Outboard Discussions

[Theis]

That is interesting. I am assuming that you have the copper nipples going right into the exhaust ports on the back of the motor.

I didn't do it that way. I built a small plenum (about 3"long and the width of the shaft housing) so that the exhaust is perhaps cooled in this plenum. The exhaust exits from this plenum. The inside of the plenum is a formed piece of thin aluminum, shaped so it will stay attached. It is then firmly held in place by the fiberglass which covers it and extends over the shaft housing.

Perhaps this aluminum sheet, in contact with the shaft housing, is providing sufficient heat dissipation so that the exiting exhaust gas is not particularly hot. The total contact area between the lower unit housing and the formed piect of sheet aluminum is perhaps 4 square inches.

Of course, the exiting exhaust might not be as hot as well.

[mrgnstrn]

no fittings, just literally stuck the two copper tubes (small flexible stuff) into the two relief ports. one was 5/16" and the other was like 1/8". and they stay in there by friction, and a little bit of bend in the tubing that i stick in there. sometimes if i wiggle them, they fall out. It is a 9.9 mercury for reference.
the tubes first come out of the motor pointing down, then gooseneck up and over to the stbd fwd corner of the laz, where the vent port is.
and the copper tubing is stiff enough to stay in position, but you can bend it as needed.
but yes, it gets really hot. i would say like as hot a really hot tap water.

[Theis]

Your copper tubing is acting as a heat sink for the exhaust - which is probably about the temperature of hot water (since the engine is water cooled). But that is not "hot" in terms of neoprene of plastic. Being copper, the tubes readily transmit heat to your fingers (or anything else - copper being a super conductor) which is why they feel so warm/hot.

If the tubing were made out of plastic, it would not get as hot to touch.

A couple items to check with your system:

1. With the heat, and the difference in metals, there electrylysis/corrosion. You might be better served using aluminum tubing.

2. Is the seal where the tubing meets the lower unit ssolid. You might want to use some sort of sealant to be sure that no exhaust is leaking around the stuck tubes.

[c_amos]

Bump

Bump

[Theis]

The deeper the shaft, and hence the exhaust, the more important it becomes to vent the exhause relief outlets obove the wate line. The deeper shaft increases the back pressure throught the exhaust outlet in the lower unit, particularly when the motor is idling or at low speeds. This will therefore increase the amount of exhaust that exits via the pressure relief holes (so there is no back pressure, regardless of the level of the lower unit exhaust outlet). When operating at higher speeds the through prop exhaust sucks the exhaust out (or is designed to do so - but perhaps not completely) A prop/exhaust that is one foot lower than a shorter version increases the back pressure by 62 lbs/inch.

But still I would opt for a longer prop shaft -and in no case take a standard length because it pops out of the water - in my experience. Other than as mentioned above, I don't see any disadvantage to as long a shaft as you can get.

[Edgewood]

The ultra long shaft(25") that I am considering comes standard with Alternator, which is a plus.

[Edgewood]

What is best 15" or 20" or 25"?

[Mike Goodwin]

20" fits the boat and keeps the prop in the water.

[c_amos]

20" fits the boat and keeps the prop in the water.

Add another vote for 20" from me.

The longer shafts (9.9 merc long shaft, and johnson 8) I have seen on Ariels don't 'bite' any better then mine, and my 20" Yamaha 6 has never come out of the water on me.

I agree with Peter, in that I might not go with a 15" shaft for fear it would not stay below the surface.

The old Suzuki 8 that I had was a couple inches shorter(17"?), and it never came out, but would get close enough to cavitate in a bad chop (but still useable). I would not use a short shaft on an outboard if it were going to hang on a bracket mount or a transom (like the P-26) since they tend to pop out of the water more then the 'outboard in the well' like we have.

I am sure that with a 25" shaft, the prop gets 'cleaner' water deeper, but it also produces more drag there when sailing. Having motored Ariel's with both, I prefer a 20" shaft, and will probably re-power with the same. (and will not go over 8 hp FWIW).

[Howard]

A thread from the dead...bump indeed.

I was just thinking the opposite as I dangle mine (20")off the back and can almost bury it if I want. Middle position on my Garelick mount keeps it buried most of the time, plus I can turn on a dime with it off the back.

Add another vote for 20" from me.

The longer shafts (9.9 merc long shaft, and johnson 8) I have seen on Ariels don't 'bite' any better then mine, and my 20" Yamaha 6 has never come out of the water on me.

I agree with Peter, in that I might not go with a 15" shaft for fear it would not stay below the surface.

The old Suzuki 8 that I had was a couple inches shorter(17"?), and it never came out, but would get close enough to cavitate in a bad chop (but still useable). I would not use a short shaft on an outboard if it were going to hang on a bracket mount or a transom (like the P-26) since they tend to pop out of the water more then the 'outboard in the well' like we have.

I am sure that with a 25" shaft, the prop gets 'cleaner' water deeper, but it also produces more drag there when sailing. Having motored Ariel's with both, I prefer a 20" shaft, and will probably re-power with the same. (and will not go over 8 hp FWIW).

[Orca]

Please note my post in the Tohatsu 6 area looking for feedback on first hand experience between the 20" and 25" shafts on the new 4 strokes. Ed

[Bill]

The January issue of Trailer Boats included the specifications for all of the current outboard engines. Those of you who want info about the Mercury Verado (16 cylinders and 275 hp), stern drives or Diesels will have to check the magazine. We are just copying listings for the 6 & 8 hp 4-cycle engines:

Engine & HP Weight & List $P

Honda 5 *----- 60-lbs $1700
Honda 8 ----- 77-lbs $2160

Johnson 6 ----- 56-lbs $1996
Johnson 9.9**--- 97-lbs $2350

Mercury 6 ----- 55-lbs $1727
Mercury 8 ----- 84-lbs $1870

Nissan 6 ----- 55-lbs $1514
Nissan 8 ----- 82-lbs $1820

Suzuki 6 ----- 55-lbs $1741
Suzuki 9.9**-- 97-lbs $2595

Tohatsu 6 ----- 55-lbs $1484
Tohatsu 8 ----- 82-lbs $1781

Yamaha 6 ----- 83-lbs $2130
Yamaha 8 ----- 83-lbs $2240

* no 6-hp
** no 8-hp

As noted before, the Mercury, Nissan, Suzuki and Tohatsu all use Tohatsu’s basic engine, although the some companies have brand specific accessories (such as Nissan's vertical pull starting rope setup).

[cbs]

my commander came with a 9.9 honda outboard that was jammed in the well, to big1 i am trading it in, any suggestions , on hp. 4-5-6-* ?

[Mike Goodwin]

6 hp. Nissan fits with ease and drives the boat to hull speed, weighs in at 50lbs or so.

[Bill]

my commander came with a 9.9 honda outboard that was jammed in the well, to big1 i am trading it in, any suggestions , on hp. 4-5-6-* ?

Use the search function for outboard. There has been much discussed on this subject.