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Mounting An Auxiliary Motor


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Hello Raiders


I have acquired a small auxiliary motor which I will use when going offshore.  My boat's main motor (60hp Yam 2 stroke) has never given me cause for concer, and I already have a reserve fuel system, but I want the additional peace of mind.


It seems to me that I will need a bracket which can be mounted on a horizontal surface, because of the design of the stern of my boat.


Is this something I could tackle myself, or would I be wiser to take it to The Man?  I am reasonably handy, have rebuilt 4 cylinder car and single cylinder motor cycle engines and recently replace the water pump and re-sealed a small outboard.


Pic of the boat to show what I mean.  I intend mounting the aux motor to the left of the main motor...



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There are ones available for horizontal surfaces. I forget the brand name but they are a fairly expensive high quality stainless steel model. It shouldn't be difficult to fit as long as you have access to the inside to tighten the bolts. It may be a bit hard to deploy and operate looking at your transom set up. 

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Not worth the effort (in my opinion) unbalanced boat, most are not powerful enough to make decent headway, need to be used often to make reliable, the chances of being out on your own these days is slim to none, then the chances of actually breaking down are slim too, certainly possible but......

Edited by noelm
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  • 3 weeks later...
On 10/24/2021 at 3:31 PM, JustJames said:

it seems to me that I will need a bracket which can be mounted on a horizontal surface, because of the design of the stern of my boat.

I'm late to this chat, I had an Aux on my 6.3m Haines for many years when the main motor was a thirsty two stroke. 

If your primary use is "peace of mind" then your main concerns will be mounting, weight distribution and operation when the Aux is deployed.

Here's my experiences with an Aux ... pick out of that what may be of help.

This is the ally powder coated bracket that  I had "the man"  weld for me ... it was fitted to a flat section similar to yours.


This is how the Aux sat:


I also carried a live bait tank (35L) on the other side of the main motor, to balance the Aux and help with weight distribution. You can see it in the picture above.

My rig is a fair bit bigger than yours, 2T on the water and I had a 15hp 4st Aux (50kg) .. it would move the boat at 6kts (11kmh) which was enough to troll lures. I also linked the Aux to the main motor so I could steer from the helm. The Aux usually sat tilted up and I had to weld a special H bracket to keep it there as the little tilt holder on the side of the motor was only designed to be used for maintenance - not hold it tilted when underway - they snap !  I could reach out from the stern and depoly the H-bracket and the Aux without too much effort. 

You can see the H bracket in the next shot.


Now to @noelm's valid comments. Was it worth it?

Well in my case I bought the boat with a 225HP Yam of unknown hours and condition. I added the Aux for safety as it was cheaper than replacing the main donk. 4yrs later I sold the Yam and put on a 200HP 2st EFI but kept the Aux. The new 200 was much more reliable but still thirsty - trollng it used 12L/hr ... the Aux used less then 4L/hr. In my case, the Aux could only be used for trolling out wide, it didn't have the grunt to safely troll head lands. In addition it only worked for me as a trolling motor because i had the steering linked with the main motor and the Aux had forward controls. But using it for trolling it had regular use - remember lack of use kills outboards - and if you have not used it regularly it may not work when you are most relying on it. 

Now regarding peace of mind: In the 20 odd years I had the 200hp and the Aux, I only had one engine failure on the 200 motor which required us to limp back using the Aux - it is a rare occurrence. We were about 8km off Barrenjoey, but there were many boats around, I'm sure if we didn't have the Aux we could have got a tow without needing to fall back on Maritime. If we had been boating in enclosed waters, there would have been even more boats to wave down.  So if you are just doing it for peace of mind you really need to consider where you are typically boating - and will you be so isolated that you need an Aux. Because if you are so isolated, then you need to start thinking about separate fuel, batteries etc.

So in hindsight, I got use out of my Aux, but it was more due to fuel efficiency rather  than safety/peace of mind. There was a fair bit more in my set up than just solving how to bolt it on.

Final point, bear in mind that running 2 motors you double your annual maintenance costs.

Cheers Zoran

PS - Since re-powering with a new 150HP 4st main motor, I have removed the Aux. The new 150 trolls at around 6/hr and going forward with the new motor tech I do not see a need for an Aux.



Edited by zmk1962
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Thanks Zoran (and everybody else) for your comments and input.


The reason to add a second motor is for peace of mind when heading out wide.  


My boat has an underfloor tank, and I have a removeable secondary tank with its own hose and bulb.


There are 2 batteries which are switched, and an aux would be cable start, so independent of the batteries. 

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14 hours ago, JustJames said:

Thanks Zoran (and everybody else) for your comments and input.

No probs. Enjoy the project. Perhaps start by strapping a water filled bin where you plan to mount the Aux to test the effect of the aux weight on the boat ride and trim. Also position yourself where you think you will be operating the Aux - it sounds like you’ll be tiller steering from the rear - again to test the trim and whether you need to consider a tiller extension. The aux won’t have enough power to get you on the plane so to get the most out of it you want the hull to ride as level as possible. Being mounted to one side, offset from the centerline, it will have a tendency to push the hull into a turn, if the hull is tilted as well it will exacerbate the inefficiency. 
cheers Zoran 

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