posted 10-21-2004 07:05 PM ET (US)            

I'm in the process of putting on a 9.9-HP Yamaha high-thrust four-stroke on my 1985 Montauk. This is probably more motor than is needed for trolling or emergency backup. There will be lots of trips for me where the 9.9 will function as the main motor, horsepower-limited waters, shallow swamps, etc. The standard prop on this motor cannot drive any boat faster than 13-MPH, but that's higher than I need. I figure it's going to provide me any displacement speed I want, with some thrust left over. The high thrust motors have huge props that turn slower.

I have a Yamaha four-stroke 50-HP on, so don't have the weight problems that those with larger motors have, so can tolerate the 100-lb. weight. With moving the battery out of the stern the net change is about 50-lbs. at the stern. Be sure and think through your own weight situation. That may rule out some motors.

The motor I have is a long, 20-inch shaft version. In the starboard mounting spot it will have, that places the cavitation plate just slightly below the bottom of the transom there. I put it on temporary when it arrived just to check and it looks real good. The majority of the prop will be higher than the deepest part of the boat in the center, making it real good for shallow running. Since this motor is not expected to plane the boat, there will be lots of water depth around it. I don't think a short shaft motor would work as that would place the prop behind the transom rather than under--Boston Whaler recommend the long-shaft. A 25-inch or extra-long would definitely be way too long.

I will be bolting the motor to the hull through its lower bracket holes. Don't want to have to worry about clamps coming loose, though they will be used too. There is wood in the transom there for exactly this purpose. No bracket, though I may make up some padding pieces to protect the hull and deal with its curvature on top.

I'm also making this a full remote installation. The motor came used with a partial conversion to remote which I'm completing. Think about remote, sitting back in the stern corner running a motor did not appeal to me when I could do it at the console. You can convert a tiller Yamaha to remote, but there is a fair bundle of parts involved, and you don't want to do a half way job like was done on my motor. Better to get a remote motor.

To my mind if you don't need maximum speed from the installation, just trolling and emergency, the high thrust 8-HP with remote and power tilt is worth looking at. There's a T8 installation detailed in the reference section, though on a OUTRAGE 22. The T8 uses lower pitch propellers, so won't make the speed of a T9.9. Do note we are not talking plane speed, you will only do displacement with either. The T8 actually weighs slightly more than the T9.9 due to the tilt.

If not going for the high thrust engines, the other brand I'd look at is Honda. I have a Honda 50 on another boat and am very happy with it.

posted 10-21-2004 10:46 PM ET (US)            

My last Yamaha was a high-thrust 8, and it was plenty to push my MUCH heavier 21 footer.

posted 10-22-2004 07:47 AM ET (US)            

There is a cap that fits over the end of the rubrail where it meets the transom. I removed it and cut back some of the rubrail (around 12") and then put the cap on the new end. It looks quite good. I bored one hole through the transom, gooped plenty of 3M 5200 in the hole, and then mounted the motor with one of the brackets going right through the transom. That way the motor CANNOT fall off--unless it takes a piece of transom with it!

Another note: I put a tee in the main motor's fuel line in between the the primer bulb and the motor. I then ran the kicker's fuel line from this tee, including another primer bulb. Therefore both motors run off the same fuel tank and it works great.

Although when stationary the boat lists a little to the side, when underway the weight is negligible.

posted 10-22-2004 04:51 PM ET (US)            

Any of these engines will have two bolt holes on the clamp that will be lined up with the wood. I'd be really nervous depending on one bolt. Clamps can work loose. On one bolt you might find the motor pivoting around the bolt.

The idea mentioned by some that this is a emergency motor should be considered. Emergencies don't just happen on nice days, calm seas, light winds. Think storm and waves, think worst case. At least if you are going with a 6, go with the high thrust. That should give you steerage in most situations.

In my case it's not just a trolling motor and possible emergency motor, but a part time main motor. Thus I went with the 9.9. And I have a big weight advantage as the main is a 50-HP four-stroke.

Another difference between the 8-HP high-thrust and 9.9-HP high-thrust is available propellers. The 8 uses less pitch, which will limit top speed more than the 9.9. Check the pitch, use the prop calculations available elsewhere on the site and see what maximum speed you get at maximum motor RPM. No matter how well the boat moves that's all you will get. I believe the 6 uses the same dual thrust prop as the 8, but its lower horsepower may limit its effective use of it.

Going with a standard motor (high RPM propeller) is going to result in lots of propeller slip. The prop will be turning faster than it should for displacement speeds, with lots of slip at higher throttle settings. Yes the boat moves, but at poor gas usage. Those motors are designed to get really light boats on plane, thus they are set up for higher speed. The very reason why there is a high thrust series.

Note that Honda does not have high thrust, but it's gear ratios are not as bad as some.

posted 10-24-2004 09:49 AM ET (US)            

The Propeller Calculator can be found at:

http://continuouswave.com/cgi-bin/propcalc.pl

The article on installation of a Yamaha T-8 auxiliary motor is available at:
Mounting a Yamaha T8 Four-Stroke Kicker
On a 1992 OUTRAGE 22 with Evinrude 225-HP Main Engine
http://continuouswave.com/whaler/reference/yamahaT8Kicker.html

posted 10-24-2004 10:06 AM ET (US)            

Marine engine mechanics that I trust have recommended using a 3-way valve fitting in place of a simple Tee to connect the two motors to the fuel supply, if sharing a common tank.

In any case, it seems you ought to use two primer bulbs. In this way the check valve in the primer bulb may help prevent fuel from being sucked out of one engine (that is not running) by the other engine's fuel pump (i.e., the engine that is running).

posted 10-24-2004 02:44 PM ET (US)            

Lots of great suggestions here and I will give you mine..

You already have a 90hp Johnson 2 stroke.
Do you premix the oil and fuel or are you using the oiling system?
If you are using the oiling system, then you are running straight gas out of the fuel tank(s). In this case, a 4 stroke would work great without having to add another oiler to a 2 stroke kicker, you would just run the straight gas from the tank(s).

I would recommend the 8hp Johnson 4 stroke as it is lighter than the 9.9 4 stroke Johnson. The 9.9hp 4 stroke Johnson is made by Suzuki and I believe the 8hp is made by Johnson.

Weight:

8hp Johnson = 88 pounds (rope)

9.9hp Johnson/Suzuki = 99 pounds (rope version)
9.9hp Johnson/Suzuki = 107 pounds (electric)

As many people have mentioned already on this site, the looks of matching main and kicker engines are the way to go.. They simply look great.

I don't feel electric start for me is the way to go. The engine is heavier and you need another battery which adds more weight yet. I prefer the rope start model and you can add engine controls at the helm with a factory adapter kit from Johnson.

I had an 8hp 4 stroke evinrude on my prior Montauk and tried usiing the tiller and a seat in the back.... Hated it... Hated the seat and hated sitting back there... I sold the 4 stroke and bought an 8hp Evinrude 2 stroke kicker..
I also added the factory engine control adapter kit and purchased a Dual Binnacle engine control at the helm. Works fantastic..
When you are ready for trolling, step to the back and lower the motor, pull start the engine, and you are ready to use it from the helm. The steering is connected to the main motor via a Stainless Steel Rod kit made now by Panther Marine. When you are finished trolling, step to the back and push the Red button on the end of the tiller handle and raise the engine... Works great for me and I don't have the extra weight of an electric engine or the battery.

Here is a photo of the engine setup on my prior Montauk:
http://users.sisqtel.net/jkriz/Montauk/rear-inside.jpg

Here is a setup of a OMC Dual Binnacle of another Montauk I converted:
http://users.sisqtel.net/blewis/Montauk/dual_binnacle.jpg

And yet more photos of the setup on my Outrage 18 using the same configurations:
http://users.sisqtel.net/jkriz/Outrage/rear-inside.jpg
http://users.sisqtel.net/jkriz/Outrage/console.jpg

Note that there is only one key switch on the console on both boats for the main engine only.
Also, there is only one trim switch in the Binnacle Control Handle.
I took off the Dual switches and replaced them with a single.

Maybe your Bombardier dealer will hang an 8hp 4 stroke on the back so you get an idea of how it will look. Although looks aren't everything, having the same brand of engines hanging off the back makes it much easier to connect both engine to the fuel system and the engine control system as they would be using (in this case) ALL OMC/Bombardier parts....