Auxiliary Engine for a 4.65m RIB.

[Flamair]

As detailed elsewhere on RIBNET, I am in the process of purchasing a 4.65m Avon RIB with a 60hp Yam 2 stroke. As I intend eventually to use it for short coastal passages i am wondering what would make a suitable auxiliary, particulary regarding it actually fitting on the transom. I already own a Yam 8hp 2 stroke, but fear that may be too big a unit physically.

Anyone with far better knowledge than I cast any wisdom for me?

Many thanks folks!

[beamishken]

Originally Posted by Flamair

As detailed elsewhere on RIBNET, I am in the process of purchasing a 4.65m Avon RIB with a 60hp Yam 2 stroke. As I intend eventually to use it for short coastal passages i am wondering what would make a suitable auxiliary, particulary regarding it actually fitting on the transom. I already own a Yam 8hp 2 stroke, but fear that may be too big a unit physically.

Anyone with far better knowledge than I cast any wisdom for me?

Many thanks folks!

If you already have the 8hp I'd be trying to utilize it if you can there are various types of transom bracket available, fixed or rise & fall which may assist on making the 8 fit the space. Your 8 is excellent for power to weight & the only thing that would be a meaningful amount smaller & lighter would be a lightweigh 2 - 3.5 2 stroke like the yam 2b or merc marriner or tohatsu lightweights. Which would probably be fine but if you can manage the 8 then saves buying another engine & if you do need it the extra hp will be welcome.
Dont worry too much about getting the av plate level with the bottom of the hull as you wont need it for displacement speeds. As long as the prop is far enough into the water to push it along it will be fine as an aux

[Matt]

If it fits well enough, then stick with it. I have a 5 on my 8.3 and it’s a bit on the small side, it’s better to throttle back but have some power in reserve. And as Ken says, my aux is way off going below the full depth of the transom. I just run it low enough that it doesn’t ventilate the prop and it pushes it fine. The only limit is reverse is fairly useless, but that’s not the purpose of the aux anyway.

[Flamair]

Many thanks chaps, appreciate the input. I will see if I can make the 8hp work. I must admit, it's been 100% reliable and i don't really want to part with it!

Where would you suggest looking for the transom brackets?

[Matt]

Full Power.
https://youtu.be/cTyC3Bp8cUk

I have this bracket. It does the job and means that on full lift and tilt the motor is well clear. You need to measure up and see what fits your setup though.
https://www.ebay.co.uk/itm/404098334...mis&media=COPY

[Peter_C]

The general rule is one HP per meter. The transom width may dictate what will fit. The transom depth determines the necessary shaft length, with a general rule of long shaft main, requires a long shaft kicker.

Personally I am not a fan of having a kicker mounted on a movable bracket as they tend to bounce around hard in rough water. If a mount is even needed one could be made from plywood, and glassed over.

[Matt]

That is a good general rule for sizing.

The bracket - also true. I am careful with mine - it does bounce. But packaging limitations meant I couldn't do much else.

[Peter_C]

I would be curious to see a transom photo of said Avon 4.65 boat! In searching google for images there doesn't appear to be much room. Might require tipping the main before deploying the aux. Preference is always to leave the main down for steering and set the aux straight ahead, but they are probably too close. Might even require tipping the main to starboard just to clear the aux kicker for deployment.