Kicker motor location-gctid814506

[rmitch]

I have a single diesel 2650 and have been working to get her in the water. I want a kicker motor for backup and secondarily for fishing. I am looking for a 9.9 Mercury bigfoot or similar and I have a question about location either port or starboard of the main engine outdrive. Every boat I see with a kicker has it on the port side, is there a reason? The starboard side is a better location because I just put in a shower inside the cockpit on the port side. Any comments?

[Patrevan]

I have a 2006 265 and went through this process several years ago, before finally settling on a 9.9 Tohatsu fat prop (lower gearing) extra long shaft. It has electric start and tilt/trim. You only asked about placement, so I'll only comment on that specifically. I would have went dead center, but a couple issues arise there - when the main is tilted fully up, it would be uncomfortably close to the kicker when its fully down. Plus the plumbing and electrical then crosses the swim step in the middle, really limiting available useful space on the swimstep and making the plumbing more vunerable to being kicked and of course increased trip hazard. My transom door is on the starboard side (exits onto the swimstep), really making any consideration for putting the kicker on the starboard side a mute point. Be mindful that the further from center you go decreases the ability of the kicker to steer you effectively.

[rossi45]

Another consideration is, if you are mooring your boat on a dock or marina. Think about which side of the boat will be tied to the dock. I had the unfortunate pleasure of having my boat tied to a dock on the port side for a summer and always had to either lower the kicker or climb over it to get onto the swim platform to the transom door.

[Solandri]

When you mount a kicker off the centerline of the boat, in addition to pushing it forward, it also imparts a torque making the boat want to yaw to one side. Basically you're pushing on one side of the boat, so any time you push the boat forward, you're also rotating it (making it yaw).

• [li]If the kicker is on the port side, it will make the boat yaw to the right.
  
  [li]If it's on the starboard side, it will make the boat yaw to the left.

A prop will also make a boat's stern "walk" - the rotation of the prop combined with the forward force it's generating creates a perpendicular (gyroscopic) force to the side. Most kicker outboards use a right-hand prop. When going forward, a RH prop's walk will push the stern of the boat to the starboard. Since it's pushing the stern to starboard, that will make the boat's orientation yaw to the left.

• [li]If you mount the kicker on the port side, the torque (right yaw) and prop walk (left yaw) will tend to cancel each other out.
  
  [li]If you mount the kicker on the starboard, both the torque (left yaw) and prop walk (left yaw) will reinforce each other. You can compensate for this by aiming the prop to the side, but this results in a larger deviation between the direction the motor is pointed and the direction of travel, and less fuel efficiency since part of your thrust is now being used to keep your boat pointed straight, instead of pushing it forward.

Edit: The prop walk direction is reversed if you operate the engine in reverse. But so is the torque from the reverse thrust. So mounting it on the port side yields slightly better control. I doubt you'll see much savings from improved fuel efficiency for a few seconds of backing up however. It's a bigger deal when you use the kicker to troll for hours.

Also a RH prop spins clockwise (when going forward) as viewed from behind the boat. If the boat pitches and the kicker prop breaks the surface of the water, it will throw water up predominantly on the port side. If the kicker is mounted on the port side, it will throw water to the side of the boat If the kicker is mounted on the starboard side, it will throw water up at the transom. The water should also be going backwards so hopefully none of it will land in your boat. But with water flying every which way, away from the boat is better.

On my Yamaha T8, the tiller is attached on the port side, but all the controls (start, stop, tilt, gear shift, labels for throttle) are designed to be accessed with you standing to the starboard of the motor. It'd still be usable if it were mounted on the starboard side, but I'd have to reach around the tiller to access these controls. It's definitely designed to be mounted on the port side.

[rmitch]

Thanks Solandri, and all. Good logical post. The yaw to the right is probably similar to P factor on a single engine airplane and I know about that. Same problem, different drive direction so different correction. Prop walk is something I need to learn on this boat, I never had a single although I was around some when doing the loop and some of those guys with singles knew how to walk the stern in using the prop. BTW, do these 9 hp engines have a trim tab under the cavitation plate to take some of the yaw correction out?

I do not have an opening in the transom, because of handrails mounted on the top of the transom you cross the transom in the center from the swim platform. It sounds like the correct engineering way is to mount it on the port side. However, at least now I know what the problems are if I decide to move it to starboard.