including type A-1 fuel lines, metal water separator, and correct venting.

 

[Plandeck]

Re: Nissan Outboard below deck

Your boat could maybe use a saildrive. Yuck. But to install an OB will require building up a well to get the motor at the correct height. There are some Olsons with that setup, as well as old Cal's that have a well in the cockpit sole. Keep in mind that a below-decks installation will require USCG safety considerations, such as for fuel lines, filters, and venting.

My HR-28 has the OB in a lazarette compartment well, and while technically exposed to the "outside" air, I do all the below-decks setups, including type A-1 fuel lines, metal water separator, and correct venting.

Thank you for the reply. I am familiar with "well" set ups for OB motors. Both Cape Dories and Piersons have these. I'm talking about something a little bit different. The OB below deck setup involves caulking around the lower unit where it passes through the hull, rather than sitting in an open well. The question really boils down to whether installing the engin this way all the way down below the cockpit floor to where the actual water level is just below the power head will affect the exhaust....I mean will A)water enter through the prop exhaust when the motor isn't running and foul the ports? for example when healing, and B)will the exhaust out the ports when the motor starts up generate enough pressure to exit the prop when there is water so far up the exhaust line? Basically, no, the motor will not be at the "correct" height relative the water level - what is the effect of this viz. the prop exhaust?

To respond to the other question, my feeling is that the drag from the prop should be mitigated because the lower unit and prop exits the hull just behind the keel. See the attached JPG file.

 

[Georgesalmon]

Re: Nissan Outboard below deck

Dom't know about your brand of motor. All of mine have outlet for exhaust/water outlets way above the prop. Just below the cowling so there is no backpressure at idle speeds. When at speed and moving forward the exhaust is scavanged out of the prop hub. I think you'll have problems with exhaust pressure starting and at slow speed and water entering the engine cyclinders when stopped.

 

[TOHATSU GURU]

Re: Nissan Outboard below deck

And the answer is still no. There is no effect on the back pressure due to the engine being installed below sea level on this application.

and

A) No is the answer, but obviously water stays in engine up to the depth it is immersed.

B) Yes is the answer as the water will not go up into the engine any more than it would in a normal installation.

 

[isaksp00]

Re: Nissan Outboard below deck

How would you seal the leg going through the hull tightly enough, accounting for vibration, possibly striking a submerged object, etc. so it would not be a sinking risk? I have never heard of an installation like that, which seems like it might mean it isn't safe. Of course, I have limited experience, so maybe it has been done. I wonder if your insurance would cover any loss related to such a mod.

 

[TOHATSU GURU]

Re: Nissan Outboard below deck

Normally you wouldn't seal it other than by a tight rubber seal. However, if you create an airlock on that compartment that would prevent water from coming in. In the end, the risk and work involved in doing this would be excessive so the best advice is to drop the idea completely and hang the engine off the back of the boat like everyone else.

 

[pvanv]

Re: Nissan Outboard below deck

Normally you wouldn't seal it other than by a tight rubber seal. However, if you create an airlock on that compartment that would prevent water from coming in. In the end, the risk and work involved in doing this would be excessive so the best advice is to drop the idea completely and hang the engine off the back of the boat like everyone else.

Amen. Stay with the stern bracket. You already have the setup, access is easier, and no extra marinization is needed.

The idle port would dump exhaust into the boat. The "seal" (how would you seal the shift rod?) would leak (unless setup as a saildrive), the "inboard" installation would require all USCG and NMMA belowdecks installation techniques be used (including backfire arrestor), and the drag would be excessive. Marine growth on the motor leg and LU would be a maintenance issue too. Not to mention that you would have water so far up that you might get some in the cylinders. On a 4-stroke, odds are that an exhaust valve could be open, allowing splash/slosh into the cylinder, leading to liquid lock... on a 2-stroke, it would likely just run back out, but no guarantee. BTW, heeling would raise the motor, not lower it, as it would be on centerline.

A lot of people do very creative things, and sometimes they get lucky. Heck, I have even seen a "home-marinized" briggs horizontal motor converted to water cooling, installed as an inboard auxiliary. Yes, it has inboard fuel tank with outside vent, and a belt-driven cooling pump, complete with thermostat! Doesn't mean that it's cost effective nor something any "normal" mechanic would want to work on. But it does work... at least for the owner/designer.

 

[Plandeck]

Re: Nissan Outboard below deck

hmmm...the shift rod leak problem is a question...hmm...I haven't dissembled the lower unit yet, but hopefully the shift lever within the lower unit is sealed. This would solve the problem since where the lever rod enters the lower unit will be above the seal with the hull and not exposed to water. But I suppose the only way to find out if A) there is increased backpressure on the exhaust at startup and during idle due to the higher water level up the exhaust channel and B) whether water might splash up into an open valve when not running and kill any hope of a spark...is to do it. The motor is a 2006 8hp Nissan and I don't see any mention of exhaust venting except through the prop in the SELOC manual nor from the parts diagrams available on line. There is some secondary cooling water drain down the exhaust channel besides being pumped out in a stream from the rear of the upper unit, but this doesn't seem like it would be a problem....As for cost, this approach must be the cheapest way to convert to an inboard...no more bending over the the transom while in a full heal and sailing solo, better weight distribution with the motor located down low near the keel instead of cantilevered off the stern, and no more spider web covered outobard to deal with, and more room at the stern for access to the water and for installing a wheel instead of a tiller. Just remove the lower unit from the motor (4 bolts), cut a hole in the hull, install a 2x12 below deck to hold the motor bracket, cut a hole in the cockpit floor, lower the motor through and onto the 2x12, expoxy and then caulk around the intermediate unit where it passes through the hull, perhaps a couple of bolts through the hull and the horizontal fin on the motor where it meets the hull cutout, reinstall the lower unit below the hull, add a drainage line for the water from the motor and voila! IB instead of OB. Some other small matters like, adding ventilation ports to the compartment for gas fumes, install a remote control linkage, and work out a way to keep the manual pull start so as not to rely only on the electric start, then install a raised hatch over the hole in the cockpit floor and you're done.

 

[pvanv]

Re: Nissan Outboard below deck

No.
You will likely have a ton of work getting the motor mounted.
Dump the Seloc manual, grab a Factory service manual for better details; there is an idle exhaust port.
There is no "Year" for servicing a Tohatsu/Nissan, only model/serial; you likely have an NSF8A or A2 4-stroke.
The shift rod is open to the powerhead; there is water inside the exhaust housing.
Adding RC is a good idea; you can do that with the transom mount.
A 2x12 in the bottom of the boat will rot in a couple of years.
Your hull seal will be a real and ongoing leak issue.
You will have a lot of trouble getting a survey that approves your installation for insurance.

 

[Plandeck]

Re: Nissan Outboard below deck

wow...I'm glad your'e not my mechanic...

 

[pvanv]

Re: Nissan Outboard below deck

wow...I'm glad your'e not my mechanic...

Just the voice of experience.
Take a look at my avatar, which is my Hinterhoeller HR28, and you will see a Nissan 9.8A3 projecting through the lazarette area of the hull...

 

[Plandeck]

Re: Nissan Outboard below deck

...if progress had listened to experience like yours we would still be peering out of caves...forget boats...two years to rot a below deck
2x12 is a bit of an exageration.

 

[pvanv]

Re: Nissan Outboard below deck

...if progress had listened to experience like yours we would still be peering out of caves...forget boats...two years to rot a below deck
2x12 is a bit of an exageration.

You asked; I responded. Take the advice; or not. It's not my boat, mon.

 

[Plandeck]

Re: Nissan Outboard below deck

Attached is photo of my lower unit gearbox with 3 areas that I propose to seal with generous amount of caulk. Sealing the exhaust should prevent water from entering the lower unit gearbox which projects below the hull. The exhaust from the motor will then exit by modifying the idle exhaust port with an exhaust pipe below deck to take all exhaust gasses out the stern. Any comments?

 

[TOHATSU GURU]

Re: Nissan Outboard below deck

Nein

 

[Outsider]

Re: Nissan Outboard below deck

Any comments?

 

[Packard8]

Re: Nissan Outboard below deck

Any comments?

Billy Bob & Cooter should be consulted. They both hold degrees in Agro-American Engineering.